
Ada Reference Manual, ISO/IEC 8652:1995(E){ with COR.1:2000}

 
 
 


 
 


 

 
 
 
 


 


Ada Reference Manual

 

ISO/IEC 8652:1995(E)

{with Technical Corrigendum 1}

 

Language and Standard Libraries

 











Copyright © 1992,1993,1994,1995 Intermetrics, Inc.

Copyright © 2000 The MITRE Corporation, Inc.



 






Ada Reference Manual - Language and Standard Libraries

Copyright © 1992, 1993, 1994, 1995, Intermetrics, Inc.

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Technical Corrigendum 1

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                              Table of Contents


Foreword to this version of the Ada Reference Manual

Foreword

Introduction

1. General
    1.1 Scope
        1.1.1 Extent
        1.1.2 Structure
        1.1.3 Conformity of an Implementation with the Standard
        1.1.4 Method of Description and Syntax Notation
        1.1.5 Classification of Errors
    1.2 Normative References
    1.3 Definitions

2. Lexical Elements
    2.1 Character Set
    2.2 Lexical Elements, Separators, and Delimiters
    2.3 Identifiers
    2.4 Numeric Literals
        2.4.1 Decimal Literals
        2.4.2 Based Literals
    2.5 Character Literals
    2.6 String Literals
    2.7 Comments
    2.8 Pragmas
    2.9 Reserved Words

3. Declarations and Types
    3.1 Declarations
    3.2 Types and Subtypes
        3.2.1 Type Declarations
        3.2.2 Subtype Declarations
        3.2.3 Classification of Operations
    3.3 Objects and Named Numbers
        3.3.1 Object Declarations
        3.3.2 Number Declarations
    3.4 Derived Types and Classes
        3.4.1 Derivation Classes
    3.5 Scalar Types
        3.5.1 Enumeration Types
        3.5.2 Character Types
        3.5.3 Boolean Types
        3.5.4 Integer Types
        3.5.5 Operations of Discrete Types
        3.5.6 Real Types
        3.5.7 Floating Point Types
        3.5.8 Operations of Floating Point Types
        3.5.9 Fixed Point Types
        3.5.10 Operations of Fixed Point Types
    3.6 Array Types
        3.6.1 Index Constraints and Discrete Ranges
        3.6.2 Operations of Array Types
        3.6.3 String Types
    3.7 Discriminants
        3.7.1 Discriminant Constraints
        3.7.2 Operations of Discriminated Types
    3.8 Record Types
        3.8.1 Variant Parts and Discrete Choices
    3.9 Tagged Types and Type Extensions
        3.9.1 Type Extensions
        3.9.2 Dispatching Operations of Tagged Types
        3.9.3 Abstract Types and Subprograms
    3.10 Access Types
        3.10.1 Incomplete Type Declarations
        3.10.2 Operations of Access Types
    3.11 Declarative Parts
        3.11.1 Completions of Declarations

4. Names and Expressions
    4.1 Names
        4.1.1 Indexed Components
        4.1.2 Slices
        4.1.3 Selected Components
        4.1.4 Attributes
    4.2 Literals
    4.3 Aggregates
        4.3.1 Record Aggregates
        4.3.2 Extension Aggregates
        4.3.3 Array Aggregates
    4.4 Expressions
    4.5 Operators and Expression Evaluation
        4.5.1 Logical Operators and Short-circuit Control Forms
        4.5.2 Relational Operators and Membership Tests
        4.5.3 Binary Adding Operators
        4.5.4 Unary Adding Operators
        4.5.5 Multiplying Operators
        4.5.6 Highest Precedence Operators
    4.6 Type Conversions
    4.7 Qualified Expressions
    4.8 Allocators
    4.9 Static Expressions and Static Subtypes
        4.9.1 Statically Matching Constraints and Subtypes

5. Statements
    5.1 Simple and Compound Statements - Sequences of Statements
    5.2 Assignment Statements
    5.3 If Statements
    5.4 Case Statements
    5.5 Loop Statements
    5.6 Block Statements
    5.7 Exit Statements
    5.8 Goto Statements

6. Subprograms
    6.1 Subprogram Declarations
    6.2 Formal Parameter Modes
    6.3 Subprogram Bodies
        6.3.1 Conformance Rules
        6.3.2 Inline Expansion of Subprograms
    6.4 Subprogram Calls
        6.4.1 Parameter Associations
    6.5 Return Statements
    6.6 Overloading of Operators

7. Packages
    7.1 Package Specifications and Declarations
    7.2 Package Bodies
    7.3 Private Types and Private Extensions
        7.3.1 Private Operations
    7.4 Deferred Constants
    7.5 Limited Types
    7.6 User-Defined Assignment and Finalization
        7.6.1 Completion and Finalization

8. Visibility Rules
    8.1 Declarative Region
    8.2 Scope of Declarations
    8.3 Visibility
    8.4 Use Clauses
    8.5 Renaming Declarations
        8.5.1 Object Renaming Declarations
        8.5.2 Exception Renaming Declarations
        8.5.3 Package Renaming Declarations
        8.5.4 Subprogram Renaming Declarations
        8.5.5 Generic Renaming Declarations
    8.6 The Context of Overload Resolution

9. Tasks and Synchronization
    9.1 Task Units and Task Objects
    9.2 Task Execution - Task Activation
    9.3 Task Dependence - Termination of Tasks
    9.4 Protected Units and Protected Objects
    9.5 Intertask Communication
        9.5.1 Protected Subprograms and Protected Actions
        9.5.2 Entries and Accept Statements
        9.5.3 Entry Calls
        9.5.4 Requeue Statements
    9.6 Delay Statements, Duration, and Time
    9.7 Select Statements
        9.7.1 Selective Accept
        9.7.2 Timed Entry Calls
        9.7.3 Conditional Entry Calls
        9.7.4 Asynchronous Transfer of Control
    9.8 Abort of a Task - Abort of a Sequence of Statements
    9.9 Task and Entry Attributes
    9.10 Shared Variables
    9.11 Example of Tasking and Synchronization

10. Program Structure and Compilation Issues
    10.1 Separate Compilation
        10.1.1 Compilation Units - Library Units
        10.1.2 Context Clauses - With Clauses
        10.1.3 Subunits of Compilation Units
        10.1.4 The Compilation Process
        10.1.5 Pragmas and Program Units
        10.1.6 Environment-Level Visibility Rules
    10.2 Program Execution
        10.2.1 Elaboration Control

11. Exceptions
    11.1 Exception Declarations
    11.2 Exception Handlers
    11.3 Raise Statements
    11.4 Exception Handling
        11.4.1 The Package Exceptions
        11.4.2 Example of Exception Handling
    11.5 Suppressing Checks
    11.6 Exceptions and Optimization

12. Generic Units
    12.1 Generic Declarations
    12.2 Generic Bodies
    12.3 Generic Instantiation
    12.4 Formal Objects
    12.5 Formal Types
        12.5.1 Formal Private and Derived Types
        12.5.2 Formal Scalar Types
        12.5.3 Formal Array Types
        12.5.4 Formal Access Types
    12.6 Formal Subprograms
    12.7 Formal Packages
    12.8 Example of a Generic Package

13. Representation Issues
    13.1 Operational and Representation Items
    13.2 Pragma Pack
    13.3 Operational and Representation Attributes
    13.4 Enumeration Representation Clauses
    13.5 Record Layout
        13.5.1 Record Representation Clauses
        13.5.2 Storage Place Attributes
        13.5.3 Bit Ordering
    13.6 Change of Representation
    13.7 The Package System
        13.7.1 The Package System.Storage_Elements
        13.7.2 The Package System.Address_To_Access_Conversions
    13.8 Machine Code Insertions
    13.9 Unchecked Type Conversions
        13.9.1 Data Validity
        13.9.2 The Valid Attribute
    13.10 Unchecked Access Value Creation
    13.11 Storage Management
        13.11.1 The Max_Size_In_Storage_Elements Attribute
        13.11.2 Unchecked Storage Deallocation
        13.11.3 Pragma Controlled
    13.12 Pragma Restrictions
    13.13 Streams
        13.13.1 The Package Streams
        13.13.2 Stream-Oriented Attributes
    13.14 Freezing Rules

The Standard Libraries

A. Predefined Language Environment
    A.1 The Package Standard
    A.2 The Package Ada
    A.3 Character Handling
        A.3.1 The Package Characters
        A.3.2 The Package Characters.Handling
        A.3.3 The Package Characters.Latin_1
    A.4 String Handling
        A.4.1 The Package Strings
        A.4.2 The Package Strings.Maps
        A.4.3 Fixed-Length String Handling
        A.4.4 Bounded-Length String Handling
        A.4.5 Unbounded-Length String Handling
        A.4.6 String-Handling Sets and Mappings
        A.4.7 Wide_String Handling
    A.5 The Numerics Packages
        A.5.1 Elementary Functions
        A.5.2 Random Number Generation
        A.5.3 Attributes of Floating Point Types
        A.5.4 Attributes of Fixed Point Types
    A.6 Input-Output
    A.7 External Files and File Objects
    A.8 Sequential and Direct Files
        A.8.1 The Generic Package Sequential_IO
        A.8.2 File Management
        A.8.3 Sequential Input-Output Operations
        A.8.4 The Generic Package Direct_IO
        A.8.5 Direct Input-Output Operations
    A.9 The Generic Package Storage_IO
    A.10 Text Input-Output
        A.10.1 The Package Text_IO
        A.10.2 Text File Management
        A.10.3 Default Input, Output, and Error Files
        A.10.4 Specification of Line and Page Lengths
        A.10.5 Operations on Columns, Lines, and Pages
        A.10.6 Get and Put Procedures
        A.10.7 Input-Output of Characters and Strings
        A.10.8 Input-Output for Integer Types
        A.10.9 Input-Output for Real Types
        A.10.10 Input-Output for Enumeration Types
    A.11 Wide Text Input-Output
    A.12 Stream Input-Output
        A.12.1 The Package Streams.Stream_IO
        A.12.2 The Package Text_IO.Text_Streams
        A.12.3 The Package Wide_Text_IO.Text_Streams
    A.13 Exceptions in Input-Output
    A.14 File Sharing
    A.15 The Package Command_Line

B. Interface to Other Languages
    B.1 Interfacing Pragmas
    B.2 The Package Interfaces
    B.3 Interfacing with C
        B.3.1 The Package Interfaces.C.Strings
        B.3.2 The Generic Package Interfaces.C.Pointers
    B.4 Interfacing with COBOL
    B.5 Interfacing with Fortran

C. Systems Programming
    C.1 Access to Machine Operations
    C.2 Required Representation Support
    C.3 Interrupt Support
        C.3.1 Protected Procedure Handlers
        C.3.2 The Package Interrupts
    C.4 Preelaboration Requirements
    C.5 Pragma Discard_Names
    C.6 Shared Variable Control
    C.7 Task Identification and Attributes
        C.7.1 The Package Task_Identification
        C.7.2 The Package Task_Attributes

D. Real-Time Systems
    D.1 Task Priorities
    D.2 Priority Scheduling
        D.2.1 The Task Dispatching Model
        D.2.2 The Standard Task Dispatching Policy
    D.3 Priority Ceiling Locking
    D.4 Entry Queuing Policies
    D.5 Dynamic Priorities
    D.6 Preemptive Abort
    D.7 Tasking Restrictions
    D.8 Monotonic Time
    D.9 Delay Accuracy
    D.10 Synchronous Task Control
    D.11 Asynchronous Task Control
    D.12 Other Optimizations and Determinism Rules

E. Distributed Systems
    E.1 Partitions
    E.2 Categorization of Library Units
        E.2.1 Shared Passive Library Units
        E.2.2 Remote Types Library Units
        E.2.3 Remote Call Interface Library Units
    E.3 Consistency of a Distributed System
    E.4 Remote Subprogram Calls
        E.4.1 Pragma Asynchronous
        E.4.2 Example of Use of a Remote Access-to-Class-Wide Type
    E.5 Partition Communication Subsystem

F. Information Systems
    F.1 Machine_Radix Attribute Definition Clause
    F.2 The Package Decimal
    F.3 Edited Output for Decimal Types
        F.3.1 Picture String Formation
        F.3.2 Edited Output Generation
        F.3.3 The Package Text_IO.Editing
        F.3.4 The Package Wide_Text_IO.Editing

G. Numerics
    G.1 Complex Arithmetic
        G.1.1 Complex Types
        G.1.2 Complex Elementary Functions
        G.1.3 Complex Input-Output
        G.1.4 The Package Wide_Text_IO.Complex_IO
    G.2 Numeric Performance Requirements
        G.2.1 Model of Floating Point Arithmetic
        G.2.2 Model-Oriented Attributes of Floating Point Types
        G.2.3 Model of Fixed Point Arithmetic
        G.2.4 Accuracy Requirements for the Elementary Functions
        G.2.5 Performance Requirements for Random Number Generation
        G.2.6 Accuracy Requirements for Complex Arithmetic

H. Safety and Security
    H.1 Pragma Normalize_Scalars
    H.2 Documentation of Implementation Decisions
    H.3 Reviewable Object Code
        H.3.1 Pragma Reviewable
        H.3.2 Pragma Inspection_Point
    H.4 Safety and Security Restrictions

J. Obsolescent Features
    J.1 Renamings of Ada 83 Library Units
    J.2 Allowed Replacements of Characters
    J.3 Reduced Accuracy Subtypes
    J.4 The Constrained Attribute
    J.5 ASCII
    J.6 Numeric_Error
    J.7 At Clauses
        J.7.1 Interrupt Entries
    J.8 Mod Clauses
    J.9 The Storage_Size Attribute

K. Language-Defined Attributes

L. Language-Defined Pragmas

M. Implementation-Defined Characteristics

N. Glossary

P. Syntax Summary

Index



            Foreword to this version of the Ada Reference Manual


0.1/1 {The International Standard for the programming language Ada is ISO/IEC
8652:1995(E).}

0.2/1 {The Ada Working Group ISO/IEC JTC1/SC 22/WG 9 is tasked by ISO with the
work item to interpret and maintain the International Standard and to produce
Technical Corrigenda, as appropriate. The technical work on the International
Standard is performed by the Ada Rapporteur Group (ARG) of WG 9. In September
2000, WG 9 approved and forwarded Technical Corrigendum 1 to SC 22 for ISO
approval, which was granted in February 2001.}

0.3/1 {The Technical Corrigendum lists the individual changes that need to be
made to the text of the International Standard to correct errors, omissions or
inconsistencies. Once approved, the corrections specified in Technical
Corrigendum 1 will be part of the International Standard ISO/IEC 8652:1995(E).}

0.4/1 {When ISO publishes Technical Corrigendum 1, it is unlikely that ISO
will also publish a document that merges the Technical Corrigendum changes
into the text of the International Standard. However, ISO rules require that
the project editor for the Technical Corrigendum be able to produce such a
document on demand.}

0.5/1 {This version of the Ada Reference Manual is what the project editor
would provide to ISO in response to such a request. It incorporates the
changes specified in the Technical Corrigendum into the text of ISO/IEC
8652:1995(E). It should be understood that the publication of any ISO document
involves changes in general format, boilerplate, headers, etc., as well as a
review by professional editors that may introduce editorial changes to the
text. This version of the Ada Reference Manual is therefore neither an
official ISO document, nor a version guaranteed to be identical to an official
ISO document, should ISO decide to reprint the International Standard
incorporating an approved Technical Corrigendum. It is nevertheless a best
effort to be as close as possible to the technical content of such an updated
document. In the case of a conflict between this document and a Technical
Corrigendum 1 approved by ISO (or between this document and the original
8652:1995 in the case of paragraphs not changed by Technical Corrigendum 1),
the other documents contain the official text of the International Standard
ISO/IEC 8652:1995(E).}

0.6/1 {As it is very inconvenient to have the Reference Manual for Ada
specified in two documents, this consolidated version of the Ada Reference
Manual is made available to the public.}

{Using this version of the Ada Reference Manual}

0.7/1 {This document has been revised with the corrections specified in
Technical Corrigendum 1 (ISO/IEC 8652:1995/COR1:2000). In addition, a variety
of editorial errors have been corrected.}

0.8/1 {Changes to the original 8652:1995 can be identified by the version
number /1 following the paragraph number. Paragraphs not so marked are
unchanged by Technical Corrigendum 1 or editorial corrections. Paragraph
numbers of unchanged paragraphs are the same as in the original Ada Reference
Manual. In addition, some versions of this document include revision bars near
the paragraph numbers. Where paragraphs are inserted, the paragraph numbers
are of the form pp.nn, where pp is the number of the preceding paragraph, and
nn is an insertion number. For instance, the first paragraph inserted after
paragraph 8 is numbered 8.1, the second paragraph inserted is numbered 8.2,
and so on. Deleted paragraphs are indicated by the text This paragraph was
deleted. Deleted paragraphs include empty paragraphs that were numbered in the
original Ada Reference Manual.}

{Acknowledgements for this version of the Ada Reference Manual}

0.9/1 {The editor [R. Brukardt (USA)] would like to thank the many people
whose hard work and assistance has made this revision possible.}

0.10/1 {Thanks go out to all of the members of the ISO/IEC JTC 1/SC 22/WG 9
Ada Rapporteur Group, whose work on creating and editing the wording
corrections was critical to the entire process. Especially valuable
contributions came from the chairman of the ARG, E. Ploedereder (Germany), who
kept the process moving; J. Barnes (UK) and K. Ishihata (Japan), whose
extremely detailed reviews kept the editor on his toes; G. Dismukes (USA), M.
Kamrad (USA), P. Leroy (France), S. Michell (Canada), T. Taft (USA), J. Tokar
(USA), and other members too numerous to mention.}

0.11/1 {Special thanks go to R. Duff (USA) for his explanations of the
previous system of formatting of these documents during the tedious conversion
to more modern formats. Special thanks also go to the convener of ISO/IEC JTC
1/SC 22/WG 9, J. Moore (USA), without whose help and support the corrigendum
and this consolidated reference manual would not have been possible.}


                                  Foreword


1     ISO (the International Organization for Standardization) and IEC (the
International Electrotechnical Commission) form the specialized system for
worldwide standardization. National bodies that are members of ISO or IEC
participate in the development of International Standards through technical
committees established by the respective organization to deal with particular
fields of technical activity. ISO and IEC technical committees collaborate in
fields of mutual interest. Other international organizations, governmental and
non-governmental, in liaison with ISO and IEC, also take part in the work.

2     In the field of information technology, ISO and IEC have established a
joint technical committee, ISO/IEC JTC 1. Draft International Standards
adopted by the joint technical committee are circulated to national bodies for
voting. Publication as an International Standard requires approval by at least
75 % of the national bodies casting a vote.

3     International Standard ISO/IEC 8652 was prepared by Joint Technical
Committee ISO/IEC JTC 1, Information Technology.

4     This second edition cancels and replaces the first edition (ISO
8652:1987), of which it constitutes a technical revision.

5     Annexes A to J form an integral part of this International Standard.
Annexes K to P are for information only.


                                Introduction


1     This is the Ada Reference Manual.

2     Other available Ada documents include:

3     Rationale for the Ada Programming Language - 1995 edition, which gives
      an introduction to the new features of Ada, and explains the rationale
      behind them. Programmers should read this first.

4/1   This paragraph was deleted.[Changes to Ada - 1987 to 1995. This document
      lists in detail the changes made to the 1987 edition of the standard.]

5     The Annotated Ada Reference Manual (AARM). The AARM contains all of the
      text in the RM95, plus various annotations. It is intended primarily for
      compiler writers, validation test writers, and others who wish to study
      the fine details. The annotations include detailed rationale for
      individual rules and explanations of some of the more arcane
      interactions among the rules.

Design Goals

6     Ada was originally designed with three overriding concerns: program
reliability and maintenance, programming as a human activity, and efficiency.
This revision to the language was designed to provide greater flexibility and
extensibility, additional control over storage management and synchronization,
and standardized packages oriented toward supporting important application
areas, while at the same time retaining the original emphasis on reliability,
maintainability, and efficiency.

7     The need for languages that promote reliability and simplify maintenance
is well established. Hence emphasis was placed on program readability over
ease of writing. For example, the rules of the language require that program
variables be explicitly declared and that their type be specified. Since the
type of a variable is invariant, compilers can ensure that operations on
variables are compatible with the properties intended for objects of the type.
Furthermore, error-prone notations have been avoided, and the syntax of the
language avoids the use of encoded forms in favor of more English-like
constructs. Finally, the language offers support for separate compilation of
program units in a way that facilitates program development and maintenance,
and which provides the same degree of checking between units as within a unit.

8     Concern for the human programmer was also stressed during the design.
Above all, an attempt was made to keep to a relatively small number of
underlying concepts integrated in a consistent and systematic way while
continuing to avoid the pitfalls of excessive involution. The design
especially aims to provide language constructs that correspond intuitively to
the normal expectations of users.

9     Like many other human activities, the development of programs is
becoming ever more decentralized and distributed. Consequently, the ability to
assemble a program from independently produced software components continues
to be a central idea in the design. The concepts of packages, of private
types, and of generic units are directly related to this idea, which has
ramifications in many other aspects of the language. An allied concern is the
maintenance of programs to match changing requirements; type extension and the
hierarchical library enable a program to be modified while minimizing
disturbance to existing tested and trusted components.

10    No language can avoid the problem of efficiency. Languages that require
over-elaborate compilers, or that lead to the inefficient use of storage or
execution time, force these inefficiencies on all machines and on all
programs. Every construct of the language was examined in the light of present
implementation techniques. Any proposed construct whose implementation was
unclear or that required excessive machine resources was rejected.

Language Summary

11    An Ada program is composed of one or more program units. Program units
may be subprograms (which define executable algorithms), packages (which
define collections of entities), task units (which define concurrent
computations), protected units (which define operations for the coordinated
sharing of data between tasks), or generic units (which define parameterized
forms of packages and subprograms). Each program unit normally consists of two
parts: a specification, containing the information that must be visible to
other units, and a body, containing the implementation details, which need not
be visible to other units. Most program units can be compiled separately.

12    This distinction of the specification and body, and the ability to
compile units separately, allows a program to be designed, written, and tested
as a set of largely independent software components.

13    An Ada program will normally make use of a library of program units of
general utility. The language provides means whereby individual organizations
can construct their own libraries. All libraries are structured in a
hierarchical manner; this enables the logical decomposition of a subsystem
into individual components. The text of a separately compiled program unit
must name the library units it requires.

14    Program Units

15    A subprogram is the basic unit for expressing an algorithm. There are
two kinds of subprograms: procedures and functions. A procedure is the means
of invoking a series of actions. For example, it may read data, update
variables, or produce some output. It may have parameters, to provide a
controlled means of passing information between the procedure and the point of
call. A function is the means of invoking the computation of a value. It is
similar to a procedure, but in addition will return a result.

16    A package is the basic unit for defining a collection of logically
related entities. For example, a package can be used to define a set of type
declarations and associated operations. Portions of a package can be hidden
from the user, thus allowing access only to the logical properties expressed
by the package specification.

17    Subprogram and package units may be compiled separately and arranged in
hierarchies of parent and child units giving fine control over visibility of
the logical properties and their detailed implementation.

18    A task unit is the basic unit for defining a task whose sequence of
actions may be executed concurrently with those of other tasks. Such tasks may
be implemented on multicomputers, multiprocessors, or with interleaved
execution on a single processor. A task unit may define either a single
executing task or a task type permitting the creation of any number of similar
tasks.

19    A protected unit is the basic unit for defining protected operations for
the coordinated use of data shared between tasks. Simple mutual exclusion is
provided automatically, and more elaborate sharing protocols can be defined. A
protected operation can either be a subprogram or an entry. A protected entry
specifies a Boolean expression (an entry barrier) that must be true before the
body of the entry is executed. A protected unit may define a single protected
object or a protected type permitting the creation of several similar objects.

20    Declarations and Statements

21    The body of a program unit generally contains two parts: a declarative
part, which defines the logical entities to be used in the program unit, and a
sequence of statements, which defines the execution of the program unit.

22    The declarative part associates names with declared entities. For
example, a name may denote a type, a constant, a variable, or an exception. A
declarative part also introduces the names and parameters of other nested
subprograms, packages, task units, protected units, and generic units to be
used in the program unit.

23    The sequence of statements describes a sequence of actions that are to
be performed. The statements are executed in succession (unless a transfer of
control causes execution to continue from another place).

24    An assignment statement changes the value of a variable. A procedure
call invokes execution of a procedure after associating any actual parameters
provided at the call with the corresponding formal parameters.

25    Case statements and if statements allow the selection of an enclosed
sequence of statements based on the value of an expression or on the value of
a condition.

26    The loop statement provides the basic iterative mechanism in the
language. A loop statement specifies that a sequence of statements is to be
executed repeatedly as directed by an iteration scheme, or until an exit
statement is encountered.

27    A block statement comprises a sequence of statements preceded by the
declaration of local entities used by the statements.

28    Certain statements are associated with concurrent execution. A delay
statement delays the execution of a task for a specified duration or until a
specified time. An entry call statement is written as a procedure call
statement; it requests an operation on a task or on a protected object,
blocking the caller until the operation can be performed. A called task may
accept an entry call by executing a corresponding accept statement, which
specifies the actions then to be performed as part of the rendezvous with the
calling task. An entry call on a protected object is processed when the
corresponding entry barrier evaluates to true, whereupon the body of the entry
is executed. The requeue statement permits the provision of a service as a
number of related activities with preference control. One form of the select
statement allows a selective wait for one of several alternative rendezvous.
Other forms of the select statement allow conditional or timed entry calls and
the asynchronous transfer of control in response to some triggering event.

29    Execution of a program unit may encounter error situations in which
normal program execution cannot continue. For example, an arithmetic
computation may exceed the maximum allowed value of a number, or an attempt
may be made to access an array component by using an incorrect index value. To
deal with such error situations, the statements of a program unit can be
textually followed by exception handlers that specify the actions to be taken
when the error situation arises. Exceptions can be raised explicitly by a
raise statement.

30    Data Types

31    Every object in the language has a type, which characterizes a set of
values and a set of applicable operations. The main classes of types are
elementary types (comprising enumeration, numeric, and access types) and
composite types (including array and record types).

32    An enumeration type defines an ordered set of distinct enumeration
literals, for example a list of states or an alphabet of characters. The
enumeration types Boolean, Character, and Wide_Character are predefined.

33    Numeric types provide a means of performing exact or approximate
numerical computations. Exact computations use integer types, which denote
sets of consecutive integers. Approximate computations use either fixed point
types, with absolute bounds on the error, or floating point types, with
relative bounds on the error. The numeric types Integer, Float, and Duration
are predefined.

34    Composite types allow definitions of structured objects with related
components. The composite types in the language include arrays and records. An
array is an object with indexed components of the same type. A record is an
object with named components of possibly different types. Task and protected
types are also forms of composite types. The array types String and
Wide_String are predefined.

35    Record, task, and protected types may have special components called
discriminants which parameterize the type. Variant record structures that
depend on the values of discriminants can be defined within a record type.

36    Access types allow the construction of linked data structures. A value
of an access type represents a reference to an object declared as aliased or
to an object created by the evaluation of an allocator. Several variables of
an access type may designate the same object, and components of one object may
designate the same or other objects. Both the elements in such linked data
structures and their relation to other elements can be altered during program
execution. Access types also permit references to subprograms to be stored,
passed as parameters, and ultimately dereferenced as part of an indirect call.

37    Private types permit restricted views of a type. A private type can be
defined in a package so that only the logically necessary properties are made
visible to the users of the type. The full structural details that are
externally irrelevant are then only available within the package and any child
units.

38    From any type a new type may be defined by derivation. A type, together
with its derivatives (both direct and indirect) form a derivation class.
Class-wide operations may be defined that accept as a parameter an operand of
any type in a derivation class. For record and private types, the derivatives
may be extensions of the parent type. Types that support these object-oriented
capabilities of class-wide operations and type extension must be tagged, so
that the specific type of an operand within a derivation class can be
identified at run time. When an operation of a tagged type is applied to an
operand whose specific type is not known until run time, implicit dispatching
is performed based on the tag of the operand.

39    The concept of a type is further refined by the concept of a subtype,
whereby a user can constrain the set of allowed values of a type. Subtypes can
be used to define subranges of scalar types, arrays with a limited set of
index values, and records and private types with particular discriminant
values.

40    Other Facilities

41    Representation clauses can be used to specify the mapping between types
and features of an underlying machine. For example, the user can specify that
objects of a given type must be represented with a given number of bits, or
that the components of a record are to be represented using a given storage
layout. Other features allow the controlled use of low level, nonportable, or
implementation-dependent aspects, including the direct insertion of machine
code.

42    The predefined environment of the language provides for input-output and
other capabilities (such as string manipulation and random number generation)
by means of standard library packages. Input-output is supported for values of
user-defined as well as of predefined types. Standard means of representing
values in display form are also provided. Other standard library packages are
defined in annexes of the standard to support systems with specialized
requirements.

43    Finally, the language provides a powerful means of parameterization of
program units, called generic program units. The generic parameters can be
types and subprograms (as well as objects and packages) and so allow general
algorithms and data structures to be defined that are applicable to all types
of a given class.

Language Changes

44    This International Standard replaces the first edition of 1987. In this
edition, the following major language changes have been incorporated:

45    Support for standard 8-bit and 16-bit character sets. See Section 2,
      3.5.2, 3.6.3, A.1, A.3, and A.4.

46    Object-oriented programming with run-time polymorphism. See the
      discussions of classes, derived types, tagged types, record extensions,
      and private extensions in clauses 3.4, 3.9, and 7.3. See also the new
      forms of generic formal parameters that are allowed by 12.5.1, ``
      Formal Private and Derived Types'' and 12.7, ``Formal Packages''.

47    Access types have been extended to allow an access value to designate a
      subprogram or an object declared by an object declaration (as opposed to
      just a heap-allocated object). See 3.10.

48    Efficient data-oriented synchronization is provided via protected types.
      See Section 9.

49    The library units of a library may be organized into a hierarchy of
      parent and child units. See Section 10.

50    Additional support has been added for interfacing to other languages.
      See Annex B.

51    The Specialized Needs Annexes have been added to provide specific
      support for certain application areas:

    52    Annex C, ``Systems Programming''

    53    Annex D, ``Real-Time Systems''

    54    Annex E, ``Distributed Systems''

    55    Annex F, ``Information Systems''

    56    Annex G, ``Numerics''

    57    Annex H, ``Safety and Security''



Instructions for Comment Submission

58/1  Informal comments on this International Standard may be sent via e-mail
to {ada-comment@ada-auth.org}[ada-comment@sw-eng.falls-church.va.us]. If
appropriate, the Project Editor will initiate the defect correction procedure.

59    Comments should use the following format:

60         !topic Title summarizing comment
           !reference RM95-ss.ss(pp)
           !from Author Name yy-mm-dd
           !keywords keywords related to topic
           !discussion
      
           text of discussion

61    where ss.ss is the section, clause or subclause number, pp is the
paragraph number where applicable, and yy-mm-dd is the date the comment was
sent. The date is optional, as is the !keywords line.

62/1  [Multiple comments per e-mail message are acceptable.] Please use a
descriptive ``Subject'' in your e-mail message{, and limit each message to a
single comment.}[.]

63    When correcting typographical errors or making minor wording
suggestions, please put the correction directly as the topic of the comment;
use square brackets [ ] to indicate text to be omitted and curly braces { } to
indicate text to be added, and provide enough context to make the nature of
the suggestion self-evident or put additional information in the body of the
comment, for example:

64         !topic [c]{C}haracter
           !topic it[']s meaning is not defined

65    Formal requests for interpretations and for reporting defects in this
International Standard may be made in accordance with the ISO/IEC JTC1
Directives and the ISO/IEC JTC1/SC22 policy for interpretations. National
Bodies may submit a Defect Report to ISO/IEC JTC1/SC22 for resolution under
the JTC1 procedures. A response will be provided and, if appropriate, a
Technical Corrigendum will be issued in accordance with the procedures.



Acknowledgements

66    This International Standard was prepared by the Ada 9X Mapping/Revision
Team based at Intermetrics, Inc., which has included: W. Carlson, Program
Manager; T. Taft, Technical Director; J. Barnes (consultant); B. Brosgol
(consultant); R. Duff (Oak Tree Software); M. Edwards; C. Garrity; R.
Hilliard; O. Pazy (consultant); D. Rosenfeld; L. Shafer; W. White; M. Woodger.

67    The following consultants to the Ada 9X Project contributed to the
Specialized Needs Annexes: T. Baker (Real-Time/Systems Programming - SEI,
FSU); K. Dritz (Numerics - Argonne National Laboratory); A. Gargaro
(Distributed Systems - Computer Sciences); J. Goodenough (Real-Time/Systems
Programming - SEI); J. McHugh (Secure Systems - consultant); B. Wichmann
(Safety-Critical Systems - NPL: UK).

68    This work was regularly reviewed by the Ada 9X Distinguished Reviewers
and the members of the Ada 9X Rapporteur Group (XRG): E. Ploedereder, Chairman
of DRs and XRG (University of Stuttgart: Germany); B. Bardin (Hughes); J.
Barnes (consultant: UK); B. Brett (DEC); B. Brosgol (consultant); R. Brukardt
(RR Software); N. Cohen (IBM); R. Dewar (NYU); G. Dismukes (TeleSoft); A.
Evans (consultant); A. Gargaro (Computer Sciences); M. Gerhardt (ESL); J.
Goodenough (SEI); S. Heilbrunner (University of Salzburg: Austria); P.
Hilfinger (UC/Berkeley); B. Källberg (CelsiusTech: Sweden); M. Kamrad II
(Unisys); J. van Katwijk (Delft University of Technology: The Netherlands); V.
Kaufman (Russia); P. Kruchten (Rational); R. Landwehr (CCI: Germany); C.
Lester (Portsmouth Polytechnic: UK); L. Månsson (TELIA Research: Sweden); S.
Michell (Multiprocessor Toolsmiths: Canada); M. Mills (US Air Force); D. Pogge
(US Navy); K. Power (Boeing); O. Roubine (Verdix: France); A. Strohmeier
(Swiss Fed Inst of Technology: Switzerland); W. Taylor (consultant: UK); J.
Tokar (Tartan); E. Vasilescu (Grumman); J. Vladik (Prospeks s.r.o.: Czech
Republic); S. Van Vlierberghe (OFFIS: Belgium).

69    Other valuable feedback influencing the revision process was provided by
the Ada 9X Language Precision Team (Odyssey Research Associates), the Ada 9X
User/Implementer Teams (AETECH, Tartan, TeleSoft), the Ada 9X Implementation
Analysis Team (New York University) and the Ada community-at-large.

70    Special thanks go to R. Mathis, Convenor of ISO/IEC JTC1/SC22 Working
Group 9.

71    The Ada 9X Project was sponsored by the Ada Joint Program Office.
Christine M. Anderson at the Air Force Phillips Laboratory (Kirtland AFB, NM)
was the project manager.



Changes

72    The International Standard is the same as this version of the Reference
Manual, except:

73    This list of Changes is not included in the International Standard.

74    The ``Acknowledgements'' page is not included in the International
      Standard.

75    The text in the running headers and footers on each page is slightly
      different in the International Standard.

76    The title page(s) are different in the International Standard.

77    This document is formatted for 8.5-by-11-inch paper, whereas the
      International Standard is formatted for A4 paper (210-by-297mm); thus,
      the page breaks are in different places.

77.1/1 {The ``Foreword to this version of the Ada Reference Manual'' clause is
      not included in the International Standard.}






=====================================================================

INTERNATIONAL STANDARD                                 ISO/IEC 8652:1995(E){
with COR.1:2000}


=====================================================================

 
 
 


Information technology - Programming

Languages - Ada

 
 
 



                             Section 1: General


1     Ada is a programming language designed to support the construction of
long-lived, highly reliable software systems. The language includes facilities
to define packages of related types, objects, and operations. The packages may
be parameterized and the types may be extended to support the construction of
libraries of reusable, adaptable software components. The operations may be
implemented as subprograms using conventional sequential control structures,
or as entries that include synchronization of concurrent threads of control as
part of their invocation. The language treats modularity in the physical sense
as well, with a facility to support separate compilation.

2     The language includes a complete facility for the support of real-time,
concurrent programming. Errors can be signaled as exceptions and handled
explicitly. The language also covers systems programming; this requires
precise control over the representation of data and access to system-dependent
properties. Finally, a predefined environment of standard packages is
provided, including facilities for, among others, input-output, string
manipulation, numeric elementary functions, and random number generation.


1.1 Scope


1     This International Standard specifies the form and meaning of programs
written in Ada. Its purpose is to promote the portability of Ada programs to a
variety of data processing systems.


1.1.1 Extent


1     This International Standard specifies:

2     The form of a program written in Ada;

3     The effect of translating and executing such a program;

4     The manner in which program units may be combined to form Ada programs;

5     The language-defined library units that a conforming implementation is
      required to supply;

6     The permissible variations within the standard, and the manner in which
      they are to be documented;

7     Those violations of the standard that a conforming implementation is
      required to detect, and the effect of attempting to translate or execute
      a program containing such violations;

8     Those violations of the standard that a conforming implementation is not
      required to detect.

9     This International Standard does not specify:

10    The means whereby a program written in Ada is transformed into object
      code executable by a processor;

11    The means whereby translation or execution of programs is invoked and
      the executing units are controlled;

12    The size or speed of the object code, or the relative execution speed of
      different language constructs;

13    The form or contents of any listings produced by implementations; in
      particular, the form or contents of error or warning messages;

14    The effect of unspecified execution.

15    The size of a program or program unit that will exceed the capacity of a
      particular conforming implementation.


1.1.2 Structure


1     This International Standard contains thirteen sections, fourteen
annexes, and an index.

2     The core of the Ada language consists of:

3     Sections 1 through 13

4     Annex A, ``Predefined Language Environment''

5     Annex B, ``Interface to Other Languages''

6     Annex J, ``Obsolescent Features''

7     The following Specialized Needs Annexes define features that are needed
by certain application areas:

8     Annex C, ``Systems Programming''

9     Annex D, ``Real-Time Systems''

10    Annex E, ``Distributed Systems''

11    Annex F, ``Information Systems''

12    Annex G, ``Numerics''

13    Annex H, ``Safety and Security''

14    The core language and the Specialized Needs Annexes are normative,
except that the material in each of the items listed below is informative:

15    Text under a NOTES or Examples heading.

16    Each clause or subclause whose title starts with the word ``Example'' or
      ``Examples''.

17    All implementations shall conform to the core language. In addition, an
implementation may conform separately to one or more Specialized Needs Annexes.

18    The following Annexes are informative:

19    Annex K, ``Language-Defined Attributes''

20    Annex L, ``Language-Defined Pragmas''

21    Annex M, ``Implementation-Defined Characteristics''

22    Annex N, ``Glossary''

23    Annex P, ``Syntax Summary''

24    Each section is divided into clauses and subclauses that have a common
structure. Each section, clause, and subclause first introduces its subject.
After the introductory text, text is labeled with the following headings:


                                   Syntax

25    Syntax rules (indented).


                            Name Resolution Rules

26    Compile-time rules that are used in name resolution, including overload
resolution.


                               Legality Rules

27    Rules that are enforced at compile time. A construct is legal if it
obeys all of the Legality Rules.


                              Static Semantics

28    A definition of the compile-time effect of each construct.


                           Post-Compilation Rules

29    Rules that are enforced before running a partition. A partition is legal
if its compilation units are legal and it obeys all of the
Post-Compilation Rules.


                              Dynamic Semantics

30    A definition of the run-time effect of each construct.


                          Bounded (Run-Time) Errors

31    Situations that result in bounded (run-time) errors (see 1.1.5).


                             Erroneous Execution

32    Situations that result in erroneous execution (see 1.1.5).


                         Implementation Requirements

33    Additional requirements for conforming implementations.


                         Documentation Requirements

34    Documentation requirements for conforming implementations.


                                   Metrics

35    Metrics that are specified for the time/space properties of the
execution of certain language constructs.


                         Implementation Permissions

36    Additional permissions given to the implementer.


                            Implementation Advice

37    Optional advice given to the implementer. The word ``should'' is used to
indicate that the advice is a recommendation, not a requirement. It is
implementation defined whether or not a given recommendation is obeyed.

      NOTES

38    1  Notes emphasize consequences of the rules described in the
      (sub)clause or elsewhere. This material is informative.


                                  Examples

39    Examples illustrate the possible forms of the constructs described. This
material is informative.


1.1.3 Conformity of an Implementation with the Standard



                         Implementation Requirements

1     A conforming implementation shall:

2     Translate and correctly execute legal programs written in Ada, provided
      that they are not so large as to exceed the capacity of the
      implementation;

3     Identify all programs or program units that are so large as to exceed
      the capacity of the implementation (or raise an appropriate exception at
      run time);

4     Identify all programs or program units that contain errors whose
      detection is required by this International Standard;

5     Supply all language-defined library units required by this International
      Standard;

6     Contain no variations except those explicitly permitted by this
      International Standard, or those that are impossible or impractical to
      avoid given the implementation's execution environment;

7     Specify all such variations in the manner prescribed by this
      International Standard.

8     The external effect of the execution of an Ada program is defined in
terms of its interactions with its external environment. The following are
defined as external interactions:

9     Any interaction with an external file (see A.7);

10    The execution of certain code_statements (see 13.8); which
      code_statements cause external interactions is implementation defined.

11    Any call on an imported subprogram (see Annex B), including any
      parameters passed to it;

12    Any result returned or exception propagated from a main subprogram (see
      10.2) or an exported subprogram (see Annex B) to an external caller;

13    Any read or update of an atomic or volatile object (see C.6);

14    The values of imported and exported objects (see Annex B) at the time of
      any other interaction with the external environment.

15    A conforming implementation of this International Standard shall produce
for the execution of a given Ada program a set of interactions with the
external environment whose order and timing are consistent with the
definitions and requirements of this International Standard for the semantics
of the given program.

16    An implementation that conforms to this Standard shall support each
capability required by the core language as specified. In addition, an
implementation that conforms to this Standard may conform to one or more
Specialized Needs Annexes (or to none). Conformance to a Specialized Needs
Annex means that each capability required by the Annex is provided as
specified.

17    An implementation conforming to this International Standard may provide
additional attributes, library units, and pragmas. However, it shall not
provide any attribute, library unit, or pragma having the same name as an
attribute, library unit, or pragma (respectively) specified in a Specialized
Needs Annex unless the provided construct is either as specified in the
Specialized Needs Annex or is more limited in capability than that required by
the Annex. A program that attempts to use an unsupported capability of an
Annex shall either be identified by the implementation before run time or
shall raise an exception at run time.


                         Documentation Requirements

18    Certain aspects of the semantics are defined to be either implementation
defined or unspecified. In such cases, the set of possible effects is
specified, and the implementation may choose any effect in the set.
Implementations shall document their behavior in implementation-defined
situations, but documentation is not required for unspecified situations. The
implementation-defined characteristics are summarized in Annex M.

19    The implementation may choose to document implementation-defined
behavior either by documenting what happens in general, or by providing some
mechanism for the user to determine what happens in a particular case.


                            Implementation Advice

20    If an implementation detects the use of an unsupported Specialized Needs
Annex feature at run time, it should raise Program_Error if feasible.

21    If an implementation wishes to provide implementation-defined extensions
to the functionality of a language-defined library unit, it should normally do
so by adding children to the library unit.

      NOTES

22    2  The above requirements imply that an implementation conforming to
      this Standard may support some of the capabilities required by a
      Specialized Needs Annex without supporting all required capabilities.


1.1.4 Method of Description and Syntax Notation


1     The form of an Ada program is described by means of a context-free
syntax together with context-dependent requirements expressed by narrative
rules.

2     The meaning of Ada programs is described by means of narrative rules
defining both the effects of each construct and the composition rules for
constructs.

3     The context-free syntax of the language is described using a simple
variant of Backus-Naur Form. In particular:

4     Lower case words in a sans-serif font, some containing embedded
      underlines, are used to denote syntactic categories, for example:

    5     case_statement

6     Boldface words are used to denote reserved words, for example:

    7     array

8     Square brackets enclose optional items. Thus the two following rules are
      equivalent.

    9     return_statement ::= return [expression];
          return_statement ::= return; | return expression;

10    Curly brackets enclose a repeated item. The item may appear zero or more
      times; the repetitions occur from left to right as with an equivalent
      left-recursive rule. Thus the two following rules are equivalent.

    11    term ::= factor {multiplying_operator factor}
          term ::= factor | term multiplying_operator factor

12    A vertical line separates alternative items unless it occurs immediately
      after an opening curly bracket, in which case it stands for itself:

    13    constraint ::= scalar_constraint | composite_constraint
          discrete_choice_list ::= discrete_choice {| discrete_choice}

14    If the name of any syntactic category starts with an italicized part, it
      is equivalent to the category name without the italicized part. The
      italicized part is intended to convey some semantic information. For
      example subtype_name and task_name are both equivalent to name alone.

15    A syntactic category is a nonterminal in the grammar defined in BNF
under ``Syntax.'' Names of syntactic categories are set in a different font,
like_this.

16    A construct is a piece of text (explicit or implicit) that is an
instance of a syntactic category defined under ``Syntax.''

17    A constituent of a construct is the construct itself, or any construct
appearing within it.

18    Whenever the run-time semantics defines certain actions to happen in an
arbitrary order, this means that the implementation shall arrange for these
actions to occur in a way that is equivalent to some sequential order,
following the rules that result from that sequential order. When evaluations
are defined to happen in an arbitrary order, with conversion of the results to
some subtypes, or with some run-time checks, the evaluations, conversions, and
checks may be arbitrarily interspersed, so long as each expression is
evaluated before converting or checking its value. Note that the effect of a
program can depend on the order chosen by the implementation. This can happen,
for example, if two actual parameters of a given call have side effects.

      NOTES

19    3  The syntax rules describing structured constructs are presented in a
      form that corresponds to the recommended paragraphing. For example, an
      if_statement is defined as:

20    if_statement ::=
          if condition then
            sequence_of_statements
         {elsif condition then
            sequence_of_statements}
         [else
            sequence_of_statements]
          end if;

21    4  The line breaks and indentation in the syntax rules indicate the
      recommended line breaks and indentation in the corresponding constructs.
      The preferred places for other line breaks are after semicolons.


1.1.5 Classification of Errors



                         Implementation Requirements

1     The language definition classifies errors into several different
categories:

2     Errors that are required to be detected prior to run time by every Ada
      implementation;

3     These errors correspond to any violation of a rule given in this
      International Standard, other than those listed below. In particular,
      violation of any rule that uses the terms shall, allowed, permitted,
      legal, or illegal belongs to this category. Any program that contains
      such an error is not a legal Ada program; on the other hand, the fact
      that a program is legal does not mean, per se, that the program is free
      from other forms of error.

4     The rules are further classified as either compile time rules, or post
      compilation rules, depending on whether a violation has to be detected
      at the time a compilation unit is submitted to the compiler, or may be
      postponed until the time a compilation unit is incorporated into a
      partition of a program.

5     Errors that are required to be detected at run time by the execution of
      an Ada program;

6     The corresponding error situations are associated with the names of the
      predefined exceptions. Every Ada compiler is required to generate code
      that raises the corresponding exception if such an error situation
      arises during program execution. If such an error situation is certain
      to arise in every execution of a construct, then an implementation is
      allowed (although not required) to report this fact at compilation time.

7     Bounded errors;

8     The language rules define certain kinds of errors that need not be
      detected either prior to or during run time, but if not detected, the
      range of possible effects shall be bounded. The errors of this category
      are called bounded errors. The possible effects of a given bounded error
      are specified for each such error, but in any case one possible effect
      of a bounded error is the raising of the exception Program_Error.

9     Erroneous execution.

10    In addition to bounded errors, the language rules define certain kinds
      of errors as leading to erroneous execution. Like bounded errors, the
      implementation need not detect such errors either prior to or during run
      time. Unlike bounded errors, there is no language-specified bound on the
      possible effect of erroneous execution; the effect is in general not
      predictable.


                         Implementation Permissions

11    An implementation may provide nonstandard modes of operation. Typically
these modes would be selected by a pragma or by a command line switch when the
compiler is invoked. When operating in a nonstandard mode, the implementation
may reject compilation_units that do not conform to additional requirements
associated with the mode, such as an excessive number of warnings or violation
of coding style guidelines. Similarly, in a nonstandard mode, the
implementation may apply special optimizations or alternative algorithms that
are only meaningful for programs that satisfy certain criteria specified by
the implementation. In any case, an implementation shall support a standard
mode that conforms to the requirements of this International Standard; in
particular, in the standard mode, all legal compilation_units shall be
accepted.


                            Implementation Advice

12    If an implementation detects a bounded error or erroneous execution, it
should raise Program_Error.


1.2 Normative References


1     The following standards contain provisions which, through reference in
this text, constitute provisions of this International Standard. At the time
of publication, the editions indicated were valid. All standards are subject
to revision, and parties to agreements based on this International Standard
are encouraged to investigate the possibility of applying the most recent
editions of the standards indicated below. Members of IEC and ISO maintain
registers of currently valid International Standards.

2     ISO/IEC 646:1991, Information technology - ISO 7-bit coded character set
for information interchange.

3     ISO/IEC 1539:1991, Information technology - Programming languages -
FORTRAN.

4     ISO 1989:1985, Programming languages - COBOL.

5     ISO/IEC 6429:1992, Information technology - Control functions for coded
graphic character sets.

6     ISO/IEC 8859-1:1987, Information processing - 8-bit single-byte coded
character sets - Part 1: Latin alphabet No. 1.

7     ISO/IEC 9899:1990, Programming languages - C.

8/1   ISO/IEC 10646-1:1993, Information technology - Universal Multiple-Octet
Coded Character Set (UCS) - Part 1: Architecture and Basic Multilingual
Plane{, supplemented by Technical Corrigendum 1:1996.}[.]


1.3 Definitions


1     Terms are defined throughout this International Standard, indicated by
italic type. Terms explicitly defined in this International Standard are not
to be presumed to refer implicitly to similar terms defined elsewhere. Terms
not defined in this International Standard are to be interpreted according to
the Webster's Third New International Dictionary of the English Language.
Informal descriptions of some terms are also given in Annex N, ``Glossary''.



                         Section 2: Lexical Elements


1     The text of a program consists of the texts of one or more compilations.
The text of a compilation is a sequence of lexical elements, each composed of
characters; the rules of composition are given in this section. Pragmas, which
provide certain information for the compiler, are also described in this
section.


2.1 Character Set


1     The only characters allowed outside of comments are the
graphic_characters and format_effectors.


                                   Syntax

2     character ::= graphic_character | format_effector
       | other_control_function

3     graphic_character ::= identifier_letter | digit | space_character
       | special_character


                              Static Semantics

4     The character repertoire for the text of an Ada program consists of the
collection of characters called the Basic Multilingual Plane (BMP) of the ISO
10646 Universal Multiple-Octet Coded Character Set, plus a set of
format_effectors and, in comments only, a set of other_control_functions; the
coded representation for these characters is implementation defined (it need
not be a representation defined within ISO-10646-1).

5     The description of the language definition in this International
Standard uses the graphic symbols defined for Row 00: Basic Latin and Row 00:
Latin-1 Supplement of the ISO 10646 BMP; these correspond to the graphic
symbols of ISO 8859-1 (Latin-1); no graphic symbols are used in this
International Standard for characters outside of Row 00 of the BMP. The actual
set of graphic symbols used by an implementation for the visual representation
of the text of an Ada program is not specified.

6     The categories of characters are defined as follows:

7     identifier_letter
              upper_case_identifier_letter | lower_case_identifier_letter

8     upper_case_identifier_letter
              Any character of Row 00 of ISO 10646 BMP whose name begins ``
              Latin Capital Letter''.

9     lower_case_identifier_letter
              Any character of Row 00 of ISO 10646 BMP whose name begins ``
              Latin Small Letter''.

10    digit   One of the characters 0, 1, 2, 3, 4, 5, 6, 7, 8, or 9.

11    space_character
              The character of ISO 10646 BMP named ``Space''.

12    special_character
              Any character of the ISO 10646 BMP that is not reserved for a
              control function, and is not the space_character, an
              identifier_letter, or a digit.

13    format_effector
              The control functions of ISO 6429 called character tabulation
              (HT), line tabulation (VT), carriage return (CR), line feed
              (LF), and form feed (FF).

14    other_control_function
              Any control function, other than a format_effector, that is
              allowed in a comment; the set of other_control_functions allowed
              in comments is implementation defined.

15    The following names are used when referring to certain
special_characters:

      symbol

         "
         #
         &
         '
         (
         )
         *
         +
         ,
         -
         .
         /


name

quotation mark
number sign
ampersand
apostrophe, tick
left parenthesis
right parenthesis
asterisk, multiply
plus sign
comma
hyphen-minus, minus
full stop, dot, point
solidus, divide


      symbol

         :
         ;
         <
         =
         >
         _
         |
         [
         ]
         {
         }


name

colon
semicolon
less-than sign
equals sign
greater-than sign
low line, underline
vertical line
left square bracket
right square bracket
left curly bracket
right curly bracket


                         Implementation Permissions

16    In a nonstandard mode, the implementation may support a different
character repertoire; in particular, the set of characters that are considered
identifier_letters can be extended or changed to conform to local conventions.

      NOTES

17    1  Every code position of ISO 10646 BMP that is not reserved for a
      control function is defined to be a graphic_character by this
      International Standard. This includes all code positions other than 0000
      - 001F, 007F - 009F, and FFFE - FFFF.

18    2  The language does not specify the source representation of programs.


2.2 Lexical Elements, Separators, and Delimiters



                              Static Semantics

1     The text of a program consists of the texts of one or more compilations.
The text of each compilation is a sequence of separate lexical elements. Each
lexical element is formed from a sequence of characters, and is either a
delimiter, an identifier, a reserved word, a numeric_literal, a
character_literal, a string_literal, or a comment. The meaning of a program
depends only on the particular sequences of lexical elements that form its
compilations, excluding comments.

2     The text of a compilation is divided into lines. In general, the
representation for an end of line is implementation defined. However, a
sequence of one or more format_effectors other than character tabulation (HT)
signifies at least one end of line.

3     In some cases an explicit separator is required to separate adjacent
lexical elements. A separator is any of a space character, a format effector,
or the end of a line, as follows:

4     A space character is a separator except within a comment, a
      string_literal, or a character_literal.

5     Character tabulation (HT) is a separator except within a comment.

6     The end of a line is always a separator.

7     One or more separators are allowed between any two adjacent lexical
elements, before the first of each compilation, or after the last. At least
one separator is required between an identifier, a reserved word, or a
numeric_literal and an adjacent identifier, reserved word, or numeric_literal.

8     A delimiter is either one of the following special characters

9     &    '    (    )    *    +    ,    -    .    /    :    ;    <    =    >    |

10    or one of the following compound delimiters each composed of two
adjacent special characters

11    =>    ..    **    :=    /=    >=    <=    <<    >>    <>

12    Each of the special characters listed for single character delimiters is
a single delimiter except if this character is used as a character of a
compound delimiter, or as a character of a comment, string_literal,
character_literal, or numeric_literal.

13    The following names are used when referring to compound delimiters:

      delimiter

         =>
         ..
         **
         :=

         /=

         >=
         <=
         <<
         >>
         <>


name

arrow
double dot
double star, exponentiate
assignment (pronounced:
   ``becomes'')
inequality (pronounced:
   ``not equal'')
greater than or equal
less than or equal
left label bracket
right label bracket
box




                         Implementation Requirements

14    An implementation shall support lines of at least 200 characters in
length, not counting any characters used to signify the end of a line. An
implementation shall support lexical elements of at least 200 characters in
length. The maximum supported line length and lexical element length are
implementation defined.


2.3 Identifiers


1     Identifiers are used as names.


                                   Syntax

2     identifier ::= 
         identifier_letter {[underline] letter_or_digit}

3     letter_or_digit ::= identifier_letter | digit

4     An identifier shall not be a reserved word.


                              Static Semantics

5     All characters of an identifier are significant, including any underline
character. Identifiers differing only in the use of corresponding upper and
lower case letters are considered the same.


                         Implementation Permissions

6     In a nonstandard mode, an implementation may support other upper/lower
case equivalence rules for identifiers, to accommodate local conventions.


                                  Examples

7     Examples of identifiers:

8     Count      X    Get_Symbol   Ethelyn   Marion
      
      Snobol_4   X1   Page_Count    Store_Next_Item


2.4 Numeric Literals


1     There are two kinds of numeric_literals, real literals and integer
literals. A real literal is a numeric_literal that includes a point; an
integer literal is a numeric_literal without a point.


                                   Syntax

2     numeric_literal ::= decimal_literal | based_literal

      NOTES

3     3  The type of an integer literal is universal_integer. The type of a
      real literal is universal_real.


2.4.1 Decimal Literals


1     A decimal_literal is a numeric_literal in the conventional decimal
notation (that is, the base is ten).


                                   Syntax

2     decimal_literal ::= numeral [.numeral] [exponent]

3     numeral ::= digit {[underline] digit}

4     exponent ::= E [+] numeral | E - numeral

5     An exponent for an integer literal shall not have a minus sign.


                              Static Semantics

6     An underline character in a numeric_literal does not affect its meaning.
The letter E of an exponent can be written either in lower case or in upper
case, with the same meaning.

7     An exponent indicates the power of ten by which the value of the
decimal_literal without the exponent is to be multiplied to obtain the value
of the decimal_literal with the exponent.


                                  Examples

8     Examples of decimal literals:

9     12        0      1E6    123_456      --  integer literals
      
      12.0      0.0    0.456  3.14159_26   --  real literals


2.4.2 Based Literals


1     A based_literal is a numeric_literal expressed in a form that specifies
the base explicitly.


                                   Syntax

2     based_literal ::= 
         base # based_numeral [.based_numeral] # [exponent]

3     base ::= numeral

4     based_numeral ::= 
         extended_digit {[underline] extended_digit}

5     extended_digit ::= digit | A | B | C | D | E | F


                               Legality Rules

6     The base (the numeric value of the decimal numeral preceding the first
#) shall be at least two and at most sixteen. The extended_digits A through F
represent the digits ten through fifteen, respectively. The value of each
extended_digit of a based_literal shall be less than the base.


                              Static Semantics

7     The conventional meaning of based notation is assumed. An exponent
indicates the power of the base by which the value of the based_literal
without the exponent is to be multiplied to obtain the value of the
based_literal with the exponent. The base and the exponent, if any, are in
decimal notation.

8     The extended_digits A through F can be written either in lower case or
in upper case, with the same meaning.


                                  Examples

9     Examples of based literals:

10    2#1111_1111#       16#FF#       016#0ff#               
      --  integer literals of value 255
      16#E#E1            2#1110_0000#                        
      --  integer literals of value 224
      16#F.FF#E+2        2#1.1111_1111_1110#E11              
      --  real literals of value 4095.0


2.5 Character Literals


1     A character_literal is formed by enclosing a graphic character between
two apostrophe characters.


                                   Syntax

2     character_literal ::= 'graphic_character'

      NOTES

3     4  A character_literal is an enumeration literal of a character type.
      See 3.5.2.


                                  Examples

4     Examples of character literals:

5     'A'     '*'     '''     ' '


2.6 String Literals


1     A string_literal is formed by a sequence of graphic characters (possibly
none) enclosed between two quotation marks used as string brackets. They are
used to represent operator_symbols (see 6.1), values of a string type (see
4.2), and array subaggregates (see 4.3.3).


                                   Syntax

2     string_literal ::= "{string_element}"

3     string_element ::= "" | non_quotation_mark_graphic_character

4     A string_element is either a pair of quotation marks (""), or a single
      graphic_character other than a quotation mark.


                              Static Semantics

5     The sequence of characters of a string_literal is formed from the
sequence of string_elements between the bracketing quotation marks, in the
given order, with a string_element that is "" becoming a single quotation mark
in the sequence of characters, and any other string_element being reproduced
in the sequence.

6     A null string literal is a string_literal with no string_elements
between the quotation marks.

      NOTES

7     5  An end of line cannot appear in a string_literal.


                                  Examples

8     Examples of string literals:

9     "Message of the day:"
      
      ""                 --  a null string literal
      " "   "A"   """"      --  three string literals of length 1
      
      "Characters such as $, %, and } are allowed in string literals"


2.7 Comments


1     A comment starts with two adjacent hyphens and extends up to the end of
the line.


                                   Syntax

2     comment ::= --{non_end_of_line_character}

3     A comment may appear on any line of a program.


                              Static Semantics

4     The presence or absence of comments has no influence on whether a
program is legal or illegal. Furthermore, comments do not influence the
meaning of a program; their sole purpose is the enlightenment of the human
reader.


                                  Examples

5     Examples of comments:

6     --  the last sentence above echoes the Algol 68 report 
      
      end;  --  processing of Line is complete 
      
      --  a long comment may be split onto
      --  two or more consecutive lines   
      
      ----------------  the first two hyphens start the comment  


2.8 Pragmas


1     A pragma is a compiler directive. There are language-defined pragmas
that give instructions for optimization, listing control, etc. An
implementation may support additional (implementation-defined) pragmas.


                                   Syntax

2     pragma ::= 
         pragma identifier [(pragma_argument_association
       {, pragma_argument_association})];

3     pragma_argument_association ::= 
           [pragma_argument_identifier =>] name
         | [pragma_argument_identifier =>] expression

4     In a pragma, any pragma_argument_associations without a
      pragma_argument_identifier shall precede any associations with a
      pragma_argument_identifier.

5     Pragmas are only allowed at the following places in a program:

    6     After a semicolon delimiter, but not within a formal_part or
          discriminant_part.

    7     At any place where the syntax rules allow a construct defined by a
          syntactic category whose name ends with "declaration", "statement",
          "clause", or "alternative", or one of the syntactic categories
          variant or exception_handler; but not in place of such a construct.
          Also at any place where a compilation_unit would be allowed.

8     Additional syntax rules and placement restrictions exist for specific
      pragmas.

9     The name of a pragma is the identifier following the reserved word
pragma. The name or expression of a pragma_argument_association is a pragma
argument.

10    An identifier specific to a pragma is an identifier that is used in a
pragma argument with special meaning for that pragma.


                              Static Semantics

11    If an implementation does not recognize the name of a pragma, then it
has no effect on the semantics of the program. Inside such a pragma, the only
rules that apply are the Syntax Rules.


                              Dynamic Semantics

12    Any pragma that appears at the place of an executable construct is
executed. Unless otherwise specified for a particular pragma, this execution
consists of the evaluation of each evaluable pragma argument in an arbitrary
order.


                         Implementation Requirements

13    The implementation shall give a warning message for an unrecognized
pragma name.


                         Implementation Permissions

14    An implementation may provide implementation-defined pragmas; the name
of an implementation-defined pragma shall differ from those of the
language-defined pragmas.

15    An implementation may ignore an unrecognized pragma even if it violates
some of the Syntax Rules, if detecting the syntax error is too complex.


                            Implementation Advice

16    Normally, implementation-defined pragmas should have no semantic effect
for error-free programs; that is, if the implementation-defined pragmas are
removed from a working program, the program should still be legal, and should
still have the same semantics.

17    Normally, an implementation should not define pragmas that can make an
illegal program legal, except as follows:

18    A pragma used to complete a declaration, such as a pragma Import;

19    A pragma used to configure the environment by adding, removing, or
      replacing library_items.


                                   Syntax

20    The forms of List, Page, and Optimize pragmas are as follows:

21      pragma List(identifier);

22      pragma Page;

23      pragma Optimize(identifier);

24    Other pragmas are defined throughout this International Standard, and
      are summarized in Annex L.


                              Static Semantics

25    A pragma List takes one of the identifiers On or Off as the single
argument. This pragma is allowed anywhere a pragma is allowed. It specifies
that listing of the compilation is to be continued or suspended until a List
pragma with the opposite argument is given within the same compilation. The
pragma itself is always listed if the compiler is producing a listing.

26    A pragma Page is allowed anywhere a pragma is allowed. It specifies that
the program text which follows the pragma should start on a new page (if the
compiler is currently producing a listing).

27    A pragma Optimize takes one of the identifiers Time, Space, or Off as
the single argument. This pragma is allowed anywhere a pragma is allowed, and
it applies until the end of the immediately enclosing declarative region, or
for a pragma at the place of a compilation_unit, to the end of the
compilation. It gives advice to the implementation as to whether time or space
is the primary optimization criterion, or that optional optimizations should
be turned off. It is implementation defined how this advice is followed.


                                  Examples

28    Examples of pragmas:

29    pragma List(Off); -- turn off listing generation
      pragma Optimize(Off); -- turn off optional optimizations
      pragma Inline(Set_Mask); -- generate code for Set_Mask inline
      pragma Suppress(Range_Check, On => Index); -- turn off range checking on Index




2.9 Reserved Words



                                   Syntax

1/1   This paragraph was deleted.[ ]

2     The following are the reserved words (ignoring upper/lower case
      distinctions):

          abort
          abs
          abstract
          accept
          access
          aliased
          all
          and
          array
          at

          begin
          body

          case
          constant

          declare
          delay
          delta
          digits
          do


          else
          elsif
          end
          entry
          exception
          exit

          for
          function

          generic
          goto

          if
          in
          is

          limited
          loop

          mod


          new
          not
          null

          of
          or
          others
          out

          package
          pragma
          private
          procedure
          protected

          raise
          range
          record
          rem
          renames
          requeue


          return
          reverse

          select
          separate
          subtype

          tagged
          task
          terminate
          then
          type

          until
          use

          when
          while
          with

          xor

      NOTES

3     6  The reserved words appear in lower case boldface in this
      International Standard, except when used in the designator of an
      attribute (see 4.1.4). Lower case boldface is also used for a reserved
      word in a string_literal used as an operator_symbol. This is merely a
      convention - programs may be written in whatever typeface is desired and
      available.



                      Section 3: Declarations and Types


1     This section describes the types in the language and the rules for
declaring constants, variables, and named numbers.


3.1 Declarations


1     The language defines several kinds of named entities that are declared
by declarations. The entity's name is defined by the declaration, usually by a
defining_identifier, but sometimes by a defining_character_literal or defining_-
operator_symbol.

2     There are several forms of declaration. A basic_declaration is a form of
declaration defined as follows.


                                   Syntax

3     basic_declaration ::= 
           type_declaration           | subtype_declaration
         | object_declaration         | number_declaration
         | subprogram_declaration     | abstract_subprogram_declaration
         | package_declaration        | renaming_declaration
         | exception_declaration      | generic_declaration
         | generic_instantiation

4     defining_identifier ::= identifier


                              Static Semantics

5     A declaration is a language construct that associates a name with (a
view of) an entity. A declaration may appear explicitly in the program text
(an explicit declaration), or may be supposed to occur at a given place in the
text as a consequence of the semantics of another construct (an implicit
declaration).

6     Each of the following is defined to be a declaration: any
basic_declaration; an enumeration_literal_specification; a discriminant_-
specification; a component_declaration; a loop_parameter_specification; a
parameter_specification; a subprogram_body; an entry_declaration; an entry_-
index_specification; a choice_parameter_specification; a generic_formal_-
parameter_declaration.

7     All declarations contain a definition for a view of an entity. A view
consists of an identification of the entity (the entity of the view), plus
view-specific characteristics that affect the use of the entity through that
view (such as mode of access to an object, formal parameter names and defaults
for a subprogram, or visibility to components of a type). In most cases, a
declaration also contains the definition for the entity itself (a
renaming_declaration is an example of a declaration that does not define a new
entity, but instead defines a view of an existing entity (see 8.5)).

8     For each declaration, the language rules define a certain region of text
called the scope of the declaration (see 8.2). Most declarations associate an
identifier with a declared entity. Within its scope, and only there, there are
places where it is possible to use the identifier to refer to the declaration,
the view it defines, and the associated entity; these places are defined by
the visibility rules (see 8.3). At such places the identifier is said to be a
name of the entity (the direct_name or selector_name); the name is said to
denote the declaration, the view, and the associated entity (see 8.6). The
declaration is said to declare the name, the view, and in most cases, the
entity itself.

9     As an alternative to an identifier, an enumeration literal can be
declared with a character_literal as its name (see 3.5.1), and a function can
be declared with an operator_symbol as its name (see 6.1).

10    The syntax rules use the terms defining_identifier, defining_character_-
literal, and defining_operator_symbol for the defining occurrence of a name;
these are collectively called defining names. The terms direct_name and
selector_name are used for usage occurrences of identifiers,
character_literals, and operator_symbols. These are collectively called usage
names.


                              Dynamic Semantics

11    The process by which a construct achieves its run-time effect is called
execution. This process is also called elaboration for declarations and
evaluation for expressions. One of the terms execution, elaboration, or
evaluation is defined by this International Standard for each construct that
has a run-time effect.

      NOTES

12    1  At compile time, the declaration of an entity declares the entity. At
      run time, the elaboration of the declaration creates the entity.


3.2 Types and Subtypes



                              Static Semantics

1     A type is characterized by a set of values, and a set of primitive
operations which implement the fundamental aspects of its semantics. An object
of a given type is a run-time entity that contains (has) a value of the type.

2     Types are grouped into classes of types, reflecting the similarity of
their values and primitive operations. There exist several language-defined
classes of types (see NOTES below). Elementary types are those whose values
are logically indivisible; composite types are those whose values are composed
of component values.

3     The elementary types are the scalar types (discrete and real) and the
access types (whose values provide access to objects or subprograms). Discrete
types are either integer types or are defined by enumeration of their values
(enumeration types). Real types are either floating point types or fixed point
types.

4     The composite types are the record types, record extensions, array
types, task types, and protected types. A private type or private extension
represents a partial view (see 7.3) of a type, providing support for data
abstraction. A partial view is a composite type.

5     Certain composite types (and partial views thereof) have special
components called discriminants whose values affect the presence, constraints,
or initialization of other components. Discriminants can be thought of as
parameters of the type.

6     The term subcomponent is used in this International Standard in place of
the term component to indicate either a component, or a component of another
subcomponent. Where other subcomponents are excluded, the term component is
used instead. Similarly, a part of an object or value is used to mean the
whole object or value, or any set of its subcomponents.

7     The set of possible values for an object of a given type can be
subjected to a condition that is called a constraint (the case of a null
constraint that specifies no restriction is also included); the rules for
which values satisfy a given kind of constraint are given in 3.5 for
range_constraints, 3.6.1 for index_constraints, and 3.7.1 for
discriminant_constraints.

8     A subtype of a given type is a combination of the type, a constraint on
values of the type, and certain attributes specific to the subtype. The given
type is called the type of the subtype. Similarly, the associated constraint
is called the constraint of the subtype. The set of values of a subtype
consists of the values of its type that satisfy its constraint. Such values
belong to the subtype.

9     A subtype is called an unconstrained subtype if its type has unknown
discriminants, or if its type allows range, index, or discriminant
constraints, but the subtype does not impose such a constraint; otherwise, the
subtype is called a constrained subtype (since it has no unconstrained
characteristics).

      NOTES

10    2  Any set of types that is closed under derivation (see 3.4) can be
      called a ``class'' of types. However, only certain classes are used in
      the description of the rules of the language - generally those that have
      their own particular set of primitive operations (see 3.2.3), or that
      correspond to a set of types that are matched by a given kind of generic
      formal type (see 12.5). The following are examples of ``interesting''
      language-defined classes: elementary, scalar, discrete, enumeration,
      character, boolean, integer, signed integer, modular, real, floating
      point, fixed point, ordinary fixed point, decimal fixed point, numeric,
      access, access-to-object, access-to-subprogram, composite, array,
      string, (untagged) record, tagged, task, protected, nonlimited. Special
      syntax is provided to define types in each of these classes.

11    These language-defined classes are organized like this:

    12    all types
            elementary
               scalar
                  discrete
                     enumeration
                        character
                        boolean
                        other enumeration
                     integer
                        signed integer
                        modular integer
                  real
                     floating point
                     fixed point
                        ordinary fixed point
                        decimal fixed point
               access
                  access-to-object
                  access-to-subprogram
            composite
               array
                  string
                  other array
               untagged record
               tagged
               task
               protected

13    The classes ``numeric'' and ``nonlimited'' represent other
      classification dimensions and do not fit into the above strictly
      hierarchical picture.


3.2.1 Type Declarations


1     A type_declaration declares a type and its first subtype.


                                   Syntax

2     type_declaration ::=  full_type_declaration
         | incomplete_type_declaration
         | private_type_declaration
         | private_extension_declaration

3     full_type_declaration ::= 
           type defining_identifier [known_discriminant_part
      ] is type_definition;
         | task_type_declaration
         | protected_type_declaration

4     type_definition ::= 
           enumeration_type_definition   | integer_type_definition
         | real_type_definition          | array_type_definition
         | record_type_definition        | access_type_definition
         | derived_type_definition


                               Legality Rules

5     A given type shall not have a subcomponent whose type is the given type
itself.


                              Static Semantics

6     The defining_identifier of a type_declaration denotes the first subtype
of the type. The known_discriminant_part, if any, defines the discriminants of
the type (see 3.7, ``Discriminants''). The remainder of the type_declaration
defines the remaining characteristics of (the view of) the type.

7     A type defined by a type_declaration is a named type; such a type has
one or more nameable subtypes. Certain other forms of declaration also include
type definitions as part of the declaration for an object (including a
parameter or a discriminant). The type defined by such a declaration is
anonymous - it has no nameable subtypes. For explanatory purposes, this
International Standard sometimes refers to an anonymous type by a pseudo-name,
written in italics, and uses such pseudo-names at places where the syntax
normally requires an identifier. For a named type whose first subtype is T,
this International Standard sometimes refers to the type of T as simply ``the
type T.''

8     A named type that is declared by a full_type_declaration, or an
anonymous type that is defined as part of declaring an object of the type, is
called a full type. The type_definition, task_definition,
protected_definition, or access_definition that defines a full type is called
a full type definition. Types declared by other forms of type_declaration are
not separate types; they are partial or incomplete views of some full type.

9     The definition of a type implicitly declares certain predefined
operators that operate on the type, according to what classes the type
belongs, as specified in 4.5, ``Operators and Expression Evaluation''.

10    The predefined types (for example the types Boolean, Wide_Character,
Integer, root_integer, and universal_integer) are the types that are defined
in a predefined library package called Standard; this package also includes
the (implicit) declarations of their predefined operators. The package
Standard is described in A.1.


                              Dynamic Semantics

11    The elaboration of a full_type_declaration consists of the elaboration
of the full type definition. Each elaboration of a full type definition
creates a distinct type and its first subtype.


                                  Examples

12    Examples of type definitions:

13    (White, Red, Yellow, Green, Blue, Brown, Black)
      range 1 .. 72
      array(1 .. 10) of Integer

14    Examples of type declarations:

15    type Color  is (White, Red, Yellow, Green, Blue, Brown, Black);
      type Column is range 1 .. 72;
      type Table  is array(1 .. 10) of Integer;

      NOTES

16    3  Each of the above examples declares a named type. The identifier
      given denotes the first subtype of the type. Other named subtypes of the
      type can be declared with subtype_declarations (see 3.2.2). Although
      names do not directly denote types, a phrase like ``the type Column'' is
      sometimes used in this International Standard to refer to the type of
      Column, where Column denotes the first subtype of the type. For an
      example of the definition of an anonymous type, see the declaration of
      the array Color_Table in 3.3.1; its type is anonymous - it has no
      nameable subtypes.


3.2.2 Subtype Declarations


1     A subtype_declaration declares a subtype of some previously declared
type, as defined by a subtype_indication.


                                   Syntax

2     subtype_declaration ::= 
         subtype defining_identifier is subtype_indication;

3     subtype_indication ::=  subtype_mark [constraint]

4     subtype_mark ::= subtype_name

5     constraint ::= scalar_constraint | composite_constraint

6     scalar_constraint ::= 
           range_constraint | digits_constraint | delta_constraint

7     composite_constraint ::= 
           index_constraint | discriminant_constraint


                            Name Resolution Rules

8     A subtype_mark shall resolve to denote a subtype. The type determined by
a subtype_mark is the type of the subtype denoted by the subtype_mark.


                              Dynamic Semantics

9     The elaboration of a subtype_declaration consists of the elaboration of
the subtype_indication. The elaboration of a subtype_indication creates a new
subtype. If the subtype_indication does not include a constraint, the new
subtype has the same (possibly null) constraint as that denoted by the
subtype_mark. The elaboration of a subtype_indication that includes a
constraint proceeds as follows:

10    The constraint is first elaborated.

11    A check is then made that the constraint is compatible with the subtype
      denoted by the subtype_mark.

12    The condition imposed by a constraint is the condition obtained after
elaboration of the constraint. The rules defining compatibility are given for
each form of constraint in the appropriate subclause. These rules are such
that if a constraint is compatible with a subtype, then the condition imposed
by the constraint cannot contradict any condition already imposed by the
subtype on its values. The exception Constraint_Error is raised if any check
of compatibility fails.

      NOTES

13    4  A scalar_constraint may be applied to a subtype of an appropriate
      scalar type (see 3.5, 3.5.9, and J.3), even if the subtype is already
      constrained. On the other hand, a composite_constraint may be applied to
      a composite subtype (or an access-to-composite subtype) only if the
      composite subtype is unconstrained (see 3.6.1 and 3.7.1).


                                  Examples

14    Examples of subtype declarations:

15    subtype Rainbow   is Color range Red .. Blue;        --  see 3.2.1
      subtype Red_Blue  is Rainbow;
      subtype Int       is Integer;
      subtype Small_Int is Integer range -10 .. 10;
      subtype Up_To_K   is Column range 1 .. K;            --  see 3.2.1
      subtype Square    is Matrix(1 .. 10, 1 .. 10);       --  see 3.6
      subtype Male      is Person(Sex => M);               --  see 3.10.1


3.2.3 Classification of Operations



                              Static Semantics

1     An operation operates on a type T if it yields a value of type T, if it
has an operand whose expected type (see 8.6) is T, or if it has an access
parameter (see 6.1) designating T. A predefined operator, or other
language-defined operation such as assignment or a membership test, that
operates on a type, is called a predefined operation of the type. The
primitive operations of a type are the predefined operations of the type, plus
any user-defined primitive subprograms.

2     The primitive subprograms of a specific type are defined as follows:

3     The predefined operators of the type (see 4.5);

4     For a derived type, the inherited (see 3.4) user-defined subprograms;

5     For an enumeration type, the enumeration literals (which are considered
      parameterless functions - see 3.5.1);

6     For a specific type declared immediately within a package_specification,
      any subprograms (in addition to the enumeration literals) that are
      explicitly declared immediately within the same package_specification
      and that operate on the type;

7     Any subprograms not covered above that are explicitly declared
      immediately within the same declarative region as the type and that
      override (see 8.3) other implicitly declared primitive subprograms of
      the type.

8     A primitive subprogram whose designator is an operator_symbol is called
a primitive operator.


3.3 Objects and Named Numbers


1     Objects are created at run time and contain a value of a given type. An
object can be created and initialized as part of elaborating a declaration,
evaluating an allocator, aggregate, or function_call, or passing a parameter
by copy. Prior to reclaiming the storage for an object, it is finalized if
necessary (see 7.6.1).


                              Static Semantics

2     All of the following are objects:

3     the entity declared by an object_declaration;

4     a formal parameter of a subprogram, entry, or generic subprogram;

5     a generic formal object;

6     a loop parameter;

7     a choice parameter of an exception_handler;

8     an entry index of an entry_body;

9     the result of dereferencing an access-to-object value (see 4.1);

10    the result of evaluating a function_call (or the equivalent operator
      invocation - see 6.6);

11    the result of evaluating an aggregate;

12    a component, slice, or view conversion of another object.

13    An object is either a constant object or a variable object. The value of
a constant object cannot be changed between its initialization and its
finalization, whereas the value of a variable object can be changed.
Similarly, a view of an object is either a constant or a variable. All views
of a constant object are constant. A constant view of a variable object cannot
be used to modify the value of the variable. The terms constant and variable
by themselves refer to constant and variable views of objects.

14    The value of an object is read when the value of any part of the object
is evaluated, or when the value of an enclosing object is evaluated. The value
of a variable is updated when an assignment is performed to any part of the
variable, or when an assignment is performed to an enclosing object.

15    Whether a view of an object is constant or variable is determined by the
definition of the view. The following (and no others) represent constants:

16    an object declared by an object_declaration with the reserved word
      constant;

17    a formal parameter or generic formal object of mode in;

18    a discriminant;

19    a loop parameter, choice parameter, or entry index;

20    the dereference of an access-to-constant value;

21    the result of evaluating a function_call or an aggregate;

22    a selected_component, indexed_component, slice, or view conversion of a
      constant.

23    At the place where a view of an object is defined, a nominal subtype is
associated with the view. The object's actual subtype (that is, its subtype)
can be more restrictive than the nominal subtype of the view; it always is if
the nominal subtype is an indefinite subtype. A subtype is an indefinite
subtype if it is an unconstrained array subtype, or if it has unknown
discriminants or unconstrained discriminants without defaults (see 3.7);
otherwise the subtype is a definite subtype (all elementary subtypes are
definite subtypes). A class-wide subtype is defined to have unknown
discriminants, and is therefore an indefinite subtype. An indefinite subtype
does not by itself provide enough information to create an object; an
additional constraint or explicit initialization expression is necessary (see
3.3.1). A component cannot have an indefinite nominal subtype.

24    A named number provides a name for a numeric value known at compile
time. It is declared by a number_declaration.

      NOTES

25    5  A constant cannot be the target of an assignment operation, nor be
      passed as an in out or out parameter, between its initialization and
      finalization, if any.

26    6  The nominal and actual subtypes of an elementary object are always
      the same. For a discriminated or array object, if the nominal subtype is
      constrained then so is the actual subtype.


3.3.1 Object Declarations


1     An object_declaration declares a stand-alone object with a given nominal
subtype and, optionally, an explicit initial value given by an initialization
expression. For an array, task, or protected object, the object_declaration
may include the definition of the (anonymous) type of the object.


                                   Syntax

2     object_declaration ::= 
          defining_identifier_list
       : [aliased] [constant] subtype_indication [:= expression];
        | defining_identifier_list
       : [aliased] [constant] array_type_definition [:= expression];
        | single_task_declaration
        | single_protected_declaration

3     defining_identifier_list ::= 
        defining_identifier {, defining_identifier}


                            Name Resolution Rules

4     For an object_declaration with an expression following the compound
delimiter :=, the type expected for the expression is that of the object. This
expression is called the initialization expression.


                               Legality Rules

5     An object_declaration without the reserved word constant declares a
variable object. If it has a subtype_indication or an array_type_definition
that defines an indefinite subtype, then there shall be an initialization
expression. An initialization expression shall not be given if the object is
of a limited type.


                              Static Semantics

6     An object_declaration with the reserved word constant declares a
constant object. If it has an initialization expression, then it is called a
full constant declaration. Otherwise it is called a deferred constant
declaration. The rules for deferred constant declarations are given in clause
7.4. The rules for full constant declarations are given in this subclause.

7     Any declaration that includes a defining_identifier_list with more than
one defining_identifier is equivalent to a series of declarations each
containing one defining_identifier from the list, with the rest of the text of
the declaration copied for each declaration in the series, in the same order
as the list. The remainder of this International Standard relies on this
equivalence; explanations are given for declarations with a single
defining_identifier.

8     The subtype_indication or full type definition of an object_declaration
defines the nominal subtype of the object. The object_declaration declares an
object of the type of the nominal subtype.


                              Dynamic Semantics

9     If a composite object declared by an object_declaration has an
unconstrained nominal subtype, then if this subtype is indefinite or the
object is constant or aliased (see 3.10) the actual subtype of this object is
constrained. The constraint is determined by the bounds or discriminants (if
any) of its initial value; the object is said to be constrained by its initial
value. In the case of an aliased object, this initial value may be either
explicit or implicit; in the other cases, an explicit initial value is
required. When not constrained by its initial value, the actual and nominal
subtypes of the object are the same. If its actual subtype is constrained, the
object is called a constrained object.

10    For an object_declaration without an initialization expression, any
initial values for the object or its subcomponents are determined by the
implicit initial values defined for its nominal subtype, as follows:

11    The implicit initial value for an access subtype is the null value of
      the access type.

12    The implicit initial (and only) value for each discriminant of a
      constrained discriminated subtype is defined by the subtype.

13    For a (definite) composite subtype, the implicit initial value of each
      component with a default_expression is obtained by evaluation of this
      expression and conversion to the component's nominal subtype (which
      might raise Constraint_Error - see 4.6, ``Type Conversions''), unless
      the component is a discriminant of a constrained subtype (the previous
      case), or is in an excluded variant (see 3.8.1). For each component that
      does not have a default_expression, any implicit initial values are
      those determined by the component's nominal subtype.

14    For a protected or task subtype, there is an implicit component (an
      entry queue) corresponding to each entry, with its implicit initial
      value being an empty queue.

15    The elaboration of an object_declaration proceeds in the following
sequence of steps:

16    1.  The subtype_indication, array_type_definition,
          single_task_declaration, or single_protected_declaration is first
          elaborated. This creates the nominal subtype (and the anonymous type
          in the latter three cases).

17    2.  If the object_declaration includes an initialization expression, the
          (explicit) initial value is obtained by evaluating the expression
          and converting it to the nominal subtype (which might raise
          Constraint_Error - see 4.6).

18/1  3.  The object is created, and, if there is not an initialization
          expression, any per-object expressions (see 3.8) are
          {elaborated}[evaluated] and any implicit initial values for the
          object or for its subcomponents are obtained as determined by the
          nominal subtype.

19    4.  Any initial values (whether explicit or implicit) are assigned to
          the object or to the corresponding subcomponents. As described in
          5.2 and 7.6, Initialize and Adjust procedures can be called.

20    For the third step above, the object creation and any elaborations and
evaluations are performed in an arbitrary order, except that if the
default_expression for a discriminant is evaluated to obtain its initial
value, then this evaluation is performed before that of the default_expression
for any component that depends on the discriminant, and also before that of
any default_expression that includes the name of the discriminant. The
evaluations of the third step and the assignments of the fourth step are
performed in an arbitrary order, except that each evaluation is performed
before the resulting value is assigned.

21    There is no implicit initial value defined for a scalar subtype. In the
absence of an explicit initialization, a newly created scalar object might
have a value that does not belong to its subtype (see 13.9.1 and H.1).

      NOTES

22    7  Implicit initial values are not defined for an indefinite subtype,
      because if an object's nominal subtype is indefinite, an explicit
      initial value is required.

23    8  As indicated above, a stand-alone object is an object declared by an
      object_declaration. Similar definitions apply to ``stand-alone
      constant'' and ``stand-alone variable.'' A subcomponent of an object is not a
      stand-alone object, nor is an object that is created by an allocator. An
      object declared by a loop_parameter_specification,
      parameter_specification, entry_index_specification,
      choice_parameter_specification, or a formal_object_declaration is not
      called a stand-alone object.

24    9  The type of a stand-alone object cannot be abstract (see 3.9.3).


                                  Examples

25    Example of a multiple object declaration:

26    --  the multiple object declaration 

27    John, Paul : Person_Name := new Person(Sex => M);  --  see 3.10.1

28    --  is equivalent to the two single object declarations in the order given

29    John : Person_Name := new Person(Sex => M);
      Paul : Person_Name := new Person(Sex => M);

30    Examples of variable declarations:

31    Count, Sum  : Integer;
      Size        : Integer range 0 .. 10_000 := 0;
      Sorted      : Boolean := False;
      Color_Table : array(1 .. Max) of Color;
      Option      : Bit_Vector(1 .. 10) := (others => True);
      Hello       : constant String := "Hi, world.";

32    Examples of constant declarations:

33    Limit     : constant Integer := 10_000;
      Low_Limit : constant Integer := Limit/10;
      Tolerance : constant Real := Dispersion(1.15);


3.3.2 Number Declarations


1     A number_declaration declares a named number.


                                   Syntax

2     number_declaration ::= 
           defining_identifier_list : constant := static_expression;


                            Name Resolution Rules

3     The static_expression given for a number_declaration is expected to be
of any numeric type.


                               Legality Rules

4     The static_expression given for a number declaration shall be a static
expression, as defined by clause 4.9.


                              Static Semantics

5     The named number denotes a value of type universal_integer if the type
of the static_expression is an integer type. The named number denotes a value
of type universal_real if the type of the static_expression is a real type.

6     The value denoted by the named number is the value of the
static_expression, converted to the corresponding universal type.


                              Dynamic Semantics

7     The elaboration of a number_declaration has no effect.


                                  Examples

8     Examples of number declarations:

9     Two_Pi        : constant := 2.0*Ada.Numerics.Pi;   -- a real number (see A.5
      )

10    Max           : constant := 500;                   -- an integer number
      Max_Line_Size : constant := Max/6                  -- the integer 83
      Power_16      : constant := 2**16;                 -- the integer 65_536
      One, Un, Eins : constant := 1;                     -- three different names for 1


3.4 Derived Types and Classes


1     A derived_type_definition defines a new type (and its first subtype)
whose characteristics are derived from those of a parent type.


                                   Syntax

2     derived_type_definition ::= [abstract] new parent_subtype_indication
       [record_extension_part]


                               Legality Rules

3     The parent_subtype_indication defines the parent subtype; its type is
the parent type.

4     A type shall be completely defined (see 3.11.1) prior to being specified
as the parent type in a derived_type_definition - the full_type_declarations
for the parent type and any of its subcomponents have to precede the
derived_type_definition.

5     If there is a record_extension_part, the derived type is called a record
extension of the parent type. A record_extension_part shall be provided if and
only if the parent type is a tagged type.


                              Static Semantics

6     The first subtype of the derived type is unconstrained if a
known_discriminant_part is provided in the declaration of the derived type, or
if the parent subtype is unconstrained. Otherwise, the constraint of the first
subtype corresponds to that of the parent subtype in the following sense: it
is the same as that of the parent subtype except that for a range constraint
(implicit or explicit), the value of each bound of its range is replaced by
the corresponding value of the derived type.

7     The characteristics of the derived type are defined as follows:

8     Each class of types that includes the parent type also includes the
      derived type.

9     If the parent type is an elementary type or an array type, then the set
      of possible values of the derived type is a copy of the set of possible
      values of the parent type. For a scalar type, the base range of the
      derived type is the same as that of the parent type.

10    If the parent type is a composite type other than an array type, then
      the components, protected subprograms, and entries that are declared for
      the derived type are as follows:

    11    The discriminants specified by a new known_discriminant_part, if
          there is one; otherwise, each discriminant of the parent type
          (implicitly declared in the same order with the same specifications)
          - in the latter case, the discriminants are said to be inherited, or
          if unknown in the parent, are also unknown in the derived type;

    12    Each nondiscriminant component, entry, and protected subprogram of
          the parent type, implicitly declared in the same order with the same
          declarations; these components, entries, and protected subprograms
          are said to be inherited;

    13    Each component declared in a record_extension_part, if any.

14    Declarations of components, protected subprograms, and entries, whether
      implicit or explicit, occur immediately within the declarative region of
      the type, in the order indicated above, following the parent
      subtype_indication.

15    The derived type is limited if and only if the parent type is limited.

16    For each predefined operator of the parent type, there is a
      corresponding predefined operator of the derived type.

17    For each user-defined primitive subprogram (other than a user-defined
      equality operator - see below) of the parent type that already exists at
      the place of the derived_type_definition, there exists a corresponding
      inherited primitive subprogram of the derived type with the same
      defining name. Primitive user-defined equality operators of the parent
      type are also inherited by the derived type, except when the derived
      type is a nonlimited record extension, and the inherited operator would
      have a profile that is type conformant with the profile of the
      corresponding predefined equality operator; in this case, the
      user-defined equality operator is not inherited, but is rather
      incorporated into the implementation of the predefined equality operator
      of the record extension (see 4.5.2).

18    The profile of an inherited subprogram (including an inherited
      enumeration literal) is obtained from the profile of the corresponding
      (user-defined) primitive subprogram of the parent type, after systematic
      replacement of each subtype of its profile (see 6.1) that is of the
      parent type with a corresponding subtype of the derived type. For a
      given subtype of the parent type, the corresponding subtype of the
      derived type is defined as follows:

    19    If the declaration of the derived type has neither a
          known_discriminant_part nor a record_extension_part, then the
          corresponding subtype has a constraint that corresponds (as defined
          above for the first subtype of the derived type) to that of the
          given subtype.

    20    If the derived type is a record extension, then the corresponding
          subtype is the first subtype of the derived type.

    21    If the derived type has a new known_discriminant_part but is not a
          record extension, then the corresponding subtype is constrained to
          those values that when converted to the parent type belong to the
          given subtype (see 4.6).

22    The same formal parameters have default_expressions in the profile of
      the inherited subprogram. Any type mismatch due to the systematic
      replacement of the parent type by the derived type is handled as part of
      the normal type conversion associated with parameter passing - see
      6.4.1.

23    If a primitive subprogram of the parent type is visible at the place of
the derived_type_definition, then the corresponding inherited subprogram is
implicitly declared immediately after the derived_type_definition. Otherwise,
the inherited subprogram is implicitly declared later or not at all, as
explained in 7.3.1.

24    A derived type can also be defined by a private_extension_declaration
(see 7.3) or a formal_derived_type_definition (see 12.5.1). Such a derived
type is a partial view of the corresponding full or actual type.

25    All numeric types are derived types, in that they are implicitly derived
from a corresponding root numeric type (see 3.5.4 and 3.5.6).


                              Dynamic Semantics

26    The elaboration of a derived_type_definition creates the derived type
and its first subtype, and consists of the elaboration of the
subtype_indication and the record_extension_part, if any. If the subtype_-
indication depends on a discriminant, then only those expressions that do not
depend on a discriminant are evaluated.

27    For the execution of a call on an inherited subprogram, a call on the
corresponding primitive subprogram of the parent type is performed; the normal
conversion of each actual parameter to the subtype of the corresponding formal
parameter (see 6.4.1) performs any necessary type conversion as well. If the
result type of the inherited subprogram is the derived type, the result of
calling the parent's subprogram is converted to the derived type.

      NOTES

28    10  Classes are closed under derivation - any class that contains a type
      also contains its derivatives. Operations available for a given class of
      types are available for the derived types in that class.

29    11  Evaluating an inherited enumeration literal is equivalent to
      evaluating the corresponding enumeration literal of the parent type, and
      then converting the result to the derived type. This follows from their
      equivalence to parameterless functions.

30    12  A generic subprogram is not a subprogram, and hence cannot be a
      primitive subprogram and cannot be inherited by a derived type. On the
      other hand, an instance of a generic subprogram can be a primitive
      subprogram, and hence can be inherited.

31    13  If the parent type is an access type, then the parent and the
      derived type share the same storage pool; there is a null access value
      for the derived type and it is the implicit initial value for the type.
      See 3.10.

32    14  If the parent type is a boolean type, the predefined relational
      operators of the derived type deliver a result of the predefined type
      Boolean (see 4.5.2). If the parent type is an integer type, the right
      operand of the predefined exponentiation operator is of the predefined
      type Integer (see 4.5.6).

33    15  Any discriminants of the parent type are either all inherited, or
      completely replaced with a new set of discriminants.

34    16  For an inherited subprogram, the subtype of a formal parameter of
      the derived type need not have any value in common with the first
      subtype of the derived type.

35    17  If the reserved word abstract is given in the declaration of a type,
      the type is abstract (see 3.9.3).


                                  Examples

36    Examples of derived type declarations:

37    type Local_Coordinate is new Coordinate;   --  two different types
      type Midweek is new Day range Tue .. Thu;  --  see 3.5.1
      type Counter is new Positive;              --  same range as Positive 

38    type Special_Key is new Key_Manager.Key;   --  see 7.3.1
        -- the inherited subprograms have the following specifications: 
        --         procedure Get_Key(K : out Special_Key);
        --         function "<"(X,Y : Special_Key) return Boolean;


3.4.1 Derivation Classes


1     In addition to the various language-defined classes of types, types can
be grouped into derivation classes.


                              Static Semantics

2     A derived type is derived from its parent type directly; it is derived
indirectly from any type from which its parent type is derived. The derivation
class of types for a type T (also called the class rooted at T) is the set
consisting of T (the root type of the class) and all types derived from T
(directly or indirectly) plus any associated universal or class-wide types
(defined below).

3     Every type is either a specific type, a class-wide type, or a universal
type. A specific type is one defined by a type_declaration, a
formal_type_declaration, or a full type definition embedded in a declaration
for an object. Class-wide and universal types are implicitly defined, to act
as representatives for an entire class of types, as follows:

4     Class-wide types
              Class-wide types are defined for (and belong to) each derivation
              class rooted at a tagged type (see 3.9). Given a subtype S of a
              tagged type T, S'Class is the subtype_mark for a corresponding
              subtype of the tagged class-wide type T'Class. Such types are
              called ``class-wide'' because when a formal parameter is defined
              to be of a class-wide type T'Class, an actual parameter of any
              type in the derivation class rooted at T is acceptable (see
              8.6).

        5     The set of values for a class-wide type T'Class is the
              discriminated union of the set of values of each specific type
              in the derivation class rooted at T (the tag acts as the
              implicit discriminant - see 3.9). Class-wide types have no
              primitive subprograms of their own. However, as explained in
              3.9.2, operands of a class-wide type T'Class can be used as part
              of a dispatching call on a primitive subprogram of the type T.
              The only components (including discriminants) of T'Class that
              are visible are those of T. If S is a first subtype, then
              S'Class is a first subtype.

6     Universal types
              Universal types are defined for (and belong to) the integer,
              real, and fixed point classes, and are referred to in this
              standard as respectively, universal_integer, universal_real, and
              universal_fixed. These are analogous to class-wide types for
              these language-defined numeric classes. As with class-wide
              types, if a formal parameter is of a universal type, then an
              actual parameter of any type in the corresponding class is
              acceptable. In addition, a value of a universal type (including
              an integer or real numeric_literal) is ``universal'' in that it
              is acceptable where some particular type in the class is
              expected (see 8.6).

        7     The set of values of a universal type is the undiscriminated
              union of the set of values possible for any definable type in
              the associated class. Like class-wide types, universal types
              have no primitive subprograms of their own. However, their ``
              universality'' allows them to be used as operands with the
              primitive subprograms of any type in the corresponding class.

8     The integer and real numeric classes each have a specific root type in
addition to their universal type, named respectively root_integer and
root_real.

9     A class-wide or universal type is said to cover all of the types in its
class. A specific type covers only itself.

10    A specific type T2 is defined to be a descendant of a type T1 if T2 is
the same as T1, or if T2 is derived (directly or indirectly) from T1. A
class-wide type T2'Class is defined to be a descendant of type T1 if T2 is a
descendant of T1. Similarly, the universal types are defined to be descendants
of the root types of their classes. If a type T2 is a descendant of a type T1,
then T1 is called an ancestor of T2. The ultimate ancestor of a type is the
ancestor of the type that is not a descendant of any other type.

11    An inherited component (including an inherited discriminant) of a
derived type is inherited from a given ancestor of the type if the
corresponding component was inherited by each derived type in the chain of
derivations going back to the given ancestor.

      NOTES

12    18  Because operands of a universal type are acceptable to the
      predefined operators of any type in their class, ambiguity can result.
      For universal_integer and universal_real, this potential ambiguity is
      resolved by giving a preference (see 8.6) to the predefined operators of
      the corresponding root types (root_integer and root_real, respectively).
      Hence, in an apparently ambiguous expression like

    13    1 + 4 < 7

14    where each of the literals is of type universal_integer, the predefined
      operators of root_integer will be preferred over those of other specific
      integer types, thereby resolving the ambiguity.


3.5 Scalar Types


1     Scalar types comprise enumeration types, integer types, and real types.
Enumeration types and integer types are called discrete types; each value of a
discrete type has a position number which is an integer value. Integer types
and real types are called numeric types. All scalar types are ordered, that
is, all relational operators are predefined for their values.


                                   Syntax

2     range_constraint ::=  range range

3     range ::=  range_attribute_reference
         | simple_expression .. simple_expression

4     A range has a lower bound and an upper bound and specifies a subset of
the values of some scalar type (the type of the range). A range with lower
bound L and upper bound R is described by ``L .. R''. If R is less than L,
then the range is a null range, and specifies an empty set of values.
Otherwise, the range specifies the values of the type from the lower bound to
the upper bound, inclusive. A value belongs to a range if it is of the type of
the range, and is in the subset of values specified by the range. A value
satisfies a range constraint if it belongs to the associated range. One range
is included in another if all values that belong to the first range also
belong to the second.


                            Name Resolution Rules

5     For a subtype_indication containing a range_constraint, either directly
or as part of some other scalar_constraint, the type of the range shall
resolve to that of the type determined by the subtype_mark of the
subtype_indication. For a range of a given type, the simple_expressions of the
range (likewise, the simple_expressions of the equivalent range for a
range_attribute_reference) are expected to be of the type of the range.


                              Static Semantics

6     The base range of a scalar type is the range of finite values of the
type that can be represented in every unconstrained object of the type; it is
also the range supported at a minimum for intermediate values during the
evaluation of expressions involving predefined operators of the type.

7     A constrained scalar subtype is one to which a range constraint applies.
The range of a constrained scalar subtype is the range associated with the
range constraint of the subtype. The range of an unconstrained scalar subtype
is the base range of its type.


                              Dynamic Semantics

8     A range is compatible with a scalar subtype if and only if it is either
a null range or each bound of the range belongs to the range of the subtype. A
range_constraint is compatible with a scalar subtype if and only if its range
is compatible with the subtype.

9     The elaboration of a range_constraint consists of the evaluation of the
range. The evaluation of a range determines a lower bound and an upper bound.
If simple_expressions are given to specify bounds, the evaluation of the range
evaluates these simple_expressions in an arbitrary order, and converts them to
the type of the range. If a range_attribute_reference is given, the evaluation
of the range consists of the evaluation of the range_attribute_reference.

10    Attributes

11    For every scalar subtype S, the following attributes are defined:

12    S'First S'First denotes the lower bound of the range of S. The value of
              this attribute is of the type of S.

13    S'Last  S'Last denotes the upper bound of the range of S. The value of
              this attribute is of the type of S.

14    S'Range S'Range is equivalent to the range S'First .. S'Last.

15    S'Base  S'Base denotes an unconstrained subtype of the type of S. This
              unconstrained subtype is called the base subtype of the type.

16    S'Min   S'Min denotes a function with the following specification:

            17    function S'Min(Left, Right : S'Base)
                    return S'Base

        18    The function returns the lesser of the values of the two
              parameters.

19    S'Max   S'Max denotes a function with the following specification:

            20    function S'Max(Left, Right : S'Base)
                    return S'Base

        21    The function returns the greater of the values of the two
              parameters.

22    S'Succ  S'Succ denotes a function with the following specification:

            23    function S'Succ(Arg : S'Base)
                    return S'Base

        24    For an enumeration type, the function returns the value whose
              position number is one more than that of the value of Arg;
              Constraint_Error is raised if there is no such value of the
              type. For an integer type, the function returns the result of
              adding one to the value of Arg. For a fixed point type, the
              function returns the result of adding small to the value of Arg.
              For a floating point type, the function returns the machine
              number (as defined in 3.5.7) immediately above the value of Arg;
              Constraint_Error is raised if there is no such machine number.

25    S'Pred  S'Pred denotes a function with the following specification:

            26    function S'Pred(Arg : S'Base)
                    return S'Base

        27    For an enumeration type, the function returns the value whose
              position number is one less than that of the value of Arg;
              Constraint_Error is raised if there is no such value of the
              type. For an integer type, the function returns the result of
              subtracting one from the value of Arg. For a fixed point type,
              the function returns the result of subtracting small from the
              value of Arg. For a floating point type, the function returns
              the machine number (as defined in 3.5.7) immediately below the
              value of Arg; Constraint_Error is raised if there is no such
              machine number.

28    S'Wide_Image
              S'Wide_Image denotes a function with the following
              specification:

            29    function S'Wide_Image(Arg : S'Base)
                    return Wide_String

        30    The function returns an image of the value of Arg, that is, a
              sequence of characters representing the value in display form.
              The lower bound of the result is one.

        31    The image of an integer value is the corresponding decimal
              literal, without underlines, leading zeros, exponent, or
              trailing spaces, but with a single leading character that is
              either a minus sign or a space.

        32    The image of an enumeration value is either the corresponding
              identifier in upper case or the corresponding character literal
              (including the two apostrophes); neither leading nor trailing
              spaces are included. For a nongraphic character (a value of a
              character type that has no enumeration literal associated with
              it), the result is a corresponding language-defined or
              implementation-defined name in upper case (for example, the
              image of the nongraphic character identified as nul is ``NUL'
              ' - the quotes are not part of the image).

        33    The image of a floating point value is a decimal real literal
              best approximating the value (rounded away from zero if halfway
              between) with a single leading character that is either a minus
              sign or a space, a single digit (that is nonzero unless the
              value is zero), a decimal point, S'Digits-1 (see 3.5.8) digits
              after the decimal point (but one if S'Digits is one), an upper
              case E, the sign of the exponent (either + or -), and two or
              more digits (with leading zeros if necessary) representing the
              exponent. If S'Signed_Zeros is True, then the leading character
              is a minus sign for a negatively signed zero.

        34    The image of a fixed point value is a decimal real literal best
              approximating the value (rounded away from zero if halfway
              between) with a single leading character that is either a minus
              sign or a space, one or more digits before the decimal point
              (with no redundant leading zeros), a decimal point, and S'Aft
              (see 3.5.10) digits after the decimal point.

35    S'Image S'Image denotes a function with the following specification:

            36    function S'Image(Arg : S'Base)
                    return String

        37    The function returns an image of the value of Arg as a String.
              The lower bound of the result is one. The image has the same
              sequence of graphic characters as that defined for S'Wide_Image
              if all the graphic characters are defined in Character;
              otherwise the sequence of characters is implementation defined
              (but no shorter than that of S'Wide_Image for the same value of
              Arg).

38    S'Wide_Width
              S'Wide_Width denotes the maximum length of a Wide_String
              returned by S'Wide_Image over all values of the subtype S. It
              denotes zero for a subtype that has a null range. Its type is
              universal_integer.

39    S'Width S'Width denotes the maximum length of a String returned by
              S'Image over all values of the subtype S. It denotes zero for a
              subtype that has a null range. Its type is universal_integer.

40    S'Wide_Value
              S'Wide_Value denotes a function with the following
              specification:

            41    function S'Wide_Value(Arg : Wide_String)
                    return S'Base

        42    This function returns a value given an image of the value as a
              Wide_String, ignoring any leading or trailing spaces.

        43    For the evaluation of a call on S'Wide_Value for an enumeration
              subtype S, if the sequence of characters of the parameter
              (ignoring leading and trailing spaces) has the syntax of an
              enumeration literal and if it corresponds to a literal of the
              type of S (or corresponds to the result of S'Wide_Image for a
              nongraphic character of the type), the result is the
              corresponding enumeration value; otherwise Constraint_Error is
              raised.

        44    For the evaluation of a call on S'Wide_Value (or S'Value) for an
              integer subtype S, if the sequence of characters of the
              parameter (ignoring leading and trailing spaces) has the syntax
              of an integer literal, with an optional leading sign character
              (plus or minus for a signed type; only plus for a modular type),
              and the corresponding numeric value belongs to the base range of
              the type of S, then that value is the result; otherwise
              Constraint_Error is raised.

        45    For the evaluation of a call on S'Wide_Value (or S'Value) for a
              real subtype S, if the sequence of characters of the parameter
              (ignoring leading and trailing spaces) has the syntax of one of
              the following:

            46    numeric_literal

            47    numeral.[exponent]

            48    .numeral[exponent]

            49    base#based_numeral.#[exponent]

            50    base#.based_numeral#[exponent]

        51    with an optional leading sign character (plus or minus), and if
              the corresponding numeric value belongs to the base range of the
              type of S, then that value is the result; otherwise
              Constraint_Error is raised. The sign of a zero value is
              preserved (positive if none has been specified) if
              S'Signed_Zeros is True.

52    S'Value S'Value denotes a function with the following specification:

            53    function S'Value(Arg : String)
                    return S'Base

        54    This function returns a value given an image of the value as a
              String, ignoring any leading or trailing spaces.

        55    For the evaluation of a call on S'Value for an enumeration
              subtype S, if the sequence of characters of the parameter
              (ignoring leading and trailing spaces) has the syntax of an
              enumeration literal and if it corresponds to a literal of the
              type of S (or corresponds to the result of S'Image for a value
              of the type), the result is the corresponding enumeration value;
              otherwise Constraint_Error is raised. For a numeric subtype S,
              the evaluation of a call on S'Value with Arg of type String is
              equivalent to a call on S'Wide_Value for a corresponding Arg of
              type Wide_String.


                         Implementation Permissions

56    An implementation may extend the Wide_Value, Value, Wide_Image, and
Image attributes of a floating point type to support special values such as
infinities and NaNs.

      NOTES

57    19  The evaluation of S'First or S'Last never raises an exception. If a
      scalar subtype S has a nonnull range, S'First and S'Last belong to this
      range. These values can, for example, always be assigned to a variable
      of subtype S.

58    20  For a subtype of a scalar type, the result delivered by the
      attributes Succ, Pred, and Value might not belong to the subtype;
      similarly, the actual parameters of the attributes Succ, Pred, and Image
      need not belong to the subtype.

59    21  For any value V (including any nongraphic character) of an
      enumeration subtype S, S'Value(S'Image(V)) equals V, as does
      S'Wide_Value(S'Wide_Image(V)). Neither expression ever raises
      Constraint_Error.


                                  Examples

60    Examples of ranges:

61    -10 .. 10
      X .. X + 1
      0.0 .. 2.0*Pi
      Red .. Green     -- see 3.5.1
      1 .. 0           -- a null range
      Table'Range      -- a range attribute reference (see 3.6)

62    Examples of range constraints:

63    range -999.0 .. +999.0
      range S'First+1 .. S'Last-1


3.5.1 Enumeration Types


1     An enumeration_type_definition defines an enumeration type.


                                   Syntax

2     enumeration_type_definition ::= 
         (enumeration_literal_specification
       {, enumeration_literal_specification})

3     enumeration_literal_specification ::=  defining_identifier
       | defining_character_literal

4     defining_character_literal ::= character_literal


                               Legality Rules

5     The defining_identifiers and defining_character_literals listed in an
enumeration_type_definition shall be distinct.


                              Static Semantics

6     Each enumeration_literal_specification is the explicit declaration of
the corresponding enumeration literal: it declares a parameterless function,
whose defining name is the defining_identifier or defining_character_literal,
and whose result type is the enumeration type.

7     Each enumeration literal corresponds to a distinct value of the
enumeration type, and to a distinct position number. The position number of
the value of the first listed enumeration literal is zero; the position number
of the value of each subsequent enumeration literal is one more than that of
its predecessor in the list.

8     The predefined order relations between values of the enumeration type
follow the order of corresponding position numbers.

9     If the same defining_identifier or defining_character_literal is
specified in more than one enumeration_type_definition, the corresponding
enumeration literals are said to be overloaded. At any place where an
overloaded enumeration literal occurs in the text of a program, the type of
the enumeration literal has to be determinable from the context (see 8.6).


                              Dynamic Semantics

10    The elaboration of an enumeration_type_definition creates the
enumeration type and its first subtype, which is constrained to the base range
of the type.

11    When called, the parameterless function associated with an enumeration
literal returns the corresponding value of the enumeration type.

      NOTES

12    22  If an enumeration literal occurs in a context that does not
      otherwise suffice to determine the type of the literal, then
      qualification by the name of the enumeration type is one way to resolve
      the ambiguity (see 4.7).


                                  Examples

13    Examples of enumeration types and subtypes:

14    type Day    is (Mon, Tue, Wed, Thu, Fri, Sat, Sun);
      type Suit   is (Clubs, Diamonds, Hearts, Spades);
      type Gender is (M, F);
      type Level  is (Low, Medium, Urgent);
      type Color  is (White, Red, Yellow, Green, Blue, Brown, Black);
      type Light  is (Red, Amber, Green); -- Red and Green are overloaded

15    type Hexa   is ('A', 'B', 'C', 'D', 'E', 'F');
      type Mixed  is ('A', 'B', '*', B, None, '?', '%');

16    subtype Weekday is Day   range Mon .. Fri;
      subtype Major   is Suit  range Hearts .. Spades;
      subtype Rainbow is Color range Red .. Blue;  --  the Color Red, not the Light


3.5.2 Character Types



                              Static Semantics

1     An enumeration type is said to be a character type if at least one of
its enumeration literals is a character_literal.

2     The predefined type Character is a character type whose values
correspond to the 256 code positions of Row 00 (also known as Latin-1) of the
ISO 10646 Basic Multilingual Plane (BMP). Each of the graphic characters of
Row 00 of the BMP has a corresponding character_literal in Character. Each of
the nongraphic positions of Row 00 (0000-001F and 007F-009F) has a
corresponding language-defined name, which is not usable as an enumeration
literal, but which is usable with the attributes (Wide_)Image and
(Wide_)Value; these names are given in the definition of type Character in
A.1, ``The Package Standard'', but are set in italics.

3     The predefined type Wide_Character is a character type whose values
correspond to the 65536 code positions of the ISO 10646 Basic Multilingual
Plane (BMP). Each of the graphic characters of the BMP has a corresponding
character_literal in Wide_Character. The first 256 values of Wide_Character
have the same character_literal or language-defined name as defined for
Character. The last 2 values of Wide_Character correspond to the nongraphic
positions FFFE and FFFF of the BMP, and are assigned the language-defined
names FFFE and FFFF. As with the other language-defined names for nongraphic
characters, the names FFFE and FFFF are usable only with the attributes
(Wide_)Image and (Wide_)Value; they are not usable as enumeration literals.
All other values of Wide_Character are considered graphic characters, and have
a corresponding character_literal.


                         Implementation Permissions

4     In a nonstandard mode, an implementation may provide other
interpretations for the predefined types Character and Wide_Character, to
conform to local conventions.


                            Implementation Advice

5     If an implementation supports a mode with alternative interpretations
for Character and Wide_Character, the set of graphic characters of Character
should nevertheless remain a proper subset of the set of graphic characters of
Wide_Character. Any character set ``localizations'' should be reflected in the
results of the subprograms defined in the language-defined package
Characters.Handling (see A.3) available in such a mode. In a mode with an
alternative interpretation of Character, the implementation should also
support a corresponding change in what is a legal identifier_letter.

      NOTES

6     23  The language-defined library package Characters.Latin_1 (see A.3.3)
      includes the declaration of constants denoting control characters, lower
      case characters, and special characters of the predefined type
      Character.

7     24  A conventional character set such as EBCDIC can be declared as a
      character type; the internal codes of the characters can be specified by
      an enumeration_representation_clause as explained in clause 13.4.


                                  Examples

8     Example of a character type:

9     type Roman_Digit is ('I', 'V', 'X', 'L', 'C', 'D', 'M');


3.5.3 Boolean Types



                              Static Semantics

1     There is a predefined enumeration type named Boolean, declared in the
visible part of package Standard. It has the two enumeration literals False
and True ordered with the relation False < True. Any descendant of the
predefined type Boolean is called a boolean type.


3.5.4 Integer Types


1     An integer_type_definition defines an integer type; it defines either a
signed integer type, or a modular integer type. The base range of a signed
integer type includes at least the values of the specified range. A modular
type is an integer type with all arithmetic modulo a specified positive
modulus; such a type corresponds to an unsigned type with wrap-around
semantics.


                                   Syntax

2     integer_type_definition ::= signed_integer_type_definition
       | modular_type_definition

3     signed_integer_type_definition ::= range static_simple_expression
       .. static_simple_expression

4     modular_type_definition ::= mod static_expression


                            Name Resolution Rules

5     Each simple_expression in a signed_integer_type_definition is expected
to be of any integer type; they need not be of the same type. The expression
in a modular_type_definition is likewise expected to be of any integer type.


                               Legality Rules

6     The simple_expressions of a signed_integer_type_definition shall be
static, and their values shall be in the range System.Min_Int ..
System.Max_Int.

7     The expression of a modular_type_definition shall be static, and its
value (the modulus) shall be positive, and shall be no greater than
System.Max_Binary_Modulus if a power of 2, or no greater than
System.Max_Nonbinary_Modulus if not.


                              Static Semantics

8     The set of values for a signed integer type is the (infinite) set of
mathematical integers, though only values of the base range of the type are
fully supported for run-time operations. The set of values for a modular
integer type are the values from 0 to one less than the modulus, inclusive.

9     A signed_integer_type_definition defines an integer type whose base
range includes at least the values of the simple_expressions and is symmetric
about zero, excepting possibly an extra negative value. A
signed_integer_type_definition also defines a constrained first subtype of the
type, with a range whose bounds are given by the values of the
simple_expressions, converted to the type being defined.

10    A modular_type_definition defines a modular type whose base range is
from zero to one less than the given modulus. A modular_type_definition also
defines a constrained first subtype of the type with a range that is the same
as the base range of the type.

11    There is a predefined signed integer subtype named Integer, declared in
the visible part of package Standard. It is constrained to the base range of
its type.

12    Integer has two predefined subtypes, declared in the visible part of
package Standard:

13    subtype Natural  is Integer range 0 .. Integer'Last;
      subtype Positive is Integer range 1 .. Integer'Last;

14    A type defined by an integer_type_definition is implicitly derived from
root_integer, an anonymous predefined (specific) integer type, whose base
range is System.Min_Int .. System.Max_Int. However, the base range of the new
type is not inherited from root_integer, but is instead determined by the
range or modulus specified by the integer_type_definition. Integer literals
are all of the type universal_integer, the universal type (see 3.4.1) for the
class rooted at root_integer, allowing their use with the operations of any
integer type.

15    The position number of an integer value is equal to the value.

16    For every modular subtype S, the following attribute is defined:

17    S'Modulus
              S'Modulus yields the modulus of the type of S, as a value of the
              type universal_integer.


                              Dynamic Semantics

18    The elaboration of an integer_type_definition creates the integer type
and its first subtype.

19    For a modular type, if the result of the execution of a predefined
operator (see 4.5) is outside the base range of the type, the result is
reduced modulo the modulus of the type to a value that is within the base
range of the type.

20    For a signed integer type, the exception Constraint_Error is raised by
the execution of an operation that cannot deliver the correct result because
it is outside the base range of the type. For any integer type,
Constraint_Error is raised by the operators "/", "rem", and "mod" if the right
operand is zero.


                         Implementation Requirements

21    In an implementation, the range of Integer shall include the range
-2**15+1 .. +2**15-1.

22    If Long_Integer is predefined for an implementation, then its range
shall include the range -2**31+1 .. +2**31-1.

23    System.Max_Binary_Modulus shall be at least 2**16.


                         Implementation Permissions

24    For the execution of a predefined operation of a signed integer type,
the implementation need not raise Constraint_Error if the result is outside
the base range of the type, so long as the correct result is produced.

25    An implementation may provide additional predefined signed integer
types, declared in the visible part of Standard, whose first subtypes have
names of the form Short_Integer, Long_Integer, Short_Short_Integer,
Long_Long_Integer, etc. Different predefined integer types are allowed to have
the same base range. However, the range of Integer should be no wider than
that of Long_Integer. Similarly, the range of Short_Integer (if provided)
should be no wider than Integer. Corresponding recommendations apply to any
other predefined integer types. There need not be a named integer type
corresponding to each distinct base range supported by an implementation. The
range of each first subtype should be the base range of its type.

26    An implementation may provide nonstandard integer types, descendants of
root_integer that are declared outside of the specification of package
Standard, which need not have all the standard characteristics of a type
defined by an integer_type_definition. For example, a nonstandard integer type
might have an asymmetric base range or it might not be allowed as an array or
loop index (a very long integer). Any type descended from a nonstandard
integer type is also nonstandard. An implementation may place arbitrary
restrictions on the use of such types; it is implementation defined whether
operators that are predefined for ``any integer type'' are defined for a
particular nonstandard integer type. In any case, such types are not permitted
as explicit_generic_actual_parameters for formal scalar types - see 12.5.2.

27    For a one's complement machine, the high bound of the base range of a
modular type whose modulus is one less than a power of 2 may be equal to the
modulus, rather than one less than the modulus. It is implementation defined
for which powers of 2, if any, this permission is exercised.

27.1/1 {For a one's complement machine, implementations may support non-binary
modulus values greater than System.Max_Nonbinary_Modulus. It is implementation
defined which specific values greater than System.Max_Nonbinary_Modulus, if
any, are supported.}


                            Implementation Advice

28    An implementation should support Long_Integer in addition to Integer if
the target machine supports 32-bit (or longer) arithmetic. No other named
integer subtypes are recommended for package Standard. Instead, appropriate
named integer subtypes should be provided in the library package Interfaces
(see B.2).

29    An implementation for a two's complement machine should support modular
types with a binary modulus up to System.Max_Int*2+2. An implementation should
support a nonbinary modulus up to Integer'Last.

      NOTES

30    25  Integer literals are of the anonymous predefined integer type
      universal_integer. Other integer types have no literals. However, the
      overload resolution rules (see 8.6, ``
      The Context of Overload Resolution'') allow expressions of the type
      universal_integer whenever an integer type is expected.

31    26  The same arithmetic operators are predefined for all signed integer
      types defined by a signed_integer_type_definition (see 4.5, ``
      Operators and Expression Evaluation''). For modular types, these same
      operators are predefined, plus bit-wise logical operators (and, or, xor,
      and not). In addition, for the unsigned types declared in the
      language-defined package Interfaces (see B.2), functions are defined
      that provide bit-wise shifting and rotating.

32    27  Modular types match a generic_formal_parameter_declaration of the
      form "type T is mod <>;"; signed integer types match "type T is range
      <>;" (see 12.5.2).


                                  Examples

33    Examples of integer types and subtypes:

34    type Page_Num  is range 1 .. 2_000;
      type Line_Size is range 1 .. Max_Line_Size;

35    subtype Small_Int   is Integer   range -10 .. 10;
      subtype Column_Ptr  is Line_Size range 1 .. 10;
      subtype Buffer_Size is Integer   range 0 .. Max;

36    type Byte        is mod 256; -- an unsigned byte
      type Hash_Index  is mod 97;  -- modulus is prime


3.5.5 Operations of Discrete Types



                              Static Semantics

1     For every discrete subtype S, the following attributes are defined:

2     S'Pos   S'Pos denotes a function with the following specification:

            3     function S'Pos(Arg : S'Base)
                    return universal_integer

        4     This function returns the position number of the value of Arg,
              as a value of type universal_integer.

5     S'Val   S'Val denotes a function with the following specification:

            6     function S'Val(Arg : universal_integer)
                    return S'Base

        7     This function returns a value of the type of S whose position
              number equals the value of Arg. For the evaluation of a call on
              S'Val, if there is no value in the base range of its type with
              the given position number, Constraint_Error is raised.


                            Implementation Advice

8     For the evaluation of a call on S'Pos for an enumeration subtype, if the
value of the operand does not correspond to the internal code for any
enumeration literal of its type (perhaps due to an uninitialized variable),
then the implementation should raise Program_Error. This is particularly
important for enumeration types with noncontiguous internal codes specified by
an enumeration_representation_clause.

      NOTES

9     28  Indexing and loop iteration use values of discrete types.

10    29  The predefined operations of a discrete type include the assignment
      operation, qualification, the membership tests, and the relational
      operators; for a boolean type they include the short-circuit control
      forms and the logical operators; for an integer type they include type
      conversion to and from other numeric types, as well as the binary and
      unary adding operators - and +, the multiplying operators, the unary
      operator abs, and the exponentiation operator. The assignment operation
      is described in 5.2. The other predefined operations are described in
      Section 4.

11    30  As for all types, objects of a discrete type have Size and Address
      attributes (see 13.3).

12    31  For a subtype of a discrete type, the result delivered by the
      attribute Val might not belong to the subtype; similarly, the actual
      parameter of the attribute Pos need not belong to the subtype. The
      following relations are satisfied (in the absence of an exception) by
      these attributes:

13       S'Val(S'Pos(X)) = X
         S'Pos(S'Val(N)) = N


                                  Examples

14    Examples of attributes of discrete subtypes:

15    --  For the types and subtypes declared in subclause 3.5.1
       the following hold: 

16    --  Color'First   = White,   Color'Last   = Black
      --  Rainbow'First = Red,     Rainbow'Last = Blue

17    --  Color'Succ(Blue) = Rainbow'Succ(Blue) = Brown
      --  Color'Pos(Blue)  = Rainbow'Pos(Blue)  = 4
      --  Color'Val(0)     = Rainbow'Val(0)     = White


3.5.6 Real Types


1     Real types provide approximations to the real numbers, with relative
bounds on errors for floating point types, and with absolute bounds for fixed
point types.


                                   Syntax

2     real_type_definition ::= 
         floating_point_definition | fixed_point_definition


                              Static Semantics

3     A type defined by a real_type_definition is implicitly derived from
root_real, an anonymous predefined (specific) real type. Hence, all real
types, whether floating point or fixed point, are in the derivation class
rooted at root_real.

4     Real literals are all of the type universal_real, the universal type
(see 3.4.1) for the class rooted at root_real, allowing their use with the
operations of any real type. Certain multiplying operators have a result type
of universal_fixed (see 4.5.5), the universal type for the class of fixed
point types, allowing the result of the multiplication or division to be used
where any specific fixed point type is expected.


                              Dynamic Semantics

5     The elaboration of a real_type_definition consists of the elaboration of
the floating_point_definition or the fixed_point_definition.


                         Implementation Requirements

6     An implementation shall perform the run-time evaluation of a use of a
predefined operator of root_real with an accuracy at least as great as that of
any floating point type definable by a floating_point_definition.


                         Implementation Permissions

7     For the execution of a predefined operation of a real type, the
implementation need not raise Constraint_Error if the result is outside the
base range of the type, so long as the correct result is produced, or the
Machine_Overflows attribute of the type is false (see G.2).

8     An implementation may provide nonstandard real types, descendants of
root_real that are declared outside of the specification of package Standard,
which need not have all the standard characteristics of a type defined by a
real_type_definition. For example, a nonstandard real type might have an
asymmetric or unsigned base range, or its predefined operations might wrap
around or ``saturate'' rather than overflow (modular or saturating
arithmetic), or it might not conform to the accuracy model (see G.2). Any type
descended from a nonstandard real type is also nonstandard. An implementation
may place arbitrary restrictions on the use of such types; it is
implementation defined whether operators that are predefined for ``any real
type'' are defined for a particular nonstandard real type. In any case, such
types are not permitted as explicit_generic_actual_parameters for formal
scalar types - see 12.5.2.

      NOTES

9     32  As stated, real literals are of the anonymous predefined real type
      universal_real. Other real types have no literals. However, the overload
      resolution rules (see 8.6) allow expressions of the type universal_real
      whenever a real type is expected.


3.5.7 Floating Point Types


1     For floating point types, the error bound is specified as a relative
precision by giving the required minimum number of significant decimal digits.


                                   Syntax

2     floating_point_definition ::= 
        digits static_expression [real_range_specification]

3     real_range_specification ::= 
        range static_simple_expression .. static_simple_expression


                            Name Resolution Rules

4     The requested decimal precision, which is the minimum number of
significant decimal digits required for the floating point type, is specified
by the value of the expression given after the reserved word digits. This
expression is expected to be of any integer type.

5     Each simple_expression of a real_range_specification is expected to be
of any real type; the types need not be the same.


                               Legality Rules

6     The requested decimal precision shall be specified by a static
expression whose value is positive and no greater than System.Max_Base_Digits.
Each simple_expression of a real_range_specification shall also be static. If
the real_range_specification is omitted, the requested decimal precision shall
be no greater than System.Max_Digits.

7     A floating_point_definition is illegal if the implementation does not
support a floating point type that satisfies the requested decimal precision
and range.


                              Static Semantics

8     The set of values for a floating point type is the (infinite) set of
rational numbers. The machine numbers of a floating point type are the values
of the type that can be represented exactly in every unconstrained variable of
the type. The base range (see 3.5) of a floating point type is symmetric
around zero, except that it can include some extra negative values in some
implementations.

9     The base decimal precision of a floating point type is the number of
decimal digits of precision representable in objects of the type. The safe
range of a floating point type is that part of its base range for which the
accuracy corresponding to the base decimal precision is preserved by all
predefined operations.

10    A floating_point_definition defines a floating point type whose base
decimal precision is no less than the requested decimal precision. If a
real_range_specification is given, the safe range of the floating point type
(and hence, also its base range) includes at least the values of the simple
expressions given in the real_range_specification. If a
real_range_specification is not given, the safe (and base) range of the type
includes at least the values of the range -10.0**(4*D) .. +10.0**(4*D) where D
is the requested decimal precision. The safe range might include other values
as well. The attributes Safe_First and Safe_Last give the actual bounds of the
safe range.

11    A floating_point_definition also defines a first subtype of the type. If
a real_range_specification is given, then the subtype is constrained to a
range whose bounds are given by a conversion of the values of the
simple_expressions of the real_range_specification to the type being defined.
Otherwise, the subtype is unconstrained.

12    There is a predefined, unconstrained, floating point subtype named
Float, declared in the visible part of package Standard.


                              Dynamic Semantics

13    The elaboration of a floating_point_definition creates the floating
point type and its first subtype.


                         Implementation Requirements

14    In an implementation that supports floating point types with 6 or more
digits of precision, the requested decimal precision for Float shall be at
least 6.

15    If Long_Float is predefined for an implementation, then its requested
decimal precision shall be at least 11.


                         Implementation Permissions

16    An implementation is allowed to provide additional predefined floating
point types, declared in the visible part of Standard, whose (unconstrained)
first subtypes have names of the form Short_Float, Long_Float,
Short_Short_Float, Long_Long_Float, etc. Different predefined floating point
types are allowed to have the same base decimal precision. However, the
precision of Float should be no greater than that of Long_Float. Similarly,
the precision of Short_Float (if provided) should be no greater than Float.
Corresponding recommendations apply to any other predefined floating point
types. There need not be a named floating point type corresponding to each
distinct base decimal precision supported by an implementation.


                            Implementation Advice

17    An implementation should support Long_Float in addition to Float if the
target machine supports 11 or more digits of precision. No other named
floating point subtypes are recommended for package Standard. Instead,
appropriate named floating point subtypes should be provided in the library
package Interfaces (see B.2).

      NOTES

18    33  If a floating point subtype is unconstrained, then assignments to
      variables of the subtype involve only Overflow_Checks, never
      Range_Checks.


                                  Examples

19    Examples of floating point types and subtypes:

20    type Coefficient is digits 10 range -1.0 .. 1.0;

21    type Real is digits 8;
      type Mass is digits 7 range 0.0 .. 1.0E35;

22    subtype Probability is Real range 0.0 .. 1.0;   --   a subtype with a smaller range


3.5.8 Operations of Floating Point Types



                              Static Semantics

1     The following attribute is defined for every floating point subtype S:

2/1   S'Digits
              S'Digits denotes the requested decimal precision for the subtype
              S. The value of this attribute is of the type universal_integer.
              The requested decimal precision of the base subtype of a
              floating point type T is defined to be the largest value of d
              for which {
              }ceiling(d * log(10) / log(T'Machine_Radix)) + {g}[1] <=
              T'Model_Mantissa{
              where g is 0 if Machine_Radix is a positive power of 10 and 1
              otherwise}.

      NOTES

3     34  The predefined operations of a floating point type include the
      assignment operation, qualification, the membership tests, and explicit
      conversion to and from other numeric types. They also include the
      relational operators and the following predefined arithmetic operators:
      the binary and unary adding operators - and +, certain multiplying
      operators, the unary operator abs, and the exponentiation operator.

4     35  As for all types, objects of a floating point type have Size and
      Address attributes (see 13.3). Other attributes of floating point types
      are defined in A.5.3.


3.5.9 Fixed Point Types


1     A fixed point type is either an ordinary fixed point type, or a decimal
fixed point type. The error bound of a fixed point type is specified as an
absolute value, called the delta of the fixed point type.


                                   Syntax

2     fixed_point_definition ::= ordinary_fixed_point_definition
       | decimal_fixed_point_definition

3     ordinary_fixed_point_definition ::= 
         delta static_expression  real_range_specification

4     decimal_fixed_point_definition ::= 
         delta static_expression digits static_expression
       [real_range_specification]

5     digits_constraint ::= 
         digits static_expression [range_constraint]


                            Name Resolution Rules

6     For a type defined by a fixed_point_definition, the delta of the type is
specified by the value of the expression given after the reserved word delta;
this expression is expected to be of any real type. For a type defined by a
decimal_fixed_point_definition (a decimal fixed point type), the number of
significant decimal digits for its first subtype (the digits of the first
subtype) is specified by the expression given after the reserved word digits;
this expression is expected to be of any integer type.


                               Legality Rules

7     In a fixed_point_definition or digits_constraint, the expressions given
after the reserved words delta and digits shall be static; their values shall
be positive.

8     The set of values of a fixed point type comprise the integral multiples
of a number called the small of the type. For a type defined by an
ordinary_fixed_point_definition (an ordinary fixed point type), the small may
be specified by an attribute_definition_clause (see 13.3); if so specified, it
shall be no greater than the delta of the type. If not specified, the small of
an ordinary fixed point type is an implementation-defined power of two less
than or equal to the delta.

9     For a decimal fixed point type, the small equals the delta; the delta
shall be a power of 10. If a real_range_specification is given, both bounds of
the range shall be in the range -(10**digits-1)*delta .. +(10**digits-1)*delta.

10    A fixed_point_definition is illegal if the implementation does not
support a fixed point type with the given small and specified range or digits.

11    For a subtype_indication with a digits_constraint, the subtype_mark
shall denote a decimal fixed point subtype.


                              Static Semantics

12    The base range (see 3.5) of a fixed point type is symmetric around zero,
except possibly for an extra negative value in some implementations.

13    An ordinary_fixed_point_definition defines an ordinary fixed point type
whose base range includes at least all multiples of small that are between the
bounds specified in the real_range_specification. The base range of the type
does not necessarily include the specified bounds themselves. An ordinary_-
fixed_point_definition also defines a constrained first subtype of the type,
with each bound of its range given by the closer to zero of:

14    the value of the conversion to the fixed point type of the corresponding
      expression of the real_range_specification;

15    the corresponding bound of the base range.

16    A decimal_fixed_point_definition defines a decimal fixed point type
whose base range includes at least the range -(10**digits-1)*delta ..
+(10**digits-1)*delta. A decimal_fixed_point_definition also defines a
constrained first subtype of the type. If a real_range_specification is given,
the bounds of the first subtype are given by a conversion of the values of the
expressions of the real_range_specification. Otherwise, the range of the first
subtype is -(10**digits-1)*delta .. +(10**digits-1)*delta.


                              Dynamic Semantics

17    The elaboration of a fixed_point_definition creates the fixed point type
and its first subtype.

18    For a digits_constraint on a decimal fixed point subtype with a given
delta, if it does not have a range_constraint, then it specifies an implicit
range -(10**D-1)*delta .. +(10**D-1)*delta, where D is the value of the
expression. A digits_constraint is compatible with a decimal fixed point
subtype if the value of the expression is no greater than the digits of the
subtype, and if it specifies (explicitly or implicitly) a range that is
compatible with the subtype.

19    The elaboration of a digits_constraint consists of the elaboration of
the range_constraint, if any. If a range_constraint is given, a check is made
that the bounds of the range are both in the range -(10**D-1)*delta ..
+(10**D-1)*delta, where D is the value of the (static) expression given after
the reserved word digits. If this check fails, Constraint_Error is raised.


                         Implementation Requirements

20    The implementation shall support at least 24 bits of precision
(including the sign bit) for fixed point types.


                         Implementation Permissions

21    Implementations are permitted to support only smalls that are a power of
two. In particular, all decimal fixed point type declarations can be
disallowed. Note however that conformance with the Information Systems Annex
requires support for decimal smalls, and decimal fixed point type declarations
with digits up to at least 18.

      NOTES

22    36  The base range of an ordinary fixed point type need not include the
      specified bounds themselves so that the range specification can be given
      in a natural way, such as:

23       type Fraction is delta 2.0**(-15) range -1.0 .. 1.0;
        

24    With 2's complement hardware, such a type could have a signed 16-bit
      representation, using 1 bit for the sign and 15 bits for fraction,
      resulting in a base range of -1.0 .. 1.0-2.0**(-15).


                                  Examples

25    Examples of fixed point types and subtypes:

26    type Volt is delta 0.125 range 0.0 .. 255.0;

27      --  A pure fraction which requires all the available
        --  space in a word can be declared as the type Fraction:
      type Fraction is delta System.Fine_Delta range -1.0 .. 1.0;
        --  Fraction'Last = 1.0 - System.Fine_Delta

28    type Money is delta 0.01 digits 15;  -- decimal fixed point
      subtype Salary is Money digits 10;
        -- Money'Last = 10.0**13 - 0.01, Salary'Last = 10.0**8 - 0.01


3.5.10 Operations of Fixed Point Types



                              Static Semantics

1     The following attributes are defined for every fixed point subtype S:

2/1   S'Small S'Small denotes the small of the type of S. The value of this
              attribute is of the type universal_real. Small may be specified
              for nonderived{ ordinary} fixed point types via an attribute_-
              definition_clause (see 13.3); the expression of such a clause
              shall be static.

3     S'Delta S'Delta denotes the delta of the fixed point subtype S. The
              value of this attribute is of the type universal_real.

4     S'Fore  S'Fore yields the minimum number of characters needed before the
              decimal point for the decimal representation of any value of the
              subtype S, assuming that the representation does not include an
              exponent, but includes a one-character prefix that is either a
              minus sign or a space. (This minimum number does not include
              superfluous zeros or underlines, and is at least 2.) The value
              of this attribute is of the type universal_integer.

5     S'Aft   S'Aft yields the number of decimal digits needed after the
              decimal point to accommodate the delta of the subtype S, unless
              the delta of the subtype S is greater than 0.1, in which case
              the attribute yields the value one. (S'Aft is the smallest
              positive integer N for which (10**N)*S'Delta is greater than or
              equal to one.) The value of this attribute is of the type
              universal_integer.

6     The following additional attributes are defined for every decimal fixed
point subtype S:

7     S'Digits
              S'Digits denotes the digits of the decimal fixed point subtype
              S, which corresponds to the number of decimal digits that are
              representable in objects of the subtype. The value of this
              attribute is of the type universal_integer. Its value is
              determined as follows:

            8     For a first subtype or a subtype defined by a
                  subtype_indication with a digits_constraint, the digits is
                  the value of the expression given after the reserved word
                  digits;

            9     For a subtype defined by a subtype_indication without a
                  digits_constraint, the digits of the subtype is the same as
                  that of the subtype denoted by the subtype_mark in the
                  subtype_indication.

            10    The digits of a base subtype is the largest integer D such
                  that the range -(10**D-1)*delta .. +(10**D-1)*delta is
                  included in the base range of the type.

11    S'Scale S'Scale denotes the scale of the subtype S, defined as the value
              N such that S'Delta = 10.0**(-N). The scale indicates the
              position of the point relative to the rightmost significant
              digits of values of subtype S. The value of this attribute is of
              the type universal_integer.

12    S'Round S'Round denotes a function with the following specification:

            13    function S'Round(X : universal_real)
                    return S'Base

        14    The function returns the value obtained by rounding X (away from
              0, if X is midway between two values of the type of S).

      NOTES

15    37  All subtypes of a fixed point type will have the same value for the
      Delta attribute, in the absence of delta_constraints (see J.3).

16    38  S'Scale is not always the same as S'Aft for a decimal subtype; for
      example, if S'Delta = 1.0 then S'Aft is 1 while S'Scale is 0.

17    39  The predefined operations of a fixed point type include the
      assignment operation, qualification, the membership tests, and explicit
      conversion to and from other numeric types. They also include the
      relational operators and the following predefined arithmetic operators:
      the binary and unary adding operators - and +, multiplying operators,
      and the unary operator abs.

18    40  As for all types, objects of a fixed point type have Size and
      Address attributes (see 13.3). Other attributes of fixed point types are
      defined in A.5.4.


3.6 Array Types


1     An array object is a composite object consisting of components which all
have the same subtype. The name for a component of an array uses one or more
index values belonging to specified discrete types. The value of an array
object is a composite value consisting of the values of the components.


                                   Syntax

2     array_type_definition ::= 
         unconstrained_array_definition | constrained_array_definition

3     unconstrained_array_definition ::= 
         array(index_subtype_definition {, index_subtype_definition
      }) of component_definition

4     index_subtype_definition ::= subtype_mark range <>

5     constrained_array_definition ::= 
         array (discrete_subtype_definition {, discrete_subtype_definition
      }) of component_definition

6     discrete_subtype_definition ::= discrete_subtype_indication | range

7     component_definition ::= [aliased] subtype_indication


                            Name Resolution Rules

8     For a discrete_subtype_definition that is a range, the range shall
resolve to be of some specific discrete type; which discrete type shall be
determined without using any context other than the bounds of the range itself
(plus the preference for root_integer - see 8.6).


                               Legality Rules

9     Each index_subtype_definition or discrete_subtype_definition in an
array_type_definition defines an index subtype; its type (the index type)
shall be discrete.

10    The subtype defined by the subtype_indication of a component_definition
(the component subtype) shall be a definite subtype.

11    Within the definition of a nonlimited composite type (or a limited
composite type that later in its immediate scope becomes nonlimited - see
7.3.1 and 7.5), if a component_definition contains the reserved word aliased
and the type of the component is discriminated, then the nominal subtype of
the component shall be constrained.


                              Static Semantics

12    An array is characterized by the number of indices (the dimensionality
of the array), the type and position of each index, the lower and upper bounds
for each index, and the subtype of the components. The order of the indices is
significant.

13    A one-dimensional array has a distinct component for each possible index
value. A multidimensional array has a distinct component for each possible
sequence of index values that can be formed by selecting one value for each
index position (in the given order). The possible values for a given index are
all the values between the lower and upper bounds, inclusive; this range of
values is called the index range. The bounds of an array are the bounds of its
index ranges. The length of a dimension of an array is the number of values of
the index range of the dimension (zero for a null range). The length of a
one-dimensional array is the length of its only dimension.

14    An array_type_definition defines an array type and its first subtype.
For each object of this array type, the number of indices, the type and
position of each index, and the subtype of the components are as in the type
definition; the values of the lower and upper bounds for each index belong to
the corresponding index subtype of its type, except for null arrays (see
3.6.1).

15    An unconstrained_array_definition defines an array type with an
unconstrained first subtype. Each index_subtype_definition defines the
corresponding index subtype to be the subtype denoted by the subtype_mark. The
compound delimiter <> (called a box) of an index_subtype_definition stands for
an undefined range (different objects of the type need not have the same
bounds).

16    A constrained_array_definition defines an array type with a constrained
first subtype. Each discrete_subtype_definition defines the corresponding
index subtype, as well as the corresponding index range for the constrained
first subtype. The constraint of the first subtype consists of the bounds of
the index ranges.

17    The discrete subtype defined by a discrete_subtype_definition is either
that defined by the subtype_indication, or a subtype determined by the range
as follows:

18    If the type of the range resolves to root_integer, then the
      discrete_subtype_definition defines a subtype of the predefined type
      Integer with bounds given by a conversion to Integer of the bounds of
      the range;

19    Otherwise, the discrete_subtype_definition defines a subtype of the type
      of the range, with the bounds given by the range.

20    The component_definition of an array_type_definition defines the nominal
subtype of the components. If the reserved word aliased appears in the
component_definition, then each component of the array is aliased (see 3.10).


                              Dynamic Semantics

21    The elaboration of an array_type_definition creates the array type and
its first subtype, and consists of the elaboration of any discrete_subtype_-
definitions and the component_definition.

22/1  The elaboration of a discrete_subtype_definition {that does not contain
any per-object expressions} creates the discrete subtype, and consists of the
elaboration of the subtype_indication or the evaluation of the range. {The
elaboration of a discrete_subtype_definition that contains one or more
per-object expressions is defined in 3.8.} The elaboration of a component_-
definition in an array_type_definition consists of the elaboration of the
subtype_indication. The elaboration of any discrete_subtype_definitions and
the elaboration of the component_definition are performed in an arbitrary
order.

      NOTES

23    41  All components of an array have the same subtype. In particular, for
      an array of components that are one-dimensional arrays, this means that
      all components have the same bounds and hence the same length.

24    42  Each elaboration of an array_type_definition creates a distinct
      array type. A consequence of this is that each object whose
      object_declaration contains an array_type_definition is of its own
      unique type.


                                  Examples

25    Examples of type declarations with unconstrained array definitions:

26    type Vector     is array(Integer  range <>) of Real;
      type Matrix     is array(Integer  range <>, Integer range <>) of Real;
      type Bit_Vector is array(Integer  range <>) of Boolean;
      type Roman      is array(Positive range <>) of Roman_Digit; -- see 3.5.2

27    Examples of type declarations with constrained array definitions:

28    type Table    is array(1 .. 10) of Integer;
      type Schedule is array(Day) of Boolean;
      type Line     is array(1 .. Max_Line_Size) of Character;

29    Examples of object declarations with array type definitions:

30    Grid : array(1 .. 80, 1 .. 100) of Boolean;
      Mix  : array(Color range Red .. Green) of Boolean;
      Page : array(Positive range <>) of Line :=  --  an array of arrays
        (1 | 50  => Line'(1 | Line'Last => '+', others => '-'),  -- see 4.3.3
         2 .. 49 => Line'(1 | Line'Last => '|', others => ' '));
          -- Page is constrained by its initial value to (1..50)


3.6.1 Index Constraints and Discrete Ranges


1     An index_constraint determines the range of possible values for every
index of an array subtype, and thereby the corresponding array bounds.


                                   Syntax

2     index_constraint ::=  (discrete_range {, discrete_range})

3     discrete_range ::= discrete_subtype_indication | range


                            Name Resolution Rules

4     The type of a discrete_range is the type of the subtype defined by the
subtype_indication, or the type of the range. For an index_constraint, each
discrete_range shall resolve to be of the type of the corresponding index.


                               Legality Rules

5     An index_constraint shall appear only in a subtype_indication whose
subtype_mark denotes either an unconstrained array subtype, or an
unconstrained access subtype whose designated subtype is an unconstrained
array subtype; in either case, the index_constraint shall provide a
discrete_range for each index of the array type.


                              Static Semantics

6     A discrete_range defines a range whose bounds are given by the range, or
by the range of the subtype defined by the subtype_indication.


                              Dynamic Semantics

7     An index_constraint is compatible with an unconstrained array subtype if
and only if the index range defined by each discrete_range is compatible (see
3.5) with the corresponding index subtype. If any of the discrete_ranges
defines a null range, any array thus constrained is a null array, having no
components. An array value satisfies an index_constraint if at each index
position the array value and the index_constraint have the same index bounds.

8     The elaboration of an index_constraint consists of the evaluation of the
discrete_range(s), in an arbitrary order. The evaluation of a discrete_range
consists of the elaboration of the subtype_indication or the evaluation of the
range.

      NOTES

9     43  The elaboration of a subtype_indication consisting of a subtype_mark
      followed by an index_constraint checks the compatibility of the
      index_constraint with the subtype_mark (see 3.2.2).

10    44  Even if an array value does not satisfy the index constraint of an
      array subtype, Constraint_Error is not raised on conversion to the array
      subtype, so long as the length of each dimension of the array value and
      the array subtype match. See 4.6.


                                  Examples

11    Examples of array declarations including an index constraint:

12    Board     : Matrix(1 .. 8,  1 .. 8);  --  see 3.6
      Rectangle : Matrix(1 .. 20, 1 .. 30);
      Inverse   : Matrix(1 .. N,  1 .. N);  --  N need not be static 

13    Filter    : Bit_Vector(0 .. 31);

14    Example of array declaration with a constrained array subtype:

15    My_Schedule : Schedule;  --  all arrays of type Schedule have the same bounds

16    Example of record type with a component that is an array:

17    type Var_Line(Length : Natural) is
         record
            Image : String(1 .. Length);
         end record;

18    Null_Line : Var_Line(0);  --  Null_Line.Image is a null array


3.6.2 Operations of Array Types



                               Legality Rules

1     The argument N used in the attribute_designators for the N-th dimension
of an array shall be a static expression of some integer type. The value of N
shall be positive (nonzero) and no greater than the dimensionality of the
array.


                              Static Semantics

2/1   The following attributes are defined for a {prefix}[prefix] A that is of
an array type (after any implicit dereference), or denotes a constrained array
subtype:

3     A'First A'First denotes the lower bound of the first index range; its
              type is the corresponding index type.

4     A'First(N)
              A'First(N) denotes the lower bound of the N-th index range; its
              type is the corresponding index type.

5     A'Last  A'Last denotes the upper bound of the first index range; its
              type is the corresponding index type.

6     A'Last(N)
              A'Last(N) denotes the upper bound of the N-th index range; its
              type is the corresponding index type.

7     A'Range A'Range is equivalent to the range A'First .. A'Last, except
              that the prefix A is only evaluated once.

8     A'Range(N)
              A'Range(N) is equivalent to the range A'First(N) .. A'Last(N),
              except that the prefix A is only evaluated once.

9     A'Length
              A'Length denotes the number of values of the first index range
              (zero for a null range); its type is universal_integer.

10    A'Length(N)
              A'Length(N) denotes the number of values of the N-th index range
              (zero for a null range); its type is universal_integer.


                            Implementation Advice

11    An implementation should normally represent multidimensional arrays in
row-major order, consistent with the notation used for multidimensional array
aggregates (see 4.3.3). However, if a pragma Convention(Fortran, ...) applies
to a multidimensional array type, then column-major order should be used
instead (see B.5, ``Interfacing with Fortran'').

      NOTES

12    45  The attribute_references A'First and A'First(1) denote the same
      value. A similar relation exists for the attribute_references A'Last,
      A'Range, and A'Length. The following relation is satisfied (except for a
      null array) by the above attributes if the index type is an integer
      type:

13       A'Length(N) = A'Last(N) - A'First(N) + 1

14    46  An array type is limited if its component type is limited (see 7.5).

15    47  The predefined operations of an array type include the membership
      tests, qualification, and explicit conversion. If the array type is not
      limited, they also include assignment and the predefined equality
      operators. For a one-dimensional array type, they include the predefined
      concatenation operators (if nonlimited) and, if the component type is
      discrete, the predefined relational operators; if the component type is
      boolean, the predefined logical operators are also included.

16    48  A component of an array can be named with an indexed_component. A
      value of an array type can be specified with an array_aggregate, unless
      the array type is limited. For a one-dimensional array type, a slice of
      the array can be named; also, string literals are defined if the
      component type is a character type.


                                  Examples

17    Examples (using arrays declared in the examples of subclause 3.6.1):

18    --  Filter'First      =   0   Filter'Last       =  31   Filter'Length =  32
      --  Rectangle'Last(1) =  20   Rectangle'Last(2) =  30


3.6.3 String Types



                              Static Semantics

1     A one-dimensional array type whose component type is a character type is
called a string type.

2     There are two predefined string types, String and Wide_String, each
indexed by values of the predefined subtype Positive; these are declared in
the visible part of package Standard:

3     subtype Positive is Integer range 1 .. Integer'Last;

4     type String is array(Positive range <>) of Character;
      type Wide_String is array(Positive range <>) of Wide_Character;
      

      NOTES

5     49  String literals (see 2.6 and 4.2) are defined for all string types.
      The concatenation operator & is predefined for string types, as for all
      nonlimited one-dimensional array types. The ordering operators <, <=, >,
      and >= are predefined for string types, as for all one-dimensional
      discrete array types; these ordering operators correspond to
      lexicographic order (see 4.5.2).


                                  Examples

6     Examples of string objects:

7     Stars      : String(1 .. 120) := (1 .. 120 => '*' );
      Question   : constant String  := "How many characters?";
                                                                   
      -- Question'First = 1, Question'Last = 20
                                                                   
      -- Question'Length = 20 (the number of characters)

8     Ask_Twice  : String  := Question & Question;                 
      -- constrained to (1..40)
      Ninety_Six : constant Roman   := "XCVI";                     
      -- see 3.5.2 and 3.6


3.7 Discriminants


1     A composite type (other than an array type) can have discriminants,
which parameterize the type. A known_discriminant_part specifies the
discriminants of a composite type. A discriminant of an object is a component
of the object, and is either of a discrete type or an access type. An
unknown_discriminant_part in the declaration of a partial view of a type
specifies that the discriminants of the type are unknown for the given view;
all subtypes of such a partial view are indefinite subtypes.


                                   Syntax

2     discriminant_part ::= unknown_discriminant_part
       | known_discriminant_part

3     unknown_discriminant_part ::= (<>)

4     known_discriminant_part ::= 
         (discriminant_specification {; discriminant_specification})

5     discriminant_specification ::= 
         defining_identifier_list : subtype_mark [:= default_expression]
       | defining_identifier_list : access_definition
       [:= default_expression]

6     default_expression ::= expression


                            Name Resolution Rules

7     The expected type for the default_expression of a
discriminant_specification is that of the corresponding discriminant.


                               Legality Rules

8/1   A {discriminant_part}[known_discriminant_part] is only permitted in a
declaration for a composite type that is not an array type (this includes
generic formal types){. A}[; a] type declared with a known_discriminant_part
is called a discriminated type, as is a type that inherits (known)
discriminants.

9     The subtype of a discriminant may be defined by a subtype_mark, in which
case the subtype_mark shall denote a discrete or access subtype, or it may be
defined by an access_definition (in which case the subtype_mark of the
access_definition may denote any kind of subtype). A discriminant that is
defined by an access_definition is called an access discriminant and is of an
anonymous general access-to-variable type whose designated subtype is denoted
by the subtype_mark of the access_definition.

10    A discriminant_specification for an access discriminant shall appear
only in the declaration for a task or protected type, or for a type with the
reserved word limited in its (full) definition or in that of one of its
ancestors. In addition to the places where Legality Rules normally apply (see
12.3), this rule applies also in the private part of an instance of a generic
unit.

11    Default_expressions shall be provided either for all or for none of the
discriminants of a known_discriminant_part. No default_expressions are
permitted in a known_discriminant_part in a declaration of a tagged type or a
generic formal type.

12    For a type defined by a derived_type_definition, if a
known_discriminant_part is provided in its declaration, then:

13    The parent subtype shall be constrained;

14    If the parent type is not a tagged type, then each discriminant of the
      derived type shall be used in the constraint defining the parent subtype;

15    If a discriminant is used in the constraint defining the parent subtype,
      the subtype of the discriminant shall be statically compatible (see
      4.9.1) with the subtype of the corresponding parent discriminant.

16    The type of the default_expression, if any, for an access discriminant
shall be convertible to the anonymous access type of the discriminant (see
4.6).


                              Static Semantics

17    A discriminant_specification declares a discriminant; the subtype_mark
denotes its subtype unless it is an access discriminant, in which case the
discriminant's subtype is the anonymous access-to-variable subtype defined by
the access_definition.

18    For a type defined by a derived_type_definition, each discriminant of
the parent type is either inherited, constrained to equal some new
discriminant of the derived type, or constrained to the value of an
expression. When inherited or constrained to equal some new discriminant, the
parent discriminant and the discriminant of the derived type are said to
correspond. Two discriminants also correspond if there is some common
discriminant to which they both correspond. A discriminant corresponds to
itself as well. If a discriminant of a parent type is constrained to a
specific value by a derived_type_definition, then that discriminant is said to
be specified by that derived_type_definition.

19    A constraint that appears within the definition of a discriminated type
depends on a discriminant of the type if it names the discriminant as a bound
or discriminant value. A component_definition depends on a discriminant if its
constraint depends on the discriminant, or on a discriminant that corresponds
to it.

20    A component depends on a discriminant if:

21    Its component_definition depends on the discriminant; or

22    It is declared in a variant_part that is governed by the discriminant; or

23    It is a component inherited as part of a derived_type_definition, and
      the constraint of the parent_subtype_indication depends on the
      discriminant; or

24    It is a subcomponent of a component that depends on the discriminant.

25    Each value of a discriminated type includes a value for each component
of the type that does not depend on a discriminant; this includes the
discriminants themselves. The values of discriminants determine which other
component values are present in the value of the discriminated type.

26    A type declared with a known_discriminant_part is said to have known
discriminants; its first subtype is unconstrained. A type declared with an
unknown_discriminant_part is said to have unknown discriminants. A type
declared without a discriminant_part has no discriminants, unless it is a
derived type; if derived, such a type has the same sort of discriminants
(known, unknown, or none) as its parent (or ancestor) type. A tagged
class-wide type also has unknown discriminants. Any subtype of a type with
unknown discriminants is an unconstrained and indefinite subtype (see 3.2 and
3.3).


                              Dynamic Semantics

27    An access_definition is elaborated when the value of a corresponding
access discriminant is defined, either by evaluation of its default_expression
or by elaboration of a discriminant_constraint. The elaboration of an
access_definition creates the anonymous access type. When the expression
defining the access discriminant is evaluated, it is converted to this
anonymous access type (see 4.6).

      NOTES

28    50  If a discriminated type has default_expressions for its
      discriminants, then unconstrained variables of the type are permitted,
      and the values of the discriminants can be changed by an assignment to
      such a variable. If defaults are not provided for the discriminants,
      then all variables of the type are constrained, either by explicit
      constraint or by their initial value; the values of the discriminants of
      such a variable cannot be changed after initialization.

29    51  The default_expression for a discriminant of a type is evaluated
      when an object of an unconstrained subtype of the type is created.

30    52  Assignment to a discriminant of an object (after its initialization)
      is not allowed, since the name of a discriminant is a constant; neither
      assignment_statements nor assignments inherent in passing as an in out
      or out parameter are allowed. Note however that the value of a
      discriminant can be changed by assigning to the enclosing object,
      presuming it is an unconstrained variable.

31    53  A discriminant that is of a named access type is not called an
      access discriminant; that term is used only for discriminants defined by
      an access_definition.


                                  Examples

32    Examples of discriminated types:

33    type Buffer(Size : Buffer_Size := 100)  is        -- see 3.5.4
         record
            Pos   : Buffer_Size := 0;
            Value : String(1 .. Size);
         end record;

34    type Matrix_Rec(Rows, Columns : Integer) is
         record
            Mat : Matrix(1 .. Rows, 1 .. Columns);       -- see 3.6
         end record;

35    type Square(Side : Integer) is new
         Matrix_Rec(Rows => Side, Columns => Side);

36    type Double_Square(Number : Integer) is
         record
            Left  : Square(Number);
            Right : Square(Number);
         end record;

37    type Item(Number : Positive) is
         record
            Content : Integer;
            --  no component depends on the discriminant
         end record;


3.7.1 Discriminant Constraints


1     A discriminant_constraint specifies the values of the discriminants for
a given discriminated type.


                                   Syntax

2     discriminant_constraint ::= 
         (discriminant_association {, discriminant_association})

3     discriminant_association ::= 
         [discriminant_selector_name {| discriminant_selector_name
      } =>] expression

4     A discriminant_association is said to be named if it has one or more
      discriminant_selector_names; it is otherwise said to be positional. In a
      discriminant_constraint, any positional associations shall precede any
      named associations.


                            Name Resolution Rules

5     Each selector_name of a named discriminant_association shall resolve to
denote a discriminant of the subtype being constrained; the discriminants so
named are the associated discriminants of the named association. For a
positional association, the associated discriminant is the one whose
discriminant_specification occurred in the corresponding position in the known_-
discriminant_part that defined the discriminants of the subtype being
constrained.

6     The expected type for the expression in a discriminant_association is
that of the associated discriminant(s).


                               Legality Rules

7/1   A discriminant_constraint is only allowed in a subtype_indication whose
subtype_mark denotes either an unconstrained discriminated subtype, or an
unconstrained access subtype whose designated subtype is an unconstrained
discriminated subtype. {However, in the case of a general access subtype, a
discriminant_constraint is illegal if there is a place within the immediate
scope of the designated subtype where the designated subtype's view is
constrained.}

8     A named discriminant_association with more than one selector_name is
allowed only if the named discriminants are all of the same type. A
discriminant_constraint shall provide exactly one value for each discriminant
of the subtype being constrained.

9     The expression associated with an access discriminant shall be of a type
convertible to the anonymous access type.


                              Dynamic Semantics

10    A discriminant_constraint is compatible with an unconstrained
discriminated subtype if each discriminant value belongs to the subtype of the
corresponding discriminant.

11    A composite value satisfies a discriminant constraint if and only if
each discriminant of the composite value has the value imposed by the
discriminant constraint.

12    For the elaboration of a discriminant_constraint, the expressions in the
discriminant_associations are evaluated in an arbitrary order and converted to
the type of the associated discriminant (which might raise Constraint_Error -
see 4.6); the expression of a named association is evaluated (and converted)
once for each associated discriminant. The result of each evaluation and
conversion is the value imposed by the constraint for the associated
discriminant.

      NOTES

13    54  The rules of the language ensure that a discriminant of an object
      always has a value, either from explicit or implicit initialization.


                                  Examples

14    Examples (using types declared above in clause 3.7):

15    Large   : Buffer(200);  --  constrained, always 200 characters
                              --   (explicit discriminant value)
      Message : Buffer;       --  unconstrained, initially 100 characters
                              --   (default discriminant value)
      Basis   : Square(5);    --  constrained, always 5 by 5
      Illegal : Square;       --  illegal, a Square has to be constrained


3.7.2 Operations of Discriminated Types


1     If a discriminated type has default_expressions for its discriminants,
then unconstrained variables of the type are permitted, and the discriminants
of such a variable can be changed by assignment to the variable. For a formal
parameter of such a type, an attribute is provided to determine whether the
corresponding actual parameter is constrained or unconstrained.


                              Static Semantics

2     For a prefix A that is of a discriminated type (after any implicit
dereference), the following attribute is defined:

3     A'Constrained
              Yields the value True if A denotes a constant, a value, or a
              constrained variable, and False otherwise.


                             Erroneous Execution

4     The execution of a construct is erroneous if the construct has a
constituent that is a name denoting a subcomponent that depends on
discriminants, and the value of any of these discriminants is changed by this
execution between evaluating the name and the last use (within this execution)
of the subcomponent denoted by the name.


3.8 Record Types


1     A record object is a composite object consisting of named components.
The value of a record object is a composite value consisting of the values of
the components.


                                   Syntax

2     record_type_definition ::= 
      [[abstract] tagged] [limited] record_definition

3     record_definition ::= 
          record
             component_list
          end record
        | null record

4     component_list ::= 
            component_item {component_item}
         | {component_item} variant_part
         |  null;

5/1   component_item ::= component_declaration | {aspect_clause
      }[representation_clause]

6     component_declaration ::= 
         defining_identifier_list : component_definition
       [:= default_expression];


                            Name Resolution Rules

7     The expected type for the default_expression, if any, in a
component_declaration is the type of the component.


                               Legality Rules

8     A default_expression is not permitted if the component is of a limited
type.

9     Each component_declaration declares a component of the record type.
Besides components declared by component_declarations, the components of a
record type include any components declared by discriminant_specifications of
the record type declaration. The identifiers of all components of a record
type shall be distinct.

10    Within a type_declaration, a name that denotes a component, protected
subprogram, or entry of the type is allowed only in the following cases:

11    A name that denotes any component, protected subprogram, or entry is
      allowed within a representation item that occurs within the declaration
      of the composite type.

12    A name that denotes a noninherited discriminant is allowed within the
      declaration of the type, but not within the discriminant_part. If the
      discriminant is used to define the constraint of a component, the bounds
      of an entry family, or the constraint of the parent subtype in a
      derived_type_definition then its name shall appear alone as a
      direct_name (not as part of a larger expression or expanded name). A
      discriminant shall not be used to define the constraint of a scalar
      component.

13    If the name of the current instance of a type (see 8.6) is used to
define the constraint of a component, then it shall appear as a direct_name
that is the prefix of an attribute_reference whose result is of an access
type, and the attribute_reference shall appear alone.


                              Static Semantics

14    The component_definition of a component_declaration defines the
(nominal) subtype of the component. If the reserved word aliased appears in
the component_definition, then the component is aliased (see 3.10).

15    If the component_list of a record type is defined by the reserved word
null and there are no discriminants, then the record type has no components
and all records of the type are null records. A record_definition of null
record is equivalent to record null; end record.


                              Dynamic Semantics

16    The elaboration of a record_type_definition creates the record type and
its first subtype, and consists of the elaboration of the record_definition.
The elaboration of a record_definition consists of the elaboration of its
component_list, if any.

17    The elaboration of a component_list consists of the elaboration of the
component_items and variant_part, if any, in the order in which they appear.
The elaboration of a component_declaration consists of the elaboration of the
component_definition.

18/1  Within the definition of a composite type, if a component_definition or
discrete_subtype_definition (see 9.5.2) includes a name that denotes a
discriminant of the type, or that is an attribute_reference whose prefix
denotes the current instance of the type, the expression containing the name
is called a per-object expression, and the {constraint or range}[constraint]
being defined is called a per-object constraint. For the elaboration of a
component_definition of a component_declaration{ or the discrete_subtype_-
definition of an entry_declaration for an entry family (see 9.5.2)}, if the
constraint {or range} of the subtype_indication {or
discrete_subtype_definition} is not a per-object constraint, then the
subtype_indication {or discrete_subtype_definition} is elaborated. On the
other hand, if the constraint {or range} is a per-object constraint, then the
elaboration consists of the evaluation of any included expression that is not
part of a per-object expression. {Each such expression is evaluated once
unless it is part of a named association in a discriminant constraint, in
which case it is evaluated once for each associated discriminant.}

18.1/1 {When a per-object constraint is elaborated (as part of creating an
object), each per-object expression of the constraint is evaluated. For other
expressions, the values determined during the elaboration of the component_-
definition or entry_declaration are used. Any checks associated with the
enclosing subtype_indication or discrete_subtype_definition are performed,
including the subtype compatibility check (see 3.2.2), and the associated
subtype is created.}

      NOTES

19    55  A component_declaration with several identifiers is equivalent to a
      sequence of single component_declarations, as explained in 3.3.1.

20    56  The default_expression of a record component is only evaluated upon
      the creation of a default-initialized object of the record type
      (presuming the object has the component, if it is in a variant_part -
      see 3.3.1).

21    57  The subtype defined by a component_definition (see 3.6) has to be a
      definite subtype.

22    58  If a record type does not have a variant_part, then the same
      components are present in all values of the type.

23    59  A record type is limited if it has the reserved word limited in its
      definition, or if any of its components are limited (see 7.5).

24    60  The predefined operations of a record type include membership tests,
      qualification, and explicit conversion. If the record type is
      nonlimited, they also include assignment and the predefined equality
      operators.

25    61  A component of a record can be named with a selected_component. A
      value of a record can be specified with a record_aggregate, unless the
      record type is limited.


                                  Examples

26    Examples of record type declarations:

27    type Date is
         record
            Day   : Integer range 1 .. 31;
            Month : Month_Name;
            Year  : Integer range 0 .. 4000;
         end record;

28    type Complex is
         record
            Re : Real := 0.0;
            Im : Real := 0.0;
         end record;

29    Examples of record variables:

30    Tomorrow, Yesterday : Date;
      A, B, C : Complex;

31    -- both components of A, B, and C are implicitly initialized to zero 


3.8.1 Variant Parts and Discrete Choices


1     A record type with a variant_part specifies alternative lists of
components. Each variant defines the components for the value or values of the
discriminant covered by its discrete_choice_list.


                                   Syntax

2     variant_part ::= 
         case discriminant_direct_name is
             variant
            {variant}
         end case;

3     variant ::= 
         when discrete_choice_list =>
            component_list

4     discrete_choice_list ::= discrete_choice {| discrete_choice}

5     discrete_choice ::= expression | discrete_range | others


                            Name Resolution Rules

6     The discriminant_direct_name shall resolve to denote a discriminant
(called the discriminant of the variant_part) specified in the
known_discriminant_part of the full_type_declaration that contains the
variant_part. The expected type for each discrete_choice in a variant is the
type of the discriminant of the variant_part.


                               Legality Rules

7     The discriminant of the variant_part shall be of a discrete type.

8     The expressions and discrete_ranges given as discrete_choices in a
variant_part shall be static. The discrete_choice others shall appear alone in
a discrete_choice_list, and such a discrete_choice_list, if it appears, shall
be the last one in the enclosing construct.

9     A discrete_choice is defined to cover a value in the following cases:

10    A discrete_choice that is an expression covers a value if the value
      equals the value of the expression converted to the expected type.

11    A discrete_choice that is a discrete_range covers all values (possibly
      none) that belong to the range.

12    The discrete_choice others covers all values of its expected type that
      are not covered by previous discrete_choice_lists of the same construct.

13    A discrete_choice_list covers a value if one of its discrete_choices
covers the value.

14    The possible values of the discriminant of a variant_part shall be
covered as follows:

15    If the discriminant is of a static constrained scalar subtype, then each
      non-others discrete_choice shall cover only values in that subtype, and
      each value of that subtype shall be covered by some discrete_choice
      (either explicitly or by others);

16    If the type of the discriminant is a descendant of a generic formal
      scalar type then the variant_part shall have an others discrete_choice;

17    Otherwise, each value of the base range of the type of the discriminant
      shall be covered (either explicitly or by others).

18    Two distinct discrete_choices of a variant_part shall not cover the same
value.


                              Static Semantics

19    If the component_list of a variant is specified by null, the variant has
no components.

20    The discriminant of a variant_part is said to govern the variant_part
and its variants. In addition, the discriminant of a derived type governs a
variant_part and its variants if it corresponds (see 3.7) to the discriminant
of the variant_part.


                              Dynamic Semantics

21    A record value contains the values of the components of a particular
variant only if the value of the discriminant governing the variant is covered
by the discrete_choice_list of the variant. This rule applies in turn to any
further variant that is, itself, included in the component_list of the given
variant.

22    The elaboration of a variant_part consists of the elaboration of the
component_list of each variant in the order in which they appear.


                                  Examples

23    Example of record type with a variant part:

24    type Device is (Printer, Disk, Drum);
      type State  is (Open, Closed);

25    type Peripheral(Unit : Device := Disk) is
         record
            Status : State;
            case Unit is
               when Printer =>
                  Line_Count : Integer range 1 .. Page_Size;
               when others =>
                  Cylinder   : Cylinder_Index;
                  Track      : Track_Number;
               end case;
            end record;

26    Examples of record subtypes:

27    subtype Drum_Unit is Peripheral(Drum);
      subtype Disk_Unit is Peripheral(Disk);

28    Examples of constrained record variables:

29    Writer   : Peripheral(Unit  => Printer);
      Archive  : Disk_Unit;


3.9 Tagged Types and Type Extensions


1     Tagged types and type extensions support object-oriented programming,
based on inheritance with extension and run-time polymorphism via dispatching
operations.


                              Static Semantics

2     A record type or private type that has the reserved word tagged in its
declaration is called a tagged type. When deriving from a tagged type,
additional components may be defined. As for any derived type, additional
primitive subprograms may be defined, and inherited primitive subprograms may
be overridden. The derived type is called an extension of the ancestor type,
or simply a type extension. Every type extension is also a tagged type, and is
either a record extension or a private extension of some other tagged type. A
record extension is defined by a derived_type_definition with a
record_extension_part. A private extension, which is a partial view of a
record extension, can be declared in the visible part of a package (see 7.3)
or in a generic formal part (see 12.5.1).

3     An object of a tagged type has an associated (run-time) tag that
identifies the specific tagged type used to create the object originally. The
tag of an operand of a class-wide tagged type T'Class controls which
subprogram body is to be executed when a primitive subprogram of type T is
applied to the operand (see 3.9.2); using a tag to control which body to
execute is called dispatching.

4     The tag of a specific tagged type identifies the full_type_declaration
of the type. If a declaration for a tagged type occurs within a
generic_package_declaration, then the corresponding type declarations in
distinct instances of the generic package are associated with distinct tags.
For a tagged type that is local to a generic package body, the language does
not specify whether repeated instantiations of the generic body result in
distinct tags.

5     The following language-defined library package exists:

6     package Ada.Tags is
          type Tag is private;

7         function Expanded_Name(T : Tag) return String;
          function External_Tag(T : Tag) return String;
          function Internal_Tag(External : String) return Tag;

8         Tag_Error : exception;

9     private
         ... -- not specified by the language
      end Ada.Tags;

10    The function Expanded_Name returns the full expanded name of the first
subtype of the specific type identified by the tag, in upper case, starting
with a root library unit. The result is implementation defined if the type is
declared within an unnamed block_statement.

11    The function External_Tag returns a string to be used in an external
representation for the given tag. The call External_Tag(S'Tag) is equivalent
to the attribute_reference S'External_Tag (see 13.3).

12    The function Internal_Tag returns the tag that corresponds to the given
external tag, or raises Tag_Error if the given string is not the external tag
for any specific type of the partition.

13    For every subtype S of a tagged type T (specific or class-wide), the
following attributes are defined:

14    S'Class S'Class denotes a subtype of the class-wide type (called T'Class
              in this International Standard) for the class rooted at T (or if
              S already denotes a class-wide subtype, then S'Class is the same
              as S).

        15    S'Class is unconstrained. However, if S is constrained, then the
              values of S'Class are only those that when converted to the type
              T belong to S.

16    S'Tag   S'Tag denotes the tag of the type T (or if T is class-wide, the
              tag of the root type of the corresponding class). The value of
              this attribute is of type Tag.

17    Given a prefix X that is of a class-wide tagged type (after any implicit
dereference), the following attribute is defined:

18    X'Tag   X'Tag denotes the tag of X. The value of this attribute is of
              type Tag.


                              Dynamic Semantics

19    The tag associated with an object of a tagged type is determined as
follows:

20    The tag of a stand-alone object, a component, or an aggregate of a
      specific tagged type T identifies T.

21    The tag of an object created by an allocator for an access type with a
      specific designated tagged type T, identifies T.

22    The tag of an object of a class-wide tagged type is that of its
      initialization expression.

23    The tag of the result returned by a function whose result type is a
      specific tagged type T identifies T.

24    The tag of the result returned by a function with a class-wide result
      type is that of the return expression.

25    The tag is preserved by type conversion and by parameter passing. The
tag of a value is the tag of the associated object (see 6.2).


                         Implementation Permissions

26    The implementation of the functions in Ada.Tags may raise Tag_Error if
no specific type corresponding to the tag passed as a parameter exists in the
partition at the time the function is called.

      NOTES

27    62  A type declared with the reserved word tagged should normally be
      declared in a package_specification, so that new primitive subprograms
      can be declared for it.

28    63  Once an object has been created, its tag never changes.

29    64  Class-wide types are defined to have unknown discriminants (see
      3.7). This means that objects of a class-wide type have to be explicitly
      initialized (whether created by an object_declaration or an allocator),
      and that aggregates have to be explicitly qualified with a specific type
      when their expected type is class-wide.

30    65  If S denotes an untagged private type whose full type is tagged,
      then S'Class is also allowed before the full type definition, but only
      in the private part of the package in which the type is declared (see
      7.3.1). Similarly, the Class attribute is defined for incomplete types
      whose full type is tagged, but only within the library unit in which the
      incomplete type is declared (see 3.10.1).


                                  Examples

31    Examples of tagged record types:

32    type Point is tagged
        record
          X, Y : Real := 0.0;
        end record;

33    type Expression is tagged null record;
        -- Components will be added by each extension


3.9.1 Type Extensions


1     Every type extension is a tagged type, and is either a record extension
or a private extension of some other tagged type.


                                   Syntax

2     record_extension_part ::= with record_definition


                               Legality Rules

3     The parent type of a record extension shall not be a class-wide type. If
the parent type is nonlimited, then each of the components of the
record_extension_part shall be nonlimited. The accessibility level (see
3.10.2) of a record extension shall not be statically deeper than that of its
parent type. In addition to the places where Legality Rules normally apply
(see 12.3), these rules apply also in the private part of an instance of a
generic unit.

4     A type extension shall not be declared in a generic body if the parent
type is declared outside that body.


                              Dynamic Semantics

5     The elaboration of a record_extension_part consists of the elaboration
of the record_definition.

      NOTES

6     66  The term ``type extension'' refers to a type as a whole. The term
      ``extension part'' refers to the piece of text that defines the
      additional components (if any) the type extension has relative to its
      specified ancestor type.

7     67  The accessibility rules imply that a tagged type declared in a
      library package_specification can be extended only at library level or
      as a generic formal. When the extension is declared immediately within a
      package_body, primitive subprograms are inherited and are overridable,
      but new primitive subprograms cannot be added.

8     68  A name that denotes a component (including a discriminant) of the
      parent type is not allowed within the record_extension_part. Similarly,
      a name that denotes a component defined within the record_extension_part
      is not allowed within the record_extension_part. It is permissible to
      use a name that denotes a discriminant of the record extension,
      providing there is a new known_discriminant_part in the enclosing type
      declaration. (The full rule is given in 3.8.)

9     69  Each visible component of a record extension has to have a unique
      name, whether the component is (visibly) inherited from the parent type
      or declared in the record_extension_part (see 8.3).


                                  Examples

10    Examples of record extensions (of types defined above in 3.9):

11    type Painted_Point is new Point with
        record
          Paint : Color := White;
        end record;
          -- Components X and Y are inherited

12    Origin : constant Painted_Point := (X | Y => 0.0, Paint => Black);

13    type Literal is new Expression with
        record                 -- a leaf in an Expression tree
          Value : Real;
        end record;

14    type Expr_Ptr is access all Expression'Class;
                                     -- see 3.10

15    type Binary_Operation is new Expression with
        record                 -- an internal node in an Expression tree
          Left, Right : Expr_Ptr;
        end record;

16    type Addition is new Binary_Operation with null record;
      type Subtraction is new Binary_Operation with null record;
        -- No additional components needed for these extensions

17    Tree : Expr_Ptr :=         -- A tree representation of ``
      5.0 + (13.0-7.0)''
         new Addition'(
            Left  => new Literal'(Value => 5.0),
            Right => new Subtraction'(
               Left  => new Literal'(Value => 13.0),
               Right => new Literal'(Value => 7.0)));


3.9.2 Dispatching Operations of Tagged Types


1     The primitive subprograms of a tagged type are called dispatching
operations. A dispatching operation can be called using a statically
determined controlling tag, in which case the body to be executed is
determined at compile time. Alternatively, the controlling tag can be
dynamically determined, in which case the call dispatches to a body that is
determined at run time; such a call is termed a dispatching call. As explained
below, the properties of the operands and the context of a particular call on
a dispatching operation determine how the controlling tag is determined, and
hence whether or not the call is a dispatching call. Run-time polymorphism is
achieved when a dispatching operation is called by a dispatching call.


                              Static Semantics

2     A call on a dispatching operation is a call whose name or prefix denotes
the declaration of a primitive subprogram of a tagged type, that is, a
dispatching operation. A controlling operand in a call on a dispatching
operation of a tagged type T is one whose corresponding formal parameter is of
type T or is of an anonymous access type with designated type T; the
corresponding formal parameter is called a controlling formal parameter. If
the controlling formal parameter is an access parameter, the controlling
operand is the object designated by the actual parameter, rather than the
actual parameter itself. If the call is to a (primitive) function with result
type T, then the call has a controlling result - the context of the call can
control the dispatching.

3     A name or expression of a tagged type is either statically tagged,
dynamically tagged, or tag indeterminate, according to whether, when used as a
controlling operand, the tag that controls dispatching is determined
statically by the operand's (specific) type, dynamically by its tag at run
time, or from context. A qualified_expression or parenthesized expression is
statically, dynamically, or indeterminately tagged according to its operand.
For other kinds of names and expressions, this is determined as follows:

4     The name or expression is statically tagged if it is of a specific
      tagged type and, if it is a call with a controlling result, it has at
      least one statically tagged controlling operand;

5     The name or expression is dynamically tagged if it is of a class-wide
      type, or it is a call with a controlling result and at least one
      dynamically tagged controlling operand;

6     The name or expression is tag indeterminate if it is a call with a
      controlling result, all of whose controlling operands (if any) are tag
      indeterminate.

7/1   A type_conversion is statically or dynamically tagged according to
whether the type determined by the subtype_mark is specific or class-wide,
respectively. {For an object that is designated by an expression whose
expected type is an anonymous access-to-specific tagged type, the object is
dynamically tagged if the expression, ignoring enclosing parentheses, is of
the form X'Access, where X is of a class-wide type, or is of the form new
T'(...), where T denotes a class-wide subtype. Otherwise, the object}[For a
controlling operand that is designated by an actual parameter, the controlling
operand] is statically or dynamically tagged according to whether the
designated type {of the type of the expression}[of the actual parameter] is
specific or class-wide, respectively.


                               Legality Rules

8     A call on a dispatching operation shall not have both dynamically tagged
and statically tagged controlling operands.

9/1   If the expected type for an expression or name is some specific tagged
type, then the expression or name shall not be dynamically tagged unless it is
a controlling operand in a call on a dispatching operation. Similarly, if the
expected type for an expression is an anonymous access-to-specific tagged
type, then the {object designated by the expression shall not be dynamically
tagged unless it is}[expression shall not be of an access-to-class-wide type
unless it designates] a controlling operand in a call on a dispatching
operation.

10/1  In the declaration of a dispatching operation of a tagged type,
everywhere a subtype of the tagged type appears as a subtype of the profile
(see 6.1), it shall statically match the first subtype of the tagged type. If
the dispatching operation overrides an inherited subprogram, it shall be
subtype conformant with the inherited subprogram. {The convention of an
inherited or overriding dispatching operation is the convention of the
corresponding primitive operation of the parent type. An explicitly
declared}[A] dispatching operation shall not be of convention Intrinsic.[ If a
dispatching operation overrides the predefined equals operator, then it shall
be of convention Ada (either explicitly or by default - see 6.3.1).]

11    The default_expression for a controlling formal parameter of a
dispatching operation shall be tag indeterminate. A controlling formal
parameter that is an access parameter shall not have a default_expression.

12    A given subprogram shall not be a dispatching operation of two or more
distinct tagged types.

13    The explicit declaration of a primitive subprogram of a tagged type
shall occur before the type is frozen (see 13.14). For example, new
dispatching operations cannot be added after objects or values of the type
exist, nor after deriving a record extension from it, nor after a body.


                              Dynamic Semantics

14    For the execution of a call on a dispatching operation of a type T, the
controlling tag value determines which subprogram body is executed. The
controlling tag value is defined as follows:

15    If one or more controlling operands are statically tagged, then the
      controlling tag value is statically determined to be the tag of T.

16    If one or more controlling operands are dynamically tagged, then the
      controlling tag value is not statically determined, but is rather
      determined by the tags of the controlling operands. If there is more
      than one dynamically tagged controlling operand, a check is made that
      they all have the same tag. If this check fails, Constraint_Error is
      raised unless the call is a function_call whose name denotes the
      declaration of an equality operator (predefined or user defined) that
      returns Boolean, in which case the result of the call is defined to
      indicate inequality, and no subprogram_body is executed. This check is
      performed prior to evaluating any tag-indeterminate controlling
      operands.

17    If all of the controlling operands are tag-indeterminate, then:

    18    If the call has a controlling result and is itself a (possibly
          parenthesized or qualified) controlling operand of an enclosing call
          on a dispatching operation of type T, then its controlling tag value
          is determined by the controlling tag value of this enclosing call;

    19    Otherwise, the controlling tag value is statically determined to be
          the tag of type T.

20    For the execution of a call on a dispatching operation, the body
executed is the one for the corresponding primitive subprogram of the specific
type identified by the controlling tag value. The body for an explicitly
declared dispatching operation is the corresponding explicit body for the
subprogram. The body for an implicitly declared dispatching operation that is
overridden is the body for the overriding subprogram, even if the overriding
occurs in a private part. The body for an inherited dispatching operation that
is not overridden is the body of the corresponding subprogram of the parent or
ancestor type.

      NOTES

21    70  The body to be executed for a call on a dispatching operation is
      determined by the tag; it does not matter whether that tag is determined
      statically or dynamically, and it does not matter whether the
      subprogram's declaration is visible at the place of the call.

22    71  This subclause covers calls on primitive subprograms of a tagged
      type. Rules for tagged type membership tests are described in 4.5.2.
      Controlling tag determination for an assignment_statement is described
      in 5.2.

23    72  A dispatching call can dispatch to a body whose declaration is not
      visible at the place of the call.

24    73  A call through an access-to-subprogram value is never a dispatching
      call, even if the access value designates a dispatching operation.
      Similarly a call whose prefix denotes a subprogram_renaming_declaration
      cannot be a dispatching call unless the renaming itself is the
      declaration of a primitive subprogram.


3.9.3 Abstract Types and Subprograms


1     An abstract type is a tagged type intended for use as a parent type for
type extensions, but which is not allowed to have objects of its own. An
abstract subprogram is a subprogram that has no body, but is intended to be
overridden at some point when inherited. Because objects of an abstract type
cannot be created, a dispatching call to an abstract subprogram always
dispatches to some overriding body.


                               Legality Rules

2     An abstract type is a specific type that has the reserved word abstract
in its declaration. Only a tagged type is allowed to be declared abstract.

3     A subprogram declared by an abstract_subprogram_declaration (see 6.1) is
an abstract subprogram. If it is a primitive subprogram of a tagged type, then
the tagged type shall be abstract.

4     For a derived type, if the parent or ancestor type has an abstract
primitive subprogram, or a primitive function with a controlling result, then:

5     If the derived type is abstract or untagged, the inherited subprogram is
      abstract.

6     Otherwise, the subprogram shall be overridden with a nonabstract
      subprogram; for a type declared in the visible part of a package, the
      overriding may be either in the visible or the private part. However, if
      the type is a generic formal type, the subprogram need not be overridden
      for the formal type itself; a nonabstract version will necessarily be
      provided by the actual type.

7     A call on an abstract subprogram shall be a dispatching call;
nondispatching calls to an abstract subprogram are not allowed.

8     The type of an aggregate, or of an object created by an
object_declaration or an allocator, or a generic formal object of mode in,
shall not be abstract. The type of the target of an assignment operation (see
5.2) shall not be abstract. The type of a component shall not be abstract. If
the result type of a function is abstract, then the function shall be
abstract.

9     If a partial view is not abstract, the corresponding full view shall not
be abstract. If a generic formal type is abstract, then for each primitive
subprogram of the formal that is not abstract, the corresponding primitive
subprogram of the actual shall not be abstract.

10    For an abstract type declared in a visible part, an abstract primitive
subprogram shall not be declared in the private part, unless it is overriding
an abstract subprogram implicitly declared in the visible part. For a tagged
type declared in a visible part, a primitive function with a controlling
result shall not be declared in the private part, unless it is overriding a
function implicitly declared in the visible part.

11    A generic actual subprogram shall not be an abstract subprogram. The
prefix of an attribute_reference for the Access, Unchecked_Access, or Address
attributes shall not denote an abstract subprogram.

      NOTES

12    74  Abstractness is not inherited; to declare an abstract type, the
      reserved word abstract has to be used in the declaration of the type
      extension.

13    75  A class-wide type is never abstract. Even if a class is rooted at an
      abstract type, the class-wide type for the class is not abstract, and an
      object of the class-wide type can be created; the tag of such an object
      will identify some nonabstract type in the class.


                                  Examples

14    Example of an abstract type representing a set of natural numbers:

15    package Sets is
          subtype Element_Type is Natural;
          type Set is abstract tagged null record;
          function Empty return Set is abstract;
          function Union(Left, Right : Set) return Set is abstract;
          function Intersection(Left, Right : Set) return Set is abstract;
          function Unit_Set(Element : Element_Type) return Set is abstract;
          procedure Take(Element : out Element_Type;
                         From : in out Set) is abstract;
      end Sets;

      NOTES

16    76  Notes on the example: Given the above abstract type, one could then
      derive various (nonabstract) extensions of the type, representing
      alternative implementations of a set. One might use a bit vector, but
      impose an upper bound on the largest element representable, while
      another might use a hash table, trading off space for flexibility.


3.10 Access Types


1     A value of an access type (an access value) provides indirect access to
the object or subprogram it designates. Depending on its type, an access value
can designate either subprograms, objects created by allocators (see 4.8), or
more generally aliased objects of an appropriate type.


                                   Syntax

2     access_type_definition ::= 
          access_to_object_definition
        | access_to_subprogram_definition

3     access_to_object_definition ::= 
          access [general_access_modifier] subtype_indication

4     general_access_modifier ::= all | constant

5     access_to_subprogram_definition ::= 
          access [protected] procedure parameter_profile
        | access [protected] function  parameter_and_result_profile

6     access_definition ::= access subtype_mark


                              Static Semantics

7/1   There are two kinds of access types, access-to-object types, whose
values designate objects, and access-to-subprogram types, whose values
designate subprograms. Associated with an access-to-object type is a storage
pool; several access types may share the same storage pool. {All descendants
of an access type share the same storage pool.} A storage pool is an area of
storage used to hold dynamically allocated objects (called pool elements)
created by allocators; storage pools are described further in 13.11, ``
Storage Management''.

8     Access-to-object types are further subdivided into pool-specific access
types, whose values can designate only the elements of their associated
storage pool, and general access types, whose values can designate the
elements of any storage pool, as well as aliased objects created by
declarations rather than allocators, and aliased subcomponents of other
objects.

9     A view of an object is defined to be aliased if it is defined by an
object_declaration or component_definition with the reserved word aliased, or
by a renaming of an aliased view. In addition, the dereference of an
access-to-object value denotes an aliased view, as does a view conversion (see
4.6) of an aliased view. Finally, the current instance of a limited type, and
a formal parameter or generic formal object of a tagged type are defined to be
aliased. Aliased views are the ones that can be designated by an access value.
If the view defined by an object_declaration is aliased, and the type of the
object has discriminants, then the object is constrained; if its nominal
subtype is unconstrained, then the object is constrained by its initial value.
Similarly, if the object created by an allocator has discriminants, the object
is constrained, either by the designated subtype, or by its initial value.

10    An access_to_object_definition defines an access-to-object type and its
first subtype; the subtype_indication defines the designated subtype of the
access type. If a general_access_modifier appears, then the access type is a
general access type. If the modifier is the reserved word constant, then the
type is an access-to-constant type; a designated object cannot be updated
through a value of such a type. If the modifier is the reserved word all, then
the type is an access-to-variable type; a designated object can be both read
and updated through a value of such a type. If no general_access_modifier
appears in the access_to_object_definition, the access type is a pool-specific
access-to-variable type.

11    An access_to_subprogram_definition defines an access-to-subprogram type
and its first subtype; the parameter_profile or parameter_and_result_profile
defines the designated profile of the access type. There is a calling
convention associated with the designated profile; only subprograms with this
calling convention can be designated by values of the access type. By default,
the calling convention is ``protected'' if the reserved word protected
appears, and ``Ada'' otherwise. See Annex B for how to override this default.

12    An access_definition defines an anonymous general access-to-variable
type; the subtype_mark denotes its designated subtype. An access_definition is
used in the specification of an access discriminant (see 3.7) or an access
parameter (see 6.1).

13    For each (named) access type, there is a literal null which has a null
access value designating no entity at all. The null value of a named access
type is the default initial value of the type. Other values of an access type
are obtained by evaluating an attribute_reference for the Access or
Unchecked_Access attribute of an aliased view of an object or non-intrinsic
subprogram, or, in the case of a named access-to-object type, an allocator,
which returns an access value designating a newly created object (see 3.10.2
).

14/1  All subtypes of an access-to-subprogram type are constrained. The first
subtype of a type defined by an {access_definition}[access_type_definition] or
an access_to_object_definition is unconstrained if the designated subtype is
an unconstrained array or discriminated {subtype}[type]; otherwise it is
constrained.


                              Dynamic Semantics

15    A composite_constraint is compatible with an unconstrained access
subtype if it is compatible with the designated subtype. An access value
satisfies a composite_constraint of an access subtype if it equals the null
value of its type or if it designates an object whose value satisfies the
constraint.

16    The elaboration of an access_type_definition creates the access type and
its first subtype. For an access-to-object type, this elaboration includes the
elaboration of the subtype_indication, which creates the designated subtype.

17    The elaboration of an access_definition creates an anonymous general
access-to-variable type (this happens as part of the initialization of an
access parameter or access discriminant).

      NOTES

18    77  Access values are called ``pointers'' or ``references'' in some
      other languages.

19    78  Each access-to-object type has an associated storage pool; several
      access types can share the same pool. An object can be created in the
      storage pool of an access type by an allocator (see 4.8) for the access
      type. A storage pool (roughly) corresponds to what some other languages
      call a ``heap.'' See 13.11 for a discussion of pools.

20    79  Only index_constraints and discriminant_constraints can be applied
      to access types (see 3.6.1 and 3.7.1).


                                  Examples

21    Examples of access-to-object types:

22    type Peripheral_Ref is access Peripheral;  --  see 3.8.1
      type Binop_Ptr is access all Binary_Operation'Class;
                                                 -- general access-to-class-wide, see 3.9.1

23    Example of an access subtype:

24    subtype Drum_Ref is Peripheral_Ref(Drum);  --  see 3.8.1

25    Example of an access-to-subprogram type:

26    type Message_Procedure is access procedure (M : in String := "Error!");
      procedure Default_Message_Procedure(M : in String);
      Give_Message : Message_Procedure := Default_Message_Procedure'Access;
      ...
      procedure Other_Procedure(M : in String);
      ...
      Give_Message := Other_Procedure'Access;
      ...
      Give_Message("File not found.");  -- call with parameter (.all is optional)
      Give_Message.all;                 -- call with no parameters


3.10.1 Incomplete Type Declarations


1     There are no particular limitations on the designated type of an access
type. In particular, the type of a component of the designated type can be
another access type, or even the same access type. This permits mutually
dependent and recursive access types. An incomplete_type_declaration can be
used to introduce a type to be used as a designated type, while deferring its
full definition to a subsequent full_type_declaration.


                                   Syntax

2     incomplete_type_declaration ::= type defining_identifier
       [discriminant_part];


                               Legality Rules

3     An incomplete_type_declaration requires a completion, which shall be a
full_type_declaration. If the incomplete_type_declaration occurs immediately
within either the visible part of a package_specification or a declarative_-
part, then the full_type_declaration shall occur later and immediately within
this visible part or declarative_part. If the incomplete_type_declaration
occurs immediately within the private part of a given package_specification,
then the full_type_declaration shall occur later and immediately within either
the private part itself, or the declarative_part of the corresponding package_-
body.

4     If an incomplete_type_declaration has a known_discriminant_part, then a
full_type_declaration that completes it shall have a fully conforming
(explicit) known_discriminant_part (see 6.3.1). If an
incomplete_type_declaration has no discriminant_part (or an
unknown_discriminant_part), then a corresponding full_type_declaration is
nevertheless allowed to have discriminants, either explicitly, or inherited
via derivation.

5     The only allowed uses of a name that denotes an
incomplete_type_declaration are as follows:

6     as the subtype_mark in the subtype_indication of an
      access_to_object_definition; the only form of constraint allowed in this
      subtype_indication is a discriminant_constraint;

7     as the subtype_mark defining the subtype of a parameter or result of an
      access_to_subprogram_definition;

8     as the subtype_mark in an access_definition;

9     as the prefix of an attribute_reference whose attribute_designator is
      Class; such an attribute_reference is similarly restricted to the uses
      allowed here; when used in this way, the corresponding full_type_-
      declaration shall declare a tagged type, and the attribute_reference
      shall occur in the same library unit as the incomplete_type_declaration.

10    A dereference (whether implicit or explicit - see 4.1) shall not be of
an incomplete type.


                              Static Semantics

11    An incomplete_type_declaration declares an incomplete type and its first
subtype; the first subtype is unconstrained if a known_discriminant_part
appears.


                              Dynamic Semantics

12    The elaboration of an incomplete_type_declaration has no effect.

      NOTES

13    80  Within a declarative_part, an incomplete_type_declaration and a
      corresponding full_type_declaration cannot be separated by an
      intervening body. This is because a type has to be completely defined
      before it is frozen, and a body freezes all types declared prior to it
      in the same declarative_part (see 13.14).


                                  Examples

14    Example of a recursive type:

15    type Cell;  --  incomplete type declaration
      type Link is access Cell;

16    type Cell is
         record
            Value  : Integer;
            Succ   : Link;
            Pred   : Link;
         end record;

17    Head   : Link  := new Cell'(0, null, null);
      Next   : Link  := Head.Succ;

18    Examples of mutually dependent access types:

19    type Person(<>);    -- incomplete type declaration
      type Car;           -- incomplete type declaration

20    type Person_Name is access Person;
      type Car_Name    is access all Car;

21    type Car is
         record
            Number  : Integer;
            Owner   : Person_Name;
         end record;

22    type Person(Sex : Gender) is
         record
            Name     : String(1 .. 20);
            Birth    : Date;
            Age      : Integer range 0 .. 130;
            Vehicle  : Car_Name;
            case Sex is
               when M => Wife           : Person_Name(Sex => F);
               when F => Husband        : Person_Name(Sex => M);
            end case;
         end record;

23    My_Car, Your_Car, Next_Car : Car_Name := new Car;  -- see 4.8
      George : Person_Name := new Person(M);
         ...
      George.Vehicle := Your_Car;


3.10.2 Operations of Access Types


1     The attribute Access is used to create access values designating aliased
objects and non-intrinsic subprograms. The ``accessibility'' rules prevent
dangling references (in the absence of uses of certain unchecked features -
see Section 13).


                            Name Resolution Rules

2     For an attribute_reference with attribute_designator Access (or
Unchecked_Access - see 13.10), the expected type shall be a single access
type; the prefix of such an attribute_reference is never interpreted as an
implicit_dereference. If the expected type is an access-to-subprogram type,
then the expected profile of the prefix is the designated profile of the
access type.


                              Static Semantics

3     The accessibility rules, which prevent dangling references, are written
in terms of accessibility levels, which reflect the run-time nesting of
masters. As explained in 7.6.1, a master is the execution of a task_body, a
block_statement, a subprogram_body, an entry_body, or an accept_statement. An
accessibility level is deeper than another if it is more deeply nested at run
time. For example, an object declared local to a called subprogram has a
deeper accessibility level than an object declared local to the calling
subprogram. The accessibility rules for access types require that the
accessibility level of an object designated by an access value be no deeper
than that of the access type. This ensures that the object will live at least
as long as the access type, which in turn ensures that the access value cannot
later designate an object that no longer exists. The Unchecked_Access
attribute may be used to circumvent the accessibility rules.

4     A given accessibility level is said to be statically deeper than another
if the given level is known at compile time (as defined below) to be deeper
than the other for all possible executions. In most cases, accessibility is
enforced at compile time by Legality Rules. Run-time accessibility checks are
also used, since the Legality Rules do not cover certain cases involving
access parameters and generic packages.

5     Each master, and each entity and view created by it, has an
accessibility level:

6     The accessibility level of a given master is deeper than that of each
      dynamically enclosing master, and deeper than that of each master upon
      which the task executing the given master directly depends (see 9.3).

7     An entity or view created by a declaration has the same accessibility
      level as the innermost enclosing master, except in the cases of renaming
      and derived access types described below. A parameter of a master has
      the same accessibility level as the master.

8     The accessibility level of a view of an object or subprogram defined by
      a renaming_declaration is the same as that of the renamed view.

9     The accessibility level of a view conversion is the same as that of the
      operand.

10    For a function whose result type is a return-by-reference type, the
      accessibility level of the result object is the same as that of the
      master that elaborated the function body. For any other function, the
      accessibility level of the result object is that of the execution of the
      called function.

11    The accessibility level of a derived access type is the same as that of
      its ultimate ancestor.

12    The accessibility level of the anonymous access type of an access
      discriminant is the same as that of the containing object or associated
      constrained subtype.

13    The accessibility level of the anonymous access type of an access
      parameter is the same as that of the view designated by the actual. If
      the actual is an allocator, this is the accessibility level of the
      execution of the called subprogram.

14    The accessibility level of an object created by an allocator is the same
      as that of the access type.

15    The accessibility level of a view of an object or subprogram denoted by
      a dereference of an access value is the same as that of the access type.

16    The accessibility level of a component, protected subprogram, or entry
      of (a view of) a composite object is the same as that of (the view of)
      the composite object.

17    One accessibility level is defined to be statically deeper than another
in the following cases:

18    For a master that is statically nested within another master, the
      accessibility level of the inner master is statically deeper than that
      of the outer master.

19    The statically deeper relationship does not apply to the accessibility
      level of the anonymous type of an access parameter; that is, such an
      accessibility level is not considered to be statically deeper, nor
      statically shallower, than any other.

20    For determining whether one level is statically deeper than another when
      within a generic package body, the generic package is presumed to be
      instantiated at the same level as where it was declared; run-time checks
      are needed in the case of more deeply nested instantiations.

21    For determining whether one level is statically deeper than another when
      within the declarative region of a type_declaration, the current
      instance of the type is presumed to be an object created at a deeper
      level than that of the type.

22    The accessibility level of all library units is called the library
level; a library-level declaration or entity is one whose accessibility level
is the library level.

23    The following attribute is defined for a prefix X that denotes an
aliased view of an object:

24/1  X'Access
              X'Access yields an access value that designates the object
              denoted by X. The type of X'Access is an access-to-object type,
              as determined by the expected type. The expected type shall be a
              general access type. X shall denote an aliased view of an
              object, including possibly the current instance (see 8.6) of a
              limited type within its definition, or a formal parameter or
              generic formal object of a tagged type. The view denoted by the
              prefix X shall satisfy the following additional requirements,
              presuming the expected type for X'Access is the general access
              type A{ with designated type D}:

            25    If A is an access-to-variable type, then the view shall be a
                  variable; on the other hand, if A is an access-to-constant
                  type, the view may be either a constant or a variable.

            26    The view shall not be a subcomponent that depends on
                  discriminants of a variable whose nominal subtype is
                  unconstrained, unless this subtype is indefinite, or the
                  variable is aliased.

            27/1  If {A is a named access type and D is a tagged type}[the
                  designated type of A is tagged], then the type of the view
                  shall be covered by {D}[the designated type]; {if A is
                  anonymous and D is tagged, then the type of the view shall
                  be either D'Class or a type covered by D;} if {D is
                  untagged}[A's designated type is not tagged], then the type
                  of the view shall be {D}[the same], and [either ]A's
                  designated subtype shall {either }statically match the
                  nominal subtype of the view{ or be}[, or the designated
                  subtype shall be] discriminated and unconstrained;

            28    The accessibility level of the view shall not be statically
                  deeper than that of the access type A. In addition to the
                  places where Legality Rules normally apply (see 12.3), this
                  rule applies also in the private part of an instance of a
                  generic unit.

        29    A check is made that the accessibility level of X is not deeper
              than that of the access type A. If this check fails,
              Program_Error is raised.

        30    If the nominal subtype of X does not statically match the
              designated subtype of A, a view conversion of X to the
              designated subtype is evaluated (which might raise
              Constraint_Error - see 4.6) and the value of X'Access designates
              that view.

31    The following attribute is defined for a prefix P that denotes a
subprogram:

32    P'Access
              P'Access yields an access value that designates the subprogram
              denoted by P. The type of P'Access is an access-to-subprogram
              type (S), as determined by the expected type. The accessibility
              level of P shall not be statically deeper than that of S. In
              addition to the places where Legality Rules normally apply (see
              12.3), this rule applies also in the private part of an instance
              of a generic unit. The profile of P shall be subtype-conformant
              with the designated profile of S, and shall not be Intrinsic. If
              the subprogram denoted by P is declared within a generic body, S
              shall be declared within the generic body.

      NOTES

33    81  The Unchecked_Access attribute yields the same result as the Access
      attribute for objects, but has fewer restrictions (see 13.10). There are
      other predefined operations that yield access values: an allocator can
      be used to create an object, and return an access value that designates
      it (see 4.8); evaluating the literal null yields a null access value
      that designates no entity at all (see 4.2).

34    82  The predefined operations of an access type also include the
      assignment operation, qualification, and membership tests. Explicit
      conversion is allowed between general access types with matching
      designated subtypes; explicit conversion is allowed between
      access-to-subprogram types with subtype conformant profiles (see 4.6).
      Named access types have predefined equality operators; anonymous access
      types do not (see 4.5.2).

35    83  The object or subprogram designated by an access value can be named
      with a dereference, either an explicit_dereference or an
      implicit_dereference. See 4.1.

36    84  A call through the dereference of an access-to-subprogram value is
      never a dispatching call.

37    85  The accessibility rules imply that it is not possible to use the
      Access attribute to implement ``downward closures'' - that is, to pass a
      more-nested subprogram as a parameter to a less-nested subprogram, as
      might be desired for example for an iterator abstraction. Instead,
      downward closures can be implemented using generic formal subprograms
      (see 12.6). Note that Unchecked_Access is not allowed for subprograms.

38    86  Note that using an access-to-class-wide tagged type with a
      dispatching operation is a potentially more structured alternative to
      using an access-to-subprogram type.

39    87  An implementation may consider two access-to-subprogram values to be
      unequal, even though they designate the same subprogram. This might be
      because one points directly to the subprogram, while the other points to
      a special prologue that performs an Elaboration_Check and then jumps to
      the subprogram. See 4.5.2.


                                  Examples

40    Example of use of the Access attribute:

41    Martha : Person_Name := new Person(F);       -- see 3.10.1
      Cars   : array (1..2) of aliased Car;
         ...
      Martha.Vehicle := Cars(1)'Access;
      George.Vehicle := Cars(2)'Access;


3.11 Declarative Parts


1     A declarative_part contains declarative_items (possibly none).


                                   Syntax

2     declarative_part ::= {declarative_item}

3     declarative_item ::= 
          basic_declarative_item | body

4/1   basic_declarative_item ::= 
          basic_declaration | {aspect_clause}[representation_clause
      ] | use_clause

5     body ::= proper_body | body_stub

6     proper_body ::= 
          subprogram_body | package_body | task_body | protected_body


                              Dynamic Semantics

7     The elaboration of a declarative_part consists of the elaboration of the
declarative_items, if any, in the order in which they are given in the
declarative_part.

8     An elaborable construct is in the elaborated state after the normal
completion of its elaboration. Prior to that, it is not yet elaborated.

9     For a construct that attempts to use a body, a check (Elaboration_Check)
is performed, as follows:

10/1  For a call to a (non-protected) subprogram that has an explicit body, a
      check is made that the {body}[subprogram_body] is already elaborated.
      This check and the evaluations of any actual parameters of the call are
      done in an arbitrary order.

11    For a call to a protected operation of a protected type (that has a body
      - no check is performed if a pragma Import applies to the protected
      type), a check is made that the protected_body is already elaborated.
      This check and the evaluations of any actual parameters of the call are
      done in an arbitrary order.

12    For the activation of a task, a check is made by the activator that the
      task_body is already elaborated. If two or more tasks are being
      activated together (see 9.2), as the result of the elaboration of a
      declarative_part or the initialization for the object created by an
      allocator, this check is done for all of them before activating any of
      them.

13    For the instantiation of a generic unit that has a body, a check is made
      that this body is already elaborated. This check and the evaluation of
      any explicit_generic_actual_parameters of the instantiation are done in
      an arbitrary order.

14    The exception Program_Error is raised if any of these checks fails.


3.11.1 Completions of Declarations


1/1   Declarations sometimes come in two parts. A declaration that requires a
second part is said to require completion. The second part is called the
completion of the declaration (and of the entity declared), and is either
another declaration, a body, or a pragma. {A body is a body, an entry_body, or
a renaming-as-body (see 8.5.4).}


                            Name Resolution Rules

2     A construct that can be a completion is interpreted as the completion of
a prior declaration only if:

3     The declaration and the completion occur immediately within the same
      declarative region;

4     The defining name or defining_program_unit_name in the completion is the
      same as in the declaration, or in the case of a pragma, the pragma
      applies to the declaration;

5     If the declaration is overloadable, then the completion either has a
      type-conformant profile, or is a pragma.


                               Legality Rules

6     An implicit declaration shall not have a completion. For any explicit
declaration that is specified to require completion, there shall be a
corresponding explicit completion.

7     At most one completion is allowed for a given declaration. Additional
requirements on completions appear where each kind of completion is defined.

8     A type is completely defined at a place that is after its full type
definition (if it has one) and after all of its subcomponent types are
completely defined. A type shall be completely defined before it is frozen
(see 13.14 and 7.3).

      NOTES

9     88  Completions are in principle allowed for any kind of explicit
      declaration. However, for some kinds of declaration, the only allowed
      completion is a pragma Import, and implementations are not required to
      support pragma Import for every kind of entity.

10    89  There are rules that prevent premature uses of declarations that
      have a corresponding completion. The Elaboration_Checks of 3.11 prevent
      such uses at run time for subprograms, protected operations, tasks, and
      generic units. The rules of 13.14, ``Freezing Rules'' prevent, at
      compile time, premature uses of other entities such as private types and
      deferred constants.



                      Section 4: Names and Expressions


1     The rules applicable to the different forms of name and expression, and
to their evaluation, are given in this section.


4.1 Names


1     Names can denote declared entities, whether declared explicitly or
implicitly (see 3.1). Names can also denote objects or subprograms designated
by access values; the results of type_conversions or function_calls;
subcomponents and slices of objects and values; protected subprograms, single
entries, entry families, and entries in families of entries. Finally, names
can denote attributes of any of the foregoing.


                                   Syntax

2     name ::= 
           direct_name          | explicit_dereference
         | indexed_component    | slice
         | selected_component   | attribute_reference
         | type_conversion      | function_call
         | character_literal

3     direct_name ::= identifier | operator_symbol

4     prefix ::= name | implicit_dereference

5     explicit_dereference ::= name.all

6     implicit_dereference ::= name

7     Certain forms of name (indexed_components, selected_components, slices,
and attributes) include a prefix that is either itself a name that denotes
some related entity, or an implicit_dereference of an access value that
designates some related entity.


                            Name Resolution Rules

8     The name in a dereference (either an implicit_dereference or an
explicit_dereference) is expected to be of any access type.


                              Static Semantics

9     If the type of the name in a dereference is some access-to-object type
T, then the dereference denotes a view of an object, the nominal subtype of
the view being the designated subtype of T.

10    If the type of the name in a dereference is some access-to-subprogram
type S, then the dereference denotes a view of a subprogram, the profile of
the view being the designated profile of S.


                              Dynamic Semantics

11    The evaluation of a name determines the entity denoted by the name. This
evaluation has no other effect for a name that is a direct_name or a
character_literal.

12    The evaluation of a name that has a prefix includes the evaluation of
the prefix. The evaluation of a prefix consists of the evaluation of the name
or the implicit_dereference. The prefix denotes the entity denoted by the name
or the implicit_dereference.

13    The evaluation of a dereference consists of the evaluation of the name
and the determination of the object or subprogram that is designated by the
value of the name. A check is made that the value of the name is not the null
access value. Constraint_Error is raised if this check fails. The dereference
denotes the object or subprogram designated by the value of the name.


                                  Examples

14    Examples of direct names:

15    Pi        -- the direct name of a number                 (see 3.3.2)
      Limit     -- the direct name of a constant               (see 3.3.1)
      Count     -- the direct name of a scalar variable        (see 3.3.1)
      Board     -- the direct name of an array variable        (see 3.6.1)
      Matrix    -- the direct name of a type                   (see 3.6)
      Random    -- the direct name of a function               (see 6.1)
      Error     -- the direct name of an exception             (see 11.1)

16    Examples of dereferences:

17    Next_Car.all          
      --  explicit dereference denoting the object designated by
                            --  the access variable Next_Car (see 3.10.1)
      Next_Car.Owner        --  selected component with implicit dereference;
                            --  same as Next_Car.all.Owner


4.1.1 Indexed Components


1     An indexed_component denotes either a component of an array or an entry
in a family of entries.


                                   Syntax

2     indexed_component ::= prefix(expression {, expression})


                            Name Resolution Rules

3     The prefix of an indexed_component with a given number of expressions
shall resolve to denote an array (after any implicit dereference) with the
corresponding number of index positions, or shall resolve to denote an entry
family of a task or protected object (in which case there shall be only one
expression).

4     The expected type for each expression is the corresponding index type.


                              Static Semantics

5     When the prefix denotes an array, the indexed_component denotes the
component of the array with the specified index value(s). The nominal subtype
of the indexed_component is the component subtype of the array type.

6     When the prefix denotes an entry family, the indexed_component denotes
the individual entry of the entry family with the specified index value.


                              Dynamic Semantics

7     For the evaluation of an indexed_component, the prefix and the
expressions are evaluated in an arbitrary order. The value of each expression
is converted to the corresponding index type. A check is made that each index
value belongs to the corresponding index range of the array or entry family
denoted by the prefix. Constraint_Error is raised if this check fails.


                                  Examples

8     Examples of indexed components:

9      My_Schedule(Sat)     --  a component of a one-dimensional array               
      (see 3.6.1)
       Page(10)             --  a component of a one-dimensional array               
      (see 3.6)
       Board(M, J + 1)      --  a component of a two-dimensional array               
      (see 3.6.1)
       Page(10)(20)         --  a component of a component                           
      (see 3.6)
       Request(Medium)      --  an entry in a family of entries                      
      (see 9.1)
       Next_Frame(L)(M, N)  --  a component of a function call                       
      (see 6.1)

      NOTES

10    1  Notes on the examples: Distinct notations are used for components of
      multidimensional arrays (such as Board) and arrays of arrays (such as
      Page). The components of an array of arrays are arrays and can therefore
      be indexed. Thus Page(10)(20) denotes the 20th component of Page(10). In
      the last example Next_Frame(L) is a function call returning an access
      value that designates a two-dimensional array.


4.1.2 Slices


1     A slice denotes a one-dimensional array formed by a sequence of
consecutive components of a one-dimensional array. A slice of a variable is a
variable; a slice of a constant is a constant; a slice of a value is a value.


                                   Syntax

2     slice ::= prefix(discrete_range)


                            Name Resolution Rules

3     The prefix of a slice shall resolve to denote a one-dimensional array
(after any implicit dereference).

4     The expected type for the discrete_range of a slice is the index type of
the array type.


                              Static Semantics

5     A slice denotes a one-dimensional array formed by the sequence of
consecutive components of the array denoted by the prefix, corresponding to
the range of values of the index given by the discrete_range.

6     The type of the slice is that of the prefix. Its bounds are those
defined by the discrete_range.


                              Dynamic Semantics

7     For the evaluation of a slice, the prefix and the discrete_range are
evaluated in an arbitrary order. If the slice is not a null slice (a slice
where the discrete_range is a null range), then a check is made that the
bounds of the discrete_range belong to the index range of the array denoted by
the prefix. Constraint_Error is raised if this check fails.

      NOTES

8     2  A slice is not permitted as the prefix of an Access
      attribute_reference, even if the components or the array as a whole are
      aliased. See 3.10.2.

9     3  For a one-dimensional array A, the slice A(N .. N) denotes an array
      that has only one component; its type is the type of A. On the other
      hand, A(N) denotes a component of the array A and has the corresponding
      component type.


                                  Examples

10    Examples of slices:

11      Stars(1 .. 15)        --  a slice of 15 characters                   
      (see 3.6.3)
        Page(10 .. 10 + Size) --  a slice of 1 + Size components             
      (see 3.6)
        Page(L)(A .. B)       --  a slice of the array Page(L)               
      (see 3.6)
        Stars(1 .. 0)         --  a null slice                               
      (see 3.6.3)
        My_Schedule(Weekday)  --  bounds given by subtype                    
      (see 3.6.1 and 3.5.1)
        Stars(5 .. 15)(K)     --  same as Stars(K)                           
      (see 3.6.3)
                              --  provided that K is in 5 .. 15


4.1.3 Selected Components


1     Selected_components are used to denote components (including
discriminants), entries, entry families, and protected subprograms; they are
also used as expanded names as described below.


                                   Syntax

2     selected_component ::= prefix . selector_name

3     selector_name ::= identifier | character_literal | operator_symbol


                            Name Resolution Rules

4     A selected_component is called an expanded name if, according to the
visibility rules, at least one possible interpretation of its prefix denotes a
package or an enclosing named construct (directly, not through a
subprogram_renaming_declaration or generic_renaming_declaration).

5     A selected_component that is not an expanded name shall resolve to
denote one of the following:

6     A component (including a discriminant):

7     The prefix shall resolve to denote an object or value of some non-array
      composite type (after any implicit dereference). The selector_name shall
      resolve to denote a discriminant_specification of the type, or, unless
      the type is a protected type, a component_declaration of the type. The
      selected_component denotes the corresponding component of the object or
      value.

8     A single entry, an entry family, or a protected subprogram:

9     The prefix shall resolve to denote an object or value of some task or
      protected type (after any implicit dereference). The selector_name shall
      resolve to denote an entry_declaration or subprogram_declaration
      occurring (implicitly or explicitly) within the visible part of that
      type. The selected_component denotes the corresponding entry, entry
      family, or protected subprogram.

10    An expanded name shall resolve to denote a declaration that occurs
immediately within a named declarative region, as follows:

11    The prefix shall resolve to denote either a package (including the
      current instance of a generic package, or a rename of a package), or an
      enclosing named construct.

12    The selector_name shall resolve to denote a declaration that occurs
      immediately within the declarative region of the package or enclosing
      construct (the declaration shall be visible at the place of the expanded
      name - see 8.3). The expanded name denotes that declaration.

13    If the prefix does not denote a package, then it shall be a direct_name
      or an expanded name, and it shall resolve to denote a program unit
      (other than a package), the current instance of a type, a
      block_statement, a loop_statement, or an accept_statement (in the case
      of an accept_statement or entry_body, no family index is allowed); the
      expanded name shall occur within the declarative region of this
      construct. Further, if this construct is a callable construct and the
      prefix denotes more than one such enclosing callable construct, then the
      expanded name is ambiguous, independently of the selector_name.


                              Dynamic Semantics

14    The evaluation of a selected_component includes the evaluation of the
prefix.

15    For a selected_component that denotes a component of a variant, a check
is made that the values of the discriminants are such that the value or object
denoted by the prefix has this component. The exception Constraint_Error is
raised if this check fails.


                                  Examples

16    Examples of selected components:

17      Tomorrow.Month     --  a record component                               
      (see 3.8)
        Next_Car.Owner     --  a record component                               
      (see 3.10.1)
        Next_Car.Owner.Age --  a record component                               
      (see 3.10.1)
                           --  the previous two lines involve implicit dereferences
        Writer.Unit        --  a record component (a discriminant)              
      (see 3.8.1)
        Min_Cell(H).Value  --  a record component of the result                 
      (see 6.1)
                           --  of the function call Min_Cell(H)
        Control.Seize      --  an entry of a protected object                   
      (see 9.4)
        Pool(K).Write      --  an entry of the task Pool(K)                     
      (see 9.4)

18    Examples of expanded names:

19      Key_Manager."<"      --  an operator of the visible part of a package          
      (see 7.3.1)
        Dot_Product.Sum      --  a variable declared in a function body                
      (see 6.1)
        Buffer.Pool          --  a variable declared in a protected unit               
      (see 9.11)
        Buffer.Read          --  an entry of a protected unit                          
      (see 9.11)
        Swap.Temp            --  a variable declared in a block statement              
      (see 5.6)
        Standard.Boolean     --  the name of a predefined type                         
      (see A.1)


4.1.4 Attributes


1     An attribute is a characteristic of an entity that can be queried via an
attribute_reference or a range_attribute_reference.


                                   Syntax

2     attribute_reference ::= prefix'attribute_designator

3     attribute_designator ::= 
          identifier[(static_expression)]
        | Access | Delta | Digits

4     range_attribute_reference ::= prefix'range_attribute_designator

5     range_attribute_designator ::= Range[(static_expression)]


                            Name Resolution Rules

6     In an attribute_reference, if the attribute_designator is for an
attribute defined for (at least some) objects of an access type, then the
prefix is never interpreted as an implicit_dereference; otherwise (and for all
range_attribute_references), if the type of the name within the prefix is of
an access type, the prefix is interpreted as an implicit_dereference.
Similarly, if the attribute_designator is for an attribute defined for (at
least some) functions, then the prefix is never interpreted as a parameterless
function_call; otherwise (and for all range_attribute_references), if the
prefix consists of a name that denotes a function, it is interpreted as a
parameterless function_call.

7     The expression, if any, in an attribute_designator or
range_attribute_designator is expected to be of any integer type.


                               Legality Rules

8     The expression, if any, in an attribute_designator or
range_attribute_designator shall be static.


                              Static Semantics

9     An attribute_reference denotes a value, an object, a subprogram, or some
other kind of program entity.

10    A range_attribute_reference X'Range(N) is equivalent to the range
X'First(N) .. X'Last(N), except that the prefix is only evaluated once.
Similarly, X'Range is equivalent to X'First .. X'Last, except that the prefix
is only evaluated once.


                              Dynamic Semantics

11    The evaluation of an attribute_reference (or range_attribute_reference)
consists of the evaluation of the prefix.


                         Implementation Permissions

12/1  An implementation may provide implementation-defined attributes; the
identifier for an implementation-defined attribute shall differ from those of
the language-defined attributes{ unless supplied for compatibility with a
previous edition of this International Standard}.

      NOTES

13    4  Attributes are defined throughout this International Standard, and
      are summarized in Annex K.

14/1  5  In general, the name in a prefix of an attribute_reference (or a
      range_attribute_reference) has to be resolved without using any context.
      However, in the case of the Access attribute, the expected type for the
      {prefix}[prefix] has to be a single access type, and if it is an
      access-to-subprogram type (see 3.10.2) then the resolution of the name
      can use the fact that the profile of the callable entity denoted by the
      prefix has to be type conformant with the designated profile of the
      access type.


                                  Examples

15    Examples of attributes:

16    Color'First        -- minimum value of the enumeration type Color              
      (see 3.5.1)
      Rainbow'Base'First -- same as Color'First                                      
      (see 3.5.1)
      Real'Digits        -- precision of the type Real                               
      (see 3.5.7)
      Board'Last(2)      -- upper bound of the second dimension of Board             
      (see 3.6.1)
      Board'Range(1)     -- index range of the first dimension of Board              
      (see 3.6.1)
      Pool(K)'Terminated -- True if task Pool(K) is terminated                       
      (see 9.1)
      Date'Size          -- number of bits for records of type Date                  
      (see 3.8)
      Message'Address    -- address of the record variable Message                   
      (see 3.7.1)


4.2 Literals


1     A literal represents a value literally, that is, by means of notation
suited to its kind. A literal is either a numeric_literal, a
character_literal, the literal null, or a string_literal.


                            Name Resolution Rules

2     The expected type for a literal null shall be a single access type.

3     For a name that consists of a character_literal, either its expected
type shall be a single character type, in which case it is interpreted as a
parameterless function_call that yields the corresponding value of the
character type, or its expected profile shall correspond to a parameterless
function with a character result type, in which case it is interpreted as the
name of the corresponding parameterless function declared as part of the
character type's definition (see 3.5.1). In either case, the character_literal
denotes the enumeration_literal_specification.

4     The expected type for a primary that is a string_literal shall be a
single string type.


                               Legality Rules

5     A character_literal that is a name shall correspond to a
defining_character_literal of the expected type, or of the result type of the
expected profile.

6     For each character of a string_literal with a given expected string
type, there shall be a corresponding defining_character_literal of the
component type of the expected string type.

7     A literal null shall not be of an anonymous access type, since such
types do not have a null value (see 3.10).


                              Static Semantics

8     An integer literal is of type universal_integer. A real literal is of
type universal_real.


                              Dynamic Semantics

9     The evaluation of a numeric literal, or the literal null, yields the
represented value.

10    The evaluation of a string_literal that is a primary yields an array
value containing the value of each character of the sequence of characters of
the string_literal, as defined in 2.6. The bounds of this array value are
determined according to the rules for positional_array_aggregates (see 4.3.3
), except that for a null string literal, the upper bound is the predecessor
of the lower bound.

11    For the evaluation of a string_literal of type T, a check is made that
the value of each character of the string_literal belongs to the component
subtype of T. For the evaluation of a null string literal, a check is made
that its lower bound is greater than the lower bound of the base range of the
index type. The exception Constraint_Error is raised if either of these checks
fails.

      NOTES

12    6  Enumeration literals that are identifiers rather than
      character_literals follow the normal rules for identifiers when used in
      a name (see 4.1 and 4.1.3). Character_literals used as selector_names
      follow the normal rules for expanded names (see 4.1.3).


                                  Examples

13    Examples of literals:

14    3.14159_26536      --  a real literal
      1_345              --  an integer literal
      'A'                --  a character literal
      "Some Text"        --  a string literal 


4.3 Aggregates


1     An aggregate combines component values into a composite value of an
array type, record type, or record extension.


                                   Syntax

2     aggregate ::= record_aggregate | extension_aggregate
       | array_aggregate


                            Name Resolution Rules

3     The expected type for an aggregate shall be a single nonlimited array
type, record type, or record extension.


                               Legality Rules

4     An aggregate shall not be of a class-wide type.


                              Dynamic Semantics

5     For the evaluation of an aggregate, an anonymous object is created and
values for the components or ancestor part are obtained (as described in the
subsequent subclause for each kind of the aggregate) and assigned into the
corresponding components or ancestor part of the anonymous object. Obtaining
the values and the assignments occur in an arbitrary order. The value of the
aggregate is the value of this object.

6     If an aggregate is of a tagged type, a check is made that its value
belongs to the first subtype of the type. Constraint_Error is raised if this
check fails.


4.3.1 Record Aggregates


1     In a record_aggregate, a value is specified for each component of the
record or record extension value, using either a named or a positional
association.


                                   Syntax

2     record_aggregate ::= (record_component_association_list)

3     record_component_association_list ::= 
          record_component_association {, record_component_association}
        | null record

4     record_component_association ::= 
         [ component_choice_list => ] expression

5     component_choice_list ::= 
           component_selector_name {| component_selector_name}
         | others

6     A record_component_association is a named component association if it
      has a component_choice_list; otherwise, it is a positional component
      association. Any positional component associations shall precede any
      named component associations. If there is a named association with a
      component_choice_list of others, it shall come last.

7     In the record_component_association_list for a record_aggregate, if
      there is only one association, it shall be a named association.


                            Name Resolution Rules

8     The expected type for a record_aggregate shall be a single nonlimited
record type or record extension.

9     For the record_component_association_list of a record_aggregate, all
components of the composite value defined by the aggregate are needed; for the
association list of an extension_aggregate, only those components not
determined by the ancestor expression or subtype are needed (see 4.3.2). Each
selector_name in a record_component_association shall denote a needed
component (including possibly a discriminant).

10    The expected type for the expression of a record_component_association
is the type of the associated component(s); the associated component(s) are as
follows:

11    For a positional association, the component (including possibly a
      discriminant) in the corresponding relative position (in the declarative
      region of the type), counting only the needed components;

12    For a named association with one or more component_selector_names, the
      named component(s);

13    For a named association with the reserved word others, all needed
      components that are not associated with some previous association.


                               Legality Rules

14    If the type of a record_aggregate is a record extension, then it shall
be a descendant of a record type, through one or more record extensions (and
no private extensions).

15    If there are no components needed in a given
record_component_association_list, then the reserved words null record shall
appear rather than a list of record_component_associations.

16    Each record_component_association shall have at least one associated
component, and each needed component shall be associated with exactly one
record_component_association. If a record_component_association has two or
more associated components, all of them shall be of the same type.

17    If the components of a variant_part are needed, then the value of a
discriminant that governs the variant_part shall be given by a static
expression.


                              Dynamic Semantics

18    The evaluation of a record_aggregate consists of the evaluation of the
record_component_association_list.

19    For the evaluation of a record_component_association_list, any
per-object constraints (see 3.8) for components specified in the association
list are elaborated and any expressions are evaluated and converted to the
subtype of the associated component. Any constraint elaborations and
expression evaluations (and conversions) occur in an arbitrary order, except
that the expression for a discriminant is evaluated (and converted) prior to
the elaboration of any per-object constraint that depends on it, which in turn
occurs prior to the evaluation and conversion of the expression for the
component with the per-object constraint.

20    The expression of a record_component_association is evaluated (and
converted) once for each associated component.

      NOTES

21    7  For a record_aggregate with positional associations, expressions
      specifying discriminant values appear first since the
      known_discriminant_part is given first in the declaration of the type;
      they have to be in the same order as in the known_discriminant_part.


                                  Examples

22    Example of a record aggregate with positional associations:

23    (4, July, 1776)                                       --  see 3.8 

24    Examples of record aggregates with named associations:

25    (Day => 4, Month => July, Year => 1776)
      (Month => July, Day => 4, Year => 1776)

26    (Disk, Closed, Track => 5, Cylinder => 12)            --  see 3.8.1
      (Unit => Disk, Status => Closed, Cylinder => 9, Track => 1)

27    Example of component association with several choices:

28    (Value => 0, Succ|Pred => new Cell'(0, null, null))   --  see 3.10.1

29     --  The allocator is evaluated twice: Succ and Pred designate different cells

30    Examples of record aggregates for tagged types (see 3.9 and 3.9.1):

31    Expression'(null record)
      Literal'(Value => 0.0)
      Painted_Point'(0.0, Pi/2.0, Paint => Red)


4.3.2 Extension Aggregates


1     An extension_aggregate specifies a value for a type that is a record
extension by specifying a value or subtype for an ancestor of the type,
followed by associations for any components not determined by the
ancestor_part.


                                   Syntax

2     extension_aggregate ::= 
          (ancestor_part with record_component_association_list)

3     ancestor_part ::= expression | subtype_mark


                            Name Resolution Rules

4     The expected type for an extension_aggregate shall be a single
nonlimited type that is a record extension. If the ancestor_part is an
expression, it is expected to be of any nonlimited tagged type.


                               Legality Rules

5     If the ancestor_part is a subtype_mark, it shall denote a specific
tagged subtype. The type of the extension_aggregate shall be derived from the
type of the ancestor_part, through one or more record extensions (and no
private extensions).


                              Static Semantics

6     For the record_component_association_list of an extension_aggregate, the
only components needed are those of the composite value defined by the
aggregate that are not inherited from the type of the ancestor_part, plus any
inherited discriminants if the ancestor_part is a subtype_mark that denotes an
unconstrained subtype.


                              Dynamic Semantics

7     For the evaluation of an extension_aggregate, the record_component_-
association_list is evaluated. If the ancestor_part is an expression, it is
also evaluated; if the ancestor_part is a subtype_mark, the components of the
value of the aggregate not given by the record_component_association_list are
initialized by default as for an object of the ancestor type. Any implicit
initializations or evaluations are performed in an arbitrary order, except
that the expression for a discriminant is evaluated prior to any other
evaluation or initialization that depends on it.

8     If the type of the ancestor_part has discriminants that are not
inherited by the type of the extension_aggregate, then, unless the
ancestor_part is a subtype_mark that denotes an unconstrained subtype, a check
is made that each discriminant of the ancestor has the value specified for a
corresponding discriminant, either in the record_component_association_-
list, or in the derived_type_definition for some ancestor of the type of the
extension_aggregate. Constraint_Error is raised if this check fails.

      NOTES

9     8  If all components of the value of the extension_aggregate are
      determined by the ancestor_part, then the record_component_association_-
      list is required to be simply null record.

10    9  If the ancestor_part is a subtype_mark, then its type can be
      abstract. If its type is controlled, then as the last step of evaluating
      the aggregate, the Initialize procedure of the ancestor type is called,
      unless the Initialize procedure is abstract (see 7.6).


                                  Examples

11    Examples of extension aggregates (for types defined in 3.9.1):

12    Painted_Point'(Point with Red)
      (Point'(P) with Paint => Black)

13    (Expression with Left => 1.2, Right => 3.4)
      Addition'(Binop with null record)
                   -- presuming Binop is of type Binary_Operation


4.3.3 Array Aggregates


1     In an array_aggregate, a value is specified for each component of an
array, either positionally or by its index. For a positional_array_aggregate,
the components are given in increasing-index order, with a final others, if
any, representing any remaining components. For a named_array_aggregate, the
components are identified by the values covered by the discrete_choices.


                                   Syntax

2     array_aggregate ::= 
        positional_array_aggregate | named_array_aggregate

3     positional_array_aggregate ::= 
          (expression, expression {, expression})
        | (expression {, expression}, others => expression)

4     named_array_aggregate ::= 
          (array_component_association {, array_component_association})

5     array_component_association ::= 
          discrete_choice_list => expression

6     An n-dimensional array_aggregate is one that is written as n levels of
nested array_aggregates (or at the bottom level, equivalent string_literals).
For the multidimensional case (n >= 2) the array_aggregates (or equivalent
string_literals) at the n-1 lower levels are called subaggregates of the
enclosing n-dimensional array_aggregate. The expressions of the bottom level
subaggregates (or of the array_aggregate itself if one-dimensional) are called
the array component expressions of the enclosing n-dimensional
array_aggregate.


                            Name Resolution Rules

7     The expected type for an array_aggregate (that is not a subaggregate)
shall be a single nonlimited array type. The component type of this array type
is the expected type for each array component expression of the
array_aggregate.

8     The expected type for each discrete_choice in any discrete_choice_list
of a named_array_aggregate is the type of the corresponding index; the
corresponding index for an array_aggregate that is not a subaggregate is the
first index of its type; for an (n-m)-dimensional subaggregate within an
array_aggregate of an n-dimensional type, the corresponding index is the index
in position m+1.


                               Legality Rules

9     An array_aggregate of an n-dimensional array type shall be written as an
n-dimensional array_aggregate.

10    An others choice is allowed for an array_aggregate only if an applicable
index constraint applies to the array_aggregate. An applicable index
constraint is a constraint provided by certain contexts where an
array_aggregate is permitted that can be used to determine the bounds of the
array value specified by the aggregate. Each of the following contexts (and
none other) defines an applicable index constraint:

11    For an explicit_actual_parameter, an explicit_generic_actual_parameter,
      the expression of a return_statement, the initialization expression in
      an object_declaration, or a default_expression (for a parameter or a
      component), when the nominal subtype of the corresponding formal
      parameter, generic formal parameter, function result, object, or
      component is a constrained array subtype, the applicable index
      constraint is the constraint of the subtype;

12    For the expression of an assignment_statement where the name denotes an
      array variable, the applicable index constraint is the constraint of the
      array variable;

13    For the operand of a qualified_expression whose subtype_mark denotes a
      constrained array subtype, the applicable index constraint is the
      constraint of the subtype;

14    For a component expression in an aggregate, if the component's nominal
      subtype is a constrained array subtype, the applicable index constraint
      is the constraint of the subtype;

15    For a parenthesized expression, the applicable index constraint is that,
      if any, defined for the expression.

16    The applicable index constraint applies to an array_aggregate that
appears in such a context, as well as to any subaggregates thereof. In the
case of an explicit_actual_parameter (or default_expression) for a call on a
generic formal subprogram, no applicable index constraint is defined.

17    The discrete_choice_list of an array_component_association is allowed to
have a discrete_choice that is a nonstatic expression or that is a
discrete_range that defines a nonstatic or null range, only if it is the
single discrete_choice of its discrete_choice_list, and there is only one
array_component_association in the array_aggregate.

18    In a named_array_aggregate with more than one discrete_choice, no two
discrete_choices are allowed to cover the same value (see 3.8.1); if there is
no others choice, the discrete_choices taken together shall exactly cover a
contiguous sequence of values of the corresponding index type.

19    A bottom level subaggregate of a multidimensional array_aggregate of a
given array type is allowed to be a string_literal only if the component type
of the array type is a character type; each character of such a string_literal
shall correspond to a defining_character_literal of the component type.


                              Static Semantics

20    A subaggregate that is a string_literal is equivalent to one that is a
positional_array_aggregate of the same length, with each expression being the
character_literal for the corresponding character of the string_literal.


                              Dynamic Semantics

21    The evaluation of an array_aggregate of a given array type proceeds in
two steps:

22    1.  Any discrete_choices of this aggregate and of its subaggregates are
          evaluated in an arbitrary order, and converted to the corresponding
          index type;

23    2.  The array component expressions of the aggregate are evaluated in an
          arbitrary order and their values are converted to the component
          subtype of the array type; an array component expression is
          evaluated once for each associated component.

24    The bounds of the index range of an array_aggregate (including a
subaggregate) are determined as follows:

25    For an array_aggregate with an others choice, the bounds are those of
      the corresponding index range from the applicable index constraint;

26    For a positional_array_aggregate (or equivalent string_literal) without
      an others choice, the lower bound is that of the corresponding index
      range in the applicable index constraint, if defined, or that of the
      corresponding index subtype, if not; in either case, the upper bound is
      determined from the lower bound and the number of expressions (or the
      length of the string_literal);

27    For a named_array_aggregate without an others choice, the bounds are
      determined by the smallest and largest index values covered by any
      discrete_choice_list.

28    For an array_aggregate, a check is made that the index range defined by
its bounds is compatible with the corresponding index subtype.

29    For an array_aggregate with an others choice, a check is made that no
expression is specified for an index value outside the bounds determined by
the applicable index constraint.

30    For a multidimensional array_aggregate, a check is made that all
subaggregates that correspond to the same index have the same bounds.

31    The exception Constraint_Error is raised if any of the above checks
fail.

      NOTES

32    10  In an array_aggregate, positional notation may only be used with two
      or more expressions; a single expression in parentheses is interpreted
      as a parenthesized_expression. A named_array_aggregate, such as (1 =>
      X), may be used to specify an array with a single component.


                                  Examples

33    Examples of array aggregates with positional associations:

34    (7, 9, 5, 1, 3, 2, 4, 8, 6, 0)
      Table'(5, 8, 4, 1, others => 0)  --  see 3.6 

35    Examples of array aggregates with named associations:

36    (1 .. 5 => (1 .. 8 => 0.0))      --  two-dimensional
      (1 .. N => new Cell)             --  N new cells, in particular for N = 0

37    Table'(2 | 4 | 10 => 1, others => 0)
      Schedule'(Mon .. Fri => True,  others => False)  --  see 3.6
      Schedule'(Wed | Sun  => False, others => True)
      Vector'(1 => 2.5)                                --  single-component vector

38    Examples of two-dimensional array aggregates:

39    -- Three aggregates for the same value of subtype Matrix(1..2,1..3) (see 3.6
      ):

40    ((1.1, 1.2, 1.3), (2.1, 2.2, 2.3))
      (1 => (1.1, 1.2, 1.3), 2 => (2.1, 2.2, 2.3))
      (1 => (1 => 1.1, 2 => 1.2, 3 => 1.3), 2 => (1 => 2.1, 2 => 2.2, 3 => 2.3))

41    Examples of aggregates as initial values:

42    A : Table := (7, 9, 5, 1, 3, 2, 4, 8, 6, 0);        -- A(1)=7, A(10)=0
      B : Table := (2 | 4 | 10 => 1, others => 0);        -- B(1)=0, B(10)=1
      C : constant Matrix := (1 .. 5 => (1 .. 8 => 0.0)); -- C'Last(1)=5, C'Last(2)=8

43    D : Bit_Vector(M .. N) := (M .. N => True);         -- see 3.6
      E : Bit_Vector(M .. N) := (others => True);
      F : String(1 .. 1) := (1 => 'F');  -- a one component aggregate: same as "F"


4.4 Expressions


1     An expression is a formula that defines the computation or retrieval of
a value. In this International Standard, the term ``expression'' refers to a
construct of the syntactic category expression or of any of the other five
syntactic categories defined below.


                                   Syntax

2     expression ::= 
           relation {and relation}  | relation {and then relation}
         | relation {or relation}  | relation {or else relation}
         | relation {xor relation}

3     relation ::= 
           simple_expression [relational_operator simple_expression]
         | simple_expression [not] in range
         | simple_expression [not] in subtype_mark

4     simple_expression ::= [unary_adding_operator] term
       {binary_adding_operator term}

5     term ::= factor {multiplying_operator factor}

6     factor ::= primary [** primary] | abs primary | not primary

7     primary ::= 
         numeric_literal | null | string_literal | aggregate
       | name | qualified_expression | allocator | (expression)


                            Name Resolution Rules

8     A name used as a primary shall resolve to denote an object or a value.


                              Static Semantics

9     Each expression has a type; it specifies the computation or retrieval of
a value of that type.


                              Dynamic Semantics

10    The value of a primary that is a name denoting an object is the value of
the object.


                         Implementation Permissions

11    For the evaluation of a primary that is a name denoting an object of an
unconstrained numeric subtype, if the value of the object is outside the base
range of its type, the implementation may either raise Constraint_Error or
return the value of the object.


                                  Examples

12    Examples of primaries:

13    4.0                --  real literal
      Pi                 --  named number
      (1 .. 10 => 0)     --  array aggregate
      Sum                --  variable
      Integer'Last       --  attribute
      Sine(X)            --  function call
      Color'(Blue)       --  qualified expression
      Real(M*N)          --  conversion
      (Line_Count + 10)  --  parenthesized expression 

14    Examples of expressions:

15    Volume                      -- primary
      not Destroyed               -- factor
      2*Line_Count                -- term  
      -4.0                        -- simple expression
      -4.0 + A                    -- simple expression
      B**2 - 4.0*A*C              -- simple expression
      Password(1 .. 3) = "Bwv"    -- relation
      Count in Small_Int          -- relation
      Count not in Small_Int      -- relation
      Index = 0 or Item_Hit       -- expression
      (Cold and Sunny) or Warm    -- expression (parentheses are required)
      A**(B**C)                   -- expression (parentheses are required)


4.5 Operators and Expression Evaluation


1     The language defines the following six categories of operators (given in
order of increasing precedence). The corresponding operator_symbols, and only
those, can be used as designators in declarations of functions for
user-defined operators. See 6.6, ``Overloading of Operators''.


                                   Syntax

2     logical_operator ::=                         and | or  | xor

3     relational_operator ::=                     
       =   | /=  | <   | <= | > | >=

4     binary_adding_operator ::=                   +   | -   | &

5     unary_adding_operator ::=                    +   | -

6     multiplying_operator ::=                     *   | /   | mod | rem

7     highest_precedence_operator ::=              **  | abs | not


                              Static Semantics

8     For a sequence of operators of the same precedence level, the operators
are associated with their operands in textual order from left to right.
Parentheses can be used to impose specific associations.

9     For each form of type definition, certain of the above operators are
predefined; that is, they are implicitly declared immediately after the type
definition. For each such implicit operator declaration, the parameters are
called Left and Right for binary operators; the single parameter is called
Right for unary operators. An expression of the form X op Y, where op is a
binary operator, is equivalent to a function_call of the form "op"(X, Y). An
expression of the form op Y, where op is a unary operator, is equivalent to a
function_call of the form "op"(Y). The predefined operators and their effects
are described in subclauses 4.5.1 through 4.5.6.


                              Dynamic Semantics

10    The predefined operations on integer types either yield the
mathematically correct result or raise the exception Constraint_Error. For
implementations that support the Numerics Annex, the predefined operations on
real types yield results whose accuracy is defined in Annex G, or raise the
exception Constraint_Error.


                         Implementation Requirements

11    The implementation of a predefined operator that delivers a result of an
integer or fixed point type may raise Constraint_Error only if the result is
outside the base range of the result type.

12    The implementation of a predefined operator that delivers a result of a
floating point type may raise Constraint_Error only if the result is outside
the safe range of the result type.


                         Implementation Permissions

13    For a sequence of predefined operators of the same precedence level (and
in the absence of parentheses imposing a specific association), an
implementation may impose any association of the operators with operands so
long as the result produced is an allowed result for the left-to-right
association, but ignoring the potential for failure of language-defined checks
in either the left-to-right or chosen order of association.

      NOTES

14    11  The two operands of an expression of the form X op Y, where op is a
      binary operator, are evaluated in an arbitrary order, as for any
      function_call (see 6.4).


                                  Examples

15    Examples of precedence:

16    not Sunny or Warm    --  same as (not Sunny) or Warm
      X > 4.0 and Y > 0.0  --  same as (X > 4.0) and (Y > 0.0)

17    -4.0*A**2            --  same as -(4.0 * (A**2))
      abs(1 + A) + B       --  same as (abs (1 + A)) + B
      Y**(-3)              --  parentheses are necessary
      A / B * C            --  same as (A/B)*C
      A + (B + C)          --  evaluate B + C before adding it to A 


4.5.1 Logical Operators and Short-circuit Control Forms



                            Name Resolution Rules

1     An expression consisting of two relations connected by and then or or
else (a short-circuit control form) shall resolve to be of some boolean type;
the expected type for both relations is that same boolean type.


                              Static Semantics

2     The following logical operators are predefined for every boolean type T,
for every modular type T, and for every one-dimensional array type T whose
component type is a boolean type:

3     function "and"(Left, Right : T) return T
      function "or" (Left, Right : T) return T
      function "xor"(Left, Right : T) return T

4     For boolean types, the predefined logical operators and, or, and xor
perform the conventional operations of conjunction, inclusive disjunction, and
exclusive disjunction, respectively.

5     For modular types, the predefined logical operators are defined on a
bit-by-bit basis, using the binary representation of the value of the operands
to yield a binary representation for the result, where zero represents False
and one represents True. If this result is outside the base range of the type,
a final subtraction by the modulus is performed to bring the result into the
base range of the type.

6     The logical operators on arrays are performed on a
component-by-component basis on matching components (as for equality - see
4.5.2), using the predefined logical operator for the component type. The
bounds of the resulting array are those of the left operand.


                              Dynamic Semantics

7     The short-circuit control forms and then and or else deliver the same
result as the corresponding predefined and and or operators for boolean types,
except that the left operand is always evaluated first, and the right operand
is not evaluated if the value of the left operand determines the result.

8     For the logical operators on arrays, a check is made that for each
component of the left operand there is a matching component of the right
operand, and vice versa. Also, a check is made that each component of the
result belongs to the component subtype. The exception Constraint_Error is
raised if either of the above checks fails.

      NOTES

9     12  The conventional meaning of the logical operators is given by the
      following truth table:

    10          A                   B                 (A and B)           
          (A or B)                (A xor B)
          
              True                True                True                True                
          False
              True                False               False               True                
          True
              False               True                False               True                
          True
              False               False               False               
          False                   False


                                  Examples

11    Examples of logical operators:

12    Sunny or Warm
      Filter(1 .. 10) and Filter(15 .. 24)   --   see 3.6.1 

13    Examples of short-circuit control forms:

14    Next_Car.Owner /= null and then Next_Car.Owner.Age > 25   --   see 3.10.1
      N = 0 or else A(N) = Hit_Value


4.5.2 Relational Operators and Membership Tests


1     The equality operators = (equals) and /= (not equals) are predefined for
nonlimited types. The other relational_operators are the ordering operators <
(less than), <= (less than or equal), > (greater than), and >= (greater than
or equal). The ordering operators are predefined for scalar types, and for
discrete array types, that is, one-dimensional array types whose components
are of a discrete type.

2     A membership test, using in or not in, determines whether or not a value
belongs to a given subtype or range, or has a tag that identifies a type that
is covered by a given type. Membership tests are allowed for all types.


                            Name Resolution Rules

3     The tested type of a membership test is the type of the range or the
type determined by the subtype_mark. If the tested type is tagged, then the
simple_expression shall resolve to be of a type that covers or is covered by
the tested type; if untagged, the expected type for the simple_expression is
the tested type.


                               Legality Rules

4     For a membership test, if the simple_expression is of a tagged
class-wide type, then the tested type shall be (visibly) tagged.


                              Static Semantics

5     The result type of a membership test is the predefined type Boolean.

6     The equality operators are predefined for every specific type T that is
not limited, and not an anonymous access type, with the following
specifications:

7     function "=" (Left, Right : T) return Boolean
      function "/="(Left, Right : T) return Boolean

8     The ordering operators are predefined for every specific scalar type T,
and for every discrete array type T, with the following specifications:

9     function "<" (Left, Right : T) return Boolean
      function "<="(Left, Right : T) return Boolean
      function ">" (Left, Right : T) return Boolean
      function ">="(Left, Right : T) return Boolean


                              Dynamic Semantics

10    For discrete types, the predefined relational operators are defined in
terms of corresponding mathematical operations on the position numbers of the
values of the operands.

11    For real types, the predefined relational operators are defined in terms
of the corresponding mathematical operations on the values of the operands,
subject to the accuracy of the type.

12    Two access-to-object values are equal if they designate the same object,
or if both are equal to the null value of the access type.

13    Two access-to-subprogram values are equal if they are the result of the
same evaluation of an Access attribute_reference, or if both are equal to the
null value of the access type. Two access-to-subprogram values are unequal if
they designate different subprograms. It is unspecified whether two access
values that designate the same subprogram but are the result of distinct
evaluations of Access attribute_references are equal or unequal.

14    For a type extension, predefined equality is defined in terms of the
primitive (possibly user-defined) equals operator of the parent type and of
any tagged components of the extension part, and predefined equality for any
other components not inherited from the parent type.

15    For a private type, if its full type is tagged, predefined equality is
defined in terms of the primitive equals operator of the full type; if the
full type is untagged, predefined equality for the private type is that of its
full type.

16    For other composite types, the predefined equality operators (and
certain other predefined operations on composite types - see 4.5.1 and 4.6)
are defined in terms of the corresponding operation on matching components,
defined as follows:

17    For two composite objects or values of the same non-array type, matching
      components are those that correspond to the same component_declaration
      or discriminant_specification;

18    For two one-dimensional arrays of the same type, matching components are
      those (if any) whose index values match in the following sense: the
      lower bounds of the index ranges are defined to match, and the
      successors of matching indices are defined to match;

19    For two multidimensional arrays of the same type, matching components
      are those whose index values match in successive index positions.

20    The analogous definitions apply if the types of the two objects or
values are convertible, rather than being the same.

21    Given the above definition of matching components, the result of the
predefined equals operator for composite types (other than for those composite
types covered earlier) is defined as follows:

22    If there are no components, the result is defined to be True;

23    If there are unmatched components, the result is defined to be False;

24    Otherwise, the result is defined in terms of the primitive equals
      operator for any matching tagged components, and the predefined equals
      for any matching untagged components.

24.1/1 {For any composite type, the order in which "=" is called for
components is unspecified. Furthermore, if the result can be determined before
calling "=" on some components, it is unspecified whether "=" is called on
those components.}

25    The predefined "/=" operator gives the complementary result to the
predefined "=" operator.

26    For a discrete array type, the predefined ordering operators correspond
to lexicographic order using the predefined order relation of the component
type: A null array is lexicographically less than any array having at least
one component. In the case of nonnull arrays, the left operand is
lexicographically less than the right operand if the first component of the
left operand is less than that of the right; otherwise the left operand is
lexicographically less than the right operand only if their first components
are equal and the tail of the left operand is lexicographically less than that
of the right (the tail consists of the remaining components beyond the first
and can be null).

27    For the evaluation of a membership test, the simple_expression and the
range (if any) are evaluated in an arbitrary order.

28    A membership test using in yields the result True if:

29    The tested type is scalar, and the value of the simple_expression
      belongs to the given range, or the range of the named subtype; or

30    The tested type is not scalar, and the value of the simple_expression
      satisfies any constraints of the named subtype, and, if the type of the
      simple_expression is class-wide, the value has a tag that identifies a
      type covered by the tested type.

31    Otherwise the test yields the result False.

32    A membership test using not in gives the complementary result to the
corresponding membership test using in.


                         Implementation Requirements

32.1/1 {For all nonlimited types declared in language-defined packages, the
"=" and "/=" operators of the type shall behave as if they were the predefined
equality operators for the purposes of the equality of composite types and
generic formal types.}

      NOTES

33    13  No exception is ever raised by a membership test, by a predefined
      ordering operator, or by a predefined equality operator for an
      elementary type, but an exception can be raised by the evaluation of the
      operands. A predefined equality operator for a composite type can only
      raise an exception if the type has a tagged part whose primitive equals
      operator propagates an exception.

34    14  If a composite type has components that depend on discriminants, two
      values of this type have matching components if and only if their
      discriminants are equal. Two nonnull arrays have matching components if
      and only if the length of each dimension is the same for both.


                                  Examples

35    Examples of expressions involving relational operators and membership
tests:

36    X /= Y

37    "" < "A" and "A" < "Aa"     --  True
      "Aa" < "B" and "A" < "A  "  --  True

38    My_Car = null               -- true if My_Car has been set to null (see 3.10.1
      )
      My_Car = Your_Car           -- true if we both share the same car
      My_Car.all = Your_Car.all   -- true if the two cars are identical

39    N not in 1 .. 10            -- range membership test
      Today in Mon .. Fri         -- range membership test
      Today in Weekday            -- subtype membership test (see 3.5.1)
      Archive in Disk_Unit        -- subtype membership test (see 3.8.1)
      Tree.all in Addition'Class  -- class membership test (see 3.9.1)


4.5.3 Binary Adding Operators



                              Static Semantics

1     The binary adding operators + (addition) and - (subtraction) are
predefined for every specific numeric type T with their conventional meaning.
They have the following specifications:

2     function "+"(Left, Right : T) return T
      function "-"(Left, Right : T) return T

3     The concatenation operators & are predefined for every nonlimited,
one-dimensional array type T with component type C. They have the following
specifications:

4     function "&"(Left : T; Right : T) return T
      function "&"(Left : T; Right : C) return T
      function "&"(Left : C; Right : T) return T
      function "&"(Left : C; Right : C) return T


                              Dynamic Semantics

5     For the evaluation of a concatenation with result type T, if both
operands are of type T, the result of the concatenation is a one-dimensional
array whose length is the sum of the lengths of its operands, and whose
components comprise the components of the left operand followed by the
components of the right operand. If the left operand is a null array, the
result of the concatenation is the right operand. Otherwise, the lower bound
of the result is determined as follows:

6     If the ultimate ancestor of the array type was defined by a
      constrained_array_definition, then the lower bound of the result is that
      of the index subtype;

7     If the ultimate ancestor of the array type was defined by an
      unconstrained_array_definition, then the lower bound of the result is
      that of the left operand.

8     The upper bound is determined by the lower bound and the length. A check
is made that the upper bound of the result of the concatenation belongs to the
range of the index subtype, unless the result is a null array.
Constraint_Error is raised if this check fails.

9     If either operand is of the component type C, the result of the
concatenation is given by the above rules, using in place of such an operand
an array having this operand as its only component (converted to the component
subtype) and having the lower bound of the index subtype of the array type as
its lower bound.

10    The result of a concatenation is defined in terms of an assignment to an
anonymous object, as for any function call (see 6.5).

      NOTES

11    15  As for all predefined operators on modular types, the binary adding
      operators + and - on modular types include a final reduction modulo the
      modulus if the result is outside the base range of the type.


                                  Examples

12    Examples of expressions involving binary adding operators:

13    Z + 0.1      --  Z has to be of a real type 

14    "A" & "BCD"  --  concatenation of two string literals
      'A' & "BCD"  --  concatenation of a character literal and a string literal
      'A' & 'A'    --  concatenation of two character literals 


4.5.4 Unary Adding Operators



                              Static Semantics

1     The unary adding operators + (identity) and - (negation) are predefined
for every specific numeric type T with their conventional meaning. They have
the following specifications:

2     function "+"(Right : T) return T
      function "-"(Right : T) return T

      NOTES

3     16  For modular integer types, the unary adding operator -, when given a
      nonzero operand, returns the result of subtracting the value of the
      operand from the modulus; for a zero operand, the result is zero.


4.5.5 Multiplying Operators



                              Static Semantics

1     The multiplying operators * (multiplication), / (division), mod
(modulus), and rem (remainder) are predefined for every specific integer type
T:

2     function "*"  (Left, Right : T) return T
      function "/"  (Left, Right : T) return T
      function "mod"(Left, Right : T) return T
      function "rem"(Left, Right : T) return T

3     Signed integer multiplication has its conventional meaning.

4     Signed integer division and remainder are defined by the relation:

5     A = (A/B)*B + (A rem B)

6     where (A rem B) has the sign of A and an absolute value less than the
absolute value of B. Signed integer division satisfies the identity:

7     (-A)/B = -(A/B) = A/(-B)

8     The signed integer modulus operator is defined such that the result of A
mod B has the sign of B and an absolute value less than the absolute value of
B; in addition, for some signed integer value N, this result satisfies the
relation:

9     A = B*N + (A mod B)

10    The multiplying operators on modular types are defined in terms of the
corresponding signed integer operators, followed by a reduction modulo the
modulus if the result is outside the base range of the type (which is only
possible for the "*" operator).

11    Multiplication and division operators are predefined for every specific
floating point type T:

12    function "*"(Left, Right : T) return T
      function "/"(Left, Right : T) return T

13    The following multiplication and division operators, with an operand of
the predefined type Integer, are predefined for every specific fixed point
type T:

14    function "*"(Left : T; Right : Integer) return T
      function "*"(Left : Integer; Right : T) return T
      function "/"(Left : T; Right : Integer) return T

15    All of the above multiplying operators are usable with an operand of an
appropriate universal numeric type. The following additional multiplying
operators for root_real are predefined, and are usable when both operands are
of an appropriate universal or root numeric type, and the result is allowed to
be of type root_real, as in a number_declaration:

16    function "*"(Left, Right : root_real) return root_real
      function "/"(Left, Right : root_real) return root_real

17    function "*"(Left : root_real; Right : root_integer) return root_real
      function "*"(Left : root_integer; Right : root_real) return root_real
      function "/"(Left : root_real; Right : root_integer) return root_real

18    Multiplication and division between any two fixed point types are
provided by the following two predefined operators:

19    function "*"(Left, Right : universal_fixed) return universal_fixed
      function "/"(Left, Right : universal_fixed) return universal_fixed


                               Legality Rules

20    The above two fixed-fixed multiplying operators shall not be used in a
context where the expected type for the result is itself universal_fixed - the
context has to identify some other numeric type to which the result is to be
converted, either explicitly or implicitly.


                              Dynamic Semantics

21    The multiplication and division operators for real types have their
conventional meaning. For floating point types, the accuracy of the result is
determined by the precision of the result type. For decimal fixed point types,
the result is truncated toward zero if the mathematical result is between two
multiples of the small of the specific result type (possibly determined by
context); for ordinary fixed point types, if the mathematical result is
between two multiples of the small, it is unspecified which of the two is the
result.

22    The exception Constraint_Error is raised by integer division, rem, and
mod if the right operand is zero. Similarly, for a real type T with
T'Machine_Overflows True, division by zero raises Constraint_Error.

      NOTES

23    17  For positive A and B, A/B is the quotient and A rem B is the
      remainder when A is divided by B. The following relations are satisfied
      by the rem operator:

24         A  rem (-B) =   A rem B
         (-A) rem   B  = -(A rem B)

25    18  For any signed integer K, the following identity holds:

26       A mod B   =   (A + K*B) mod B

27    The relations between signed integer division, remainder, and modulus
      are illustrated by the following table:

28       A      B   A/B   A rem B  A mod B     A     B    A/B   A rem B   A mod B

29       10     5    2       0        0       -10    5    -2       0         0
         11     5    2       1        1       -11    5    -2      -1         4
         12     5    2       2        2       -12    5    -2      -2         3
         13     5    2       3        3       -13    5    -2      -3         2
         14     5    2       4        4       -14    5    -2      -4         1

30       A      B   A/B   A rem B  A mod B     A     B    A/B   A rem B   A mod B
      
         10    -5   -2       0        0       -10   -5     2       0         0
         11    -5   -2       1       -4       -11   -5     2      -1        -1
         12    -5   -2       2       -3       -12   -5     2      -2        -2
         13    -5   -2       3       -2       -13   -5     2      -3        -3
         14    -5   -2       4       -1       -14   -5     2      -4        -4


                                  Examples

31    Examples of expressions involving multiplying operators:

32    I : Integer := 1;
      J : Integer := 2;
      K : Integer := 3;

33    X : Real := 1.0;                      --     see 3.5.7
      Y : Real := 2.0;

34    F : Fraction := 0.25;                 --     see 3.5.9
      G : Fraction := 0.5;

35    Expression            Value          Result Type
      
      I*J                   2              same as I and J, that is, Integer
      K/J                   1              same as K and J, that is, Integer
      K mod J               1              same as K and J, that is, Integer
      
      X/Y                   0.5            same as X and Y, that is, Real
      F/2                   0.125          same as F, that is, Fraction
      
      3*F                   0.75           same as F, that is, Fraction
      0.75*G                0.375          
      universal_fixed, implicitly convertible
                                           to any fixed point type
      Fraction(F*G)         0.125          
      Fraction, as stated by the conversion
      Real(J)*Y             4.0            
      Real, the type of both operands after
                                           conversion of J


4.5.6 Highest Precedence Operators



                              Static Semantics

1     The highest precedence unary operator abs (absolute value) is predefined
for every specific numeric type T, with the following specification:

2     function "abs"(Right : T) return T

3     The highest precedence unary operator not (logical negation) is
predefined for every boolean type T, every modular type T, and for every
one-dimensional array type T whose components are of a boolean type, with the
following specification:

4     function "not"(Right : T) return T

5     The result of the operator not for a modular type is defined as the
difference between the high bound of the base range of the type and the value
of the operand. For a binary modulus, this corresponds to a bit-wise
complement of the binary representation of the value of the operand.

6     The operator not that applies to a one-dimensional array of boolean
components yields a one-dimensional boolean array with the same bounds; each
component of the result is obtained by logical negation of the corresponding
component of the operand (that is, the component that has the same index
value). A check is made that each component of the result belongs to the
component subtype; the exception Constraint_Error is raised if this check
fails.

7     The highest precedence exponentiation operator ** is predefined for
every specific integer type T with the following specification:

8     function "**"(Left : T; Right : Natural) return T

9     Exponentiation is also predefined for every specific floating point type
as well as root_real, with the following specification (where T is root_real
or the floating point type):

10    function "**"(Left : T; Right : Integer'Base) return T

11    The right operand of an exponentiation is the exponent. The expression
X**N with the value of the exponent N positive is equivalent to the expression
X*X*...X (with N-1 multiplications) except that the multiplications are
associated in an arbitrary order. With N equal to zero, the result is one.
With the value of N negative (only defined for a floating point operand), the
result is the reciprocal of the result using the absolute value of N as the
exponent.


                         Implementation Permissions

12    The implementation of exponentiation for the case of a negative exponent
is allowed to raise Constraint_Error if the intermediate result of the
repeated multiplications is outside the safe range of the type, even though
the final result (after taking the reciprocal) would not be. (The best machine
approximation to the final result in this case would generally be 0.0.)

      NOTES

13    19  As implied by the specification given above for exponentiation of an
      integer type, a check is made that the exponent is not negative.
      Constraint_Error is raised if this check fails.


4.6 Type Conversions


1     Explicit type conversions, both value conversions and view conversions,
are allowed between closely related types as defined below. This clause also
defines rules for value and view conversions to a particular subtype of a
type, both explicit ones and those implicit in other constructs.


                                   Syntax

2     type_conversion ::= 
          subtype_mark(expression)
        | subtype_mark(name)

3     The target subtype of a type_conversion is the subtype denoted by the
subtype_mark. The operand of a type_conversion is the expression or name
within the parentheses; its type is the operand type.

4     One type is convertible to a second type if a type_conversion with the
first type as operand type and the second type as target type is legal
according to the rules of this clause. Two types are convertible if each is
convertible to the other.

5/1   A type_conversion whose operand is the name of an object is called a
view conversion if {both }its target type {and operand type are}[is] tagged,
or if it appears as an actual parameter of mode out or in out; other
type_conversions are called value conversions.


                            Name Resolution Rules

6     The operand of a type_conversion is expected to be of any type.

7     The operand of a view conversion is interpreted only as a name; the
operand of a value conversion is interpreted as an expression.


                               Legality Rules

8     If the target type is a numeric type, then the operand type shall be a
numeric type.

9     If the target type is an array type, then the operand type shall be an
array type. Further:

10    The types shall have the same dimensionality;

11/1  Corresponding index types shall be convertible;[ and]

12/1  The component subtypes shall statically match{; and}[.]

12.1/1 {In a view conversion, the target type and the operand type shall both
      or neither have aliased components.}

13    If the target type is a general access type, then the operand type shall
be an access-to-object type. Further:

14    If the target type is an access-to-variable type, then the operand type
      shall be an access-to-variable type;

15    If the target designated type is tagged, then the operand designated
      type shall be convertible to the target designated type;

16    If the target designated type is not tagged, then the designated types
      shall be the same, and either the designated subtypes shall statically
      match or the target designated subtype shall be discriminated and
      unconstrained; and

17    The accessibility level of the operand type shall not be statically
      deeper than that of the target type. In addition to the places where
      Legality Rules normally apply (see 12.3), this rule applies also in the
      private part of an instance of a generic unit.

18    If the target type is an access-to-subprogram type, then the operand
type shall be an access-to-subprogram type. Further:

19    The designated profiles shall be subtype-conformant.

20    The accessibility level of the operand type shall not be statically
      deeper than that of the target type. In addition to the places where
      Legality Rules normally apply (see 12.3), this rule applies also in the
      private part of an instance of a generic unit. If the operand type is
      declared within a generic body, the target type shall be declared within
      the generic body.

21    If the target type is not included in any of the above four cases, there
shall be a type that is an ancestor of both the target type and the operand
type. Further, if the target type is tagged, then either:

22    The operand type shall be covered by or descended from the target type;
      or

23    The operand type shall be a class-wide type that covers the target type.

24    In a view conversion for an untagged type, the target type shall be
convertible (back) to the operand type.


                              Static Semantics

25    A type_conversion that is a value conversion denotes the value that is
the result of converting the value of the operand to the target subtype.

26    A type_conversion that is a view conversion denotes a view of the object
denoted by the operand. This view is a variable of the target type if the
operand denotes a variable; otherwise it is a constant of the target type.

27    The nominal subtype of a type_conversion is its target subtype.


                              Dynamic Semantics

28    For the evaluation of a type_conversion that is a value conversion, the
operand is evaluated, and then the value of the operand is converted to a
corresponding value of the target type, if any. If there is no value of the
target type that corresponds to the operand value, Constraint_Error is raised;
this can only happen on conversion to a modular type, and only when the
operand value is outside the base range of the modular type. Additional rules
follow:

29    Numeric Type Conversion

    30    If the target and the operand types are both integer types, then the
          result is the value of the target type that corresponds to the same
          mathematical integer as the operand.

    31    If the target type is a decimal fixed point type, then the result is
          truncated (toward 0) if the value of the operand is not a multiple
          of the small of the target type.

    32    If the target type is some other real type, then the result is
          within the accuracy of the target type (see G.2, ``
          Numeric Performance Requirements'', for implementations that support
          the Numerics Annex).

    33    If the target type is an integer type and the operand type is real,
          the result is rounded to the nearest integer (away from zero if
          exactly halfway between two integers).

34    Enumeration Type Conversion

    35    The result is the value of the target type with the same position
          number as that of the operand value.

36    Array Type Conversion

    37    If the target subtype is a constrained array subtype, then a check
          is made that the length of each dimension of the value of the
          operand equals the length of the corresponding dimension of the
          target subtype. The bounds of the result are those of the target
          subtype.

    38    If the target subtype is an unconstrained array subtype, then the
          bounds of the result are obtained by converting each bound of the
          value of the operand to the corresponding index type of the target
          type. For each nonnull index range, a check is made that the bounds
          of the range belong to the corresponding index subtype.

    39    In either array case, the value of each component of the result is
          that of the matching component of the operand value (see 4.5.2).

40    Composite (Non-Array) Type Conversion

    41    The value of each nondiscriminant component of the result is that of
          the matching component of the operand value.

    42    The tag of the result is that of the operand. If the operand type is
          class-wide, a check is made that the tag of the operand identifies a
          (specific) type that is covered by or descended from the target
          type.

    43    For each discriminant of the target type that corresponds to a
          discriminant of the operand type, its value is that of the
          corresponding discriminant of the operand value; if it corresponds
          to more than one discriminant of the operand type, a check is made
          that all these discriminants are equal in the operand value.

    44    For each discriminant of the target type that corresponds to a
          discriminant that is specified by the derived_type_definition for
          some ancestor of the operand type (or if class-wide, some ancestor
          of the specific type identified by the tag of the operand), its
          value in the result is that specified by the
          derived_type_definition.

    45    For each discriminant of the operand type that corresponds to a
          discriminant that is specified by the derived_type_definition for
          some ancestor of the target type, a check is made that in the
          operand value it equals the value specified for it.

    46    For each discriminant of the result, a check is made that its value
          belongs to its subtype.

47    Access Type Conversion

    48    For an access-to-object type, a check is made that the accessibility
          level of the operand type is not deeper than that of the target
          type.

    49    If the target type is an anonymous access type, a check is made that
          the value of the operand is not null; if the target is not an
          anonymous access type, then the result is null if the operand value
          is null.

    50    If the operand value is not null, then the result designates the
          same object (or subprogram) as is designated by the operand value,
          but viewed as being of the target designated subtype (or profile);
          any checks associated with evaluating a conversion to the target
          designated subtype are performed.

51    After conversion of the value to the target type, if the target subtype
is constrained, a check is performed that the value satisfies this constraint.

52    For the evaluation of a view conversion, the operand name is evaluated,
and a new view of the object denoted by the operand is created, whose type is
the target type; if the target type is composite, checks are performed as
above for a value conversion.

53    The properties of this new view are as follows:

54/1  If the target type is composite, the bounds or discriminants (if any) of
      the view are as defined above for a value conversion; each
      nondiscriminant component of the view denotes the matching component of
      the operand object; the subtype of the view is constrained if either the
      target subtype or the operand object is constrained, {or if the target
      subtype is indefinite,} or if the operand type is a descendant of the
      target type, and has discriminants that were not inherited from the
      target type;

55    If the target type is tagged, then an assignment to the view assigns to
      the corresponding part of the object denoted by the operand; otherwise,
      an assignment to the view assigns to the object, after converting the
      assigned value to the subtype of the object (which might raise
      Constraint_Error);

56    Reading the value of the view yields the result of converting the value
      of the operand object to the target subtype (which might raise
      Constraint_Error), except if the object is of an access type and the
      view conversion is passed as an out parameter; in this latter case, the
      value of the operand object is used to initialize the formal parameter
      without checking against any constraint of the target subtype (see
      6.4.1).

57    If an Accessibility_Check fails, Program_Error is raised. Any other
check associated with a conversion raises Constraint_Error if it fails.

58    Conversion to a type is the same as conversion to an unconstrained
subtype of the type.

      NOTES

59    20  In addition to explicit type_conversions, type conversions are
      performed implicitly in situations where the expected type and the
      actual type of a construct differ, as is permitted by the type
      resolution rules (see 8.6). For example, an integer literal is of the
      type universal_integer, and is implicitly converted when assigned to a
      target of some specific integer type. Similarly, an actual parameter of
      a specific tagged type is implicitly converted when the corresponding
      formal parameter is of a class-wide type.

60    21  Even when the expected and actual types are the same, implicit
      subtype conversions are performed to adjust the array bounds (if any) of
      an operand to match the desired target subtype, or to raise
      Constraint_Error if the (possibly adjusted) value does not satisfy the
      constraints of the target subtype.

61    A ramification of the overload resolution rules is that the operand of
      an (explicit) type_conversion cannot be the literal null, an allocator,
      an aggregate, a string_literal, a character_literal, or an
      attribute_reference for an Access or Unchecked_Access attribute.
      Similarly, such an expression enclosed by parentheses is not allowed. A
      qualified_expression (see 4.7) can be used instead of such a
      type_conversion.

62    22  The constraint of the target subtype has no effect for a
      type_conversion of an elementary type passed as an out parameter. Hence,
      it is recommended that the first subtype be specified as the target to
      minimize confusion (a similar recommendation applies to renaming and
      generic formal in out objects).


                                  Examples

63    Examples of numeric type conversion:

64    Real(2*J)      --  value is converted to floating point
      Integer(1.6)   --  value is 2
      Integer(-0.4)  --  value is 0

65    Example of conversion between derived types:

66    type A_Form is new B_Form;

67    X : A_Form;
      Y : B_Form;

68    X := A_Form(Y);
      Y := B_Form(X);  --  the reverse conversion 

69    Examples of conversions between array types:

70    type Sequence is array (Integer range <>) of Integer;
      subtype Dozen is Sequence(1 .. 12);
      Ledger : array(1 .. 100) of Integer;

71    Sequence(Ledger)            --  bounds are those of Ledger
      Sequence(Ledger(31 .. 42))  --  bounds are 31 and 42
      Dozen(Ledger(31 .. 42))     --  bounds are those of Dozen 


4.7 Qualified Expressions


1     A qualified_expression is used to state explicitly the type, and to
verify the subtype, of an operand that is either an expression or an
aggregate.


                                   Syntax

2     qualified_expression ::= 
         subtype_mark'(expression) | subtype_mark'aggregate


                            Name Resolution Rules

3     The operand (the expression or aggregate) shall resolve to be of the
type determined by the subtype_mark, or a universal type that covers it.


                              Dynamic Semantics

4     The evaluation of a qualified_expression evaluates the operand (and if
of a universal type, converts it to the type determined by the subtype_mark)
and checks that its value belongs to the subtype denoted by the subtype_mark.
The exception Constraint_Error is raised if this check fails.

      NOTES

5     23  When a given context does not uniquely identify an expected type, a
      qualified_expression can be used to do so. In particular, if an
      overloaded name or aggregate is passed to an overloaded subprogram, it
      might be necessary to qualify the operand to resolve its type.


                                  Examples

6     Examples of disambiguating expressions using qualification:

7     type Mask is (Fix, Dec, Exp, Signif);
      type Code is (Fix, Cla, Dec, Tnz, Sub);

8     Print (Mask'(Dec));  --  Dec is of type Mask
      Print (Code'(Dec));  --  Dec is of type Code 

9     for J in Code'(Fix) .. Code'(Dec) loop ... -- qualification needed for either Fix or Dec
      for J in Code range Fix .. Dec loop ...    -- qualification unnecessary
      for J in Code'(Fix) .. Dec loop ...        -- qualification unnecessary for Dec

10    Dozen'(1 | 3 | 5 | 7 => 2, others => 0) -- see 4.6 


4.8 Allocators


1     The evaluation of an allocator creates an object and yields an access
value that designates the object.


                                   Syntax

2     allocator ::= 
         new subtype_indication | new qualified_expression


                            Name Resolution Rules

3/1   The expected type for an allocator shall be a single access-to-object
type {with}[whose] designated type {D such that either D} covers the type
determined by the subtype_mark of the subtype_indication or
qualified_expression{, or the expected type is anonymous and the determined
type is D'Class}.


                               Legality Rules

4     An initialized allocator is an allocator with a qualified_expression. An
uninitialized allocator is one with a subtype_indication. In the
subtype_indication of an uninitialized allocator, a constraint is permitted
only if the subtype_mark denotes an unconstrained composite subtype; if there
is no constraint, then the subtype_mark shall denote a definite subtype.

5     If the type of the allocator is an access-to-constant type, the
allocator shall be an initialized allocator. If the designated type is
limited, the allocator shall be an uninitialized allocator.


                              Static Semantics

6     If the designated type of the type of the allocator is elementary, then
the subtype of the created object is the designated subtype. If the designated
type is composite, then the created object is always constrained; if the
designated subtype is constrained, then it provides the constraint of the
created object; otherwise, the object is constrained by its initial value
(even if the designated subtype is unconstrained with defaults).


                              Dynamic Semantics

7     For the evaluation of an allocator, the elaboration of the
subtype_indication or the evaluation of the qualified_expression is performed
first. For the evaluation of an initialized allocator, an object of the
designated type is created and the value of the qualified_expression is
converted to the designated subtype and assigned to the object.

8     For the evaluation of an uninitialized allocator:

9     If the designated type is elementary, an object of the designated
      subtype is created and any implicit initial value is assigned;

10/1  If the designated type is composite, an object of the designated type is
      created with tag, if any, determined by the subtype_mark of the
      subtype_indication; any per-object constraints on subcomponents are
      elaborated {(see 3.8) }and any implicit initial values for the
      subcomponents of the object are obtained as determined by the
      subtype_indication and assigned to the corresponding subcomponents. A
      check is made that the value of the object belongs to the designated
      subtype. Constraint_Error is raised if this check fails. This check and
      the initialization of the object are performed in an arbitrary order.

11    If the created object contains any tasks, they are activated (see 9.2).
Finally, an access value that designates the created object is returned.

      NOTES

12    24  Allocators cannot create objects of an abstract type. See 3.9.3.

13    25  If any part of the created object is controlled, the initialization
      includes calls on corresponding Initialize or Adjust procedures. See
      7.6.

14    26  As explained in 13.11, ``Storage Management'', the storage for an
      object allocated by an allocator comes from a storage pool (possibly
      user defined). The exception Storage_Error is raised by an allocator if
      there is not enough storage. Instances of Unchecked_Deallocation may be
      used to explicitly reclaim storage.

15    27  Implementations are permitted, but not required, to provide garbage
      collection (see 13.11.3).


                                  Examples

16    Examples of allocators:

17    new Cell'(0, null, null)                          -- initialized explicitly, see 3.10.1
      new Cell'(Value => 0, Succ => null, Pred => null) -- initialized explicitly
      new Cell                                          -- not initialized

18    new Matrix(1 .. 10, 1 .. 20)                      -- the bounds only are given
      new Matrix'(1 .. 10 => (1 .. 20 => 0.0))          -- initialized explicitly

19    new Buffer(100)                                   -- the discriminant only is given
      new Buffer'(Size => 80, Pos => 0, Value => (1 .. 80 => 'A')) -- initialized explicitly

20    Expr_Ptr'(new Literal)                  -- allocator for access-to-class-wide type, see 3.9.1
      Expr_Ptr'(new Literal'(Expression with 3.5))      -- initialized explicitly


4.9 Static Expressions and Static Subtypes


1     Certain expressions of a scalar or string type are defined to be static.
Similarly, certain discrete ranges are defined to be static, and certain
scalar and string subtypes are defined to be static subtypes. Static means
determinable at compile time, using the declared properties or values of the
program entities.

2     A static expression is a scalar or string expression that is one of the
following:

3     a numeric_literal;

4     a string_literal of a static string subtype;

5     a name that denotes the declaration of a named number or a static
      constant;

6     a function_call whose function_name or function_prefix statically
      denotes a static function, and whose actual parameters, if any (whether
      given explicitly or by default), are all static expressions;

7     an attribute_reference that denotes a scalar value, and whose prefix
      denotes a static scalar subtype;

8     an attribute_reference whose prefix statically denotes a statically
      constrained array object or array subtype, and whose
      attribute_designator is First, Last, or Length, with an optional
      dimension;

9     a type_conversion whose subtype_mark denotes a static scalar subtype,
      and whose operand is a static expression;

10    a qualified_expression whose subtype_mark denotes a static (scalar or
      string) subtype, and whose operand is a static expression;

11    a membership test whose simple_expression is a static expression, and
      whose range is a static range or whose subtype_mark denotes a static
      (scalar or string) subtype;

12    a short-circuit control form both of whose relations are static
      expressions;

13    a static expression enclosed in parentheses.

14    A name statically denotes an entity if it denotes the entity and:

15    It is a direct_name, expanded name, or character_literal, and it denotes
      a declaration other than a renaming_declaration; or

16    It is an attribute_reference whose prefix statically denotes some
      entity; or

17    It denotes a renaming_declaration with a name that statically denotes
      the renamed entity.

18    A static function is one of the following:

19    a predefined operator whose parameter and result types are all scalar
      types none of which are descendants of formal scalar types;

20    a predefined concatenation operator whose result type is a string type;

21    an enumeration literal;

22    a language-defined attribute that is a function, if the prefix denotes a
      static scalar subtype, and if the parameter and result types are scalar.

23    In any case, a generic formal subprogram is not a static function.

24    A static constant is a constant view declared by a full constant
declaration or an object_renaming_declaration with a static nominal subtype,
having a value defined by a static scalar expression or by a static string
expression whose value has a length not exceeding the maximum length of a
string_literal in the implementation.

25    A static range is a range whose bounds are static expressions, or a
range_attribute_reference that is equivalent to such a range. A static
discrete_range is one that is a static range or is a subtype_indication that
defines a static scalar subtype. The base range of a scalar type is a static
range, unless the type is a descendant of a formal scalar type.

26    A static subtype is either a static scalar subtype or a static string
subtype. A static scalar subtype is an unconstrained scalar subtype whose type
is not a descendant of a formal scalar type, or a constrained scalar subtype
formed by imposing a compatible static constraint on a static scalar subtype.
A static string subtype is an unconstrained string subtype whose index subtype
and component subtype are static (and whose type is not a descendant of a
formal array type), or a constrained string subtype formed by imposing a
compatible static constraint on a static string subtype. In any case, the
subtype of a generic formal object of mode in out, and the result subtype of a
generic formal function, are not static.

27    The different kinds of static constraint are defined as follows:

28    A null constraint is always static;

29    A scalar constraint is static if it has no range_constraint, or one with
      a static range;

30    An index constraint is static if each discrete_range is static, and each
      index subtype of the corresponding array type is static;

31    A discriminant constraint is static if each expression of the constraint
      is static, and the subtype of each discriminant is static.

32    A subtype is statically constrained if it is constrained, and its
constraint is static. An object is statically constrained if its nominal
subtype is statically constrained, or if it is a static string constant.


                               Legality Rules

33    A static expression is evaluated at compile time except when it is part
of the right operand of a static short-circuit control form whose value is
determined by its left operand. This evaluation is performed exactly, without
performing Overflow_Checks. For a static expression that is evaluated:

34    The expression is illegal if its evaluation fails a language-defined
      check other than Overflow_Check.

35    If the expression is not part of a larger static expression, then its
      value shall be within the base range of its expected type. Otherwise,
      the value may be arbitrarily large or small.

36    If the expression is of type universal_real and its expected type is a
      decimal fixed point type, then its value shall be a multiple of the
      small of the decimal type.

37    The last two restrictions above do not apply if the expected type is a
descendant of a formal scalar type (or a corresponding actual type in an
instance).


                         Implementation Requirements

38    For a real static expression that is not part of a larger static
expression, and whose expected type is not a descendant of a formal scalar
type, the implementation shall round or truncate the value (according to the
Machine_Rounds attribute of the expected type) to the nearest machine number
of the expected type; if the value is exactly half-way between two machine
numbers, any rounding shall be performed away from zero. If the expected type
is a descendant of a formal scalar type, no special rounding or truncating is
required - normal accuracy rules apply (see Annex G).

      NOTES

39    28  An expression can be static even if it occurs in a context where
      staticness is not required.

40    29  A static (or run-time) type_conversion from a real type to an
      integer type performs rounding. If the operand value is exactly half-way
      between two integers, the rounding is performed away from zero.


                                  Examples

41    Examples of static expressions:

42    1 + 1       -- 2
      abs(-10)*3  -- 30

43    Kilo : constant := 1000;
      Mega : constant := Kilo*Kilo;   -- 1_000_000
      Long : constant := Float'Digits*2;

44    Half_Pi    : constant := Pi/2;           -- see 3.3.2
      Deg_To_Rad : constant := Half_Pi/90;
      Rad_To_Deg : constant := 1.0/Deg_To_Rad; -- equivalent to 1.0/((3.14159_26536/2)/90)


4.9.1 Statically Matching Constraints and Subtypes



                              Static Semantics

1     A constraint statically matches another constraint if both are null
constraints, both are static and have equal corresponding bounds or
discriminant values, or both are nonstatic and result from the same
elaboration of a constraint of a subtype_indication or the same evaluation of
a range of a discrete_subtype_definition.

2     A subtype statically matches another subtype of the same type if they
have statically matching constraints. Two anonymous access subtypes statically
match if their designated subtypes statically match.

3     Two ranges of the same type statically match if both result from the
same evaluation of a range, or if both are static and have equal corresponding
bounds.

4     A constraint is statically compatible with a scalar subtype if it
statically matches the constraint of the subtype, or if both are static and
the constraint is compatible with the subtype. A constraint is statically
compatible with an access or composite subtype if it statically matches the
constraint of the subtype, or if the subtype is unconstrained. One subtype is
statically compatible with a second subtype if the constraint of the first is
statically compatible with the second subtype.



                            Section 5: Statements


1     A statement defines an action to be performed upon its execution.

2     This section describes the general rules applicable to all statements.
Some statements are discussed in later sections: Procedure_call_statements and
return_statements are described in 6, ``Subprograms''. Entry_call_statements,
requeue_statements, delay_statements, accept_statements, select_statements,
and abort_statements are described in 9, ``Tasks and Synchronization''. Raise_-
statements are described in 11, ``Exceptions'', and code_statements in 13. The
remaining forms of statements are presented in this section.


5.1 Simple and Compound Statements - Sequences of Statements


1     A statement is either simple or compound. A simple_statement encloses no
other statement. A compound_statement can enclose simple_statements and other
compound_statements.


                                   Syntax

2     sequence_of_statements ::= statement {statement}

3     statement ::= 
         {label} simple_statement | {label} compound_statement

4     simple_statement ::= null_statement
         | assignment_statement            | exit_statement
         | goto_statement                  | procedure_call_statement
         | return_statement                | entry_call_statement
         | requeue_statement               | delay_statement
         | abort_statement                 | raise_statement
         | code_statement

5     compound_statement ::= 
           if_statement                    | case_statement
         | loop_statement                  | block_statement
         | accept_statement                | select_statement

6     null_statement ::= null;

7     label ::= <<label_statement_identifier>>

8     statement_identifier ::= direct_name

9     The direct_name of a statement_identifier shall be an identifier (not an
      operator_symbol).


                            Name Resolution Rules

10    The direct_name of a statement_identifier shall resolve to denote its
corresponding implicit declaration (see below).


                               Legality Rules

11    Distinct identifiers shall be used for all statement_identifiers that
appear in the same body, including inner block_statements but excluding inner
program units.


                              Static Semantics

12    For each statement_identifier, there is an implicit declaration (with
the specified identifier) at the end of the declarative_part of the innermost
block_statement or body that encloses the statement_identifier. The implicit
declarations occur in the same order as the statement_identifiers occur in the
source text. If a usage name denotes such an implicit declaration, the entity
it denotes is the label, loop_statement, or block_statement with the given
statement_identifier.


                              Dynamic Semantics

13    The execution of a null_statement has no effect.

14    A transfer of control is the run-time action of an exit_statement,
return_statement, goto_statement, or requeue_statement, selection of a
terminate_alternative, raising of an exception, or an abort, which causes the
next action performed to be one other than what would normally be expected
from the other rules of the language. As explained in 7.6.1, a transfer of
control can cause the execution of constructs to be completed and then left,
which may trigger finalization.

15    The execution of a sequence_of_statements consists of the execution of
the individual statements in succession until the sequence_ is completed.

      NOTES

16    1  A statement_identifier that appears immediately within the
      declarative region of a named loop_statement or an accept_statement is
      nevertheless implicitly declared immediately within the declarative
      region of the innermost enclosing body or block_statement; in other
      words, the expanded name for a named statement is not affected by
      whether the statement occurs inside or outside a named loop or an
      accept_statement - only nesting within block_statements is relevant to
      the form of its expanded name.


                                  Examples

17    Examples of labeled statements:

18    <<Here>> <<Ici>> <<Aqui>> <<Hier>> null;

19    <<After>> X := 1;


5.2 Assignment Statements


1     An assignment_statement replaces the current value of a variable with
the result of evaluating an expression.


                                   Syntax

2     assignment_statement ::= 
         variable_name := expression;

3     The execution of an assignment_statement includes the evaluation of the
expression and the assignment of the value of the expression into the target.
An assignment operation (as opposed to an assignment_statement) is performed
in other contexts as well, including object initialization and by-copy
parameter passing. The target of an assignment operation is the view of the
object to which a value is being assigned; the target of an assignment_-
statement is the variable denoted by the variable_name.


                            Name Resolution Rules

4     The variable_name of an assignment_statement is expected to be of any
nonlimited type. The expected type for the expression is the type of the
target.


                               Legality Rules

5     The target denoted by the variable_name shall be a variable.

6     If the target is of a tagged class-wide type T'Class, then the
expression shall either be dynamically tagged, or of type T and
tag-indeterminate (see 3.9.2).


                              Dynamic Semantics

7     For the execution of an assignment_statement, the variable_name and the
expression are first evaluated in an arbitrary order.

8     When the type of the target is class-wide:

9     If the expression is tag-indeterminate (see 3.9.2), then the controlling
      tag value for the expression is the tag of the target;

10    Otherwise (the expression is dynamically tagged), a check is made that
      the tag of the value of the expression is the same as that of the
      target; if this check fails, Constraint_Error is raised.

11    The value of the expression is converted to the subtype of the target.
The conversion might raise an exception (see 4.6).

12    In cases involving controlled types, the target is finalized, and an
anonymous object might be used as an intermediate in the assignment, as
described in 7.6.1, ``Completion and Finalization''. In any case, the
converted value of the expression is then assigned to the target, which
consists of the following two steps:

13    The value of the target becomes the converted value.

14    If any part of the target is controlled, its value is adjusted as
      explained in clause 7.6.

      NOTES

15    2  The tag of an object never changes; in particular, an
      assignment_statement does not change the tag of the target.

16    3  The values of the discriminants of an object designated by an access
      value cannot be changed (not even by assigning a complete value to the
      object itself) since such objects are always constrained; however,
      subcomponents of such objects may be unconstrained.


                                  Examples

17    Examples of assignment statements:

18    Value := Max_Value - 1;
      Shade := Blue;

19    Next_Frame(F)(M, N) := 2.5;        --  see 4.1.1
      U := Dot_Product(V, W);            --  see 6.3

20    Writer := (Status => Open, Unit => Printer, Line_Count => 60);  -- see 3.8.1
      Next_Car.all := (72074, null);    --  see 3.10.1

21    Examples involving scalar subtype conversions:

22    I, J : Integer range 1 .. 10 := 5;
      K    : Integer range 1 .. 20 := 15;
       ...

23    I := J;  --  identical ranges
      K := J;  --  compatible ranges
      J := K;  --  will raise Constraint_Error if K > 10

24    Examples involving array subtype conversions:

25    A : String(1 .. 31);
      B : String(3 .. 33);
       ...

26    A := B;  --  same number of components

27    A(1 .. 9)  := "tar sauce";
      A(4 .. 12) := A(1 .. 9);  --  A(1 .. 12) = "tartar sauce"

      NOTES

28    4  Notes on the examples: Assignment_statements are allowed even in the
      case of overlapping slices of the same array, because the variable_name
      and expression are both evaluated before copying the value into the
      variable. In the above example, an implementation yielding A(1 .. 12) =
      "tartartartar" would be incorrect.


5.3 If Statements


1     An if_statement selects for execution at most one of the enclosed
sequences_of_statements, depending on the (truth) value of one or more
corresponding conditions.


                                   Syntax

2     if_statement ::= 
          if condition then
            sequence_of_statements
         {elsif condition then
            sequence_of_statements}
         [else
            sequence_of_statements]
          end if;

3     condition ::= boolean_expression


                            Name Resolution Rules

4     A condition is expected to be of any boolean type.


                              Dynamic Semantics

5     For the execution of an if_statement, the condition specified after if,
and any conditions specified after elsif, are evaluated in succession
(treating a final else as elsif True then), until one evaluates to True or all
conditions are evaluated and yield False. If a condition evaluates to True,
then the corresponding sequence_of_statements is executed; otherwise none of
them is executed.


                                  Examples

6     Examples of if statements:

7     if Month = December and Day = 31 then
         Month := January;
         Day   := 1;
         Year  := Year + 1;
      end if;

8     if Line_Too_Short then
         raise Layout_Error;
      elsif Line_Full then
         New_Line;
         Put(Item);
      else
         Put(Item);
      end if;

9     if My_Car.Owner.Vehicle /= My_Car then            --  see 3.10.1
         Report ("Incorrect data");
      end if;


5.4 Case Statements


1     A case_statement selects for execution one of a number of alternative
sequences_of_statements; the chosen alternative is defined by the value of an
expression.


                                   Syntax

2     case_statement ::= 
         case expression is
             case_statement_alternative
            {case_statement_alternative}
         end case;

3     case_statement_alternative ::= 
         when discrete_choice_list =>
            sequence_of_statements


                            Name Resolution Rules

4     The expression is expected to be of any discrete type. The expected type
for each discrete_choice is the type of the expression.


                               Legality Rules

5     The expressions and discrete_ranges given as discrete_choices of a
case_statement shall be static. A discrete_choice others, if present, shall
appear alone and in the last discrete_choice_list.

6     The possible values of the expression shall be covered as follows:

7     If the expression is a name (including a type_conversion or a
      function_call) having a static and constrained nominal subtype, or is a
      qualified_expression whose subtype_mark denotes a static and constrained
      scalar subtype, then each non-others discrete_choice shall cover only
      values in that subtype, and each value of that subtype shall be covered
      by some discrete_choice (either explicitly or by others).

8     If the type of the expression is root_integer, universal_integer, or a
      descendant of a formal scalar type, then the case_statement shall have
      an others discrete_choice.

9     Otherwise, each value of the base range of the type of the expression
      shall be covered (either explicitly or by others).

10    Two distinct discrete_choices of a case_statement shall not cover the
same value.


                              Dynamic Semantics

11    For the execution of a case_statement the expression is first evaluated.

12    If the value of the expression is covered by the discrete_choice_-
list of some case_statement_alternative, then the sequence_of_statements of
the _alternative is executed.

13    Otherwise (the value is not covered by any discrete_choice_list, perhaps
due to being outside the base range), Constraint_Error is raised.

      NOTES

14    5  The execution of a case_statement chooses one and only one
      alternative. Qualification of the expression of a case_statement by a
      static subtype can often be used to limit the number of choices that
      need be given explicitly.


                                  Examples

15    Examples of case statements:

16    case Sensor is
         when Elevation         => Record_Elevation(Sensor_Value);
         when Azimuth           => Record_Azimuth  (Sensor_Value);
         when Distance          => Record_Distance (Sensor_Value);
         when others            => null;
      end case;

17    case Today is
         when Mon               => Compute_Initial_Balance;
         when Fri               => Compute_Closing_Balance;
         when Tue .. Thu        => Generate_Report(Today);
         when Sat .. Sun        => null;
      end case;

18    case Bin_Number(Count) is
         when 1          => Update_Bin(1);
         when 2          => Update_Bin(2);
         when 3 | 4      =>
            Empty_Bin(1);
            Empty_Bin(2);
         when others     => raise Error;
      end case;


5.5 Loop Statements


1     A loop_statement includes a sequence_of_statements that is to be
executed repeatedly, zero or more times.


                                   Syntax

2     loop_statement ::= 
         [loop_statement_identifier:]
            [iteration_scheme] loop
               sequence_of_statements
             end loop [loop_identifier];

3     iteration_scheme ::= while condition
         | for loop_parameter_specification

4     loop_parameter_specification ::= 
         defining_identifier in [reverse] discrete_subtype_definition

5     If a loop_statement has a loop_statement_identifier, then the identifier
      shall be repeated after the end loop; otherwise, there shall not be an
      identifier after the end loop.


                              Static Semantics

6     A loop_parameter_specification declares a loop parameter, which is an
object whose subtype is that defined by the discrete_subtype_definition.


                              Dynamic Semantics

7     For the execution of a loop_statement, the sequence_of_statements is
executed repeatedly, zero or more times, until the loop_statement is complete.
The loop_statement is complete when a transfer of control occurs that
transfers control out of the loop, or, in the case of an iteration_scheme, as
specified below.

8     For the execution of a loop_statement with a while iteration_scheme, the
condition is evaluated before each execution of the sequence_of_statements; if
the value of the condition is True, the sequence_of_statements is executed; if
False, the execution of the loop_statement is complete.

9     For the execution of a loop_statement with a for iteration_scheme, the
loop_parameter_specification is first elaborated. This elaboration creates the
loop parameter and elaborates the discrete_subtype_definition. If the discrete_-
subtype_definition defines a subtype with a null range, the execution of the
loop_statement is complete. Otherwise, the sequence_of_statements is executed
once for each value of the discrete subtype defined by the discrete_subtype_-
definition (or until the loop is left as a consequence of a transfer of
control). Prior to each such iteration, the corresponding value of the
discrete subtype is assigned to the loop parameter. These values are assigned
in increasing order unless the reserved word reverse is present, in which case
the values are assigned in decreasing order.

      NOTES

10    6  A loop parameter is a constant; it cannot be updated within the
      sequence_of_statements of the loop (see 3.3).

11    7  An object_declaration should not be given for a loop parameter, since
      the loop parameter is automatically declared by the
      loop_parameter_specification. The scope of a loop parameter extends from
      the loop_parameter_specification to the end of the loop_statement, and
      the visibility rules are such that a loop parameter is only visible
      within the sequence_of_statements of the loop.

12    8  The discrete_subtype_definition of a for loop is elaborated just
      once. Use of the reserved word reverse does not alter the discrete
      subtype defined, so that the following iteration_schemes are not
      equivalent; the first has a null range.

13    for J in reverse 1 .. 0
      for J in 0 .. 1


                                  Examples

14    Example of a loop statement without an iteration scheme:

15    loop
         Get(Current_Character);
         exit when Current_Character = '*';
      end loop;

16    Example of a loop statement with a while iteration scheme:

17    while Bid(N).Price < Cut_Off.Price loop
         Record_Bid(Bid(N).Price);
         N := N + 1;
      end loop;

18    Example of a loop statement with a for iteration scheme:

19    for J in Buffer'Range loop     --  works even with a null range
         if Buffer(J) /= Space then
            Put(Buffer(J));
         end if;
      end loop;

20    Example of a loop statement with a name:

21    Summation:
         while Next /= Head loop       -- see 3.10.1
            Sum  := Sum + Next.Value;
            Next := Next.Succ;
         end loop Summation;


5.6 Block Statements


1     A block_statement encloses a handled_sequence_of_statements optionally
preceded by a declarative_part.


                                   Syntax

2     block_statement ::= 
         [block_statement_identifier:]
             [declare
                  declarative_part]
              begin
                  handled_sequence_of_statements
              end [block_identifier];

3     If a block_statement has a block_statement_identifier, then the
      identifier shall be repeated after the end; otherwise, there shall not
      be an identifier after the end.


                              Static Semantics

4     A block_statement that has no explicit declarative_part has an implicit
empty declarative_part.


                              Dynamic Semantics

5     The execution of a block_statement consists of the elaboration of its
declarative_part followed by the execution of its
handled_sequence_of_statements.


                                  Examples

6     Example of a block statement with a local variable:

7     Swap:
         declare
            Temp : Integer;
         begin
            Temp := V; V := U; U := Temp;
         end Swap;


5.7 Exit Statements


1     An exit_statement is used to complete the execution of an enclosing
loop_statement; the completion is conditional if the exit_statement includes a
condition.


                                   Syntax

2     exit_statement ::= 
         exit [loop_name] [when condition];


                            Name Resolution Rules

3     The loop_name, if any, in an exit_statement shall resolve to denote a
loop_statement.


                               Legality Rules

4     Each exit_statement applies to a loop_statement; this is the loop_-
statement being exited. An exit_statement with a name is only allowed within
the loop_statement denoted by the name, and applies to that loop_statement. An
exit_statement without a name is only allowed within a loop_statement, and
applies to the innermost enclosing one. An exit_statement that applies to a
given loop_statement shall not appear within a body or accept_statement, if
this construct is itself enclosed by the given loop_statement.


                              Dynamic Semantics

5     For the execution of an exit_statement, the condition, if present, is
first evaluated. If the value of the condition is True, or if there is no
condition, a transfer of control is done to complete the loop_statement. If
the value of the condition is False, no transfer of control takes place.

      NOTES

6     9  Several nested loops can be exited by an exit_statement that names
      the outer loop.


                                  Examples

7     Examples of loops with exit statements:

8     for N in 1 .. Max_Num_Items loop
         Get_New_Item(New_Item);
         Merge_Item(New_Item, Storage_File);
         exit when New_Item = Terminal_Item;
      end loop;

9     Main_Cycle:
         loop
            --  initial statements
            exit Main_Cycle when Found;
            --  final statements
         end loop Main_Cycle;


5.8 Goto Statements


1     A goto_statement specifies an explicit transfer of control from this
statement to a target statement with a given label.


                                   Syntax

2     goto_statement ::= goto label_name;


                            Name Resolution Rules

3     The label_name shall resolve to denote a label; the statement with that
label is the target statement.


                               Legality Rules

4     The innermost sequence_of_statements that encloses the target statement
shall also enclose the goto_statement. Furthermore, if a goto_statement is
enclosed by an accept_statement or a body, then the target statement shall not
be outside this enclosing construct.


                              Dynamic Semantics

5     The execution of a goto_statement transfers control to the target
statement, completing the execution of any compound_statement that encloses
the goto_statement but does not enclose the target.

      NOTES

6     10  The above rules allow transfer of control to a statement of an
      enclosing sequence_of_statements but not the reverse. Similarly, they
      prohibit transfers of control such as between alternatives of a
      case_statement, if_statement, or select_statement; between
      exception_handlers; or from an exception_handler of a
      handled_sequence_of_statements back to its sequence_of_statements.


                                  Examples

7     Example of a loop containing a goto statement:

8     <<Sort>>
      for I in 1 .. N-1 loop
         if A(I) > A(I+1) then
            Exchange(A(I), A(I+1));
            goto Sort;
         end if;
      end loop;



                           Section 6: Subprograms


1     A subprogram is a program unit or intrinsic operation whose execution is
invoked by a subprogram call. There are two forms of subprogram: procedures
and functions. A procedure call is a statement; a function call is an
expression and returns a value. The definition of a subprogram can be given in
two parts: a subprogram declaration defining its interface, and a
subprogram_body defining its execution. Operators and enumeration literals are
functions.

2     A callable entity is a subprogram or entry (see Section 9). A callable
entity is invoked by a call; that is, a subprogram call or entry call. A
callable construct is a construct that defines the action of a call upon a
callable entity: a subprogram_body, entry_body, or accept_statement.


6.1 Subprogram Declarations


1     A subprogram_declaration declares a procedure or function.


                                   Syntax

2     subprogram_declaration ::= subprogram_specification;

3     abstract_subprogram_declaration ::= subprogram_specification
       is abstract;

4     subprogram_specification ::= 
           procedure defining_program_unit_name  parameter_profile
         | function defining_designator  parameter_and_result_profile

5     designator ::= [parent_unit_name . ]identifier | operator_symbol

6     defining_designator ::= defining_program_unit_name
       | defining_operator_symbol

7     defining_program_unit_name ::= [parent_unit_name
       . ]defining_identifier

8     The optional parent_unit_name is only allowed for library units (see
      10.1.1).

9     operator_symbol ::= string_literal

10    The sequence of characters in an operator_symbol shall correspond to an
      operator belonging to one of the six classes of operators defined in
      clause 4.5 (spaces are not allowed and the case of letters is not
      significant).

11    defining_operator_symbol ::= operator_symbol

12    parameter_profile ::= [formal_part]

13    parameter_and_result_profile ::= [formal_part] return subtype_mark

14    formal_part ::= 
         (parameter_specification {; parameter_specification})

15    parameter_specification ::= 
          defining_identifier_list : mode  subtype_mark
       [:= default_expression]
        | defining_identifier_list : access_definition
       [:= default_expression]

16    mode ::= [in] | in out | out


                            Name Resolution Rules

17    A formal parameter is an object directly visible within a
subprogram_body that represents the actual parameter passed to the subprogram
in a call; it is declared by a parameter_specification. For a formal
parameter, the expected type for its default_expression, if any, is that of
the formal parameter.


                               Legality Rules

18    The parameter mode of a formal parameter conveys the direction of
information transfer with the actual parameter: in, in out, or out. Mode in is
the default, and is the mode of a parameter defined by an access_definition.
The formal parameters of a function, if any, shall have the mode in.

19    A default_expression is only allowed in a parameter_specification for a
formal parameter of mode in.

20    A subprogram_declaration or a generic_subprogram_declaration requires a
completion: a body, a renaming_declaration (see 8.5), or a pragma Import (see
B.1). A completion is not allowed for an abstract_subprogram_declaration.

21    A name that denotes a formal parameter is not allowed within the
formal_part in which it is declared, nor within the formal_part of a
corresponding body or accept_statement.


                              Static Semantics

22    The profile of (a view of) a callable entity is either a
parameter_profile or parameter_and_result_profile; it embodies information
about the interface to that entity - for example, the profile includes
information about parameters passed to the callable entity. All callable
entities have a profile - enumeration literals, other subprograms, and
entries. An access-to-subprogram type has a designated profile. Associated
with a profile is a calling convention. A subprogram_declaration declares a
procedure or a function, as indicated by the initial reserved word, with name
and profile as given by its specification.

23    The nominal subtype of a formal parameter is the subtype denoted by the
subtype_mark, or defined by the access_definition, in the
parameter_specification.

24    An access parameter is a formal in parameter specified by an
access_definition. An access parameter is of an anonymous general
access-to-variable type (see 3.10). Access parameters allow dispatching calls
to be controlled by access values.

25    The subtypes of a profile are:

26    For any non-access parameters, the nominal subtype of the parameter.

27    For any access parameters, the designated subtype of the parameter type.

28    For any result, the result subtype.

29    The types of a profile are the types of those subtypes.

30    A subprogram declared by an abstract_subprogram_declaration is abstract;
a subprogram declared by a subprogram_declaration is not. See 3.9.3, ``
Abstract Types and Subprograms''.


                              Dynamic Semantics

31    The elaboration of a subprogram_declaration or an
abstract_subprogram_declaration has no effect.

      NOTES

32    1  A parameter_specification with several identifiers is equivalent to a
      sequence of single parameter_specifications, as explained in 3.3.

33    2  Abstract subprograms do not have bodies, and cannot be used in a
      nondispatching call (see 3.9.3, ``Abstract Types and Subprograms'').

34    3  The evaluation of default_expressions is caused by certain calls, as
      described in 6.4.1. They are not evaluated during the elaboration of the
      subprogram declaration.

35    4  Subprograms can be called recursively and can be called concurrently
      from multiple tasks.


                                  Examples

36    Examples of subprogram declarations:

37    procedure Traverse_Tree;
      procedure Increment(X : in out Integer);
      procedure Right_Indent(Margin : out Line_Size);          --  see 3.5.4
      procedure Switch(From, To : in out Link);                --  see 3.10.1

38    function Random return Probability;                      --  see 3.5.7

39    function Min_Cell(X : Link) return Cell;                 --  see 3.10.1
      function Next_Frame(K : Positive) return Frame;          --  see 3.10
      function Dot_Product(Left, Right : Vector) return Real;  --  see 3.6

40    function "*"(Left, Right : Matrix) return Matrix;        --  see 3.6

41    Examples of in parameters with default expressions:

42    procedure Print_Header(Pages  : in Natural;
                  Header : in Line    :=  (1 .. Line'Last => ' ');  --  see 3.6
                  Center : in Boolean := True);


6.2 Formal Parameter Modes


1     A parameter_specification declares a formal parameter of mode in, in
out, or out.


                              Static Semantics

2     A parameter is passed either by copy or by reference. When a parameter
is passed by copy, the formal parameter denotes a separate object from the
actual parameter, and any information transfer between the two occurs only
before and after executing the subprogram. When a parameter is passed by
reference, the formal parameter denotes (a view of) the object denoted by the
actual parameter; reads and updates of the formal parameter directly reference
the actual parameter object.

3     A type is a by-copy type if it is an elementary type, or if it is a
descendant of a private type whose full type is a by-copy type. A parameter of
a by-copy type is passed by copy.

4     A type is a by-reference type if it is a descendant of one of the
following:

5     a tagged type;

6     a task or protected type;

7     a nonprivate type with the reserved word limited in its declaration;

8     a composite type with a subcomponent of a by-reference type;

9     a private type whose full type is a by-reference type.

10    A parameter of a by-reference type is passed by reference. Each value of
a by-reference type has an associated object. For a parenthesized expression,
qualified_expression, or type_conversion, this object is the one associated
with the operand.

11    For parameters of other types, it is unspecified whether the parameter
is passed by copy or by reference.


                          Bounded (Run-Time) Errors

12    If one name denotes a part of a formal parameter, and a second name
denotes a part of a distinct formal parameter or an object that is not part of
a formal parameter, then the two names are considered distinct access paths.
If an object is of a type for which the parameter passing mechanism is not
specified, then it is a bounded error to assign to the object via one access
path, and then read the value of the object via a distinct access path, unless
the first access path denotes a part of a formal parameter that no longer
exists at the point of the second access (due to leaving the corresponding
callable construct). The possible consequences are that Program_Error is
raised, or the newly assigned value is read, or some old value of the object
is read.

      NOTES

13    5  A formal parameter of mode in is a constant view (see 3.3); it cannot
      be updated within the subprogram_body.


6.3 Subprogram Bodies


1     A subprogram_body specifies the execution of a subprogram.


                                   Syntax

2     subprogram_body ::= 
          subprogram_specification is
             declarative_part
          begin
              handled_sequence_of_statements
          end [designator];

3     If a designator appears at the end of a subprogram_body, it shall repeat
      the defining_designator of the subprogram_specification.


                               Legality Rules

4     In contrast to other bodies, a subprogram_body need not be the
completion of a previous declaration, in which case the body declares the
subprogram. If the body is a completion, it shall be the completion of a
subprogram_declaration or generic_subprogram_declaration. The profile of a
subprogram_body that completes a declaration shall conform fully to that of
the declaration.


                              Static Semantics

5     A subprogram_body is considered a declaration. It can either complete a
previous declaration, or itself be the initial declaration of the subprogram.


                              Dynamic Semantics

6     The elaboration of a non-generic subprogram_body has no other effect
than to establish that the subprogram can from then on be called without
failing the Elaboration_Check.

7     The execution of a subprogram_body is invoked by a subprogram call. For
this execution the declarative_part is elaborated, and the
handled_sequence_of_statements is then executed.


                                  Examples

8     Example of procedure body:

9     procedure Push(E : in Element_Type; S : in out Stack) is
      begin
         if S.Index = S.Size then
            raise Stack_Overflow;
         else
            S.Index := S.Index + 1;
            S.Space(S.Index) := E;
         end if;
      end Push;

10    Example of a function body:

11    function Dot_Product(Left, Right : Vector) return Real is
         Sum : Real := 0.0;
      begin
         Check(Left'First = Right'First and Left'Last = Right'Last);
         for J in Left'Range loop
            Sum := Sum + Left(J)*Right(J);
         end loop;
         return Sum;
      end Dot_Product;


6.3.1 Conformance Rules


1     When subprogram profiles are given in more than one place, they are
required to conform in one of four ways: type conformance, mode conformance,
subtype conformance, or full conformance.


                              Static Semantics

2/1   As explained in B.1, ``Interfacing Pragmas'', a convention can be
specified for an entity. {Unless this International Standard states otherwise,
the default convention of an entity is Ada.} For a callable entity or
access-to-subprogram type, the convention is called the calling convention.
The following conventions are defined by the language:

3     The default calling convention for any subprogram not listed below is
      Ada. A pragma Convention, Import, or Export may be used to override the
      default calling convention (see B.1).

4     The Intrinsic calling convention represents subprograms that are ``
      built in'' to the compiler. The default calling convention is Intrinsic
      for the following:

    5     an enumeration literal;

    6     a "/=" operator declared implicitly due to the declaration of "="
          (see 6.6);

    7     any other implicitly declared subprogram unless it is a dispatching
          operation of a tagged type;

    8     an inherited subprogram of a generic formal tagged type with unknown
          discriminants;

    9     an attribute that is a subprogram;

    10    a subprogram declared immediately within a protected_body.

11    The Access attribute is not allowed for Intrinsic subprograms.

12    The default calling convention is protected for a protected subprogram,
      and for an access-to-subprogram type with the reserved word protected in
      its definition.

13    The default calling convention is entry for an entry.

13.1/1 {If not specified above as Intrinsic, the calling convention for any
      inherited or overriding dispatching operation of a tagged type is that
      of the corresponding subprogram of the parent type. The default calling
      convention for a new dispatching operation of a tagged type is the
      convention of the type.}

14    Of these four conventions, only Ada and Intrinsic are allowed as a
convention_identifier in a pragma Convention, Import, or Export.

15    Two profiles are type conformant if they have the same number of
parameters, and both have a result if either does, and corresponding parameter
and result types are the same, or, for access parameters, corresponding
designated types are the same.

16    Two profiles are mode conformant if they are type-conformant, and
corresponding parameters have identical modes, and, for access parameters, the
designated subtypes statically match.

17    Two profiles are subtype conformant if they are mode-conformant,
corresponding subtypes of the profile statically match, and the associated
calling conventions are the same. The profile of a generic formal subprogram
is not subtype-conformant with any other profile.

18    Two profiles are fully conformant if they are subtype-conformant, and
corresponding parameters have the same names and have default_expressions that
are fully conformant with one another.

19    Two expressions are fully conformant if, after replacing each use of an
operator with the equivalent function_call:

20    each constituent construct of one corresponds to an instance of the same
      syntactic category in the other, except that an expanded name may
      correspond to a direct_name (or character_literal) or to a different
      expanded name in the other; and

21    each direct_name, character_literal, and selector_name that is not part
      of the prefix of an expanded name in one denotes the same declaration as
      the corresponding direct_name, character_literal, or selector_name in
      the other; and

21.1/1 {each attribute_designator in one must be the same as the corresponding
      attribute_designator in the other; and}

22    each primary that is a literal in one has the same value as the
      corresponding literal in the other.

23    Two known_discriminant_parts are fully conformant if they have the same
number of discriminants, and discriminants in the same positions have the same
names, statically matching subtypes, and default_expressions that are fully
conformant with one another.

24    Two discrete_subtype_definitions are fully conformant if they are both
subtype_indications or are both ranges, the subtype_marks (if any) denote the
same subtype, and the corresponding simple_expressions of the ranges (if any)
fully conform.


                         Implementation Permissions

25    An implementation may declare an operator declared in a language-defined
library unit to be intrinsic.


6.3.2 Inline Expansion of Subprograms


1     Subprograms may be expanded in line at the call site.


                                   Syntax

2     The form of a pragma Inline, which is a program unit pragma (see
      10.1.5), is as follows:

3       pragma Inline(name {, name});


                               Legality Rules

4     The pragma shall apply to one or more callable entities or generic
subprograms.


                              Static Semantics

5     If a pragma Inline applies to a callable entity, this indicates that
inline expansion is desired for all calls to that entity. If a pragma Inline
applies to a generic subprogram, this indicates that inline expansion is
desired for all calls to all instances of that generic subprogram.


                         Implementation Permissions

6     For each call, an implementation is free to follow or to ignore the
recommendation expressed by the pragma.

      NOTES

7     6  The name in a pragma Inline can denote more than one entity in the
      case of overloading. Such a pragma applies to all of the denoted
      entities.


6.4 Subprogram Calls


1     A subprogram call is either a procedure_call_statement or a
function_call; it invokes the execution of the subprogram_body. The call
specifies the association of the actual parameters, if any, with formal
parameters of the subprogram.


                                   Syntax

2     procedure_call_statement ::= 
          procedure_name;
        | procedure_prefix actual_parameter_part;

3     function_call ::= 
          function_name
        | function_prefix actual_parameter_part

4     actual_parameter_part ::= 
          (parameter_association {, parameter_association})

5     parameter_association ::= 
         [formal_parameter_selector_name =>] explicit_actual_parameter

6     explicit_actual_parameter ::= expression | variable_name

7     A parameter_association is named or positional according to whether or
      not the formal_parameter_selector_name is specified. Any positional
      associations shall precede any named associations. Named associations
      are not allowed if the prefix in a subprogram call is an attribute_-
      reference.


                            Name Resolution Rules

8     The name or prefix given in a procedure_call_statement shall resolve to
denote a callable entity that is a procedure, or an entry renamed as (viewed
as) a procedure. The name or prefix given in a function_call shall resolve to
denote a callable entity that is a function. When there is an actual_parameter_-
part, the prefix can be an implicit_dereference of an access-to-subprogram
value.

9     A subprogram call shall contain at most one association for each formal
parameter. Each formal parameter without an association shall have a
default_expression (in the profile of the view denoted by the name or prefix).
This rule is an overloading rule (see 8.6).


                              Dynamic Semantics

10    For the execution of a subprogram call, the name or prefix of the call
is evaluated, and each parameter_association is evaluated (see 6.4.1). If a
default_expression is used, an implicit parameter_association is assumed for
this rule. These evaluations are done in an arbitrary order. The subprogram_-
body is then executed. Finally, if the subprogram completes normally, then
after it is left, any necessary assigning back of formal to actual parameters
occurs (see 6.4.1).

11    The exception Program_Error is raised at the point of a function_call if
the function completes normally without executing a return_statement.

12    A function_call denotes a constant, as defined in 6.5; the nominal
subtype of the constant is given by the result subtype of the function.


                                  Examples

13    Examples of procedure calls:

14    Traverse_Tree;                                               --  see 6.1
      Print_Header(128, Title, True);                              --  see 6.1

15    Switch(From => X, To => Next);                               --  see 6.1
      Print_Header(128, Header => Title, Center => True);          --  see 6.1
      Print_Header(Header => Title, Center => True, Pages => 128); --  see 6.1

16    Examples of function calls:

17    Dot_Product(U, V)   --  see 6.1 and 6.3
      Clock               --  see 9.6
      F.all               --  presuming F is of an access-to-subprogram type - see 3.10

18    Examples of procedures with default expressions:

19    procedure Activate(Process : in Process_Name;
                         After   : in Process_Name := No_Process;
                         Wait    : in Duration := 0.0;
                         Prior   : in Boolean := False);

20    procedure Pair(Left, Right : in Person_Name := new Person);   --  see 3.10.1

21    Examples of their calls:

22    Activate(X);
      Activate(X, After => Y);
      Activate(X, Wait => 60.0, Prior => True);
      Activate(X, Y, 10.0, False);

23    Pair;
      Pair(Left => new Person, Right => new Person);

      NOTES

24    7  If a default_expression is used for two or more parameters in a
      multiple parameter_specification, the default_expression is evaluated
      once for each omitted parameter. Hence in the above examples, the two
      calls of Pair are equivalent.


                                  Examples

25    Examples of overloaded subprograms:

26    procedure Put(X : in Integer);
      procedure Put(X : in String);

27    procedure Set(Tint   : in Color);
      procedure Set(Signal : in Light);

28    Examples of their calls:

29    Put(28);
      Put("no possible ambiguity here");

30    Set(Tint   => Red);
      Set(Signal => Red);
      Set(Color'(Red));

31    --  Set(Red) would be ambiguous since Red may
      --  denote a value either of type Color or of type Light


6.4.1 Parameter Associations


1     A parameter association defines the association between an actual
parameter and a formal parameter.


                            Name Resolution Rules

2     The formal_parameter_selector_name of a parameter_association shall
resolve to denote a parameter_specification of the view being called.

3     The actual parameter is either the explicit_actual_parameter given in a
parameter_association for a given formal parameter, or the corresponding
default_expression if no parameter_association is given for the formal
parameter. The expected type for an actual parameter is the type of the
corresponding formal parameter.

4     If the mode is in, the actual is interpreted as an expression;
otherwise, the actual is interpreted only as a name, if possible.


                               Legality Rules

5     If the mode is in out or out, the actual shall be a name that denotes a
variable.

6     The type of the actual parameter associated with an access parameter
shall be convertible (see 4.6) to its anonymous access type.


                              Dynamic Semantics

7     For the evaluation of a parameter_association:

8     The actual parameter is first evaluated.

9     For an access parameter, the access_definition is elaborated, which
      creates the anonymous access type.

10    For a parameter (of any mode) that is passed by reference (see 6.2), a
      view conversion of the actual parameter to the nominal subtype of the
      formal parameter is evaluated, and the formal parameter denotes that
      conversion.

11    For an in or in out parameter that is passed by copy (see 6.2), the
      formal parameter object is created, and the value of the actual
      parameter is converted to the nominal subtype of the formal parameter
      and assigned to the formal.

12    For an out parameter that is passed by copy, the formal parameter object
      is created, and:

        13    For an access type, the formal parameter is initialized from the
              value of the actual, without a constraint check;

        14    For a composite type with discriminants or that has implicit
              initial values for any subcomponents (see 3.3.1), the behavior
              is as for an in out parameter passed by copy.

        15    For any other type, the formal parameter is uninitialized. If
              composite, a view conversion of the actual parameter to the
              nominal subtype of the formal is evaluated (which might raise
              Constraint_Error), and the actual subtype of the formal is that
              of the view conversion. If elementary, the actual subtype of the
              formal is given by its nominal subtype.

16    A formal parameter of mode in out or out with discriminants is
constrained if either its nominal subtype or the actual parameter is
constrained.

17    After normal completion and leaving of a subprogram, for each in out or
out parameter that is passed by copy, the value of the formal parameter is
converted to the subtype of the variable given as the actual parameter and
assigned to it. These conversions and assignments occur in an arbitrary order.


6.5 Return Statements


1     A return_statement is used to complete the execution of the innermost
enclosing subprogram_body, entry_body, or accept_statement.


                                   Syntax

2     return_statement ::= return [expression];


                            Name Resolution Rules

3     The expression, if any, of a return_statement is called the return
expression. The result subtype of a function is the subtype denoted by the
subtype_mark after the reserved word return in the profile of the function.
The expected type for a return expression is the result type of the
corresponding function.


                               Legality Rules

4     A return_statement shall be within a callable construct, and it applies
to the innermost one. A return_statement shall not be within a body that is
within the construct to which the return_statement applies.

5     A function body shall contain at least one return_statement that applies
to the function body, unless the function contains code_statements. A
return_statement shall include a return expression if and only if it applies
to a function body.


                              Dynamic Semantics

6     For the execution of a return_statement, the expression (if any) is
first evaluated and converted to the result subtype.

7     If the result type is class-wide, then the tag of the result is the tag
of the value of the expression.

8     If the result type is a specific tagged type:

9     If it is limited, then a check is made that the tag of the value of the
      return expression identifies the result type. Constraint_Error is raised
      if this check fails.

10    If it is nonlimited, then the tag of the result is that of the result
      type.

11    A type is a return-by-reference type if it is a descendant of one of the
following:

12    a tagged limited type;

13    a task or protected type;

14    a nonprivate type with the reserved word limited in its declaration;

15    a composite type with a subcomponent of a return-by-reference type;

16    a private type whose full type is a return-by-reference type.

17    If the result type is a return-by-reference type, then a check is made
that the return expression is one of the following:

18    a name that denotes an object view whose accessibility level is not
      deeper than that of the master that elaborated the function body; or

19    a parenthesized expression or qualified_expression whose operand is one
      of these kinds of expressions.

20    The exception Program_Error is raised if this check fails.

21    For a function with a return-by-reference result type the result is
returned by reference; that is, the function call denotes a constant view of
the object associated with the value of the return expression. For any other
function, the result is returned by copy; that is, the converted value is
assigned into an anonymous constant created at the point of the
return_statement, and the function call denotes that object.

22    Finally, a transfer of control is performed which completes the
execution of the callable construct to which the return_statement applies, and
returns to the caller.


                                  Examples

23    Examples of return statements:

24    return;                         -- in a procedure body, entry_body, or accept_statement
      return Key_Value(Last_Index);   -- in a function body


6.6 Overloading of Operators


1     An operator is a function whose designator is an operator_symbol.
Operators, like other functions, may be overloaded.


                            Name Resolution Rules

2     Each use of a unary or binary operator is equivalent to a function_call
with function_prefix being the corresponding operator_symbol, and with
(respectively) one or two positional actual parameters being the operand(s) of
the operator (in order).


                               Legality Rules

3     The subprogram_specification of a unary or binary operator shall have
one or two parameters, respectively. A generic function instantiation whose
designator is an operator_symbol is only allowed if the specification of the
generic function has the corresponding number of parameters.

4     Default_expressions are not allowed for the parameters of an operator
(whether the operator is declared with an explicit subprogram_specification or
by a generic_instantiation).

5     An explicit declaration of "/=" shall not have a result type of the
predefined type Boolean.


                              Static Semantics

6     A declaration of "=" whose result type is Boolean implicitly declares a
declaration of "/=" that gives the complementary result.

      NOTES

7     8  The operators "+" and "-" are both unary and binary operators, and
      hence may be overloaded with both one- and two-parameter functions.


                                  Examples

8     Examples of user-defined operators:

9     function "+" (Left, Right : Matrix) return Matrix;
      function "+" (Left, Right : Vector) return Vector;
      
      --  assuming that A, B, and C are of the type Vector
      --  the following two statements are equivalent:
      
      A := B + C;
      A := "+"(B, C);



                             Section 7: Packages


1     Packages are program units that allow the specification of groups of
logically related entities. Typically, a package contains the declaration of a
type (often a private type or private extension) along with the declarations
of primitive subprograms of the type, which can be called from outside the
package, while their inner workings remain hidden from outside users.


7.1 Package Specifications and Declarations


1     A package is generally provided in two parts: a package_specification
and a package_body. Every package has a package_specification, but not all
packages have a package_body.


                                   Syntax

2     package_declaration ::= package_specification;

3     package_specification ::= 
          package defining_program_unit_name is
            {basic_declarative_item}
         [private
            {basic_declarative_item}]
          end [[parent_unit_name.]identifier]

4     If an identifier or parent_unit_name.identifier appears at the end of a
      package_specification, then this sequence of lexical elements shall
      repeat the defining_program_unit_name.


                               Legality Rules

5     A package_declaration or generic_package_declaration requires a
completion (a body) if it contains any declarative_item that requires a
completion, but whose completion is not in its package_specification.


                              Static Semantics

6     The first list of declarative_items of a package_specification of a
package other than a generic formal package is called the visible part of the
package. The optional list of declarative_items after the reserved word
private (of any package_specification) is called the private part of the
package. If the reserved word private does not appear, the package has an
implicit empty private part.

7     An entity declared in the private part of a package is visible only
within the declarative region of the package itself (including any child units
- see 10.1.1). In contrast, expanded names denoting entities declared in the
visible part can be used even outside the package; furthermore, direct
visibility of such entities can be achieved by means of use_clauses (see
4.1.3 and 8.4).


                              Dynamic Semantics

8     The elaboration of a package_declaration consists of the elaboration of
its basic_declarative_items in the given order.

      NOTES

9     1  The visible part of a package contains all the information that
      another program unit is able to know about the package.

10    2  If a declaration occurs immediately within the specification of a
      package, and the declaration has a corresponding completion that is a
      body, then that body has to occur immediately within the body of the
      package.


                                  Examples

11    Example of a package declaration:

12    package Rational_Numbers is

13       type Rational is
            record
               Numerator   : Integer;
               Denominator : Positive;
            end record;

14       function "="(X,Y : Rational) return Boolean;

15       function "/"  (X,Y : Integer)  return Rational;  --  to construct a rational number

16       function "+"  (X,Y : Rational) return Rational;
         function "-"  (X,Y : Rational) return Rational;
         function "*"  (X,Y : Rational) return Rational;
         function "/"  (X,Y : Rational) return Rational;
      end Rational_Numbers;

17    There are also many examples of package declarations in the predefined
language environment (see Annex A).


7.2 Package Bodies


1     In contrast to the entities declared in the visible part of a package,
the entities declared in the package_body are visible only within the
package_body itself. As a consequence, a package with a package_body can be
used for the construction of a group of related subprograms in which the
logical operations available to clients are clearly isolated from the internal
entities.


                                   Syntax

2     package_body ::= 
          package body defining_program_unit_name is
             declarative_part
         [begin
              handled_sequence_of_statements]
          end [[parent_unit_name.]identifier];

3     If an identifier or parent_unit_name.identifier appears at the end of a
      package_body, then this sequence of lexical elements shall repeat the
      defining_program_unit_name.


                               Legality Rules

4     A package_body shall be the completion of a previous package_declaration
or generic_package_declaration. A library package_declaration or library
generic_package_declaration shall not have a body unless it requires a body;
pragma Elaborate_Body can be used to require a library_unit_declaration to
have a body (see 10.2.1) if it would not otherwise require one.


                              Static Semantics

5     In any package_body without statements there is an implicit null_-
statement. For any package_declaration without an explicit completion, there
is an implicit package_body containing a single null_statement. For a
noninstance, nonlibrary package, this body occurs at the end of the
declarative_part of the innermost enclosing program unit or block_statement;
if there are several such packages, the order of the implicit package_bodies
is unspecified. (For an instance, the implicit package_body occurs at the
place of the instantiation (see 12.3). For a library package, the place is
partially determined by the elaboration dependences (see Section 10).)


                              Dynamic Semantics

6     For the elaboration of a nongeneric package_body, its declarative_-
part is first elaborated, and its handled_sequence_of_statements is then
executed.

      NOTES

7     3  A variable declared in the body of a package is only visible within
      this body and, consequently, its value can only be changed within the
      package_body. In the absence of local tasks, the value of such a
      variable remains unchanged between calls issued from outside the package
      to subprograms declared in the visible part. The properties of such a
      variable are similar to those of a ``static'' variable of C.

8     4  The elaboration of the body of a subprogram explicitly declared in
      the visible part of a package is caused by the elaboration of the body
      of the package. Hence a call of such a subprogram by an outside program
      unit raises the exception Program_Error if the call takes place before
      the elaboration of the package_body (see 3.11).


                                  Examples

9     Example of a package body (see 7.1):

10    package body Rational_Numbers is

11       procedure Same_Denominator (X,Y : in out Rational) is
         begin
            --  reduces X and Y to the same denominator:
            ...
         end Same_Denominator;

12       function "="(X,Y : Rational) return Boolean is
            U : Rational := X;
            V : Rational := Y;
         begin
            Same_Denominator (U,V);
            return U.Numerator = V.Numerator;
         end "=";

13       function "/" (X,Y : Integer) return Rational is
         begin
            if Y > 0 then
               return (Numerator => X,  Denominator => Y);
            else
               return (Numerator => -X, Denominator => -Y);
            end if;
         end "/";

14       function "+" (X,Y : Rational) return Rational is ... end "+";
         function "-" (X,Y : Rational) return Rational is ... end "-";
         function "*" (X,Y : Rational) return Rational is ... end "*";
         function "/" (X,Y : Rational) return Rational is ... end "/";

15    end Rational_Numbers;


7.3 Private Types and Private Extensions


1     The declaration (in the visible part of a package) of a type as a
private type or private extension serves to separate the characteristics that
can be used directly by outside program units (that is, the logical
properties) from other characteristics whose direct use is confined to the
package (the details of the definition of the type itself). See 3.9.1 for an
overview of type extensions.


                                   Syntax

2     private_type_declaration ::= 
         type defining_identifier [discriminant_part
      ] is [[abstract] tagged] [limited] private;

3     private_extension_declaration ::= 
         type defining_identifier [discriminant_part] is
           [abstract] new ancestor_subtype_indication with private;


                               Legality Rules

4     A private_type_declaration or private_extension_declaration declares a
partial view of the type; such a declaration is allowed only as a
declarative_item of the visible part of a package, and it requires a
completion, which shall be a full_type_declaration that occurs as a
declarative_item of the private part of the package. The view of the type
declared by the full_type_declaration is called the full view. A generic
formal private type or a generic formal private extension is also a partial
view.

5     A type shall be completely defined before it is frozen (see 3.11.1 and
13.14). Thus, neither the declaration of a variable of a partial view of a
type, nor the creation by an allocator of an object of the partial view are
allowed before the full declaration of the type. Similarly, before the full
declaration, the name of the partial view cannot be used in a
generic_instantiation or in a representation item.

6     A private type is limited if its declaration includes the reserved word
limited; a private extension is limited if its ancestor type is limited. If
the partial view is nonlimited, then the full view shall be nonlimited. If a
tagged partial view is limited, then the full view shall be limited. On the
other hand, if an untagged partial view is limited, the full view may be
limited or nonlimited.

7     If the partial view is tagged, then the full view shall be tagged. On
the other hand, if the partial view is untagged, then the full view may be
tagged or untagged. In the case where the partial view is untagged and the
full view is tagged, no derivatives of the partial view are allowed within the
immediate scope of the partial view; derivatives of the full view are allowed.

8     The ancestor subtype of a private_extension_declaration is the subtype
defined by the ancestor_subtype_indication; the ancestor type shall be a
specific tagged type. The full view of a private extension shall be derived
(directly or indirectly) from the ancestor type. In addition to the places
where Legality Rules normally apply (see 12.3), the requirement that the
ancestor be specific applies also in the private part of an instance of a
generic unit.

9     If the declaration of a partial view includes a known_discriminant_part,
then the full_type_declaration shall have a fully conforming (explicit)
known_discriminant_part (see 6.3.1, ``Conformance Rules''). The ancestor
subtype may be unconstrained; the parent subtype of the full view is required
to be constrained (see 3.7).

10    If a private extension inherits known discriminants from the ancestor
subtype, then the full view shall also inherit its discriminants from the
ancestor subtype, and the parent subtype of the full view shall be constrained
if and only if the ancestor subtype is constrained.

11    If a partial view has unknown discriminants, then the
full_type_declaration may define a definite or an indefinite subtype, with or
without discriminants.

12    If a partial view has neither known nor unknown discriminants, then the
full_type_declaration shall define a definite subtype.

13    If the ancestor subtype of a private extension has constrained
discriminants, then the parent subtype of the full view shall impose a
statically matching constraint on those discriminants.


                              Static Semantics

14    A private_type_declaration declares a private type and its first
subtype. Similarly, a private_extension_declaration declares a private
extension and its first subtype.

15    A declaration of a partial view and the corresponding
full_type_declaration define two views of a single type. The declaration of a
partial view together with the visible part define the operations that are
available to outside program units; the declaration of the full view together
with the private part define other operations whose direct use is possible
only within the declarative region of the package itself. Moreover, within the
scope of the declaration of the full view, the characteristics of the type are
determined by the full view; in particular, within its scope, the full view
determines the classes that include the type, which components, entries, and
protected subprograms are visible, what attributes and other predefined
operations are allowed, and whether the first subtype is static. See 7.3.1.

16    A private extension inherits components (including discriminants unless
there is a new discriminant_part specified) and user-defined primitive
subprograms from its ancestor type, in the same way that a record extension
inherits components and user-defined primitive subprograms from its parent
type (see 3.4).


                              Dynamic Semantics

17    The elaboration of a private_type_declaration creates a partial view of
a type. The elaboration of a private_extension_declaration elaborates the
ancestor_subtype_indication, and creates a partial view of a type.

      NOTES

18    5  The partial view of a type as declared by a private_type_declaration
      is defined to be a composite view (in 3.2). The full view of the type
      might or might not be composite. A private extension is also composite,
      as is its full view.

19    6  Declaring a private type with an unknown_discriminant_part is a way
      of preventing clients from creating uninitialized objects of the type;
      they are then forced to initialize each object by calling some operation
      declared in the visible part of the package. If such a type is also
      limited, then no objects of the type can be declared outside the scope
      of the full_type_declaration, restricting all object creation to the
      package defining the type. This allows complete control over all storage
      allocation for the type. Objects of such a type can still be passed as
      parameters, however.

20    7  The ancestor type specified in a private_extension_declaration and
      the parent type specified in the corresponding declaration of a record
      extension given in the private part need not be the same - the parent
      type of the full view can be any descendant of the ancestor type. In
      this case, for a primitive subprogram that is inherited from the
      ancestor type and not overridden, the formal parameter names and default
      expressions (if any) come from the corresponding primitive subprogram of
      the specified ancestor type, while the body comes from the corresponding
      primitive subprogram of the parent type of the full view. See 3.9.2.


                                  Examples

21    Examples of private type declarations:

22    type Key is private;
      type File_Name is limited private;

23    Example of a private extension declaration:

24    type List is new Ada.Finalization.Controlled with private;


7.3.1 Private Operations


1     For a type declared in the visible part of a package or generic package,
certain operations on the type do not become visible until later in the
package - either in the private part or the body. Such private operations are
available only inside the declarative region of the package or generic
package.


                              Static Semantics

2     The predefined operators that exist for a given type are determined by
the classes to which the type belongs. For example, an integer type has a
predefined "+" operator. In most cases, the predefined operators of a type are
declared immediately after the definition of the type; the exceptions are
explained below. Inherited subprograms are also implicitly declared
immediately after the definition of the type, except as stated below.

3/1   For a composite type, the characteristics (see 7.3) of the type are
determined in part by the characteristics of its component types. At the place
where the composite type is declared, the only characteristics of component
types used are those characteristics visible at that place. If later
{immediately within the declarative region in which the composite type is
declared}[within the immediate scope of the composite type] additional
characteristics become visible for a component type, then any corresponding
characteristics become visible for the composite type. Any additional
predefined operators are implicitly declared at that place.

4/1   The corresponding rule applies to a type defined by a
derived_type_definition, if there is a place {immediately within the
declarative region in which the type is declared}[within its immediate scope]
where additional characteristics of its parent type become visible.

5/1   For example, an array type whose component type is limited private
becomes nonlimited if the full view of the component type is nonlimited and
visible at some later place {immediately within the declarative region in
which the array type is declared.}[within the immediate scope of the array
type.] In such a case, the predefined "=" operator is implicitly declared at
that place, and assignment is allowed after that place.

6/1   Inherited primitive subprograms follow a different rule. For a
derived_type_definition, each inherited primitive subprogram is implicitly
declared at the earliest place, if any, {immediately within the declarative
region in which}[within the immediate scope of] the type_declaration{ occurs},
but after the type_declaration, where the corresponding declaration from the
parent is visible. If there is no such place, then the inherited subprogram is
not declared at all. An inherited subprogram that is not declared at all
cannot be named in a call and cannot be overridden, but for a tagged type, it
is possible to dispatch to it.

7     For a private_extension_declaration, each inherited subprogram is
declared immediately after the private_extension_declaration if the
corresponding declaration from the ancestor is visible at that place.
Otherwise, the inherited subprogram is not declared for the private extension,
though it might be for the full type.

8     The Class attribute is defined for tagged subtypes in 3.9. In addition,
for every subtype S of an untagged private type whose full view is tagged, the
following attribute is defined:

9     S'Class Denotes the class-wide subtype corresponding to the full view of
              S. This attribute is allowed only from the beginning of the
              private part in which the full view is declared, until the
              declaration of the full view. After the full view, the Class
              attribute of the full view can be used.

      NOTES

10    8  Because a partial view and a full view are two different views of one
      and the same type, outside of the defining package the characteristics
      of the type are those defined by the visible part. Within these outside
      program units the type is just a private type or private extension, and
      any language rule that applies only to another class of types does not
      apply. The fact that the full declaration might implement a private type
      with a type of a particular class (for example, as an array type) is
      relevant only within the declarative region of the package itself
      including any child units.

11    The consequences of this actual implementation are, however, valid
      everywhere. For example: any default initialization of components takes
      place; the attribute Size provides the size of the full view;
      finalization is still done for controlled components of the full view;
      task dependence rules still apply to components that are task objects.

12    9  Partial views provide assignment (unless the view is limited),
      membership tests, selected components for the selection of discriminants
      and inherited components, qualification, and explicit conversion.

13    10  For a subtype S of a partial view, S'Size is defined (see 13.3). For
      an object A of a partial view, the attributes A'Size and A'Address are
      defined (see 13.3). The Position, First_Bit, and Last_Bit attributes are
      also defined for discriminants and inherited components.


                                  Examples

14    Example of a type with private operations:

15    package Key_Manager is
         type Key is private;
         Null_Key : constant Key; -- a deferred constant declaration (see 7.4)
         procedure Get_Key(K : out Key);
         function "<" (X, Y : Key) return Boolean;
      private
         type Key is new Natural;
         Null_Key : constant Key := Key'First;
      end Key_Manager;

16    package body Key_Manager is
         Last_Key : Key := Null_Key;
         procedure Get_Key(K : out Key) is
         begin
            Last_Key := Last_Key + 1;
            K := Last_Key;
         end Get_Key;

17       function "<" (X, Y : Key) return Boolean is
         begin
            return Natural(X) < Natural(Y);
         end "<";
      end Key_Manager;

      NOTES

18    11  Notes on the example: Outside of the package Key_Manager, the
      operations available for objects of type Key include assignment, the
      comparison for equality or inequality, the procedure Get_Key and the
      operator "<"; they do not include other relational operators such as
      ">=", or arithmetic operators.

19    The explicitly declared operator "<" hides the predefined operator "<"
      implicitly declared by the full_type_declaration. Within the body of the
      function, an explicit conversion of X and Y to the subtype Natural is
      necessary to invoke the "<" operator of the parent type. Alternatively,
      the result of the function could be written as not (X >= Y), since the
      operator ">=" is not redefined.

20    The value of the variable Last_Key, declared in the package body,
      remains unchanged between calls of the procedure Get_Key. (See also the
      NOTES of 7.2.)


7.4 Deferred Constants


1     Deferred constant declarations may be used to declare constants in the
visible part of a package, but with the value of the constant given in the
private part. They may also be used to declare constants imported from other
languages (see Annex B).


                               Legality Rules

2     A deferred constant declaration is an object_declaration with the
reserved word constant but no initialization expression. The constant declared
by a deferred constant declaration is called a deferred constant. A deferred
constant declaration requires a completion, which shall be a full constant
declaration (called the full declaration of the deferred constant), or a
pragma Import (see Annex B).

3     A deferred constant declaration that is completed by a full constant
declaration shall occur immediately within the visible part of a
package_specification. For this case, the following additional rules apply to
the corresponding full declaration:

4     The full declaration shall occur immediately within the private part of
      the same package;

5     The deferred and full constants shall have the same type;

6     If the subtype defined by the subtype_indication in the deferred
      declaration is constrained, then the subtype defined by the
      subtype_indication in the full declaration shall match it statically. On
      the other hand, if the subtype of the deferred constant is
      unconstrained, then the full declaration is still allowed to impose a
      constraint. The constant itself will be constrained, like all constants;

7     If the deferred constant declaration includes the reserved word aliased,
      then the full declaration shall also.

8     A deferred constant declaration that is completed by a pragma Import
need not appear in the visible part of a package_specification, and has no
full constant declaration.

9     The completion of a deferred constant declaration shall occur before the
constant is frozen (see 7.4).


                              Dynamic Semantics

10    The elaboration of a deferred constant declaration elaborates the
subtype_indication or (only allowed in the case of an imported constant) the
array_type_definition.

      NOTES

11    12  The full constant declaration for a deferred constant that is of a
      given private type or private extension is not allowed before the
      corresponding full_type_declaration. This is a consequence of the
      freezing rules for types (see 13.14).


                                  Examples

12    Examples of deferred constant declarations:

13    Null_Key : constant Key;      -- see 7.3.1

14    CPU_Identifier : constant String(1..8);
      pragma Import(Assembler, CPU_Identifier, Link_Name => "CPU_ID");
                                    -- see B.1


7.5 Limited Types


1     A limited type is (a view of) a type for which the assignment operation
is not allowed. A nonlimited type is a (view of a) type for which the
assignment operation is allowed.


                               Legality Rules

2     If a tagged record type has any limited components, then the reserved
word limited shall appear in its record_type_definition.


                              Static Semantics

3     A type is limited if it is a descendant of one of the following:

4     a type with the reserved word limited in its definition;

5     a task or protected type;

6     a composite type with a limited component.

7     Otherwise, the type is nonlimited.

8     There are no predefined equality operators for a limited type.

      NOTES

9     13  The following are consequences of the rules for limited types:

    10    An initialization expression is not allowed in an object_declaration
          if the type of the object is limited.

    11    A default expression is not allowed in a component_declaration if
          the type of the record component is limited.

    12    An initialized allocator is not allowed if the designated type is
          limited.

    13    A generic formal parameter of mode in must not be of a limited type.

14    14  Aggregates are not available for a limited composite type.
      Concatenation is not available for a limited array type.

15    15  The rules do not exclude a default_expression for a formal parameter
      of a limited type; they do not exclude a deferred constant of a limited
      type if the full declaration of the constant is of a nonlimited type.

16    16  As illustrated in 7.3.1, an untagged limited type can become
      nonlimited under certain circumstances.


                                  Examples

17    Example of a package with a limited type:

18    package IO_Package is
         type File_Name is limited private;

19       procedure Open (F : in out File_Name);
         procedure Close(F : in out File_Name);
         procedure Read (F : in File_Name; Item : out Integer);
         procedure Write(F : in File_Name; Item : in  Integer);
      private
         type File_Name is
            limited record
               Internal_Name : Integer := 0;
            end record;
      end IO_Package;

20    package body IO_Package is
         Limit : constant := 200;
         type File_Descriptor is record  ...  end record;
         Directory : array (1 .. Limit) of File_Descriptor;
         ...
         procedure Open (F : in out File_Name) is  ...  end;
         procedure Close(F : in out File_Name) is  ...  end;
         procedure Read (F : in File_Name; Item : out Integer) is ... end;
         procedure Write(F : in File_Name; Item : in  Integer) is ... end;
      begin
         ...
      end IO_Package;

      NOTES

21    17  Notes on the example: In the example above, an outside subprogram
      making use of IO_Package may obtain a file name by calling Open and
      later use it in calls to Read and Write. Thus, outside the package, a
      file name obtained from Open acts as a kind of password; its internal
      properties (such as containing a numeric value) are not known and no
      other operations (such as addition or comparison of internal names) can
      be performed on a file name. Most importantly, clients of the package
      cannot make copies of objects of type File_Name.

22    This example is characteristic of any case where complete control over
      the operations of a type is desired. Such packages serve a dual purpose.
      They prevent a user from making use of the internal structure of the
      type. They also implement the notion of an encapsulated data type where
      the only operations on the type are those given in the package
      specification.

23    The fact that the full view of File_Name is explicitly declared limited
      means that parameter passing and function return will always be by
      reference (see 6.2 and 6.5).


7.6 User-Defined Assignment and Finalization


1     Three kinds of actions are fundamental to the manipulation of objects:
initialization, finalization, and assignment. Every object is initialized,
either explicitly or by default, after being created (for example, by an
object_declaration or allocator). Every object is finalized before being
destroyed (for example, by leaving a subprogram_body containing an
object_declaration, or by a call to an instance of Unchecked_Deallocation). An
assignment operation is used as part of assignment_statements, explicit
initialization, parameter passing, and other operations.

2     Default definitions for these three fundamental operations are provided
by the language, but a controlled type gives the user additional control over
parts of these operations. In particular, the user can define, for a
controlled type, an Initialize procedure which is invoked immediately after
the normal default initialization of a controlled object, a Finalize procedure
which is invoked immediately before finalization of any of the components of a
controlled object, and an Adjust procedure which is invoked as the last step
of an assignment to a (nonlimited) controlled object.


                              Static Semantics

3     The following language-defined library package exists:

4/1   package Ada.Finalization is
          pragma Preelaborate(Finalization);{
          pragma Remote_Types(Finalization);}

5         type Controlled is abstract tagged private;

6         procedure Initialize  (Object : in out Controlled);
          procedure Adjust      (Object : in out Controlled);
          procedure Finalize    (Object : in out Controlled);

7         type Limited_Controlled is abstract tagged limited private;

8         procedure Initialize  (Object : in out Limited_Controlled);
          procedure Finalize    (Object : in out Limited_Controlled);
      private
          ... -- not specified by the language
      end Ada.Finalization;

9     A controlled type is a descendant of Controlled or Limited_Controlled.
The (default) implementations of Initialize, Adjust, and Finalize have no
effect. The predefined "=" operator of type Controlled always returns True,
since this operator is incorporated into the implementation of the predefined
equality operator of types derived from Controlled, as explained in 4.5.2. The
type Limited_Controlled is like Controlled, except that it is limited and it
lacks the primitive subprogram Adjust.


                              Dynamic Semantics

10    During the elaboration of an object_declaration, for every controlled
subcomponent of the object that is not assigned an initial value (as defined
in 3.3.1), Initialize is called on that subcomponent. Similarly, if the object
as a whole is controlled and is not assigned an initial value, Initialize is
called on the object. The same applies to the evaluation of an allocator, as
explained in 4.8.

11/1  For an extension_aggregate whose ancestor_part is a subtype_mark, {for
each controlled subcomponent of the ancestor part, either Initialize is
called, or its initial value is assigned, as appropriate}[Initialize is called
on all controlled subcomponents of the ancestor part]; if the type of the
ancestor part is itself controlled, the Initialize procedure of the ancestor
type is called, unless that Initialize procedure is abstract.

12    Initialize and other initialization operations are done in an arbitrary
order, except as follows. Initialize is applied to an object after
initialization of its subcomponents, if any (including both implicit
initialization and Initialize calls). If an object has a component with an
access discriminant constrained by a per-object expression, Initialize is
applied to this component after any components that do not have such
discriminants. For an object with several components with such a discriminant,
Initialize is applied to them in order of their component_declarations. For an
allocator, any task activations follow all calls on Initialize.

13    When a target object with any controlled parts is assigned a value,
either when created or in a subsequent assignment_statement, the assignment
operation proceeds as follows:

14    The value of the target becomes the assigned value.

15    The value of the target is adjusted.

16    To adjust the value of a (nonlimited) composite object, the values of
the components of the object are first adjusted in an arbitrary order, and
then, if the object is controlled, Adjust is called. Adjusting the value of an
elementary object has no effect, nor does adjusting the value of a composite
object with no controlled parts.

17    For an assignment_statement, after the name and expression have been
evaluated, and any conversion (including constraint checking) has been done,
an anonymous object is created, and the value is assigned into it; that is,
the assignment operation is applied. (Assignment includes value adjustment.)
The target of the assignment_statement is then finalized. The value of the
anonymous object is then assigned into the target of the assignment_statement.
Finally, the anonymous object is finalized. As explained below, the
implementation may eliminate the intermediate anonymous object, so this
description subsumes the one given in 5.2, ``Assignment Statements''.


                         Implementation Requirements

17.1/1 {For an aggregate of a controlled type whose value is assigned, other
than by an assignment_statement or a return_statement, the implementation
shall not create a separate anonymous object for the aggregate. The aggregate
value shall be constructed directly in the target of the assignment operation
and Adjust is not called on the target object.}


                         Implementation Permissions

18    An implementation is allowed to relax the above rules (for nonlimited
controlled types) in the following ways:

19    For an assignment_statement that assigns to an object the value of that
      same object, the implementation need not do anything.

20    For an assignment_statement for a noncontrolled type, the implementation
      may finalize and assign each component of the variable separately
      (rather than finalizing the entire variable and assigning the entire new
      value) unless a discriminant of the variable is changed by the
      assignment.

21    For an aggregate or function call whose value is assigned into a target
      object, the implementation need not create a separate anonymous object
      if it can safely create the value of the aggregate or function call
      directly in the target object. Similarly, for an assignment_statement,
      the implementation need not create an anonymous object if the value
      being assigned is the result of evaluating a name denoting an object
      (the source object) whose storage cannot overlap with the target. If the
      source object might overlap with the target object, then the
      implementation can avoid the need for an intermediary anonymous object
      by exercising one of the above permissions and perform the assignment
      one component at a time (for an overlapping array assignment), or not at
      all (for an assignment where the target and the source of the assignment
      are the same object). Even if an anonymous object is created, the
      implementation may move its value to the target object as part of the
      assignment without re-adjusting so long as the anonymous object has no
      aliased subcomponents.


7.6.1 Completion and Finalization


1     This subclause defines completion and leaving of the execution of
constructs and entities. A master is the execution of a construct that
includes finalization of local objects after it is complete (and after waiting
for any local tasks - see 9.3), but before leaving. Other constructs and
entities are left immediately upon completion.


                              Dynamic Semantics

2     The execution of a construct or entity is complete when the end of that
execution has been reached, or when a transfer of control (see 5.1) causes it
to be abandoned. Completion due to reaching the end of execution, or due to
the transfer of control of an exit_, return_, goto_, or requeue_statement or
of the selection of a terminate_alternative is normal completion. Completion
is abnormal otherwise - when control is transferred out of a construct due to
abort or the raising of an exception.

3     After execution of a construct or entity is complete, it is left,
meaning that execution continues with the next action, as defined for the
execution that is taking place. Leaving an execution happens immediately after
its completion, except in the case of a master: the execution of a task_body,
a block_statement, a subprogram_body, an entry_body, or an accept_statement. A
master is finalized after it is complete, and before it is left.

4     For the finalization of a master, dependent tasks are first awaited, as
explained in 9.3. Then each object whose accessibility level is the same as
that of the master is finalized if the object was successfully initialized and
still exists. These actions are performed whether the master is left by
reaching the last statement or via a transfer of control. When a transfer of
control causes completion of an execution, each included master is finalized
in order, from innermost outward.

5     For the finalization of an object:

6     If the object is of an elementary type, finalization has no effect;

7     If the object is of a controlled type, the Finalize procedure is called;

8     If the object is of a protected type, the actions defined in 9.4 are
      performed;

9     If the object is of a composite type, then after performing the above
      actions, if any, every component of the object is finalized in an
      arbitrary order, except as follows: if the object has a component with
      an access discriminant constrained by a per-object expression, this
      component is finalized before any components that do not have such
      discriminants; for an object with several components with such a
      discriminant, they are finalized in the reverse of the order of their
      component_declarations.

10    Immediately before an instance of Unchecked_Deallocation reclaims the
storage of an object, the object is finalized. If an instance of
Unchecked_Deallocation is never applied to an object created by an allocator,
the object will still exist when the corresponding master completes, and it
will be finalized then.

11    The order in which the finalization of a master performs finalization of
objects is as follows: Objects created by declarations in the master are
finalized in the reverse order of their creation. For objects that were
created by allocators for an access type whose ultimate ancestor is declared
in the master, this rule is applied as though each such object that still
exists had been created in an arbitrary order at the first freezing point (see
13.14) of the ultimate ancestor type.

12    The target of an assignment statement is finalized before copying in the
new value, as explained in 7.6.

13/1  {If the object_name in an object_renaming_declaration, or the actual
parameter for a generic formal in out parameter in a generic_instantiation,
denotes any part of an anonymous object created by a function call, the
anonymous object is not finalized until after it is no longer accessible via
any name. Otherwise, an}[The] anonymous object[s] created by {a }function
{call or}[calls and] by {an }aggregate{ is}[s are] finalized no later than the
end of the innermost enclosing declarative_item or statement; if that is a
compound_statement, {the object is}[they are] finalized before starting the
execution of any statement within the compound_statement.

13.1/1 {If a transfer of control or raising of an exception occurs prior to
performing a finalization of an anonymous object, the anonymous object is
finalized as part of the finalizations due to be performed for the object's
innermost enclosing master.}


                          Bounded (Run-Time) Errors

14/1  It is a bounded error for a call on Finalize or Adjust {that occurs as
part of object finalization or assignment }to propagate an exception. The
possible consequences depend on what action invoked the Finalize or Adjust
operation:

15    For a Finalize invoked as part of an assignment_statement, Program_Error
      is raised at that point.

16/1  {For an Adjust invoked as part of the initialization of a controlled
      object, other adjustments due to be performed might or might not be
      performed, and then Program_Error is raised. During its propagation,
      finalization might or might not be applied to objects whose Adjust
      failed.} For an Adjust invoked as part of an assignment
      {statement}[operation], any other adjustments due to be performed are
      performed, and then Program_Error is raised.

17    For a Finalize invoked as part of a call on an instance of
      Unchecked_Deallocation, any other finalizations due to be performed are
      performed, and then Program_Error is raised.

17.1/1 {For a Finalize invoked as part of the finalization of the anonymous
      object created by a function call or aggregate, any other finalizations
      due to be performed are performed, and then Program_Error is raised.}

17.2/1 {For a Finalize invoked due to reaching the end of the execution of a
      master, any other finalizations associated with the master are
      performed, and Program_Error is raised immediately after leaving the
      master.}

18    For a Finalize invoked by the transfer of control of an exit_, return_,
      goto_, or requeue_statement, Program_Error is raised no earlier than
      after the finalization of the master being finalized when the exception
      occurred, and no later than the point where normal execution would have
      continued. Any other finalizations due to be performed up to that point
      are performed before raising Program_Error.

19    For a Finalize invoked by a transfer of control that is due to raising
      an exception, any other finalizations due to be performed for the same
      master are performed; Program_Error is raised immediately after leaving
      the master.

20    For a Finalize invoked by a transfer of control due to an abort or
      selection of a terminate alternative, the exception is ignored; any
      other finalizations due to be performed are performed.

      NOTES

21    18  The rules of Section 10 imply that immediately prior to partition
      termination, Finalize operations are applied to library-level controlled
      objects (including those created by allocators of library-level access
      types, except those already finalized). This occurs after waiting for
      library-level tasks to terminate.

22    19  A constant is only constant between its initialization and
      finalization. Both initialization and finalization are allowed to change
      the value of a constant.

23    20  Abort is deferred during certain operations related to controlled
      types, as explained in 9.8. Those rules prevent an abort from causing a
      controlled object to be left in an ill-defined state.

24    21  The Finalize procedure is called upon finalization of a controlled
      object, even if Finalize was called earlier, either explicitly or as
      part of an assignment; hence, if a controlled type is visibly controlled
      (implying that its Finalize primitive is directly callable), or is
      nonlimited (implying that assignment is allowed), its Finalize procedure
      should be designed to have no ill effect if it is applied a second time
      to the same object.



                         Section 8: Visibility Rules


1     The rules defining the scope of declarations and the rules defining
which identifiers, character_literals, and operator_symbols are visible at (or
from) various places in the text of the program are described in this section.
The formulation of these rules uses the notion of a declarative region.

2     As explained in Section 3, a declaration declares a view of an entity
and associates a defining name with that view. The view comprises an
identification of the viewed entity, and possibly additional properties. A
usage name denotes a declaration. It also denotes the view declared by that
declaration, and denotes the entity of that view. Thus, two different usage
names might denote two different views of the same entity; in this case they
denote the same entity.


8.1 Declarative Region



                              Static Semantics

1     For each of the following constructs, there is a portion of the program
text called its declarative region, within which nested declarations can
occur:

2     any declaration, other than that of an enumeration type, that is not a
      completion of a previous declaration;

3     a block_statement;

4     a loop_statement;

5     an accept_statement;

6     an exception_handler.

7     The declarative region includes the text of the construct together with
additional text determined (recursively), as follows:

8     If a declaration is included, so is its completion, if any.

9     If the declaration of a library unit (including Standard - see 10.1.1)
      is included, so are the declarations of any child units (and their
      completions, by the previous rule). The child declarations occur after
      the declaration.

10    If a body_stub is included, so is the corresponding subunit.

11    If a type_declaration is included, then so is a corresponding
      record_representation_clause, if any.

12    The declarative region of a declaration is also called the declarative
region of any view or entity declared by the declaration.

13    A declaration occurs immediately within a declarative region if this
region is the innermost declarative region that encloses the declaration (the
immediately enclosing declarative region), not counting the declarative region
(if any) associated with the declaration itself.

14    A declaration is local to a declarative region if the declaration occurs
immediately within the declarative region. An entity is local to a declarative
region if the entity is declared by a declaration that is local to the
declarative region.

15    A declaration is global to a declarative region if the declaration
occurs immediately within another declarative region that encloses the
declarative region. An entity is global to a declarative region if the entity
is declared by a declaration that is global to the declarative region.

      NOTES

16    1  The children of a parent library unit are inside the parent's
      declarative region, even though they do not occur inside the parent's
      declaration or body. This implies that one can use (for example) "P.Q"
      to refer to a child of P whose defining name is Q, and that after "use
      P;" Q can refer (directly) to that child.

17    2  As explained above and in 10.1.1, ``
      Compilation Units - Library Units'', all library units are descendants
      of Standard, and so are contained in the declarative region of Standard.
      They are not inside the declaration or body of Standard, but they are
      inside its declarative region.

18    3  For a declarative region that comes in multiple parts, the text of
      the declarative region does not contain any text that might appear
      between the parts. Thus, when a portion of a declarative region is said
      to extend from one place to another in the declarative region, the
      portion does not contain any text that might appear between the parts of
      the declarative region.


8.2 Scope of Declarations


1     For each declaration, the language rules define a certain portion of the
program text called the scope of the declaration. The scope of a declaration
is also called the scope of any view or entity declared by the declaration.
Within the scope of an entity, and only there, there are places where it is
legal to refer to the declared entity. These places are defined by the rules
of visibility and overloading.


                              Static Semantics

2     The immediate scope of a declaration is a portion of the declarative
region immediately enclosing the declaration. The immediate scope starts at
the beginning of the declaration, except in the case of an overloadable
declaration, in which case the immediate scope starts just after the place
where the profile of the callable entity is determined (which is at the end of
the _specification for the callable entity, or at the end of the
generic_instantiation if an instance). The immediate scope extends to the end
of the declarative region, with the following exceptions:

3     The immediate scope of a library_item includes only its semantic
      dependents.

4     The immediate scope of a declaration in the private part of a library
      unit does not include the visible part of any public descendant of that
      library unit.

5     The visible part of (a view of) an entity is a portion of the text of
its declaration containing declarations that are visible from outside. The
private part of (a view of) an entity that has a visible part contains all
declarations within the declaration of (the view of) the entity, except those
in the visible part; these are not visible from outside. Visible and private
parts are defined only for these kinds of entities: callable entities, other
program units, and composite types.

6     The visible part of a view of a callable entity is its profile.

7     The visible part of a composite type other than a task or protected type
      consists of the declarations of all components declared (explicitly or
      implicitly) within the type_declaration.

8     The visible part of a generic unit includes the generic_formal_part. For
      a generic package, it also includes the first list of
      basic_declarative_items of the package_specification. For a generic
      subprogram, it also includes the profile.

9     The visible part of a package, task unit, or protected unit consists of
      declarations in the program unit's declaration other than those
      following the reserved word private, if any; see 7.1 and 12.7 for
      packages, 9.1 for task units, and 9.4 for protected units.

10    The scope of a declaration always contains the immediate scope of the
declaration. In addition, for a given declaration that occurs immediately
within the visible part of an outer declaration, or is a public child of an
outer declaration, the scope of the given declaration extends to the end of
the scope of the outer declaration, except that the scope of a library_item
includes only its semantic dependents.

11    The immediate scope of a declaration is also the immediate scope of the
entity or view declared by the declaration. Similarly, the scope of a
declaration is also the scope of the entity or view declared by the
declaration.

      NOTES

12    4  There are notations for denoting visible declarations that are not
      directly visible. For example, parameter_specifications are in the
      visible part of a subprogram_declaration so that they can be used in
      named-notation calls appearing outside the called subprogram. For
      another example, declarations of the visible part of a package can be
      denoted by expanded names appearing outside the package, and can be made
      directly visible by a use_clause.


8.3 Visibility


1     The visibility rules, given below, determine which declarations are
visible and directly visible at each place within a program. The visibility
rules apply to both explicit and implicit declarations.


                              Static Semantics

2     A declaration is defined to be directly visible at places where a name
consisting of only an identifier or operator_symbol is sufficient to denote
the declaration; that is, no selected_component notation or special context
(such as preceding => in a named association) is necessary to denote the
declaration. A declaration is defined to be visible wherever it is directly
visible, as well as at other places where some name (such as a
selected_component) can denote the declaration.

3     The syntactic category direct_name is used to indicate contexts where
direct visibility is required. The syntactic category selector_name is used to
indicate contexts where visibility, but not direct visibility, is required.

4     There are two kinds of direct visibility: immediate visibility and
use-visibility. A declaration is immediately visible at a place if it is
directly visible because the place is within its immediate scope. A
declaration is use-visible if it is directly visible because of a use_clause
(see 8.4). Both conditions can apply.

5     A declaration can be hidden, either from direct visibility, or from all
visibility, within certain parts of its scope. Where hidden from all
visibility, it is not visible at all (neither using a direct_name nor a
selector_name). Where hidden from direct visibility, only direct visibility is
lost; visibility using a selector_name is still possible.

6     Two or more declarations are overloaded if they all have the same
defining name and there is a place where they are all directly visible.

7     The declarations of callable entities (including enumeration literals)
are overloadable, meaning that overloading is allowed for them.

8     Two declarations are homographs if they have the same defining name,
and, if both are overloadable, their profiles are type conformant. An inner
declaration hides any outer homograph from direct visibility.

9/1   Two homographs are not generally allowed immediately within the same
declarative region unless one overrides the other (see Legality Rules below).
{The only declarations that are overridable are the implicit declarations for
predefined operators and inherited primitive subprograms.} A declaration
overrides another homograph that occurs immediately within the same
declarative region in the following cases:

10/1  {A declaration that is not overridable overrides one that is
      overridable}[An explicit declaration overrides an implicit declaration
      of a primitive subprogram], regardless of which declaration occurs
      first;

11    The implicit declaration of an inherited operator overrides that of a
      predefined operator;

12    An implicit declaration of an inherited subprogram overrides a previous
      implicit declaration of an inherited subprogram.

13    For an implicit declaration of a primitive subprogram in a generic unit,
      there is a copy of this declaration in an instance. However, a whole new
      set of primitive subprograms is implicitly declared for each type
      declared within the visible part of the instance. These new declarations
      occur immediately after the type declaration, and override the copied
      ones. The copied ones can be called only from within the instance; the
      new ones can be called only from outside the instance, although for
      tagged types, the body of a new one can be executed by a call to an old
      one.

14    A declaration is visible within its scope, except where hidden from all
visibility, as follows:

15    An overridden declaration is hidden from all visibility within the scope
      of the overriding declaration.

16    A declaration is hidden from all visibility until the end of the
      declaration, except:

    17    For a record type or record extension, the declaration is hidden
          from all visibility only until the reserved word record;

    18    For a package_declaration, task declaration, protected declaration,
          generic_package_declaration, or subprogram_body, the declaration is
          hidden from all visibility only until the reserved word is of the
          declaration.

19    If the completion of a declaration is a declaration, then within the
      scope of the completion, the first declaration is hidden from all
      visibility. Similarly, a discriminant_specification or parameter_-
      specification is hidden within the scope of a corresponding discriminant_-
      specification or parameter_specification of a corresponding completion,
      or of a corresponding accept_statement.

20    The declaration of a library unit (including a
      library_unit_renaming_declaration) is hidden from all visibility except
      at places that are within its declarative region or within the scope of
      a with_clause that mentions it. For each declaration or renaming of a
      generic unit as a child of some parent generic package, there is a
      corresponding declaration nested immediately within each instance of the
      parent. Such a nested declaration is hidden from all visibility except
      at places that are within the scope of a with_clause that mentions the
      child.

21    A declaration with a defining_identifier or defining_operator_symbol is
immediately visible (and hence directly visible) within its immediate scope
except where hidden from direct visibility, as follows:

22    A declaration is hidden from direct visibility within the immediate
      scope of a homograph of the declaration, if the homograph occurs within
      an inner declarative region;

23    A declaration is also hidden from direct visibility where hidden from
      all visibility.


                            Name Resolution Rules

24    A direct_name shall resolve to denote a directly visible declaration
whose defining name is the same as the direct_name. A selector_name shall
resolve to denote a visible declaration whose defining name is the same as the
selector_name.

25    These rules on visibility and direct visibility do not apply in a
context_clause, a parent_unit_name, or a pragma that appears at the place of a
compilation_unit. For those contexts, see the rules in 10.1.6, ``
Environment-Level Visibility Rules''.


                               Legality Rules

26/1  {A non-overridable}[An explicit] declaration is illegal if there is a
homograph occurring immediately within the same declarative region that is
visible at the place of the declaration, and is not hidden from all visibility
by the {non-overridable}[explicit] declaration. {In addition, a type extension
is illegal if somewhere within its immediate scope it has two visible
components with the same name.} Similarly, the context_clause for a subunit is
illegal if it mentions (in a with_clause) some library unit, and there is a
homograph of the library unit that is visible at the place of the
corresponding stub, and the homograph and the mentioned library unit are both
declared immediately within the same declarative region. These rules also
apply to dispatching operations declared in the visible part of an instance of
a generic unit. However, they do not apply to other overloadable declarations
in an instance; such declarations may have type conformant profiles in the
instance, so long as the corresponding declarations in the generic were not
type conformant.

      NOTES

27    5  Visibility for compilation units follows from the definition of the
      environment in 10.1.4, except that it is necessary to apply a
      with_clause to obtain visibility to a library_unit_declaration or
      library_unit_renaming_declaration.

28    6  In addition to the visibility rules given above, the meaning of the
      occurrence of a direct_name or selector_name at a given place in the
      text can depend on the overloading rules (see 8.6).

29    7  Not all contexts where an identifier, character_literal, or
      operator_symbol are allowed require visibility of a corresponding
      declaration. Contexts where visibility is not required are identified by
      using one of these three syntactic categories directly in a syntax rule,
      rather than using direct_name or selector_name.


8.4 Use Clauses


1     A use_package_clause achieves direct visibility of declarations that
appear in the visible part of a package; a use_type_clause achieves direct
visibility of the primitive operators of a type.


                                   Syntax

2     use_clause ::= use_package_clause | use_type_clause

3     use_package_clause ::= use package_name {, package_name};

4     use_type_clause ::= use type subtype_mark {, subtype_mark};


                               Legality Rules

5     A package_name of a use_package_clause shall denote a package.


                              Static Semantics

6     For each use_clause, there is a certain region of text called the scope
of the use_clause. For a use_clause within a context_clause of a
library_unit_declaration or library_unit_renaming_declaration, the scope is
the entire declarative region of the declaration. For a use_clause within a
context_clause of a body, the scope is the entire body and any subunits
(including multiply nested subunits). The scope does not include
context_clauses themselves.

7     For a use_clause immediately within a declarative region, the scope is
the portion of the declarative region starting just after the use_clause and
extending to the end of the declarative region. However, the scope of a
use_clause in the private part of a library unit does not include the visible
part of any public descendant of that library unit.

8     For each package denoted by a package_name of a use_package_clause whose
scope encloses a place, each declaration that occurs immediately within the
declarative region of the package is potentially use-visible at this place if
the declaration is visible at this place. For each type T or T'Class
determined by a subtype_mark of a use_type_clause whose scope encloses a
place, the declaration of each primitive operator of type T is potentially
use-visible at this place if its declaration is visible at this place.

9     A declaration is use-visible if it is potentially use-visible, except in
these naming-conflict cases:

10    A potentially use-visible declaration is not use-visible if the place
      considered is within the immediate scope of a homograph of the
      declaration.

11    Potentially use-visible declarations that have the same identifier are
      not use-visible unless each of them is an overloadable declaration.


                              Dynamic Semantics

12    The elaboration of a use_clause has no effect.


                                  Examples

13    Example of a use clause in a context clause:

14    with Ada.Calendar; use Ada;

15    Example of a use type clause:

16    use type Rational_Numbers.Rational; -- see 7.1
      Two_Thirds: Rational_Numbers.Rational := 2/3;


8.5 Renaming Declarations


1     A renaming_declaration declares another name for an entity, such as an
object, exception, package, subprogram, entry, or generic unit. Alternatively,
a subprogram_renaming_declaration can be the completion of a previous
subprogram_declaration.


                                   Syntax

2     renaming_declaration ::= 
            object_renaming_declaration
          | exception_renaming_declaration
          | package_renaming_declaration
          | subprogram_renaming_declaration
          | generic_renaming_declaration


                              Dynamic Semantics

3     The elaboration of a renaming_declaration evaluates the name that
follows the reserved word renames and thereby determines the view and entity
denoted by this name (the renamed view and renamed entity). A name that
denotes the renaming_declaration denotes (a new view of) the renamed entity.

      NOTES

4     8  Renaming may be used to resolve name conflicts and to act as a
      shorthand. Renaming with a different identifier or operator_symbol does
      not hide the old name; the new name and the old name need not be visible
      at the same places.

5     9  A task or protected object that is declared by an explicit
      object_declaration can be renamed as an object. However, a single task
      or protected object cannot be renamed since the corresponding type is
      anonymous (meaning it has no nameable subtypes). For similar reasons, an
      object of an anonymous array or access type cannot be renamed.

6     10  A subtype defined without any additional constraint can be used to
      achieve the effect of renaming another subtype (including a task or
      protected subtype) as in

7        subtype Mode is Ada.Text_IO.File_Mode;


8.5.1 Object Renaming Declarations


1     An object_renaming_declaration is used to rename an object.


                                   Syntax

2     object_renaming_declaration ::= defining_identifier : subtype_mark
       renames object_name;


                            Name Resolution Rules

3     The type of the object_name shall resolve to the type determined by the
subtype_mark.


                               Legality Rules

4     The renamed entity shall be an object.

5/1   The renamed entity shall not be a subcomponent that depends on
discriminants of a variable whose nominal subtype is unconstrained, unless
this subtype is indefinite, or the variable is aliased. A slice of an array
shall not be renamed if this restriction disallows renaming of the array. {In
addition to the places where Legality Rules normally apply, these rules apply
also in the private part of an instance of a generic unit. These rules also
apply for a renaming that appears in the body of a generic unit, with the
additional requirement that even if the nominal subtype of the variable is
indefinite, its type shall not be a descendant of an untagged generic formal
derived type.}


                              Static Semantics

6     An object_renaming_declaration declares a new view of the renamed object
whose properties are identical to those of the renamed view. Thus, the
properties of the renamed object are not affected by the renaming_declaration.
In particular, its value and whether or not it is a constant are unaffected;
similarly, the constraints that apply to an object are not affected by
renaming (any constraint implied by the subtype_mark of the
object_renaming_declaration is ignored).


                                  Examples

7     Example of renaming an object:

8     declare
         L : Person renames Leftmost_Person; -- see 3.10.1
      begin
         L.Age := L.Age + 1;
      end;


8.5.2 Exception Renaming Declarations


1     An exception_renaming_declaration is used to rename an exception.


                                   Syntax

2     exception_renaming_declaration ::= defining_identifier
       : exception renames exception_name;


                               Legality Rules

3     The renamed entity shall be an exception.


                              Static Semantics

4     An exception_renaming_declaration declares a new view of the renamed
exception.


                                  Examples

5     Example of renaming an exception:

6     EOF : exception renames Ada.IO_Exceptions.End_Error; -- see A.13


8.5.3 Package Renaming Declarations


1     A package_renaming_declaration is used to rename a package.


                                   Syntax

2     package_renaming_declaration ::= package defining_program_unit_name
       renames package_name;


                               Legality Rules

3     The renamed entity shall be a package.


                              Static Semantics

4     A package_renaming_declaration declares a new view of the renamed
package.


                                  Examples

5     Example of renaming a package:

6     package TM renames Table_Manager;


8.5.4 Subprogram Renaming Declarations


1     A subprogram_renaming_declaration can serve as the completion of a
subprogram_declaration; such a renaming_declaration is called a
renaming-as-body. A subprogram_renaming_declaration that is not a completion
is called a renaming-as-declaration, and is used to rename a subprogram
(possibly an enumeration literal) or an entry.


                                   Syntax

2     subprogram_renaming_declaration ::= subprogram_specification
       renames callable_entity_name;


                            Name Resolution Rules

3     The expected profile for the callable_entity_name is the profile given
in the subprogram_specification.


                               Legality Rules

4     The profile of a renaming-as-declaration shall be mode-conformant with
that of the renamed callable entity.

5/1   The profile of a renaming-as-body [shall be subtype-conformant with that
of the renamed callable entity, and ]shall conform fully to that of the
declaration it completes. If the renaming-as-body completes that declaration
before the subprogram it declares is frozen, {the profile shall be
mode-conformant with that of the renamed callable entity and }the subprogram
it declares takes its convention from the renamed subprogram; otherwise{, the
profile shall be subtype-conformant with that of the renamed callable entity
and} the convention of the renamed subprogram shall not be Intrinsic. {A
renaming-as-body is illegal if the declaration occurs before the subprogram
whose declaration it completes is frozen, and the renaming renames the
subprogram itself, through one or more subprogram renaming declarations, none
of whose subprograms has been frozen.}

6     A name that denotes a formal parameter of the subprogram_specification
is not allowed within the callable_entity_name.


                              Static Semantics

7     A renaming-as-declaration declares a new view of the renamed entity. The
profile of this new view takes its subtypes, parameter modes, and calling
convention from the original profile of the callable entity, while taking the
formal parameter names and default_expressions from the profile given in the
subprogram_renaming_declaration. The new view is a function or procedure,
never an entry.


                              Dynamic Semantics

7.1/1 {For a call to a subprogram whose body is given as a renaming-as-body,
the execution of the renaming-as-body is equivalent to the execution of a
subprogram_body that simply calls the renamed subprogram with its formal
parameters as the actual parameters and, if it is a function, returns the
value of the call.}

8     For a call on a renaming of a dispatching subprogram that is overridden,
if the overriding occurred before the renaming, then the body executed is that
of the overriding declaration, even if the overriding declaration is not
visible at the place of the renaming; otherwise, the inherited or predefined
subprogram is called.


                          Bounded (Run-Time) Errors

8.1/1 {If a subprogram directly or indirectly renames itself, then it is a
bounded error to call that subprogram. Possible consequences are that
Program_Error or Storage_Error is raised, or that the call results in infinite
recursion.}

      NOTES

9     11  A procedure can only be renamed as a procedure. A function whose
      defining_designator is either an identifier or an operator_symbol can be
      renamed with either an identifier or an operator_symbol; for renaming as
      an operator, the subprogram specification given in the
      renaming_declaration is subject to the rules given in 6.6 for operator
      declarations. Enumeration literals can be renamed as functions;
      similarly, attribute_references that denote functions (such as
      references to Succ and Pred) can be renamed as functions. An entry can
      only be renamed as a procedure; the new name is only allowed to appear
      in contexts that allow a procedure name. An entry of a family can be
      renamed, but an entry family cannot be renamed as a whole.

10    12  The operators of the root numeric types cannot be renamed because
      the types in the profile are anonymous, so the corresponding
      specifications cannot be written; the same holds for certain attributes,
      such as Pos.

11    13  Calls with the new name of a renamed entry are
      procedure_call_statements and are not allowed at places where the syntax
      requires an entry_call_statement in conditional_ and timed_entry_calls,
      nor in an asynchronous_select; similarly, the Count attribute is not
      available for the new name.

12    14  The primitiveness of a renaming-as-declaration is determined by its
      profile, and by where it occurs, as for any declaration of (a view of) a
      subprogram; primitiveness is not determined by the renamed view. In
      order to perform a dispatching call, the subprogram name has to denote a
      primitive subprogram, not a non-primitive renaming of a primitive
      subprogram.


                                  Examples

13    Examples of subprogram renaming declarations:

14    procedure My_Write(C : in Character) renames Pool(K).Write; --  see 4.1.3

15    function Real_Plus(Left, Right : Real   ) return Real    renames "+";
      function Int_Plus (Left, Right : Integer) return Integer renames "+";

16    function Rouge return Color renames Red;  --  see 3.5.1
      function Rot   return Color renames Red;
      function Rosso return Color renames Rouge;

17    function Next(X : Color) return Color renames Color'Succ; -- see 3.5.1

18    Example of a subprogram renaming declaration with new parameter names:

19    function "*" (X,Y : Vector) return Real renames Dot_Product; -- see 6.1

20    Example of a subprogram renaming declaration with a new default
expression:

21    function Minimum(L : Link := Head) return Cell renames Min_Cell; -- see 6.1


8.5.5 Generic Renaming Declarations


1     A generic_renaming_declaration is used to rename a generic unit.


                                   Syntax

2     generic_renaming_declaration ::= 
          generic package       defining_program_unit_name
       renames generic_package_name;
        | generic procedure     defining_program_unit_name
       renames generic_procedure_name;
        | generic function      defining_program_unit_name
       renames generic_function_name;


                               Legality Rules

3     The renamed entity shall be a generic unit of the corresponding kind.


                              Static Semantics

4     A generic_renaming_declaration declares a new view of the renamed
generic unit.

      NOTES

5     15  Although the properties of the new view are the same as those of the
      renamed view, the place where the generic_renaming_declaration occurs
      may affect the legality of subsequent renamings and instantiations that
      denote the generic_renaming_declaration, in particular if the renamed
      generic unit is a library unit (see 10.1.1).


                                  Examples

6     Example of renaming a generic unit:

7     generic package Enum_IO renames Ada.Text_IO.Enumeration_IO;  -- see A.10.10


8.6 The Context of Overload Resolution


1     Because declarations can be overloaded, it is possible for an occurrence
of a usage name to have more than one possible interpretation; in most cases,
ambiguity is disallowed. This clause describes how the possible
interpretations resolve to the actual interpretation.

2     Certain rules of the language (the Name Resolution Rules) are considered
``overloading rules''. If a possible interpretation violates an overloading
rule, it is assumed not to be the intended interpretation; some other possible
interpretation is assumed to be the actual interpretation. On the other hand,
violations of non-overloading rules do not affect which interpretation is
chosen; instead, they cause the construct to be illegal. To be legal, there
usually has to be exactly one acceptable interpretation of a construct that is
a ``complete context'', not counting any nested complete contexts.

3     The syntax rules of the language and the visibility rules given in 8.3
determine the possible interpretations. Most type checking rules (rules that
require a particular type, or a particular class of types, for example) are
overloading rules. Various rules for the matching of formal and actual
parameters are overloading rules.


                            Name Resolution Rules

4     Overload resolution is applied separately to each complete context, not
counting inner complete contexts. Each of the following constructs is a
complete context:

5     A context_item.

6     A declarative_item or declaration.

7     A statement.

8     A pragma_argument_association.

9     The expression of a case_statement.

10    An (overall) interpretation of a complete context embodies its meaning,
and includes the following information about the constituents of the complete
context, not including constituents of inner complete contexts:

11    for each constituent of the complete context, to which syntactic
      categories it belongs, and by which syntax rules; and

12    for each usage name, which declaration it denotes (and, therefore, which
      view and which entity it denotes); and

13    for a complete context that is a declarative_item, whether or not it is
      a completion of a declaration, and (if so) which declaration it
      completes.

14    A possible interpretation is one that obeys the syntax rules and the
visibility rules. An acceptable interpretation is a possible interpretation
that obeys the overloading rules, that is, those rules that specify an
expected type or expected profile, or specify how a construct shall resolve or
be interpreted.

15    The interpretation of a constituent of a complete context is determined
from the overall interpretation of the complete context as a whole. Thus, for
example, ``interpreted as a function_call,'' means that the construct's
interpretation says that it belongs to the syntactic category function_call.

16    Each occurrence of a usage name denotes the declaration determined by
its interpretation. It also denotes the view declared by its denoted
declaration, except in the following cases:

17    If a usage name appears within the declarative region of a
      type_declaration and denotes that same type_declaration, then it denotes
      the current instance of the type (rather than the type itself). The
      current instance of a type is the object or value of the type that is
      associated with the execution that evaluates the usage name.

18    If a usage name appears within the declarative region of a
      generic_declaration (but not within its generic_formal_part) and it
      denotes that same generic_declaration, then it denotes the current
      instance of the generic unit (rather than the generic unit itself). See
      also 12.3.

19    A usage name that denotes a view also denotes the entity of that view.

20    The expected type for a given expression, name, or other construct
determines, according to the type resolution rules given below, the types
considered for the construct during overload resolution. The type resolution
rules provide support for class-wide programming, universal numeric literals,
dispatching operations, and anonymous access types:

21    If a construct is expected to be of any type in a class of types, or of
      the universal or class-wide type for a class, then the type of the
      construct shall resolve to a type in that class or to a universal type
      that covers the class.

22    If the expected type for a construct is a specific type T, then the type
      of the construct shall resolve either to T, or:

        23    to T'Class; or

        24    to a universal type that covers T; or

        25    when T is an anonymous access type (see 3.10) with designated
              type D, to an access-to-variable type whose designated type is
              D'Class or is covered by D.

26    In certain contexts, such as in a subprogram_renaming_declaration, the
Name Resolution Rules define an expected profile for a given name; in such
cases, the name shall resolve to the name of a callable entity whose profile
is type conformant with the expected profile.


                               Legality Rules

27    When the expected type for a construct is required to be a single type
in a given class, the type expected for the construct shall be determinable
solely from the context in which the construct appears, excluding the
construct itself, but using the requirement that it be in the given class; the
type of the construct is then this single expected type. Furthermore, the
context shall not be one that expects any type in some class that contains
types of the given class; in particular, the construct shall not be the
operand of a type_conversion.

28    A complete context shall have at least one acceptable interpretation; if
there is exactly one, then that one is chosen.

29    There is a preference for the primitive operators (and ranges) of the
root numeric types root_integer and root_real. In particular, if two
acceptable interpretations of a constituent of a complete context differ only
in that one is for a primitive operator (or range) of the type root_integer or
root_real, and the other is not, the interpretation using the primitive
operator (or range) of the root numeric type is preferred.

30    For a complete context, if there is exactly one overall acceptable
interpretation where each constituent's interpretation is the same as or
preferred (in the above sense) over those in all other overall acceptable
interpretations, then that one overall acceptable interpretation is chosen.
Otherwise, the complete context is ambiguous.

31    A complete context other than a pragma_argument_association shall not be
ambiguous.

32    A complete context that is a pragma_argument_association is allowed to
be ambiguous (unless otherwise specified for the particular pragma), but only
if every acceptable interpretation of the pragma argument is as a name that
statically denotes a callable entity. Such a name denotes all of the
declarations determined by its interpretations, and all of the views declared
by these declarations.

      NOTES

33    16  If a usage name has only one acceptable interpretation, then it
      denotes the corresponding entity. However, this does not mean that the
      usage name is necessarily legal since other requirements exist which are
      not considered for overload resolution; for example, the fact that an
      expression is static, whether an object is constant, mode and subtype
      conformance rules, freezing rules, order of elaboration, and so on.

34    Similarly, subtypes are not considered for overload resolution (the
      violation of a constraint does not make a program illegal but raises an
      exception during program execution).



                    Section 9: Tasks and Synchronization


1     The execution of an Ada program consists of the execution of one or more
tasks. Each task represents a separate thread of control that proceeds
independently and concurrently between the points where it interacts with
other tasks. The various forms of task interaction are described in this
section, and include:

2     the activation and termination of a task;

3     a call on a protected subprogram of a protected object, providing
      exclusive read-write access, or concurrent read-only access to shared
      data;

4     a call on an entry, either of another task, allowing for synchronous
      communication with that task, or of a protected object, allowing for
      asynchronous communication with one or more other tasks using that same
      protected object;

5     a timed operation, including a simple delay statement, a timed entry
      call or accept, or a timed asynchronous select statement (see next item);

6     an asynchronous transfer of control as part of an asynchronous select
      statement, where a task stops what it is doing and begins execution at a
      different point in response to the completion of an entry call or the
      expiration of a delay;

7     an abort statement, allowing one task to cause the termination of
      another task.

8     In addition, tasks can communicate indirectly by reading and updating
(unprotected) shared variables, presuming the access is properly synchronized
through some other kind of task interaction.


                              Static Semantics

9     The properties of a task are defined by a corresponding task declaration
and task_body, which together define a program unit called a task unit.


                              Dynamic Semantics

10    Over time, tasks proceed through various states. A task is initially
inactive; upon activation, and prior to its termination it is either blocked
(as part of some task interaction) or ready to run. While ready, a task
competes for the available execution resources that it requires to run.

      NOTES

11    1  Concurrent task execution may be implemented on multicomputers,
      multiprocessors, or with interleaved execution on a single physical
      processor. On the other hand, whenever an implementation can determine
      that the required semantic effects can be achieved when parts of the
      execution of a given task are performed by different physical processors
      acting in parallel, it may choose to perform them in this way.


9.1 Task Units and Task Objects


1     A task unit is declared by a task declaration, which has a corresponding
task_body. A task declaration may be a task_type_declaration, in which case it
declares a named task type; alternatively, it may be a
single_task_declaration, in which case it defines an anonymous task type, as
well as declaring a named task object of that type.


                                   Syntax

2     task_type_declaration ::= 
         task type defining_identifier [known_discriminant_part
      ] [is task_definition];

3     single_task_declaration ::= 
         task defining_identifier [is task_definition];

4     task_definition ::= 
           {task_item}
        [ private
           {task_item}]
        end [task_identifier]

5/1   task_item ::= entry_declaration | {aspect_clause
      }[representation_clause]

6     task_body ::= 
         task body defining_identifier is
           declarative_part
         begin
           handled_sequence_of_statements
         end [task_identifier];

7     If a task_identifier appears at the end of a task_definition or
      task_body, it shall repeat the defining_identifier.


                               Legality Rules

8     A task declaration requires a completion, which shall be a task_body,
and every task_body shall be the completion of some task declaration.


                              Static Semantics

9     A task_definition defines a task type and its first subtype. The first
list of task_items of a task_definition, together with the known_discriminant_-
part, if any, is called the visible part of the task unit. The optional list
of task_items after the reserved word private is called the private part of
the task unit.

9.1/1 {For a task declaration without a task_definition, a task_definition
without task_items is assumed.}


                              Dynamic Semantics

10    The elaboration of a task declaration elaborates the task_definition.
The elaboration of a single_task_declaration also creates an object of an
(anonymous) task type.

11    The elaboration of a task_definition creates the task type and its first
subtype; it also includes the elaboration of the entry_declarations in the
given order.

12/1  As part of the initialization of a task object, any
{aspect_clauses}[representation_clauses] and any per-object constraints
associated with entry_declarations of the corresponding task_definition are
elaborated in the given order.

13    The elaboration of a task_body has no effect other than to establish
that tasks of the type can from then on be activated without failing the
Elaboration_Check.

14    The execution of a task_body is invoked by the activation of a task of
the corresponding type (see 9.2).

15    The content of a task object of a given task type includes:

16    The values of the discriminants of the task object, if any;

17    An entry queue for each entry of the task object;

18    A representation of the state of the associated task.

      NOTES

19    2  Within the declaration or body of a task unit, the name of the task
      unit denotes the current instance of the unit (see 8.6), rather than the
      first subtype of the corresponding task type (and thus the name cannot
      be used as a subtype_mark).

20    3  The notation of a selected_component can be used to denote a
      discriminant of a task (see 4.1.3). Within a task unit, the name of a
      discriminant of the task type denotes the corresponding discriminant of
      the current instance of the unit.

21    4  A task type is a limited type (see 7.5), and hence has neither an
      assignment operation nor predefined equality operators. If an
      application needs to store and exchange task identities, it can do so by
      defining an access type designating the corresponding task objects and
      by using access values for identification purposes. Assignment is
      available for such an access type as for any access type. Alternatively,
      if the implementation supports the Systems Programming Annex, the
      Identity attribute can be used for task identification (see C.7).


                                  Examples

22    Examples of declarations of task types:

23    task type Server is
         entry Next_Work_Item(WI : in Work_Item);
         entry Shut_Down;
      end Server;

24    task type Keyboard_Driver(ID : Keyboard_ID := New_ID) is
         entry Read (C : out Character);
         entry Write(C : in  Character);
      end Keyboard_Driver;

25    Examples of declarations of single tasks:

26    task Controller is
         entry Request(Level)(D : Item);  --  a family of entries
      end Controller;

27    task Parser is
         entry Next_Lexeme(L : in  Lexical_Element);
         entry Next_Action(A : out Parser_Action);
      end;

28    task User;  --  has no entries

29    Examples of task objects:

30    Agent    : Server;
      Teletype : Keyboard_Driver(TTY_ID);
      Pool     : array(1 .. 10) of Keyboard_Driver;

31    Example of access type designating task objects:

32    type Keyboard is access Keyboard_Driver;
      Terminal : Keyboard := new Keyboard_Driver(Term_ID);


9.2 Task Execution - Task Activation



                              Dynamic Semantics

1     The execution of a task of a given task type consists of the execution
of the corresponding task_body. The initial part of this execution is called
the activation of the task; it consists of the elaboration of the
declarative_part of the task_body. Should an exception be propagated by the
elaboration of its declarative_part, the activation of the task is defined to
have failed, and it becomes a completed task.

2     A task object (which represents one task) can be created either as part
of the elaboration of an object_declaration occurring immediately within some
declarative region, or as part of the evaluation of an allocator. All tasks
created by the elaboration of object_declarations of a single declarative
region (including subcomponents of the declared objects) are activated
together. Similarly, all tasks created by the evaluation of a single allocator
are activated together. The activation of a task is associated with the
innermost allocator or object_declaration that is responsible for its
creation.

3     For tasks created by the elaboration of object_declarations of a given
declarative region, the activations are initiated within the context of the
handled_sequence_of_statements (and its associated exception_handlers if any -
see 11.2), just prior to executing the statements of the _sequence. For a
package without an explicit body or an explicit
handled_sequence_of_statements, an implicit body or an implicit null_statement
is assumed, as defined in 7.2.

4     For tasks created by the evaluation of an allocator, the activations are
initiated as the last step of evaluating the allocator, after completing any
initialization for the object created by the allocator, and prior to returning
the new access value.

5     The task that created the new tasks and initiated their activations (the
activator) is blocked until all of these activations complete (successfully or
not). Once all of these activations are complete, if the activation of any of
the tasks has failed (due to the propagation of an exception), Tasking_Error
is raised in the activator, at the place at which it initiated the
activations. Otherwise, the activator proceeds with its execution normally.
Any tasks that are aborted prior to completing their activation are ignored
when determining whether to raise Tasking_Error.

6     Should the task that created the new tasks never reach the point where
it would initiate the activations (due to an abort or the raising of an
exception), the newly created tasks become terminated and are never activated.

      NOTES

7     5  An entry of a task can be called before the task has been activated.

8     6  If several tasks are activated together, the execution of any of
      these tasks need not await the end of the activation of the other tasks.

9     7  A task can become completed during its activation either because of
      an exception or because it is aborted (see 9.8).


                                  Examples

10    Example of task activation:

11    procedure P is
         A, B : Server;    --  elaborate the task objects A, B
         C    : Server;    --  elaborate the task object C
      begin
         --  the tasks A, B, C are activated together before the first statement
         ...
      end;


9.3 Task Dependence - Termination of Tasks



                              Dynamic Semantics

1     Each task (other than an environment task - see 10.2) depends on one or
more masters (see 7.6.1), as follows:

2     If the task is created by the evaluation of an allocator for a given
      access type, it depends on each master that includes the elaboration of
      the declaration of the ultimate ancestor of the given access type.

3     If the task is created by the elaboration of an object_declaration, it
      depends on each master that includes this elaboration.

4     Furthermore, if a task depends on a given master, it is defined to
depend on the task that executes the master, and (recursively) on any master
of that task.

5     A task is said to be completed when the execution of its corresponding
task_body is completed. A task is said to be terminated when any finalization
of the task_body has been performed (see 7.6.1). The first step of finalizing
a master (including a task_body) is to wait for the termination of any tasks
dependent on the master. The task executing the master is blocked until all
the dependents have terminated. Any remaining finalization is then performed
and the master is left.

6/1   Completion of a task (and the corresponding task_body) can occur when
the task is blocked at a select_statement with an [an ]open
terminate_alternative (see 9.7.1); the open terminate_alternative is selected
if and only if the following conditions are satisfied:

7     The task depends on some completed master;

8     Each task that depends on the master considered is either already
      terminated or similarly blocked at a select_statement with an open
      terminate_alternative.

9     When both conditions are satisfied, the task considered becomes
completed, together with all tasks that depend on the master considered that
are not yet completed.

      NOTES

10    8  The full view of a limited private type can be a task type, or can
      have subcomponents of a task type. Creation of an object of such a type
      creates dependences according to the full type.

11    9  An object_renaming_declaration defines a new view of an existing
      entity and hence creates no further dependence.

12    10  The rules given for the collective completion of a group of tasks
      all blocked on select_statements with open terminate_alternatives ensure
      that the collective completion can occur only when there are no
      remaining active tasks that could call one of the tasks being
      collectively completed.

13    11  If two or more tasks are blocked on select_statements with open
      terminate_alternatives, and become completed collectively, their
      finalization actions proceed concurrently.

14    12  The completion of a task can occur due to any of the following:

    15    the raising of an exception during the elaboration of the
          declarative_part of the corresponding task_body;

    16    the completion of the handled_sequence_of_statements of the
          corresponding task_body;

    17    the selection of an open terminate_alternative of a select_statement
          in the corresponding task_body;

    18    the abort of the task.


                                  Examples

19    Example of task dependence:

20    declare
         type Global is access Server;        --  see 9.1
         A, B : Server;
         G    : Global;
      begin
         --  activation of A and B
         declare
            type Local is access Server;
            X : Global := new Server;  --  activation of X.all
            L : Local  := new Server;  --  activation of L.all
            C : Server;
         begin
            --  activation of C
            G := X;  --  both G and X designate the same task object
            ...
         end;  --  await termination of C and L.all (but not X.all)
         ...
      end;  --  await termination of A, B, and G.all


9.4 Protected Units and Protected Objects


1     A protected object provides coordinated access to shared data, through
calls on its visible protected operations, which can be protected subprograms
or protected entries. A protected unit is declared by a protected declaration,
which has a corresponding protected_body. A protected declaration may be a
protected_type_declaration, in which case it declares a named protected type;
alternatively, it may be a single_protected_declaration, in which case it
defines an anonymous protected type, as well as declaring a named protected
object of that type.


                                   Syntax

2     protected_type_declaration ::= 
        protected type defining_identifier [known_discriminant_part
      ] is protected_definition;

3     single_protected_declaration ::= 
        protected defining_identifier is protected_definition;

4     protected_definition ::= 
          { protected_operation_declaration }
      [ private
          { protected_element_declaration } ]
        end [protected_identifier]

5/1   protected_operation_declaration ::= subprogram_declaration
           | entry_declaration
           | {aspect_clause}[representation_clause]

6     protected_element_declaration ::= protected_operation_declaration
           | component_declaration

7     protected_body ::= 
        protected body defining_identifier is
         { protected_operation_item }
        end [protected_identifier];

8/1   protected_operation_item ::= subprogram_declaration
           | subprogram_body
           | entry_body
           | {aspect_clause}[representation_clause]

9     If a protected_identifier appears at the end of a protected_definition
      or protected_body, it shall repeat the defining_identifier.


                               Legality Rules

10    A protected declaration requires a completion, which shall be a
protected_body, and every protected_body shall be the completion of some
protected declaration.


                              Static Semantics

11    A protected_definition defines a protected type and its first subtype.
The list of protected_operation_declarations of a protected_definition,
together with the known_discriminant_part, if any, is called the visible part
of the protected unit. The optional list of protected_element_declarations
after the reserved word private is called the private part of the protected
unit.


                              Dynamic Semantics

12    The elaboration of a protected declaration elaborates the
protected_definition. The elaboration of a single_protected_declaration also
creates an object of an (anonymous) protected type.

13    The elaboration of a protected_definition creates the protected type and
its first subtype; it also includes the elaboration of the
component_declarations and protected_operation_declarations in the given order.

14    As part of the initialization of a protected object, any per-object
constraints (see 3.8) are elaborated.

15    The elaboration of a protected_body has no other effect than to
establish that protected operations of the type can from then on be called
without failing the Elaboration_Check.

16    The content of an object of a given protected type includes:

17    The values of the components of the protected object, including
      (implicitly) an entry queue for each entry declared for the protected
      object;

18    A representation of the state of the execution resource associated with
      the protected object (one such resource is associated with each
      protected object).

19    The execution resource associated with a protected object has to be
acquired to read or update any components of the protected object; it can be
acquired (as part of a protected action - see 9.5.1) either for concurrent
read-only access, or for exclusive read-write access.

20    As the first step of the finalization of a protected object, each call
remaining on any entry queue of the object is removed from its queue and
Program_Error is raised at the place of the corresponding
entry_call_statement.

      NOTES

21    13  Within the declaration or body of a protected unit, the name of the
      protected unit denotes the current instance of the unit (see 8.6),
      rather than the first subtype of the corresponding protected type (and
      thus the name cannot be used as a subtype_mark).

22    14  A selected_component can be used to denote a discriminant of a
      protected object (see 4.1.3). Within a protected unit, the name of a
      discriminant of the protected type denotes the corresponding
      discriminant of the current instance of the unit.

23    15  A protected type is a limited type (see 7.5), and hence has neither
      an assignment operation nor predefined equality operators.

24    16  The bodies of the protected operations given in the protected_body
      define the actions that take place upon calls to the protected
      operations.

25    17  The declarations in the private part are only visible within the
      private part and the body of the protected unit.


                                  Examples

26    Example of declaration of protected type and corresponding body:

27    protected type Resource is
         entry Seize;
         procedure Release;
      private
         Busy : Boolean := False;
      end Resource;

28    protected body Resource is
         entry Seize when not Busy is
         begin
            Busy := True;
         end Seize;

29       procedure Release is
         begin
            Busy := False;
         end Release;
      end Resource;

30    Example of a single protected declaration and corresponding body:

31    protected Shared_Array is
         --  Index, Item, and Item_Array are global types
         function  Component    (N : in Index) return Item;
         procedure Set_Component(N : in Index; E : in  Item);
      private
         Table : Item_Array(Index) := (others => Null_Item);
      end Shared_Array;

32    protected body Shared_Array is
         function Component(N : in Index) return Item is
         begin
            return Table(N);
         end Component;

33       procedure Set_Component(N : in Index; E : in Item) is
         begin
            Table(N) := E;
         end Set_Component;
      end Shared_Array;

34    Examples of protected objects:

35    Control  : Resource;
      Flags    : array(1 .. 100) of Resource;


9.5 Intertask Communication


1     The primary means for intertask communication is provided by calls on
entries and protected subprograms. Calls on protected subprograms allow
coordinated access to shared data objects. Entry calls allow for blocking the
caller until a given condition is satisfied (namely, that the corresponding
entry is open - see 9.5.3), and then communicating data or control information
directly with another task or indirectly via a shared protected object.


                              Static Semantics

2     Any call on an entry or on a protected subprogram identifies a target
object for the operation, which is either a task (for an entry call) or a
protected object (for an entry call or a protected subprogram call). The
target object is considered an implicit parameter to the operation, and is
determined by the operation name (or prefix) used in the call on the
operation, as follows:

3     If it is a direct_name or expanded name that denotes the declaration (or
      body) of the operation, then the target object is implicitly specified
      to be the current instance of the task or protected unit immediately
      enclosing the operation; such a call is defined to be an internal call;

4     If it is a selected_component that is not an expanded name, then the
      target object is explicitly specified to be the task or protected object
      denoted by the prefix of the name; such a call is defined to be an
      external call;

5     If the name or prefix is a dereference (implicit or explicit) of an
      access-to-protected-subprogram value, then the target object is
      determined by the prefix of the Access attribute_reference that produced
      the access value originally, and the call is defined to be an external
      call;

6     If the name or prefix denotes a subprogram_renaming_declaration, then
      the target object is as determined by the name of the renamed entity.

7     A corresponding definition of target object applies to a
requeue_statement (see 9.5.4), with a corresponding distinction between an
internal requeue and an external requeue.


                              Dynamic Semantics

8     Within the body of a protected operation, the current instance (see
8.6) of the immediately enclosing protected unit is determined by the target
object specified (implicitly or explicitly) in the call (or requeue) on the
protected operation.

9     Any call on a protected procedure or entry of a target protected object
is defined to be an update to the object, as is a requeue on such an entry.


9.5.1 Protected Subprograms and Protected Actions


1     A protected subprogram is a subprogram declared immediately within a
protected_definition. Protected procedures provide exclusive read-write access
to the data of a protected object; protected functions provide concurrent
read-only access to the data.


                              Static Semantics

2     Within the body of a protected function (or a function declared
immediately within a protected_body), the current instance of the enclosing
protected unit is defined to be a constant (that is, its subcomponents may be
read but not updated). Within the body of a protected procedure (or a
procedure declared immediately within a protected_body), and within an
entry_body, the current instance is defined to be a variable (updating is
permitted).


                              Dynamic Semantics

3     For the execution of a call on a protected subprogram, the evaluation of
the name or prefix and of the parameter associations, and any assigning back
of in out or out parameters, proceeds as for a normal subprogram call (see
6.4). If the call is an internal call (see 9.5), the body of the subprogram is
executed as for a normal subprogram call. If the call is an external call,
then the body of the subprogram is executed as part of a new protected action
on the target protected object; the protected action completes after the body
of the subprogram is executed. A protected action can also be started by an
entry call (see 9.5.3).

4     A new protected action is not started on a protected object while
another protected action on the same protected object is underway, unless both
actions are the result of a call on a protected function. This rule is
expressible in terms of the execution resource associated with the protected
object:

5     Starting a protected action on a protected object corresponds to
      acquiring the execution resource associated with the protected object,
      either for concurrent read-only access if the protected action is for a
      call on a protected function, or for exclusive read-write access
      otherwise;

6     Completing the protected action corresponds to releasing the associated
      execution resource.

7     After performing an operation on a protected object other than a call on
a protected function, but prior to completing the associated protected action,
the entry queues (if any) of the protected object are serviced (see 9.5.3).


                          Bounded (Run-Time) Errors

8     During a protected action, it is a bounded error to invoke an operation
that is potentially blocking. The following are defined to be potentially
blocking operations:

9     a select_statement;

10    an accept_statement;

11    an entry_call_statement;

12    a delay_statement;

13    an abort_statement;

14    task creation or activation;

15    an external call on a protected subprogram (or an external requeue) with
      the same target object as that of the protected action;

16    a call on a subprogram whose body contains a potentially blocking
      operation.

17    If the bounded error is detected, Program_Error is raised. If not
detected, the bounded error might result in deadlock or a (nested) protected
action on the same target object.

18    Certain language-defined subprograms are potentially blocking. In
particular, the subprograms of the language-defined input-output packages that
manipulate files (implicitly or explicitly) are potentially blocking. Other
potentially blocking subprograms are identified where they are defined. When
not specified as potentially blocking, a language-defined subprogram is
nonblocking.

      NOTES

19    18  If two tasks both try to start a protected action on a protected
      object, and at most one is calling a protected function, then only one
      of the tasks can proceed. Although the other task cannot proceed, it is
      not considered blocked, and it might be consuming processing resources
      while it awaits its turn. There is no language-defined ordering or
      queuing presumed for tasks competing to start a protected action - on a
      multiprocessor such tasks might use busy-waiting; for monoprocessor
      considerations, see D.3, ``Priority Ceiling Locking''.

20    19  The body of a protected unit may contain declarations and bodies for
      local subprograms. These are not visible outside the protected unit.

21    20  The body of a protected function can contain internal calls on other
      protected functions, but not protected procedures, because the current
      instance is a constant. On the other hand, the body of a protected
      procedure can contain internal calls on both protected functions and
      procedures.

22    21  From within a protected action, an internal call on a protected
      subprogram, or an external call on a protected subprogram with a
      different target object is not considered a potentially blocking
      operation.


                                  Examples

23    Examples of protected subprogram calls (see 9.4):

24    Shared_Array.Set_Component(N, E);
      E := Shared_Array.Component(M);
      Control.Release;


9.5.2 Entries and Accept Statements


1     Entry_declarations, with the corresponding entry_bodies or
accept_statements, are used to define potentially queued operations on tasks
and protected objects.


                                   Syntax

2     entry_declaration ::= 
         entry defining_identifier [(discrete_subtype_definition
      )] parameter_profile;

3     accept_statement ::= 
         accept entry_direct_name [(entry_index)] parameter_profile [do
           handled_sequence_of_statements
         end [entry_identifier]];

4     entry_index ::= expression

5     entry_body ::= 
        entry defining_identifier  entry_body_formal_part  entry_barrier is
          declarative_part
        begin
          handled_sequence_of_statements
        end [entry_identifier];

6     entry_body_formal_part ::= [(entry_index_specification
      )] parameter_profile

7     entry_barrier ::= when condition

8     entry_index_specification ::= for defining_identifier
       in discrete_subtype_definition

9     If an entry_identifier appears at the end of an accept_statement, it
      shall repeat the entry_direct_name. If an entry_identifier appears at
      the end of an entry_body, it shall repeat the defining_identifier.

10    An entry_declaration is allowed only in a protected or task declaration.


                            Name Resolution Rules

11    In an accept_statement, the expected profile for the entry_direct_name
is that of the entry_declaration; the expected type for an entry_index is that
of the subtype defined by the discrete_subtype_definition of the corresponding
entry_declaration.

12    Within the handled_sequence_of_statements of an accept_statement, if a
selected_component has a prefix that denotes the corresponding
entry_declaration, then the entity denoted by the prefix is the accept_-
statement, and the selected_component is interpreted as an expanded name (see
4.1.3); the selector_name of the selected_component has to be the identifier
for some formal parameter of the accept_statement.


                               Legality Rules

13    An entry_declaration in a task declaration shall not contain a
specification for an access parameter (see 3.10).

14    For an accept_statement, the innermost enclosing body shall be a
task_body, and the entry_direct_name shall denote an entry_declaration in the
corresponding task declaration; the profile of the accept_statement shall
conform fully to that of the corresponding entry_declaration. An accept_-
statement shall have a parenthesized entry_index if and only if the
corresponding entry_declaration has a discrete_subtype_definition.

15    An accept_statement shall not be within another accept_statement that
corresponds to the same entry_declaration, nor within an asynchronous_select
inner to the enclosing task_body.

16    An entry_declaration of a protected unit requires a completion, which
shall be an entry_body, and every entry_body shall be the completion of an
entry_declaration of a protected unit. The profile of the entry_body shall
conform fully to that of the corresponding declaration.

17    An entry_body_formal_part shall have an entry_index_specification if and
only if the corresponding entry_declaration has a discrete_subtype_definition.
In this case, the discrete_subtype_definitions of the entry_declaration and
the entry_index_specification shall fully conform to one another (see 6.3.1).

18    A name that denotes a formal parameter of an entry_body is not allowed
within the entry_barrier of the entry_body.


                              Static Semantics

19    The parameter modes defined for parameters in the parameter_profile of
an entry_declaration are the same as for a subprogram_declaration and have the
same meaning (see 6.2).

20    An entry_declaration with a discrete_subtype_definition (see 3.6)
declares a family of distinct entries having the same profile, with one such
entry for each value of the entry index subtype defined by the discrete_-
subtype_definition. A name for an entry of a family takes the form of an
indexed_component, where the prefix denotes the entry_declaration for the
family, and the index value identifies the entry within the family. The term
single entry is used to refer to any entry other than an entry of an entry
family.

21    In the entry_body for an entry family, the entry_index_specification
declares a named constant whose subtype is the entry index subtype defined by
the corresponding entry_declaration; the value of the named entry index
identifies which entry of the family was called.


                              Dynamic Semantics

22/1  {The elaboration of an entry_declaration for an entry family consists of
the elaboration of the discrete_subtype_definition, as described in 3.8.}[For
the elaboration of an entry_declaration for an entry family, if the discrete_-
subtype_definition contains no per-object expressions (see 3.8), then the
discrete_subtype_definition is elaborated. Otherwise, the elaboration of the
entry_declaration consists of the evaluation of any expression of the discrete_-
subtype_definition that is not a per-object expression (or part of one).] The
elaboration of an entry_declaration for a single entry has no effect.

23    The actions to be performed when an entry is called are specified by the
corresponding accept_statements (if any) for an entry of a task unit, and by
the corresponding entry_body for an entry of a protected unit.

24    For the execution of an accept_statement, the entry_index, if any, is
first evaluated and converted to the entry index subtype; this index value
identifies which entry of the family is to be accepted. Further execution of
the accept_statement is then blocked until a caller of the corresponding entry
is selected (see 9.5.3), whereupon the handled_sequence_of_statements, if any,
of the accept_statement is executed, with the formal parameters associated
with the corresponding actual parameters of the selected entry call. Upon
completion of the handled_sequence_of_statements, the accept_statement
completes and is left. When an exception is propagated from the
handled_sequence_of_statements of an accept_statement, the same exception is
also raised by the execution of the corresponding entry_call_statement.

25    The above interaction between a calling task and an accepting task is
called a rendezvous. After a rendezvous, the two tasks continue their
execution independently.

26    An entry_body is executed when the condition of the entry_barrier
evaluates to True and a caller of the corresponding single entry, or entry of
the corresponding entry family, has been selected (see 9.5.3). For the
execution of the entry_body, the declarative_part of the entry_body is
elaborated, and the handled_sequence_of_statements of the body is executed, as
for the execution of a subprogram_body. The value of the named entry index, if
any, is determined by the value of the entry index specified in the entry_name
of the selected entry call (or intermediate requeue_statement - see 9.5.4).

      NOTES

27    22  A task entry has corresponding accept_statements (zero or more),
      whereas a protected entry has a corresponding entry_body (exactly one).

28    23  A consequence of the rule regarding the allowed placements of
      accept_statements is that a task can execute accept_statements only for
      its own entries.

29    24  A return_statement (see 6.5) or a requeue_statement (see 9.5.4) may
      be used to complete the execution of an accept_statement or an
      entry_body.

30    25  The condition in the entry_barrier may reference anything visible
      except the formal parameters of the entry. This includes the entry index
      (if any), the components (including discriminants) of the protected
      object, the Count attribute of an entry of that protected object, and
      data global to the protected unit.

31    The restriction against referencing the formal parameters within an
      entry_barrier ensures that all calls of the same entry see the same
      barrier value. If it is necessary to look at the parameters of an entry
      call before deciding whether to handle it, the entry_barrier can be `
      `when True'' and the caller can be requeued (on some private entry) when
      its parameters indicate that it cannot be handled immediately.


                                  Examples

32    Examples of entry declarations:

33    entry Read(V : out Item);
      entry Seize;
      entry Request(Level)(D : Item);  --  a family of entries

34    Examples of accept statements:

35    accept Shut_Down;

36    accept Read(V : out Item) do
         V := Local_Item;
      end Read;

37    accept Request(Low)(D : Item) do
         ...
      end Request;


9.5.3 Entry Calls


1     An entry_call_statement (an entry call) can appear in various contexts.
A simple entry call is a stand-alone statement that represents an
unconditional call on an entry of a target task or a protected object. Entry
calls can also appear as part of select_statements (see 9.7).


                                   Syntax

2     entry_call_statement ::= entry_name [actual_parameter_part];


                            Name Resolution Rules

3     The entry_name given in an entry_call_statement shall resolve to denote
an entry. The rules for parameter associations are the same as for subprogram
calls (see 6.4 and 6.4.1).


                              Static Semantics

4     The entry_name of an entry_call_statement specifies (explicitly or
implicitly) the target object of the call, the entry or entry family, and the
entry index, if any (see 9.5).


                              Dynamic Semantics

5     Under certain circumstances (detailed below), an entry of a task or
protected object is checked to see whether it is open or closed:

6     An entry of a task is open if the task is blocked on an accept_statement
      that corresponds to the entry (see 9.5.2), or on a selective_accept (see
      9.7.1) with an open accept_alternative that corresponds to the entry;
      otherwise it is closed.

7     An entry of a protected object is open if the condition of the
      entry_barrier of the corresponding entry_body evaluates to True;
      otherwise it is closed. If the evaluation of the condition propagates an
      exception, the exception Program_Error is propagated to all current
      callers of all entries of the protected object.

8     For the execution of an entry_call_statement, evaluation of the name and
of the parameter associations is as for a subprogram call (see 6.4). The entry
call is then issued: For a call on an entry of a protected object, a new
protected action is started on the object (see 9.5.1). The named entry is
checked to see if it is open; if open, the entry call is said to be selected
immediately, and the execution of the call proceeds as follows:

9     For a call on an open entry of a task, the accepting task becomes ready
      and continues the execution of the corresponding accept_statement (see
      9.5.2).

10    For a call on an open entry of a protected object, the corresponding
      entry_body is executed (see 9.5.2) as part of the protected action.

11    If the accept_statement or entry_body completes other than by a requeue
(see 9.5.4), return is made to the caller (after servicing the entry queues -
see below); any necessary assigning back of formal to actual parameters
occurs, as for a subprogram call (see 6.4.1); such assignments take place
outside of any protected action.

12    If the named entry is closed, the entry call is added to an entry queue
(as part of the protected action, for a call on a protected entry), and the
call remains queued until it is selected or cancelled; there is a separate
(logical) entry queue for each entry of a given task or protected object
(including each entry of an entry family).

13    When a queued call is selected, it is removed from its entry queue.
Selecting a queued call from a particular entry queue is called servicing the
entry queue. An entry with queued calls can be serviced under the following
circumstances:

14    When the associated task reaches a corresponding accept_statement, or a
      selective_accept with a corresponding open accept_alternative;

15    If after performing, as part of a protected action on the associated
      protected object, an operation on the object other than a call on a
      protected function, the entry is checked and found to be open.

16    If there is at least one call on a queue corresponding to an open entry,
then one such call is selected according to the entry queuing policy in effect
(see below), and the corresponding accept_statement or entry_body is executed
as above for an entry call that is selected immediately.

17    The entry queuing policy controls selection among queued calls both for
task and protected entry queues. The default entry queuing policy is to select
calls on a given entry queue in order of arrival. If calls from two or more
queues are simultaneously eligible for selection, the default entry queuing
policy does not specify which queue is serviced first. Other entry queuing
policies can be specified by pragmas (see D.4).

18    For a protected object, the above servicing of entry queues continues
until there are no open entries with queued calls, at which point the
protected action completes.

19    For an entry call that is added to a queue, and that is not the
triggering_statement of an asynchronous_select (see 9.7.4), the calling task
is blocked until the call is cancelled, or the call is selected and a
corresponding accept_statement or entry_body completes without requeuing. In
addition, the calling task is blocked during a rendezvous.

20    An attempt can be made to cancel an entry call upon an abort (see 9.8)
and as part of certain forms of select_statement (see 9.7.2, 9.7.3, and
9.7.4). The cancellation does not take place until a point (if any) when the
call is on some entry queue, and not protected from cancellation as part of a
requeue (see 9.5.4); at such a point, the call is removed from the entry queue
and the call completes due to the cancellation. The cancellation of a call on
an entry of a protected object is a protected action, and as such cannot take
place while any other protected action is occurring on the protected object.
Like any protected action, it includes servicing of the entry queues (in case
some entry barrier depends on a Count attribute).

21    A call on an entry of a task that has already completed its execution
raises the exception Tasking_Error at the point of the call; similarly, this
exception is raised at the point of the call if the called task completes its
execution or becomes abnormal before accepting the call or completing the
rendezvous (see 9.8). This applies equally to a simple entry call and to an
entry call as part of a select_statement.


                         Implementation Permissions

22    An implementation may perform the sequence of steps of a protected
action using any thread of control; it need not be that of the task that
started the protected action. If an entry_body completes without requeuing,
then the corresponding calling task may be made ready without waiting for the
entire protected action to complete.

23    When the entry of a protected object is checked to see whether it is
open, the implementation need not reevaluate the condition of the
corresponding entry_barrier if no variable or attribute referenced by the
condition (directly or indirectly) has been altered by the execution (or
cancellation) of a protected procedure or entry call on the object since the
condition was last evaluated.

24    An implementation may evaluate the conditions of all entry_barriers of a
given protected object any time any entry of the object is checked to see if
it is open.

25    When an attempt is made to cancel an entry call, the implementation need
not make the attempt using the thread of control of the task (or interrupt)
that initiated the cancellation; in particular, it may use the thread of
control of the caller itself to attempt the cancellation, even if this might
allow the entry call to be selected in the interim.

      NOTES

26    26  If an exception is raised during the execution of an entry_body, it
      is propagated to the corresponding caller (see 11.4).

27    27  For a call on a protected entry, the entry is checked to see if it
      is open prior to queuing the call, and again thereafter if its Count
      attribute (see 9.9) is referenced in some entry barrier.

28    28  In addition to simple entry calls, the language permits timed,
      conditional, and asynchronous entry calls (see 9.7.2, 9.7.3, and see
      9.7.4).

29    29  The condition of an entry_barrier is allowed to be evaluated by an
      implementation more often than strictly necessary, even if the
      evaluation might have side effects. On the other hand, an implementation
      need not reevaluate the condition if nothing it references was updated
      by an intervening protected action on the protected object, even if the
      condition references some global variable that might have been updated
      by an action performed from outside of a protected action.


                                  Examples

30    Examples of entry calls:

31    Agent.Shut_Down;                      --  see 9.1
      Parser.Next_Lexeme(E);                --  see 9.1
      Pool(5).Read(Next_Char);              --  see 9.1
      Controller.Request(Low)(Some_Item);   --  see 9.1
      Flags(3).Seize;                       --  see 9.4


9.5.4 Requeue Statements


1     A requeue_statement can be used to complete an accept_statement or
entry_body, while redirecting the corresponding entry call to a new (or the
same) entry queue. Such a requeue can be performed with or without allowing an
intermediate cancellation of the call, due to an abort or the expiration of a
delay.


                                   Syntax

2     requeue_statement ::= requeue entry_name [with abort];


                            Name Resolution Rules

3     The entry_name of a requeue_statement shall resolve to denote an entry
(the target entry) that either has no parameters, or that has a profile that
is type conformant (see 6.3.1) with the profile of the innermost enclosing
entry_body or accept_statement.


                               Legality Rules

4     A requeue_statement shall be within a callable construct that is either
an entry_body or an accept_statement, and this construct shall be the
innermost enclosing body or callable construct.

5     If the target entry has parameters, then its profile shall be subtype
conformant with the profile of the innermost enclosing callable construct.

6     In a requeue_statement of an accept_statement of some task unit, either
the target object shall be a part of a formal parameter of the
accept_statement, or the accessibility level of the target object shall not be
equal to or statically deeper than any enclosing accept_statement of the task
unit. In a requeue_statement of an entry_body of some protected unit, either
the target object shall be a part of a formal parameter of the entry_body, or
the accessibility level of the target object shall not be statically deeper
than that of the entry_declaration.


                              Dynamic Semantics

7     The execution of a requeue_statement proceeds by first evaluating the
entry_name, including the prefix identifying the target task or protected
object and the expression identifying the entry within an entry family, if
any. The entry_body or accept_statement enclosing the requeue_statement is
then completed, finalized, and left (see 7.6.1).

8     For the execution of a requeue on an entry of a target task, after
leaving the enclosing callable construct, the named entry is checked to see if
it is open and the requeued call is either selected immediately or queued, as
for a normal entry call (see 9.5.3).

9     For the execution of a requeue on an entry of a target protected object,
after leaving the enclosing callable construct:

10    if the requeue is an internal requeue (that is, the requeue is back on
      an entry of the same protected object - see 9.5), the call is added to
      the queue of the named entry and the ongoing protected action continues
      (see 9.5.1);

11    if the requeue is an external requeue (that is, the target protected
      object is not implicitly the same as the current object - see 9.5), a
      protected action is started on the target object and proceeds as for a
      normal entry call (see 9.5.3).

12    If the new entry named in the requeue_statement has formal parameters,
then during the execution of the accept_statement or entry_body corresponding
to the new entry, the formal parameters denote the same objects as did the
corresponding formal parameters of the callable construct completed by the
requeue. In any case, no parameters are specified in a requeue_statement; any
parameter passing is implicit.

13    If the requeue_statement includes the reserved words with abort (it is a
requeue-with-abort), then:

14    if the original entry call has been aborted (see 9.8), then the requeue
      acts as an abort completion point for the call, and the call is
      cancelled and no requeue is performed;

15    if the original entry call was timed (or conditional), then the original
      expiration time is the expiration time for the requeued call.

16    If the reserved words with abort do not appear, then the call remains
protected against cancellation while queued as the result of the
requeue_statement.

      NOTES

17    30  A requeue is permitted from a single entry to an entry of an entry
      family, or vice-versa. The entry index, if any, plays no part in the
      subtype conformance check between the profiles of the two entries; an
      entry index is part of the entry_name for an entry of a family.


                                  Examples

18    Examples of requeue statements:

19    requeue Request(Medium) with abort;
                          -- requeue on a member of an entry family of the current task, see 9.1

20    requeue Flags(I).Seize;
                          -- requeue on an entry of an array component, see 9.4


9.6 Delay Statements, Duration, and Time


1     A delay_statement is used to block further execution until a specified
expiration time is reached. The expiration time can be specified either as a
particular point in time (in a delay_until_statement), or in seconds from the
current time (in a delay_relative_statement). The language-defined package
Calendar provides definitions for a type Time and associated operations,
including a function Clock that returns the current time.


                                   Syntax

2     delay_statement ::= delay_until_statement | delay_relative_statement

3     delay_until_statement ::= delay until delay_expression;

4     delay_relative_statement ::= delay delay_expression;


                            Name Resolution Rules

5     The expected type for the delay_expression in a delay_relative_statement
is the predefined type Duration. The delay_expression in a
delay_until_statement is expected to be of any nonlimited type.


                               Legality Rules

6     There can be multiple time bases, each with a corresponding clock, and a
corresponding time type. The type of the delay_expression in a
delay_until_statement shall be a time type - either the type Time defined in
the language-defined package Calendar (see below), or some other
implementation-defined time type (see D.8).


                              Static Semantics

7     There is a predefined fixed point type named Duration, declared in the
visible part of package Standard; a value of type Duration is used to
represent the length of an interval of time, expressed in seconds. The type
Duration is not specific to a particular time base, but can be used with any
time base.

8     A value of the type Time in package Calendar, or of some other
implementation-defined time type, represents a time as reported by a
corresponding clock.

9     The following language-defined library package exists:

10    
      package Ada.Calendar is
        type Time is private;

11      subtype Year_Number  is Integer range 1901 .. 2099;
        subtype Month_Number is Integer range 1 .. 12;
        subtype Day_Number   is Integer range 1 .. 31;
        subtype Day_Duration is Duration range 0.0 .. 86_400.0;

12      function Clock return Time;

13      function Year   (Date : Time) return Year_Number;
        function Month  (Date : Time) return Month_Number;
        function Day    (Date : Time) return Day_Number;
        function Seconds(Date : Time) return Day_Duration;

14      procedure Split (Date  : in Time;
                         Year    : out Year_Number;
                         Month   : out Month_Number;
                         Day     : out Day_Number;
                         Seconds : out Day_Duration);

15      function Time_Of(Year  : Year_Number;
                         Month   : Month_Number;
                         Day     : Day_Number;
                         Seconds : Day_Duration := 0.0)
         return Time;

16      function "+" (Left : Time;   Right : Duration) return Time;
        function "+" (Left : Duration; Right : Time) return Time;
        function "-" (Left : Time;   Right : Duration) return Time;
        function "-" (Left : Time;   Right : Time) return Duration;

17      function "<" (Left, Right : Time) return Boolean;
        function "<="(Left, Right : Time) return Boolean;
        function ">" (Left, Right : Time) return Boolean;
        function ">="(Left, Right : Time) return Boolean;

18      Time_Error : exception;

19    private
         ... -- not specified by the language
      end Ada.Calendar;


                              Dynamic Semantics

20    For the execution of a delay_statement, the delay_expression is first
evaluated. For a delay_until_statement, the expiration time for the delay is
the value of the delay_expression, in the time base associated with the type
of the expression. For a delay_relative_statement, the expiration time is
defined as the current time, in the time base associated with relative delays,
plus the value of the delay_expression converted to the type Duration, and
then rounded up to the next clock tick. The time base associated with relative
delays is as defined in D.9, ``Delay Accuracy'' or is implementation defined.

21    The task executing a delay_statement is blocked until the expiration
time is reached, at which point it becomes ready again. If the expiration time
has already passed, the task is not blocked.

22    If an attempt is made to cancel the delay_statement (as part of an
asynchronous_select or abort - see 9.7.4 and 9.8), the _statement is cancelled
if the expiration time has not yet passed, thereby completing the
delay_statement.

23    The time base associated with the type Time of package Calendar is
implementation defined. The function Clock of package Calendar returns a value
representing the current time for this time base. The implementation-defined
value of the named number System.Tick (see 13.7) is an approximation of the
length of the real-time interval during which the value of Calendar.Clock
remains constant.

24    The functions Year, Month, Day, and Seconds return the corresponding
values for a given value of the type Time, as appropriate to an
implementation-defined timezone; the procedure Split returns all four
corresponding values. Conversely, the function Time_Of combines a year number,
a month number, a day number, and a duration, into a value of type Time. The
operators "+" and "-" for addition and subtraction of times and durations, and
the relational operators for times, have the conventional meaning.

25    If Time_Of is called with a seconds value of 86_400.0, the value
returned is equal to the value of Time_Of for the next day with a seconds
value of 0.0. The value returned by the function Seconds or through the
Seconds parameter of the procedure Split is always less than 86_400.0.

26/1  The exception Time_Error is raised by the function Time_Of if the actual
parameters do not form a proper date. This exception is also raised by the
operators "+" and "-" if the result is not representable in the type Time or
Duration, as appropriate. This exception is also raised by the function{s}
Year{, Month, Day, and Seconds and}[or] the procedure Split if the year number
of the given date is outside of the range of the subtype Year_Number.


                         Implementation Requirements

27    The implementation of the type Duration shall allow representation of
time intervals (both positive and negative) up to at least 86400 seconds (one
day); Duration'Small shall not be greater than twenty milliseconds. The
implementation of the type Time shall allow representation of all dates with
year numbers in the range of Year_Number; it may allow representation of other
dates as well (both earlier and later).


                         Implementation Permissions

28    An implementation may define additional time types (see D.8).

29    An implementation may raise Time_Error if the value of a
delay_expression in a delay_until_statement of a select_statement represents a
time more than 90 days past the current time. The actual limit, if any, is
implementation-defined.


                            Implementation Advice

30    Whenever possible in an implementation, the value of Duration'Small
should be no greater than 100 microseconds.

31    The time base for delay_relative_statements should be monotonic; it need
not be the same time base as used for Calendar.Clock.

      NOTES

32    31  A delay_relative_statement with a negative value of the
      delay_expression is equivalent to one with a zero value.

33    32  A delay_statement may be executed by the environment task;
      consequently delay_statements may be executed as part of the elaboration
      of a library_item or the execution of the main subprogram. Such
      statements delay the environment task (see 10.2).

34    33  A delay_statement is an abort completion point and a potentially
      blocking operation, even if the task is not actually blocked.

35    34  There is no necessary relationship between System.Tick (the
      resolution of the clock of package Calendar) and Duration'Small (the
      small of type Duration).

36    35  Additional requirements associated with delay_statements are given
      in D.9, ``Delay Accuracy''.


                                  Examples

37    Example of a relative delay statement:

38    delay 3.0;  -- delay 3.0 seconds

39    Example of a periodic task:

40    declare
         use Ada.Calendar;
         Next_Time : Time := Clock + Period;
                            -- Period is a global constant of type Duration
      begin
         loop               -- repeated every Period seconds
            delay until Next_Time;
            ... -- perform some actions
            Next_Time := Next_Time + Period;
         end loop;
      end;


9.7 Select Statements


1     There are four forms of the select_statement. One form provides a
selective wait for one or more select_alternatives. Two provide timed and
conditional entry calls. The fourth provides asynchronous transfer of control.


                                   Syntax

2     select_statement ::= 
         selective_accept
        | timed_entry_call
        | conditional_entry_call
        | asynchronous_select


                                  Examples

3     Example of a select statement:

4     select
         accept Driver_Awake_Signal;
      or
         delay 30.0*Seconds;
         Stop_The_Train;
      end select;


9.7.1 Selective Accept


1     This form of the select_statement allows a combination of waiting for,
and selecting from, one or more alternatives. The selection may depend on
conditions associated with each alternative of the selective_accept.


                                   Syntax

2     selective_accept ::= 
        select
         [guard]
           select_alternative
      { or
         [guard]
           select_alternative }
      [ else
         sequence_of_statements ]
        end select;

3     guard ::= when condition =>

4     select_alternative ::= 
         accept_alternative
        | delay_alternative
        | terminate_alternative

5     accept_alternative ::= 
        accept_statement [sequence_of_statements]

6     delay_alternative ::= 
        delay_statement [sequence_of_statements]

7     terminate_alternative ::= terminate;

8     A selective_accept shall contain at least one accept_alternative. In
      addition, it can contain:

    9     a terminate_alternative (only one); or

    10    one or more delay_alternatives; or

    11    an else part (the reserved word else followed by a
          sequence_of_statements).

12    These three possibilities are mutually exclusive.


                               Legality Rules

13    If a selective_accept contains more than one delay_alternative, then all
shall be delay_relative_statements, or all shall be delay_until_statements for
the same time type.


                              Dynamic Semantics

14    A select_alternative is said to be open if it is not immediately
preceded by a guard, or if the condition of its guard evaluates to True. It is
said to be closed otherwise.

15    For the execution of a selective_accept, any guard conditions are
evaluated; open alternatives are thus determined. For an open
delay_alternative, the delay_expression is also evaluated. Similarly, for an
open accept_alternative for an entry of a family, the entry_index is also
evaluated. These evaluations are performed in an arbitrary order, except that
a delay_expression or entry_index is not evaluated until after evaluating the
corresponding condition, if any. Selection and execution of one open
alternative, or of the else part, then completes the execution of the
selective_accept; the rules for this selection are described below.

16    Open accept_alternatives are first considered. Selection of one such
alternative takes place immediately if the corresponding entry already has
queued calls. If several alternatives can thus be selected, one of them is
selected according to the entry queuing policy in effect (see 9.5.3 and D.4).
When such an alternative is selected, the selected call is removed from its
entry queue and the handled_sequence_of_statements (if any) of the
corresponding accept_statement is executed; after the rendezvous completes any
subsequent sequence_of_statements of the alternative is executed. If no
selection is immediately possible (in the above sense) and there is no else
part, the task blocks until an open alternative can be selected.

17    Selection of the other forms of alternative or of an else part is
performed as follows:

18    An open delay_alternative is selected when its expiration time is
      reached if no accept_alternative or other delay_alternative can be
      selected prior to the expiration time. If several delay_alternatives
      have this same expiration time, one of them is selected according to the
      queuing policy in effect (see D.4); the default queuing policy chooses
      arbitrarily among the delay_alternatives whose expiration time has
      passed.

19    The else part is selected and its sequence_of_statements is executed if
      no accept_alternative can immediately be selected; in particular, if all
      alternatives are closed.

20    An open terminate_alternative is selected if the conditions stated at
      the end of clause 9.3 are satisfied.

21    The exception Program_Error is raised if all alternatives are closed and
there is no else part.

      NOTES

22    36  A selective_accept is allowed to have several open
      delay_alternatives. A selective_accept is allowed to have several open
      accept_alternatives for the same entry.


                                  Examples

23    Example of a task body with a selective accept:

24    task body Server is
         Current_Work_Item : Work_Item;
      begin
         loop
            select
               accept Next_Work_Item(WI : in Work_Item) do
                  Current_Work_Item := WI;
                end;
                Process_Work_Item(Current_Work_Item);
            or
               accept Shut_Down;
               exit;       -- Premature shut down requested
            or
               terminate;  -- Normal shutdown at end of scope
            end select;
         end loop;
      end Server;


9.7.2 Timed Entry Calls


1     A timed_entry_call issues an entry call that is cancelled if the call
(or a requeue-with-abort of the call) is not selected before the expiration
time is reached.


                                   Syntax

2     timed_entry_call ::= 
        select
         entry_call_alternative
        or
         delay_alternative
        end select;

3     entry_call_alternative ::= 
        entry_call_statement [sequence_of_statements]


                              Dynamic Semantics

4     For the execution of a timed_entry_call, the entry_name and the actual
parameters are evaluated, as for a simple entry call (see 9.5.3). The
expiration time (see 9.6) for the call is determined by evaluating the
delay_expression of the delay_alternative; the entry call is then issued.

5     If the call is queued (including due to a requeue-with-abort), and not
selected before the expiration time is reached, an attempt to cancel the call
is made. If the call completes due to the cancellation, the optional
sequence_of_statements of the delay_alternative is executed; if the entry call
completes normally, the optional sequence_of_statements of the
entry_call_alternative is executed.


                                  Examples

6     Example of a timed entry call:

7     select
         Controller.Request(Medium)(Some_Item);
      or
         delay 45.0;
         --  controller too busy, try something else
      end select;


9.7.3 Conditional Entry Calls


1     A conditional_entry_call issues an entry call that is then cancelled if
it is not selected immediately (or if a requeue-with-abort of the call is not
selected immediately).


                                   Syntax

2     conditional_entry_call ::= 
        select
         entry_call_alternative
        else
         sequence_of_statements
        end select;


                              Dynamic Semantics

3     The execution of a conditional_entry_call is defined to be equivalent to
the execution of a timed_entry_call with a delay_alternative specifying an
immediate expiration time and the same sequence_of_statements as given after
the reserved word else.

      NOTES

4     37  A conditional_entry_call may briefly increase the Count attribute of
      the entry, even if the conditional call is not selected.


                                  Examples

5     Example of a conditional entry call:

6     procedure Spin(R : in Resource) is
      begin
         loop
            select
               R.Seize;
               return;
            else
               null;  --  busy waiting
            end select;
         end loop;
      end;


9.7.4 Asynchronous Transfer of Control


1     An asynchronous select_statement provides asynchronous transfer of
control upon completion of an entry call or the expiration of a delay.


                                   Syntax

2     asynchronous_select ::= 
        select
         triggering_alternative
        then abort
         abortable_part
        end select;

3     triggering_alternative ::= triggering_statement
       [sequence_of_statements]

4     triggering_statement ::= entry_call_statement | delay_statement

5     abortable_part ::= sequence_of_statements


                              Dynamic Semantics

6     For the execution of an asynchronous_select whose triggering_statement
is an entry_call_statement, the entry_name and actual parameters are evaluated
as for a simple entry call (see 9.5.3), and the entry call is issued. If the
entry call is queued (or requeued-with-abort), then the abortable_part is
executed. If the entry call is selected immediately, and never
requeued-with-abort, then the abortable_part is never started.

7     For the execution of an asynchronous_select whose triggering_statement
is a delay_statement, the delay_expression is evaluated and the expiration
time is determined, as for a normal delay_statement. If the expiration time
has not already passed, the abortable_part is executed.

8     If the abortable_part completes and is left prior to completion of the
triggering_statement, an attempt to cancel the triggering_statement is made.
If the attempt to cancel succeeds (see 9.5.3 and 9.6), the asynchronous_select
is complete.

9     If the triggering_statement completes other than due to cancellation,
the abortable_part is aborted (if started but not yet completed - see 9.8). If
the triggering_statement completes normally, the optional
sequence_of_statements of the triggering_alternative is executed after the
abortable_part is left.


                                  Examples

10    Example of a main command loop for a command interpreter:

11    loop
          select
              Terminal.Wait_For_Interrupt;
              Put_Line("Interrupted");
          then abort
              -- This will be abandoned upon terminal interrupt
              Put_Line("-> ");
              Get_Line(Command, Last);
              Process_Command(Command(1..Last));
          end select;
      end loop;

12    Example of a time-limited calculation:

13    select
         delay 5.0;
         Put_Line("Calculation does not converge");
      then abort
         -- This calculation should finish in 5.0 seconds;
         --  if not, it is assumed to diverge.
         Horribly_Complicated_Recursive_Function(X, Y);
      end select;


9.8 Abort of a Task - Abort of a Sequence of Statements


1     An abort_statement causes one or more tasks to become abnormal, thus
preventing any further interaction with such tasks. The completion of the
triggering_statement of an asynchronous_select causes a sequence_of_statements
to be aborted.


                                   Syntax

2     abort_statement ::= abort task_name {, task_name};


                            Name Resolution Rules

3     Each task_name is expected to be of any task type; they need not all be
of the same task type.


                              Dynamic Semantics

4     For the execution of an abort_statement, the given task_names are
evaluated in an arbitrary order. Each named task is then aborted, which
consists of making the task abnormal and aborting the execution of the
corresponding task_body, unless it is already completed.

5     When the execution of a construct is aborted (including that of a task_-
body or of a sequence_of_statements), the execution of every construct
included within the aborted execution is also aborted, except for executions
included within the execution of an abort-deferred operation; the execution of
an abort-deferred operation continues to completion without being affected by
the abort; the following are the abort-deferred operations:

6     a protected action;

7     waiting for an entry call to complete (after having initiated the
      attempt to cancel it - see below);

8     waiting for the termination of dependent tasks;

9     the execution of an Initialize procedure as the last step of the default
      initialization of a controlled object;

10    the execution of a Finalize procedure as part of the finalization of a
      controlled object;

11    an assignment operation to an object with a controlled part.

12    The last three of these are discussed further in 7.6.

13    When a master is aborted, all tasks that depend on that master are
aborted.

14    The order in which tasks become abnormal as the result of an
abort_statement or the abort of a sequence_of_statements is not specified by
the language.

15    If the execution of an entry call is aborted, an immediate attempt is
made to cancel the entry call (see 9.5.3). If the execution of a construct is
aborted at a time when the execution is blocked, other than for an entry call,
at a point that is outside the execution of an abort-deferred operation, then
the execution of the construct completes immediately. For an abort due to an
abort_statement, these immediate effects occur before the execution of the
abort_statement completes. Other than for these immediate cases, the execution
of a construct that is aborted does not necessarily complete before the
abort_statement completes. However, the execution of the aborted construct
completes no later than its next abort completion point (if any) that occurs
outside of an abort-deferred operation; the following are abort completion
points for an execution:

16    the point where the execution initiates the activation of another task;

17    the end of the activation of a task;

18    the start or end of the execution of an entry call, accept_statement,
      delay_statement, or abort_statement;

19    the start of the execution of a select_statement, or of the
      sequence_of_statements of an exception_handler.


                          Bounded (Run-Time) Errors

20    An attempt to execute an asynchronous_select as part of the execution of
an abort-deferred operation is a bounded error. Similarly, an attempt to
create a task that depends on a master that is included entirely within the
execution of an abort-deferred operation is a bounded error. In both cases,
Program_Error is raised if the error is detected by the implementation;
otherwise the operations proceed as they would outside an abort-deferred
operation, except that an abort of the abortable_part or the created task
might or might not have an effect.


                             Erroneous Execution

21    If an assignment operation completes prematurely due to an abort, the
assignment is said to be disrupted; the target of the assignment or its parts
can become abnormal, and certain subsequent uses of the object can be
erroneous, as explained in 13.9.1.

      NOTES

22    38  An abort_statement should be used only in situations requiring
      unconditional termination.

23    39  A task is allowed to abort any task it can name, including itself.

24    40  Additional requirements associated with abort are given in D.6, `
      `Preemptive Abort''.


9.9 Task and Entry Attributes



                              Dynamic Semantics

1     For a prefix T that is of a task type (after any implicit dereference),
the following attributes are defined:

2     T'Callable
              Yields the value True when the task denoted by T is callable,
              and False otherwise; a task is callable unless it is completed
              or abnormal. The value of this attribute is of the predefined
              type Boolean.

3     T'Terminated
              Yields the value True if the task denoted by T is terminated,
              and False otherwise. The value of this attribute is of the
              predefined type Boolean.

4     For a prefix E that denotes an entry of a task or protected unit, the
following attribute is defined. This attribute is only allowed within the body
of the task or protected unit, but excluding, in the case of an entry of a
task unit, within any program unit that is, itself, inner to the body of the
task unit.

5     E'Count Yields the number of calls presently queued on the entry E of
              the current instance of the unit. The value of this attribute is
              of the type universal_integer.

      NOTES

6     41  For the Count attribute, the entry can be either a single entry or
      an entry of a family. The name of the entry or entry family can be
      either a direct_name or an expanded name.

7     42  Within task units, algorithms interrogating the attribute E'Count
      should take precautions to allow for the increase of the value of this
      attribute for incoming entry calls, and its decrease, for example with
      timed_entry_calls. Also, a conditional_entry_call may briefly increase
      this value, even if the conditional call is not accepted.

8     43  Within protected units, algorithms interrogating the attribute
      E'Count in the entry_barrier for the entry E should take precautions to
      allow for the evaluation of the condition of the barrier both before and
      after queuing a given caller.


9.10 Shared Variables



                              Static Semantics

1     If two different objects, including nonoverlapping parts of the same
object, are independently addressable, they can be manipulated concurrently by
two different tasks without synchronization. Normally, any two nonoverlapping
objects are independently addressable. However, if packing, record layout, or
Component_Size is specified for a given composite object, then it is
implementation defined whether or not two nonoverlapping parts of that
composite object are independently addressable.


                              Dynamic Semantics

2     Separate tasks normally proceed independently and concurrently with one
another. However, task interactions can be used to synchronize the actions of
two or more tasks to allow, for example, meaningful communication by the
direct updating and reading of variables shared between the tasks. The actions
of two different tasks are synchronized in this sense when an action of one
task signals an action of the other task; an action A1 is defined to signal an
action A2 under the following circumstances:

3     If A1 and A2 are part of the execution of the same task, and the
      language rules require A1 to be performed before A2;

4     If A1 is the action of an activator that initiates the activation of a
      task, and A2 is part of the execution of the task that is activated;

5     If A1 is part of the activation of a task, and A2 is the action of
      waiting for completion of the activation;

6     If A1 is part of the execution of a task, and A2 is the action of
      waiting for the termination of the task;

6.1/1 {If A1 is the termination of a task T, and A2 is either the evaluation
      of the expression T'Terminated or a call to
      Ada.Task_Identification.Is_Terminated with an actual parameter that
      identifies T (see C.7.1);}

7     If A1 is the action of issuing an entry call, and A2 is part of the
      corresponding execution of the appropriate entry_body or
      accept_statement.

8     If A1 is part of the execution of an accept_statement or entry_body, and
      A2 is the action of returning from the corresponding entry call;

9     If A1 is part of the execution of a protected procedure body or
      entry_body for a given protected object, and A2 is part of a later
      execution of an entry_body for the same protected object;

10    If A1 signals some action that in turn signals A2.


                             Erroneous Execution

11    Given an action of assigning to an object, and an action of reading or
updating a part of the same object (or of a neighboring object if the two are
not independently addressable), then the execution of the actions is erroneous
unless the actions are sequential. Two actions are sequential if one of the
following is true:

12    One action signals the other;

13    Both actions occur as part of the execution of the same task;

14    Both actions occur as part of protected actions on the same protected
      object, and at most one of the actions is part of a call on a protected
      function of the protected object.

15    A pragma Atomic or Atomic_Components may also be used to ensure that
certain reads and updates are sequential - see C.6.


9.11 Example of Tasking and Synchronization



                                  Examples

1     The following example defines a buffer protected object to smooth
variations between the speed of output of a producing task and the speed of
input of some consuming task. For instance, the producing task might have the
following structure:

2     task Producer;

3     task body Producer is
         Char : Character;
      begin
         loop
            ... --  produce the next character Char
            Buffer.Write(Char);
            exit when Char = ASCII.EOT;
         end loop;
      end Producer;

4     and the consuming task might have the following structure:

5     task Consumer;

6     task body Consumer is
         Char : Character;
      begin
         loop
            Buffer.Read(Char);
            exit when Char = ASCII.EOT;
            ... --  consume the character Char
         end loop;
      end Consumer;

7     The buffer object contains an internal pool of characters managed in a
round-robin fashion. The pool has two indices, an In_Index denoting the space
for the next input character and an Out_Index denoting the space for the next
output character.

8     protected Buffer is
         entry Read (C : out Character);
         entry Write(C : in  Character);
      private
         Pool      : String(1 .. 100);
         Count     : Natural := 0;
         In_Index, Out_Index : Positive := 1;
      end Buffer;

9     protected body Buffer is
         entry Write(C : in Character)
            when Count < Pool'Length is
         begin
            Pool(In_Index) := C;
            In_Index := (In_Index mod Pool'Length) + 1;
            Count    := Count + 1;
         end Write;

10       entry Read(C : out Character)
            when Count > 0 is
         begin
            C := Pool(Out_Index);
            Out_Index := (Out_Index mod Pool'Length) + 1;
            Count     := Count - 1;
         end Read;
      end Buffer;



            Section 10: Program Structure and Compilation Issues


1     The overall structure of programs and the facilities for separate
compilation are described in this section. A program is a set of partitions,
each of which may execute in a separate address space, possibly on a separate
computer.

2     As explained below, a partition is constructed from library units.
Syntactically, the declaration of a library unit is a library_item, as is the
body of a library unit. An implementation may support a concept of a program
library (or simply, a ``library''), which contains library_items and their
subunits. Library units may be organized into a hierarchy of children,
grandchildren, and so on.

3     This section has two clauses: 10.1, ``Separate Compilation'' discusses
compile-time issues related to separate compilation. 10.2, ``
Program Execution'' discusses issues related to what is traditionally known as
``link time'' and ``run time'' - building and executing partitions.


10.1 Separate Compilation


1     A program unit is either a package, a task unit, a protected unit, a
protected entry, a generic unit, or an explicitly declared subprogram other
than an enumeration literal. Certain kinds of program units can be separately
compiled. Alternatively, they can appear physically nested within other
program units.

2     The text of a program can be submitted to the compiler in one or more
compilations. Each compilation is a succession of compilation_units. A
compilation_unit contains either the declaration, the body, or a renaming of a
program unit. The representation for a compilation is implementation-defined.

3     A library unit is a separately compiled program unit, and is always a
package, subprogram, or generic unit. Library units may have other (logically
nested) library units as children, and may have other program units physically
nested within them. A root library unit, together with its children and
grandchildren and so on, form a subsystem.


                         Implementation Permissions

4     An implementation may impose implementation-defined restrictions on
compilations that contain multiple compilation_units.


10.1.1 Compilation Units - Library Units


1     A library_item is a compilation unit that is the declaration, body, or
renaming of a library unit. Each library unit (except Standard) has a parent
unit, which is a library package or generic library package. A library unit is
a child of its parent unit. The root library units are the children of the
predefined library package Standard.


                                   Syntax

2     compilation ::= {compilation_unit}

3     compilation_unit ::= 
          context_clause library_item
        | context_clause subunit

4     library_item ::= [private] library_unit_declaration
        | library_unit_body
        | [private] library_unit_renaming_declaration

5     library_unit_declaration ::= 
           subprogram_declaration   | package_declaration
         | generic_declaration      | generic_instantiation

6     library_unit_renaming_declaration ::= 
         package_renaming_declaration
       | generic_renaming_declaration
       | subprogram_renaming_declaration

7     library_unit_body ::= subprogram_body | package_body

8     parent_unit_name ::= name

9     A library unit is a program unit that is declared by a library_item.
When a program unit is a library unit, the prefix ``library'' is used to refer
to it (or ``generic library'' if generic), as well as to its declaration and
body, as in ``library procedure'', ``library package_body'', or ``generic
library package''. The term compilation unit is used to refer to a
compilation_unit. When the meaning is clear from context, the term is also
used to refer to the library_item of a compilation_unit or to the proper_body
of a subunit (that is, the compilation_unit without the context_clause and the
separate (parent_unit_name)).

10    The parent declaration of a library_item (and of the library unit) is
the declaration denoted by the parent_unit_name, if any, of the defining_-
program_unit_name of the library_item. If there is no parent_unit_name, the
parent declaration is the declaration of Standard, the library_item is a root
library_item, and the library unit (renaming) is a root library unit
(renaming). The declaration and body of Standard itself have no parent
declaration. The parent unit of a library_item or library unit is the library
unit declared by its parent declaration.

11    The children of a library unit occur immediately within the declarative
region of the declaration of the library unit. The ancestors of a library unit
are itself, its parent, its parent's parent, and so on. (Standard is an
ancestor of every library unit.) The descendant relation is the inverse of the
ancestor relation.

12    A library_unit_declaration or a library_unit_renaming_declaration is
private if the declaration is immediately preceded by the reserved word
private; it is otherwise public. A library unit is private or public according
to its declaration. The public descendants of a library unit are the library
unit itself, and the public descendants of its public children. Its other
descendants are private descendants.


                               Legality Rules

13    The parent unit of a library_item shall be a library package or generic
library package.

14    If a defining_program_unit_name of a given declaration or body has a
parent_unit_name, then the given declaration or body shall be a library_item.
The body of a program unit shall be a library_item if and only if the
declaration of the program unit is a library_item. In a
library_unit_renaming_declaration, the (old) name shall denote a library_item.

15    A parent_unit_name (which can be used within a
defining_program_unit_name of a library_item and in the separate clause of a
subunit), and each of its prefixes, shall not denote a renaming_declaration.
On the other hand, a name that denotes a library_unit_renaming_declaration is
allowed in a with_clause and other places where the name of a library unit is
allowed.

16    If a library package is an instance of a generic package, then every
child of the library package shall either be itself an instance or be a
renaming of a library unit.

17    A child of a generic library package shall either be itself a generic
unit or be a renaming of some other child of the same generic unit. The
renaming of a child of a generic package shall occur only within the
declarative region of the generic package.

18    A child of a parent generic package shall be instantiated or renamed
only within the declarative region of the parent generic.

19    For each declaration or renaming of a generic unit as a child of some
parent generic package, there is a corresponding declaration nested
immediately within each instance of the parent. This declaration is visible
only within the scope of a with_clause that mentions the child generic unit.

20    A library subprogram shall not override a primitive subprogram.

21    The defining name of a function that is a compilation unit shall not be
an operator_symbol.


                              Static Semantics

22    A subprogram_renaming_declaration that is a
library_unit_renaming_declaration is a renaming-as-declaration, not a
renaming-as-body.

23    There are two kinds of dependences among compilation units:

24    The semantic dependences (see below) are the ones needed to check the
      compile-time rules across compilation unit boundaries; a compilation
      unit depends semantically on the other compilation units needed to
      determine its legality. The visibility rules are based on the semantic
      dependences.

25    The elaboration dependences (see 10.2) determine the order of
      elaboration of library_items.

26    A library_item depends semantically upon its parent declaration. A
subunit depends semantically upon its parent body. A library_unit_body depends
semantically upon the corresponding library_unit_declaration, if any. A
compilation unit depends semantically upon each library_item mentioned in a
with_clause of the compilation unit. In addition, if a given compilation unit
contains an attribute_reference of a type defined in another compilation unit,
then the given compilation unit depends semantically upon the other
compilation unit. The semantic dependence relationship is transitive.

      NOTES

27    1  A simple program may consist of a single compilation unit. A
      compilation need not have any compilation units; for example, its text
      can consist of pragmas.

28    2  The designator of a library function cannot be an operator_symbol,
      but a nonlibrary renaming_declaration is allowed to rename a library
      function as an operator. Within a partition, two library subprograms are
      required to have distinct names and hence cannot overload each other.
      However, renaming_declarations are allowed to define overloaded names
      for such subprograms, and a locally declared subprogram is allowed to
      overload a library subprogram. The expanded name Standard.L can be used
      to denote a root library unit L (unless the declaration of Standard is
      hidden) since root library unit declarations occur immediately within
      the declarative region of package Standard.


                                  Examples

29    Examples of library units:

30    package Rational_Numbers.IO is  -- public child of Rational_Numbers, see 7.1
         procedure Put(R : in  Rational);
         procedure Get(R : out Rational);
      end Rational_Numbers.IO;

31    private procedure Rational_Numbers.Reduce(R : in out Rational);
                                      -- private child of Rational_Numbers

32    with Rational_Numbers.Reduce;   -- refer to a private child
      package body Rational_Numbers is
         ...
      end Rational_Numbers;

33    with Rational_Numbers.IO; use Rational_Numbers;
      with Ada.Text_io;               -- see A.10
      procedure Main is               -- a root library procedure
         R : Rational;
      begin
         R := 5/3;                    -- construct a rational number, see 7.1
         Ada.Text_IO.Put("The answer is: ");
         IO.Put(R);
         Ada.Text_IO.New_Line;
      end Main;

34    with Rational_Numbers.IO;
      package Rational_IO renames Rational_Numbers.IO;
                                      -- a library unit renaming declaration

35    Each of the above library_items can be submitted to the compiler
separately.


10.1.2 Context Clauses - With Clauses


1     A context_clause is used to specify the library_items whose names are
needed within a compilation unit.


                                   Syntax

2     context_clause ::= {context_item}

3     context_item ::= with_clause | use_clause

4     with_clause ::= with library_unit_name {, library_unit_name};


                            Name Resolution Rules

5     The scope of a with_clause that appears on a library_unit_declaration or
library_unit_renaming_declaration consists of the entire declarative region of
the declaration, which includes all children and subunits. The scope of a
with_clause that appears on a body consists of the body, which includes all
subunits.

6     A library_item is mentioned in a with_clause if it is denoted by a
library_unit_name or a prefix in the with_clause.

7     Outside its own declarative region, the declaration or renaming of a
library unit can be visible only within the scope of a with_clause that
mentions it. The visibility of the declaration or renaming of a library unit
otherwise follows from its placement in the environment.


                               Legality Rules

8     If a with_clause of a given compilation_unit mentions a private child of
some library unit, then the given compilation_unit shall be either the
declaration of a private descendant of that library unit or the body or
subunit of a (public or private) descendant of that library unit.

      NOTES

9     3  A library_item mentioned in a with_clause of a compilation unit is
      visible within the compilation unit and hence acts just like an ordinary
      declaration. Thus, within a compilation unit that mentions its
      declaration, the name of a library package can be given in use_clauses
      and can be used to form expanded names, a library subprogram can be
      called, and instances of a generic library unit can be declared. If a
      child of a parent generic package is mentioned in a with_clause, then
      the corresponding declaration nested within each visible instance is
      visible within the compilation unit.


10.1.3 Subunits of Compilation Units


1     Subunits are like child units, with these (important) differences:
subunits support the separate compilation of bodies only (not declarations);
the parent contains a body_stub to indicate the existence and place of each of
its subunits; declarations appearing in the parent's body can be visible
within the subunits.


                                   Syntax

2     body_stub ::= subprogram_body_stub | package_body_stub
       | task_body_stub | protected_body_stub

3     subprogram_body_stub ::= subprogram_specification is separate;

4     package_body_stub ::= package body defining_identifier is separate;

5     task_body_stub ::= task body defining_identifier is separate;

6     protected_body_stub ::= protected body defining_identifier is separate;

7     subunit ::= separate (parent_unit_name) proper_body


                               Legality Rules

8     The parent body of a subunit is the body of the program unit denoted by
its parent_unit_name. The term subunit is used to refer to a subunit and also
to the proper_body of a subunit.

9     The parent body of a subunit shall be present in the current
environment, and shall contain a corresponding body_stub with the same
defining_identifier as the subunit.

10    A package_body_stub shall be the completion of a package_declaration or
generic_package_declaration; a task_body_stub shall be the completion of a
task_declaration; a protected_body_stub shall be the completion of a protected_-
declaration.

11    In contrast, a subprogram_body_stub need not be the completion of a
previous declaration, in which case the _stub declares the subprogram. If the
_stub is a completion, it shall be the completion of a subprogram_declaration
or generic_subprogram_declaration. The profile of a subprogram_body_stub that
completes a declaration shall conform fully to that of the declaration.

12    A subunit that corresponds to a body_stub shall be of the same kind
(package_, subprogram_, task_, or protected_) as the body_stub. The profile of
a subprogram_body subunit shall be fully conformant to that of the
corresponding body_stub.

13    A body_stub shall appear immediately within the declarative_part of a
compilation unit body. This rule does not apply within an instance of a
generic unit.

14    The defining_identifiers of all body_stubs that appear immediately
within a particular declarative_part shall be distinct.


                           Post-Compilation Rules

15    For each body_stub, there shall be a subunit containing the
corresponding proper_body.

      NOTES

16    4  The rules in 10.1.4, ``The Compilation Process'' say that a body_stub
      is equivalent to the corresponding proper_body. This implies:

    17    Visibility within a subunit is the visibility that would be obtained
          at the place of the corresponding body_stub (within the parent body)
          if the context_clause of the subunit were appended to that of the
          parent body.

    18    The effect of the elaboration of a body_stub is to elaborate the
          subunit.


                                  Examples

19    The package Parent is first written without subunits:

20    package Parent is
          procedure Inner;
      end Parent;

21    with Ada.Text_IO;
      package body Parent is
          Variable : String := "Hello, there.";
          procedure Inner is
          begin
              Ada.Text_IO.Put_Line(Variable);
          end Inner;
      end Parent;

22    The body of procedure Inner may be turned into a subunit by rewriting
the package body as follows (with the declaration of Parent remaining the
same):

23    package body Parent is
          Variable : String := "Hello, there.";
          procedure Inner is separate;
      end Parent;

24    with Ada.Text_IO;
      separate(Parent)
      procedure Inner is
      begin
          Ada.Text_IO.Put_Line(Variable);
      end Inner;


10.1.4 The Compilation Process


1     Each compilation unit submitted to the compiler is compiled in the
context of an environment declarative_part (or simply, an environment), which
is a conceptual declarative_part that forms the outermost declarative region
of the context of any compilation. At run time, an environment forms the
declarative_part of the body of the environment task of a partition (see
10.2, ``Program Execution'').

2     The declarative_items of the environment are library_items appearing in
an order such that there are no forward semantic dependences. Each included
subunit occurs in place of the corresponding stub. The visibility rules apply
as if the environment were the outermost declarative region, except that with_-
clauses are needed to make declarations of library units visible (see 10.1.2).

3     The mechanisms for creating an environment and for adding and replacing
compilation units within an environment are implementation defined.


                            Name Resolution Rules

4/1   If a library_unit_body that is a subprogram_body is submitted to the
compiler, it is interpreted only as a completion if a library_unit_declaration
[for a subprogram or a generic subprogram ]with the same
defining_program_unit_name already exists in the environment {for a subprogram
other than an instance of a generic subprogram or for a generic subprogram
}(even if the profile of the body is not type conformant with that of the
declaration); otherwise the subprogram_body is interpreted as both the
declaration and body of a library subprogram.


                               Legality Rules

5     When a compilation unit is compiled, all compilation units upon which it
depends semantically shall already exist in the environment; the set of these
compilation units shall be consistent in the sense that the new compilation
unit shall not semantically depend (directly or indirectly) on two different
versions of the same compilation unit, nor on an earlier version of itself.


                         Implementation Permissions

6     The implementation may require that a compilation unit be legal before
inserting it into the environment.

7     When a compilation unit that declares or renames a library unit is added
to the environment, the implementation may remove from the environment any
preexisting library_item with the same defining_program_unit_name. When a
compilation unit that is a subunit or the body of a library unit is added to
the environment, the implementation may remove from the environment any
preexisting version of the same compilation unit. When a given compilation
unit is removed from the environment, the implementation may also remove any
compilation unit that depends semantically upon the given one. If the given
compilation unit contains the body of a subprogram to which a pragma Inline
applies, the implementation may also remove any compilation unit containing a
call to that subprogram.

      NOTES

8     5  The rules of the language are enforced across compilation and
      compilation unit boundaries, just as they are enforced within a single
      compilation unit.

9     6  An implementation may support a concept of a library, which contains
      library_items. If multiple libraries are supported, the implementation
      has to define how a single environment is constructed when a compilation
      unit is submitted to the compiler. Naming conflicts between different
      libraries might be resolved by treating each library as the root of a
      hierarchy of child library units.

10    7  A compilation unit containing an instantiation of a separately
      compiled generic unit does not semantically depend on the body of the
      generic unit. Therefore, replacing the generic body in the environment
      does not result in the removal of the compilation unit containing the
      instantiation.


10.1.5 Pragmas and Program Units


1     This subclause discusses pragmas related to program units, library
units, and compilations.


                            Name Resolution Rules

2     Certain pragmas are defined to be program unit pragmas. A name given as
the argument of a program unit pragma shall resolve to denote the declarations
or renamings of one or more program units that occur immediately within the
declarative region or compilation in which the pragma immediately occurs, or
it shall resolve to denote the declaration of the immediately enclosing
program unit (if any); the pragma applies to the denoted program unit(s). If
there are no names given as arguments, the pragma applies to the immediately
enclosing program unit.


                               Legality Rules

3     A program unit pragma shall appear in one of these places:

4     At the place of a compilation_unit, in which case the pragma shall
      immediately follow in the same compilation (except for other pragmas) a
      library_unit_declaration that is a subprogram_declaration, generic_-
      subprogram_declaration, or generic_instantiation, and the pragma shall
      have an argument that is a name denoting that declaration.

5/1   Immediately within the declaration of a program unit and before any
      nested declaration{ (but not within a generic formal part)}, in which
      case the argument, if any, shall be a direct_name that denotes the
      immediately enclosing program unit declaration.

6     At the place of a declaration other than the first, of a
      declarative_part or program unit declaration, in which case the pragma
      shall have an argument, which shall be a direct_name that denotes one or
      more of the following (and nothing else): a subprogram_declaration, a
      generic_subprogram_declaration, or a generic_instantiation, of the same
      declarative_part or program unit declaration.

7     Certain program unit pragmas are defined to be library unit pragmas. The
name, if any, in a library unit pragma shall denote the declaration of a
library unit.


                              Static Semantics

7.1/1 {A library unit pragma that applies to a generic unit does not apply to
its instances, unless a specific rule for the pragma specifies the contrary.}


                            Implementation Advice

7.2/1 {When applied to a generic unit, a program unit pragma that is not a
library unit pragma should apply to each instance of the generic unit for
which there is not an overriding pragma applied directly to the instance.}


                           Post-Compilation Rules

8     Certain pragmas are defined to be configuration pragmas; they shall
appear before the first compilation_unit of a compilation. They are generally
used to select a partition-wide or system-wide option. The pragma applies to
all compilation_units appearing in the compilation, unless there are none, in
which case it applies to all future compilation_units compiled into the same
environment.


                         Implementation Permissions

9     An implementation may place restrictions on configuration pragmas, so
long as it allows them when the environment contains no library_items other
than those of the predefined environment.


10.1.6 Environment-Level Visibility Rules


1     The normal visibility rules do not apply within a parent_unit_name or a
context_clause, nor within a pragma that appears at the place of a compilation
unit. The special visibility rules for those contexts are given here.


                              Static Semantics

2     Within the parent_unit_name at the beginning of a library_item, and
within a with_clause, the only declarations that are visible are those that
are library_items of the environment, and the only declarations that are
directly visible are those that are root library_items of the environment.
Notwithstanding the rules of 4.1.3, an expanded name in a with_clause may
consist of a prefix that denotes a generic package and a selector_name that
denotes a child of that generic package. (The child is necessarily a generic
unit; see 10.1.1.)

3     Within a use_clause or pragma that is within a context_clause, each
library_item mentioned in a previous with_clause of the same context_clause is
visible, and each root library_item so mentioned is directly visible. In
addition, within such a use_clause, if a given declaration is visible or
directly visible, each declaration that occurs immediately within the given
declaration's visible part is also visible. No other declarations are visible
or directly visible.

4     Within the parent_unit_name of a subunit, library_items are visible as
they are in the parent_unit_name of a library_item; in addition, the
declaration corresponding to each body_stub in the environment is also
visible.

5     Within a pragma that appears at the place of a compilation unit, the
immediately preceding library_item and each of its ancestors is visible. The
ancestor root library_item is directly visible.




10.2 Program Execution


1     An Ada program consists of a set of partitions, which can execute in
parallel with one another, possibly in a separate address space, and possibly
on a separate computer.


                           Post-Compilation Rules

2     A partition is a program or part of a program that can be invoked from
outside the Ada implementation. For example, on many systems, a partition
might be an executable file generated by the system linker. The user can
explicitly assign library units to a partition. The assignment is done in an
implementation-defined manner. The compilation units included in a partition
are those of the explicitly assigned library units, as well as other
compilation units needed by those library units. The compilation units needed
by a given compilation unit are determined as follows (unless specified
otherwise via an implementation-defined pragma, or by some other
implementation-defined means):

3     A compilation unit needs itself;

4     If a compilation unit is needed, then so are any compilation units upon
      which it depends semantically;

5     If a library_unit_declaration is needed, then so is any corresponding
      library_unit_body;

6     If a compilation unit with stubs is needed, then so are any
      corresponding subunits.

7     The user can optionally designate (in an implementation-defined manner)
one subprogram as the main subprogram for the partition. A main subprogram, if
specified, shall be a subprogram.

8     Each partition has an anonymous environment task, which is an implicit
outermost task whose execution elaborates the library_items of the environment
declarative_part, and then calls the main subprogram, if there is one. A
partition's execution is that of its tasks.

9     The order of elaboration of library units is determined primarily by the
elaboration dependences. There is an elaboration dependence of a given
library_item upon another if the given library_item or any of its subunits
depends semantically on the other library_item. In addition, if a given
library_item or any of its subunits has a pragma Elaborate or Elaborate_All
that mentions another library unit, then there is an elaboration dependence of
the given library_item upon the body of the other library unit, and, for
Elaborate_All only, upon each library_item needed by the declaration of the
other library unit.

10    The environment task for a partition has the following structure:

11    task Environment_Task;

12    task body Environment_Task is
          ... (1) -- The environment declarative_part
                  -- (that is, the sequence of library_items) goes here.
      begin
          ... (2) -- Call the main subprogram, if there is one.
      end Environment_Task;

13    The environment declarative_part at (1) is a sequence of
declarative_items consisting of copies of the library_items included in the
partition. The order of elaboration of library_items is the order in which
they appear in the environment declarative_part:

14    The order of all included library_items is such that there are no
      forward elaboration dependences.

15    Any included library_unit_declaration to which a pragma Elaborate_Body
      applies is immediately followed by its library_unit_body, if included.

16    All library_items declared pure occur before any that are not declared
      pure.

17    All preelaborated library_items occur before any that are not
      preelaborated.

18    There shall be a total order of the library_items that obeys the above
rules. The order is otherwise implementation defined.

19    The full expanded names of the library units and subunits included in a
given partition shall be distinct.

20    The sequence_of_statements of the environment task (see (2) above)
consists of either:

21    A call to the main subprogram, if the partition has one. If the main
      subprogram has parameters, they are passed; where the actuals come from
      is implementation defined. What happens to the result of a main function
      is also implementation defined.

22    or:

23    A null_statement, if there is no main subprogram.

24    The mechanisms for building and running partitions are implementation
defined. These might be combined into one operation, as, for example, in
dynamic linking, or ``load-and-go'' systems.


                              Dynamic Semantics

25    The execution of a program consists of the execution of a set of
partitions. Further details are implementation defined. The execution of a
partition starts with the execution of its environment task, ends when the
environment task terminates, and includes the executions of all tasks of the
partition. The execution of the (implicit) task_body of the environment task
acts as a master for all other tasks created as part of the execution of the
partition. When the environment task completes (normally or abnormally), it
waits for the termination of all such tasks, and then finalizes any remaining
objects of the partition.


                          Bounded (Run-Time) Errors

26    Once the environment task has awaited the termination of all other tasks
of the partition, any further attempt to create a task (during finalization)
is a bounded error, and may result in the raising of Program_Error either upon
creation or activation of the task. If such a task is activated, it is not
specified whether the task is awaited prior to termination of the environment
task.


                         Implementation Requirements

27    The implementation shall ensure that all compilation units included in a
partition are consistent with one another, and are legal according to the
rules of the language.


                         Implementation Permissions

28    The kind of partition described in this clause is known as an active
partition. An implementation is allowed to support other kinds of partitions,
with implementation-defined semantics.

29    An implementation may restrict the kinds of subprograms it supports as
main subprograms. However, an implementation is required to support all main
subprograms that are public parameterless library procedures.

30    If the environment task completes abnormally, the implementation may
abort any dependent tasks.

      NOTES

31    8  An implementation may provide inter-partition communication
      mechanism(s) via special packages and pragmas. Standard pragmas for
      distribution and methods for specifying inter-partition communication
      are defined in Annex E, ``Distributed Systems''. If no such mechanisms
      are provided, then each partition is isolated from all others, and
      behaves as a program in and of itself.

32    9  Partitions are not required to run in separate address spaces. For
      example, an implementation might support dynamic linking via the
      partition concept.

33    10  An order of elaboration of library_items that is consistent with the
      partial ordering defined above does not always ensure that each
      library_unit_body is elaborated before any other compilation unit whose
      elaboration necessitates that the library_unit_body be already
      elaborated. (In particular, there is no requirement that the body of a
      library unit be elaborated as soon as possible after the
      library_unit_declaration is elaborated, unless the pragmas in subclause
      10.2.1 are used.)

34    11  A partition (active or otherwise) need not have a main subprogram.
      In such a case, all the work done by the partition would be done by
      elaboration of various library_items, and by tasks created by that
      elaboration. Passive partitions, which cannot have main subprograms, are
      defined in Annex E, ``Distributed Systems''.


10.2.1 Elaboration Control


1     This subclause defines pragmas that help control the elaboration order
of library_items.


                                   Syntax

2     The form of a pragma Preelaborate is as follows:

3       pragma Preelaborate[(library_unit_name)];

4     A pragma Preelaborate is a library unit pragma.


                               Legality Rules

5     An elaborable construct is preelaborable unless its elaboration performs
any of the following actions:

6     The execution of a statement other than a null_statement.

7     A call to a subprogram other than a static function.

8     The evaluation of a primary that is a name of an object, unless the name
      is a static expression, or statically denotes a discriminant of an
      enclosing type.

9     The creation of a default-initialized object (including a component) of
      a descendant of a private type, private extension, controlled type, task
      type, or protected type with entry_declarations; similarly the
      evaluation of an extension_aggregate with an ancestor subtype_mark
      denoting a subtype of such a type.

10    A generic body is preelaborable only if elaboration of a corresponding
instance body would not perform any such actions, presuming that the actual
for each formal private type (or extension) is a private type (or extension),
and the actual for each formal subprogram is a user-defined subprogram.

11/1  If a pragma Preelaborate (or pragma Pure - see below) applies to a
library unit, then it is preelaborated. If a library unit is preelaborated,
then its declaration, if any, and body, if any, are elaborated prior to all
non-preelaborated library_items of the partition. {The declaration and body of
a preelaborated library unit, and all subunits that are elaborated as part of
elaborating the library unit,}[All compilation units of a preelaborated
library unit] shall be preelaborable. In addition to the places where
Legality Rules normally apply (see 12.3), this rule applies also in the
private part of an instance of a generic unit. In addition, all compilation
units of a preelaborated library unit shall depend semantically only on
compilation units of other preelaborated library units.


                            Implementation Advice

12    In an implementation, a type declared in a preelaborated package should
have the same representation in every elaboration of a given version of the
package, whether the elaborations occur in distinct executions of the same
program, or in executions of distinct programs or partitions that include the
given version.


                                   Syntax

13    The form of a pragma Pure is as follows:

14      pragma Pure[(library_unit_name)];

15    A pragma Pure is a library unit pragma.


                               Legality Rules

16    A pure library_item is a preelaborable library_item that does not
contain the declaration of any variable or named access type, except within a
subprogram, generic subprogram, task unit, or protected unit.

17    A pragma Pure is used to declare that a library unit is pure. If a
pragma Pure applies to a library unit, then its compilation units shall be
pure, and they shall depend semantically only on compilation units of other
library units that are declared pure.


                         Implementation Permissions

18    If a library unit is declared pure, then the implementation is permitted
to omit a call on a library-level subprogram of the library unit if the
results are not needed after the call. Similarly, it may omit such a call and
simply reuse the results produced by an earlier call on the same subprogram,
provided that none of the parameters are of a limited type, and the addresses
and values of all by-reference actual parameters, and the values of all
by-copy-in actual parameters, are the same as they were at the earlier call.
This permission applies even if the subprogram produces other side effects
when called.


                                   Syntax

19    The form of a pragma Elaborate, Elaborate_All, or Elaborate_Body is as
      follows:

20      pragma Elaborate(library_unit_name{, library_unit_name});

21      pragma Elaborate_All(library_unit_name{, library_unit_name});

22      pragma Elaborate_Body[(library_unit_name)];

23    A pragma Elaborate or Elaborate_All is only allowed within a
      context_clause.

24    A pragma Elaborate_Body is a library unit pragma.


                               Legality Rules

25    If a pragma Elaborate_Body applies to a declaration, then the
declaration requires a completion (a body).


                              Static Semantics

26    A pragma Elaborate specifies that the body of the named library unit is
elaborated before the current library_item. A pragma Elaborate_All specifies
that each library_item that is needed by the named library unit declaration is
elaborated before the current library_item. A pragma Elaborate_Body specifies
that the body of the library unit is elaborated immediately after its
declaration.

      NOTES

27    12  A preelaborated library unit is allowed to have non-preelaborable
      children.

28    13  A library unit that is declared pure is allowed to have impure
      children.



                           Section 11: Exceptions


1     This section defines the facilities for dealing with errors or other
exceptional situations that arise during program execution. An exception
represents a kind of exceptional situation; an occurrence of such a situation
(at run time) is called an exception occurrence. To raise an exception is to
abandon normal program execution so as to draw attention to the fact that the
corresponding situation has arisen. Performing some actions in response to the
arising of an exception is called handling the exception.

2     An exception_declaration declares a name for an exception. An exception
is raised initially either by a raise_statement or by the failure of a
language-defined check. When an exception arises, control can be transferred
to a user-provided exception_handler at the end of a handled_sequence_of_-
statements, or it can be propagated to a dynamically enclosing execution.


11.1 Exception Declarations


1     An exception_declaration declares a name for an exception.


                                   Syntax

2     exception_declaration ::= defining_identifier_list : exception;


                              Static Semantics

3     Each single exception_declaration declares a name for a different
exception. If a generic unit includes an exception_declaration, the
exception_declarations implicitly generated by different instantiations of the
generic unit refer to distinct exceptions (but all have the same
defining_identifier). The particular exception denoted by an exception name is
determined at compilation time and is the same regardless of how many times
the exception_declaration is elaborated.

4     The predefined exceptions are the ones declared in the declaration of
package Standard: Constraint_Error, Program_Error, Storage_Error, and
Tasking_Error; one of them is raised when a language-defined check fails.


                              Dynamic Semantics

5     The elaboration of an exception_declaration has no effect.

6     The execution of any construct raises Storage_Error if there is
insufficient storage for that execution. The amount of storage needed for the
execution of constructs is unspecified.


                                  Examples

7     Examples of user-defined exception declarations:

8     Singular : exception;
      Error    : exception;
      Overflow, Underflow : exception;


11.2 Exception Handlers


1     The response to one or more exceptions is specified by an
exception_handler.


                                   Syntax

2     handled_sequence_of_statements ::= 
           sequence_of_statements
        [exception
           exception_handler
          {exception_handler}]

3     exception_handler ::= 
        when [choice_parameter_specification:] exception_choice
       {| exception_choice} =>
           sequence_of_statements

4     choice_parameter_specification ::= defining_identifier

5     exception_choice ::= exception_name | others


                               Legality Rules

6     A choice with an exception_name covers the named exception. A choice
with others covers all exceptions not named by previous choices of the same
handled_sequence_of_statements. Two choices in different exception_handlers of
the same handled_sequence_of_statements shall not cover the same exception.

7     A choice with others is allowed only for the last handler of a
handled_sequence_of_statements and as the only choice of that handler.

8     An exception_name of a choice shall not denote an exception declared in
a generic formal package.


                              Static Semantics

9     A choice_parameter_specification declares a choice parameter, which is a
constant object of type Exception_Occurrence (see 11.4.1). During the handling
of an exception occurrence, the choice parameter, if any, of the handler
represents the exception occurrence that is being handled.


                              Dynamic Semantics

10    The execution of a handled_sequence_of_statements consists of the
execution of the sequence_of_statements. The optional handlers are used to
handle any exceptions that are propagated by the sequence_of_statements.


                                  Examples

11    Example of an exception handler:

12    begin
         Open(File, In_File, "input.txt");   -- see A.8.2
      exception
         when E : Name_Error =>
            Put("Cannot open input file : ");
            Put_Line(Exception_Message(E));  -- see 11.4.1
            raise;
      end;


11.3 Raise Statements


1     A raise_statement raises an exception.


                                   Syntax

2     raise_statement ::= raise [exception_name];


                               Legality Rules

3     The name, if any, in a raise_statement shall denote an exception. A
raise_statement with no exception_name (that is, a re-raise statement) shall
be within a handler, but not within a body enclosed by that handler.


                              Dynamic Semantics

4     To raise an exception is to raise a new occurrence of that exception, as
explained in 11.4. For the execution of a raise_statement with an
exception_name, the named exception is raised. For the execution of a re-raise
statement, the exception occurrence that caused transfer of control to the
innermost enclosing handler is raised again.


                                  Examples

5     Examples of raise statements:

6     raise Ada.IO_Exceptions.Name_Error;   -- see A.13

7     raise;                                -- re-raise the current exception


11.4 Exception Handling


1     When an exception occurrence is raised, normal program execution is
abandoned and control is transferred to an applicable exception_handler, if
any. To handle an exception occurrence is to respond to the exceptional event.
To propagate an exception occurrence is to raise it again in another context;
that is, to fail to respond to the exceptional event in the present context.


                              Dynamic Semantics

2     Within a given task, if the execution of construct a is defined by this
International Standard to consist (in part) of the execution of construct b,
then while b is executing, the execution of a is said to dynamically enclose
the execution of b. The innermost dynamically enclosing execution of a given
execution is the dynamically enclosing execution that started most recently.

3     When an exception occurrence is raised by the execution of a given
construct, the rest of the execution of that construct is abandoned; that is,
any portions of the execution that have not yet taken place are not performed.
The construct is first completed, and then left, as explained in 7.6.1. Then:

4     If the construct is a task_body, the exception does not propagate
      further;

5     If the construct is the sequence_of_statements of a
      handled_sequence_of_statements that has a handler with a choice covering
      the exception, the occurrence is handled by that handler;

6     Otherwise, the occurrence is propagated to the innermost dynamically
      enclosing execution, which means that the occurrence is raised again in
      that context.

7     When an occurrence is handled by a given handler, the
choice_parameter_specification, if any, is first elaborated, which creates the
choice parameter and initializes it to the occurrence. Then, the
sequence_of_statements of the handler is executed; this execution replaces the
abandoned portion of the execution of the sequence_of_statements.

      NOTES

8     1  Note that exceptions raised in a declarative_part of a body are not
      handled by the handlers of the handled_sequence_of_statements of that
      body.


11.4.1 The Package Exceptions



                              Static Semantics

1     The following language-defined library package exists:

2     
      package Ada.Exceptions is
          type Exception_Id is private;
          Null_Id : constant Exception_Id;
          function Exception_Name(Id : Exception_Id) return String;

3         type Exception_Occurrence is limited private;
          type Exception_Occurrence_Access is access all Exception_Occurrence;
          Null_Occurrence : constant Exception_Occurrence;

4         procedure Raise_Exception(E : in Exception_Id;
                                    Message : in String := "");
          function Exception_Message(X : Exception_Occurrence) return String;
          procedure Reraise_Occurrence(X : in Exception_Occurrence);

5         function Exception_Identity(X : Exception_Occurrence)
                                      return Exception_Id;
          function Exception_Name(X : Exception_Occurrence) return String;
              -- Same as Exception_Name(Exception_Identity(X)).
          function Exception_Information
      (X : Exception_Occurrence) return String;

6         procedure Save_Occurrence(Target : out Exception_Occurrence;
                                    Source : in Exception_Occurrence);
          function Save_Occurrence(Source : Exception_Occurrence)
                                   return Exception_Occurrence_Access;
      private
         ... -- not specified by the language
      end Ada.Exceptions;

7     Each distinct exception is represented by a distinct value of type
Exception_Id. Null_Id does not represent any exception, and is the default
initial value of type Exception_Id. Each occurrence of an exception is
represented by a value of type Exception_Occurrence. Null_Occurrence does not
represent any exception occurrence, and is the default initial value of type
Exception_Occurrence.

8/1   For a {prefix}[prefix] E that denotes an exception, the following
attribute is defined:

9     E'Identity
              E'Identity returns the unique identity of the exception. The
              type of this attribute is Exception_Id.

10    Raise_Exception raises a new occurrence of the identified exception. In
this case, Exception_Message returns the Message parameter of Raise_Exception.
For a raise_statement with an exception_name, Exception_Message returns
implementation-defined information about the exception occurrence.
Reraise_Occurrence reraises the specified exception occurrence.

11    Exception_Identity returns the identity of the exception of the
occurrence.

12    The Exception_Name functions return the full expanded name of the
exception, in upper case, starting with a root library unit. For an exception
declared immediately within package Standard, the defining_identifier is
returned. The result is implementation defined if the exception is declared
within an unnamed block_statement.

13    Exception_Information returns implementation-defined information about
the exception occurrence.

14    Raise_Exception and Reraise_Occurrence have no effect in the case of
Null_Id or Null_Occurrence. Exception_Message, Exception_Identity,
Exception_Name, and Exception_Information raise Constraint_Error for a Null_Id
or Null_Occurrence.

15    The Save_Occurrence procedure copies the Source to the Target. The
Save_Occurrence function uses an allocator of type Exception_Occurrence_Access
to create a new object, copies the Source to this new object, and returns an
access value designating this new object; the result may be deallocated using
an instance of Unchecked_Deallocation.


                         Implementation Requirements

16    The implementation of the Write attribute (see 13.13.2) of
Exception_Occurrence shall support writing a representation of an exception
occurrence to a stream; the implementation of the Read attribute of
Exception_Occurrence shall support reconstructing an exception occurrence from
a stream (including one written in a different partition).


                         Implementation Permissions

17    An implementation of Exception_Name in a space-constrained environment
may return the defining_identifier instead of the full expanded name.

18    The string returned by Exception_Message may be truncated (to no less
than 200 characters) by the Save_Occurrence procedure (not the function), the
Reraise_Occurrence procedure, and the re-raise statement.


                            Implementation Advice

19    Exception_Message (by default) and Exception_Information should produce
information useful for debugging. Exception_Message should be short (about one
line), whereas Exception_Information can be long. Exception_Message should not
include the Exception_Name. Exception_Information should include both the
Exception_Name and the Exception_Message.


11.4.2 Example of Exception Handling



                                  Examples

1     Exception handling may be used to separate the detection of an error
from the response to that error:

2     with Ada.Exceptions;
      use Ada;
      package File_System is
          type File_Handle is limited private;

3         File_Not_Found : exception;
          procedure Open(F : in out File_Handle; Name : String);
              -- raises File_Not_Found if named file does not exist

4         End_Of_File : exception;
          procedure Read(F : in out File_Handle; Data : out Data_Type);
              -- raises End_Of_File if the file is not open

5         ...
      end File_System;

6     package body File_System is
          procedure Open(F : in out File_Handle; Name : String) is
          begin
              if File_Exists(Name) then
                  ...
              else
                  Exceptions.Raise_Exception(File_Not_Found'Identity,
                                            "File not found: " & Name & ".");
              end if;
          end Open;

7         procedure Read(F : in out File_Handle; Data : out Data_Type) is
          begin
              if F.Current_Position <= F.Last_Position then
                  ...
              else
                  raise End_Of_File;
              end if;
          end Read;

8         ...

9     end File_System;

10    with Ada.Text_IO;
      with Ada.Exceptions;
      with File_System; use File_System;
      use Ada;
      procedure Main is
      begin
          ... -- call operations in File_System
      exception
          when End_Of_File =>
              Close(Some_File);
          when Not_Found_Error : File_Not_Found =>
              Text_IO.Put_Line(Exceptions.Exception_Message(Not_Found_Error));
          when The_Error : others =>
              Text_IO.Put_Line("Unknown error:");
              if Verbosity_Desired then
                  Text_IO.Put_Line(Exceptions.Exception_Information(The_Error));
              else
                  Text_IO.Put_Line(Exceptions.Exception_Name(The_Error));
                  Text_IO.Put_Line(Exceptions.Exception_Message(The_Error));
              end if;
              raise;
      end Main;

11    In the above example, the File_System package contains information about
detecting certain exceptional situations, but it does not specify how to
handle those situations. Procedure Main specifies how to handle them; other
clients of File_System might have different handlers, even though the
exceptional situations arise from the same basic causes.


11.5 Suppressing Checks


1     A pragma Suppress gives permission to an implementation to omit certain
language-defined checks.

2     A language-defined check (or simply, a ``check'') is one of the
situations defined by this International Standard that requires a check to be
made at run time to determine whether some condition is true. A check fails
when the condition being checked is false, causing an exception to be raised.


                                   Syntax

3     The form of a pragma Suppress is as follows:

4       pragma Suppress(identifier [, [On =>] name]);

5     A pragma Suppress is allowed only immediately within a declarative_part,
      immediately within a package_specification, or as a configuration
      pragma.


                               Legality Rules

6     The identifier shall be the name of a check. The name (if present) shall
statically denote some entity.

7     For a pragma Suppress that is immediately within a package_specification
and includes a name, the name shall denote an entity (or several overloaded
subprograms) declared immediately within the package_specification.


                              Static Semantics

8     A pragma Suppress gives permission to an implementation to omit the
named check from the place of the pragma to the end of the innermost enclosing
declarative region, or, if the pragma is given in a package_specification and
includes a name, to the end of the scope of the named entity. If the pragma
includes a name, the permission applies only to checks performed on the named
entity, or, for a subtype, on objects and values of its type. Otherwise, the
permission applies to all entities. If permission has been given to suppress a
given check, the check is said to be suppressed.

9     The following are the language-defined checks:

10    The following checks correspond to situations in which the exception
      Constraint_Error is raised upon failure.

11/1  Access_Check
              When evaluating a dereference (explicit or implicit), check that
              the value of the name is not null. When passing an actual
              parameter to a formal access parameter, check that the value of
              the actual parameter is not null. {When evaluating a
              discriminant_association for an access discriminant, check that
              the value of the discriminant is not null.}

12    Discriminant_Check
              Check that the discriminants of a composite value have the
              values imposed by a discriminant constraint. Also, when
              accessing a record component, check that it exists for the
              current discriminant values.

13    Division_Check
              Check that the second operand is not zero for the operations /,
              rem and mod.

14    Index_Check
              Check that the bounds of an array value are equal to the
              corresponding bounds of an index constraint. Also, when
              accessing a component of an array object, check for each
              dimension that the given index value belongs to the range
              defined by the bounds of the array object. Also, when accessing
              a slice of an array object, check that the given discrete range
              is compatible with the range defined by the bounds of the array
              object.

15    Length_Check
              Check that two arrays have matching components, in the case of
              array subtype conversions, and logical operators for arrays of
              boolean components.

16    Overflow_Check
              Check that a scalar value is within the base range of its type,
              in cases where the implementation chooses to raise an exception
              instead of returning the correct mathematical result.

17    Range_Check
              Check that a scalar value satisfies a range constraint. Also,
              for the elaboration of a subtype_indication, check that the
              constraint (if present) is compatible with the subtype denoted
              by the subtype_mark. Also, for an aggregate, check that an index
              or discriminant value belongs to the corresponding subtype.
              Also, check that when the result of an operation yields an
              array, the value of each component belongs to the component
              subtype.

18    Tag_Check
              Check that operand tags in a dispatching call are all equal.
              Check for the correct tag on tagged type conversions, for an
              assignment_statement, and when returning a tagged limited object
              from a function.

19    The following checks correspond to situations in which the exception
      Program_Error is raised upon failure.

20    Elaboration_Check
              When a subprogram or protected entry is called, a task
              activation is accomplished, or a generic instantiation is
              elaborated, check that the body of the corresponding unit has
              already been elaborated.

21    Accessibility_Check
              Check the accessibility level of an entity or view.

22    The following check corresponds to situations in which the exception
      Storage_Error is raised upon failure.

23    Storage_Check
              Check that evaluation of an allocator does not require more
              space than is available for a storage pool. Check that the space
              available for a task or subprogram has not been exceeded.

24    The following check corresponds to all situations in which any
      predefined exception is raised.

25    All_Checks
              Represents the union of all checks; suppressing All_Checks
              suppresses all checks.


                             Erroneous Execution

26    If a given check has been suppressed, and the corresponding error
situation occurs, the execution of the program is erroneous.


                         Implementation Permissions

27    An implementation is allowed to place restrictions on Suppress pragmas.
An implementation is allowed to add additional check names, with
implementation-defined semantics. When Overflow_Check has been suppressed, an
implementation may also suppress an unspecified subset of the Range_Checks.


                            Implementation Advice

28    The implementation should minimize the code executed for checks that
have been suppressed.

      NOTES

29    2  There is no guarantee that a suppressed check is actually removed;
      hence a pragma Suppress should be used only for efficiency reasons.


                                  Examples

30    Examples of suppressing checks:

31    pragma Suppress(Range_Check);
      pragma Suppress(Index_Check, On => Table);


11.6 Exceptions and Optimization


1     This clause gives permission to the implementation to perform certain
``optimizations'' that do not necessarily preserve the canonical semantics.


                              Dynamic Semantics

2     The rest of this International Standard (outside this clause) defines
the canonical semantics of the language. The canonical semantics of a given
(legal) program determines a set of possible external effects that can result
from the execution of the program with given inputs.

3     As explained in 1.1.3, ``
Conformity of an Implementation with the Standard'', the external effect of a
program is defined in terms of its interactions with its external environment.
Hence, the implementation can perform any internal actions whatsoever, in any
order or in parallel, so long as the external effect of the execution of the
program is one that is allowed by the canonical semantics, or by the rules of
this clause.


                         Implementation Permissions

4     The following additional permissions are granted to the implementation:

5     An implementation need not always raise an exception when a
      language-defined check fails. Instead, the operation that failed the
      check can simply yield an undefined result. The exception need be raised
      by the implementation only if, in the absence of raising it, the value
      of this undefined result would have some effect on the external
      interactions of the program. In determining this, the implementation
      shall not presume that an undefined result has a value that belongs to
      its subtype, nor even to the base range of its type, if scalar. Having
      removed the raise of the exception, the canonical semantics will in
      general allow the implementation to omit the code for the check, and
      some or all of the operation itself.

6     If an exception is raised due to the failure of a language-defined
      check, then upon reaching the corresponding exception_handler (or the
      termination of the task, if none), the external interactions that have
      occurred need reflect only that the exception was raised somewhere
      within the execution of the sequence_of_statements with the handler (or
      the task_body), possibly earlier (or later if the interactions are
      independent of the result of the checked operation) than that defined by
      the canonical semantics, but not within the execution of some
      abort-deferred operation or independent subprogram that does not
      dynamically enclose the execution of the construct whose check failed.
      An independent subprogram is one that is defined outside the library
      unit containing the construct whose check failed, and has no Inline
      pragma applied to it. Any assignment that occurred outside of such
      abort-deferred operations or independent subprograms can be disrupted by
      the raising of the exception, causing the object or its parts to become
      abnormal, and certain subsequent uses of the object to be erroneous, as
      explained in 13.9.1.

      NOTES

7     3  The permissions granted by this clause can have an effect on the
      semantics of a program only if the program fails a language-defined
      check.



                          Section 12: Generic Units


1     A generic unit is a program unit that is either a generic subprogram or
a generic package. A generic unit is a template, which can be parameterized,
and from which corresponding (nongeneric) subprograms or packages can be
obtained. The resulting program units are said to be instances of the original
generic unit.

2     A generic unit is declared by a generic_declaration. This form of
declaration has a generic_formal_part declaring any generic formal parameters.
An instance of a generic unit is obtained as the result of a
generic_instantiation with appropriate generic actual parameters for the
generic formal parameters. An instance of a generic subprogram is a
subprogram. An instance of a generic package is a package.

3     Generic units are templates. As templates they do not have the
properties that are specific to their nongeneric counterparts. For example, a
generic subprogram can be instantiated but it cannot be called. In contrast,
an instance of a generic subprogram is a (nongeneric) subprogram; hence, this
instance can be called but it cannot be used to produce further instances.


12.1 Generic Declarations


1     A generic_declaration declares a generic unit, which is either a generic
subprogram or a generic package. A generic_declaration includes a
generic_formal_part declaring any generic formal parameters. A generic formal
parameter can be an object; alternatively (unlike a parameter of a
subprogram), it can be a type, a subprogram, or a package.


                                   Syntax

2     generic_declaration ::= generic_subprogram_declaration
       | generic_package_declaration

3     generic_subprogram_declaration ::= 
           generic_formal_part  subprogram_specification;

4     generic_package_declaration ::= 
           generic_formal_part  package_specification;

5     generic_formal_part ::= generic {generic_formal_parameter_declaration
       | use_clause}

6     generic_formal_parameter_declaration ::= 
            formal_object_declaration
          | formal_type_declaration
          | formal_subprogram_declaration
          | formal_package_declaration

7     The only form of subtype_indication allowed within a generic_formal_part
      is a subtype_mark (that is, the subtype_indication shall not include an
      explicit constraint). The defining name of a generic subprogram shall be
      an identifier (not an operator_symbol).


                              Static Semantics

8     A generic_declaration declares a generic unit - a generic package,
generic procedure or generic function, as appropriate.

9     An entity is a generic formal entity if it is declared by a
generic_formal_parameter_declaration. ``Generic formal,'' or simply ``
formal,'' is used as a prefix in referring to objects, subtypes (and types),
functions, procedures and packages, that are generic formal entities, as well
as to their respective declarations. Examples: ``generic formal procedure'' or
a ``formal integer type declaration.''


                              Dynamic Semantics

10    The elaboration of a generic_declaration has no effect.

      NOTES

11    1  Outside a generic unit a name that denotes the generic_declaration
      denotes the generic unit. In contrast, within the declarative region of
      the generic unit, a name that denotes the generic_declaration denotes
      the current instance.

12    2  Within a generic subprogram_body, the name of this program unit acts
      as the name of a subprogram. Hence this name can be overloaded, and it
      can appear in a recursive call of the current instance. For the same
      reason, this name cannot appear after the reserved word new in a
      (recursive) generic_instantiation.

13    3  A default_expression or default_name appearing in a
      generic_formal_part is not evaluated during elaboration of the
      generic_formal_part; instead, it is evaluated when used. (The usual
      visibility rules apply to any name used in a default: the denoted
      declaration therefore has to be visible at the place of the expression.)


                                  Examples

14    Examples of generic formal parts:

15    generic     --  parameterless 

16    generic
         Size : Natural;  --  formal object 

17    generic
         Length : Integer := 200;          -- formal object with a default expression

18       Area   : Integer := Length*Length; -- formal object with a default expression

19    generic
         type Item  is private;                       -- formal type
         type Index is (<>);                          -- formal type
         type Row   is array(Index range <>) of Item; -- formal type
         with function "<"(X, Y : Item) return Boolean;    -- formal subprogram 

20    Examples of generic declarations declaring generic subprograms Exchange
and Squaring:

21    generic
         type Elem is private;
      procedure Exchange(U, V : in out Elem);

22    generic
         type Item is private;
         with function "*"(U, V : Item) return Item is <>;
      function Squaring(X : Item) return Item;

23    Example of a generic declaration declaring a generic package:

24    generic
         type Item   is private;
         type Vector is array (Positive range <>) of Item;
         with function Sum(X, Y : Item) return Item;
      package On_Vectors is
         function Sum  (A, B : Vector) return Vector;
         function Sigma(A    : Vector) return Item;
         Length_Error : exception;
      end On_Vectors;




12.2 Generic Bodies


1     The body of a generic unit (a generic body) is a template for the
instance bodies. The syntax of a generic body is identical to that of a
nongeneric body.


                              Dynamic Semantics

2     The elaboration of a generic body has no other effect than to establish
that the generic unit can from then on be instantiated without failing the
Elaboration_Check. If the generic body is a child of a generic package, then
its elaboration establishes that each corresponding declaration nested in an
instance of the parent (see 10.1.1) can from then on be instantiated without
failing the Elaboration_Check.

      NOTES

3     4  The syntax of generic subprograms implies that a generic subprogram
      body is always the completion of a declaration.


                                  Examples

4     Example of a generic procedure body:

5     procedure Exchange(U, V : in out Elem) is  -- see 12.1
         T : Elem;  --  the generic formal type
      begin
         T := U;
         U := V;
         V := T;
      end Exchange;

6     Example of a generic function body:

7     function Squaring(X : Item) return Item is  --  see 12.1
      begin
         return X*X;  --  the formal operator "*"
      end Squaring;

8     Example of a generic package body:

9     package body On_Vectors is  --  see 12.1

10       function Sum(A, B : Vector) return Vector is
            Result : Vector(A'Range); --  the formal type Vector
            Bias   : constant Integer := B'First - A'First;
         begin
            if A'Length /= B'Length then
               raise Length_Error;
            end if;

11          for N in A'Range loop
               Result(N) := Sum(A(N), B(N + Bias)); -- the formal function Sum
            end loop;
            return Result;
         end Sum;

12       function Sigma(A : Vector) return Item is
            Total : Item := A(A'First); --  the formal type Item
         begin
            for N in A'First + 1 .. A'Last loop
               Total := Sum(Total, A(N)); --  the formal function Sum
            end loop;
            return Total;
         end Sigma;
      end On_Vectors;


12.3 Generic Instantiation


1     An instance of a generic unit is declared by a generic_instantiation.


                                   Syntax

2     generic_instantiation ::= 
           package defining_program_unit_name is
               new generic_package_name [generic_actual_part];
         | procedure defining_program_unit_name is
               new generic_procedure_name [generic_actual_part];
         | function defining_designator is
               new generic_function_name [generic_actual_part];

3     generic_actual_part ::= 
         (generic_association {, generic_association})

4     generic_association ::= 
         [generic_formal_parameter_selector_name
       =>] explicit_generic_actual_parameter

5     explicit_generic_actual_parameter ::= expression | variable_name
         | subprogram_name | entry_name | subtype_mark
         | package_instance_name

6     A generic_association is named or positional according to whether or not
      the generic_formal_parameter_selector_name is specified. Any positional
      associations shall precede any named associations.

7     The generic actual parameter is either the
explicit_generic_actual_parameter given in a generic_parameter_association for
each formal, or the corresponding default_expression or default_name if no
generic_parameter_association is given for the formal. When the meaning is
clear from context, the term ``generic actual,'' or simply ``actual,'' is used
as a synonym for ``generic actual parameter'' and also for the view denoted by
one, or the value of one.


                               Legality Rules

8     In a generic_instantiation for a particular kind of program unit
(package, procedure, or function), the name shall denote a generic unit of the
corresponding kind (generic package, generic procedure, or generic function,
respectively).

9     The generic_formal_parameter_selector_name of a generic_association
shall denote a generic_formal_parameter_declaration of the generic unit being
instantiated. If two or more formal subprograms have the same defining name,
then named associations are not allowed for the corresponding actuals.

10    A generic_instantiation shall contain at most one generic_association
for each formal. Each formal without an association shall have a
default_expression or subprogram_default.

11    In a generic unit Legality Rules are enforced at compile time of the
generic_declaration and generic body, given the properties of the formals. In
the visible part and formal part of an instance, Legality Rules are enforced
at compile time of the generic_instantiation, given the properties of the
actuals. In other parts of an instance, Legality Rules are not enforced; this
rule does not apply when a given rule explicitly specifies otherwise.


                              Static Semantics

12    A generic_instantiation declares an instance; it is equivalent to the
instance declaration (a package_declaration or subprogram_declaration)
immediately followed by the instance body, both at the place of the
instantiation.

13    The instance is a copy of the text of the template. Each use of a formal
parameter becomes (in the copy) a use of the actual, as explained below. An
instance of a generic package is a package, that of a generic procedure is a
procedure, and that of a generic function is a function.

14    The interpretation of each construct within a generic declaration or
body is determined using the overloading rules when that generic declaration
or body is compiled. In an instance, the interpretation of each (copied)
construct is the same, except in the case of a name that denotes the
generic_declaration or some declaration within the generic unit; the
corresponding name in the instance then denotes the corresponding copy of the
denoted declaration. The overloading rules do not apply in the instance.

15    In an instance, a generic_formal_parameter_declaration declares a view
whose properties are identical to those of the actual, except as specified in
12.4, ``Formal Objects'' and 12.6, ``Formal Subprograms''. Similarly, for a
declaration within a generic_formal_parameter_declaration, the corresponding
declaration in an instance declares a view whose properties are identical to
the corresponding declaration within the declaration of the actual.

16    Implicit declarations are also copied, and a name that denotes an
implicit declaration in the generic denotes the corresponding copy in the
instance. However, for a type declared within the visible part of the generic,
a whole new set of primitive subprograms is implicitly declared for use
outside the instance, and may differ from the copied set if the properties of
the type in some way depend on the properties of some actual type specified in
the instantiation. For example, if the type in the generic is derived from a
formal private type, then in the instance the type will inherit subprograms
from the corresponding actual type.

17    These new implicit declarations occur immediately after the type
declaration in the instance, and override the copied ones. The copied ones can
be called only from within the instance; the new ones can be called only from
outside the instance, although for tagged types, the body of a new one can be
executed by a call to an old one.

18    In the visible part of an instance, an explicit declaration overrides an
implicit declaration if they are homographs, as described in 8.3. On the other
hand, an explicit declaration in the private part of an instance overrides an
implicit declaration in the instance, only if the corresponding explicit
declaration in the generic overrides a corresponding implicit declaration in
the generic. Corresponding rules apply to the other kinds of overriding
described in 8.3.


                           Post-Compilation Rules

19    Recursive generic instantiation is not allowed in the following sense:
if a given generic unit includes an instantiation of a second generic unit,
then the instance generated by this instantiation shall not include an
instance of the first generic unit (whether this instance is generated
directly, or indirectly by intermediate instantiations).


                              Dynamic Semantics

20    For the elaboration of a generic_instantiation, each generic_association
is first evaluated. If a default is used, an implicit generic_association is
assumed for this rule. These evaluations are done in an arbitrary order,
except that the evaluation for a default actual takes place after the
evaluation for another actual if the default includes a name that denotes the
other one. Finally, the instance declaration and body are elaborated.

21    For the evaluation of a generic_association the generic actual parameter
is evaluated. Additional actions are performed in the case of a formal object
of mode in (see 12.4).

      NOTES

22    5  If a formal type is not tagged, then the type is treated as an
      untagged type within the generic body. Deriving from such a type in a
      generic body is permitted; the new type does not get a new tag value,
      even if the actual is tagged. Overriding operations for such a derived
      type cannot be dispatched to from outside the instance.


                                  Examples

23    Examples of generic instantiations (see 12.1):

24    procedure Swap is new Exchange(Elem => Integer);
      procedure Swap is new Exchange(Character);                  
      --  Swap is overloaded 
      function Square is new Squaring(Integer);                   
      --  "*" of Integer used by default
      function Square is new Squaring(Item => Matrix, "*" => Matrix_Product);
      function Square is new Squaring(Matrix, Matrix_Product); -- same as previous    

25    package Int_Vectors is new On_Vectors(Integer, Table, "+");

26    Examples of uses of instantiated units:

27    Swap(A, B);
      A := Square(A);

28    T : Table(1 .. 5) := (10, 20, 30, 40, 50);
      N : Integer := Int_Vectors.Sigma(T);  --  150 (see 12.2, ``
      Generic Bodies'' for the body of Sigma)

29    use Int_Vectors;
      M : Integer := Sigma(T);  --  150


12.4 Formal Objects


1     A generic formal object can be used to pass a value or variable to a
generic unit.


                                   Syntax

2     formal_object_declaration ::= 
          defining_identifier_list : mode subtype_mark
       [:= default_expression];


                            Name Resolution Rules

3     The expected type for the default_expression, if any, of a formal object
is the type of the formal object.

4     For a generic formal object of mode in, the expected type for the actual
is the type of the formal.

5     For a generic formal object of mode in out, the type of the actual shall
resolve to the type of the formal.


                               Legality Rules

6     If a generic formal object has a default_expression, then the mode shall
be in (either explicitly or by default); otherwise, its mode shall be either
in or in out.

7     For a generic formal object of mode in, the actual shall be an
expression. For a generic formal object of mode in out, the actual shall be a
name that denotes a variable for which renaming is allowed (see 8.5.1).

8     The type of a generic formal object of mode in shall be nonlimited.


                              Static Semantics

9     A formal_object_declaration declares a generic formal object. The
default mode is in. For a formal object of mode in, the nominal subtype is the
one denoted by the subtype_mark in the declaration of the formal. For a formal
object of mode in out, its type is determined by the subtype_mark in the
declaration; its nominal subtype is nonstatic, even if the subtype_mark
denotes a static subtype.

10    In an instance, a formal_object_declaration of mode in declares a new
stand-alone constant object whose initialization expression is the actual,
whereas a formal_object_declaration of mode in out declares a view whose
properties are identical to those of the actual.


                              Dynamic Semantics

11    For the evaluation of a generic_association for a formal object of mode
in, a constant object is created, the value of the actual parameter is
converted to the nominal subtype of the formal object, and assigned to the
object, including any value adjustment - see 7.6.

      NOTES

12    6  The constraints that apply to a generic formal object of mode in out
      are those of the corresponding generic actual parameter (not those
      implied by the subtype_mark that appears in the
      formal_object_declaration). Therefore, to avoid confusion, it is
      recommended that the name of a first subtype be used for the declaration
      of such a formal object.


12.5 Formal Types


1     A generic formal subtype can be used to pass to a generic unit a subtype
whose type is in a certain class of types.


                                   Syntax

2     formal_type_declaration ::= 
          type defining_identifier[discriminant_part
      ] is formal_type_definition;

3     formal_type_definition ::= 
            formal_private_type_definition
          | formal_derived_type_definition
          | formal_discrete_type_definition
          | formal_signed_integer_type_definition
          | formal_modular_type_definition
          | formal_floating_point_definition
          | formal_ordinary_fixed_point_definition
          | formal_decimal_fixed_point_definition
          | formal_array_type_definition
          | formal_access_type_definition


                               Legality Rules

4     For a generic formal subtype, the actual shall be a subtype_mark; it
denotes the (generic) actual subtype.


                              Static Semantics

5     A formal_type_declaration declares a (generic) formal type, and its
first subtype, the (generic) formal subtype.

6     The form of a formal_type_definition determines a class to which the
formal type belongs. For a formal_private_type_definition the reserved words
tagged and limited indicate the class (see 12.5.1). For a
formal_derived_type_definition the class is the derivation class rooted at the
ancestor type. For other formal types, the name of the syntactic category
indicates the class; a formal_discrete_type_definition defines a discrete
type, and so on.


                               Legality Rules

7     The actual type shall be in the class determined for the formal.


                              Static Semantics

8/1   The formal type also belongs to each class that contains the determined
class. The primitive subprograms of the type are as for any type in the
determined class. For a formal type other than a formal derived type, these
are the predefined operators of the type{. For an elementary formal type, the
predefined operators are implicitly declared immediately after the declaration
of the formal type. For a composite formal type, the predefined operators are
implicitly declared either immediately after the declaration of the formal
type, or later in its immediate scope according to the rules of 7.3.1.}[; they
are implicitly declared immediately after the declaration of the formal type.]
In an instance, the copy of such an implicit declaration declares a view of
the predefined operator of the actual type, even if this operator has been
overridden for the actual type. The rules specific to formal derived types are
given in 12.5.1.

      NOTES

9     7  Generic formal types, like all types, are not named. Instead, a name
      can denote a generic formal subtype. Within a generic unit, a generic
      formal type is considered as being distinct from all other (formal or
      nonformal) types.

10    8  A discriminant_part is allowed only for certain kinds of types, and
      therefore only for certain kinds of generic formal types. See 3.7.


                                  Examples

11    Examples of generic formal types:

12    type Item is private;
      type Buffer(Length : Natural) is limited private;

13    type Enum  is (<>);
      type Int   is range <>;
      type Angle is delta <>;
      type Mass  is digits <>;

14    type Table is array (Enum) of Item;

15    Example of a generic formal part declaring a formal integer type:

16    generic
         type Rank is range <>;
         First  : Rank := Rank'First;
         Second : Rank := First + 1;  --  the operator "+" of the type Rank  


12.5.1 Formal Private and Derived Types


1     The class determined for a formal private type can be either limited or
nonlimited, and either tagged or untagged; no more specific class is known for
such a type. The class determined for a formal derived type is the derivation
class rooted at the ancestor type.


                                   Syntax

2     formal_private_type_definition ::= [[abstract] tagged] [limited] private

3     formal_derived_type_definition ::= [abstract] new subtype_mark
       [with private]


                               Legality Rules

4     If a generic formal type declaration has a known_discriminant_part, then
it shall not include a default_expression for a discriminant.

5     The ancestor subtype of a formal derived type is the subtype denoted by
the subtype_mark of the formal_derived_type_definition. For a formal derived
type declaration, the reserved words with private shall appear if and only if
the ancestor type is a tagged type; in this case the formal derived type is a
private extension of the ancestor type and the ancestor shall not be a
class-wide type. Similarly, the optional reserved word abstract shall appear
only if the ancestor type is a tagged type.

6     If the formal subtype is definite, then the actual subtype shall also be
definite.

7     For a generic formal derived type with no discriminant_part:

8     If the ancestor subtype is constrained, the actual subtype shall be
      constrained, and shall be statically compatible with the ancestor;

9     If the ancestor subtype is an unconstrained access or composite subtype,
      the actual subtype shall be unconstrained.

10    If the ancestor subtype is an unconstrained discriminated subtype, then
      the actual shall have the same number of discriminants, and each
      discriminant of the actual shall correspond to a discriminant of the
      ancestor, in the sense of 3.7.

11    The declaration of a formal derived type shall not have a
known_discriminant_part. For a generic formal private type with a
known_discriminant_part:

12    The actual type shall be a type with the same number of discriminants.

13    The actual subtype shall be unconstrained.

14    The subtype of each discriminant of the actual type shall statically
      match the subtype of the corresponding discriminant of the formal type.

15    For a generic formal type with an unknown_discriminant_part, the actual
may, but need not, have discriminants, and may be definite or indefinite.


                              Static Semantics

16    The class determined for a formal private type is as follows:

17    Type Definition                        Determined Class
      
      limited private                        the class of all types
      private                                the class of all nonlimited types
      tagged limited private                 the class of all tagged types
      tagged private                         
      the class of all nonlimited tagged types

18    The presence of the reserved word abstract determines whether the actual
type may be abstract.

19    A formal private or derived type is a private or derived type,
respectively. A formal derived tagged type is a private extension. A formal
private or derived type is abstract if the reserved word abstract appears in
its declaration.

20    If the ancestor type is a composite type that is not an array type, the
formal type inherits components from the ancestor type (including
discriminants if a new discriminant_part is not specified), as for a derived
type defined by a derived_type_definition (see 3.4).

21/1  For a formal derived type, the predefined operators and inherited
user-defined subprograms are determined by the ancestor type, and are
implicitly declared at the earliest place, if any, within the immediate scope
of the formal type, where the corresponding primitive subprogram of the
ancestor is visible (see 7.3.1). In an instance, the copy of such an implicit
declaration declares a view of the corresponding primitive subprogram of the
ancestor{ of the formal derived type}, even if this primitive has been
overridden for the actual type. {When the ancestor of the formal derived type
is itself a formal type, the copy of the implicit declaration declares a view
of the corresponding copied operation of the ancestor.} In the case of a
formal private extension, however, the tag of the formal type is that of the
actual type, so if the tag in a call is statically determined to be that of
the formal type, the body executed will be that corresponding to the actual
type.

22/1  For a {prefix}[prefix] S that denotes a formal indefinite subtype, the
following attribute is defined:

23    S'Definite
              S'Definite yields True if the actual subtype corresponding to S
              is definite; otherwise it yields False. The value of this
              attribute is of the predefined type Boolean.

      NOTES

24    9  In accordance with the general rule that the actual type shall belong
      to the class determined for the formal (see 12.5, ``Formal Types''):

    25    If the formal type is nonlimited, then so shall be the actual;

    26    For a formal derived type, the actual shall be in the class rooted
          at the ancestor subtype.

27    10  The actual type can be abstract only if the formal type is abstract
      (see 3.9.3).

28    11  If the formal has a discriminant_part, the actual can be either
      definite or indefinite. Otherwise, the actual has to be definite.


12.5.2 Formal Scalar Types


1     A formal scalar type is one defined by any of the
formal_type_definitions in this subclause. The class determined for a formal
scalar type is discrete, signed integer, modular, floating point, ordinary
fixed point, or decimal.


                                   Syntax

2     formal_discrete_type_definition ::= (<>)

3     formal_signed_integer_type_definition ::= range <>

4     formal_modular_type_definition ::= mod <>

5     formal_floating_point_definition ::= digits <>

6     formal_ordinary_fixed_point_definition ::= delta <>

7     formal_decimal_fixed_point_definition ::= delta <> digits <>


                               Legality Rules

8     The actual type for a formal scalar type shall not be a nonstandard
numeric type.

      NOTES

9     12  The actual type shall be in the class of types implied by the
      syntactic category of the formal type definition (see 12.5, ``
      Formal Types''). For example, the actual for a
      formal_modular_type_definition shall be a modular type.


12.5.3 Formal Array Types


1     The class determined for a formal array type is the class of all array
types.


                                   Syntax

2     formal_array_type_definition ::= array_type_definition


                               Legality Rules

3     The only form of discrete_subtype_definition that is allowed within the
declaration of a generic formal (constrained) array subtype is a subtype_mark.

4     For a formal array subtype, the actual subtype shall satisfy the
following conditions:

5     The formal array type and the actual array type shall have the same
      dimensionality; the formal subtype and the actual subtype shall be
      either both constrained or both unconstrained.

6     For each index position, the index types shall be the same, and the
      index subtypes (if unconstrained), or the index ranges (if constrained),
      shall statically match (see 4.9.1).

7     The component subtypes of the formal and actual array types shall
      statically match.

8     If the formal type has aliased components, then so shall the actual.


                                  Examples

9     Example of formal array types:

10    --  given the generic package 

11    generic
         type Item   is private;
         type Index  is (<>);
         type Vector is array (Index range <>) of Item;
         type Table  is array (Index) of Item;
      package P is
         ...
      end P;

12    --  and the types 

13    type Mix    is array (Color range <>) of Boolean;
      type Option is array (Color) of Boolean;

14    --  then Mix can match Vector and Option can match Table 

15    package R is new P(Item   => Boolean, Index => Color,
                         Vector => Mix,     Table => Option);

16    --  Note that Mix cannot match Table and Option cannot match Vector


12.5.4 Formal Access Types


1     The class determined for a formal access type is the class of all access
types.


                                   Syntax

2     formal_access_type_definition ::= access_type_definition


                               Legality Rules

3     For a formal access-to-object type, the designated subtypes of the
formal and actual types shall statically match.

4     If and only if the general_access_modifier constant applies to the
formal, the actual shall be an access-to-constant type. If the
general_access_modifier all applies to the formal, then the actual shall be a
general access-to-variable type (see 3.10).

5     For a formal access-to-subprogram subtype, the designated profiles of
the formal and the actual shall be mode-conformant, and the calling convention
of the actual shall be protected if and only if that of the formal is
protected.


                                  Examples

6     Example of formal access types:

7     --  the formal types of the generic package 

8     generic
         type Node is private;
         type Link is access Node;
      package P is
         ...
      end P;

9     --  can be matched by the actual types 

10    type Car;
      type Car_Name is access Car;

11    type Car is
         record
            Pred, Succ : Car_Name;
            Number     : License_Number;
            Owner      : Person;
         end record;

12    --  in the following generic instantiation 

13    package R is new P(Node => Car, Link => Car_Name);


12.6 Formal Subprograms


1     Formal subprograms can be used to pass callable entities to a generic
unit.


                                   Syntax

2     formal_subprogram_declaration ::= with subprogram_specification
       [is subprogram_default];

3     subprogram_default ::= default_name | <>

4     default_name ::= name


                            Name Resolution Rules

5     The expected profile for the default_name, if any, is that of the formal
subprogram.

6     For a generic formal subprogram, the expected profile for the actual is
that of the formal subprogram.


                               Legality Rules

7     The profiles of the formal and any named default shall be
mode-conformant.

8     The profiles of the formal and actual shall be mode-conformant.


                              Static Semantics

9     A formal_subprogram_declaration declares a generic formal subprogram.
The types of the formal parameters and result, if any, of the formal
subprogram are those determined by the subtype_marks given in the
formal_subprogram_declaration; however, independent of the particular subtypes
that are denoted by the subtype_marks, the nominal subtypes of the formal
parameters and result, if any, are defined to be nonstatic, and unconstrained
if of an array type (no applicable index constraint is provided in a call on a
formal subprogram). In an instance, a formal_subprogram_declaration declares a
view of the actual. The profile of this view takes its subtypes and calling
convention from the original profile of the actual entity, while taking the
formal parameter names and default_expressions from the profile given in the
formal_subprogram_declaration. The view is a function or procedure, never an
entry.

10    If a generic unit has a subprogram_default specified by a box, and the
corresponding actual parameter is omitted, then it is equivalent to an
explicit actual parameter that is a usage name identical to the defining name
of the formal.

      NOTES

11    13  The matching rules for formal subprograms state requirements that
      are similar to those applying to subprogram_renaming_declarations (see
      8.5.4). In particular, the name of a parameter of the formal subprogram
      need not be the same as that of the corresponding parameter of the
      actual subprogram; similarly, for these parameters, default_expressions
      need not correspond.

12    14  The constraints that apply to a parameter of a formal subprogram are
      those of the corresponding formal parameter of the matching actual
      subprogram (not those implied by the corresponding subtype_mark in the
      _specification of the formal subprogram). A similar remark applies to
      the result of a function. Therefore, to avoid confusion, it is
      recommended that the name of a first subtype be used in any declaration
      of a formal subprogram.

13    15  The subtype specified for a formal parameter of a generic formal
      subprogram can be any visible subtype, including a generic formal
      subtype of the same generic_formal_part.

14    16  A formal subprogram is matched by an attribute of a type if the
      attribute is a function with a matching specification. An enumeration
      literal of a given type matches a parameterless formal function whose
      result type is the given type.

15    17  A default_name denotes an entity that is visible or directly visible
      at the place of the generic_declaration; a box used as a default is
      equivalent to a name that denotes an entity that is directly visible at
      the place of the _instantiation.

16    18  The actual subprogram cannot be abstract (see 3.9.3).


                                  Examples

17    Examples of generic formal subprograms:

18    with function "+"(X, Y : Item) return Item is <>;
      with function Image(X : Enum) return String is Enum'Image;
      with procedure Update is Default_Update;

19    --  given the generic procedure declaration 

20    generic
         with procedure Action (X : in Item);
      procedure Iterate(Seq : in Item_Sequence);

21    --  and the procedure 

22    procedure Put_Item(X : in Item);

23    --  the following instantiation is possible 

24    procedure Put_List is new Iterate(Action => Put_Item);


12.7 Formal Packages


1     Formal packages can be used to pass packages to a generic unit. The
formal_package_declaration declares that the formal package is an instance of
a given generic package. Upon instantiation, the actual package has to be an
instance of that generic package.


                                   Syntax

2     formal_package_declaration ::= 
          with package defining_identifier is new generic_package_name
        formal_package_actual_part;

3     formal_package_actual_part ::= 
          (<>) | [generic_actual_part]


                               Legality Rules

4     The generic_package_name shall denote a generic package (the template
for the formal package); the formal package is an instance of the template.

5     The actual shall be an instance of the template. If the
formal_package_actual_part is (<>), then the actual may be any instance of the
template; otherwise, each actual parameter of the actual instance shall match
the corresponding actual parameter of the formal package (whether the actual
parameter is given explicitly or by default), as follows:

6     For a formal object of mode in the actuals match if they are static
      expressions with the same value, or if they statically denote the same
      constant, or if they are both the literal null.

7     For a formal subtype, the actuals match if they denote statically
      matching subtypes.

8     For other kinds of formals, the actuals match if they statically denote
      the same entity.

8.1/1 {For the purposes of matching, any actual parameter that is the name of
a formal object of mode in is replaced by the formal object's actual
expression (recursively).}


                              Static Semantics

9     A formal_package_declaration declares a generic formal package.

10    The visible part of a formal package includes the first list of
basic_declarative_items of the package_specification. In addition, if the
formal_package_actual_part is (<>), it also includes the generic_formal_-
part of the template for the formal package.


12.8 Example of a Generic Package


1     The following example provides a possible formulation of stacks by means
of a generic package. The size of each stack and the type of the stack
elements are provided as generic formal parameters.


                                  Examples

2/1   This paragraph was deleted.[ ]

3     generic
         Size : Positive;
         type Item is private;
      package Stack is
         procedure Push(E : in  Item);
         procedure Pop (E : out Item);
         Overflow, Underflow : exception;
      end Stack;

4     package body Stack is

5        type Table is array (Positive range <>) of Item;
         Space : Table(1 .. Size);
         Index : Natural := 0;

6        procedure Push(E : in Item) is
         begin
            if Index >= Size then
               raise Overflow;
            end if;
            Index := Index + 1;
            Space(Index) := E;
         end Push;

7        procedure Pop(E : out Item) is
         begin
            if Index = 0 then
               raise Underflow;
            end if;
            E := Space(Index);
            Index := Index - 1;
         end Pop;

8     end Stack;

9     Instances of this generic package can be obtained as follows:

10    package Stack_Int  is new Stack(Size => 200, Item => Integer);
      package Stack_Bool is new Stack(100, Boolean);

11    Thereafter, the procedures of the instantiated packages can be called as
follows:

12    Stack_Int.Push(N);
      Stack_Bool.Push(True);

13    Alternatively, a generic formulation of the type Stack can be given as
follows (package body omitted):

14    generic
         type Item is private;
      package On_Stacks is
         type Stack(Size : Positive) is limited private;
         procedure Push(S : in out Stack; E : in  Item);
         procedure Pop (S : in out Stack; E : out Item);
         Overflow, Underflow : exception;
      private
         type Table is array (Positive range <>) of Item;
         type Stack(Size : Positive) is
            record
               Space : Table(1 .. Size);
               Index : Natural := 0;
            end record;
      end On_Stacks;

15    In order to use such a package, an instance has to be created and
thereafter stacks of the corresponding type can be declared:

16    declare
         package Stack_Real is new On_Stacks(Real); use Stack_Real;
         S : Stack(100);
      begin
         ...
         Push(S, 2.54);
         ...
      end;



                      Section 13: Representation Issues


1/1   This section describes features for querying and controlling {certain
aspects of entities}[aspects of representation] and for interfacing to
hardware.


13.1 {Operational and Representation Items} [Representation Items]


0.1/1 {Representation and operational items can be used to specify aspects of
entities. Two kinds of aspects of entities can be specified: aspects of
representation and operational aspects. Representation items specify how the
types and other entities of the language are to be mapped onto the underlying
machine. Operational items specify other properties of entities. }

1/1   There are {six}[three] kinds of representation items: {attribute_-
definition_clauses for representation attributes, enumeration_representation_-
clauses, record_representation_clauses, at_clauses, }[representation_clauses,
]component_clauses, and representation pragmas. [Representation items specify
how the types and other entities of the language are to be mapped onto the
underlying machine.] They can be provided to give more efficient
representation or to interface with features that are outside the domain of
the language (for example, peripheral hardware). [Representation items also
specify other specifiable properties of entities. A representation item
applies to an entity identified by a local_name, which denotes an entity
declared local to the current declarative region, or a library unit declared
immediately preceding a representation pragma in a compilation.]

1.1/1 {An operational item is an attribute_definition_clause for an
operational attribute.}

1.2/1 {An operational item or a representation item applies to an entity
identified by a local_name, which denotes an entity declared local to the
current declarative region, or a library unit declared immediately preceding a
representation pragma in a compilation.}


                                   Syntax

2/1   {aspect_clause}[representation_clause] ::= 
      attribute_definition_clause
            | enumeration_representation_clause
            | record_representation_clause
            | at_clause

3     local_name ::= direct_name
            | direct_name'attribute_designator
            | library_unit_name

4/1   A representation pragma is allowed only at places where {an
      aspect_clause}[a representation_clause] or compilation_unit is allowed. {}


                            Name Resolution Rules

5/1   In {an operational item or}[a] representation item, if the local_name is
a direct_name, then it shall resolve to denote a declaration (or, in the case
of a pragma, one or more declarations) that occurs immediately within the same
declarative_region as the [representation ]item. If the local_name has an
attribute_designator, then it shall resolve to denote an
implementation-defined component (see 13.5.1) or a class-wide type implicitly
declared immediately within the same declarative_region as the [representation
]item. A local_name that is a library_unit_name (only permitted in a
representation pragma) shall resolve to denote the library_item that
immediately precedes (except for other pragmas) the representation pragma.


                               Legality Rules

6/1   The local_name of a {aspect_clause}[representation_clause] or
representation pragma shall statically denote an entity (or, in the case of a
pragma, one or more entities) declared immediately preceding it in a
compilation, or within the same declarative_part, package_specification, task_-
definition, protected_definition, or record_definition as the representation
{or operational }item. If a local_name denotes a local callable entity, it may
do so through a local subprogram_renaming_declaration (as a way to resolve
ambiguity in the presence of overloading); otherwise, the local_name shall not
denote a renaming_declaration.

7     The representation of an object consists of a certain number of bits
(the size of the object). These are the bits that are normally read or updated
by the machine code when loading, storing, or operating-on the value of the
object. This includes some padding bits, when the size of the object is
greater than the size of its subtype. Such padding bits are considered to be
part of the representation of the object, rather than being gaps between
objects, if these bits are normally read and updated.

8     A representation item directly specifies an aspect of representation of
the entity denoted by the local_name, except in the case of a type-related
representation item, whose local_name shall denote a first subtype, and which
directly specifies an aspect of the subtype's type. A representation item that
names a subtype is either subtype-specific (Size and Alignment clauses) or
type-related (all others). Subtype-specific aspects may differ for different
subtypes of the same type.

8.1/1 {An operational item directly specifies an operational aspect of the
type of the subtype denoted by the local_name. The local_name of an
operational item shall denote a first subtype. An operational item that names
a subtype is type-related. }

9     A representation item that directly specifies an aspect of a subtype or
type shall appear after the type is completely defined (see 3.11.1), and
before the subtype or type is frozen (see 13.14). If a representation item is
given that directly specifies an aspect of an entity, then it is illegal to
give another representation item that directly specifies the same aspect of
the entity.

9.1/1 {An operational item that directly specifies an aspect of a type shall
appear before the type is frozen (see 13.14). If an operational item is given
that directly specifies an aspect of a type, then it is illegal to give
another operational item that directly specifies the same aspect of the type.}

10    For an untagged derived type, no type-related representation items are
allowed if the parent type is a by-reference type, or has any user-defined
primitive subprograms.

11/1  {Operational and r}[R]epresentation aspects of a generic formal
parameter are the same as those of the actual. {Operational and representation
aspects of a partial view are the same as those of the full view.} A
type-related representation item is not allowed for a descendant of a generic
formal untagged type.

12    A representation item that specifies the Size for a given subtype, or
the size or storage place for an object (including a component) of a given
subtype, shall allow for enough storage space to accommodate any value of the
subtype.

13/1  A representation {or operational }item that is not supported by the
implementation is illegal, or raises an exception at run time.


                              Static Semantics

14    If two subtypes statically match, then their subtype-specific aspects
(Size and Alignment) are the same.

15/1  A derived type inherits each type-related aspect {of representation }of
its parent type that was directly specified before the declaration of the
derived type, or (in the case where the parent is derived) that was inherited
by the parent type from the grandparent type. A derived subtype inherits each
subtype-specific aspect {of representation }of its parent subtype that was
directly specified before the declaration of the derived type, or (in the case
where the parent is derived) that was inherited by the parent subtype from the
grandparent subtype, but only if the parent subtype statically matches the
first subtype of the parent type. An inherited aspect of representation is
overridden by a subsequent representation item that specifies the same aspect
of the type or subtype.

15.1/1 {In contrast, whether operational aspects are inherited by a derived
type depends on each specific aspect. When operational aspects are inherited
by a derived type, aspects that were directly specified before the declaration
of the derived type, or (in the case where the parent is derived) that were
inherited by the parent type from the grandparent type are inherited. An
inherited operational aspect is overridden by a subsequent operational item
that specifies the same aspect of the type.}

16    Each aspect of representation of an entity is as follows:

17    If the aspect is specified for the entity, meaning that it is either
      directly specified or inherited, then that aspect of the entity is as
      specified, except in the case of Storage_Size, which specifies a
      minimum.

18    If an aspect of representation of an entity is not specified, it is
      chosen by default in an unspecified manner.

18.1/1 {If an operational aspect is specified for an entity (meaning that it
is either directly specified or inherited), then that aspect of the entity is
as specified. Otherwise, the aspect of the entity has the default value for
that aspect.}


                              Dynamic Semantics

19/1  {}[]For the elaboration of a {aspect_clause}[representation_clause], any
evaluable constructs within it are evaluated.


                         Implementation Permissions

20    An implementation may interpret aspects of representation in an
implementation-defined manner. An implementation may place
implementation-defined restrictions on representation items. A recommended
level of support is specified for representation items and related features in
each subclause. These recommendations are changed to requirements for
implementations that support the Systems Programming Annex (see C.2, ``
Required Representation Support'').


                            Implementation Advice

21    The recommended level of support for all representation items is
qualified as follows:

22    An implementation need not support representation items containing
      nonstatic expressions, except that an implementation should support a
      representation item for a given entity if each nonstatic expression in
      the representation item is a name that statically denotes a constant
      declared before the entity.

23    An implementation need not support a specification for the Size for a
      given composite subtype, nor the size or storage place for an object
      (including a component) of a given composite subtype, unless the
      constraints on the subtype and its composite subcomponents (if any) are
      all static constraints.

24    An aliased component, or a component whose type is by-reference, should
      always be allocated at an addressable location.


13.2 Pragma Pack


1     A pragma Pack specifies that storage minimization should be the main
criterion when selecting the representation of a composite type.


                                   Syntax

2     The form of a pragma Pack is as follows:

3       pragma Pack(first_subtype_local_name);


                               Legality Rules

4     The first_subtype_local_name of a pragma Pack shall denote a composite
subtype.


                              Static Semantics

5     A pragma Pack specifies the packing aspect of representation; the type
(or the extension part) is said to be packed. For a type extension, the parent
part is packed as for the parent type, and a pragma Pack causes packing only
of the extension part.


                            Implementation Advice

6     If a type is packed, then the implementation should try to minimize
storage allocated to objects of the type, possibly at the expense of speed of
accessing components, subject to reasonable complexity in addressing
calculations.

7     The recommended level of support for pragma Pack is:

8     For a packed record type, the components should be packed as tightly as
      possible subject to the Sizes of the component subtypes, and subject to
      any record_representation_clause that applies to the type; the
      implementation may, but need not, reorder components or cross aligned
      word boundaries to improve the packing. A component whose Size is
      greater than the word size may be allocated an integral number of words.

9     For a packed array type, if the component subtype's Size is less than or
      equal to the word size, and Component_Size is not specified for the
      type, Component_Size should be less than or equal to the Size of the
      component subtype, rounded up to the nearest factor of the word size.


13.3 {Operational and Representation Attributes} [Representation Attributes]


1/1   The values of certain implementation-dependent characteristics can be
obtained by interrogating appropriate {operational or }representation
attributes. Some of these attributes are specifiable via an
attribute_definition_clause.


                                   Syntax

2     attribute_definition_clause ::= 
            for local_name'attribute_designator use expression;
          | for local_name'attribute_designator use name;


                            Name Resolution Rules

3     For an attribute_definition_clause that specifies an attribute that
denotes a value, the form with an expression shall be used. Otherwise, the
form with a name shall be used.

4     For an attribute_definition_clause that specifies an attribute that
denotes a value or an object, the expected type for the expression or name is
that of the attribute. For an attribute_definition_clause that specifies an
attribute that denotes a subprogram, the expected profile for the name is the
profile required for the attribute. For an attribute_definition_clause that
specifies an attribute that denotes some other kind of entity, the name shall
resolve to denote an entity of the appropriate kind.


                               Legality Rules

5/1   An attribute_designator is allowed in an attribute_definition_clause
only if this International Standard explicitly allows it, or for an
implementation-defined attribute if the implementation allows it. Each
specifiable attribute constitutes an {operational aspect or }aspect of
representation.

6     For an attribute_definition_clause that specifies an attribute that
denotes a subprogram, the profile shall be mode conformant with the one
required for the attribute, and the convention shall be Ada. Additional
requirements are defined for particular attributes.


                              Static Semantics

7     A Size clause is an attribute_definition_clause whose
attribute_designator is Size. Similar definitions apply to the other
specifiable attributes.

8     A storage element is an addressable element of storage in the machine. A
word is the largest amount of storage that can be conveniently and efficiently
manipulated by the hardware, given the implementation's run-time model. A word
consists of an integral number of storage elements.

9/1   {The following representation attributes are defined: Address,
Alignment, Size, Storage_Size, and Component_Size.}[The following attributes
are defined:]

10/1  For a {prefix}[prefix] X that denotes an object, program unit, or label:

11    X'Address
              Denotes the address of the first of the storage elements
              allocated to X. For a program unit or label, this value refers
              to the machine code associated with the corresponding body or
              statement. The value of this attribute is of type
              System.Address.

        12    Address may be specified for stand-alone objects and for program
              units via an attribute_definition_clause.


                             Erroneous Execution

13    If an Address is specified, it is the programmer's responsibility to
ensure that the address is valid; otherwise, program execution is erroneous.


                            Implementation Advice

14    For an array X, X'Address should point at the first component of the
array, and not at the array bounds.

15    The recommended level of support for the Address attribute is:

16    X'Address should produce a useful result if X is an object that is
      aliased or of a by-reference type, or is an entity whose Address has
      been specified.

17    An implementation should support Address clauses for imported
      subprograms.

18    Objects (including subcomponents) that are aliased or of a by-reference
      type should be allocated on storage element boundaries.

19    If the Address of an object is specified, or it is imported or exported,
      then the implementation should not perform optimizations based on
      assumptions of no aliases.

      NOTES

20    1  The specification of a link name in a pragma Export (see B.1) for a
      subprogram or object is an alternative to explicit specification of its
      link-time address, allowing a link-time directive to place the
      subprogram or object within memory.

21    2  The rules for the Size attribute imply, for an aliased object X, that
      if X'Size = Storage_Unit, then X'Address points at a storage element
      containing all of the bits of X, and only the bits of X.


                              Static Semantics

22/1  For a {prefix}[prefix] X that denotes a subtype or object:

23    X'Alignment
              The Address of an object that is allocated under control of the
              implementation is an integral multiple of the Alignment of the
              object (that is, the Address modulo the Alignment is zero). The
              offset of a record component is a multiple of the Alignment of
              the component. For an object that is not allocated under control
              of the implementation (that is, one that is imported, that is
              allocated by a user-defined allocator, whose Address has been
              specified, or is designated by an access value returned by an
              instance of Unchecked_Conversion), the implementation may assume
              that the Address is an integral multiple of its Alignment. The
              implementation shall not assume a stricter alignment.

        24    The value of this attribute is of type universal_integer, and
              nonnegative; zero means that the object is not necessarily
              aligned on a storage element boundary.

        25    Alignment may be specified for first subtypes and stand-alone
              objects via an attribute_definition_clause; the expression of
              such a clause shall be static, and its value nonnegative. If the
              Alignment of a subtype is specified, then the Alignment of an
              object of the subtype is at least as strict, unless the object's
              Alignment is also specified. The Alignment of an object created
              by an allocator is that of the designated subtype.

        26    If an Alignment is specified for a composite subtype or object,
              this Alignment shall be equal to the least common multiple of
              any specified Alignments of the subcomponent subtypes, or an
              integer multiple thereof.


                             Erroneous Execution

27    Program execution is erroneous if an Address clause is given that
conflicts with the Alignment.

28    If the Alignment is specified for an object that is not allocated under
control of the implementation, execution is erroneous if the object is not
aligned according to the Alignment.


                            Implementation Advice

29    The recommended level of support for the Alignment attribute for
subtypes is:

30    An implementation should support specified Alignments that are factors
      and multiples of the number of storage elements per word, subject to the
      following:

31    An implementation need not support specified Alignments for combinations
      of Sizes and Alignments that cannot be easily loaded and stored by
      available machine instructions.

32    An implementation need not support specified Alignments that are greater
      than the maximum Alignment the implementation ever returns by default.

33    The recommended level of support for the Alignment attribute for objects
is:

34    Same as above, for subtypes, but in addition:

35    For stand-alone library-level objects of statically constrained
      subtypes, the implementation should support all Alignments supported by
      the target linker. For example, page alignment is likely to be supported
      for such objects, but not for subtypes.

      NOTES

36    3  Alignment is a subtype-specific attribute.

37    4  The Alignment of a composite object is always equal to the least
      common multiple of the Alignments of its components, or a multiple
      thereof.

38    5  A component_clause, Component_Size clause, or a pragma Pack can
      override a specified Alignment.


                              Static Semantics

39/1  For a {prefix}[prefix] X that denotes an object:

40    X'Size  Denotes the size in bits of the representation of the object.
              The value of this attribute is of the type universal_integer.

        41    Size may be specified for stand-alone objects via an
              attribute_definition_clause; the expression of such a clause
              shall be static and its value nonnegative.


                            Implementation Advice

42    The recommended level of support for the Size attribute of objects is:

43    A Size clause should be supported for an object if the specified Size is
      at least as large as its subtype's Size, and corresponds to a size in
      storage elements that is a multiple of the object's Alignment (if the
      Alignment is nonzero).


                              Static Semantics

44    For every subtype S:

45    S'Size  If S is definite, denotes the size (in bits) that the
              implementation would choose for the following objects of subtype
              S:

            46    A record component of subtype S when the record type is
                  packed.

            47    The formal parameter of an instance of Unchecked_Conversion
                  that converts from subtype S to some other subtype.

        48    If S is indefinite, the meaning is implementation defined. The
              value of this attribute is of the type universal_integer. The
              Size of an object is at least as large as that of its subtype,
              unless the object's Size is determined by a Size clause, a
              component_clause, or a Component_Size clause. Size may be
              specified for first subtypes via an attribute_definition_-
              clause; the expression of such a clause shall be static and its
              value nonnegative.


                         Implementation Requirements

49    In an implementation, Boolean'Size shall be 1.


                            Implementation Advice

50    If the Size of a subtype is specified, and allows for efficient
independent addressability (see 9.10) on the target architecture, then the
Size of the following objects of the subtype should equal the Size of the
subtype:

51    Aliased objects (including components).

52    Unaliased components, unless the Size of the component is determined by
      a component_clause or Component_Size clause.

53    A Size clause on a composite subtype should not affect the internal
layout of components.

54    The recommended level of support for the Size attribute of subtypes is:

55    The Size (if not specified) of a static discrete or fixed point subtype
      should be the number of bits needed to represent each value belonging to
      the subtype using an unbiased representation, leaving space for a sign
      bit only if the subtype contains negative values. If such a subtype is a
      first subtype, then an implementation should support a specified Size
      for it that reflects this representation.

56    For a subtype implemented with levels of indirection, the Size should
      include the size of the pointers, but not the size of what they point
      at.

      NOTES

57    6  Size is a subtype-specific attribute.

58    7  A component_clause or Component_Size clause can override a specified
      Size. A pragma Pack cannot.


                              Static Semantics

59/1  For a {prefix}[prefix] T that denotes a task object (after any implicit
dereference):

60    T'Storage_Size
              Denotes the number of storage elements reserved for the task.
              The value of this attribute is of the type universal_integer.
              The Storage_Size includes the size of the task's stack, if any.
              The language does not specify whether or not it includes other
              storage associated with the task (such as the ``task control
              block'' used by some implementations.) If a pragma Storage_Size
              is given, the value of the Storage_Size attribute is at least
              the value specified in the pragma.

61    A pragma Storage_Size specifies the amount of storage to be reserved for
the execution of a task.


                                   Syntax

62    The form of a pragma Storage_Size is as follows:

63      pragma Storage_Size(expression);

64    A pragma Storage_Size is allowed only immediately within a
      task_definition.


                            Name Resolution Rules

65    The expression of a pragma Storage_Size is expected to be of any integer
type.


                              Dynamic Semantics

66    A pragma Storage_Size is elaborated when an object of the type defined
by the immediately enclosing task_definition is created. For the elaboration
of a pragma Storage_Size, the expression is evaluated; the Storage_Size
attribute of the newly created task object is at least the value of the
expression.

67    At the point of task object creation, or upon task activation,
Storage_Error is raised if there is insufficient free storage to accommodate
the requested Storage_Size.


                              Static Semantics

68/1  For a {prefix}[prefix] X that denotes an array subtype or array object
(after any implicit dereference):

69    X'Component_Size
              Denotes the size in bits of components of the type of X. The
              value of this attribute is of type universal_integer.

        70    Component_Size may be specified for array types via an attribute_-
              definition_clause; the expression of such a clause shall be
              static, and its value nonnegative.


                            Implementation Advice

71    The recommended level of support for the Component_Size attribute is:

72    An implementation need not support specified Component_Sizes that are
      less than the Size of the component subtype.

73    An implementation should support specified Component_Sizes that are
      factors and multiples of the word size. For such Component_Sizes, the
      array should contain no gaps between components. For other
      Component_Sizes (if supported), the array should contain no gaps between
      components when packing is also specified; the implementation should
      forbid this combination in cases where it cannot support a no-gaps
      representation.


                              Static Semantics

73.1/1 {The following operational attribute is defined: External_Tag.}

74/1  For every subtype S of a tagged type T (specific or class-wide)[, the
following attribute is defined]:

75/1  S'External_Tag
              S'External_Tag denotes an external string representation for
              S'Tag; it is of the predefined type String. External_Tag may be
              specified for a specific tagged type via an
              attribute_definition_clause; the expression of such a clause
              shall be static. The default external tag representation is
              implementation defined. See 3.9.2 and 13.13.2. {The value of
              External_Tag is never inherited; the default value is always
              used unless a new value is directly specified for a type.}


                         Implementation Requirements

76    In an implementation, the default external tag for each specific tagged
type declared in a partition shall be distinct, so long as the type is
declared outside an instance of a generic body. If the compilation unit in
which a given tagged type is declared, and all compilation units on which it
semantically depends, are the same in two different partitions, then the
external tag for the type shall be the same in the two partitions. What it
means for a compilation unit to be the same in two different partitions is
implementation defined. At a minimum, if the compilation unit is not
recompiled between building the two different partitions that include it, the
compilation unit is considered the same in the two partitions.

      NOTES

77    8  The following language-defined attributes are specifiable, at least
      for some of the kinds of entities to which they apply: Address, Size,
      Component_Size, Alignment, External_Tag, Small, Bit_Order, Storage_Pool,
      Storage_Size, Write, Output, Read, Input, and Machine_Radix.

78    9  It follows from the general rules in 13.1 that if one writes ``for
      X'Size use Y;'' then the X'Size attribute_reference will return Y
      (assuming the implementation allows the Size clause). The same is true
      for all of the specifiable attributes except Storage_Size.


                                  Examples

79    Examples of attribute definition clauses:

80    Byte : constant := 8;
      Page : constant := 2**12;

81    type Medium is range 0 .. 65_000;
      for Medium'Size use 2*Byte;
      for Medium'Alignment use 2;
      Device_Register : Medium;
      for Device_Register'Size use Medium'Size;
      for Device_Register'Address use System.Storage_Elements.To_Address(16#FFFF_0020#);

82    type Short is delta 0.01 range -100.0 .. 100.0;
      for Short'Size use 15;

83    for Car_Name'Storage_Size use -- specify access type's storage pool size
              2000*((Car'Size/System.Storage_Unit) +1); -- approximately 2000 cars

84    function My_Read(Stream : access Ada.Streams.Root_Stream_Type'Class)
        return T;
      for T'Read use My_Read; -- see 13.13.2

      NOTES

85    10  Notes on the examples: In the Size clause for Short, fifteen bits is
      the minimum necessary, since the type definition requires Short'Small <=
      2**(-7).


13.4 Enumeration Representation Clauses


1     An enumeration_representation_clause specifies the internal codes for
enumeration literals.


                                   Syntax

2     enumeration_representation_clause ::= 
          for first_subtype_local_name use enumeration_aggregate;

3     enumeration_aggregate ::= array_aggregate


                            Name Resolution Rules

4     The enumeration_aggregate shall be written as a one-dimensional
array_aggregate, for which the index subtype is the unconstrained subtype of
the enumeration type, and each component expression is expected to be of any
integer type.


                               Legality Rules

5     The first_subtype_local_name of an enumeration_representation_clause
shall denote an enumeration subtype.

6     The expressions given in the array_aggregate shall be static, and shall
specify distinct integer codes for each value of the enumeration type; the
associated integer codes shall satisfy the predefined ordering relation of the
type.


                              Static Semantics

7     An enumeration_representation_clause specifies the coding aspect of
representation. The coding consists of the internal code for each enumeration
literal, that is, the integral value used internally to represent each literal.


                         Implementation Requirements

8     For nonboolean enumeration types, if the coding is not specified for the
type, then for each value of the type, the internal code shall be equal to its
position number.


                            Implementation Advice

9     The recommended level of support for enumeration_representation_clauses
is:

10    An implementation should support at least the internal codes in the
      range System.Min_Int..System.Max_Int. An implementation need not support
      enumeration_representation_clauses for boolean types.

      NOTES

11/1  11  Unchecked_Conversion may be used to query the internal codes used
      for an enumeration type. The attributes of the type, such as Succ, Pred,
      and Pos, are unaffected by the {enumeration_}representation_clause. For
      example, Pos always returns the position number, not the internal
      integer code that might have been specified in a
      {enumeration_}representation_clause.


                                  Examples

12    Example of an enumeration representation clause:

13    type Mix_Code is (ADD, SUB, MUL, LDA, STA, STZ);

14    for Mix_Code use
         (ADD => 1, SUB => 2, MUL => 3, LDA => 8, STA => 24, STZ =>33);


13.5 Record Layout


1     The (record) layout aspect of representation consists of the storage
places for some or all components, that is, storage place attributes of the
components. The layout can be specified with a record_representation_clause.


13.5.1 Record Representation Clauses


1     A record_representation_clause specifies the storage representation of
records and record extensions, that is, the order, position, and size of
components (including discriminants, if any).


                                   Syntax

2     record_representation_clause ::= 
          for first_subtype_local_name use
            record [mod_clause]
              {component_clause}
            end record;

3     component_clause ::= 
          component_local_name at position range first_bit .. last_bit;

4     position ::= static_expression

5     first_bit ::= static_simple_expression

6     last_bit ::= static_simple_expression


                            Name Resolution Rules

7     Each position, first_bit, and last_bit is expected to be of any integer
type.


                               Legality Rules

8     The first_subtype_local_name of a record_representation_clause shall
denote a specific nonlimited record or record extension subtype.

9     If the component_local_name is a direct_name, the local_name shall
denote a component of the type. For a record extension, the component shall
not be inherited, and shall not be a discriminant that corresponds to a
discriminant of the parent type. If the component_local_name has an attribute_-
designator, the direct_name of the local_name shall denote either the
declaration of the type or a component of the type, and the
attribute_designator shall denote an implementation-defined implicit component
of the type.

10    The position, first_bit, and last_bit shall be static expressions. The
value of position and first_bit shall be nonnegative. The value of last_bit
shall be no less than first_bit - 1.

11    At most one component_clause is allowed for each component of the type,
including for each discriminant (component_clauses may be given for some, all,
or none of the components). Storage places within a component_list shall not
overlap, unless they are for components in distinct variants of the same
variant_part.

12    A name that denotes a component of a type is not allowed within a
record_representation_clause for the type, except as the component_local_name
of a component_clause.


                              Static Semantics

13    A record_representation_clause (without the mod_clause) specifies the
layout. The storage place attributes (see 13.5.2) are taken from the values of
the position, first_bit, and last_bit expressions after normalizing those
values so that first_bit is less than Storage_Unit.

14    A record_representation_clause for a record extension does not override
the layout of the parent part; if the layout was specified for the parent
type, it is inherited by the record extension.


                         Implementation Permissions

15    An implementation may generate implementation-defined components (for
example, one containing the offset of another component). An implementation
may generate names that denote such implementation-defined components; such
names shall be implementation-defined attribute_references. An implemen-
tation may allow such implementation-defined names to be used in record_-
representation_clauses. An implementation can restrict such component_clauses
in any manner it sees fit.

16    If a record_representation_clause is given for an untagged derived type,
the storage place attributes for all of the components of the derived type may
differ from those of the corresponding components of the parent type, even for
components whose storage place is not specified explicitly in the record_-
representation_clause.


                            Implementation Advice

17    The recommended level of support for record_representation_clauses is:

18    An implementation should support storage places that can be extracted
      with a load, mask, shift sequence of machine code, and set with a load,
      shift, mask, store sequence, given the available machine instructions
      and run-time model.

19    A storage place should be supported if its size is equal to the Size of
      the component subtype, and it starts and ends on a boundary that obeys
      the Alignment of the component subtype.

20    If the default bit ordering applies to the declaration of a given type,
      then for a component whose subtype's Size is less than the word size,
      any storage place that does not cross an aligned word boundary should be
      supported.

21    An implementation may reserve a storage place for the tag field of a
      tagged type, and disallow other components from overlapping that place.

22    An implementation need not support a component_clause for a component of
      an extension part if the storage place is not after the storage places
      of all components of the parent type, whether or not those storage
      places had been specified.

      NOTES

23    12  If no component_clause is given for a component, then the choice of
      the storage place for the component is left to the implementation. If
      component_clauses are given for all components, the
      record_representation_clause completely specifies the representation of
      the type and will be obeyed exactly by the implementation.


                                  Examples

24    Example of specifying the layout of a record type:

25    Word : constant := 4;  --  storage element is byte, 4 bytes per word

26    type State         is (A,M,W,P);
      type Mode          is (Fix, Dec, Exp, Signif);

27    type Byte_Mask     is array (0..7)  of Boolean;
      type State_Mask    is array (State) of Boolean;
      type Mode_Mask     is array (Mode)  of Boolean;

28    type Program_Status_Word is
        record
            System_Mask        : Byte_Mask;
            Protection_Key     : Integer range 0 .. 3;
            Machine_State      : State_Mask;
            Interrupt_Cause    : Interruption_Code;
            Ilc                : Integer range 0 .. 3;
            Cc                 : Integer range 0 .. 3;
            Program_Mask       : Mode_Mask;
            Inst_Address       : Address;
      end record;

29    for Program_Status_Word use
        record
            System_Mask      at 0*Word range 0  .. 7;
            Protection_Key   at 0*Word range 10 .. 11; -- bits 8,9 unused
            Machine_State    at 0*Word range 12 .. 15;
            Interrupt_Cause  at 0*Word range 16 .. 31;
            Ilc              at 1*Word range 0  .. 1;  -- second word
            Cc               at 1*Word range 2  .. 3;
            Program_Mask     at 1*Word range 4  .. 7;
            Inst_Address     at 1*Word range 8  .. 31;
        end record;

30    for Program_Status_Word'Size use 8*System.Storage_Unit;
      for Program_Status_Word'Alignment use 8;

      NOTES

31    13  Note on the example: The record_representation_clause defines the
      record layout. The Size clause guarantees that (at least) eight storage
      elements are used for objects of the type. The Alignment clause
      guarantees that aliased, imported, or exported objects of the type will
      have addresses divisible by eight.


13.5.2 Storage Place Attributes



                              Static Semantics

1     For a component C of a composite, non-array object R, the storage place
attributes are defined:

2     R.C'Position
              Denotes the same value as R.C'Address - R'Address. The value of
              this attribute is of the type universal_integer.

3     R.C'First_Bit
              Denotes the offset, from the start of the first of the storage
              elements occupied by C, of the first bit occupied by C. This
              offset is measured in bits. The first bit of a storage element
              is numbered zero. The value of this attribute is of the type
              universal_integer.

4     R.C'Last_Bit
              Denotes the offset, from the start of the first of the storage
              elements occupied by C, of the last bit occupied by C. This
              offset is measured in bits. The value of this attribute is of
              the type universal_integer.


                            Implementation Advice

5     If a component is represented using some form of pointer (such as an
offset) to the actual data of the component, and this data is contiguous with
the rest of the object, then the storage place attributes should reflect the
place of the actual data, not the pointer. If a component is allocated
discontiguously from the rest of the object, then a warning should be
generated upon reference to one of its storage place attributes.


13.5.3 Bit Ordering


1     The Bit_Order attribute specifies the interpretation of the storage
place attributes.


                              Static Semantics

2     A bit ordering is a method of interpreting the meaning of the storage
place attributes. High_Order_First (known in the vernacular as ``big endian'
') means that the first bit of a storage element (bit 0) is the most
significant bit (interpreting the sequence of bits that represent a component
as an unsigned integer value). Low_Order_First (known in the vernacular as `
`little endian'') means the opposite: the first bit is the least significant.

3     For every specific record subtype S, the following attribute is defined:

4     S'Bit_Order
              Denotes the bit ordering for the type of S. The value of this
              attribute is of type System.Bit_Order. Bit_Order may be
              specified for specific record types via an
              attribute_definition_clause; the expression of such a clause
              shall be static.

5     If Word_Size = Storage_Unit, the default bit ordering is implementation
defined. If Word_Size > Storage_Unit, the default bit ordering is the same as
the ordering of storage elements in a word, when interpreted as an integer.

6     The storage place attributes of a component of a type are interpreted
according to the bit ordering of the type.


                            Implementation Advice

7     The recommended level of support for the nondefault bit ordering is:

8     If Word_Size = Storage_Unit, then the implementation should support the
      nondefault bit ordering in addition to the default bit ordering.


13.6 Change of Representation


1     A type_conversion (see 4.6) can be used to convert between two different
representations of the same array or record. To convert an array from one
representation to another, two array types need to be declared with matching
component subtypes, and convertible index types. If one type has packing
specified and the other does not, then explicit conversion can be used to pack
or unpack an array.

2     To convert a record from one representation to another, two record types
with a common ancestor type need to be declared, with no inherited
subprograms. Distinct representations can then be specified for the record
types, and explicit conversion between the types can be used to effect a
change in representation.


                                  Examples

3     Example of change of representation:

4     -- Packed_Descriptor and Descriptor are two different types
      -- with identical characteristics, apart from their
      -- representation

5     type Descriptor is
          record
            -- components of a descriptor
          end record;

6     type Packed_Descriptor is new Descriptor;

7     for Packed_Descriptor use
          record
            -- component clauses for some or for all components
          end record;

8     -- Change of representation can now be accomplished by explicit type conversions:

9     D : Descriptor;
      P : Packed_Descriptor;

10    P := Packed_Descriptor(D);  -- pack D
      D := Descriptor(P);         -- unpack P


13.7 The Package System


1     For each implementation there is a library package called System which
includes the definitions of certain configuration-dependent characteristics.


                              Static Semantics

2     The following language-defined library package exists:

3     
      package System is
         pragma Preelaborate(System);

4        type Name is implementation-defined-enumeration-type;
         System_Name : constant Name := implementation-defined;

5        -- System-Dependent Named Numbers:

6        Min_Int               : constant := root_integer'First;
         Max_Int               : constant := root_integer'Last;

7        Max_Binary_Modulus    : constant := implementation-defined;
         Max_Nonbinary_Modulus : constant := implementation-defined;

8        Max_Base_Digits       : constant := root_real'Digits;
         Max_Digits            : constant := implementation-defined;

9        Max_Mantissa          : constant := implementation-defined;
         Fine_Delta            : constant := implementation-defined;

10       Tick                  : constant := implementation-defined;

11       -- Storage-related Declarations:

12       type Address is implementation-defined;
         Null_Address : constant Address;

13       Storage_Unit : constant := implementation-defined;
         Word_Size    : constant := implementation-defined * Storage_Unit;
         Memory_Size  : constant := implementation-defined;

14       -- Address Comparison:
         function "<" (Left, Right : Address) return Boolean;
         function "<="(Left, Right : Address) return Boolean;
         function ">" (Left, Right : Address) return Boolean;
         function ">="(Left, Right : Address) return Boolean;
         function "=" (Left, Right : Address) return Boolean;
      -- function "/=" (Left, Right : Address) return Boolean;
         -- "/=" is implicitly defined
         pragma Convention(Intrinsic, "<");
         ... -- and so on for all language-defined subprograms in this package

15       -- Other System-Dependent Declarations:
         type Bit_Order is (High_Order_First, Low_Order_First);
         Default_Bit_Order : constant Bit_Order;

16       -- Priority-related declarations (see D.1):
         subtype Any_Priority is Integer range implementation-defined;
         subtype Priority is Any_Priority range Any_Priority'First ..
                   implementation-defined;
         subtype Interrupt_Priority is Any_Priority range Priority'Last+1 ..
                   Any_Priority'Last;

17       Default_Priority : constant Priority :=
                   (Priority'First + Priority'Last)/2;

18    private
         ... -- not specified by the language
      end System;

19    Name is an enumeration subtype. Values of type Name are the names of
alternative machine configurations handled by the implementation. System_Name
represents the current machine configuration.

20    The named numbers Fine_Delta and Tick are of the type universal_real;
the others are of the type universal_integer.

21    The meanings of the named numbers are:

22    Min_Int The smallest (most negative) value allowed for the expressions
              of a signed_integer_type_definition.

23    Max_Int The largest (most positive) value allowed for the expressions of
              a signed_integer_type_definition.

24    Max_Binary_Modulus
              A power of two such that it, and all lesser positive powers of
              two, are allowed as the modulus of a modular_type_definition.

25    Max_Nonbinary_Modulus
              A value such that it, and all lesser positive integers, are
              allowed as the modulus of a modular_type_definition.

26    Max_Base_Digits
              The largest value allowed for the requested decimal precision in
              a floating_point_definition.

27    Max_Digits
              The largest value allowed for the requested decimal precision in
              a floating_point_definition that has no
              real_range_specification. Max_Digits is less than or equal to
              Max_Base_Digits.

28    Max_Mantissa
              The largest possible number of binary digits in the mantissa of
              machine numbers of a user-defined ordinary fixed point type.
              (The mantissa is defined in Annex G.)

29    Fine_Delta
              The smallest delta allowed in an ordinary_fixed_point_definition
              that has the real_range_specification range -1.0 .. 1.0.

30    Tick    A period in seconds approximating the real time interval during
              which the value of Calendar.Clock remains constant.

31    Storage_Unit
              The number of bits per storage element.

32    Word_Size
              The number of bits per word.

33    Memory_Size
              An implementation-defined value that is intended to reflect the
              memory size of the configuration in storage elements.

34    Address is of a definite, nonlimited type. Address represents machine
addresses capable of addressing individual storage elements. Null_Address is
an address that is distinct from the address of any object or program unit.

35    See 13.5.3 for an explanation of Bit_Order and Default_Bit_Order.


                         Implementation Permissions

36    An implementation may add additional implementation-defined declarations
to package System and its children. However, it is usually better for the
implementation to provide additional functionality via implementation-defined
children of System. Package System may be declared pure.


                            Implementation Advice

37    Address should be [of ]a private type.

      NOTES

38    14  There are also some language-defined child packages of System
      defined elsewhere.


13.7.1 The Package System.Storage_Elements



                              Static Semantics

1     The following language-defined library package exists:

2     package System.Storage_Elements is
         pragma Preelaborate(System.Storage_Elements);

3        type Storage_Offset is range implementation-defined;

4        subtype Storage_Count is Storage_Offset range 0..Storage_Offset'Last;

5        type Storage_Element is mod implementation-defined;
         for Storage_Element'Size use Storage_Unit;
         type Storage_Array is array
           (Storage_Offset range <>) of aliased Storage_Element;
         for Storage_Array'Component_Size use Storage_Unit;

6        -- Address Arithmetic:

7        function "+"(Left : Address; Right : Storage_Offset)
           return Address;
         function "+"(Left : Storage_Offset; Right : Address)
           return Address;
         function "-"(Left : Address; Right : Storage_Offset)
           return Address;
         function "-"(Left, Right : Address)
           return Storage_Offset;

8        function "mod"(Left : Address; Right : Storage_Offset)
           return Storage_Offset;

9        -- Conversion to/from integers:

10       type Integer_Address is implementation-defined;
         function To_Address(Value : Integer_Address) return Address;
         function To_Integer(Value : Address) return Integer_Address;

11       pragma Convention(Intrinsic, "+");
            -- ...and so on for all language-defined subprograms declared in this package.
      end System.Storage_Elements;

12    Storage_Element represents a storage element. Storage_Offset represents
an offset in storage elements. Storage_Count represents a number of storage
elements. Storage_Array represents a contiguous sequence of storage elements.

13    Integer_Address is a (signed or modular) integer subtype. To_Address and
To_Integer convert back and forth between this type and Address.


                         Implementation Requirements

14    Storage_Offset'Last shall be greater than or equal to Integer'Last or
the largest possible storage offset, whichever is smaller.
Storage_Offset'First shall be <= (-Storage_Offset'Last).


                         Implementation Permissions

15    Package System.Storage_Elements may be declared pure.


                            Implementation Advice

16    Operations in System and its children should reflect the target
environment semantics as closely as is reasonable. For example, on most
machines, it makes sense for address arithmetic to ``wrap around.'' Operations
that do not make sense should raise Program_Error.


13.7.2 The Package System.Address_To_Access_Conversions



                              Static Semantics

1     The following language-defined generic library package exists:

2     generic
          type Object(<>) is limited private;
      package System.Address_To_Access_Conversions is
         pragma Preelaborate(Address_To_Access_Conversions);

3        type Object_Pointer is access all Object;
         function To_Pointer(Value : Address) return Object_Pointer;
         function To_Address(Value : Object_Pointer) return Address;

4        pragma Convention(Intrinsic, To_Pointer);
         pragma Convention(Intrinsic, To_Address);
      end System.Address_To_Access_Conversions;

5     The To_Pointer and To_Address subprograms convert back and forth between
values of types Object_Pointer and Address. To_Pointer(X'Address) is equal to
X'Unchecked_Access for any X that allows Unchecked_Access.
To_Pointer(Null_Address) returns null. For other addresses, the behavior is
unspecified. To_Address(null) returns Null_Address (for null of the
appropriate type). To_Address(Y), where Y /= null, returns Y.all'Address.


                         Implementation Permissions

6     An implementation may place restrictions on instantiations of
Address_To_Access_Conversions.


13.8 Machine Code Insertions


1     A machine code insertion can be achieved by a call to a subprogram whose
sequence_of_statements contains code_statements.


                                   Syntax

2     code_statement ::= qualified_expression;

3     A code_statement is only allowed in the handled_sequence_of_statements
      of a subprogram_body. If a subprogram_body contains any code_statements,
      then within this subprogram_body the only allowed form of statement is a
      code_statement (labeled or not), the only allowed declarative_items are
      use_clauses, and no exception_handler is allowed (comments and pragmas
      are allowed as usual).


                            Name Resolution Rules

4     The qualified_expression is expected to be of any type.


                               Legality Rules

5     The qualified_expression shall be of a type declared in package
System.Machine_Code.

6     A code_statement shall appear only within the scope of a with_clause
that mentions package System.Machine_Code.


                              Static Semantics

7     The contents of the library package System.Machine_Code (if provided)
are implementation defined. The meaning of code_statements is implementation
defined. Typically, each qualified_expression represents a machine instruction
or assembly directive.


                         Implementation Permissions

8     An implementation may place restrictions on code_statements. An
implementation is not required to provide package System.Machine_Code.

      NOTES

9     15  An implementation may provide implementation-defined pragmas
      specifying register conventions and calling conventions.

10    16  Machine code functions are exempt from the rule that a
      return_statement is required. In fact, return_statements are forbidden,
      since only code_statements are allowed.

11    17  Intrinsic subprograms (see 6.3.1, ``Conformance Rules'') can also be
      used to achieve machine code insertions. Interface to assembly language
      can be achieved using the features in Annex B, ``
      Interface to Other Languages''.


                                  Examples

12    Example of a code statement:

13    M : Mask;
      procedure Set_Mask; pragma Inline(Set_Mask);

14    procedure Set_Mask is
        use System.Machine_Code; -- assume ``with System.Machine_Code;''
       appears somewhere above
      begin
        SI_Format'(Code => SSM, B => M'Base_Reg, D => M'Disp);
        --  Base_Reg and Disp are implementation-defined attributes
      end Set_Mask;


13.9 Unchecked Type Conversions


1     An unchecked type conversion can be achieved by a call to an instance of
the generic function Unchecked_Conversion.


                              Static Semantics

2     The following language-defined generic library function exists:

3     generic
         type Source(<>) is limited private;
         type Target(<>) is limited private;
      function Ada.Unchecked_Conversion(S : Source) return Target;
      pragma Convention(Intrinsic, Ada.Unchecked_Conversion);
      pragma Pure(Ada.Unchecked_Conversion);


                              Dynamic Semantics

4     The size of the formal parameter S in an instance of
Unchecked_Conversion is that of its subtype. This is the actual subtype passed
to Source, except when the actual is an unconstrained composite subtype, in
which case the subtype is constrained by the bounds or discriminants of the
value of the actual expression passed to S.

5     If all of the following are true, the effect of an unchecked conversion
is to return the value of an object of the target subtype whose representation
is the same as that of the source object S:

6     S'Size = Target'Size.

7     S'Alignment = Target'Alignment.

8     The target subtype is not an unconstrained composite subtype.

9     S and the target subtype both have a contiguous representation.

10    The representation of S is a representation of an object of the target
      subtype.

11    Otherwise, the effect is implementation defined; in particular, the
result can be abnormal (see 13.9.1).


                         Implementation Permissions

12    An implementation may return the result of an unchecked conversion by
reference, if the Source type is not a by-copy type. In this case, the result
of the unchecked conversion represents simply a different (read-only) view of
the operand of the conversion.

13    An implementation may place restrictions on Unchecked_Conversion.


                            Implementation Advice

14    The Size of an array object should not include its bounds; hence, the
bounds should not be part of the converted data.

15    The implementation should not generate unnecessary run-time checks to
ensure that the representation of S is a representation of the target type. It
should take advantage of the permission to return by reference when possible.
Restrictions on unchecked conversions should be avoided unless required by the
target environment.

16    The recommended level of support for unchecked conversions is:

17    Unchecked conversions should be supported and should be reversible in
      the cases where this clause defines the result. To enable meaningful use
      of unchecked conversion, a contiguous representation should be used for
      elementary subtypes, for statically constrained array subtypes whose
      component subtype is one of the subtypes described in this paragraph,
      and for record subtypes without discriminants whose component subtypes
      are described in this paragraph.


13.9.1 Data Validity


1     Certain actions that can potentially lead to erroneous execution are not
directly erroneous, but instead can cause objects to become abnormal.
Subsequent uses of abnormal objects can be erroneous.

2     A scalar object can have an invalid representation, which means that the
object's representation does not represent any value of the object's subtype.
The primary cause of invalid representations is uninitialized variables.

3     Abnormal objects and invalid representations are explained in this
subclause.


                              Dynamic Semantics

4     When an object is first created, and any explicit or default
initializations have been performed, the object and all of its parts are in
the normal state. Subsequent operations generally leave them normal. However,
an object or part of an object can become abnormal in the following ways:

5     An assignment to the object is disrupted due to an abort (see 9.8) or
      due to the failure of a language-defined check (see 11.6).

6     The object is not scalar, and is passed to an in out or out parameter of
      an imported procedure or language-defined input procedure, if after
      return from the procedure the representation of the parameter does not
      represent a value of the parameter's subtype.

7     Whether or not an object actually becomes abnormal in these cases is not
specified. An abnormal object becomes normal again upon successful completion
of an assignment to the object as a whole.


                             Erroneous Execution

8     It is erroneous to evaluate a primary that is a name denoting an
abnormal object, or to evaluate a prefix that denotes an abnormal object.


                          Bounded (Run-Time) Errors

9     If the representation of a scalar object does not represent a value of
the object's subtype (perhaps because the object was not initialized), the
object is said to have an invalid representation. It is a bounded error to
evaluate the value of such an object. If the error is detected, either
Constraint_Error or Program_Error is raised. Otherwise, execution continues
using the invalid representation. The rules of the language outside this
subclause assume that all objects have valid representations. The semantics of
operations on invalid representations are as follows:

10    If the representation of the object represents a value of the object's
      type, the value of the type is used.

11    If the representation of the object does not represent a value of the
      object's type, the semantics of operations on such representations is
      implementation-defined, but does not by itself lead to erroneous or
      unpredictable execution, or to other objects becoming abnormal.


                             Erroneous Execution

12    A call to an imported function or an instance of Unchecked_Conversion is
erroneous if the result is scalar, and the result object has an invalid
representation.

13    The dereference of an access value is erroneous if it does not designate
an object of an appropriate type or a subprogram with an appropriate profile,
if it designates a nonexistent object, or if it is an access-to-variable value
that designates a constant object. Such an access value can exist, for
example, because of Unchecked_Deallocation, Unchecked_Access, or
Unchecked_Conversion.

      NOTES

14    18  Objects can become abnormal due to other kinds of actions that
      directly update the object's representation; such actions are generally
      considered directly erroneous, however.


13.9.2 The Valid Attribute


1     The Valid attribute can be used to check the validity of data produced
by unchecked conversion, input, interface to foreign languages, and the like.


                              Static Semantics

2     For a prefix X that denotes a scalar object (after any implicit
dereference), the following attribute is defined:

3     X'Valid Yields True if and only if the object denoted by X is normal and
              has a valid representation. The value of this attribute is of
              the predefined type Boolean.

      NOTES

4     19  Invalid data can be created in the following cases (not counting
      erroneous or unpredictable execution):

    5     an uninitialized scalar object,

    6     the result of an unchecked conversion,

    7     input,

    8     interface to another language (including machine code),

    9     aborting an assignment,

    10    disrupting an assignment due to the failure of a language-defined
          check (see 11.6), and

    11    use of an object whose Address has been specified.

12    20  X'Valid is not considered to be a read of X; hence, it is not an
      error to check the validity of invalid data.


13.10 Unchecked Access Value Creation


1     The attribute Unchecked_Access is used to create access values in an
unsafe manner - the programmer is responsible for preventing ``dangling
references.''


                              Static Semantics

2     The following attribute is defined for a prefix X that denotes an
aliased view of an object:

3     X'Unchecked_Access
              All rules and semantics that apply to X'Access (see 3.10.2)
              apply also to X'Unchecked_Access, except that, for the purposes
              of accessibility rules and checks, it is as if X were declared
              immediately within a library package.

      NOTES

4     21  This attribute is provided to support the situation where a local
      object is to be inserted into a global linked data structure, when the
      programmer knows that it will always be removed from the data structure
      prior to exiting the object's scope. The Access attribute would be
      illegal in this case (see 3.10.2, ``Operations of Access Types'').

5     22  There is no Unchecked_Access attribute for subprograms.


13.11 Storage Management


1     Each access-to-object type has an associated storage pool. The storage
allocated by an allocator comes from the pool; instances of
Unchecked_Deallocation return storage to the pool. Several access types can
share the same pool.

2     A storage pool is a variable of a type in the class rooted at
Root_Storage_Pool, which is an abstract limited controlled type. By default,
the implementation chooses a standard storage pool for each access type. The
user may define new pool types, and may override the choice of pool for an
access type by specifying Storage_Pool for the type.


                               Legality Rules

3     If Storage_Pool is specified for a given access type, Storage_Size shall
not be specified for it.


                              Static Semantics

4     The following language-defined library package exists:

5     with Ada.Finalization;
      with System.Storage_Elements;
      package System.Storage_Pools is
          pragma Preelaborate(System.Storage_Pools);

6         type Root_Storage_Pool is
              abstract new Ada.Finalization.Limited_Controlled with private;

7         procedure Allocate(
            Pool : in out Root_Storage_Pool;
            Storage_Address : out Address;
            Size_In_Storage_Elements : in Storage_Elements.Storage_Count;
            Alignment : in Storage_Elements.Storage_Count) is abstract;

8         procedure Deallocate(
            Pool : in out Root_Storage_Pool;
            Storage_Address : in Address;
            Size_In_Storage_Elements : in Storage_Elements.Storage_Count;
            Alignment : in Storage_Elements.Storage_Count) is abstract;

9         function Storage_Size(Pool : Root_Storage_Pool)
              return Storage_Elements.Storage_Count is abstract;

10    private
         ... -- not specified by the language
      end System.Storage_Pools;

11    A storage pool type (or pool type) is a descendant of Root_Storage_Pool.
The elements of a storage pool are the objects allocated in the pool by
allocators.

12/1  For every access subtype S, the following {representation }attributes
are defined:

13    S'Storage_Pool
              Denotes the storage pool of the type of S. The type of this
              attribute is Root_Storage_Pool'Class.

14    S'Storage_Size
              Yields the result of calling Storage_Size(S'Storage_Pool), which
              is intended to be a measure of the number of storage elements
              reserved for the pool. The type of this attribute is
              universal_integer.

15    Storage_Size or Storage_Pool may be specified for a non-derived
access-to-object type via an attribute_definition_clause; the name in a
Storage_Pool clause shall denote a variable.

16    An allocator of type T allocates storage from T's storage pool. If the
storage pool is a user-defined object, then the storage is allocated by
calling Allocate, passing T'Storage_Pool as the Pool parameter. The
Size_In_Storage_Elements parameter indicates the number of storage elements to
be allocated, and is no more than D'Max_Size_In_Storage_Elements, where D is
the designated subtype. The Alignment parameter is D'Alignment. The result
returned in the Storage_Address parameter is used by the allocator as the
address of the allocated storage, which is a contiguous block of memory of
Size_In_Storage_Elements storage elements. Any exception propagated by
Allocate is propagated by the allocator.

17    If Storage_Pool is not specified for a type defined by an
access_to_object_definition, then the implementation chooses a standard
storage pool for it in an implementation-defined manner. In this case, the
exception Storage_Error is raised by an allocator if there is not enough
storage. It is implementation defined whether or not the implementation
provides user-accessible names for the standard pool type(s).

18    If Storage_Size is specified for an access type, then the Storage_Size
of this pool is at least that requested, and the storage for the pool is
reclaimed when the master containing the declaration of the access type is
left. If the implementation cannot satisfy the request, Storage_Error is
raised at the point of the attribute_definition_clause. If neither
Storage_Pool nor Storage_Size are specified, then the meaning of Storage_Size
is implementation defined.

19    If Storage_Pool is specified for an access type, then the specified pool
is used.

20    The effect of calling Allocate and Deallocate for a standard storage
pool directly (rather than implicitly via an allocator or an instance of
Unchecked_Deallocation) is unspecified.


                             Erroneous Execution

21    If Storage_Pool is specified for an access type, then if Allocate can
satisfy the request, it should allocate a contiguous block of memory, and
return the address of the first storage element in Storage_Address. The block
should contain Size_In_Storage_Elements storage elements, and should be
aligned according to Alignment. The allocated storage should not be used for
any other purpose while the pool element remains in existence. If the request
cannot be satisfied, then Allocate should propagate an exception (such as
Storage_Error). If Allocate behaves in any other manner, then the program
execution is erroneous.


                         Documentation Requirements

22    An implementation shall document the set of values that a user-defined
Allocate procedure needs to accept for the Alignment parameter. An
implementation shall document how the standard storage pool is chosen, and how
storage is allocated by standard storage pools.


                            Implementation Advice

23    An implementation should document any cases in which it dynamically
allocates heap storage for a purpose other than the evaluation of an
allocator.

24    A default (implementation-provided) storage pool for an
access-to-constant type should not have overhead to support deallocation of
individual objects.

25    A storage pool for an anonymous access type should be created at the
point of an allocator for the type, and be reclaimed when the designated
object becomes inaccessible.

      NOTES

26    23  A user-defined storage pool type can be obtained by extending the
      Root_Storage_Pool type, and overriding the primitive subprograms
      Allocate, Deallocate, and Storage_Size. A user-defined storage pool can
      then be obtained by declaring an object of the type extension. The user
      can override Initialize and Finalize if there is any need for
      non-trivial initialization and finalization for a user-defined pool
      type. For example, Finalize might reclaim blocks of storage that are
      allocated separately from the pool object itself.

27    24  The writer of the user-defined allocation and deallocation
      procedures, and users of allocators for the associated access type, are
      responsible for dealing with any interactions with tasking. In
      particular:

    28    If the allocators are used in different tasks, they require mutual
          exclusion.

    29    If they are used inside protected objects, they cannot block.

    30    If they are used by interrupt handlers (see C.3, ``
          Interrupt Support''), the mutual exclusion mechanism has to work
          properly in that context.

31    25  The primitives Allocate, Deallocate, and Storage_Size are declared
      as abstract (see 3.9.3), and therefore they have to be overridden when a
      new (non-abstract) storage pool type is declared.


                                  Examples

32    To associate an access type with a storage pool object, the user first
declares a pool object of some type derived from Root_Storage_Pool. Then, the
user defines its Storage_Pool attribute, as follows:

33    Pool_Object : Some_Storage_Pool_Type;

34    type T is access Designated;
      for T'Storage_Pool use Pool_Object;

35    Another access type may be added to an existing storage pool, via:

36    for T2'Storage_Pool use T'Storage_Pool;

37    The semantics of this is implementation defined for a standard storage
pool.

38    As usual, a derivative of Root_Storage_Pool may define additional
operations. For example, presuming that Mark_Release_Pool_Type has two
additional operations, Mark and Release, the following is a possible use:

39/1  type Mark_Release_Pool_Type
         (Pool_Size : Storage_Elements.Storage_Count;
          Block_Size : Storage_Elements.Storage_Count)
              is new Root_Storage_Pool with [limited ]private;

40    ...

41    MR_Pool : Mark_Release_Pool_Type (Pool_Size => 2000,
                                        Block_Size => 100);

42    type Acc is access ...;
      for Acc'Storage_Pool use MR_Pool;
      ...

43    Mark(MR_Pool);
      ... -- Allocate objects using ``new Designated(...)''.
      Release(MR_Pool); -- Reclaim the storage.


13.11.1 The Max_Size_In_Storage_Elements Attribute


1     The Max_Size_In_Storage_Elements attribute is useful in writing
user-defined pool types.


                              Static Semantics

2     For every subtype S, the following attribute is defined:

3     S'Max_Size_In_Storage_Elements
              Denotes the maximum value for Size_In_Storage_Elements that will
              be requested via Allocate for an access type whose designated
              subtype is S. The value of this attribute is of type
              universal_integer.


13.11.2 Unchecked Storage Deallocation


1     Unchecked storage deallocation of an object designated by a value of an
access type is achieved by a call to an instance of the generic procedure
Unchecked_Deallocation.


                              Static Semantics

2     The following language-defined generic library procedure exists:

3     generic
         type Object(<>) is limited private;
         type Name   is access  Object;
      procedure Ada.Unchecked_Deallocation(X : in out Name);
      pragma Convention(Intrinsic, Ada.Unchecked_Deallocation);
      pragma Preelaborate(Ada.Unchecked_Deallocation);


                              Dynamic Semantics

4     Given an instance of Unchecked_Deallocation declared as follows:

5     procedure Free is
          new Ada.Unchecked_Deallocation(
              object_subtype_name, access_to_variable_subtype_name);

6     Procedure Free has the following effect:

7     1.  After executing Free(X), the value of X is null.

8     2.  Free(X), when X is already equal to null, has no effect.

9     3.  Free(X), when X is not equal to null first performs finalization, as
          described in 7.6. It then deallocates the storage occupied by the
          object designated by X. If the storage pool is a user-defined
          object, then the storage is deallocated by calling Deallocate,
          passing access_to_variable_subtype_name'Storage_Pool as the Pool
          parameter. Storage_Address is the value returned in the
          Storage_Address parameter of the corresponding Allocate call.
          Size_In_Storage_Elements and Alignment are the same values passed to
          the corresponding Allocate call. There is one exception: if the
          object being freed contains tasks, the object might not be
          deallocated.

10    After Free(X), the object designated by X, and any subcomponents
thereof, no longer exist; their storage can be reused for other purposes.


                          Bounded (Run-Time) Errors

11    It is a bounded error to free a discriminated, unterminated task object.
The possible consequences are:

12    No exception is raised.

13    Program_Error or Tasking_Error is raised at the point of the
      deallocation.

14    Program_Error or Tasking_Error is raised in the task the next time it
      references any of the discriminants.

15    In the first two cases, the storage for the discriminants (and for any
enclosing object if it is designated by an access discriminant of the task) is
not reclaimed prior to task termination.


                             Erroneous Execution

16    Evaluating a name that denotes a nonexistent object is erroneous. The
execution of a call to an instance of Unchecked_Deallocation is erroneous if
the object was created other than by an allocator for an access type whose
pool is Name'Storage_Pool.


                            Implementation Advice

17    For a standard storage pool, Free should actually reclaim the storage.

      NOTES

18    26  The rules here that refer to Free apply to any instance of
      Unchecked_Deallocation.

19    27  Unchecked_Deallocation cannot be instantiated for an
      access-to-constant type. This is implied by the rules of 12.5.4.


13.11.3 Pragma Controlled


1     Pragma Controlled is used to prevent any automatic reclamation of
storage (garbage collection) for the objects created by allocators of a given
access type.


                                   Syntax

2     The form of a pragma Controlled is as follows:

3       pragma Controlled(first_subtype_local_name);


                               Legality Rules

4     The first_subtype_local_name of a pragma Controlled shall denote a
non-derived access subtype.


                              Static Semantics

5     A pragma Controlled is a representation pragma that specifies the
controlled aspect of representation.

6     Garbage collection is a process that automatically reclaims storage, or
moves objects to a different address, while the objects still exist.

7     If a pragma Controlled is specified for an access type with a standard
storage pool, then garbage collection is not performed for objects in that
pool.


                         Implementation Permissions

8     An implementation need not support garbage collection, in which case, a
pragma Controlled has no effect.


13.12 Pragma Restrictions


1     A pragma Restrictions expresses the user's intent to abide by certain
restrictions. This may facilitate the construction of simpler run-time
environments.


                                   Syntax

2     The form of a pragma Restrictions is as follows:

3       pragma Restrictions(restriction{, restriction});

4     restriction ::= restriction_identifier
          | restriction_parameter_identifier => expression


                            Name Resolution Rules

5     Unless otherwise specified for a particular restriction, the expression
is expected to be of any integer type.


                               Legality Rules

6     Unless otherwise specified for a particular restriction, the expression
shall be static, and its value shall be nonnegative.


                              Static Semantics

7     The set of restrictions is implementation defined.


                           Post-Compilation Rules

8     A pragma Restrictions is a configuration pragma; unless otherwise
specified for a particular restriction, a partition shall obey the restriction
if a pragma Restrictions applies to any compilation unit included in the
partition.

8.1/1 {For the purpose of checking whether a partition contains constructs
that violate any restriction (unless specified otherwise for a particular
restriction):}

8.2/1 {Generic instances are logically expanded at the point of instantiation;}

8.3/1 {If an object of a type is declared or allocated and not explicitly
      initialized, then all expressions appearing in the definition for the
      type and any of its ancestors are presumed to be used;}

8.4/1 {A default_expression for a formal parameter or a generic formal object
      is considered to be used if and only if the corresponding actual
      parameter is not provided in a given call or instantiation.}


                         Implementation Permissions

9     An implementation may place limitations on the values of the expression
that are supported, and limitations on the supported combinations of
restrictions. The consequences of violating such limitations are
implementation defined.

9.1/1 {An implementation is permitted to omit restriction checks for code that
is recognized at compile time to be unreachable and for which no code is
generated.}

9.2/1 {Whenever enforcement of a restriction is not required prior to
execution, an implementation may nevertheless enforce the restriction prior to
execution of a partition to which the restriction applies, provided that every
execution of the partition would violate the restriction.}

      NOTES

10    28  Restrictions intended to facilitate the construction of efficient
      tasking run-time systems are defined in D.7. Safety- and
      security-related restrictions are defined in H.4.

11    29  An implementation has to enforce the restrictions in cases where
      enforcement is required, even if it chooses not to take advantage of the
      restrictions in terms of efficiency.


13.13 Streams


1     A stream is a sequence of elements comprising values from possibly
different types and allowing sequential access to these values. A stream type
is a type in the class whose root type is Streams.Root_Stream_Type. A stream
type may be implemented in various ways, such as an external sequential file,
an internal buffer, or a network channel.


13.13.1 The Package Streams



                              Static Semantics

1     The abstract type Root_Stream_Type is the root type of the class of
stream types. The types in this class represent different kinds of streams. A
new stream type is defined by extending the root type (or some other stream
type), overriding the Read and Write operations, and optionally defining
additional primitive subprograms, according to the requirements of the
particular kind of stream. The predefined stream-oriented attributes like
T'Read and T'Write make dispatching calls on the Read and Write procedures of
the Root_Stream_Type. (User-defined T'Read and T'Write attributes can also
make such calls, or can call the Read and Write attributes of other types.)

2     package Ada.Streams is
          pragma Pure(Streams);

3         type Root_Stream_Type is abstract tagged limited private;

4/1       type Stream_Element is mod implementation-defined;
          type Stream_Element_Offset is range implementation-defined;
          subtype Stream_Element_Count is
              Stream_Element_Offset range 0..Stream_Element_Offset'Last;
          type Stream_Element_Array is
              array(Stream_Element_Offset range <>) of{ aliased} Stream_Element;

5         procedure Read(
            Stream : in out Root_Stream_Type;
            Item   : out Stream_Element_Array;
            Last   : out Stream_Element_Offset) is abstract;

6         procedure Write(
            Stream : in out Root_Stream_Type;
            Item   : in Stream_Element_Array) is abstract;

7     private
         ... -- not specified by the language
      end Ada.Streams;

8     The Read operation transfers Item'Length stream elements from the
specified stream to fill the array Item. The index of the last stream element
transferred is returned in Last. Last is less than Item'Last only if the end
of the stream is reached.

9     The Write operation appends Item to the specified stream.


                         Implementation Permissions

9.1/1 {If Stream_Element'Size is not a multiple of System.Storage_Unit, then
the components of Stream_Element_Array need not be aliased.}

      NOTES

10    30  See A.12.1, ``The Package Streams.Stream_IO'' for an example of
      extending type Root_Stream_Type.


13.13.2 Stream-Oriented Attributes


1/1   The {operational attributes }Write, Read, Output, and Input [attributes
]convert values to a stream of elements and reconstruct values from a stream.


                              Static Semantics

2     For every subtype S of a specific type T, the following attributes are
defined.

3     S'Write S'Write denotes a procedure with the following specification:

            4     procedure S'Write(
                     Stream : access Ada.Streams.Root_Stream_Type'Class;
                     Item : in T)

        5     S'Write writes the value of Item to Stream.

6     S'Read  S'Read denotes a procedure with the following specification:

            7     procedure S'Read(
                     Stream : access Ada.Streams.Root_Stream_Type'Class;
                     Item : out T)

        8     S'Read reads the value of Item from Stream.

8.1/1 {For untagged derived types, the Write and Read attributes of the parent
type are inherited as specified in 13.1; otherwise, the default
implementations of these attributes are used. The default implementations of
Write and Read attributes execute as follows:}

9/1   For elementary types, the representation in terms of stream elements is
implementation defined. For composite types, the Write or Read attribute for
each component is called in [a ]canonical order{, which}[. The canonical order
of components] is last dimension varying fastest for an array, and positional
aggregate order for a record. Bounds are not included in the stream if T is an
array type. If T is a discriminated type, discriminants are included only if
they have defaults. If T is a tagged type, the tag is not included. {For type
extensions, the Write or Read attribute for the parent type is called,
followed by the Write or Read attribute of each component of the extension
part, in canonical order. For a limited type extension, if the attribute of
any ancestor type of T has been directly specified and the attribute of any
ancestor type of the type of any of the extension components which are of a
limited type has not been specified, the attribute of T shall be directly
specified.}

10    For every subtype S'Class of a class-wide type T'Class:

11    S'Class'Write
              S'Class'Write denotes a procedure with the following
              specification:

            12    procedure S'Class'Write(
                     Stream : access Ada.Streams.Root_Stream_Type'Class;
                     Item   : in T'Class)

        13    Dispatches to the subprogram denoted by the Write attribute of
              the specific type identified by the tag of Item.

14    S'Class'Read
              S'Class'Read denotes a procedure with the following
              specification:

            15    procedure S'Class'Read(
                     Stream : access Ada.Streams.Root_Stream_Type'Class;
                     Item : out T'Class)

        16    Dispatches to the subprogram denoted by the Read attribute of
              the specific type identified by the tag of Item.


                            Implementation Advice

17    If a stream element is the same size as a storage element, then the
normal in-memory representation should be used by Read and Write for scalar
objects. Otherwise, Read and Write should use the smallest number of stream
elements needed to represent all values in the base range of the scalar type.


                              Static Semantics

18    For every subtype S of a specific type T, the following attributes are
defined.

19    S'Output
              S'Output denotes a procedure with the following specification:

            20    procedure S'Output(
                     Stream : access Ada.Streams.Root_Stream_Type'Class;
                     Item : in T)

        21    S'Output writes the value of Item to Stream, including any
              bounds or discriminants.

22    S'Input S'Input denotes a function with the following specification:

            23    function S'Input(
                     Stream : access Ada.Streams.Root_Stream_Type'Class)
                     return T

        24    S'Input reads and returns one value from Stream, using any
              bounds or discriminants written by a corresponding S'Output to
              determine how much to read.

25/1  {For untagged derived types, the Output and Input attributes of the
parent type are inherited as specified in 13.1; otherwise, the default
implementations of these attributes are used. The default implementations of
Output and Input attributes execute as follows:}[Unless overridden by an
attribute_definition_clause, these subprograms execute as follows:]

26    If T is an array type, S'Output first writes the bounds, and S'Input
      first reads the bounds. If T has discriminants without defaults,
      S'Output first writes the discriminants (using S'Write for each), and
      S'Input first reads the discriminants (using S'Read for each).

27    S'Output then calls S'Write to write the value of Item to the stream.
      S'Input then creates an object (with the bounds or discriminants, if
      any, taken from the stream), initializes it with S'Read, and returns the
      value of the object.

28    For every subtype S'Class of a class-wide type T'Class:

29    S'Class'Output
              S'Class'Output denotes a procedure with the following
              specification:

            30    procedure S'Class'Output(
                     Stream : access Ada.Streams.Root_Stream_Type'Class;
                     Item   : in T'Class)

        31    First writes the external tag of Item to Stream (by calling
              String'Output(Tags.External_Tag(Item'Tag) - see 3.9) and then
              dispatches to the subprogram denoted by the Output attribute of
              the specific type identified by the tag.

32    S'Class'Input
              S'Class'Input denotes a function with the following
              specification:

            33    function S'Class'Input(
                     Stream : access Ada.Streams.Root_Stream_Type'Class)
                     return T'Class

        34    First reads the external tag from Stream and determines the
              corresponding internal tag (by calling
              Tags.Internal_Tag(String'Input(Stream)) - see 3.9) and then
              dispatches to the subprogram denoted by the Input attribute of
              the specific type identified by the internal tag; returns that
              result.

35    In the default implementation of Read and Input for a composite type,
for each scalar component that is a discriminant or whose
component_declaration includes a default_expression, a check is made that the
value returned by Read for the component belongs to its subtype.
Constraint_Error is raised if this check fails. For other scalar components,
no check is made. For each component that is of an access type, if the
implementation can detect that the value returned by Read for the component is
not a value of its subtype, Constraint_Error is raised. If the value is not a
value of its subtype and this error is not detected, the component has an
abnormal value, and erroneous execution can result (see 13.9.1).

35.1/1 {In the default implementation of Read and Input for a type, End_Error
is raised if the end of the stream is reached before the reading of a value of
the type is completed.}

36/1  The stream-oriented attributes may be specified for any type via an
attribute_definition_clause. All nonlimited types have default implementations
for these operations. An attribute_reference for one of these attributes is
illegal if the type is limited, unless the attribute has been specified by an
attribute_definition_clause{ or (for a type extension) the attribute has been
specified for an ancestor type}. For an attribute_definition_clause specifying
one of these attributes, the subtype of the Item parameter shall be the base
subtype if scalar, and the first subtype otherwise. The same rule applies to
the result of the Input function.


                         Implementation Requirements

36.1/1 {For every subtype S of a language-defined nonlimited specific type T,
the output generated by S'Output or S'Write shall be readable by S'Input or
S'Read, respectively. This rule applies across partitions if the
implementation conforms to the Distributed Systems Annex.}

      NOTES

37    31  For a definite subtype S of a type T, only T'Write and T'Read are
      needed to pass an arbitrary value of the subtype through a stream. For
      an indefinite subtype S of a type T, T'Output and T'Input will normally
      be needed, since T'Write and T'Read do not pass bounds, discriminants,
      or tags.

38    32  User-specified attributes of S'Class are not inherited by other
      class-wide types descended from S.


                                  Examples

39    Example of user-defined Write attribute:

40    procedure My_Write(
        Stream : access Ada.Streams.Root_Stream_Type'Class; Item : My_Integer'Base);
      for My_Integer'Write use My_Write;


13.14 Freezing Rules


1     This clause defines a place in the program text where each declared
entity becomes ``frozen.'' A use of an entity, such as a reference to it by
name, or (for a type) an expression of the type, causes freezing of the entity
in some contexts, as described below. The Legality Rules forbid certain kinds
of uses of an entity in the region of text where it is frozen.

2     The freezing of an entity occurs at one or more places (freezing points)
in the program text where the representation for the entity has to be fully
determined. Each entity is frozen from its first freezing point to the end of
the program text (given the ordering of compilation units defined in 10.1.4).

3/1   The end of a declarative_part, protected_body, or a declaration of a
library package or generic library package, causes freezing of each entity
declared within it, except for incomplete types. A noninstance body{ other
than a renames-as-body} causes freezing of each entity declared before it
within the same declarative_part.

4/1   A construct that (explicitly or implicitly) references an entity can
cause the freezing of the entity, as defined by subsequent paragraphs. At the
place where a construct causes freezing, each name, {expression,
implicit_dereference}[expression], or range within the construct causes
freezing:

5     The occurrence of a generic_instantiation causes freezing; also, if a
      parameter of the instantiation is defaulted, the default_expression or
      default_name for that parameter causes freezing.

6     The occurrence of an object_declaration that has no corresponding
      completion causes freezing.

7     The declaration of a record extension causes freezing of the parent
      subtype.

8/1   A static expression causes freezing where it occurs. {An object name
or}[A] nonstatic expression causes freezing where it occurs, unless the {name
or }expression is part of a default_expression, a default_name, or a
per-object expression of a component's constraint, in which case, the freezing
occurs later as part of another construct.

8.1/1 {An implicit call freezes the same entities that would be frozen by an
explicit call. This is true even if the implicit call is removed via
implementation permissions.}

8.2/1 {If an expression is implicitly converted to a type or subtype T, then
at the place where the expression causes freezing, T is frozen.}

9     The following rules define which entities are frozen at the place where
a construct causes freezing:

10    At the place where an expression causes freezing, the type of the
      expression is frozen, unless the expression is an enumeration literal
      used as a discrete_choice of the array_aggregate of an enumeration_-
      representation_clause.

11    At the place where a name causes freezing, the entity denoted by the
      name is frozen, unless the name is a prefix of an expanded name; at the
      place where an object name causes freezing, the nominal subtype
      associated with the name is frozen.

11.1/1 {At the place where an implicit_dereference causes freezing, the
      nominal subtype associated with the implicit_dereference is frozen.}

12    At the place where a range causes freezing, the type of the range is
      frozen.

13    At the place where an allocator causes freezing, the designated subtype
      of its type is frozen. If the type of the allocator is a derived type,
      then all ancestor types are also frozen.

14    At the place where a callable entity is frozen, each subtype of its
      profile is frozen. If the callable entity is a member of an entry
      family, the index subtype of the family is frozen. At the place where a
      function call causes freezing, if a parameter of the call is defaulted,
      the default_expression for that parameter causes freezing.

15    At the place where a subtype is frozen, its type is frozen. At the place
      where a type is frozen, any expressions or names within the full type
      definition cause freezing; the first subtype, and any component
      subtypes, index subtypes, and parent subtype of the type are frozen as
      well. For a specific tagged type, the corresponding class-wide type is
      frozen as well. For a class-wide type, the corresponding specific type
      is frozen as well.


                               Legality Rules

16    The explicit declaration of a primitive subprogram of a tagged type
shall occur before the type is frozen (see 3.9.2).

17    A type shall be completely defined before it is frozen (see 3.11.1 and
7.3).

18    The completion of a deferred constant declaration shall occur before the
constant is frozen (see 7.4).

19/1  {An operational or}[A] representation item that directly specifies an
aspect of an entity shall appear before the entity is frozen (see 13.1).



                                   Annex A
                                 (normative)

                       Predefined Language Environment


1     This Annex contains the specifications of library units that shall be
provided by every implementation. There are three root library units: Ada,
Interfaces, and System; other library units are children of these:

2/1    
 

      Standard - A.1
       Ada - A.2
         Asynchronous_Task_Control - D.11
         Calendar - 9.6
         Characters - A.3.1
           Handling - A.3.2
           Latin_1 - A.3.3
         Command_Line - A.15
         Decimal - F.2
         Direct_IO - A.8.4
         Dynamic_Priorities - D.5
         Exceptions - 11.4.1
         Finalization - 7.6
      {    Float_Text_IO - A.10.9
         Float_Wide_Text_IO - A.11
         Integer_Text_IO - A.10.8
         Integer_Wide_Text_IO - A.11
      }    Interrupts - C.3.2
           Names - C.3.2
         IO_Exceptions - A.13
         Numerics - A.5
           Complex_Elementary_Functions - G.1.2
           Complex_Types - G.1.1
           Discrete_Random - A.5.2
           Elementary_Functions - A.5.1
           Float_Random - A.5.2
           Generic_Complex_Elementary_Functions
                 - G.1.2
           Generic_Complex_Types - G.1.1
           Generic_Elementary_Functions - A.5.1
         Real_Time - D.8
         Sequential_IO - A.8.1
         Storage_IO - A.9
         Streams - 13.13.1
           Stream_IO - A.12.1


      Standard (...continued)
       Ada (...continued)
         Strings - A.4.1
           Bounded - A.4.4
           Fixed - A.4.3
           Maps - A.4.2
             Constants - A.4.6
           Unbounded - A.4.5
           Wide_Bounded - A.4.7
           Wide_Fixed - A.4.7
           Wide_Maps - A.4.7
             Wide_Constants - A.4.7
           Wide_Unbounded - A.4.7
         Synchronous_Task_Control - D.10
         Tags - 3.9
         Task_Attributes - C.7.2
         Task_Identification - C.7.1
         Text_IO - A.10.1
           Complex_IO - G.1.3
           Editing - F.3.3
           Text_Streams - A.12.2
         Unchecked_Conversion - 13.9
         Unchecked_Deallocation - 13.11.2
         Wide_Text_IO - A.11
           Complex_IO - G.1.3
           Editing - F.3.4
           Text_Streams - A.12.3

       Interfaces - B.2
         C - B.3
           Pointers - B.3.2
           Strings - B.3.1
         COBOL - B.4
         Fortran - B.5

       System - 13.7
         Address_To_Access_Conversions - 13.7.2
         Machine_Code - 13.8
         RPC - E.5
         Storage_Elements - 13.7.1
         Storage_Pools - 13.11


                         Implementation Requirements

3     The implementation shall ensure that each language defined subprogram is
reentrant in the sense that concurrent calls on the same subprogram perform as
specified, so long as all parameters that could be passed by reference denote
nonoverlapping objects.


                         Implementation Permissions

4     The implementation may restrict the replacement of language-defined
compilation units. The implementation may restrict children of
language-defined library units (other than Standard).


A.1 The Package Standard


1     This clause outlines the specification of the package Standard
containing all predefined identifiers in the language. The corresponding
package body is not specified by the language.

2     The operators that are predefined for the types declared in the package
Standard are given in comments since they are implicitly declared. Italics are
used for pseudo-names of anonymous types (such as root_real) and for undefined
information (such as implementation-defined).


                              Static Semantics

3     The library package Standard has the following declaration:

4     package Standard is
         pragma Pure(Standard);

5        type Boolean is (False, True);

6        -- The predefined relational operators for this type are as follows:

7/1      -- function "="   (Left, Right : Boolean{'Base}) return Boolean;
         -- function "/="  (Left, Right : Boolean{'Base}) return Boolean;
         -- function "<"   (Left, Right : Boolean{'Base}) return Boolean;
         -- function "<="  (Left, Right : Boolean{'Base}) return Boolean;
         -- function ">"   (Left, Right : Boolean{'Base}) return Boolean;
         -- function ">="  (Left, Right : Boolean{'Base}) return Boolean;

8        -- The predefined logical operators and the predefined logical
         -- negation operator are as follows:

9/1      -- function "and" (Left, Right : Boolean{'Base}) return Boolean;
         -- function "or"  (Left, Right : Boolean{'Base}) return Boolean;
         -- function "xor" (Left, Right : Boolean{'Base}) return Boolean;

10/1     -- function "not" (Right : Boolean{'Base}) return Boolean;

11       -- The integer type root_integer is predefined.
         -- The corresponding universal type is universal_integer.

12       type Integer is range implementation-defined;

13       subtype Natural  is Integer range 0 .. Integer'Last;
         subtype Positive is Integer range 1 .. Integer'Last;

14       -- The predefined operators for type Integer are as follows:

15       -- function "="  (Left, Right : Integer'Base) return Boolean;
         -- function "/=" (Left, Right : Integer'Base) return Boolean;
         -- function "<"  (Left, Right : Integer'Base) return Boolean;
         -- function "<=" (Left, Right : Integer'Base) return Boolean;
         -- function ">"  (Left, Right : Integer'Base) return Boolean;
         -- function ">=" (Left, Right : Integer'Base) return Boolean;

16       -- function "+"   (Right : Integer'Base) return Integer'Base;
         -- function "-"   (Right : Integer'Base) return Integer'Base;
         -- function "abs" (Right : Integer'Base) return Integer'Base;

17       -- function "+"   (Left, Right : Integer'Base) return Integer'Base;
         -- function "-"   (Left, Right : Integer'Base) return Integer'Base;
         -- function "*"   (Left, Right : Integer'Base) return Integer'Base;
         -- function "/"   (Left, Right : Integer'Base) return Integer'Base;
         -- function "rem" (Left, Right : Integer'Base) return Integer'Base;
         -- function "mod" (Left, Right : Integer'Base) return Integer'Base;

18       -- function "**"  (Left : Integer'Base; Right : Natural)
         --                  return Integer'Base;

19       -- The specification of each operator for the type
         -- root_integer, or for any additional predefined integer
         -- type, is obtained by replacing Integer by the name of the type
         -- in the specification of the corresponding operator of the type
         -- Integer. The right operand of the exponentiation operator
         -- remains as subtype Natural.

20       -- The floating point type root_real is predefined.
         -- The corresponding universal type is universal_real.

21       type Float is digits implementation-defined;

22       -- The predefined operators for this type are as follows:

23       -- function "="   (Left, Right : Float) return Boolean;
         -- function "/="  (Left, Right : Float) return Boolean;
         -- function "<"   (Left, Right : Float) return Boolean;
         -- function "<="  (Left, Right : Float) return Boolean;
         -- function ">"   (Left, Right : Float) return Boolean;
         -- function ">="  (Left, Right : Float) return Boolean;

24       -- function "+"   (Right : Float) return Float;
         -- function "-"   (Right : Float) return Float;
         -- function "abs" (Right : Float) return Float;

25       -- function "+"   (Left, Right : Float) return Float;
         -- function "-"   (Left, Right : Float) return Float;
         -- function "*"   (Left, Right : Float) return Float;
         -- function "/"   (Left, Right : Float) return Float;

26       -- function "**"  (Left : Float; Right : Integer'Base) return Float;

27       -- The specification of each operator for the type root_real, or for
         -- any additional predefined floating point type, is obtained by
         -- replacing Float by the name of the type in the specification of the
         -- corresponding operator of the type Float.

28       -- In addition, the following operators are predefined for the root
         -- numeric types:

29       function "*" (Left : root_integer; Right : root_real)
           return root_real;

30       function "*" (Left : root_real;    Right : root_integer)
           return root_real;

31       function "/" (Left : root_real;    Right : root_integer)
           return root_real;

32       -- The type universal_fixed is predefined.
         -- The only multiplying operators defined between
         -- fixed point types are

33       function "*" (Left : universal_fixed; Right : universal_fixed)
           return universal_fixed;

34       function "/" (Left : universal_fixed; Right : universal_fixed)
           return universal_fixed;

35          -- The declaration of type Character is based on the standard ISO 8859-1 character set.
      
            -- There are no character literals corresponding to the positions for control characters.
            -- They are indicated in italics in this definition. See 3.5.2.
      
         type Character is
           (nul,      soh,     stx,     etx,       eot,     enq,    ack,     
      bel,   --0 (16#00#) .. 7 (16#07#)
            bs,       ht,      lf,      vt,        ff,      cr,     so,      
      si,    --8 (16#08#) .. 15 (16#0F#)
      
            dle,      dc1,     dc2,     dc3,       dc4,     nak,    syn,     
      etb,   --16 (16#10#) .. 23 (16#17#)
            can,      em,      sub,     esc,       fs,      gs,     rs,      
      us,    --24 (16#18#) .. 31 (16#1F#)
      
            ' ',      '!',     '"',     '#',       '$',     '%',    '&',     
      ''',   --32 (16#20#) .. 39 (16#27#)
            '(',      ')',     '*',     '+',       ',',     '-',    '.',     
      '/',   --40 (16#28#) .. 47 (16#2F#)
      
            '0',      '1',     '2',     '3',       '4',     '5',    '6',     
      '7',   --48 (16#30#) .. 55 (16#37#)
            '8',      '9',     ':',     ';',       '<',     '=',    '>',     
      '?',   --56 (16#38#) .. 63 (16#3F#)
      
            '@',      'A',     'B',     'C',       'D',     'E',    'F',     
      'G',   --64 (16#40#) .. 71 (16#47#)
            'H',      'I',     'J',     'K',       'L',     'M',    'N',     
      'O',   --72 (16#48#) .. 79 (16#4F#)
      
            'P',      'Q',     'R',     'S',       'T',     'U',    'V',     
      'W',   --80 (16#50#) .. 87 (16#57#)
            'X',      'Y',     'Z',     '[',       '\',     ']',    '^',     
      '_',   --88 (16#58#) .. 95 (16#5F#)
      
            '`',      'a',     'b',     'c',       'd',     'e',    'f',     
      'g',   --96 (16#60#) .. 103 (16#67#)
            'h',      'i',     'j',     'k',       'l',     'm',    'n',     
      'o',   --104 (16#68#) .. 111 (16#6F#)
      
            'p',      'q',     'r',     's',       't',     'u',    'v',     
      'w',   --112 (16#70#) .. 119 (16#77#)
            'x',      'y',     'z',     '{',       '|',     '}',    '~',     
      del,   --120 (16#78#) .. 127 (16#7F#)
      
            reserved_128,      reserved_129,       bph,     nbh,                     
      --128 (16#80#) .. 131 (16#83#)
            reserved_132,      nel,     ssa,       esa,                              
      --132 (16#84#) .. 135 (16#87#)
            hts,      htj,     vts,     pld,       plu,     ri,     ss2,     
      ss3,   --136 (16#88#) .. 143 (16#8F#)
      
            dcs,      pu1,     pu2,     sts,       cch,     mw,     spa,     
      epa,   --144 (16#90#) .. 151 (16#97#)
            sos,      reserved_153,     sci,       csi,                              
      --152 (16#98#) .. 155 (16#9B#)
            st,       osc,     pm,      apc,                                         
      --156 (16#9C#) .. 159 (16#9F#)
      
            ' ',      '¡',     '¢',     '£',       '¤',     '¥',    '¦',     
      '§',   --160 (16#A0#) .. 167 (16#A7#)
            '¨',      '©',     'ª',     '«',       '¬',     '­',    '®',     
      '¯',   --168 (16#A8#) .. 175 (16#AF#)
      
            '°',      '±',     '²',     '³',       '´',     'µ',    '¶',     
      '·',   --176 (16#B0#) .. 183 (16#B7#)
            '¸',      '¹',     'º',     '»',       '¼',     '½',    '¾',     
      '¿',   --184 (16#B8#) .. 191 (16#BF#)
      
            'À',      'Á',     'Â',     'Ã',       'Ä',     'Å',    'Æ',     
      'Ç',   --192 (16#C0#) .. 199 (16#C7#)
            'È',      'É',     'Ê',     'Ë',       'Ì',     'Í',    'Î',     
      'Ï',   --200 (16#C8#) .. 207 (16#CF#)
      
            'Ð',      'Ñ',     'Ò',     'Ó',       'Ô',     'Õ',    'Ö',     
      '×',   --208 (16#D0#) .. 215 (16#D7#)
            'Ø',      'Ù',     'Ú',     'Û',       'Ü',     'Ý',    'Þ',     
      'ß',   --216 (16#D8#) .. 223 (16#DF#)
      
            'à',      'á',     'â',     'ã',       'ä',     'å',    'æ',     
      'ç',   --224 (16#E0#) .. 231 (16#E7#)
            'è',      'é',     'ê',     'ë',       'ì',     'í',    'î',     
      'ï',   --232 (16#E8#) .. 239 (16#EF#)
      
            'ð',      'ñ',     'ò',     'ó',       'ô',     'õ',    'ö',     
      '÷',   --240 (16#F0#) .. 247 (16#F7#)
            'ø',      'ù',     'ú',     'û',       'ü',     'ý',    'þ',     
      'ÿ',   --248 (16#F8#) .. 255 (16#FF#)

36       -- The predefined operators for the type Character are the same as for
         -- any enumeration type.
      
         -- The declaration of type Wide_Character is based on the standard ISO 10646 BMP character set.
         -- The first 256 positions have the same contents as type Character. See 3.5.2
      .
      
         type Wide_Character is (nul, soh ... FFFE, FFFF);
      
         package ASCII is ... end ASCII;  --Obsolescent; see J.5
      
      

37       -- Predefined string types:
      
         type String is array(Positive range <>) of Character;
         pragma Pack(String);

38       -- The predefined operators for this type are as follows:

39       --     function "="  (Left, Right: String) return Boolean;
         --     function "/=" (Left, Right: String) return Boolean;
         --     function "<"  (Left, Right: String) return Boolean;
         --     function "<=" (Left, Right: String) return Boolean;
         --     function ">"  (Left, Right: String) return Boolean;
         --     function ">=" (Left, Right: String) return Boolean;

40       --     function "&" (Left: String;    Right: String)    return String;
         --     function "&" (Left: Character; Right: String)    return String;
         --     function "&" (Left: String;    Right: Character) return String;
         --     function "&" (Left: Character; Right: Character) return String;

41       type Wide_String is array(Positive range <>) of Wide_Character;
         pragma Pack(Wide_String);

42       -- The predefined operators for this type correspond to those for String

43       type Duration
       is delta implementation-defined range implementation-defined;

44          -- The predefined operators for the type Duration are the same as for
            -- any fixed point type.

45       -- The predefined exceptions:

46       Constraint_Error: exception;
         Program_Error   : exception;
         Storage_Error   : exception;
         Tasking_Error   : exception;

47    end Standard;

48    Standard has no private part.

49    In each of the types Character and Wide_Character, the character
literals for the space character (position 32) and the non-breaking space
character (position 160) correspond to different values. Unless indicated
otherwise, each occurrence of the character literal ' ' in this International
Standard refers to the space character. Similarly, the character literals for
hyphen (position 45) and soft hyphen (position 173) correspond to different
values. Unless indicated otherwise, each occurrence of the character literal
'-' in this International Standard refers to the hyphen character.


                              Dynamic Semantics

50    Elaboration of the body of Standard has no effect.


                         Implementation Permissions

51    An implementation may provide additional predefined integer types and
additional predefined floating point types. Not all of these types need have
names.


                            Implementation Advice

52    If an implementation provides additional named predefined integer types,
then the names should end with ``Integer'' as in ``Long_Integer''. If an
implementation provides additional named predefined floating point types, then
the names should end with ``Float'' as in ``Long_Float''.

      NOTES

53    1  Certain aspects of the predefined entities cannot be completely
      described in the language itself. For example, although the enumeration
      type Boolean can be written showing the two enumeration literals False
      and True, the short-circuit control forms cannot be expressed in the
      language.

54    2  As explained in 8.1, ``Declarative Region'' and 10.1.4, ``
      The Compilation Process'', the declarative region of the package
      Standard encloses every library unit and consequently the main
      subprogram; the declaration of every library unit is assumed to occur
      within this declarative region. Library_items are assumed to be ordered
      in such a way that there are no forward semantic dependences. However,
      as explained in 8.3, ``Visibility'', the only library units that are
      visible within a given compilation unit are the library units named by
      all with_clauses that apply to the given unit, and moreover, within the
      declarative region of a given library unit, that library unit itself.

55    3  If all block_statements of a program are named, then the name of each
      program unit can always be written as an expanded name starting with
      Standard (unless Standard is itself hidden). The name of a library unit
      cannot be a homograph of a name (such as Integer) that is already
      declared in Standard.

56    4  The exception Standard.Numeric_Error is defined in J.6.


A.2 The Package Ada



                              Static Semantics

1     The following language-defined library package exists:

2     package Ada is
          pragma Pure(Ada);
      end Ada;

3     Ada serves as the parent of most of the other language-defined library
units; its declaration is empty (except for the pragma Pure).


                               Legality Rules

4     In the standard mode, it is illegal to compile a child of package Ada.


A.3 Character Handling


1     This clause presents the packages related to character processing: an
empty pure package Characters and child packages Characters.Handling and
Characters.Latin_1. The package Characters.Handling provides classification
and conversion functions for Character data, and some simple functions for
dealing with Wide_Character data. The child package Characters.Latin_1
declares a set of constants initialized to values of type Character.


A.3.1 The Package Characters



                              Static Semantics

1     The library package Characters has the following declaration:

2     package Ada.Characters is
        pragma Pure(Characters);
      end Ada.Characters;


A.3.2 The Package Characters.Handling



                              Static Semantics

1     The library package Characters.Handling has the following declaration:

2     package Ada.Characters.Handling is
        pragma Preelaborate(Handling);

3     --Character classification functions

4       function Is_Control           (Item : in Character) return Boolean;
        function Is_Graphic           (Item : in Character) return Boolean;
        function Is_Letter            (Item : in Character) return Boolean;
        function Is_Lower             (Item : in Character) return Boolean;
        function Is_Upper             (Item : in Character) return Boolean;
        function Is_Basic             (Item : in Character) return Boolean;
        function Is_Digit             (Item : in Character) return Boolean;
        function Is_Decimal_Digit     (Item : in Character) return Boolean
                           renames Is_Digit;
        function Is_Hexadecimal_Digit (Item : in Character) return Boolean;
        function Is_Alphanumeric      (Item : in Character) return Boolean;
        function Is_Special           (Item : in Character) return Boolean;

5     --Conversion functions for Character and String

6       function To_Lower (Item : in Character) return Character;
        function To_Upper (Item : in Character) return Character;
        function To_Basic (Item : in Character) return Character;

7       function To_Lower (Item : in String) return String;
        function To_Upper (Item : in String) return String;
        function To_Basic (Item : in String) return String;

8     --Classifications of and conversions between Character and ISO 646

9       subtype ISO_646 is
          Character range Character'Val(0) .. Character'Val(127);

10      function Is_ISO_646 (Item : in Character) return Boolean;
        function Is_ISO_646 (Item : in String)    return Boolean;

11      function To_ISO_646 (Item       : in Character;
                             Substitute : in ISO_646 := ' ')
          return ISO_646;

12      function To_ISO_646 (Item       : in String;
                             Substitute : in ISO_646 := ' ')
          return String;

13    --Classifications of and conversions between Wide_Character and Character.

14      function Is_Character (Item : in Wide_Character) return Boolean;
        function Is_String    (Item : in Wide_String)    return Boolean;

15      function To_Character (Item       : in Wide_Character;
                               Substitute : in Character := ' ')
          return Character;

16      function To_String    (Item       : in Wide_String;
                               Substitute : in Character := ' ')
          return String;

17      function To_Wide_Character
       (Item : in Character) return Wide_Character;

18      function To_Wide_String    (Item : in String)    return Wide_String;

19    end Ada.Characters.Handling;

20    In the description below for each function that returns a Boolean
result, the effect is described in terms of the conditions under which the
value True is returned. If these conditions are not met, then the function
returns False.

21    Each of the following classification functions has a formal Character
parameter, Item, and returns a Boolean result.

22    Is_Control
              True if Item is a control character. A control character is a
              character whose position is in one of the ranges 0..31 or
              127..159.

23    Is_Graphic
              True if Item is a graphic character. A graphic character is a
              character whose position is in one of the ranges 32..126 or
              160..255.

24    Is_Letter
              True if Item is a letter. A letter is a character that is in one
              of the ranges 'A'..'Z' or 'a'..'z', or whose position is in one
              of the ranges 192..214, 216..246, or 248..255.

25    Is_Lower
              True if Item is a lower-case letter. A lower-case letter is a
              character that is in the range 'a'..'z', or whose position is in
              one of the ranges 223..246 or 248..255.

26    Is_Upper
              True if Item is an upper-case letter. An upper-case letter is a
              character that is in the range 'A'..'Z' or whose position is in
              one of the ranges 192..214 or 216.. 222.

27    Is_Basic
              True if Item is a basic letter. A basic letter is a character
              that is in one of the ranges 'A'..'Z' and 'a'..'z', or that is
              one of the following: 'Æ', 'æ', 'Ð', 'ð', 'Þ', 'þ', or 'ß'.

28    Is_Digit
              True if Item is a decimal digit. A decimal digit is a character
              in the range '0'..'9'.

29    Is_Decimal_Digit
              A renaming of Is_Digit.

30    Is_Hexadecimal_Digit
              True if Item is a hexadecimal digit. A hexadecimal digit is a
              character that is either a decimal digit or that is in one of
              the ranges 'A' .. 'F' or 'a' .. 'f'.

31    Is_Alphanumeric
              True if Item is an alphanumeric character. An alphanumeric
              character is a character that is either a letter or a decimal
              digit.

32    Is_Special
              True if Item is a special graphic character. A special graphic
              character is a graphic character that is not alphanumeric.

33    Each of the names To_Lower, To_Upper, and To_Basic refers to two
functions: one that converts from Character to Character, and the other that
converts from String to String. The result of each Character-to-Character
function is described below, in terms of the conversion applied to Item, its
formal Character parameter. The result of each String-to-String conversion is
obtained by applying to each element of the function's String parameter the
corresponding Character-to-Character conversion; the result is the null String
if the value of the formal parameter is the null String. The lower bound of
the result String is 1.

34    To_Lower
              Returns the corresponding lower-case value for Item if
              Is_Upper(Item), and returns Item otherwise.

35    To_Upper
              Returns the corresponding upper-case value for Item if
              Is_Lower(Item) and Item has an upper-case form, and returns Item
              otherwise. The lower case letters 'ß' and 'ÿ' do not have upper
              case forms.

36    To_Basic
              Returns the letter corresponding to Item but with no diacritical
              mark, if Item is a letter but not a basic letter; returns Item
              otherwise.

37    The following set of functions test for membership in the ISO 646
character range, or convert between ISO 646 and Character.

38    Is_ISO_646
              The function whose formal parameter, Item, is of type Character
              returns True if Item is in the subtype ISO_646.

39    Is_ISO_646
              The function whose formal parameter, Item, is of type String
              returns True if Is_ISO_646(Item(I)) is True for each I in
              Item'Range.

40    To_ISO_646
              The function whose first formal parameter, Item, is of type
              Character returns Item if Is_ISO_646(Item), and returns the
              Substitute ISO_646 character otherwise.

41    To_ISO_646
              The function whose first formal parameter, Item, is of type
              String returns the String whose Range is 1..Item'Length and each
              of whose elements is given by To_ISO_646 of the corresponding
              element in Item.

42    The following set of functions test Wide_Character values for membership
in Character, or convert between corresponding characters of Wide_Character
and Character.

43    Is_Character
              Returns True if Wide_Character'Pos(Item) <=
              Character'Pos(Character'Last).

44    Is_String
              Returns True if Is_Character(Item(I)) is True for each I in
              Item'Range.

45    To_Character
              Returns the Character corresponding to Item if
              Is_Character(Item), and returns the Substitute Character
              otherwise.

46    To_String
              Returns the String whose range is 1..Item'Length and each of
              whose elements is given by To_Character of the corresponding
              element in Item.

47    To_Wide_Character
              Returns the Wide_Character X such that Character'Pos(Item) =
              Wide_Character'Pos(X).

48    To_Wide_String
              Returns the Wide_String whose range is 1..Item'Length and each
              of whose elements is given by To_Wide_Character of the
              corresponding element in Item.


                            Implementation Advice

49    If an implementation provides a localized definition of Character or
Wide_Character, then the effects of the subprograms in Characters.Handling
should reflect the localizations. See also 3.5.2.

      NOTES

50    5  A basic letter is a letter without a diacritical mark.

51    6  Except for the hexadecimal digits, basic letters, and ISO_646
      characters, the categories identified in the classification functions
      form a strict hierarchy:

    52    - Control characters

    53    - Graphic characters

    54       - Alphanumeric characters

    55           - Letters

    56               - Upper-case letters

    57               - Lower-case letters

    58           - Decimal digits

    59       - Special graphic characters


A.3.3 The Package Characters.Latin_1


1     The package Characters.Latin_1 declares constants for characters in ISO
8859-1.


                              Static Semantics

2     The library package Characters.Latin_1 has the following declaration:

3     package Ada.Characters.Latin_1 is
          pragma Pure(Latin_1);

4     -- Control characters:

5         NUL                  : constant Character := Character'Val(0);
          SOH                  : constant Character := Character'Val(1);
          STX                  : constant Character := Character'Val(2);
          ETX                  : constant Character := Character'Val(3);
          EOT                  : constant Character := Character'Val(4);
          ENQ                  : constant Character := Character'Val(5);
          ACK                  : constant Character := Character'Val(6);
          BEL                  : constant Character := Character'Val(7);
          BS                   : constant Character := Character'Val(8);
          HT                   : constant Character := Character'Val(9);
          LF                   : constant Character := Character'Val(10);
          VT                   : constant Character := Character'Val(11);
          FF                   : constant Character := Character'Val(12);
          CR                   : constant Character := Character'Val(13);
          SO                   : constant Character := Character'Val(14);
          SI                   : constant Character := Character'Val(15);

6         DLE                  : constant Character := Character'Val(16);
          DC1                  : constant Character := Character'Val(17);
          DC2                  : constant Character := Character'Val(18);
          DC3                  : constant Character := Character'Val(19);
          DC4                  : constant Character := Character'Val(20);
          NAK                  : constant Character := Character'Val(21);
          SYN                  : constant Character := Character'Val(22);
          ETB                  : constant Character := Character'Val(23);
          CAN                  : constant Character := Character'Val(24);
          EM                   : constant Character := Character'Val(25);
          SUB                  : constant Character := Character'Val(26);
          ESC                  : constant Character := Character'Val(27);
          FS                   : constant Character := Character'Val(28);
          GS                   : constant Character := Character'Val(29);
          RS                   : constant Character := Character'Val(30);
          US                   : constant Character := Character'Val(31);

7     -- ISO 646 graphic characters:

8         Space
                      : constant Character := ' ';  -- Character'Val(32)
          Exclamation
                : constant Character := '!';  -- Character'Val(33)
          Quotation
                  : constant Character := '"';  -- Character'Val(34)
          Number_Sign
                : constant Character := '#';  -- Character'Val(35)
          Dollar_Sign
                : constant Character := '$';  -- Character'Val(36)
          Percent_Sign
               : constant Character := '%';  -- Character'Val(37)
          Ampersand
                  : constant Character := '&';  -- Character'Val(38)
          Apostrophe
                 : constant Character := ''';  -- Character'Val(39)
          Left_Parenthesis
           : constant Character := '(';  -- Character'Val(40)
          Right_Parenthesis
          : constant Character := ')';  -- Character'Val(41)
          Asterisk
                   : constant Character := '*';  -- Character'Val(42)
          Plus_Sign
                  : constant Character := '+';  -- Character'Val(43)
          Comma
                      : constant Character := ',';  -- Character'Val(44)
          Hyphen
                     : constant Character := '-';  -- Character'Val(45)
          Minus_Sign           : Character renames Hyphen;
          Full_Stop
                  : constant Character := '.';  -- Character'Val(46)
          Solidus
                    : constant Character := '/';  -- Character'Val(47)

9         -- Decimal digits '0' though '9' are at positions 48 through 57

10        Colon
                      : constant Character := ':';  -- Character'Val(58)
          Semicolon
                  : constant Character := ';';  -- Character'Val(59)
          Less_Than_Sign
             : constant Character := '<';  -- Character'Val(60)
          Equals_Sign
                : constant Character := '=';  -- Character'Val(61)
          Greater_Than_Sign
          : constant Character := '>';  -- Character'Val(62)
          Question
                   : constant Character := '?';  -- Character'Val(63)
          Commercial_At
              : constant Character := '@';  -- Character'Val(64)

11        -- Letters 'A' through 'Z' are at positions 65 through 90

12        Left_Square_Bracket
        : constant Character := '[';  -- Character'Val(91)
          Reverse_Solidus
            : constant Character := '\';  -- Character'Val(92)
          Right_Square_Bracket
       : constant Character := ']';  -- Character'Val(93)
          Circumflex
                 : constant Character := '^';  -- Character'Val(94)
          Low_Line
                   : constant Character := '_';  -- Character'Val(95)

13        Grave
                      : constant Character := '`';  -- Character'Val(96)
          LC_A
                       : constant Character := 'a';  -- Character'Val(97)
          LC_B
                       : constant Character := 'b';  -- Character'Val(98)
          LC_C
                       : constant Character := 'c';  -- Character'Val(99)
          LC_D
                       : constant Character := 'd';  -- Character'Val(100)
          LC_E
                       : constant Character := 'e';  -- Character'Val(101)
          LC_F
                       : constant Character := 'f';  -- Character'Val(102)
          LC_G
                       : constant Character := 'g';  -- Character'Val(103)
          LC_H
                       : constant Character := 'h';  -- Character'Val(104)
          LC_I
                       : constant Character := 'i';  -- Character'Val(105)
          LC_J
                       : constant Character := 'j';  -- Character'Val(106)
          LC_K
                       : constant Character := 'k';  -- Character'Val(107)
          LC_L
                       : constant Character := 'l';  -- Character'Val(108)
          LC_M
                       : constant Character := 'm';  -- Character'Val(109)
          LC_N
                       : constant Character := 'n';  -- Character'Val(110)
          LC_O
                       : constant Character := 'o';  -- Character'Val(111)

14        LC_P
                       : constant Character := 'p';  -- Character'Val(112)
          LC_Q
                       : constant Character := 'q';  -- Character'Val(113)
          LC_R
                       : constant Character := 'r';  -- Character'Val(114)
          LC_S
                       : constant Character := 's';  -- Character'Val(115)
          LC_T
                       : constant Character := 't';  -- Character'Val(116)
          LC_U
                       : constant Character := 'u';  -- Character'Val(117)
          LC_V
                       : constant Character := 'v';  -- Character'Val(118)
          LC_W
                       : constant Character := 'w';  -- Character'Val(119)
          LC_X
                       : constant Character := 'x';  -- Character'Val(120)
          LC_Y
                       : constant Character := 'y';  -- Character'Val(121)
          LC_Z
                       : constant Character := 'z';  -- Character'Val(122)
          Left_Curly_Bracket
         : constant Character := '{';  -- Character'Val(123)
          Vertical_Line
              : constant Character := '|';  -- Character'Val(124)
          Right_Curly_Bracket
        : constant Character := '}';  -- Character'Val(125)
          Tilde
                      : constant Character := '~';  -- Character'Val(126)
          DEL                  : constant Character := Character'Val(127);

15    -- ISO 6429 control characters:

16        IS4                  : Character renames FS;
          IS3                  : Character renames GS;
          IS2                  : Character renames RS;
          IS1                  : Character renames US;

17        Reserved_128         : constant Character := Character'Val(128);
          Reserved_129         : constant Character := Character'Val(129);
          BPH                  : constant Character := Character'Val(130);
          NBH                  : constant Character := Character'Val(131);
          Reserved_132         : constant Character := Character'Val(132);
          NEL                  : constant Character := Character'Val(133);
          SSA                  : constant Character := Character'Val(134);
          ESA                  : constant Character := Character'Val(135);
          HTS                  : constant Character := Character'Val(136);
          HTJ                  : constant Character := Character'Val(137);
          VTS                  : constant Character := Character'Val(138);
          PLD                  : constant Character := Character'Val(139);
          PLU                  : constant Character := Character'Val(140);
          RI                   : constant Character := Character'Val(141);
          SS2                  : constant Character := Character'Val(142);
          SS3                  : constant Character := Character'Val(143);

18        DCS                  : constant Character := Character'Val(144);
          PU1                  : constant Character := Character'Val(145);
          PU2                  : constant Character := Character'Val(146);
          STS                  : constant Character := Character'Val(147);
          CCH                  : constant Character := Character'Val(148);
          MW                   : constant Character := Character'Val(149);
          SPA                  : constant Character := Character'Val(150);
          EPA                  : constant Character := Character'Val(151);

19        SOS                  : constant Character := Character'Val(152);
          Reserved_153         : constant Character := Character'Val(153);
          SCI                  : constant Character := Character'Val(154);
          CSI                  : constant Character := Character'Val(155);
          ST                   : constant Character := Character'Val(156);
          OSC                  : constant Character := Character'Val(157);
          PM                   : constant Character := Character'Val(158);
          APC                  : constant Character := Character'Val(159);

20    -- Other graphic characters:

21    -- Character positions 160 (16#A0#) .. 175 (16#AF#):
          No_Break_Space
                    : constant Character := ' ';  --Character'Val(160)
          NBSP                        : Character renames No_Break_Space;
          Inverted_Exclamation
              : constant Character := '¡';  --Character'Val(161)
          Cent_Sign
                         : constant Character := '¢';  --Character'Val(162)
          Pound_Sign
                        : constant Character := '£';  --Character'Val(163)
          Currency_Sign
                     : constant Character := '¤';  --Character'Val(164)
          Yen_Sign
                          : constant Character := '¥';  --Character'Val(165)
          Broken_Bar
                        : constant Character := '¦';  --Character'Val(166)
          Section_Sign
                      : constant Character := '§';  --Character'Val(167)
          Diaeresis
                         : constant Character := '¨';  --Character'Val(168)
          Copyright_Sign
                    : constant Character := '©';  --Character'Val(169)
          Feminine_Ordinal_Indicator
        : constant Character := 'ª';  --Character'Val(170)
          Left_Angle_Quotation
              : constant Character := '«';  --Character'Val(171)
          Not_Sign
                          : constant Character := '¬';  --Character'Val(172)
          Soft_Hyphen
                       : constant Character := '­';  --Character'Val(173)
          Registered_Trade_Mark_Sign
        : constant Character := '®';  --Character'Val(174)
          Macron
                            : constant Character := '¯';  --Character'Val(175)

22    -- Character positions 176 (16#B0#) .. 191 (16#BF#):
          Degree_Sign
                       : constant Character := '°';  --Character'Val(176)
          Ring_Above                  : Character renames Degree_Sign;
          Plus_Minus_Sign
                   : constant Character := '±';  --Character'Val(177)
          Superscript_Two
                   : constant Character := '²';  --Character'Val(178)
          Superscript_Three
                 : constant Character := '³';  --Character'Val(179)
          Acute
                             : constant Character := '´';  --Character'Val(180)
          Micro_Sign
                        : constant Character := 'µ';  --Character'Val(181)
          Pilcrow_Sign
                      : constant Character := '¶';  --Character'Val(182)
          Paragraph_Sign              : Character renames Pilcrow_Sign;
          Middle_Dot
                        : constant Character := '·';  --Character'Val(183)
          Cedilla
                           : constant Character := '¸';  --Character'Val(184)
          Superscript_One
                   : constant Character := '¹';  --Character'Val(185)
          Masculine_Ordinal_Indicator
       : constant Character := 'º';  --Character'Val(186)
          Right_Angle_Quotation
             : constant Character := '»';  --Character'Val(187)
          Fraction_One_Quarter
              : constant Character := '¼';  --Character'Val(188)
          Fraction_One_Half
                 : constant Character := '½';  --Character'Val(189)
          Fraction_Three_Quarters
           : constant Character := '¾';  --Character'Val(190)
          Inverted_Question
                 : constant Character := '¿';  --Character'Val(191)

23    -- Character positions 192 (16#C0#) .. 207 (16#CF#):
          UC_A_Grave
                        : constant Character := 'À';  --Character'Val(192)
          UC_A_Acute
                        : constant Character := 'Á';  --Character'Val(193)
          UC_A_Circumflex
                   : constant Character := 'Â';  --Character'Val(194)
          UC_A_Tilde
                        : constant Character := 'Ã';  --Character'Val(195)
          UC_A_Diaeresis
                    : constant Character := 'Ä';  --Character'Val(196)
          UC_A_Ring
                         : constant Character := 'Å';  --Character'Val(197)
          UC_AE_Diphthong
                   : constant Character := 'Æ';  --Character'Val(198)
          UC_C_Cedilla
                      : constant Character := 'Ç';  --Character'Val(199)
          UC_E_Grave
                        : constant Character := 'È';  --Character'Val(200)
          UC_E_Acute
                        : constant Character := 'É';  --Character'Val(201)
          UC_E_Circumflex
                   : constant Character := 'Ê';  --Character'Val(202)
          UC_E_Diaeresis
                    : constant Character := 'Ë';  --Character'Val(203)
          UC_I_Grave
                        : constant Character := 'Ì';  --Character'Val(204)
          UC_I_Acute
                        : constant Character := 'Í';  --Character'Val(205)
          UC_I_Circumflex
                   : constant Character := 'Î';  --Character'Val(206)
          UC_I_Diaeresis
                    : constant Character := 'Ï';  --Character'Val(207)

24    -- Character positions 208 (16#D0#) .. 223 (16#DF#):
          UC_Icelandic_Eth
                  : constant Character := 'Ð';  --Character'Val(208)
          UC_N_Tilde
                        : constant Character := 'Ñ';  --Character'Val(209)
          UC_O_Grave
                        : constant Character := 'Ò';  --Character'Val(210)
          UC_O_Acute
                        : constant Character := 'Ó';  --Character'Val(211)
          UC_O_Circumflex
                   : constant Character := 'Ô';  --Character'Val(212)
          UC_O_Tilde
                        : constant Character := 'Õ';  --Character'Val(213)
          UC_O_Diaeresis
                    : constant Character := 'Ö';  --Character'Val(214)
          Multiplication_Sign
               : constant Character := '×';  --Character'Val(215)
          UC_O_Oblique_Stroke
               : constant Character := 'Ø';  --Character'Val(216)
          UC_U_Grave
                        : constant Character := 'Ù';  --Character'Val(217)
          UC_U_Acute
                        : constant Character := 'Ú';  --Character'Val(218)
          UC_U_Circumflex
                   : constant Character := 'Û';  --Character'Val(219)
          UC_U_Diaeresis
                    : constant Character := 'Ü';  --Character'Val(220)
          UC_Y_Acute
                        : constant Character := 'Ý';  --Character'Val(221)
          UC_Icelandic_Thorn
                : constant Character := 'Þ';  --Character'Val(222)
          LC_German_Sharp_S
                 : constant Character := 'ß';  --Character'Val(223)

25    -- Character positions 224 (16#E0#) .. 239 (16#EF#):
          LC_A_Grave
                        : constant Character := 'à';  --Character'Val(224)
          LC_A_Acute
                        : constant Character := 'á';  --Character'Val(225)
          LC_A_Circumflex
                   : constant Character := 'â';  --Character'Val(226)
          LC_A_Tilde
                        : constant Character := 'ã';  --Character'Val(227)
          LC_A_Diaeresis
                    : constant Character := 'ä';  --Character'Val(228)
          LC_A_Ring
                         : constant Character := 'å';  --Character'Val(229)
          LC_AE_Diphthong
                   : constant Character := 'æ';  --Character'Val(230)
          LC_C_Cedilla
                      : constant Character := 'ç';  --Character'Val(231)
          LC_E_Grave
                        : constant Character := 'è';  --Character'Val(232)
          LC_E_Acute
                        : constant Character := 'é';  --Character'Val(233)
          LC_E_Circumflex
                   : constant Character := 'ê';  --Character'Val(234)
          LC_E_Diaeresis
                    : constant Character := 'ë';  --Character'Val(235)
          LC_I_Grave
                        : constant Character := 'ì';  --Character'Val(236)
          LC_I_Acute
                        : constant Character := 'í';  --Character'Val(237)
          LC_I_Circumflex
                   : constant Character := 'î';  --Character'Val(238)
          LC_I_Diaeresis
                    : constant Character := 'ï';  --Character'Val(239)

26    -- Character positions 240 (16#F0#) .. 255 (16#FF#):
          LC_Icelandic_Eth
                  : constant Character := 'ð';  --Character'Val(240)
          LC_N_Tilde
                        : constant Character := 'ñ';  --Character'Val(241)
          LC_O_Grave
                        : constant Character := 'ò';  --Character'Val(242)
          LC_O_Acute
                        : constant Character := 'ó';  --Character'Val(243)
          LC_O_Circumflex
                   : constant Character := 'ô';  --Character'Val(244)
          LC_O_Tilde
                        : constant Character := 'õ';  --Character'Val(245)
          LC_O_Diaeresis
                    : constant Character := 'ö';  --Character'Val(246)
          Division_Sign
                     : constant Character := '÷';  --Character'Val(247)
          LC_O_Oblique_Stroke
               : constant Character := 'ø';  --Character'Val(248)
          LC_U_Grave
                        : constant Character := 'ù';  --Character'Val(249)
          LC_U_Acute
                        : constant Character := 'ú';  --Character'Val(250)
          LC_U_Circumflex
                   : constant Character := 'û';  --Character'Val(251)
          LC_U_Diaeresis
                    : constant Character := 'ü';  --Character'Val(252)
          LC_Y_Acute
                        : constant Character := 'ý';  --Character'Val(253)
          LC_Icelandic_Thorn
                : constant Character := 'þ';  --Character'Val(254)
          LC_Y_Diaeresis
                    : constant Character := 'ÿ';  --Character'Val(255)
      end Ada.Characters.Latin_1;


                         Implementation Permissions

27    An implementation may provide additional packages as children of
Ada.Characters, to declare names for the symbols of the local character set or
other character sets.


A.4 String Handling


1     This clause presents the specifications of the package Strings and
several child packages, which provide facilities for dealing with string data.
Fixed-length, bounded-length, and unbounded-length strings are supported, for
both String and Wide_String. The string-handling subprograms include searches
for pattern strings and for characters in program-specified sets, translation
(via a character-to-character mapping), and transformation (replacing,
inserting, overwriting, and deleting of substrings).


A.4.1 The Package Strings


1     The package Strings provides declarations common to the string handling
packages.


                              Static Semantics

2     The library package Strings has the following declaration:

3     package Ada.Strings is
         pragma Pure(Strings);

4        Space      : constant Character      := ' ';
         Wide_Space : constant Wide_Character := ' ';

5        Length_Error, Pattern_Error, Index_Error, Translation_Error
       : exception;

6        type Alignment  is (Left, Right, Center);
         type Truncation is (Left, Right, Error);
         type Membership is (Inside, Outside);
         type Direction  is (Forward, Backward);
         type Trim_End   is (Left, Right, Both);
      end Ada.Strings;




A.4.2 The Package Strings.Maps


1     The package Strings.Maps defines the types, operations, and other
entities needed for character sets and character-to-character mappings.


                              Static Semantics

2     The library package Strings.Maps has the following declaration:

3     package Ada.Strings.Maps is
         pragma Preelaborate(Maps);

4        -- Representation for a set of character values:
         type Character_Set is private;

5        Null_Set : constant Character_Set;

6        type Character_Range is
           record
              Low  : Character;
              High : Character;
           end record;
         -- Represents Character range Low..High

7        type Character_Ranges
       is array (Positive range <>) of Character_Range;

8        function To_Set
          (Ranges : in Character_Ranges)return Character_Set;

9        function To_Set    (Span   : in Character_Range)return Character_Set;

10       function To_Ranges
       (Set    : in Character_Set)  return Character_Ranges;

11       function "="   (Left, Right : in Character_Set) return Boolean;

12       function "not" (Right : in Character_Set)       return Character_Set;
         function "and" (Left, Right : in Character_Set) return Character_Set;
         function "or"  (Left, Right : in Character_Set) return Character_Set;
         function "xor" (Left, Right : in Character_Set) return Character_Set;
         function "-"   (Left, Right : in Character_Set) return Character_Set;

13       function Is_In (Element : in Character;
                         Set     : in Character_Set)
            return Boolean;

14       function Is_Subset (Elements : in Character_Set;
                             Set      : in Character_Set)
            return Boolean;

15       function "<=" (Left  : in Character_Set;
                        Right : in Character_Set)
            return Boolean renames Is_Subset;

16       -- Alternative representation for a set of character values:
         subtype Character_Sequence is String;

17       function To_Set
       (Sequence  : in Character_Sequence)return Character_Set;

18       function To_Set (Singleton : in Character)     return Character_Set;

19       function To_Sequence
       (Set  : in Character_Set) return Character_Sequence;

20       -- Representation for a character to character mapping:
         type Character_Mapping is private;

21       function Value (Map     : in Character_Mapping;
                         Element : in Character)
            return Character;

22       Identity : constant Character_Mapping;

23       function To_Mapping (From, To : in Character_Sequence)
            return Character_Mapping;

24       function To_Domain (Map : in Character_Mapping)
            return Character_Sequence;
         function To_Range  (Map : in Character_Mapping)
            return Character_Sequence;

25       type Character_Mapping_Function is
            access function (From : in Character) return Character;

26    private
         ... -- not specified by the language
      end Ada.Strings.Maps;

27    An object of type Character_Set represents a set of characters.

28    Null_Set represents the set containing no characters.

29    An object Obj of type Character_Range represents the set of characters
in the range Obj.Low .. Obj.High.

30    An object Obj of type Character_Ranges represents the union of the sets
corresponding to Obj(I) for I in Obj'Range.

31    function To_Set (Ranges : in Character_Ranges) return Character_Set;

    32    If Ranges'Length=0 then Null_Set is returned; otherwise the returned
          value represents the set corresponding to Ranges.

33    function To_Set (Span : in Character_Range) return Character_Set;

    34    The returned value represents the set containing each character in
          Span.

35    function To_Ranges (Set : in Character_Set) return Character_Ranges;

    36    If Set = Null_Set then an empty Character_Ranges array is returned;
          otherwise the shortest array of contiguous ranges of Character
          values in Set, in increasing order of Low, is returned.

37    function "=" (Left, Right : in Character_Set) return Boolean;

    38    The function "=" returns True if Left and Right represent identical
          sets, and False otherwise.

39    Each of the logical operators "not", "and", "or", and "xor" returns a
Character_Set value that represents the set obtained by applying the
corresponding operation to the set(s) represented by the parameter(s) of the
operator. "-"(Left, Right) is equivalent to "and"(Left, "not"(Right)).

40    function Is_In (Element : in Character;
                      Set     : in Character_Set);
         return Boolean;

    41    Is_In returns True if Element is in Set, and False otherwise.

42    function Is_Subset (Elements : in Character_Set;
                          Set      : in Character_Set)
         return Boolean;

    43    Is_Subset returns True if Elements is a subset of Set, and False
          otherwise.

44    subtype Character_Sequence is String;

    45    The Character_Sequence subtype is used to portray a set of character
          values and also to identify the domain and range of a character
          mapping.

46    function To_Set (Sequence  : in Character_Sequence) return Character_Set;
      
      function To_Set (Singleton : in Character)          return Character_Set;

    47    Sequence portrays the set of character values that it explicitly
          contains (ignoring duplicates). Singleton portrays the set
          comprising a single Character. Each of the To_Set functions returns
          a Character_Set value that represents the set portrayed by Sequence
          or Singleton.

48    function To_Sequence (Set : in Character_Set) return Character_Sequence;

    49    The function To_Sequence returns a Character_Sequence value
          containing each of the characters in the set represented by Set, in
          ascending order with no duplicates.

50    type Character_Mapping is private;

    51    An object of type Character_Mapping represents a
          Character-to-Character mapping.

52    function Value (Map     : in Character_Mapping;
                      Element : in Character)
         return Character;

    53    The function Value returns the Character value to which Element maps
          with respect to the mapping represented by Map.

54    A character C matches a pattern character P with respect to a given
Character_Mapping value Map if Value(Map, C) = P. A string S matches a pattern
string P with respect to a given Character_Mapping if their lengths are the
same and if each character in S matches its corresponding character in the
pattern string P.

55    String handling subprograms that deal with character mappings have
parameters whose type is Character_Mapping.

56    Identity : constant Character_Mapping;

    57    Identity maps each Character to itself.

58    function To_Mapping (From, To : in Character_Sequence)
          return Character_Mapping;

    59    To_Mapping produces a Character_Mapping such that each element of
          From maps to the corresponding element of To, and each other
          character maps to itself. If From'Length /= To'Length, or if some
          character is repeated in From, then Translation_Error is propagated.

60    function To_Domain (Map : in Character_Mapping) return Character_Sequence;

    61    To_Domain returns the shortest Character_Sequence value D such that
          each character not in D maps to itself, and such that the characters
          in D are in ascending order. The lower bound of D is 1.

62    function To_Range  (Map : in Character_Mapping) return Character_Sequence;

    63/1  To_Range returns the Character_Sequence value R, [with lower bound 1
          and upper bound Map'Length,] such that if D = To_Domain(Map){, then
          R has the same bounds as D, and}[ then] D(I) maps to R(I) for each I
          in D'Range.

64    An object F of type Character_Mapping_Function maps a Character value C
to the Character value F.all(C), which is said to match C with respect to
mapping function F.

      NOTES

65    7  Character_Mapping and Character_Mapping_Function are used both for
      character equivalence mappings in the search subprograms (such as for
      case insensitivity) and as transformational mappings in the Translate
      subprograms.

66    8  To_Domain(Identity) and To_Range(Identity) each returns the null
      string.


                                  Examples

67    To_Mapping("ABCD", "ZZAB") returns a Character_Mapping that maps 'A' and
'B' to 'Z', 'C' to 'A', 'D' to 'B', and each other Character to itself.


A.4.3 Fixed-Length String Handling


1     The language-defined package Strings.Fixed provides string-handling
subprograms for fixed-length strings; that is, for values of type
Standard.String. Several of these subprograms are procedures that modify the
contents of a String that is passed as an out or an in out parameter; each has
additional parameters to control the effect when the logical length of the
result differs from the parameter's length.

2     For each function that returns a String, the lower bound of the returned
value is 1.

3     The basic model embodied in the package is that a fixed-length string
comprises significant characters and possibly padding (with space characters)
on either or both ends. When a shorter string is copied to a longer string,
padding is inserted, and when a longer string is copied to a shorter one,
padding is stripped. The Move procedure in Strings.Fixed, which takes a String
as an out parameter, allows the programmer to control these effects. Similar
control is provided by the string transformation procedures.


                              Static Semantics

4     The library package Strings.Fixed has the following declaration:

5     with Ada.Strings.Maps;
      package Ada.Strings.Fixed is
         pragma Preelaborate(Fixed);

6     -- "Copy" procedure for strings of possibly different lengths

7        procedure Move (Source  : in  String;
                         Target  : out String;
                         Drop    : in  Truncation := Error;
                         Justify : in  Alignment  := Left;
                         Pad     : in  Character  := Space);

8     -- Search subprograms

9        function Index (Source   : in String;
                         Pattern  : in String;
                         Going    : in Direction := Forward;
                         Mapping  : in Maps.Character_Mapping
                                      := Maps.Identity)
            return Natural;

10       function Index (Source   : in String;
                         Pattern  : in String;
                         Going    : in Direction := Forward;
                         Mapping  : in Maps.Character_Mapping_Function)
            return Natural;

11       function Index (Source : in String;
                         Set    : in Maps.Character_Set;
                         Test   : in Membership := Inside;
                         Going  : in Direction  := Forward)
            return Natural;

12       function Index_Non_Blank (Source : in String;
                                   Going  : in Direction := Forward)
            return Natural;

13       function Count (Source   : in String;
                         Pattern  : in String;
                         Mapping  : in Maps.Character_Mapping
                                       := Maps.Identity)
            return Natural;

14       function Count (Source   : in String;
                         Pattern  : in String;
                         Mapping  : in Maps.Character_Mapping_Function)
            return Natural;

15       function Count (Source   : in String;
                         Set      : in Maps.Character_Set)
            return Natural;

16       procedure Find_Token (Source : in String;
                               Set    : in Maps.Character_Set;
                               Test   : in Membership;
                               First  : out Positive;
                               Last   : out Natural);

17    -- String translation subprograms

18       function Translate (Source  : in String;
                             Mapping : in Maps.Character_Mapping)
            return String;

19       procedure Translate (Source  : in out String;
                              Mapping : in Maps.Character_Mapping);

20       function Translate (Source  : in String;
                             Mapping : in Maps.Character_Mapping_Function)
            return String;

21       procedure Translate (Source  : in out String;
                              Mapping : in Maps.Character_Mapping_Function);

22    -- String transformation subprograms

23       function Replace_Slice (Source   : in String;
                                 Low      : in Positive;
                                 High     : in Natural;
                                 By       : in String)
            return String;

24       procedure Replace_Slice (Source   : in out String;
                                  Low      : in Positive;
                                  High     : in Natural;
                                  By       : in String;
                                  Drop     : in Truncation := Error;
                                  Justify  : in Alignment  := Left;
                                  Pad      : in Character  := Space);

25       function Insert (Source   : in String;
                          Before   : in Positive;
                          New_Item : in String)
            return String;

26       procedure Insert (Source   : in out String;
                           Before   : in Positive;
                           New_Item : in String;
                           Drop     : in Truncation := Error);

27       function Overwrite (Source   : in String;
                             Position : in Positive;
                             New_Item : in String)
            return String;

28       procedure Overwrite (Source   : in out String;
                              Position : in Positive;
                              New_Item : in String;
                              Drop     : in Truncation := Right);

29       function Delete (Source  : in String;
                          From    : in Positive;
                          Through : in Natural)
            return String;

30       procedure Delete (Source  : in out String;
                           From    : in Positive;
                           Through : in Natural;
                           Justify : in Alignment := Left;
                           Pad     : in Character := Space);

31     --String selector subprograms
         function Trim (Source : in String;
                        Side   : in Trim_End)
            return String;

32       procedure Trim (Source  : in out String;
                         Side    : in Trim_End;
                         Justify : in Alignment := Left;
                         Pad     : in Character := Space);

33       function Trim (Source : in String;
                        Left   : in Maps.Character_Set;
                        Right  : in Maps.Character_Set)
            return String;

34       procedure Trim (Source  : in out String;
                         Left    : in Maps.Character_Set;
                         Right   : in Maps.Character_Set;
                         Justify : in Alignment := Strings.Left;
                         Pad     : in Character := Space);

35       function Head (Source : in String;
                        Count  : in Natural;
                        Pad    : in Character := Space)
            return String;

36       procedure Head (Source  : in out String;
                         Count   : in Natural;
                         Justify : in Alignment := Left;
                         Pad     : in Character := Space);

37       function Tail (Source : in String;
                        Count  : in Natural;
                        Pad    : in Character := Space)
            return String;

38       procedure Tail (Source  : in out String;
                         Count   : in Natural;
                         Justify : in Alignment := Left;
                         Pad     : in Character := Space);

39    --String constructor functions

40       function "*" (Left  : in Natural;
                       Right : in Character) return String;

41       function "*" (Left  : in Natural;
                       Right : in String) return String;

42    end Ada.Strings.Fixed;

43    The effects of the above subprograms are as follows.

44    procedure Move (Source  : in  String;
                      Target  : out String;
                      Drop    : in  Truncation := Error;
                      Justify : in  Alignment  := Left;
                      Pad     : in  Character  := Space);

    45    The Move procedure copies characters from Source to Target. If
          Source has the same length as Target, then the effect is to assign
          Source to Target. If Source is shorter than Target then:

        46    If Justify=Left, then Source is copied into the first
              Source'Length characters of Target.

        47    If Justify=Right, then Source is copied into the last
              Source'Length characters of Target.

        48    If Justify=Center, then Source is copied into the middle
              Source'Length characters of Target. In this case, if the
              difference in length between Target and Source is odd, then the
              extra Pad character is on the right.

        49    Pad is copied to each Target character not otherwise assigned.

    50    If Source is longer than Target, then the effect is based on Drop.

        51    If Drop=Left, then the rightmost Target'Length characters of
              Source are copied into Target.

        52    If Drop=Right, then the leftmost Target'Length characters of
              Source are copied into Target.

        53    If Drop=Error, then the effect depends on the value of the
              Justify parameter and also on whether any characters in Source
              other than Pad would fail to be copied:

            54    If Justify=Left, and if each of the rightmost
                  Source'Length-Target'Length characters in Source is Pad,
                  then the leftmost Target'Length characters of Source are
                  copied to Target.

            55    If Justify=Right, and if each of the leftmost
                  Source'Length-Target'Length characters in Source is Pad,
                  then the rightmost Target'Length characters of Source are
                  copied to Target.

            56    Otherwise, Length_Error is propagated.

57    function Index (Source   : in String;
                      Pattern  : in String;
                      Going    : in Direction := Forward;
                      Mapping  : in Maps.Character_Mapping
                                    := Maps.Identity)
         return Natural;
      
      function Index (Source   : in String;
                      Pattern  : in String;
                      Going    : in Direction := Forward;
                      Mapping  : in Maps.Character_Mapping_Function)
         return Natural;

    58    Each Index function searches for a slice of Source, with length
          Pattern'Length, that matches Pattern with respect to Mapping; the
          parameter Going indicates the direction of the lookup. If Going =
          Forward, then Index returns the smallest index I such that the slice
          of Source starting at I matches Pattern. If Going = Backward, then
          Index returns the largest index I such that the slice of Source
          starting at I matches Pattern. If there is no such slice, then 0 is
          returned. If Pattern is the null string then Pattern_Error is
          propagated.

59    function Index (Source : in String;
                      Set    : in Maps.Character_Set;
                      Test   : in Membership := Inside;
                      Going  : in Direction  := Forward)
         return Natural;

    60    Index searches for the first or last occurrence of any of a set of
          characters (when Test=Inside), or any of the complement of a set of
          characters (when Test=Outside). It returns the smallest index I (if
          Going=Forward) or the largest index I (if Going=Backward) such that
          Source(I) satisfies the Test condition with respect to Set; it
          returns 0 if there is no such Character in Source.

61    function Index_Non_Blank (Source : in String;
                                Going  : in Direction := Forward)
         return Natural;

    62    Returns Index(Source, Maps.To_Set(Space), Outside, Going)

63    function Count (Source   : in String;
                      Pattern  : in String;
                      Mapping  : in Maps.Character_Mapping
                                   := Maps.Identity)
         return Natural;
      
      function Count (Source   : in String;
                      Pattern  : in String;
                      Mapping  : in Maps.Character_Mapping_Function)
         return Natural;

    64    Returns the maximum number of nonoverlapping slices of Source that
          match Pattern with respect to Mapping. If Pattern is the null string
          then Pattern_Error is propagated.

65    function Count (Source   : in String;
                      Set      : in Maps.Character_Set)
         return Natural;

    66    Returns the number of occurrences in Source of characters that are
          in Set.

67    procedure Find_Token (Source : in String;
                            Set    : in Maps.Character_Set;
                            Test   : in Membership;
                            First  : out Positive;
                            Last   : out Natural);

    68/1  Find_Token returns in First and Last the indices of the beginning
          and end of the first slice of Source all of whose elements satisfy
          the Test condition, and such that the elements (if any) immediately
          before and after the slice do not satisfy the Test condition. If no
          such slice exists, then the value returned for Last is zero, and the
          value returned for First is Source'First{; however, if Source'First
          is not in Positive then Constraint_Error is raised}.

69    function Translate (Source  : in String;
                          Mapping : in Maps.Character_Mapping)
         return String;
      
      function Translate (Source  : in String;
                          Mapping : in Maps.Character_Mapping_Function)
         return String;

    70    Returns the string S whose length is Source'Length and such that
          S(I) is the character to which Mapping maps the corresponding
          element of Source, for I in 1..Source'Length.

71    procedure Translate (Source  : in out String;
                           Mapping : in Maps.Character_Mapping);
      
      procedure Translate (Source  : in out String;
                           Mapping : in Maps.Character_Mapping_Function);

    72    Equivalent to Source := Translate(Source, Mapping).

73    function Replace_Slice (Source   : in String;
                              Low      : in Positive;
                              High     : in Natural;
                              By       : in String)
         return String;

    74/1  {}[]If Low > Source'Last+1, or High < Source'First-1, then
          Index_Error is propagated. Otherwise{:}[, if High >= Low then the
          returned string comprises Source(Source'First..Low-1) & By &
          Source(High+1..Source'Last), and if High < Low then the returned
          string is Insert(Source, Before=>Low, New_Item=>By).]

        74.1/1 {If High >= Low, then the returned string comprises
              Source(Source'First..Low-1) & By & Source(High+1..Source'Last),
              but with lower bound 1.}

        74.2/1 {If High < Low, then the returned string is Insert(Source,
              Before=>Low, New_Item=>By).}

75    procedure Replace_Slice (Source   : in out String;
                               Low      : in Positive;
                               High     : in Natural;
                               By       : in String;
                               Drop     : in Truncation := Error;
                               Justify  : in Alignment  := Left;
                               Pad      : in Character  := Space);

    76    Equivalent to Move(Replace_Slice(Source, Low, High, By), Source,
          Drop, Justify, Pad).

77    function Insert (Source   : in String;
                       Before   : in Positive;
                       New_Item : in String)
         return String;

    78    Propagates Index_Error if Before is not in Source'First ..
          Source'Last+1; otherwise returns Source(Source'First..Before-1) &
          New_Item & Source(Before..Source'Last), but with lower bound 1.

79    procedure Insert (Source   : in out String;
                        Before   : in Positive;
                        New_Item : in String;
                        Drop     : in Truncation := Error);

    80    Equivalent to Move(Insert(Source, Before, New_Item), Source, Drop).

81    function Overwrite (Source   : in String;
                          Position : in Positive;
                          New_Item : in String)
         return String;

    82    Propagates Index_Error if Position is not in Source'First ..
          Source'Last+1; otherwise returns the string obtained from Source by
          consecutively replacing characters starting at Position with
          corresponding characters from New_Item. If the end of Source is
          reached before the characters in New_Item are exhausted, the
          remaining characters from New_Item are appended to the string.

83    procedure Overwrite (Source   : in out String;
                           Position : in Positive;
                           New_Item : in String;
                           Drop     : in Truncation := Right);

    84    Equivalent to Move(Overwrite(Source, Position, New_Item), Source,
          Drop).

85    function Delete (Source  : in String;
                       From    : in Positive;
                       Through : in Natural)
         return String;

    86/1  If From <= Through, the returned string is Replace_Slice(Source,
          From, Through, ""), otherwise it is Source{ with lower bound 1}.

87    procedure Delete (Source  : in out String;
                        From    : in Positive;
                        Through : in Natural;
                        Justify : in Alignment := Left;
                        Pad     : in Character := Space);

    88    Equivalent to Move(Delete(Source, From, Through), Source, Justify =>
          Justify, Pad => Pad).

89    function Trim (Source : in String;
                     Side   : in Trim_End)
        return String;

    90    Returns the string obtained by removing from Source all leading
          Space characters (if Side = Left), all trailing Space characters (if
          Side = Right), or all leading and trailing Space characters (if Side
          = Both).

91    procedure Trim (Source  : in out String;
                      Side    : in Trim_End;
                      Justify : in Alignment := Left;
                      Pad     : in Character := Space);

    92    Equivalent to Move(Trim(Source, Side), Source, Justify=>Justify,
          Pad=>Pad).

93    function Trim (Source : in String;
                     Left   : in Maps.Character_Set;
                     Right  : in Maps.Character_Set)
         return String;

    94    Returns the string obtained by removing from Source all leading
          characters in Left and all trailing characters in Right.

95    procedure Trim (Source  : in out String;
                      Left    : in Maps.Character_Set;
                      Right   : in Maps.Character_Set;
                      Justify : in Alignment := Strings.Left;
                      Pad     : in Character := Space);

    96    Equivalent to Move(Trim(Source, Left, Right), Source, Justify =>
          Justify, Pad=>Pad).

97    function Head (Source : in String;
                     Count  : in Natural;
                     Pad    : in Character := Space)
         return String;

    98    Returns a string of length Count. If Count <= Source'Length, the
          string comprises the first Count characters of Source. Otherwise its
          contents are Source concatenated with Count-Source'Length Pad
          characters.

99    procedure Head (Source  : in out String;
                      Count   : in Natural;
                      Justify : in Alignment := Left;
                      Pad     : in Character := Space);

    100   Equivalent to Move(Head(Source, Count, Pad), Source, Drop=>Error,
          Justify=>Justify, Pad=>Pad).

101   function Tail (Source : in String;
                     Count  : in Natural;
                     Pad    : in Character := Space)
         return String;

    102   Returns a string of length Count. If Count <= Source'Length, the
          string comprises the last Count characters of Source. Otherwise its
          contents are Count-Source'Length Pad characters concatenated with
          Source.

103   procedure Tail (Source  : in out String;
                      Count   : in Natural;
                      Justify : in Alignment := Left;
                      Pad     : in Character := Space);

    104   Equivalent to Move(Tail(Source, Count, Pad), Source, Drop=>Error,
          Justify=>Justify, Pad=>Pad).

105   function "*" (Left  : in Natural;
                    Right : in Character) return String;
      
      function "*" (Left  : in Natural;
                    Right : in String) return String;

    106/1 These functions replicate a character or string a specified number
          of times. The first function returns a string whose length is Left
          and each of whose elements is Right. The second function returns a
          string whose length is Left*Right'Length and whose value is the null
          string if Left = 0 and {otherwise }is (Left-1)*Right & Right {with
          lower bound 1}[otherwise].

      NOTES

107   9  In the Index and Count functions taking Pattern and Mapping
      parameters, the actual String parameter passed to Pattern should
      comprise characters occurring as target characters of the mapping.
      Otherwise the pattern will not match.

108   10  In the Insert subprograms, inserting at the end of a string is
      obtained by passing Source'Last+1 as the Before parameter.

109   11  If a null Character_Mapping_Function is passed to any of the string
      handling subprograms, Constraint_Error is propagated.


A.4.4 Bounded-Length String Handling


1     The language-defined package Strings.Bounded provides a generic package
each of whose instances yields a private type Bounded_String and a set of
operations. An object of a particular Bounded_String type represents a String
whose low bound is 1 and whose length can vary conceptually between 0 and a
maximum size established at the generic instantiation. The subprograms for
fixed-length string handling are either overloaded directly for
Bounded_String, or are modified as needed to reflect the variability in
length. Additionally, since the Bounded_String type is private, appropriate
constructor and selector operations are provided.


                              Static Semantics

2     The library package Strings.Bounded has the following declaration:

3     with Ada.Strings.Maps;
      package Ada.Strings.Bounded is
         pragma Preelaborate(Bounded);

4        generic
            Max   : Positive;    -- Maximum length of a Bounded_String
         package Generic_Bounded_Length is

5           Max_Length : constant Positive := Max;

6           type Bounded_String is private;

7           Null_Bounded_String : constant Bounded_String;

8           subtype Length_Range is Natural range 0 .. Max_Length;

9           function Length (Source : in Bounded_String) return Length_Range;

10       -- Conversion, Concatenation, and Selection functions

11          function To_Bounded_String (Source : in String;
                                        Drop   : in Truncation := Error)
               return Bounded_String;

12          function To_String (Source : in Bounded_String) return String;

13          function Append (Left, Right : in Bounded_String;
                             Drop        : in Truncation  := Error)
               return Bounded_String;

14          function Append (Left  : in Bounded_String;
                             Right : in String;
                             Drop  : in Truncation := Error)
               return Bounded_String;

15          function Append (Left  : in String;
                             Right : in Bounded_String;
                             Drop  : in Truncation := Error)
               return Bounded_String;

16          function Append (Left  : in Bounded_String;
                             Right : in Character;
                             Drop  : in Truncation := Error)
               return Bounded_String;

17          function Append (Left  : in Character;
                             Right : in Bounded_String;
                             Drop  : in Truncation := Error)
               return Bounded_String;

18          procedure Append (Source   : in out Bounded_String;
                              New_Item : in Bounded_String;
                              Drop     : in Truncation  := Error);

19          procedure Append (Source   : in out Bounded_String;
                              New_Item : in String;
                              Drop     : in Truncation  := Error);

20          procedure Append (Source   : in out Bounded_String;
                              New_Item : in Character;
                              Drop     : in Truncation  := Error);

21          function "&" (Left, Right : in Bounded_String)
               return Bounded_String;

22          function "&" (Left : in Bounded_String; Right : in String)
               return Bounded_String;

23          function "&" (Left : in String; Right : in Bounded_String)
               return Bounded_String;

24          function "&" (Left : in Bounded_String; Right : in Character)
               return Bounded_String;

25          function "&" (Left : in Character; Right : in Bounded_String)
               return Bounded_String;

26          function Element (Source : in Bounded_String;
                              Index  : in Positive)
               return Character;

27          procedure Replace_Element (Source : in out Bounded_String;
                                       Index  : in Positive;
                                       By     : in Character);

28          function Slice (Source : in Bounded_String;
                            Low    : in Positive;
                            High   : in Natural)
               return String;

29          function "="  (Left, Right : in Bounded_String) return Boolean;
            function "="  (Left : in Bounded_String; Right : in String)
              return Boolean;

30          function "="  (Left : in String; Right : in Bounded_String)
              return Boolean;

31          function "<"  (Left, Right : in Bounded_String) return Boolean;

32          function "<"  (Left : in Bounded_String; Right : in String)
              return Boolean;

33          function "<"  (Left : in String; Right : in Bounded_String)
              return Boolean;

34          function "<=" (Left, Right : in Bounded_String) return Boolean;

35          function "<="  (Left : in Bounded_String; Right : in String)
              return Boolean;

36          function "<="  (Left : in String; Right : in Bounded_String)
              return Boolean;

37          function ">"  (Left, Right : in Bounded_String) return Boolean;

38          function ">"  (Left : in Bounded_String; Right : in String)
              return Boolean;

39          function ">"  (Left : in String; Right : in Bounded_String)
              return Boolean;

40          function ">=" (Left, Right : in Bounded_String) return Boolean;

41          function ">="  (Left : in Bounded_String; Right : in String)
              return Boolean;

42          function ">="  (Left : in String; Right : in Bounded_String)
              return Boolean;

43       -- Search functions

44          function Index (Source   : in Bounded_String;
                            Pattern  : in String;
                            Going    : in Direction := Forward;
                            Mapping  : in Maps.Character_Mapping
                                       := Maps.Identity)
               return Natural;

45          function Index (Source   : in Bounded_String;
                            Pattern  : in String;
                            Going    : in Direction := Forward;
                            Mapping  : in Maps.Character_Mapping_Function)
               return Natural;

46          function Index (Source : in Bounded_String;
                            Set    : in Maps.Character_Set;
                            Test   : in Membership := Inside;
                            Going  : in Direction  := Forward)
               return Natural;

47          function Index_Non_Blank (Source : in Bounded_String;
                                      Going  : in Direction := Forward)
               return Natural;

48          function Count (Source   : in Bounded_String;
                            Pattern  : in String;
                            Mapping  : in Maps.Character_Mapping
                                         := Maps.Identity)
               return Natural;

49          function Count (Source   : in Bounded_String;
                            Pattern  : in String;
                            Mapping  : in Maps.Character_Mapping_Function)
               return Natural;

50          function Count (Source   : in Bounded_String;
                            Set      : in Maps.Character_Set)
               return Natural;

51          procedure Find_Token (Source : in Bounded_String;
                                  Set    : in Maps.Character_Set;
                                  Test   : in Membership;
                                  First  : out Positive;
                                  Last   : out Natural);

52       -- String translation subprograms

53          function Translate (Source  : in Bounded_String;
                                Mapping : in Maps.Character_Mapping)
               return Bounded_String;

54          procedure Translate (Source  : in out Bounded_String;
                                 Mapping : in Maps.Character_Mapping);

55          function Translate (Source  : in Bounded_String;
                                Mapping : in Maps.Character_Mapping_Function)
               return Bounded_String;

56          procedure Translate (Source  : in out Bounded_String;
                                 Mapping : in Maps.Character_Mapping_Function);

57       -- String transformation subprograms

58          function Replace_Slice (Source   : in Bounded_String;
                                    Low      : in Positive;
                                    High     : in Natural;
                                    By       : in String;
                                    Drop     : in Truncation := Error)
               return Bounded_String;

59          procedure Replace_Slice (Source   : in out Bounded_String;
                                     Low      : in Positive;
                                     High     : in Natural;
                                     By       : in String;
                                     Drop     : in Truncation := Error);

60          function Insert (Source   : in Bounded_String;
                             Before   : in Positive;
                             New_Item : in String;
                             Drop     : in Truncation := Error)
               return Bounded_String;

61          procedure Insert (Source   : in out Bounded_String;
                              Before   : in Positive;
                              New_Item : in String;
                              Drop     : in Truncation := Error);

62          function Overwrite (Source    : in Bounded_String;
                                Position  : in Positive;
                                New_Item  : in String;
                                Drop      : in Truncation := Error)
               return Bounded_String;

63          procedure Overwrite (Source    : in out Bounded_String;
                                 Position  : in Positive;
                                 New_Item  : in String;
                                 Drop      : in Truncation := Error);

64          function Delete (Source  : in Bounded_String;
                             From    : in Positive;
                             Through : in Natural)
               return Bounded_String;

65          procedure Delete (Source  : in out Bounded_String;
                              From    : in Positive;
                              Through : in Natural);

66    --String selector subprograms

67          function Trim (Source : in Bounded_String;
                           Side   : in Trim_End)
               return Bounded_String;
            procedure Trim (Source : in out Bounded_String;
                            Side   : in Trim_End);

68          function Trim (Source : in Bounded_String;
                           Left   : in Maps.Character_Set;
                           Right  : in Maps.Character_Set)
               return Bounded_String;

69          procedure Trim (Source : in out Bounded_String;
                            Left   : in Maps.Character_Set;
                            Right  : in Maps.Character_Set);

70          function Head (Source : in Bounded_String;
                           Count  : in Natural;
                           Pad    : in Character  := Space;
                           Drop   : in Truncation := Error)
               return Bounded_String;

71          procedure Head (Source : in out Bounded_String;
                            Count  : in Natural;
                            Pad    : in Character  := Space;
                            Drop   : in Truncation := Error);

72          function Tail (Source : in Bounded_String;
                           Count  : in Natural;
                           Pad    : in Character  := Space;
                           Drop   : in Truncation := Error)
               return Bounded_String;

73          procedure Tail (Source : in out Bounded_String;
                            Count  : in Natural;
                            Pad    : in Character  := Space;
                            Drop   : in Truncation := Error);

74    --String constructor subprograms

75          function "*" (Left  : in Natural;
                          Right : in Character)
               return Bounded_String;

76          function "*" (Left  : in Natural;
                          Right : in String)
               return Bounded_String;

77          function "*" (Left  : in Natural;
                          Right : in Bounded_String)
               return Bounded_String;

78          function Replicate (Count : in Natural;
                                Item  : in Character;
                                Drop  : in Truncation := Error)
               return Bounded_String;

79          function Replicate (Count : in Natural;
                                Item  : in String;
                                Drop  : in Truncation := Error)
               return Bounded_String;

80          function Replicate (Count : in Natural;
                                Item  : in Bounded_String;
                                Drop  : in Truncation := Error)
               return Bounded_String;

81       private
             ... -- not specified by the language
         end Generic_Bounded_Length;

82    end Ada.Strings.Bounded;

83    Null_Bounded_String represents the null string. If an object of type
Bounded_String is not otherwise initialized, it will be initialized to the
same value as Null_Bounded_String.

84    function Length (Source : in Bounded_String) return Length_Range;

    85    The Length function returns the length of the string represented by
          Source.

86    function To_Bounded_String (Source : in String;
                                  Drop   : in Truncation := Error)
         return Bounded_String;

    87    If Source'Length <= Max_Length then this function returns a
          Bounded_String that represents Source. Otherwise the effect depends
          on the value of Drop:

        88    If Drop=Left, then the result is a Bounded_String that
              represents the string comprising the rightmost Max_Length
              characters of Source.

        89    If Drop=Right, then the result is a Bounded_String that
              represents the string comprising the leftmost Max_Length
              characters of Source.

        90    If Drop=Error, then Strings.Length_Error is propagated.

91    function To_String (Source : in Bounded_String) return String;

    92    To_String returns the String value with lower bound 1 represented by
          Source. If B is a Bounded_String, then B =
          To_Bounded_String(To_String(B)).

93    Each of the Append functions returns a Bounded_String obtained by
concatenating the string or character given or represented by one of the
parameters, with the string or character given or represented by the other
parameter, and applying To_Bounded_String to the concatenation result string,
with Drop as provided to the Append function.

94    Each of the procedures Append(Source, New_Item, Drop) has the same
effect as the corresponding assignment Source := Append(Source, New_Item,
Drop).

95    Each of the "&" functions has the same effect as the corresponding
Append function, with Error as the Drop parameter.

96    function Element (Source : in Bounded_String;
                        Index  : in Positive)
         return Character;

    97    Returns the character at position Index in the string represented by
          Source; propagates Index_Error if Index > Length(Source).

98    procedure Replace_Element (Source : in out Bounded_String;
                                 Index  : in Positive;
                                 By     : in Character);

    99    Updates Source such that the character at position Index in the
          string represented by Source is By; propagates Index_Error if Index
          > Length(Source).

100   function Slice (Source : in Bounded_String;
                      Low    : in Positive;
                      High   : in Natural)
         return String;

    101/1 Returns the slice at positions Low through High in the string
          represented by Source; propagates Index_Error if Low >
          Length(Source)+1{ or High > Length(Source)}.

102   Each of the functions "=", "<", ">","<=", and ">=" returns the same
result as the corresponding String operation applied to the String values
given or represented by the two parameters.

103   Each of the search subprograms (Index, Index_Non_Blank, Count,
Find_Token) has the same effect as the corresponding subprogram in
Strings.Fixed applied to the string represented by the Bounded_String
parameter.

104   Each of the Translate subprograms, when applied to a Bounded_String, has
an analogous effect to the corresponding subprogram in Strings.Fixed. For the
Translate function, the translation is applied to the string represented by
the Bounded_String parameter, and the result is converted (via
To_Bounded_String) to a Bounded_String. For the Translate procedure, the
string represented by the Bounded_String parameter after the translation is
given by the Translate function for fixed-length strings applied to the string
represented by the original value of the parameter.

105/1 Each of the transformation subprograms (Replace_Slice, Insert,
Overwrite, Delete), selector subprograms (Trim, Head, Tail), and constructor
functions ("*") has an effect based on its corresponding subprogram in
Strings.Fixed, and Replicate is based on Fixed."*". {In the case of a
function}[For each of these subprograms], the corresponding fixed-length
string subprogram is applied to the string represented by the Bounded_String
parameter. To_Bounded_String is applied the result string, with Drop (or Error
in the case of Generic_Bounded_Length."*") determining the effect when the
string length exceeds Max_Length. {In the case of a procedure, the
corresponding function in Strings.Bounded.Generic_Bounded_Length is applied,
with the result assigned into the Source parameter.}


                            Implementation Advice

106   Bounded string objects should not be implemented by implicit pointers
and dynamic allocation.


A.4.5 Unbounded-Length String Handling


1     The language-defined package Strings.Unbounded provides a private type
Unbounded_String and a set of operations. An object of type Unbounded_String
represents a String whose low bound is 1 and whose length can vary
conceptually between 0 and Natural'Last. The subprograms for fixed-length
string handling are either overloaded directly for Unbounded_String, or are
modified as needed to reflect the flexibility in length. Since the
Unbounded_String type is private, relevant constructor and selector operations
are provided.


                              Static Semantics

2     The library package Strings.Unbounded has the following declaration:

3     with Ada.Strings.Maps;
      package Ada.Strings.Unbounded is
         pragma Preelaborate(Unbounded);

4        type Unbounded_String is private;

5        Null_Unbounded_String : constant Unbounded_String;

6        function Length (Source : in Unbounded_String) return Natural;

7        type String_Access is access all String;
         procedure Free (X : in out String_Access);

8     -- Conversion, Concatenation, and Selection functions

9        function To_Unbounded_String (Source : in String)
            return Unbounded_String;

10       function To_Unbounded_String (Length : in Natural)
            return Unbounded_String;

11       function To_String (Source : in Unbounded_String) return String;

12       procedure Append (Source   : in out Unbounded_String;
                           New_Item : in Unbounded_String);

13       procedure Append (Source   : in out Unbounded_String;
                           New_Item : in String);

14       procedure Append (Source   : in out Unbounded_String;
                           New_Item : in Character);

15       function "&" (Left, Right : in Unbounded_String)
            return Unbounded_String;

16       function "&" (Left : in Unbounded_String; Right : in String)
            return Unbounded_String;

17       function "&" (Left : in String; Right : in Unbounded_String)
            return Unbounded_String;

18       function "&" (Left : in Unbounded_String; Right : in Character)
            return Unbounded_String;

19       function "&" (Left : in Character; Right : in Unbounded_String)
            return Unbounded_String;

20       function Element (Source : in Unbounded_String;
                           Index  : in Positive)
            return Character;

21       procedure Replace_Element (Source : in out Unbounded_String;
                                    Index  : in Positive;
                                    By     : in Character);

22       function Slice (Source : in Unbounded_String;
                         Low    : in Positive;
                         High   : in Natural)
            return String;

23       function "="  (Left, Right : in Unbounded_String) return Boolean;

24       function "="  (Left : in Unbounded_String; Right : in String)
           return Boolean;

25       function "="  (Left : in String; Right : in Unbounded_String)
           return Boolean;

26       function "<"  (Left, Right : in Unbounded_String) return Boolean;

27       function "<"  (Left : in Unbounded_String; Right : in String)
           return Boolean;

28       function "<"  (Left : in String; Right : in Unbounded_String)
           return Boolean;

29       function "<=" (Left, Right : in Unbounded_String) return Boolean;

30       function "<="  (Left : in Unbounded_String; Right : in String)
           return Boolean;

31       function "<="  (Left : in String; Right : in Unbounded_String)
           return Boolean;

32       function ">"  (Left, Right : in Unbounded_String) return Boolean;

33       function ">"  (Left : in Unbounded_String; Right : in String)
           return Boolean;

34       function ">"  (Left : in String; Right : in Unbounded_String)
           return Boolean;

35       function ">=" (Left, Right : in Unbounded_String) return Boolean;

36       function ">="  (Left : in Unbounded_String; Right : in String)
           return Boolean;

37       function ">="  (Left : in String; Right : in Unbounded_String)
           return Boolean;

38    -- Search subprograms

39       function Index (Source   : in Unbounded_String;
                         Pattern  : in String;
                         Going    : in Direction := Forward;
                         Mapping  : in Maps.Character_Mapping
                                      := Maps.Identity)
            return Natural;

40       function Index (Source   : in Unbounded_String;
                         Pattern  : in String;
                         Going    : in Direction := Forward;
                         Mapping  : in Maps.Character_Mapping_Function)
            return Natural;

41       function Index (Source : in Unbounded_String;
                         Set    : in Maps.Character_Set;
                         Test   : in Membership := Inside;
                         Going  : in Direction  := Forward) return Natural;

42       function Index_Non_Blank (Source : in Unbounded_String;
                                   Going  : in Direction := Forward)
            return Natural;

43       function Count (Source   : in Unbounded_String;
                         Pattern  : in String;
                         Mapping  : in Maps.Character_Mapping
                                      := Maps.Identity)
            return Natural;

44       function Count (Source   : in Unbounded_String;
                         Pattern  : in String;
                         Mapping  : in Maps.Character_Mapping_Function)
            return Natural;

45       function Count (Source   : in Unbounded_String;
                         Set      : in Maps.Character_Set)
            return Natural;

46       procedure Find_Token (Source : in Unbounded_String;
                               Set    : in Maps.Character_Set;
                               Test   : in Membership;
                               First  : out Positive;
                               Last   : out Natural);

47    -- String translation subprograms

48       function Translate (Source  : in Unbounded_String;
                             Mapping : in Maps.Character_Mapping)
            return Unbounded_String;

49       procedure Translate (Source  : in out Unbounded_String;
                              Mapping : in Maps.Character_Mapping);

50       function Translate (Source  : in Unbounded_String;
                             Mapping : in Maps.Character_Mapping_Function)
            return Unbounded_String;

51       procedure Translate (Source  : in out Unbounded_String;
                              Mapping : in Maps.Character_Mapping_Function);

52    -- String transformation subprograms

53       function Replace_Slice (Source   : in Unbounded_String;
                                 Low      : in Positive;
                                 High     : in Natural;
                                 By       : in String)
            return Unbounded_String;

54       procedure Replace_Slice (Source   : in out Unbounded_String;
                                  Low      : in Positive;
                                  High     : in Natural;
                                  By       : in String);

55       function Insert (Source   : in Unbounded_String;
                          Before   : in Positive;
                          New_Item : in String)
            return Unbounded_String;

56       procedure Insert (Source   : in out Unbounded_String;
                           Before   : in Positive;
                           New_Item : in String);

57       function Overwrite (Source    : in Unbounded_String;
                             Position  : in Positive;
                             New_Item  : in String)
            return Unbounded_String;

58       procedure Overwrite (Source    : in out Unbounded_String;
                              Position  : in Positive;
                              New_Item  : in String);

59       function Delete (Source  : in Unbounded_String;
                          From    : in Positive;
                          Through : in Natural)
            return Unbounded_String;

60       procedure Delete (Source  : in out Unbounded_String;
                           From    : in Positive;
                           Through : in Natural);

61       function Trim (Source : in Unbounded_String;
                        Side   : in Trim_End)
            return Unbounded_String;

62       procedure Trim (Source : in out Unbounded_String;
                         Side   : in Trim_End);

63       function Trim (Source : in Unbounded_String;
                        Left   : in Maps.Character_Set;
                        Right  : in Maps.Character_Set)
            return Unbounded_String;

64       procedure Trim (Source : in out Unbounded_String;
                         Left   : in Maps.Character_Set;
                         Right  : in Maps.Character_Set);

65       function Head (Source : in Unbounded_String;
                        Count  : in Natural;
                        Pad    : in Character := Space)
            return Unbounded_String;

66       procedure Head (Source : in out Unbounded_String;
                         Count  : in Natural;
                         Pad    : in Character := Space);

67       function Tail (Source : in Unbounded_String;
                        Count  : in Natural;
                        Pad    : in Character := Space)
            return Unbounded_String;

68       procedure Tail (Source : in out Unbounded_String;
                         Count  : in Natural;
                         Pad    : in Character := Space);

69       function "*" (Left  : in Natural;
                       Right : in Character)
            return Unbounded_String;

70       function "*" (Left  : in Natural;
                       Right : in String)
            return Unbounded_String;

71       function "*" (Left  : in Natural;
                       Right : in Unbounded_String)
            return Unbounded_String;

72    private
         ... -- not specified by the language
      end Ada.Strings.Unbounded;

73    Null_Unbounded_String represents the null String. If an object of type
Unbounded_String is not otherwise initialized, it will be initialized to the
same value as Null_Unbounded_String.

74    The function Length returns the length of the String represented by
Source.

75    The type String_Access provides a (non-private) access type for explicit
processing of unbounded-length strings. The procedure Free performs an
unchecked deallocation of an object of type String_Access.

76    The function To_Unbounded_String(Source : in String) returns an
Unbounded_String that represents Source. The function
To_Unbounded_String(Length : in Natural) returns an Unbounded_String that
represents an uninitialized String whose length is Length.

77    The function To_String returns the String with lower bound 1 represented
by Source. To_String and To_Unbounded_String are related as follows:

78    If S is a String, then To_String(To_Unbounded_String(S)) = S.

79    If U is an Unbounded_String, then To_Unbounded_String(To_String(U)) = U.

80    For each of the Append procedures, the resulting string represented by
the Source parameter is given by the concatenation of the original value of
Source and the value of New_Item.

81    Each of the "&" functions returns an Unbounded_String obtained by
concatenating the string or character given or represented by one of the
parameters, with the string or character given or represented by the other
parameter, and applying To_Unbounded_String to the concatenation result string.

82    The Element, Replace_Element, and Slice subprograms have the same effect
as the corresponding bounded-length string subprograms.

83    Each of the functions "=", "<", ">","<=", and ">=" returns the same
result as the corresponding String operation applied to the String values
given or represented by Left and Right.

84    Each of the search subprograms (Index, Index_Non_Blank, Count,
Find_Token) has the same effect as the corresponding subprogram in
Strings.Fixed applied to the string represented by the Unbounded_String
parameter.

85    The Translate function has an analogous effect to the corresponding
subprogram in Strings.Fixed. The translation is applied to the string
represented by the Unbounded_String parameter, and the result is converted
(via To_Unbounded_String) to an Unbounded_String.

86    Each of the transformation functions (Replace_Slice, Insert, Overwrite,
Delete), selector functions (Trim, Head, Tail), and constructor functions
("*") is likewise analogous to its corresponding subprogram in Strings.Fixed.
For each of the subprograms, the corresponding fixed-length string subprogram
is applied to the string represented by the Unbounded_String parameter, and
To_Unbounded_String is applied the result string.

87    For each of the procedures Translate, Replace_Slice, Insert, Overwrite,
Delete, Trim, Head, and Tail, the resulting string represented by the Source
parameter is given by the corresponding function for fixed-length strings
applied to the string represented by Source's original value.


                         Implementation Requirements

88    No storage associated with an Unbounded_String object shall be lost upon
assignment or scope exit.


A.4.6 String-Handling Sets and Mappings


1     The language-defined package Strings.Maps.Constants declares
Character_Set and Character_Mapping constants corresponding to classification
and conversion functions in package Characters.Handling.


                              Static Semantics

2     The library package Strings.Maps.Constants has the following declaration:

3     package Ada.Strings.Maps.Constants is
         pragma Preelaborate(Constants);

4        Control_Set           : constant Character_Set;
         Graphic_Set           : constant Character_Set;
         Letter_Set            : constant Character_Set;
         Lower_Set             : constant Character_Set;
         Upper_Set             : constant Character_Set;
         Basic_Set             : constant Character_Set;
         Decimal_Digit_Set     : constant Character_Set;
         Hexadecimal_Digit_Set : constant Character_Set;
         Alphanumeric_Set      : constant Character_Set;
         Special_Set           : constant Character_Set;
         ISO_646_Set           : constant Character_Set;

5        Lower_Case_Map        : constant Character_Mapping;
           --Maps to lower case for letters, else identity
         Upper_Case_Map        : constant Character_Mapping;
           --Maps to upper case for letters, else identity
         Basic_Map             : constant Character_Mapping;
           --Maps to basic letter for letters, else identity

6     private
         ... -- not specified by the language
      end Ada.Strings.Maps.Constants;

7     Each of these constants represents a correspondingly named set of
characters or character mapping in Characters.Handling (see A.3.2).


A.4.7 Wide_String Handling


1     Facilities for handling strings of Wide_Character elements are found in
the packages Strings.Wide_Maps, Strings.Wide_Fixed, Strings.Wide_Bounded,
Strings.Wide_Unbounded, and Strings.Wide_Maps.Wide_Constants. They provide the
same string-handling operations as the corresponding packages for strings of
Character elements.


                              Static Semantics

2     The package Strings.Wide_Maps has the following declaration.

3     package Ada.Strings.Wide_Maps is
         pragma Preelaborate(Wide_Maps);

4        -- Representation for a set of Wide_Character values:
         type Wide_Character_Set is private;

5        Null_Set : constant Wide_Character_Set;

6        type Wide_Character_Range is
           record
               Low  : Wide_Character;
               High : Wide_Character;
           end record;
         -- Represents Wide_Character range Low..High

7        type Wide_Character_Ranges is array (Positive range <>)
            of Wide_Character_Range;

8        function To_Set    (Ranges : in Wide_Character_Ranges)
            return Wide_Character_Set;

9        function To_Set    (Span   : in Wide_Character_Range)
            return Wide_Character_Set;

10       function To_Ranges (Set    : in Wide_Character_Set)
            return Wide_Character_Ranges;

11       function "="   (Left, Right : in Wide_Character_Set) return Boolean;

12       function "not" (Right : in Wide_Character_Set)
            return Wide_Character_Set;
         function "and" (Left, Right : in Wide_Character_Set)
            return Wide_Character_Set;
         function "or"  (Left, Right : in Wide_Character_Set)
            return Wide_Character_Set;
         function "xor" (Left, Right : in Wide_Character_Set)
            return Wide_Character_Set;
         function "-"   (Left, Right : in Wide_Character_Set)
            return Wide_Character_Set;

13       function Is_In (Element : in Wide_Character;
                         Set     : in Wide_Character_Set)
            return Boolean;

14       function Is_Subset (Elements : in Wide_Character_Set;
                             Set      : in Wide_Character_Set)
            return Boolean;

15       function "<=" (Left  : in Wide_Character_Set;
                        Right : in Wide_Character_Set)
            return Boolean renames Is_Subset;

16       -- Alternative representation for a set of Wide_Character values:
         subtype Wide_Character_Sequence is Wide_String;

17       function To_Set (Sequence  : in Wide_Character_Sequence)
            return Wide_Character_Set;

18       function To_Set (Singleton : in Wide_Character)
            return Wide_Character_Set;

19       function To_Sequence (Set  : in Wide_Character_Set)
            return Wide_Character_Sequence;

20       -- Representation for a Wide_Character to Wide_Character mapping:
         type Wide_Character_Mapping is private;

21       function Value (Map     : in Wide_Character_Mapping;
                         Element : in Wide_Character)
            return Wide_Character;

22       Identity : constant Wide_Character_Mapping;

23       function To_Mapping (From, To : in Wide_Character_Sequence)
            return Wide_Character_Mapping;

24       function To_Domain (Map : in Wide_Character_Mapping)
            return Wide_Character_Sequence;

25       function To_Range  (Map : in Wide_Character_Mapping)
            return Wide_Character_Sequence;

26       type Wide_Character_Mapping_Function is
            access function (From : in Wide_Character) return Wide_Character;

27    private
         ... -- not specified by the language
      end Ada.Strings.Wide_Maps;

28    The context clause for each of the packages Strings.Wide_Fixed,
Strings.Wide_Bounded, and Strings.Wide_Unbounded identifies Strings.Wide_Maps
instead of Strings.Maps.

29    For each of the packages Strings.Fixed, Strings.Bounded,
Strings.Unbounded, and Strings.Maps.Constants the corresponding wide string
package has the same contents except that

30    Wide_Space replaces Space

31    Wide_Character replaces Character

32    Wide_String replaces String

33    Wide_Character_Set replaces Character_Set

34    Wide_Character_Mapping replaces Character_Mapping

35    Wide_Character_Mapping_Function replaces Character_Mapping_Function

36    Wide_Maps replaces Maps

37    Bounded_Wide_String replaces Bounded_String

38    Null_Bounded_Wide_String replaces Null_Bounded_String

39    To_Bounded_Wide_String replaces To_Bounded_String

40    To_Wide_String replaces To_String

41    Unbounded_Wide_String replaces Unbounded_String

42    Null_Unbounded_Wide_String replaces Null_Unbounded_String

43    Wide_String_Access replaces String_Access

44    To_Unbounded_Wide_String replaces To_Unbounded_String

45    The following additional declaration is present in
Strings.Wide_Maps.Wide_Constants:

46    Character_Set : constant Wide_Maps.Wide_Character_Set;
      --Contains each Wide_Character value WC such that Characters.Is_Character(WC) is True

      NOTES

47    12  If a null Wide_Character_Mapping_Function is passed to any of the
      Wide_String handling subprograms, Constraint_Error is propagated.

48    13  Each Wide_Character_Set constant in the package
      Strings.Wide_Maps.Wide_Constants contains no values outside the
      Character portion of Wide_Character. Similarly, each
      Wide_Character_Mapping constant in this package is the identity mapping
      when applied to any element outside the Character portion of
      Wide_Character.


A.5 The Numerics Packages


1     The library package Numerics is the parent of several child units that
provide facilities for mathematical computation. One child, the generic
package Generic_Elementary_Functions, is defined in A.5.1, together with
nongeneric equivalents; two others, the package Float_Random and the generic
package Discrete_Random, are defined in A.5.2. Additional (optional) children
are defined in Annex G, ``Numerics''.


                              Static Semantics

2/1   This paragraph was deleted.[ ]

3     package Ada.Numerics is
         pragma Pure(Numerics);
         Argument_Error : exception;
         Pi : constant :=
                3.14159_26535_89793_23846_26433_83279_50288_41971_69399_37511;
         e  : constant :=
                2.71828_18284_59045_23536_02874_71352_66249_77572_47093_69996;
      end Ada.Numerics;

4     The Argument_Error exception is raised by a subprogram in a child unit
of Numerics to signal that one or more of the actual subprogram parameters are
outside the domain of the corresponding mathematical function.


                         Implementation Permissions

5     The implementation may specify the values of Pi and e to a larger number
of significant digits.


A.5.1 Elementary Functions


1     Implementation-defined approximations to the mathematical functions
known as the ``elementary functions'' are provided by the subprograms in
Numerics.Generic_Elementary_Functions. Nongeneric equivalents of this generic
package for each of the predefined floating point types are also provided as
children of Numerics.


                              Static Semantics

2     The generic library package Numerics.Generic_Elementary_Functions has
the following declaration:

3     generic
         type Float_Type is digits <>;
      
      package Ada.Numerics.Generic_Elementary_Functions is
         pragma Pure(Generic_Elementary_Functions);

4        function Sqrt
          (X           : Float_Type'Base) return Float_Type'Base;
         function Log
           (X           : Float_Type'Base) return Float_Type'Base;
         function Log
           (X, Base     : Float_Type'Base) return Float_Type'Base;
         function Exp
           (X           : Float_Type'Base) return Float_Type'Base;
         function "**"    (Left, Right : Float_Type'Base) return Float_Type'Base;

5        function Sin
           (X           : Float_Type'Base) return Float_Type'Base;
         function Sin
           (X, Cycle    : Float_Type'Base) return Float_Type'Base;
         function Cos
           (X           : Float_Type'Base) return Float_Type'Base;
         function Cos
           (X, Cycle    : Float_Type'Base) return Float_Type'Base;
         function Tan
           (X           : Float_Type'Base) return Float_Type'Base;
         function Tan
           (X, Cycle    : Float_Type'Base) return Float_Type'Base;
         function Cot
           (X           : Float_Type'Base) return Float_Type'Base;
         function Cot
           (X, Cycle    : Float_Type'Base) return Float_Type'Base;

6        function Arcsin
        (X           : Float_Type'Base) return Float_Type'Base;
         function Arcsin
        (X, Cycle    : Float_Type'Base) return Float_Type'Base;
         function Arccos
        (X           : Float_Type'Base) return Float_Type'Base;
         function Arccos
        (X, Cycle    : Float_Type'Base) return Float_Type'Base;
         function Arctan  (Y           : Float_Type'Base;
                           X           : Float_Type'Base := 1.0)
                                                          return Float_Type'Base;
         function Arctan  (Y           : Float_Type'Base;
                           X           : Float_Type'Base := 1.0;
                           Cycle       : Float_Type'Base) return Float_Type'Base;
         function Arccot  (X           : Float_Type'Base;
                           Y           : Float_Type'Base := 1.0)
                                                          return Float_Type'Base;
         function Arccot  (X           : Float_Type'Base;
                           Y           : Float_Type'Base := 1.0;
                           Cycle       : Float_Type'Base) return Float_Type'Base;

7        function Sinh
          (X           : Float_Type'Base) return Float_Type'Base;
         function Cosh
          (X           : Float_Type'Base) return Float_Type'Base;
         function Tanh
          (X           : Float_Type'Base) return Float_Type'Base;
         function Coth
          (X           : Float_Type'Base) return Float_Type'Base;
         function Arcsinh
       (X           : Float_Type'Base) return Float_Type'Base;
         function Arccosh
       (X           : Float_Type'Base) return Float_Type'Base;
         function Arctanh
       (X           : Float_Type'Base) return Float_Type'Base;
         function Arccoth
       (X           : Float_Type'Base) return Float_Type'Base;

8     end Ada.Numerics.Generic_Elementary_Functions;

9/1   The library package Numerics.Elementary_Functions {is declared pure and
}defines the same subprograms as Numerics.Generic_Elementary_Functions, except
that the predefined type Float is systematically substituted for
Float_Type'Base throughout. Nongeneric equivalents of Numerics.Generic_-
Elementary_Functions for each of the other predefined floating point types are
defined similarly, with the names Numerics.Short_Elementary_Functions,
Numerics.Long_Elementary_Functions, etc.

10    The functions have their usual mathematical meanings. When the Base
parameter is specified, the Log function computes the logarithm to the given
base; otherwise, it computes the natural logarithm. When the Cycle parameter
is specified, the parameter X of the forward trigonometric functions (Sin,
Cos, Tan, and Cot) and the results of the inverse trigonometric functions
(Arcsin, Arccos, Arctan, and Arccot) are measured in units such that a full
cycle of revolution has the given value; otherwise, they are measured in
radians.

11    The computed results of the mathematically multivalued functions are
rendered single-valued by the following conventions, which are meant to imply
the principal branch:

12    The results of the Sqrt and Arccosh functions and that of the
      exponentiation operator are nonnegative.

13    The result of the Arcsin function is in the quadrant containing the
      point (1.0, x), where x is the value of the parameter X. This quadrant
      is I or IV; thus, the range of the Arcsin function is approximately
      -PI/2.0 to PI/2.0 (-Cycle/4.0 to Cycle/4.0, if the parameter Cycle is
      specified).

14    The result of the Arccos function is in the quadrant containing the
      point (x, 1.0), where x is the value of the parameter X. This quadrant
      is I or II; thus, the Arccos function ranges from 0.0 to approximately
      PI (Cycle/2.0, if the parameter Cycle is specified).

15    The results of the Arctan and Arccot functions are in the quadrant
      containing the point (x, y), where x and y are the values of the
      parameters X and Y, respectively. This may be any quadrant (I through
      IV) when the parameter X (resp., Y) of Arctan (resp., Arccot) is
      specified, but it is restricted to quadrants I and IV (resp., I and II)
      when that parameter is omitted. Thus, the range when that parameter is
      specified is approximately -PI to PI (-Cycle/2.0 to Cycle/2.0, if the
      parameter Cycle is specified); when omitted, the range of Arctan (resp.,
      Arccot) is that of Arcsin (resp., Arccos), as given above. When the
      point (x, y) lies on the negative x-axis, the result approximates

        16    PI (resp., -PI) when the sign of the parameter Y is positive
              (resp., negative), if Float_Type'Signed_Zeros is True;

        17    PI, if Float_Type'Signed_Zeros is False.

18    (In the case of the inverse trigonometric functions, in which a result
lying on or near one of the axes may not be exactly representable, the
approximation inherent in computing the result may place it in an adjacent
quadrant, close to but on the wrong side of the axis.)


                              Dynamic Semantics

19    The exception Numerics.Argument_Error is raised, signaling a parameter
value outside the domain of the corresponding mathematical function, in the
following cases:

20    by any forward or inverse trigonometric function with specified cycle,
      when the value of the parameter Cycle is zero or negative;

21    by the Log function with specified base, when the value of the parameter
      Base is zero, one, or negative;

22    by the Sqrt and Log functions, when the value of the parameter X is
      negative;

23    by the exponentiation operator, when the value of the left operand is
      negative or when both operands have the value zero;

24    by the Arcsin, Arccos, and Arctanh functions, when the absolute value of
      the parameter X exceeds one;

25    by the Arctan and Arccot functions, when the parameters X and Y both
      have the value zero;

26    by the Arccosh function, when the value of the parameter X is less than
      one; and

27    by the Arccoth function, when the absolute value of the parameter X is
      less than one.

28    The exception Constraint_Error is raised, signaling a pole of the
mathematical function (analogous to dividing by zero), in the following cases,
provided that Float_Type'Machine_Overflows is True:

29    by the Log, Cot, and Coth functions, when the value of the parameter X
      is zero;

30    by the exponentiation operator, when the value of the left operand is
      zero and the value of the exponent is negative;

31    by the Tan function with specified cycle, when the value of the
      parameter X is an odd multiple of the quarter cycle;

32    by the Cot function with specified cycle, when the value of the
      parameter X is zero or a multiple of the half cycle; and

33    by the Arctanh and Arccoth functions, when the absolute value of the
      parameter X is one.

34    Constraint_Error can also be raised when a finite result overflows (see
G.2.4); this may occur for parameter values sufficiently near poles, and, in
the case of some of the functions, for parameter values with sufficiently
large magnitudes. When Float_Type'Machine_Overflows is False, the result at
poles is unspecified.

35    When one parameter of a function with multiple parameters represents a
pole and another is outside the function's domain, the latter takes precedence
(i.e., Numerics.Argument_Error is raised).


                         Implementation Requirements

36    In the implementation of Numerics.Generic_Elementary_Functions, the
range of intermediate values allowed during the calculation of a final result
shall not be affected by any range constraint of the subtype Float_Type.

37    In the following cases, evaluation of an elementary function shall yield
the prescribed result, provided that the preceding rules do not call for an
exception to be raised:

38    When the parameter X has the value zero, the Sqrt, Sin, Arcsin, Tan,
      Sinh, Arcsinh, Tanh, and Arctanh functions yield a result of zero, and
      the Exp, Cos, and Cosh functions yield a result of one.

39    When the parameter X has the value one, the Sqrt function yields a
      result of one, and the Log, Arccos, and Arccosh functions yield a result
      of zero.

40    When the parameter Y has the value zero and the parameter X has a
      positive value, the Arctan and Arccot functions yield a result of zero.

41    The results of the Sin, Cos, Tan, and Cot functions with specified cycle
      are exact when the mathematical result is zero; those of the first two
      are also exact when the mathematical result is ± 1.0.

42    Exponentiation by a zero exponent yields the value one. Exponentiation
      by a unit exponent yields the value of the left operand. Exponentiation
      of the value one yields the value one. Exponentiation of the value zero
      yields the value zero.

43    Other accuracy requirements for the elementary functions, which apply
only in implementations conforming to the Numerics Annex, and then only in the
``strict'' mode defined there (see G.2), are given in G.2.4.

44    When Float_Type'Signed_Zeros is True, the sign of a zero result shall be
as follows:

45    A prescribed zero result delivered at the origin by one of the odd
      functions (Sin, Arcsin, Sinh, Arcsinh, Tan, Arctan or Arccot as a
      function of Y when X is fixed and positive, Tanh, and Arctanh) has the
      sign of the parameter X (Y, in the case of Arctan or Arccot).

46    A prescribed zero result delivered by one of the odd functions away from
      the origin, or by some other elementary function, has an
      implementation-defined sign.

47    A zero result that is not a prescribed result (i.e., one that results
      from rounding or underflow) has the correct mathematical sign.


                         Implementation Permissions

48    The nongeneric equivalent packages may, but need not, be actual
instantiations of the generic package for the appropriate predefined type.


A.5.2 Random Number Generation


1     Facilities for the generation of pseudo-random floating point numbers
are provided in the package Numerics.Float_Random; the generic package
Numerics.Discrete_Random provides similar facilities for the generation of
pseudo-random integers and pseudo-random values of enumeration types. For
brevity, pseudo-random values of any of these types are called random numbers.

2     Some of the facilities provided are basic to all applications of random
numbers. These include a limited private type each of whose objects serves as
the generator of a (possibly distinct) sequence of random numbers; a function
to obtain the ``next'' random number from a given sequence of random numbers
(that is, from its generator); and subprograms to initialize or reinitialize a
given generator to a time-dependent state or a state denoted by a single
integer.

3     Other facilities are provided specifically for advanced applications.
These include subprograms to save and restore the state of a given generator;
a private type whose objects can be used to hold the saved state of a
generator; and subprograms to obtain a string representation of a given
generator state, or, given such a string representation, the corresponding
state.


                              Static Semantics

4     The library package Numerics.Float_Random has the following declaration:

5     package Ada.Numerics.Float_Random is

6        -- Basic facilities

7        type Generator is limited private;

8        subtype Uniformly_Distributed is Float range 0.0 .. 1.0;
         function Random (Gen : Generator) return Uniformly_Distributed;

9        procedure Reset (Gen       : in Generator;
                          Initiator : in Integer);
         procedure Reset (Gen       : in Generator);

10       -- Advanced facilities

11       type State is private;

12       procedure Save  (Gen        : in  Generator;
                          To_State   : out State);
         procedure Reset (Gen        : in  Generator;
                          From_State : in  State);

13       Max_Image_Width : constant := implementation-defined integer value;

14       function Image (Of_State    : State)  return String;
         function Value (Coded_State : String) return State;

15    private
         ... -- not specified by the language
      end Ada.Numerics.Float_Random;

16    The generic library package Numerics.Discrete_Random has the following
declaration:

17    
      generic
         type Result_Subtype is (<>);
      package Ada.Numerics.Discrete_Random is

18       -- Basic facilities

19       type Generator is limited private;

20       function Random (Gen : Generator) return Result_Subtype;

21       procedure Reset (Gen       : in Generator;
                          Initiator : in Integer);
         procedure Reset (Gen       : in Generator);

22       -- Advanced facilities

23       type State is private;

24       procedure Save  (Gen        : in  Generator;
                          To_State   : out State);
         procedure Reset (Gen        : in  Generator;
                          From_State : in  State);

25       Max_Image_Width : constant := implementation-defined integer value;

26       function Image (Of_State    : State)  return String;
         function Value (Coded_State : String) return State;

27    private
         ... -- not specified by the language
      end Ada.Numerics.Discrete_Random;

28    An object of the limited private type Generator is associated with a
sequence of random numbers. Each generator has a hidden (internal) state,
which the operations on generators use to determine the position in the
associated sequence. All generators are implicitly initialized to an
unspecified state that does not vary from one program execution to another;
they may also be explicitly initialized, or reinitialized, to a time-dependent
state, to a previously saved state, or to a state uniquely denoted by an
integer value.

29    An object of the private type State can be used to hold the internal
state of a generator. Such objects are only needed if the application is
designed to save and restore generator states or to examine or manufacture
them.

30    The operations on generators affect the state and therefore the future
values of the associated sequence. The semantics of the operations on
generators and states are defined below.

31    function Random (Gen : Generator) return Uniformly_Distributed;
      function Random (Gen : Generator) return Result_Subtype;

    32    Obtains the ``next'' random number from the given generator,
          relative to its current state, according to an
          implementation-defined algorithm. The result of the function in
          Numerics.Float_Random is delivered as a value of the subtype
          Uniformly_Distributed, which is a subtype of the predefined type
          Float having a range of 0.0 .. 1.0. The result of the function in an
          instantiation of Numerics.Discrete_Random is delivered as a value of
          the generic formal subtype Result_Subtype.

33    procedure Reset (Gen       : in Generator;
                       Initiator : in Integer);
      procedure Reset (Gen       : in Generator);

    34    Sets the state of the specified generator to one that is an
          unspecified function of the value of the parameter Initiator (or to
          a time-dependent state, if only a generator parameter is specified).
          The latter form of the procedure is known as the time-dependent
          Reset procedure.

35    procedure Save  (Gen        : in  Generator;
                       To_State   : out State);
      procedure Reset (Gen        : in  Generator;
                       From_State : in  State);

    36    Save obtains the current state of a generator. Reset gives a
          generator the specified state. A generator that is reset to a state
          previously obtained by invoking Save is restored to the state it had
          when Save was invoked.

37    function Image (Of_State    : State)  return String;
      function Value (Coded_State : String) return State;

    38    Image provides a representation of a state coded (in an
          implementation-defined way) as a string whose length is bounded by
          the value of Max_Image_Width. Value is the inverse of Image:
          Value(Image(S)) = S for each state S that can be obtained from a
          generator by invoking Save.


                              Dynamic Semantics

39    Instantiation of Numerics.Discrete_Random with a subtype having a null
range raises Constraint_Error.

40/1  This paragraph was deleted.[Invoking Value with a string that is not the
image of any generator state raises Constraint_Error.]


                          Bounded (Run-Time) Errors

40.1/1 {It is a bounded error to invoke Value with a string that is not the
image of any generator state. If the error is detected, Constraint_Error or
Program_Error is raised. Otherwise, a call to Reset with the resulting state
will produce a generator such that calls to Random with this generator will
produce a sequence of values of the appropriate subtype, but which might not
be random in character. That is, the sequence of values might not fulfill the
implementation requirements of this subclause.}


                         Implementation Requirements

41    A sufficiently long sequence of random numbers obtained by successive
calls to Random is approximately uniformly distributed over the range of the
result subtype.

42    The Random function in an instantiation of Numerics.Discrete_Random is
guaranteed to yield each value in its result subtype in a finite number of
calls, provided that the number of such values does not exceed 2 (15).

43    Other performance requirements for the random number generator, which
apply only in implementations conforming to the Numerics Annex, and then only
in the ``strict'' mode defined there (see G.2), are given in G.2.5.


                         Documentation Requirements

44    No one algorithm for random number generation is best for all
applications. To enable the user to determine the suitability of the random
number generators for the intended application, the implementation shall
describe the algorithm used and shall give its period, if known exactly, or a
lower bound on the period, if the exact period is unknown. Periods that are so
long that the periodicity is unobservable in practice can be described in such
terms, without giving a numerical bound.

45    The implementation also shall document the minimum time interval between
calls to the time-dependent Reset procedure that are guaranteed to initiate
different sequences, and it shall document the nature of the strings that
Value will accept without raising Constraint_Error.


                            Implementation Advice

46    Any storage associated with an object of type Generator should be
reclaimed on exit from the scope of the object.

47    If the generator period is sufficiently long in relation to the number
of distinct initiator values, then each possible value of Initiator passed to
Reset should initiate a sequence of random numbers that does not, in a
practical sense, overlap the sequence initiated by any other value. If this is
not possible, then the mapping between initiator values and generator states
should be a rapidly varying function of the initiator value.

      NOTES

48    14  If two or more tasks are to share the same generator, then the tasks
      have to synchronize their access to the generator as for any shared
      variable (see 9.10).

49    15  Within a given implementation, a repeatable random number sequence
      can be obtained by relying on the implicit initialization of generators
      or by explicitly initializing a generator with a repeatable initiator
      value. Different sequences of random numbers can be obtained from a
      given generator in different program executions by explicitly
      initializing the generator to a time-dependent state.

50    16  A given implementation of the Random function in
      Numerics.Float_Random may or may not be capable of delivering the values
      0.0 or 1.0. Portable applications should assume that these values, or
      values sufficiently close to them to behave indistinguishably from them,
      can occur. If a sequence of random integers from some fixed range is
      needed, the application should use the Random function in an appropriate
      instantiation of Numerics.Discrete_Random, rather than transforming the
      result of the Random function in Numerics.Float_Random. However, some
      applications with unusual requirements, such as for a sequence of random
      integers each drawn from a different range, will find it more convenient
      to transform the result of the floating point Random function. For M
      >= 1, the expression

51       Integer(Float(M) * Random(G)) mod M

52    transforms the result of Random(G) to an integer uniformly distributed
      over the range 0 .. M-1; it is valid even if Random delivers 0.0 or 1.0.
      Each value of the result range is possible, provided that M is not too
      large. Exponentially distributed (floating point) random numbers with
      mean and standard deviation 1.0 can be obtained by the transformation

53       -Log(Random(G) + Float'Model_Small))

54    where Log comes from Numerics.Elementary_Functions (see A.5.1); in this
      expression, the addition of Float'Model_Small avoids the exception that
      would be raised were Log to be given the value zero, without affecting
      the result (in most implementations) when Random returns a nonzero
      value.


                                  Examples

55    Example of a program that plays a simulated dice game:

56    with Ada.Numerics.Discrete_Random;
      procedure Dice_Game is
         subtype Die is Integer range 1 .. 6;
         subtype Dice is Integer range 2*Die'First .. 2*Die'Last;
         package Random_Die is new Ada.Numerics.Discrete_Random (Die);
         use Random_Die;
         G : Generator;
         D : Dice;
      begin
         Reset (G);  -- Start the generator in a unique state in each run
         loop
            -- Roll a pair of dice; sum and process the results
            D := Random(G) + Random(G);
            ...
         end loop;
      end Dice_Game;

57    Example of a program that simulates coin tosses:

58    with Ada.Numerics.Discrete_Random;
      procedure Flip_A_Coin is
         type Coin is (Heads, Tails);
         package Random_Coin is new Ada.Numerics.Discrete_Random (Coin);
         use Random_Coin;
         G : Generator;
      begin
         Reset (G);  -- Start the generator in a unique state in each run
         loop
            -- Toss a coin and process the result
            case Random(G) is
                when Heads =>
                   ...
                when Tails =>
                   ...
            end case;
         ...
         end loop;
      end Flip_A_Coin;

59    Example of a parallel simulation of a physical system, with a separate
generator of event probabilities in each task:

60    with Ada.Numerics.Float_Random;
      procedure Parallel_Simulation is
         use Ada.Numerics.Float_Random;
         task type Worker is
            entry Initialize_Generator (Initiator : in Integer);
            ...
         end Worker;
         W : array (1 .. 10) of Worker;
         task body Worker is
            G : Generator;
            Probability_Of_Event : Uniformly_Distributed;
         begin
            accept Initialize_Generator (Initiator : in Integer) do
               Reset (G, Initiator);
            end Initialize_Generator;
            loop
               ...
               Probability_Of_Event := Random(G);
               ...
            end loop;
         end Worker;
      begin
         -- Initialize the generators in the Worker tasks to different states
         for I in W'Range loop
            W(I).Initialize_Generator (I);
         end loop;
         ... -- Wait for the Worker tasks to terminate
      end Parallel_Simulation;

      NOTES

61    17  Notes on the last example: Although each Worker task initializes its
      generator to a different state, those states will be the same in every
      execution of the program. The generator states can be initialized
      uniquely in each program execution by instantiating
      Ada.Numerics.Discrete_Random for the type Integer in the main procedure,
      resetting the generator obtained from that instance to a time-dependent
      state, and then using random integers obtained from that generator to
      initialize the generators in each Worker task.


A.5.3 Attributes of Floating Point Types



                              Static Semantics

1     The following representation-oriented attributes are defined for every
subtype S of a floating point type T.

2     S'Machine_Radix
              Yields the radix of the hardware representation of the type T.
              The value of this attribute is of the type universal_integer.

3     The values of other representation-oriented attributes of a floating
point subtype, and of the ``primitive function'' attributes of a floating
point subtype described later, are defined in terms of a particular
representation of nonzero values called the canonical form. The canonical form
(for the type T) is the form
    ± mantissa · T'Machine_Radix(exponent)
where

4     mantissa is a fraction in the number base T'Machine_Radix, the first
      digit of which is nonzero, and

5     exponent is an integer.

6     S'Machine_Mantissa
              Yields the largest value of p such that every value expressible
              in the canonical form (for the type T), having a p-digit
              mantissa and an exponent between T'Machine_Emin and
              T'Machine_Emax, is a machine number (see 3.5.7) of the type T.
              This attribute yields a value of the type universal_integer.

7     S'Machine_Emin
              Yields the smallest (most negative) value of exponent such that
              every value expressible in the canonical form (for the type T),
              having a mantissa of T'Machine_Mantissa digits, is a machine
              number (see 3.5.7) of the type T. This attribute yields a value
              of the type universal_integer.

8     S'Machine_Emax
              Yields the largest (most positive) value of exponent such that
              every value expressible in the canonical form (for the type T),
              having a mantissa of T'Machine_Mantissa digits, is a machine
              number (see 3.5.7) of the type T. This attribute yields a value
              of the type universal_integer.

9     S'Denorm
              Yields the value True if every value expressible in the form
                  ± mantissa · T'Machine_Radix(T'Machine_Emin)
              where mantissa is a nonzero T'Machine_Mantissa-digit fraction in
              the number base T'Machine_Radix, the first digit of which is
              zero, is a machine number (see 3.5.7) of the type T; yields the
              value False otherwise. The value of this attribute is of the
              predefined type Boolean.

10    The values described by the formula in the definition of S'Denorm are
called denormalized numbers. A nonzero machine number that is not a
denormalized number is a normalized number. A normalized number x of a given
type T is said to be represented in canonical form when it is expressed in the
canonical form (for the type T) with a mantissa having T'Machine_Mantissa
digits; the resulting form is the canonical-form representation of x.

11    S'Machine_Rounds
              Yields the value True if rounding is performed on inexact
              results of every predefined operation that yields a result of
              the type T; yields the value False otherwise. The value of this
              attribute is of the predefined type Boolean.

12    S'Machine_Overflows
              Yields the value True if overflow and divide-by-zero are
              detected and reported by raising Constraint_Error for every
              predefined operation that yields a result of the type T; yields
              the value False otherwise. The value of this attribute is of the
              predefined type Boolean.

13    S'Signed_Zeros
              Yields the value True if the hardware representation for the
              type T has the capability of representing both positively and
              negatively signed zeros, these being generated and used by the
              predefined operations of the type T as specified in IEC
              559:1989; yields the value False otherwise. The value of this
              attribute is of the predefined type Boolean.

14    For every value x of a floating point type T, the normalized exponent of
x is defined as follows:

15    the normalized exponent of zero is (by convention) zero;

16    for nonzero x, the normalized exponent of x is the unique integer k such
      that T'Machine_Radix(k-1) <= |x| < T'Machine_Radix(k).

17    The following primitive function attributes are defined for any subtype
S of a floating point type T.

18    S'Exponent
              S'Exponent denotes a function with the following specification:

            19    function S'Exponent (X : T)
                    return universal_integer

        20    The function yields the normalized exponent of X.

21    S'Fraction
              S'Fraction denotes a function with the following specification:

            22    function S'Fraction (X : T)
                    return T

        23    The function yields the value X · T'Machine_Radix(-k), where k
              is the normalized exponent of X. A zero result, which can only
              occur when X is zero, has the sign of X.

24    S'Compose
              S'Compose denotes a function with the following specification:

            25    function S'Compose (Fraction : T;
                                      Exponent : universal_integer)
                    return T

        26    Let v be the value Fraction · T'Machine_Radix(Exponent-k), where
              k is the normalized exponent of Fraction. If v is a machine
              number of the type T, or if |v| >= T'Model_Small, the function
              yields v; otherwise, it yields either one of the machine numbers
              of the type T adjacent to v. Constraint_Error is optionally
              raised if v is outside the base range of S. A zero result has
              the sign of Fraction when S'Signed_Zeros is True.

27    S'Scaling
              S'Scaling denotes a function with the following specification:

            28    function S'Scaling (X : T;
                                      Adjustment : universal_integer)
                    return T

        29    Let v be the value X · T'Machine_Radix(Adjustment). If v is a
              machine number of the type T, or if |v| >= T'Model_Small, the
              function yields v; otherwise, it yields either one of the
              machine numbers of the type T adjacent to v. Constraint_Error is
              optionally raised if v is outside the base range of S. A zero
              result has the sign of X when S'Signed_Zeros is True.

30    S'Floor S'Floor denotes a function with the following specification:

            31    function S'Floor (X : T)
                    return T

        32    The function yields the value Floor(X), i.e., the largest (most
              positive) integral value less than or equal to X. When X is
              zero, the result has the sign of X; a zero result otherwise has
              a positive sign.

33    S'Ceiling
              S'Ceiling denotes a function with the following specification:

            34    function S'Ceiling (X : T)
                    return T

        35    The function yields the value Ceiling(X), i.e., the smallest
              (most negative) integral value greater than or equal to X. When
              X is zero, the result has the sign of X; a zero result otherwise
              has a negative sign when S'Signed_Zeros is True.

36    S'Rounding
              S'Rounding denotes a function with the following specification:

            37    function S'Rounding (X : T)
                    return T

        38    The function yields the integral value nearest to X, rounding
              away from zero if X lies exactly halfway between two integers. A
              zero result has the sign of X when S'Signed_Zeros is True.

39    S'Unbiased_Rounding
              S'Unbiased_Rounding denotes a function with the following
              specification:

            40    function S'Unbiased_Rounding (X : T)
                    return T

        41    The function yields the integral value nearest to X, rounding
              toward the even integer if X lies exactly halfway between two
              integers. A zero result has the sign of X when S'Signed_Zeros is
              True.

42    S'Truncation
              S'Truncation denotes a function with the following
              specification:

            43    function S'Truncation (X : T)
                    return T

        44    The function yields the value Ceiling(X) when X is negative, and
              Floor(X) otherwise. A zero result has the sign of X when
              S'Signed_Zeros is True.

45    S'Remainder
              S'Remainder denotes a function with the following specification:

            46    function S'Remainder (X, Y : T)
                    return T

        47    For nonzero Y, let v be the value X - n · Y, where n is the
              integer nearest to the exact value of X/Y; if |n - X/Y|   =  
              1/2, then n is chosen to be even. If v is a machine number of
              the type T, the function yields v; otherwise, it yields zero.
              Constraint_Error is raised if Y is zero. A zero result has the
              sign of X when S'Signed_Zeros is True.

48    S'Adjacent
              S'Adjacent denotes a function with the following specification:

            49    function S'Adjacent (X, Towards : T)
                    return T

        50    If Towards   =   X, the function yields X; otherwise, it yields
              the machine number of the type T adjacent to X in the direction
              of Towards, if that machine number exists. If the result would
              be outside the base range of S, Constraint_Error is raised. When
              T'Signed_Zeros is True, a zero result has the sign of X. When
              Towards is zero, its sign has no bearing on the result.

51    S'Copy_Sign
              S'Copy_Sign denotes a function with the following specification:

            52    function S'Copy_Sign (Value, Sign : T)
                    return T

        53    If the value of Value is nonzero, the function yields a result
              whose magnitude is that of Value and whose sign is that of Sign;
              otherwise, it yields the value zero. Constraint_Error is
              optionally raised if the result is outside the base range of S.
              A zero result has the sign of Sign when S'Signed_Zeros is True.

54    S'Leading_Part
              S'Leading_Part denotes a function with the following
              specification:

            55    function S'Leading_Part (X : T;
                                           Radix_Digits : universal_integer)
                    return T

        56    Let v be the value T'Machine_Radix(k-Radix_Digits), where k is
              the normalized exponent of X. The function yields the value

            57    Floor(X/v) · v, when X is nonnegative and Radix_Digits is
                  positive;

            58    Ceiling(X/v) · v, when X is negative and Radix_Digits is
                  positive.

        59    Constraint_Error is raised when Radix_Digits is zero or
              negative. A zero result, which can only occur when X is zero,
              has the sign of X.

60    S'Machine
              S'Machine denotes a function with the following specification:

            61    function S'Machine (X : T)
                    return T

        62    If X is a machine number of the type T, the function yields X;
              otherwise, it yields the value obtained by rounding or
              truncating X to either one of the adjacent machine numbers of
              the type T. Constraint_Error is raised if rounding or truncating
              X to the precision of the machine numbers results in a value
              outside the base range of S. A zero result has the sign of X
              when S'Signed_Zeros is True.

63    The following model-oriented attributes are defined for any subtype S of
a floating point type T.

64    S'Model_Mantissa
              If the Numerics Annex is not supported, this attribute yields an
              implementation defined value that is greater than or equal to
              Ceiling(d · log(10) / log(T'Machine_Radix)) + 1, where d is the
              requested decimal precision of T, and less than or equal to the
              value of T'Machine_Mantissa. See G.2.2 for further requirements
              that apply to implementations supporting the Numerics Annex. The
              value of this attribute is of the type universal_integer.

65    S'Model_Emin
              If the Numerics Annex is not supported, this attribute yields an
              implementation defined value that is greater than or equal to
              the value of T'Machine_Emin. See G.2.2 for further requirements
              that apply to implementations supporting the Numerics Annex. The
              value of this attribute is of the type universal_integer.

66    S'Model_Epsilon
              Yields the value T'Machine_Radix(1 - T'Model_Mantissa). The
              value of this attribute is of the type universal_real.

67    S'Model_Small
              Yields the value T'Machine_Radix(T'Model_Emin - 1). The value of
              this attribute is of the type universal_real.

68    S'Model S'Model denotes a function with the following specification:

            69    function S'Model (X : T)
                    return T

        70    If the Numerics Annex is not supported, the meaning of this
              attribute is implementation defined; see G.2.2 for the
              definition that applies to implementations supporting the
              Numerics Annex.

71    S'Safe_First
              Yields the lower bound of the safe range (see 3.5.7) of the type
              T. If the Numerics Annex is not supported, the value of this
              attribute is implementation defined; see G.2.2 for the
              definition that applies to implementations supporting the
              Numerics Annex. The value of this attribute is of the type
              universal_real.

72    S'Safe_Last
              Yields the upper bound of the safe range (see 3.5.7) of the type
              T. If the Numerics Annex is not supported, the value of this
              attribute is implementation defined; see G.2.2 for the
              definition that applies to implementations supporting the
              Numerics Annex. The value of this attribute is of the type
              universal_real.


A.5.4 Attributes of Fixed Point Types



                              Static Semantics

1     The following representation-oriented attributes are defined for every
subtype S of a fixed point type T.

2     S'Machine_Radix
              Yields the radix of the hardware representation of the type T.
              The value of this attribute is of the type universal_integer.

3     S'Machine_Rounds
              Yields the value True if rounding is performed on inexact
              results of every predefined operation that yields a result of
              the type T; yields the value False otherwise. The value of this
              attribute is of the predefined type Boolean.

4     S'Machine_Overflows
              Yields the value True if overflow and divide-by-zero are
              detected and reported by raising Constraint_Error for every
              predefined operation that yields a result of the type T; yields
              the value False otherwise. The value of this attribute is of the
              predefined type Boolean.


A.6 Input-Output


1     Input-output is provided through language-defined packages, each of
which is a child of the root package Ada. The generic packages Sequential_IO
and Direct_IO define input-output operations applicable to files containing
elements of a given type. The generic package Storage_IO supports reading from
and writing to an in-memory buffer. Additional operations for text
input-output are supplied in the packages Text_IO and Wide_Text_IO.
Heterogeneous input-output is provided through the child packages Streams.-
Stream_IO and Text_IO.Text_Streams (see also 13.13). The package IO_Exceptions
defines the exceptions needed by the predefined input-output packages.


A.7 External Files and File Objects



                              Static Semantics

1     Values input from the external environment of the program, or output to
the external environment, are considered to occupy external files. An external
file can be anything external to the program that can produce a value to be
read or receive a value to be written. An external file is identified by a
string (the name). A second string (the form) gives further system-dependent
characteristics that may be associated with the file, such as the physical
organization or access rights. The conventions governing the interpretation of
such strings shall be documented.

2     Input and output operations are expressed as operations on objects of
some file type, rather than directly in terms of the external files. In the
remainder of this section, the term file is always used to refer to a file
object; the term external file is used otherwise.

3     Input-output for sequential files of values of a single element type is
defined by means of the generic package Sequential_IO. In order to define
sequential input-output for a given element type, an instantiation of this
generic unit, with the given type as actual parameter, has to be declared. The
resulting package contains the declaration of a file type (called File_Type)
for files of such elements, as well as the operations applicable to these
files, such as the Open, Read, and Write procedures.

4     Input-output for direct access files is likewise defined by a generic
package called Direct_IO. Input-output in human-readable form is defined by
the (nongeneric) packages Text_IO for Character and String data, and
Wide_Text_IO for Wide_Character and Wide_String data. Input-output for files
containing streams of elements representing values of possibly different types
is defined by means of the (nongeneric) package Streams.Stream_IO.

5     Before input or output operations can be performed on a file, the file
first has to be associated with an external file. While such an association is
in effect, the file is said to be open, and otherwise the file is said to be
closed.

6     The language does not define what happens to external files after the
completion of the main program and all the library tasks (in particular, if
corresponding files have not been closed). The effect of input-output for
access types is unspecified.

7     An open file has a current mode, which is a value of one of the
following enumeration types:

8     type File_Mode is (In_File, Inout_File, Out_File);  --  for Direct_IO

    9     These values correspond respectively to the cases where only
          reading, both reading and writing, or only writing are to be
          performed.

10    type File_Mode is (In_File, Out_File, Append_File);
      --  for Sequential_IO, Text_IO, Wide_Text_IO, and Stream_IO

    11    These values correspond respectively to the cases where only
          reading, only writing, or only appending are to be performed.

    12    The mode of a file can be changed.

13    Several file management operations are common to Sequential_IO,
Direct_IO, Text_IO, and Wide_Text_IO. These operations are described in
subclause A.8.2 for sequential and direct files. Any additional effects
concerning text input-output are described in subclause A.10.2.

14    The exceptions that can be propagated by the execution of an
input-output subprogram are defined in the package IO_Exceptions; the
situations in which they can be propagated are described following the
description of the subprogram (and in clause A.13). The exceptions
Storage_Error and Program_Error may be propagated. (Program_Error can only be
propagated due to errors made by the caller of the subprogram.) Finally,
exceptions can be propagated in certain implementation-defined situations.

      NOTES

15    18  Each instantiation of the generic packages Sequential_IO and
      Direct_IO declares a different type File_Type. In the case of Text_IO,
      Wide_Text_IO, and Streams.Stream_IO, the corresponding type File_Type is
      unique.

16    19  A bidirectional device can often be modeled as two sequential files
      associated with the device, one of mode In_File, and one of mode
      Out_File. An implementation may restrict the number of files that may be
      associated with a given external file.




A.8 Sequential and Direct Files



                              Static Semantics

1     Two kinds of access to external files are defined in this subclause:
sequential access and direct access. The corresponding file types and the
associated operations are provided by the generic packages Sequential_IO and
Direct_IO. A file object to be used for sequential access is called a
sequential file, and one to be used for direct access is called a direct file.
Access to stream files is described in A.12.1.

2     For sequential access, the file is viewed as a sequence of values that
are transferred in the order of their appearance (as produced by the program
or by the external environment). When the file is opened with mode In_File or
Out_File, transfer starts respectively from or to the beginning of the file.
When the file is opened with mode Append_File, transfer to the file starts
after the last element of the file.

3     For direct access, the file is viewed as a set of elements occupying
consecutive positions in linear order; a value can be transferred to or from
an element of the file at any selected position. The position of an element is
specified by its index, which is a number, greater than zero, of the
implementation-defined integer type Count. The first element, if any, has
index one; the index of the last element, if any, is called the current size;
the current size is zero if there are no elements. The current size is a
property of the external file.

4     An open direct file has a current index, which is the index that will be
used by the next read or write operation. When a direct file is opened, the
current index is set to one. The current index of a direct file is a property
of a file object, not of an external file.


A.8.1 The Generic Package Sequential_IO



                              Static Semantics

1     The generic library package Sequential_IO has the following declaration:

2     with Ada.IO_Exceptions;
      generic
         type Element_Type(<>) is private;
      package Ada.Sequential_IO is

3        type File_Type is limited private;

4        type File_Mode is (In_File, Out_File, Append_File);

5        -- File management

6        procedure Create(File : in out File_Type;
                          Mode : in File_Mode := Out_File;
                          Name : in String := "";
                          Form : in String := "");

7        procedure Open  (File : in out File_Type;
                          Mode : in File_Mode;
                          Name : in String;
                          Form : in String := "");

8        procedure Close (File : in out File_Type);
         procedure Delete(File : in out File_Type);
         procedure Reset (File : in out File_Type; Mode : in File_Mode);
         procedure Reset (File : in out File_Type);

9        function Mode   (File : in File_Type) return File_Mode;
         function Name   (File : in File_Type) return String;
         function Form   (File : in File_Type) return String;

10       function Is_Open(File : in File_Type) return Boolean;

11       -- Input and output operations

12       procedure Read  (File : in File_Type; Item : out Element_Type);
         procedure Write (File : in File_Type; Item : in Element_Type);

13       function End_Of_File(File : in File_Type) return Boolean;

14       -- Exceptions

15       Status_Error : exception renames IO_Exceptions.Status_Error;
         Mode_Error   : exception renames IO_Exceptions.Mode_Error;
         Name_Error   : exception renames IO_Exceptions.Name_Error;
         Use_Error    : exception renames IO_Exceptions.Use_Error;
         Device_Error : exception renames IO_Exceptions.Device_Error;
         End_Error    : exception renames IO_Exceptions.End_Error;
         Data_Error   : exception renames IO_Exceptions.Data_Error;

16    private
         ... -- not specified by the language
      end Ada.Sequential_IO;


A.8.2 File Management



                              Static Semantics

1     The procedures and functions described in this subclause provide for the
control of external files; their declarations are repeated in each of the
packages for sequential, direct, text, and stream input-output. For text
input-output, the procedures Create, Open, and Reset have additional effects
described in subclause A.10.2.

2     procedure Create(File : in out File_Type;
                       Mode : in File_Mode := default_mode;
                       Name : in String := "";
                       Form : in String := "");

    3     Establishes a new external file, with the given name and form, and
          associates this external file with the given file. The given file is
          left open. The current mode of the given file is set to the given
          access mode. The default access mode is the mode Out_File for
          sequential and text input-output; it is the mode Inout_File for
          direct input-output. For direct access, the size of the created file
          is implementation defined.

    4     A null string for Name specifies an external file that is not
          accessible after the completion of the main program (a temporary
          file). A null string for Form specifies the use of the default
          options of the implementation for the external file.

    5     The exception Status_Error is propagated if the given file is
          already open. The exception Name_Error is propagated if the string
          given as Name does not allow the identification of an external file.
          The exception Use_Error is propagated if, for the specified mode,
          the external environment does not support creation of an external
          file with the given name (in the absence of Name_Error) and form.

6     procedure Open(File : in out File_Type;
                     Mode : in File_Mode;
                     Name : in String;
                     Form : in String := "");

    7     Associates the given file with an existing external file having the
          given name and form, and sets the current mode of the given file to
          the given mode. The given file is left open.

    8     The exception Status_Error is propagated if the given file is
          already open. The exception Name_Error is propagated if the string
          given as Name does not allow the identification of an external file;
          in particular, this exception is propagated if no external file with
          the given name exists. The exception Use_Error is propagated if, for
          the specified mode, the external environment does not support
          opening for an external file with the given name (in the absence of
          Name_Error) and form.

9     procedure Close(File : in out File_Type);

    10    Severs the association between the given file and its associated
          external file. The given file is left closed. In addition, for
          sequential files, if the file being closed has mode Out_File or
          Append_File, then the last element written since the most recent
          open or reset is the last element that can be read from the file. If
          no elements have been written and the file mode is Out_File, then
          the closed file is empty. If no elements have been written and the
          file mode is Append_File, then the closed file is unchanged.

    11    The exception Status_Error is propagated if the given file is not
          open.

12    procedure Delete(File : in out File_Type);

    13    Deletes the external file associated with the given file. The given
          file is closed, and the external file ceases to exist.

    14    The exception Status_Error is propagated if the given file is not
          open. The exception Use_Error is propagated if deletion of the
          external file is not supported by the external environment.

15    procedure Reset(File : in out File_Type; Mode : in File_Mode);
      procedure Reset(File : in out File_Type);

    16    Resets the given file so that reading from its elements can be
          restarted from the beginning of the file (for modes In_File and
          Inout_File), and so that writing to its elements can be restarted at
          the beginning of the file (for modes Out_File and Inout_File) or
          after the last element of the file (for mode Append_File). In
          particular, for direct access this means that the current index is
          set to one. If a Mode parameter is supplied, the current mode of the
          given file is set to the given mode. In addition, for sequential
          files, if the given file has mode Out_File or Append_File when Reset
          is called, the last element written since the most recent open or
          reset is the last element that can be read from the file. If no
          elements have been written and the file mode is Out_File, the reset
          file is empty. If no elements have been written and the file mode is
          Append_File, then the reset file is unchanged.

    17    The exception Status_Error is propagated if the file is not open.
          The exception Use_Error is propagated if the external environment
          does not support resetting for the external file and, also, if the
          external environment does not support resetting to the specified
          mode for the external file.

18    function Mode(File : in File_Type) return File_Mode;

    19    Returns the current mode of the given file.

    20    The exception Status_Error is propagated if the file is not open.

21    function Name(File : in File_Type) return String;

    22    Returns a string which uniquely identifies the external file
          currently associated with the given file (and may thus be used in an
          Open operation). If an external environment allows alternative
          specifications of the name (for example, abbreviations), the string
          returned by the function should correspond to a full specification
          of the name.

    23    The exception Status_Error is propagated if the given file is not
          open. The exception Use_Error is propagated if the associated
          external file is a temporary file that cannot be opened by any name.

24    function Form(File : in File_Type) return String;

    25    Returns the form string for the external file currently associated
          with the given file. If an external environment allows alternative
          specifications of the form (for example, abbreviations using default
          options), the string returned by the function should correspond to a
          full specification (that is, it should indicate explicitly all
          options selected, including default options).

    26    The exception Status_Error is propagated if the given file is not
          open.

27    function Is_Open(File : in File_Type) return Boolean;

    28    Returns True if the file is open (that is, if it is associated with
          an external file), otherwise returns False.


                         Implementation Permissions

29    An implementation may propagate Name_Error or Use_Error if an attempt is
made to use an I/O feature that cannot be supported by the implementation due
to limitations in the external environment. Any such restriction should be
documented.


A.8.3 Sequential Input-Output Operations



                              Static Semantics

1     The operations available for sequential input and output are described
in this subclause. The exception Status_Error is propagated if any of these
operations is attempted for a file that is not open.

2     procedure Read(File : in File_Type; Item : out Element_Type);

    3     Operates on a file of mode In_File. Reads an element from the given
          file, and returns the value of this element in the Item parameter.

    4     The exception Mode_Error is propagated if the mode is not In_File.
          The exception End_Error is propagated if no more elements can be
          read from the given file. The exception Data_Error can be propagated
          if the element read cannot be interpreted as a value of the subtype
          Element_Type (see A.13, ``Exceptions in Input-Output'').

5     procedure Write(File : in File_Type; Item : in Element_Type);

    6     Operates on a file of mode Out_File or Append_File. Writes the value
          of Item to the given file.

    7     The exception Mode_Error is propagated if the mode is not Out_File
          or Append_File. The exception Use_Error is propagated if the
          capacity of the external file is exceeded.

8     function End_Of_File(File : in File_Type) return Boolean;

    9     Operates on a file of mode In_File. Returns True if no more elements
          can be read from the given file; otherwise returns False.

    10    The exception Mode_Error is propagated if the mode is not In_File.


A.8.4 The Generic Package Direct_IO



                              Static Semantics

1     The generic library package Direct_IO has the following declaration:

2     with Ada.IO_Exceptions;
      generic
         type Element_Type is private;
      package Ada.Direct_IO is

3        type File_Type is limited private;

4        type File_Mode is (In_File, Inout_File, Out_File);
         type Count     is range 0 .. implementation-defined;
         subtype Positive_Count is Count range 1 .. Count'Last;

5        -- File management

6        procedure Create(File : in out File_Type;
                          Mode : in File_Mode := Inout_File;
                          Name : in String := "";
                          Form : in String := "");

7        procedure Open  (File : in out File_Type;
                          Mode : in File_Mode;
                          Name : in String;
                          Form : in String := "");

8        procedure Close (File : in out File_Type);
         procedure Delete(File : in out File_Type);
         procedure Reset (File : in out File_Type; Mode : in File_Mode);
         procedure Reset (File : in out File_Type);

9        function Mode   (File : in File_Type) return File_Mode;
         function Name   (File : in File_Type) return String;
         function Form   (File : in File_Type) return String;

10       function Is_Open(File : in File_Type) return Boolean;

11       -- Input and output operations

12       procedure Read (File : in File_Type; Item : out Element_Type;
                                              From : in Positive_Count);
         procedure Read (File : in File_Type; Item : out Element_Type);

13       procedure Write(File : in File_Type; Item : in  Element_Type;
                                              To   : in Positive_Count);
         procedure Write(File : in File_Type; Item : in Element_Type);

14       procedure Set_Index(File : in File_Type; To : in Positive_Count);

15       function Index(File : in File_Type) return Positive_Count;
         function Size (File : in File_Type) return Count;

16       function End_Of_File(File : in File_Type) return Boolean;

17       -- Exceptions

18       Status_Error : exception renames IO_Exceptions.Status_Error;
         Mode_Error   : exception renames IO_Exceptions.Mode_Error;
         Name_Error   : exception renames IO_Exceptions.Name_Error;
         Use_Error    : exception renames IO_Exceptions.Use_Error;
         Device_Error : exception renames IO_Exceptions.Device_Error;
         End_Error    : exception renames IO_Exceptions.End_Error;
         Data_Error   : exception renames IO_Exceptions.Data_Error;

19    private
         ... -- not specified by the language
      end Ada.Direct_IO;


A.8.5 Direct Input-Output Operations



                              Static Semantics

1     The operations available for direct input and output are described in
this subclause. The exception Status_Error is propagated if any of these
operations is attempted for a file that is not open.

2     procedure Read(File : in File_Type; Item : out Element_Type;
                                          From : in  Positive_Count);
      procedure Read(File : in File_Type; Item : out Element_Type);

    3     Operates on a file of mode In_File or Inout_File. In the case of the
          first form, sets the current index of the given file to the index
          value given by the parameter From. Then (for both forms) returns, in
          the parameter Item, the value of the element whose position in the
          given file is specified by the current index of the file; finally,
          increases the current index by one.

    4     The exception Mode_Error is propagated if the mode of the given file
          is Out_File. The exception End_Error is propagated if the index to
          be used exceeds the size of the external file. The exception
          Data_Error can be propagated if the element read cannot be
          interpreted as a value of the subtype Element_Type (see A.13).

5     procedure Write(File : in File_Type; Item : in Element_Type;
                                           To   : in Positive_Count);
      procedure Write(File : in File_Type; Item : in Element_Type);

    6     Operates on a file of mode Inout_File or Out_File. In the case of
          the first form, sets the index of the given file to the index value
          given by the parameter To. Then (for both forms) gives the value of
          the parameter Item to the element whose position in the given file
          is specified by the current index of the file; finally, increases
          the current index by one.

    7     The exception Mode_Error is propagated if the mode of the given file
          is In_File. The exception Use_Error is propagated if the capacity of
          the external file is exceeded.

8     procedure Set_Index(File : in File_Type; To : in Positive_Count);

    9     Operates on a file of any mode. Sets the current index of the given
          file to the given index value (which may exceed the current size of
          the file).

10    function Index(File : in File_Type) return Positive_Count;

    11    Operates on a file of any mode. Returns the current index of the
          given file.

12    function Size(File : in File_Type) return Count;

    13    Operates on a file of any mode. Returns the current size of the
          external file that is associated with the given file.

14    function End_Of_File(File : in File_Type) return Boolean;

    15    Operates on a file of mode In_File or Inout_File. Returns True if
          the current index exceeds the size of the external file; otherwise
          returns False.

    16    The exception Mode_Error is propagated if the mode of the given file
          is Out_File.

      NOTES

17    20  Append_File mode is not supported for the generic package Direct_IO.


A.9 The Generic Package Storage_IO


1     The generic package Storage_IO provides for reading from and writing to
an in-memory buffer. This generic package supports the construction of
user-defined input-output packages.


                              Static Semantics

2     The generic library package Storage_IO has the following declaration:

3     with Ada.IO_Exceptions;
      with System.Storage_Elements;
      generic
         type Element_Type is private;
      package Ada.Storage_IO is
         pragma Preelaborate(Storage_IO);

4        Buffer_Size : constant System.Storage_Elements.Storage_Count :=
            implementation-defined;
         subtype Buffer_Type is
            System.Storage_Elements.Storage_Array(1..Buffer_Size);

5        -- Input and output operations

6        procedure Read (Buffer : in  Buffer_Type; Item : out Element_Type);

7        procedure Write(Buffer : out Buffer_Type; Item : in  Element_Type);

8        -- Exceptions

9        Data_Error   : exception renames IO_Exceptions.Data_Error;
      end Ada.Storage_IO;

10    In each instance, the constant Buffer_Size has a value that is the size
(in storage elements) of the buffer required to represent the content of an
object of subtype Element_Type, including any implicit levels of indirection
used by the implementation. The Read and Write procedures of Storage_IO
correspond to the Read and Write procedures of Direct_IO (see A.8.4), but with
the content of the Item parameter being read from or written into the
specified Buffer, rather than an external file.

      NOTES

11    21  A buffer used for Storage_IO holds only one element at a time; an
      external file used for Direct_IO holds a sequence of elements.


A.10 Text Input-Output



                              Static Semantics

1     This clause describes the package Text_IO, which provides facilities for
input and output in human-readable form. Each file is read or written
sequentially, as a sequence of characters grouped into lines, and as a
sequence of lines grouped into pages. The specification of the package is
given below in subclause A.10.1.

2     The facilities for file management given above, in subclauses A.8.2 and
A.8.3, are available for text input-output. In place of Read and Write,
however, there are procedures Get and Put that input values of suitable types
from text files, and output values to them. These values are provided to the
Put procedures, and returned by the Get procedures, in a parameter Item.
Several overloaded procedures of these names exist, for different types of
Item. These Get procedures analyze the input sequences of characters based on
lexical elements (see Section 2) and return the corresponding values; the Put
procedures output the given values as appropriate lexical elements. Procedures
Get and Put are also available that input and output individual characters
treated as character values rather than as lexical elements. Related to
character input are procedures to look ahead at the next character without
reading it, and to read a character ``immediately'' without waiting for an
end-of-line to signal availability.

3     In addition to the procedures Get and Put for numeric and enumeration
types of Item that operate on text files, analogous procedures are provided
that read from and write to a parameter of type String. These procedures
perform the same analysis and composition of character sequences as their
counterparts which have a file parameter.

4     For all Get and Put procedures that operate on text files, and for many
other subprograms, there are forms with and without a file parameter. Each
such Get procedure operates on an input file, and each such Put procedure
operates on an output file. If no file is specified, a default input file or a
default output file is used.

5     At the beginning of program execution the default input and output files
are the so-called standard input file and standard output file. These files
are open, have respectively the current modes In_File and Out_File, and are
associated with two implementation-defined external files. Procedures are
provided to change the current default input file and the current default
output file.

6     At the beginning of program execution a default file for
program-dependent error-related text output is the so-called standard error
file. This file is open, has the current mode Out_File, and is associated with
an implementation-defined external file. A procedure is provided to change the
current default error file.

7     From a logical point of view, a text file is a sequence of pages, a page
is a sequence of lines, and a line is a sequence of characters; the end of a
line is marked by a line terminator; the end of a page is marked by the
combination of a line terminator immediately followed by a page terminator;
and the end of a file is marked by the combination of a line terminator
immediately followed by a page terminator and then a file terminator.
Terminators are generated during output; either by calls of procedures
provided expressly for that purpose; or implicitly as part of other
operations, for example, when a bounded line length, a bounded page length, or
both, have been specified for a file.

8     The actual nature of terminators is not defined by the language and
hence depends on the implementation. Although terminators are recognized or
generated by certain of the procedures that follow, they are not necessarily
implemented as characters or as sequences of characters. Whether they are
characters (and if so which ones) in any particular implementation need not
concern a user who neither explicitly outputs nor explicitly inputs control
characters. The effect of input (Get) or output (Put) of control characters
(other than horizontal tabulation) is not specified by the language.

9     The characters of a line are numbered, starting from one; the number of
a character is called its column number. For a line terminator, a column
number is also defined: it is one more than the number of characters in the
line. The lines of a page, and the pages of a file, are similarly numbered.
The current column number is the column number of the next character or line
terminator to be transferred. The current line number is the number of the
current line. The current page number is the number of the current page. These
numbers are values of the subtype Positive_Count of the type Count (by
convention, the value zero of the type Count is used to indicate special
conditions).

10    type Count is range 0 .. implementation-defined;
      subtype Positive_Count is Count range 1 .. Count'Last;

11    For an output file or an append file, a maximum line length can be
specified and a maximum page length can be specified. If a value to be output
cannot fit on the current line, for a specified maximum line length, then a
new line is automatically started before the value is output; if, further,
this new line cannot fit on the current page, for a specified maximum page
length, then a new page is automatically started before the value is output.
Functions are provided to determine the maximum line length and the maximum
page length. When a file is opened with mode Out_File or Append_File, both
values are zero: by convention, this means that the line lengths and page
lengths are unbounded. (Consequently, output consists of a single line if the
subprograms for explicit control of line and page structure are not used.) The
constant Unbounded is provided for this purpose.


A.10.1 The Package Text_IO



                              Static Semantics

1     The library package Text_IO has the following declaration:

2     with Ada.IO_Exceptions;
      package Ada.Text_IO is

3        type File_Type is limited private;

4        type File_Mode is (In_File, Out_File, Append_File);

5        type Count is range 0 .. implementation-defined;
         subtype Positive_Count is Count range 1 .. Count'Last;
         Unbounded : constant Count := 0; -- line and page length

6        subtype Field       is Integer range 0 .. implementation-defined;
         subtype Number_Base is Integer range 2 .. 16;

7        type Type_Set is (Lower_Case, Upper_Case);

8        -- File Management

9        procedure Create (File : in out File_Type;
                           Mode : in File_Mode := Out_File;
                           Name : in String    := "";
                           Form : in String    := "");

10       procedure Open   (File : in out File_Type;
                           Mode : in File_Mode;
                           Name : in String;
                           Form : in String := "");

11       procedure Close  (File : in out File_Type);
         procedure Delete (File : in out File_Type);
         procedure Reset  (File : in out File_Type; Mode : in File_Mode);
         procedure Reset  (File : in out File_Type);

12       function  Mode   (File : in File_Type) return File_Mode;
         function  Name   (File : in File_Type) return String;
         function  Form   (File : in File_Type) return String;

13       function  Is_Open(File : in File_Type) return Boolean;

14       -- Control of default input and output files

15       procedure Set_Input (File : in File_Type);
         procedure Set_Output(File : in File_Type);
         procedure Set_Error (File : in File_Type);

16       function Standard_Input  return File_Type;
         function Standard_Output return File_Type;
         function Standard_Error  return File_Type;

17       function Current_Input   return File_Type;
         function Current_Output  return File_Type;
         function Current_Error   return File_Type;

18       type File_Access is access constant File_Type;

19       function Standard_Input  return File_Access;
         function Standard_Output return File_Access;
         function Standard_Error  return File_Access;

20       function Current_Input   return File_Access;
         function Current_Output  return File_Access;
         function Current_Error   return File_Access;

21/1  --Buffer control
         procedure Flush (File : in [out ]File_Type);
         procedure Flush;

22       -- Specification of line and page lengths

23       procedure Set_Line_Length(File : in File_Type; To : in Count);
         procedure Set_Line_Length(To   : in Count);

24       procedure Set_Page_Length(File : in File_Type; To : in Count);
         procedure Set_Page_Length(To   : in Count);

25       function  Line_Length(File : in File_Type) return Count;
         function  Line_Length return Count;

26       function  Page_Length(File : in File_Type) return Count;
         function  Page_Length return Count;

27       -- Column, Line, and Page Control

28       procedure New_Line   (File    : in File_Type;
                               Spacing : in Positive_Count := 1);
         procedure New_Line   (Spacing : in Positive_Count := 1);

29       procedure Skip_Line  (File    : in File_Type;
                               Spacing : in Positive_Count := 1);
         procedure Skip_Line  (Spacing : in Positive_Count := 1);

30       function  End_Of_Line(File : in File_Type) return Boolean;
         function  End_Of_Line return Boolean;

31       procedure New_Page   (File : in File_Type);
         procedure New_Page;

32       procedure Skip_Page  (File : in File_Type);
         procedure Skip_Page;

33       function  End_Of_Page(File : in File_Type) return Boolean;
         function  End_Of_Page return Boolean;

34       function  End_Of_File(File : in File_Type) return Boolean;
         function  End_Of_File return Boolean;

35       procedure Set_Col (File : in File_Type; To : in Positive_Count);
         procedure Set_Col (To   : in Positive_Count);

36       procedure Set_Line(File : in File_Type; To : in Positive_Count);
         procedure Set_Line(To   : in Positive_Count);

37       function Col (File : in File_Type) return Positive_Count;
         function Col  return Positive_Count;

38       function Line(File : in File_Type) return Positive_Count;
         function Line return Positive_Count;

39       function Page(File : in File_Type) return Positive_Count;
         function Page return Positive_Count;

40       -- Character Input-Output

41       procedure Get(File : in  File_Type; Item : out Character);
         procedure Get(Item : out Character);

42       procedure Put(File : in  File_Type; Item : in Character);
         procedure Put(Item : in  Character);

43       procedure Look_Ahead (File        : in  File_Type;
                               Item        : out Character;
                               End_Of_Line : out Boolean);
         procedure Look_Ahead (Item        : out Character;
                               End_Of_Line : out Boolean);

44       procedure Get_Immediate(File      : in  File_Type;
                                 Item      : out Character);
         procedure Get_Immediate(Item      : out Character);

45       procedure Get_Immediate(File      : in  File_Type;
                                 Item      : out Character;
                                 Available : out Boolean);
         procedure Get_Immediate(Item      : out Character;
                                 Available : out Boolean);

46       -- String Input-Output

47       procedure Get(File : in  File_Type; Item : out String);
         procedure Get(Item : out String);

48       procedure Put(File : in  File_Type; Item : in String);
         procedure Put(Item : in  String);

49       procedure Get_Line(File : in  File_Type;
                            Item : out String;
                            Last : out Natural);
         procedure Get_Line(Item : out String; Last : out Natural);

50       procedure Put_Line(File : in  File_Type; Item : in String);
         procedure Put_Line(Item : in  String);

51    -- Generic packages for Input-Output of Integer Types

52       generic
            type Num is range <>;
         package Integer_IO is

53          Default_Width : Field := Num'Width;
            Default_Base  : Number_Base := 10;

54          procedure Get(File  : in  File_Type;
                          Item  : out Num;
                          Width : in Field := 0);
            procedure Get(Item  : out Num;
                          Width : in  Field := 0);

55          procedure Put(File  : in File_Type;
                          Item  : in Num;
                          Width : in Field := Default_Width;
                          Base  : in Number_Base := Default_Base);
            procedure Put(Item  : in Num;
                          Width : in Field := Default_Width;
                          Base  : in Number_Base := Default_Base);
            procedure Get(From : in  String;
                          Item : out Num;
                          Last : out Positive);
            procedure Put(To   : out String;
                          Item : in Num;
                          Base : in Number_Base := Default_Base);

56       end Integer_IO;

57       generic
            type Num is mod <>;
         package Modular_IO is

58          Default_Width : Field := Num'Width;
            Default_Base  : Number_Base := 10;

59          procedure Get(File  : in  File_Type;
                          Item  : out Num;
                          Width : in Field := 0);
            procedure Get(Item  : out Num;
                          Width : in  Field := 0);

60          procedure Put(File  : in File_Type;
                          Item  : in Num;
                          Width : in Field := Default_Width;
                          Base  : in Number_Base := Default_Base);
            procedure Put(Item  : in Num;
                          Width : in Field := Default_Width;
                          Base  : in Number_Base := Default_Base);
            procedure Get(From : in  String;
                          Item : out Num;
                          Last : out Positive);
            procedure Put(To   : out String;
                          Item : in Num;
                          Base : in Number_Base := Default_Base);

61       end Modular_IO;

62       -- Generic packages for Input-Output of Real Types

63       generic
            type Num is digits <>;
         package Float_IO is

64          Default_Fore : Field := 2;
            Default_Aft  : Field := Num'Digits-1;
            Default_Exp  : Field := 3;

65          procedure Get(File  : in  File_Type;
                          Item  : out Num;
                          Width : in  Field := 0);
            procedure Get(Item  : out Num;
                          Width : in  Field := 0);

66          procedure Put(File : in File_Type;
                          Item : in Num;
                          Fore : in Field := Default_Fore;
                          Aft  : in Field := Default_Aft;
                          Exp  : in Field := Default_Exp);
            procedure Put(Item : in Num;
                          Fore : in Field := Default_Fore;
                          Aft  : in Field := Default_Aft;
                          Exp  : in Field := Default_Exp);

67          procedure Get(From : in String;
                          Item : out Num;
                          Last : out Positive);
            procedure Put(To   : out String;
                          Item : in Num;
                          Aft  : in Field := Default_Aft;
                          Exp  : in Field := Default_Exp);
         end Float_IO;

68       generic
            type Num is delta <>;
         package Fixed_IO is

69          Default_Fore : Field := Num'Fore;
            Default_Aft  : Field := Num'Aft;
            Default_Exp  : Field := 0;

70          procedure Get(File  : in  File_Type;
                          Item  : out Num;
                          Width : in  Field := 0);
            procedure Get(Item  : out Num;
                          Width : in  Field := 0);

71          procedure Put(File : in File_Type;
                          Item : in Num;
                          Fore : in Field := Default_Fore;
                          Aft  : in Field := Default_Aft;
                          Exp  : in Field := Default_Exp);
            procedure Put(Item : in Num;
                          Fore : in Field := Default_Fore;
                          Aft  : in Field := Default_Aft;
                          Exp  : in Field := Default_Exp);

72          procedure Get(From : in  String;
                          Item : out Num;
                          Last : out Positive);
            procedure Put(To   : out String;
                          Item : in Num;
                          Aft  : in Field := Default_Aft;
                          Exp  : in Field := Default_Exp);
         end Fixed_IO;

73       generic
            type Num is delta <> digits <>;
         package Decimal_IO is

74          Default_Fore : Field := Num'Fore;
            Default_Aft  : Field := Num'Aft;
            Default_Exp  : Field := 0;

75          procedure Get(File  : in  File_Type;
                          Item  : out Num;
                          Width : in  Field := 0);
            procedure Get(Item  : out Num;
                          Width : in  Field := 0);

76          procedure Put(File : in File_Type;
                          Item : in Num;
                          Fore : in Field := Default_Fore;
                          Aft  : in Field := Default_Aft;
                          Exp  : in Field := Default_Exp);
            procedure Put(Item : in Num;
                          Fore : in Field := Default_Fore;
                          Aft  : in Field := Default_Aft;
                          Exp  : in Field := Default_Exp);

77          procedure Get(From : in  String;
                          Item : out Num;
                          Last : out Positive);
            procedure Put(To   : out String;
                          Item : in Num;
                          Aft  : in Field := Default_Aft;
                          Exp  : in Field := Default_Exp);
         end Decimal_IO;

78       -- Generic package for Input-Output of Enumeration Types

79       generic
            type Enum is (<>);
         package Enumeration_IO is

80          Default_Width   : Field := 0;
            Default_Setting : Type_Set := Upper_Case;

81          procedure Get(File : in  File_Type;
                          Item : out Enum);
            procedure Get(Item : out Enum);

82          procedure Put(File  : in File_Type;
                          Item  : in Enum;
                          Width : in Field    := Default_Width;
                          Set   : in Type_Set := Default_Setting);
            procedure Put(Item  : in Enum;
                          Width : in Field    := Default_Width;
                          Set   : in Type_Set := Default_Setting);

83          procedure Get(From : in  String;
                          Item : out Enum;
                          Last : out Positive);
            procedure Put(To   : out String;
                          Item : in  Enum;
                          Set  : in  Type_Set := Default_Setting);
         end Enumeration_IO;

84    -- Exceptions

85       Status_Error : exception renames IO_Exceptions.Status_Error;
         Mode_Error   : exception renames IO_Exceptions.Mode_Error;
         Name_Error   : exception renames IO_Exceptions.Name_Error;
         Use_Error    : exception renames IO_Exceptions.Use_Error;
         Device_Error : exception renames IO_Exceptions.Device_Error;
         End_Error    : exception renames IO_Exceptions.End_Error;
         Data_Error   : exception renames IO_Exceptions.Data_Error;
         Layout_Error : exception renames IO_Exceptions.Layout_Error;
      private
         ... -- not specified by the language
      end Ada.Text_IO;


A.10.2 Text File Management



                              Static Semantics

1     The only allowed file modes for text files are the modes In_File,
Out_File, and Append_File. The subprograms given in subclause A.8.2 for the
control of external files, and the function End_Of_File given in subclause
A.8.3 for sequential input-output, are also available for text files. There is
also a version of End_Of_File that refers to the current default input file.
For text files, the procedures have the following additional effects:

2     For the procedures Create and Open: After a file with mode Out_File or
      Append_File is opened, the page length and line length are unbounded
      (both have the conventional value zero). After a file (of any mode) is
      opened, the current column, current line, and current page numbers are
      set to one. If the mode is Append_File, it is implementation defined
      whether a page terminator will separate preexisting text in the file
      from the new text to be written.

3     For the procedure Close: If the file has the current mode Out_File or
      Append_File, has the effect of calling New_Page, unless the current page
      is already terminated; then outputs a file terminator.

4     For the procedure Reset: If the file has the current mode Out_File or
      Append_File, has the effect of calling New_Page, unless the current page
      is already terminated; then outputs a file terminator. The current
      column, line, and page numbers are set to one, and the line and page
      lengths to Unbounded. If the new mode is Append_File, it is
      implementation defined whether a page terminator will separate
      preexisting text in the file from the new text to be written.

5     The exception Mode_Error is propagated by the procedure Reset upon an
attempt to change the mode of a file that is the current default input file,
the current default output file, or the current default error file.

      NOTES

6     22  An implementation can define the Form parameter of Create and Open
      to control effects including the following:

    7     the interpretation of line and column numbers for an interactive
          file, and

    8     the interpretation of text formats in a file created by a foreign
          program.


A.10.3 Default Input, Output, and Error Files



                              Static Semantics

1     The following subprograms provide for the control of the particular
default files that are used when a file parameter is omitted from a Get, Put,
or other operation of text input-output described below, or when
application-dependent error-related text is to be output.

2     procedure Set_Input(File : in File_Type);

    3     Operates on a file of mode In_File. Sets the current default input
          file to File.

    4     The exception Status_Error is propagated if the given file is not
          open. The exception Mode_Error is propagated if the mode of the
          given file is not In_File.

5     procedure Set_Output(File : in File_Type);
      procedure Set_Error (File : in File_Type);

    6     Each operates on a file of mode Out_File or Append_File. Set_Output
          sets the current default output file to File. Set_Error sets the
          current default error file to File. The exception Status_Error is
          propagated if the given file is not open. The exception Mode_Error
          is propagated if the mode of the given file is not Out_File or
          Append_File.

7     function Standard_Input return File_Type;
      function Standard_Input return File_Access;

    8     Returns the standard input file (see A.10), or an access value
          designating the standard input file, respectively.

9     function Standard_Output return File_Type;
      function Standard_Output return File_Access;

    10    Returns the standard output file (see A.10) or an access value
          designating the standard output file, respectively.

11    function Standard_Error return File_Type;
      function Standard_Error return File_Access;

    12/1  Returns the standard error file (see A.10), or an access value
          designating the standard {error}[output] file, respectively.

13    The Form strings implicitly associated with the opening of
Standard_Input, Standard_Output, and Standard_Error at the start of program
execution are implementation defined.

14    function Current_Input return File_Type;
      function Current_Input return File_Access;

    15    Returns the current default input file, or an access value
          designating the current default input file, respectively.

16    function Current_Output return File_Type;
      function Current_Output return File_Access;

    17    Returns the current default output file, or an access value
          designating the current default output file, respectively.

18    function Current_Error return File_Type;
      function Current_Error return File_Access;

    19    Returns the current default error file, or an access value
          designating the current default error file, respectively.

20/1  procedure Flush (File : in [out ]File_Type);
      procedure Flush;

    21    The effect of Flush is the same as the corresponding subprogram in
          Streams.Stream_IO (see A.12.1). If File is not explicitly specified,
          Current_Output is used.


                             Erroneous Execution

22/1  The execution of a program is erroneous if it {invokes an operation
on}[attempts to use] a current default input, default output, or default error
file{, and if the corresponding file object is closed or}[ that] no longer
exists.

23/1  This paragraph was deleted.[If the Close operation is applied to a file
object that is also serving as the default input, default output, or default
error file, then subsequent operations on such a default file are erroneous.]

      NOTES

24    23  The standard input, standard output, and standard error files cannot
      be opened, closed, reset, or deleted, because the parameter File of the
      corresponding procedures has the mode in out.

25    24  The standard input, standard output, and standard error files are
      different file objects, but not necessarily different external files.


A.10.4 Specification of Line and Page Lengths



                              Static Semantics

1     The subprograms described in this subclause are concerned with the line
and page structure of a file of mode Out_File or Append_File. They operate
either on the file given as the first parameter, or, in the absence of such a
file parameter, on the current default output file. They provide for output of
text with a specified maximum line length or page length. In these cases, line
and page terminators are output implicitly and automatically when needed. When
line and page lengths are unbounded (that is, when they have the conventional
value zero), as in the case of a newly opened file, new lines and new pages
are only started when explicitly called for.

2     In all cases, the exception Status_Error is propagated if the file to be
used is not open; the exception Mode_Error is propagated if the mode of the
file is not Out_File or Append_File.

3     procedure Set_Line_Length(File : in File_Type; To : in Count);
      procedure Set_Line_Length(To   : in Count);

    4     Sets the maximum line length of the specified output or append file
          to the number of characters specified by To. The value zero for To
          specifies an unbounded line length.

    5     The exception Use_Error is propagated if the specified line length
          is inappropriate for the associated external file.

6     procedure Set_Page_Length(File : in File_Type; To : in Count);
      procedure Set_Page_Length(To   : in Count);

    7     Sets the maximum page length of the specified output or append file
          to the number of lines specified by To. The value zero for To
          specifies an unbounded page length.

    8     The exception Use_Error is propagated if the specified page length
          is inappropriate for the associated external file.

9     function Line_Length(File : in File_Type) return Count;
      function Line_Length return Count;

    10    Returns the maximum line length currently set for the specified
          output or append file, or zero if the line length is unbounded.

11    function Page_Length(File : in File_Type) return Count;
      function Page_Length return Count;

    12    Returns the maximum page length currently set for the specified
          output or append file, or zero if the page length is unbounded.


A.10.5 Operations on Columns, Lines, and Pages



                              Static Semantics

1     The subprograms described in this subclause provide for explicit control
of line and page structure; they operate either on the file given as the first
parameter, or, in the absence of such a file parameter, on the appropriate
(input or output) current default file. The exception Status_Error is
propagated by any of these subprograms if the file to be used is not open.

2     procedure New_Line(File : in File_Type; Spacing : in Positive_Count := 1);
      procedure New_Line(Spacing : in Positive_Count := 1);

    3     Operates on a file of mode Out_File or Append_File.

    4     For a Spacing of one: Outputs a line terminator and sets the current
          column number to one. Then increments the current line number by
          one, except in the case that the current line number is already
          greater than or equal to the maximum page length, for a bounded page
          length; in that case a page terminator is output, the current page
          number is incremented by one, and the current line number is set to
          one.

    5     For a Spacing greater than one, the above actions are performed
          Spacing times.

    6     The exception Mode_Error is propagated if the mode is not Out_File
          or Append_File.

7     procedure Skip_Line(File  : in File_Type; Spacing : in Positive_Count := 1);
      procedure Skip_Line(Spacing : in Positive_Count := 1);

    8     Operates on a file of mode In_File.

    9     For a Spacing of one: Reads and discards all characters until a line
          terminator has been read, and then sets the current column number to
          one. If the line terminator is not immediately followed by a page
          terminator, the current line number is incremented by one.
          Otherwise, if the line terminator is immediately followed by a page
          terminator, then the page terminator is skipped, the current page
          number is incremented by one, and the current line number is set to
          one.

    10    For a Spacing greater than one, the above actions are performed
          Spacing times.

    11    The exception Mode_Error is propagated if the mode is not In_File.
          The exception End_Error is propagated if an attempt is made to read
          a file terminator.

12    function End_Of_Line(File : in File_Type) return Boolean;
      function End_Of_Line return Boolean;

    13    Operates on a file of mode In_File. Returns True if a line
          terminator or a file terminator is next; otherwise returns False.

    14    The exception Mode_Error is propagated if the mode is not In_File.

15    procedure New_Page(File : in File_Type);
      procedure New_Page;

    16    Operates on a file of mode Out_File or Append_File. Outputs a line
          terminator if the current line is not terminated, or if the current
          page is empty (that is, if the current column and line numbers are
          both equal to one). Then outputs a page terminator, which terminates
          the current page. Adds one to the current page number and sets the
          current column and line numbers to one.

    17    The exception Mode_Error is propagated if the mode is not Out_File
          or Append_File.

18    procedure Skip_Page(File : in File_Type);
      procedure Skip_Page;

    19    Operates on a file of mode In_File. Reads and discards all
          characters and line terminators until a page terminator has been
          read. Then adds one to the current page number, and sets the current
          column and line numbers to one.

    20    The exception Mode_Error is propagated if the mode is not In_File.
          The exception End_Error is propagated if an attempt is made to read
          a file terminator.

21    function End_Of_Page(File : in File_Type) return Boolean;
      function End_Of_Page return Boolean;

    22    Operates on a file of mode In_File. Returns True if the combination
          of a line terminator and a page terminator is next, or if a file
          terminator is next; otherwise returns False.

    23    The exception Mode_Error is propagated if the mode is not In_File.

24    function End_Of_File(File : in File_Type) return Boolean;
      function End_Of_File return Boolean;

    25    Operates on a file of mode In_File. Returns True if a file
          terminator is next, or if the combination of a line, a page, and a
          file terminator is next; otherwise returns False.

    26    The exception Mode_Error is propagated if the mode is not In_File.

27    The following subprograms provide for the control of the current
position of reading or writing in a file. In all cases, the default file is
the current output file.

28    procedure Set_Col(File : in File_Type; To : in Positive_Count);
      procedure Set_Col(To   : in Positive_Count);

    29    If the file mode is Out_File or Append_File:

        30    If the value specified by To is greater than the current column
              number, outputs spaces, adding one to the current column number
              after each space, until the current column number equals the
              specified value. If the value specified by To is equal to the
              current column number, there is no effect. If the value
              specified by To is less than the current column number, has the
              effect of calling New_Line (with a spacing of one), then outputs
              (To - 1) spaces, and sets the current column number to the
              specified value.

        31    The exception Layout_Error is propagated if the value specified
              by To exceeds Line_Length when the line length is bounded (that
              is, when it does not have the conventional value zero).

    32    If the file mode is In_File:

        33    Reads (and discards) individual characters, line terminators,
              and page terminators, until the next character to be read has a
              column number that equals the value specified by To; there is no
              effect if the current column number already equals this value.
              Each transfer of a character or terminator maintains the current
              column, line, and page numbers in the same way as a Get
              procedure (see A.10.6). (Short lines will be skipped until a
              line is reached that has a character at the specified column
              position.)

        34    The exception End_Error is propagated if an attempt is made to
              read a file terminator.

35    procedure Set_Line(File : in File_Type; To : in Positive_Count);
      procedure Set_Line(To   : in Positive_Count);

    36    If the file mode is Out_File or Append_File:

        37    If the value specified by To is greater than the current line
              number, has the effect of repeatedly calling New_Line (with a
              spacing of one), until the current line number equals the
              specified value. If the value specified by To is equal to the
              current line number, there is no effect. If the value specified
              by To is less than the current line number, has the effect of
              calling New_Page followed by a call of New_Line with a spacing
              equal to (To - 1).

        38    The exception Layout_Error is propagated if the value specified
              by To exceeds Page_Length when the page length is bounded (that
              is, when it does not have the conventional value zero).

    39    If the mode is In_File:

        40    Has the effect of repeatedly calling Skip_Line (with a spacing
              of one), until the current line number equals the value
              specified by To; there is no effect if the current line number
              already equals this value. (Short pages will be skipped until a
              page is reached that has a line at the specified line position.)

        41    The exception End_Error is propagated if an attempt is made to
              read a file terminator.

42    function Col(File : in File_Type) return Positive_Count;
      function Col return Positive_Count;

    43    Returns the current column number.

    44    The exception Layout_Error is propagated if this number exceeds
          Count'Last.

45    function Line(File : in File_Type) return Positive_Count;
      function Line return Positive_Count;

    46    Returns the current line number.

    47    The exception Layout_Error is propagated if this number exceeds
          Count'Last.

48    function Page(File : in File_Type) return Positive_Count;
      function Page return Positive_Count;

    49    Returns the current page number.

    50    The exception Layout_Error is propagated if this number exceeds
          Count'Last.

51    The column number, line number, or page number are allowed to exceed
Count'Last (as a consequence of the input or output of sufficiently many
characters, lines, or pages). These events do not cause any exception to be
propagated. However, a call of Col, Line, or Page propagates the exception
Layout_Error if the corresponding number exceeds Count'Last.

      NOTES

52    25  A page terminator is always skipped whenever the preceding line
      terminator is skipped. An implementation may represent the combination
      of these terminators by a single character, provided that it is properly
      recognized on input.


A.10.6 Get and Put Procedures



                              Static Semantics

1     The procedures Get and Put for items of the type Character, String,
numeric types, and enumeration types are described in subsequent subclauses.
Features of these procedures that are common to most of these types are
described in this subclause. The Get and Put procedures for items of type
Character and String deal with individual character values; the Get and Put
procedures for numeric and enumeration types treat the items as lexical
elements.

2     All procedures Get and Put have forms with a file parameter, written
first. Where this parameter is omitted, the appropriate (input or output)
current default file is understood to be specified. Each procedure Get
operates on a file of mode In_File. Each procedure Put operates on a file of
mode Out_File or Append_File.

3     All procedures Get and Put maintain the current column, line, and page
numbers of the specified file: the effect of each of these procedures upon
these numbers is the result of the effects of individual transfers of
characters and of individual output or skipping of terminators. Each transfer
of a character adds one to the current column number. Each output of a line
terminator sets the current column number to one and adds one to the current
line number. Each output of a page terminator sets the current column and line
numbers to one and adds one to the current page number. For input, each
skipping of a line terminator sets the current column number to one and adds
one to the current line number; each skipping of a page terminator sets the
current column and line numbers to one and adds one to the current page
number. Similar considerations apply to the procedures Get_Line, Put_Line, and
Set_Col.

4     Several Get and Put procedures, for numeric and enumeration types, have
format parameters which specify field lengths; these parameters are of the
nonnegative subtype Field of the type Integer.

5     Input-output of enumeration values uses the syntax of the corresponding
lexical elements. Any Get procedure for an enumeration type begins by skipping
any leading blanks, or line or page terminators. Get procedures for numeric or
enumeration types start by skipping leading blanks, where a blank is defined
as a space or a horizontal tabulation character. Next, characters are input
only so long as the sequence input is an initial sequence of an identifier or
of a character literal (in particular, input ceases when a line terminator is
encountered). The character or line terminator that causes input to cease
remains available for subsequent input.

6     For a numeric type, the Get procedures have a format parameter called
Width. If the value given for this parameter is zero, the Get procedure
proceeds in the same manner as for enumeration types, but using the syntax of
numeric literals instead of that of enumeration literals. If a nonzero value
is given, then exactly Width characters are input, or the characters up to a
line terminator, whichever comes first; any skipped leading blanks are
included in the count. The syntax used for numeric literals is an extended
syntax that allows a leading sign (but no intervening blanks, or line or page
terminators) and that also allows (for real types) an integer literal as well
as forms that have digits only before the point or only after the point.

7     Any Put procedure, for an item of a numeric or an enumeration type,
outputs the value of the item as a numeric literal, identifier, or character
literal, as appropriate. This is preceded by leading spaces if required by the
format parameters Width or Fore (as described in later subclauses), and then a
minus sign for a negative value; for an enumeration type, the spaces follow
instead of leading. The format given for a Put procedure is overridden if it
is insufficiently wide, by using the minimum needed width.

8     Two further cases arise for Put procedures for numeric and enumeration
types, if the line length of the specified output file is bounded (that is, if
it does not have the conventional value zero). If the number of characters to
be output does not exceed the maximum line length, but is such that they
cannot fit on the current line, starting from the current column, then (in
effect) New_Line is called (with a spacing of one) before output of the item.
Otherwise, if the number of characters exceeds the maximum line length, then
the exception Layout_Error is propagated and nothing is output.

9     The exception Status_Error is propagated by any of the procedures Get,
Get_Line, Put, and Put_Line if the file to be used is not open. The exception
Mode_Error is propagated by the procedures Get and Get_Line if the mode of the
file to be used is not In_File; and by the procedures Put and Put_Line, if the
mode is not Out_File or Append_File.

10    The exception End_Error is propagated by a Get procedure if an attempt
is made to skip a file terminator. The exception Data_Error is propagated by a
Get procedure if the sequence finally input is not a lexical element
corresponding to the type, in particular if no characters were input; for this
test, leading blanks are ignored; for an item of a numeric type, when a sign
is input, this rule applies to the succeeding numeric literal. The exception
Layout_Error is propagated by a Put procedure that outputs to a parameter of
type String, if the length of the actual string is insufficient for the output
of the item.


                                  Examples

11    In the examples, here and in subclauses A.10.8 and A.10.9, the string
quotes and the lower case letter b are not transferred: they are shown only to
reveal the layout and spaces.

12    N : Integer;
         ...
      Get(N);

13    --                        Characters at input  Sequence input  
      Value of N
      
      --                        bb-12535b           -12535  -12535
      --                        bb12_535e1b         12_535e1  125350
      --                        bb12_535e;          12_535e  
      (none) Data_Error raised

14    Example of overridden width parameter:

15    Put(Item => -23, Width => 2);  --  "-23"


A.10.7 Input-Output of Characters and Strings



                              Static Semantics

1     For an item of type Character the following procedures are provided:

2     procedure Get(File : in File_Type; Item : out Character);
      procedure Get(Item : out Character);

    3     After skipping any line terminators and any page terminators, reads
          the next character from the specified input file and returns the
          value of this character in the out parameter Item.

    4     The exception End_Error is propagated if an attempt is made to skip
          a file terminator.

5     procedure Put(File : in File_Type; Item : in Character);
      procedure Put(Item : in Character);

    6     If the line length of the specified output file is bounded (that is,
          does not have the conventional value zero), and the current column
          number exceeds it, has the effect of calling New_Line with a spacing
          of one. Then, or otherwise, outputs the given character to the file.

7     procedure Look_Ahead (File        : in  File_Type;
                            Item        : out Character;
                            End_Of_Line : out Boolean);
      procedure Look_Ahead (Item        : out Character;
                            End_Of_Line : out Boolean);

    8/1   Mode_Error is propagated if the mode of the file is not In_File.
          Sets End_Of_Line to True if at end of line, including if at end of
          page or at end of file; in each of these cases the value of Item is
          not specified. Otherwise End_Of_Line is set to False and Item is set
          to [the ]the next character (without consuming it) from the file.

9     procedure Get_Immediate(File : in  File_Type;
                              Item : out Character);
      procedure Get_Immediate(Item : out Character);

    10    Reads the next character, either control or graphic, from the
          specified File or the default input file. Mode_Error is propagated
          if the mode of the file is not In_File. End_Error is propagated if
          at the end of the file. The current column, line and page numbers
          for the file are not affected.

11    procedure Get_Immediate(File      : in  File_Type;
                              Item      : out Character;
                              Available : out Boolean);
      procedure Get_Immediate(Item      : out Character;
                              Available : out Boolean);

    12    If a character, either control or graphic, is available from the
          specified File or the default input file, then the character is
          read; Available is True and Item contains the value of this
          character. If a character is not available, then Available is False
          and the value of Item is not specified. Mode_Error is propagated if
          the mode of the file is not In_File. End_Error is propagated if at
          the end of the file. The current column, line and page numbers for
          the file are not affected.

13    For an item of type String the following procedures are provided:

14    procedure Get(File : in File_Type; Item : out String);
      procedure Get(Item : out String);

    15    Determines the length of the given string and attempts that number
          of Get operations for successive characters of the string (in
          particular, no operation is performed if the string is null).

16    procedure Put(File : in File_Type; Item : in String);
      procedure Put(Item : in String);

    17    Determines the length of the given string and attempts that number
          of Put operations for successive characters of the string (in
          particular, no operation is performed if the string is null).

18    procedure Get_Line(File : in File_Type;
                                    Item : out String;
                                    Last : out Natural);
      procedure Get_Line(Item : out String;   Last : out Natural);

    19    Reads successive characters from the specified input file and
          assigns them to successive characters of the specified string.
          Reading stops if the end of the string is met. Reading also stops if
          the end of the line is met before meeting the end of the string; in
          this case Skip_Line is (in effect) called with a spacing of 1. The
          values of characters not assigned are not specified.

    20    If characters are read, returns in Last the index value such that
          Item(Last) is the last character assigned (the index of the first
          character assigned is Item'First). If no characters are read,
          returns in Last an index value that is one less than Item'First. The
          exception End_Error is propagated if an attempt is made to skip a
          file terminator.

21    procedure Put_Line(File : in File_Type; Item : in String);
      procedure Put_Line(Item : in String);

    22    Calls the procedure Put for the given string, and then the procedure
          New_Line with a spacing of one.


                            Implementation Advice

23    The Get_Immediate procedures should be implemented with unbuffered
input. For a device such as a keyboard, input should be ``available'' if a key
has already been typed, whereas for a disk file, input should always be
available except at end of file. For a file associated with a keyboard-like
device, any line-editing features of the underlying operating system should be
disabled during the execution of Get_Immediate.

      NOTES

24    26  Get_Immediate can be used to read a single key from the keyboard `
      `immediately''; that is, without waiting for an end of line. In a call
      of Get_Immediate without the parameter Available, the caller will wait
      until a character is available.

25    27  In a literal string parameter of Put, the enclosing string bracket
      characters are not output. Each doubled string bracket character in the
      enclosed string is output as a single string bracket character, as a
      consequence of the rule for string literals (see 2.6).

26    28  A string read by Get or written by Put can extend over several
      lines. An implementation is allowed to assume that certain external
      files do not contain page terminators, in which case Get_Line and
      Skip_Line can return as soon as a line terminator is read.


A.10.8 Input-Output for Integer Types



                              Static Semantics

1     The following procedures are defined in the generic packages Integer_IO
and Modular_IO, which have to be instantiated for the appropriate signed
integer or modular type respectively (indicated by Num in the specifications).

2     Values are output as decimal or based literals, without low line
characters or exponent, and, for Integer_IO, preceded by a minus sign if
negative. The format (which includes any leading spaces and minus sign) can be
specified by an optional field width parameter. Values of widths of fields in
output formats are of the nonnegative integer subtype Field. Values of bases
are of the integer subtype Number_Base.

3     subtype Number_Base is Integer range 2 .. 16;

4     The default field width and base to be used by output procedures are
defined by the following variables that are declared in the generic packages
Integer_IO and Modular_IO:

5     Default_Width : Field := Num'Width;
      Default_Base  : Number_Base := 10;

6     The following procedures are provided:

7     procedure Get(File : in File_Type; Item : out Num; Width : in Field := 0);
      procedure Get(Item : out Num; Width : in Field := 0);

    8     If the value of the parameter Width is zero, skips any leading
          blanks, line terminators, or page terminators, then reads a plus
          sign if present or (for a signed type only) a minus sign if present,
          then reads the longest possible sequence of characters matching the
          syntax of a numeric literal without a point. If a nonzero value of
          Width is supplied, then exactly Width characters are input, or the
          characters (possibly none) up to a line terminator, whichever comes
          first; any skipped leading blanks are included in the count.

    9     Returns, in the parameter Item, the value of type Num that
          corresponds to the sequence input.

    10    The exception Data_Error is propagated if the sequence of characters
          read does not form a legal integer literal or if the value obtained
          is not of the subtype Num (for Integer_IO) or is not in the base
          range of Num (for Modular_IO).

11    procedure Put(File  : in File_Type;
                    Item  : in Num;
                    Width : in Field := Default_Width;
                    Base  : in Number_Base := Default_Base);
      
      procedure Put(Item  : in Num;
                    Width : in Field := Default_Width;
                    Base  : in Number_Base := Default_Base);

    12    Outputs the value of the parameter Item as an integer literal, with
          no low lines, no exponent, and no leading zeros (but a single zero
          for the value zero), and a preceding minus sign for a negative value.

    13    If the resulting sequence of characters to be output has fewer than
          Width characters, then leading spaces are first output to make up
          the difference.

    14    Uses the syntax for decimal literal if the parameter Base has the
          value ten (either explicitly or through Default_Base); otherwise,
          uses the syntax for based literal, with any letters in upper case.

15    procedure Get(From : in String; Item : out Num; Last : out Positive);

    16    Reads an integer value from the beginning of the given string,
          following the same rules as the Get procedure that reads an integer
          value from a file, but treating the end of the string as a file
          terminator. Returns, in the parameter Item, the value of type Num
          that corresponds to the sequence input. Returns in Last the index
          value such that From(Last) is the last character read.

    17    The exception Data_Error is propagated if the sequence input does
          not have the required syntax or if the value obtained is not of the
          subtype Num.

18    procedure Put(To   : out String;
                    Item : in Num;
                    Base : in Number_Base := Default_Base);

    19    Outputs the value of the parameter Item to the given string,
          following the same rule as for output to a file, using the length of
          the given string as the value for Width.

20    Integer_Text_IO is a library package that is a nongeneric equivalent to
Text_IO.Integer_IO for the predefined type Integer:

21    with Ada.Text_IO;
      package Ada.Integer_Text_IO is new Ada.Text_IO.Integer_IO(Integer);

22    For each predefined signed integer type, a nongeneric equivalent to
Text_IO.Integer_IO is provided, with names such as Ada.Long_Integer_Text_IO.


                         Implementation Permissions

23    The nongeneric equivalent packages may, but need not, be actual
instantiations of the generic package for the appropriate predefined type.

      NOTES

24    29  For Modular_IO, execution of Get propagates Data_Error if the
      sequence of characters read forms an integer literal outside the range
      0..Num'Last.


                                  Examples

25/1  This paragraph was deleted.[ ]

26    package Int_IO is new Integer_IO(Small_Int); use Int_IO;
      -- default format used at instantiation,
      -- Default_Width = 4, Default_Base = 10

27    Put(126);                            -- "b126"
      Put(-126, 7);                        -- "bbb-126"
      Put(126, Width => 13, Base => 2);    -- "bbb2#1111110#"


A.10.9 Input-Output for Real Types



                              Static Semantics

1     The following procedures are defined in the generic packages Float_IO,
Fixed_IO, and Decimal_IO, which have to be instantiated for the appropriate
floating point, ordinary fixed point, or decimal fixed point type respectively
(indicated by Num in the specifications).

2     Values are output as decimal literals without low line characters. The
format of each value output consists of a Fore field, a decimal point, an Aft
field, and (if a nonzero Exp parameter is supplied) the letter E and an Exp
field. The two possible formats thus correspond to:

3     Fore  .  Aft

4     and to:

5     Fore  .  Aft  E  Exp

6     without any spaces between these fields. The Fore field may include
leading spaces, and a minus sign for negative values. The Aft field includes
only decimal digits (possibly with trailing zeros). The Exp field includes the
sign (plus or minus) and the exponent (possibly with leading zeros).

7     For floating point types, the default lengths of these fields are
defined by the following variables that are declared in the generic package
Float_IO:

8     Default_Fore : Field := 2;
      Default_Aft  : Field := Num'Digits-1;
      Default_Exp  : Field := 3;

9     For ordinary or decimal fixed point types, the default lengths of these
fields are defined by the following variables that are declared in the generic
packages Fixed_IO and Decimal_IO, respectively:

10    Default_Fore : Field := Num'Fore;
      Default_Aft  : Field := Num'Aft;
      Default_Exp  : Field := 0;

11    The following procedures are provided:

12    procedure Get(File : in File_Type; Item : out Num; Width : in Field := 0);
      procedure Get(Item : out Num; Width : in Field := 0);

    13    If the value of the parameter Width is zero, skips any leading
          blanks, line terminators, or page terminators, then reads the
          longest possible sequence of characters matching the syntax of any
          of the following (see 2.4):

        14    [+|-]numeric_literal

        15    [+|-]numeral.[exponent]

        16    [+|-].numeral[exponent]

        17    [+|-]base#based_numeral.#[exponent]

        18    [+|-]base#.based_numeral#[exponent]

    19    If a nonzero value of Width is supplied, then exactly Width
          characters are input, or the characters (possibly none) up to a line
          terminator, whichever comes first; any skipped leading blanks are
          included in the count.

    20    Returns in the parameter Item the value of type Num that corresponds
          to the sequence input, preserving the sign (positive if none has
          been specified) of a zero value if Num is a floating point type and
          Num'Signed_Zeros is True.

    21    The exception Data_Error is propagated if the sequence input does
          not have the required syntax or if the value obtained is not of the
          subtype Num.

22    procedure Put(File : in File_Type;
                    Item : in Num;
                    Fore : in Field := Default_Fore;
                    Aft  : in Field := Default_Aft;
                    Exp  : in Field := Default_Exp);
      
      procedure Put(Item : in Num;
                    Fore : in Field := Default_Fore;
                    Aft  : in Field := Default_Aft;
                    Exp  : in Field := Default_Exp);

    23    Outputs the value of the parameter Item as a decimal literal with
          the format defined by Fore, Aft and Exp. If the value is negative,
          or if Num is a floating point type where Num'Signed_Zeros is True
          and the value is a negatively signed zero, then a minus sign is
          included in the integer part. If Exp has the value zero, then the
          integer part to be output has as many digits as are needed to
          represent the integer part of the value of Item, overriding Fore if
          necessary, or consists of the digit zero if the value of Item has no
          integer part.

    24    If Exp has a value greater than zero, then the integer part to be
          output has a single digit, which is nonzero except for the value 0.0
          of Item.

    25    In both cases, however, if the integer part to be output has fewer
          than Fore characters, including any minus sign, then leading spaces
          are first output to make up the difference. The number of digits of
          the fractional part is given by Aft, or is one if Aft equals zero.
          The value is rounded; a value of exactly one half in the last place
          is rounded away from zero.

    26    If Exp has the value zero, there is no exponent part. If Exp has a
          value greater than zero, then the exponent part to be output has as
          many digits as are needed to represent the exponent part of the
          value of Item (for which a single digit integer part is used), and
          includes an initial sign (plus or minus). If the exponent part to be
          output has fewer than Exp characters, including the sign, then
          leading zeros precede the digits, to make up the difference. For the
          value 0.0 of Item, the exponent has the value zero.

27    procedure Get(From : in String; Item : out Num; Last : out Positive);

    28    Reads a real value from the beginning of the given string, following
          the same rule as the Get procedure that reads a real value from a
          file, but treating the end of the string as a file terminator.
          Returns, in the parameter Item, the value of type Num that
          corresponds to the sequence input. Returns in Last the index value
          such that From(Last) is the last character read.

    29    The exception Data_Error is propagated if the sequence input does
          not have the required syntax, or if the value obtained is not of the
          subtype Num.

30    procedure Put(To   : out String;
                    Item : in Num;
                    Aft  : in Field := Default_Aft;
                    Exp  : in Field := Default_Exp);

    31    Outputs the value of the parameter Item to the given string,
          following the same rule as for output to a file, using a value for
          Fore such that the sequence of characters output exactly fills the
          string, including any leading spaces.

32    Float_Text_IO is a library package that is a nongeneric equivalent to
Text_IO.Float_IO for the predefined type Float:

33    with Ada.Text_IO;
      package Ada.Float_Text_IO is new Ada.Text_IO.Float_IO(Float);

34    For each predefined floating point type, a nongeneric equivalent to
Text_IO.Float_IO is provided, with names such as Ada.Long_Float_Text_IO.


                         Implementation Permissions

35    An implementation may extend Get and Put for floating point types to
support special values such as infinities and NaNs.

36    The implementation of Put need not produce an output value with greater
accuracy than is supported for the base subtype. The additional accuracy, if
any, of the value produced by Put when the number of requested digits in the
integer and fractional parts exceeds the required accuracy is implementation
defined.

37    The nongeneric equivalent packages may, but need not, be actual
instantiations of the generic package for the appropriate predefined type.

      NOTES

38    30  For an item with a positive value, if output to a string exactly
      fills the string without leading spaces, then output of the
      corresponding negative value will propagate Layout_Error.

39    31  The rules for the Value attribute (see 3.5) and the rules for Get
      are based on the same set of formats.


                                  Examples

40/1  This paragraph was deleted.[ ]

41    package Real_IO is new Float_IO(Real); use Real_IO;
      -- default format used at instantiation, Default_Exp = 3

42    X : Real := -123.4567;  --  digits 8      (see 3.5.7)

43    Put(X);  -- default format                                   "-
      1.2345670E+02"
      Put(X, Fore => 5, Aft => 3, Exp => 2);                       -- "bbb-
      1.235E+2"
      Put(X, 5, 3, 0);                                             -- "b-
      123.457"


A.10.10 Input-Output for Enumeration Types



                              Static Semantics

1     The following procedures are defined in the generic package
Enumeration_IO, which has to be instantiated for the appropriate enumeration
type (indicated by Enum in the specification).

2     Values are output using either upper or lower case letters for
identifiers. This is specified by the parameter Set, which is of the
enumeration type Type_Set.

3     type Type_Set is (Lower_Case, Upper_Case);

4     The format (which includes any trailing spaces) can be specified by an
optional field width parameter. The default field width and letter case are
defined by the following variables that are declared in the generic package
Enumeration_IO:

5     Default_Width   : Field := 0;
      Default_Setting : Type_Set := Upper_Case;

6     The following procedures are provided:

7     procedure Get(File : in File_Type; Item : out Enum);
      procedure Get(Item : out Enum);

    8     After skipping any leading blanks, line terminators, or page
          terminators, reads an identifier according to the syntax of this
          lexical element (lower and upper case being considered equivalent),
          or a character literal according to the syntax of this lexical
          element (including the apostrophes). Returns, in the parameter Item,
          the value of type Enum that corresponds to the sequence input.

    9     The exception Data_Error is propagated if the sequence input does
          not have the required syntax, or if the identifier or character
          literal does not correspond to a value of the subtype Enum.

10    procedure Put(File  : in File_Type;
                    Item  : in Enum;
                    Width : in Field := Default_Width;
                    Set   : in Type_Set := Default_Setting);
      
      procedure Put(Item  : in Enum;
                    Width : in Field := Default_Width;
                    Set   : in Type_Set := Default_Setting);

    11    Outputs the value of the parameter Item as an enumeration literal
          (either an identifier or a character literal). The optional
          parameter Set indicates whether lower case or upper case is used for
          identifiers; it has no effect for character literals. If the
          sequence of characters produced has fewer than Width characters,
          then trailing spaces are finally output to make up the difference.
          If Enum is a character type, the sequence of characters produced is
          as for Enum'Image(Item), as modified by the Width and Set
          parameters.

12    procedure Get(From : in String; Item : out Enum; Last : out Positive);

    13    Reads an enumeration value from the beginning of the given string,
          following the same rule as the Get procedure that reads an
          enumeration value from a file, but treating the end of the string as
          a file terminator. Returns, in the parameter Item, the value of type
          Enum that corresponds to the sequence input. Returns in Last the
          index value such that From(Last) is the last character read.

    14    The exception Data_Error is propagated if the sequence input does
          not have the required syntax, or if the identifier or character
          literal does not correspond to a value of the subtype Enum.

15    procedure Put(To   : out String;
                    Item : in Enum;
                    Set  : in Type_Set := Default_Setting);

    16    Outputs the value of the parameter Item to the given string,
          following the same rule as for output to a file, using the length of
          the given string as the value for Width.

17/1  Although the specification of the generic package Enumeration_IO would
allow instantiation for an {integer}[float] type, this is not the intended
purpose of this generic package, and the effect of such instantiations is not
defined by the language.

      NOTES

18    32  There is a difference between Put defined for characters, and for
      enumeration values. Thus

19       Ada.Text_IO.Put('A');  --  outputs the character A

20       package Char_IO is new Ada.Text_IO.Enumeration_IO(Character);
         Char_IO.Put('A');  --  outputs the character 'A', between apostrophes

21    33  The type Boolean is an enumeration type, hence Enumeration_IO can be
      instantiated for this type.


A.11 Wide Text Input-Output


1     The package Wide_Text_IO provides facilities for input and output in
human-readable form. Each file is read or written sequentially, as a sequence
of wide characters grouped into lines, and as a sequence of lines grouped into
pages.


                              Static Semantics

2     The specification of package Wide_Text_IO is the same as that for
Text_IO, except that in each Get, Look_Ahead, Get_Immediate, Get_Line, Put,
and Put_Line procedure, any occurrence of Character is replaced by
Wide_Character, and any occurrence of String is replaced by Wide_String.

3     Nongeneric equivalents of Wide_Text_IO.Integer_IO and Wide_Text_IO.-
Float_IO are provided (as for Text_IO) for each predefined numeric type, with
names such as Ada.Integer_Wide_Text_IO, Ada.Long_Integer_Wide_Text_IO,
Ada.Float_Wide_Text_IO, Ada.Long_Float_Wide_Text_IO.


A.12 Stream Input-Output


1     The packages Streams.Stream_IO, Text_IO.Text_Streams, and
Wide_Text_IO.Text_Streams provide stream-oriented operations on files.


A.12.1 The Package Streams.Stream_IO


1     The subprograms in the child package Streams.Stream_IO provide control
over stream files. Access to a stream file is either sequential, via a call on
Read or Write to transfer an array of stream elements, or positional (if
supported by the implementation for the given file), by specifying a relative
index for an element. Since a stream file can be converted to a Stream_Access
value, calling stream-oriented attribute subprograms of different element
types with the same Stream_Access value provides heterogeneous input-output.
See 13.13 for a general discussion of streams.


                              Static Semantics

1.1/1 {The elements of a stream file are stream elements. If positioning is
supported for the specified external file, a current index and current size
are maintained for the file as described in A.8. If positioning is not
supported, a current index is not maintained, and the current size is
implementation defined. }

2     The library package Streams.Stream_IO has the following declaration:

3     with Ada.IO_Exceptions;
      package Ada.Streams.Stream_IO is

4         type Stream_Access is access all Root_Stream_Type'Class;

5         type File_Type is limited private;

6         type File_Mode is (In_File, Out_File, Append_File);

7         type    Count          is range 0 .. implementation-defined;
          subtype Positive_Count is Count range 1 .. Count'Last;
            -- Index into file, in stream elements.

8         procedure Create (File : in out File_Type;
                            Mode : in File_Mode := Out_File;
                            Name : in String    := "";
                            Form : in String    := "");

9         procedure Open (File : in out File_Type;
                          Mode : in File_Mode;
                          Name : in String;
                          Form : in String := "");

10        procedure Close  (File : in out File_Type);
          procedure Delete (File : in out File_Type);
          procedure Reset  (File : in out File_Type; Mode : in File_Mode);
          procedure Reset  (File : in out File_Type);

11        function Mode (File : in File_Type) return File_Mode;
          function Name (File : in File_Type) return String;
          function Form (File : in File_Type) return String;

12        function Is_Open     (File : in File_Type) return Boolean;
          function End_Of_File (File : in File_Type) return Boolean;

13        function Stream (File : in File_Type) return Stream_Access;
              -- Return stream access for use with T'Input and T'Output

14/1  This paragraph was deleted.[ ]

15        -- Read array of stream elements from file
          procedure Read (File : in  File_Type;
                          Item : out Stream_Element_Array;
                          Last : out Stream_Element_Offset;
                          From : in  Positive_Count);

16        procedure Read (File : in  File_Type;
                          Item : out Stream_Element_Array;
                          Last : out Stream_Element_Offset);

17/1  This paragraph was deleted.[ ]

18        -- Write array of stream elements into file
          procedure Write (File : in File_Type;
                           Item : in Stream_Element_Array;
                           To   : in Positive_Count);

19        procedure Write (File : in File_Type;
                                 Item : in Stream_Element_Array);

20/1  This paragraph was deleted.[ ]

21        -- Operations on position within file

22        procedure Set_Index(File : in File_Type; To : in Positive_Count);

23        function Index(File : in File_Type) return Positive_Count;
          function Size (File : in File_Type) return Count;

24        procedure Set_Mode(File : in out File_Type; Mode : in File_Mode);

25/1      procedure Flush(File : in [out ]File_Type);

26        -- exceptions
          Status_Error : exception renames IO_Exceptions.Status_Error;
          Mode_Error   : exception renames IO_Exceptions.Mode_Error;
          Name_Error   : exception renames IO_Exceptions.Name_Error;
          Use_Error    : exception renames IO_Exceptions.Use_Error;
          Device_Error : exception renames IO_Exceptions.Device_Error;
          End_Error    : exception renames IO_Exceptions.End_Error;
          Data_Error   : exception renames IO_Exceptions.Data_Error;

27    private
         ... -- not specified by the language
      end Ada.Streams.Stream_IO;

28    The subprograms Create, Open, Close, Delete, Reset, Mode, Name, Form,
Is_Open, and End_of_File have the same effect as the corresponding subprograms
in Sequential_IO (see A.8.2).

28.1/1 {The Set_Mode procedure changes the mode of the file. If the new mode
is Append_File, the file is positioned to its end; otherwise, the position in
the file is unchanged.}

28.2/1 {The Flush procedure synchronizes the external file with the internal
file (by flushing any internal buffers) without closing the file or changing
the position. Mode_Error is propagated if the mode of the file is In_File.}

29/1  The Stream function returns a Stream_Access result from a File_Type
object, thus allowing the stream-oriented attributes Read, Write, Input, and
Output to be used on the same file for multiple types. {Stream propagates
Status_Error if File is not open.}

30    The procedures Read and Write are equivalent to the corresponding
operations in the package Streams. Read propagates Mode_Error if the mode of
File is not In_File. Write propagates Mode_Error if the mode of File is not
Out_File or Append_File. The Read procedure with a Positive_Count parameter
starts reading at the specified index. The Write procedure with a
Positive_Count parameter starts writing at the specified index.

30.1/1 {The Size function returns the current size of the file.}

31/1  The Index function returns the current [file ]index[, as a count (in
stream elements) from the beginning of the file. The position of the first
element in the file is 1].

32    The Set_Index procedure sets the current index to the specified value.

32.1/1 {If positioning is supported for the external file, the current index
is maintained as follows:}

32.2/1 {For Open and Create, if the Mode parameter is Append_File, the current
      index is set to the current size of the file plus one; otherwise, the
      current index is set to one.}

32.3/1 {For Reset, if the Mode parameter is Append_File, or no Mode parameter
      is given and the current mode is Append_File, the current index is set
      to the current size of the file plus one; otherwise, the current index
      is set to one.}

32.4/1 {For Set_Mode, if the new mode is Append_File, the current index is set
      to current size plus one; otherwise, the current index is unchanged.}

32.5/1 {For Read and Write without a Positive_Count parameter, the current
      index is incremented by the number of stream elements read or written.}

32.6/1 {For Read and Write with a Positive_Count parameter, the value of the
      current index is set to the value of the Positive_Count parameter plus
      the number of stream elements read or written.}

33    If positioning is not supported for the given file, then a call of Index
or Set_Index propagates Use_Error. Similarly, a call of Read or Write with a
Positive_Count parameter propagates Use_Error.

34/1  This paragraph was deleted.[The Size function returns the current size
of the file, in stream elements.]

35/1  This paragraph was deleted.[The Set_Mode procedure changes the mode of
the file. If the new mode is Append_File, the file is positioned to its end;
otherwise, the position in the file is unchanged.]

36/1  This paragraph was deleted.[The Flush procedure synchronizes the
external file with the internal file (by flushing any internal buffers)
without closing the file or changing the position. Mode_Error is propagated if
the mode of the file is In_File.]


                             Erroneous Execution

36.1/1 {If the File_Type object passed to the Stream function is later closed
or finalized, and the stream-oriented attributes are subsequently called
(explicitly or implicitly) on the Stream_Access value returned by Stream,
execution is erroneous. This rule applies even if the File_Type object was
opened again after it had been closed.}


A.12.2 The Package Text_IO.Text_Streams


1     The package Text_IO.Text_Streams provides a function for treating a text
file as a stream.


                              Static Semantics

2     The library package Text_IO.Text_Streams has the following declaration:

3     with Ada.Streams;
      package Ada.Text_IO.Text_Streams is
         type Stream_Access is access all Streams.Root_Stream_Type'Class;

4        function Stream (File : in File_Type) return Stream_Access;
      end Ada.Text_IO.Text_Streams;

5     The Stream function has the same effect as the corresponding function in
Streams.Stream_IO.

      NOTES

6     34  The ability to obtain a stream for a text file allows Current_Input,
      Current_Output, and Current_Error to be processed with the functionality
      of streams, including the mixing of text and binary input-output, and
      the mixing of binary input-output for different types.

7     35  Performing operations on the stream associated with a text file does
      not affect the column, line, or page counts.


A.12.3 The Package Wide_Text_IO.Text_Streams


1     The package Wide_Text_IO.Text_Streams provides a function for treating a
wide text file as a stream.


                              Static Semantics

2     The library package Wide_Text_IO.Text_Streams has the following
declaration:

3     with Ada.Streams;
      package Ada.Wide_Text_IO.Text_Streams is
         type Stream_Access is access all Streams.Root_Stream_Type'Class;

4        function Stream (File : in File_Type) return Stream_Access;
      end Ada.Wide_Text_IO.Text_Streams;

5     The Stream function has the same effect as the corresponding function in
Streams.Stream_IO.


A.13 Exceptions in Input-Output


1     The package IO_Exceptions defines the exceptions needed by the
predefined input-output packages.


                              Static Semantics

2     The library package IO_Exceptions has the following declaration:

3     package Ada.IO_Exceptions is
         pragma Pure(IO_Exceptions);

4        Status_Error : exception;
         Mode_Error   : exception;
         Name_Error   : exception;
         Use_Error    : exception;
         Device_Error : exception;
         End_Error    : exception;
         Data_Error   : exception;
         Layout_Error : exception;

5     end Ada.IO_Exceptions;

6     If more than one error condition exists, the corresponding exception
that appears earliest in the following list is the one that is propagated.

7     The exception Status_Error is propagated by an attempt to operate upon a
file that is not open, and by an attempt to open a file that is already open.

8     The exception Mode_Error is propagated by an attempt to read from, or
test for the end of, a file whose current mode is Out_File or Append_File, and
also by an attempt to write to a file whose current mode is In_File. In the
case of Text_IO, the exception Mode_Error is also propagated by specifying a
file whose current mode is Out_File or Append_File in a call of Set_Input,
Skip_Line, End_Of_Line, Skip_Page, or End_Of_Page; and by specifying a file
whose current mode is In_File in a call of Set_Output, Set_Line_Length,
Set_Page_Length, Line_Length, Page_Length, New_Line, or New_Page.

9     The exception Name_Error is propagated by a call of Create or Open if
the string given for the parameter Name does not allow the identification of
an external file. For example, this exception is propagated if the string is
improper, or, alternatively, if either none or more than one external file
corresponds to the string.

10    The exception Use_Error is propagated if an operation is attempted that
is not possible for reasons that depend on characteristics of the external
file. For example, this exception is propagated by the procedure Create, among
other circumstances, if the given mode is Out_File but the form specifies an
input only device, if the parameter Form specifies invalid access rights, or
if an external file with the given name already exists and overwriting is not
allowed.

11    The exception Device_Error is propagated if an input-output operation
cannot be completed because of a malfunction of the underlying system.

12    The exception End_Error is propagated by an attempt to skip (read past)
the end of a file.

13    The exception Data_Error can be propagated by the procedure Read (or by
the Read attribute) if the element read cannot be interpreted as a value of
the required subtype. This exception is also propagated by a procedure Get
(defined in the package Text_IO) if the input character sequence fails to
satisfy the required syntax, or if the value input does not belong to the
range of the required subtype.

14    The exception Layout_Error is propagated (in text input-output) by Col,
Line, or Page if the value returned exceeds Count'Last. The exception
Layout_Error is also propagated on output by an attempt to set column or line
numbers in excess of specified maximum line or page lengths, respectively
(excluding the unbounded cases). It is also propagated by an attempt to Put
too many characters to a string.


                         Documentation Requirements

15    The implementation shall document the conditions under which Name_Error,
Use_Error and Device_Error are propagated.


                         Implementation Permissions

16    If the associated check is too complex, an implementation need not
propagate Data_Error as part of a procedure Read (or the Read attribute) if
the value read cannot be interpreted as a value of the required subtype.


                             Erroneous Execution

17    If the element read by the procedure Read (or by the Read attribute)
cannot be interpreted as a value of the required subtype, but this is not
detected and Data_Error is not propagated, then the resulting value can be
abnormal, and subsequent references to the value can lead to erroneous
execution, as explained in 13.9.1.


A.14 File Sharing



                              Dynamic Semantics

1     It is not specified by the language whether the same external file can
be associated with more than one file object. If such sharing is supported by
the implementation, the following effects are defined:

2     Operations on one text file object do not affect the column, line, and
      page numbers of any other file object.

3/1   This paragraph was deleted.[Standard_Input and Standard_Output are
      associated with distinct external files, so operations on one of these
      files cannot affect operations on the other file. In particular, reading
      from Standard_Input does not affect the current page, line, and column
      numbers for Standard_Output, nor does writing to Standard_Output affect
      the current page, line, and column numbers for Standard_Input.]

4     For direct and stream files, the current index is a property of each
      file object; an operation on one file object does not affect the current
      index of any other file object.

5     For direct and stream files, the current size of the file is a property
      of the external file.

6     All other effects are identical.


A.15 The Package Command_Line


1     The package Command_Line allows a program to obtain the values of its
arguments and to set the exit status code to be returned on normal
termination.


                              Static Semantics

2     The library package Ada.Command_Line has the following declaration:

3     package Ada.Command_Line is
        pragma Preelaborate(Command_Line);

4       function Argument_Count return Natural;

5       function Argument (Number : in Positive) return String;

6       function Command_Name return String;

7       type Exit_Status is implementation-defined integer type;

8       Success : constant Exit_Status;
        Failure : constant Exit_Status;

9       procedure Set_Exit_Status (Code : in Exit_Status);

10    private
        ... -- not specified by the language
      end Ada.Command_Line;
      

11    function Argument_Count return Natural;

    12    If the external execution environment supports passing arguments to
          a program, then Argument_Count returns the number of arguments
          passed to the program invoking the function. Otherwise it returns 0.
          The meaning of ``number of arguments'' is implementation defined.

13    function Argument (Number : in Positive) return String;

    14    If the external execution environment supports passing arguments to
          a program, then Argument returns an implementation-defined value
          corresponding to the argument at relative position Number. If Number
          is outside the range 1..Argument_Count, then Constraint_Error is
          propagated.

15    function Command_Name return String;

    16    If the external execution environment supports passing arguments to
          a program, then Command_Name returns an implementation-defined value
          corresponding to the name of the command invoking the program;
          otherwise Command_Name returns the null string.

16.1/1 {type Exit_Status is implementation-defined integer type;}

    17    The type Exit_Status represents the range of exit status values
          supported by the external execution environment. The constants
          Success and Failure correspond to success and failure, respectively.

18    procedure Set_Exit_Status (Code : in Exit_Status);

    19    If the external execution environment supports returning an exit
          status from a program, then Set_Exit_Status sets Code as the status.
          Normal termination of a program returns as the exit status the value
          most recently set by Set_Exit_Status, or, if no such value has been
          set, then the value Success. If a program terminates abnormally, the
          status set by Set_Exit_Status is ignored, and an
          implementation-defined exit status value is set.

    20    []If the external execution environment does not support returning
          an exit value from a program, then Set_Exit_Status does nothing.


                         Implementation Permissions

21    An alternative declaration is allowed for package Command_Line if
different functionality is appropriate for the external execution environment.

      NOTES

22    36  Argument_Count, Argument, and Command_Name correspond to the C
      language's argc, argv[n] (for n>0) and argv[0], respectively.



                                   Annex B
                                 (normative)

                        Interface to Other Languages


1     This Annex describes features for writing mixed-language programs.
General interface support is presented first; then specific support for C,
COBOL, and Fortran is defined, in terms of language interface packages for
each of these languages.


B.1 Interfacing Pragmas


1     A pragma Import is used to import an entity defined in a foreign
language into an Ada program, thus allowing a foreign-language subprogram to
be called from Ada, or a foreign-language variable to be accessed from Ada. In
contrast, a pragma Export is used to export an Ada entity to a foreign
language, thus allowing an Ada subprogram to be called from a foreign
language, or an Ada object to be accessed from a foreign language. The pragmas
Import and Export are intended primarily for objects and subprograms, although
implementations are allowed to support other entities.

2     A pragma Convention is used to specify that an Ada entity should use the
conventions of another language. It is intended primarily for types and ``
callback'' subprograms. For example, ``pragma Convention(Fortran, Matrix);'
' implies that Matrix should be represented according to the conventions of
the supported Fortran implementation, namely column-major order.

3     A pragma Linker_Options is used to specify the system linker parameters
needed when a given compilation unit is included in a partition.


                                   Syntax

4     An interfacing pragma is a representation pragma that is one of the
      pragmas Import, Export, or Convention. Their forms, together with that
      of the related pragma Linker_Options, are as follows:

5       pragma Import(
           [Convention =>] convention_identifier, [Entity =>] local_name
        [, [External_Name =>] string_expression] [, [Link_Name =>]
      string_expression]);

6       pragma Export(
           [Convention =>] convention_identifier, [Entity =>] local_name
        [, [External_Name =>] string_expression] [, [Link_Name =>]
      string_expression]);

7       pragma Convention([Convention =>] convention_identifier,[Entity =>]
      local_name);

8       pragma Linker_Options(string_expression);

9     A pragma Linker_Options is allowed only at the place of a
      declarative_item.

9.1/1 {For pragmas Import and Export, the argument for Link_Name shall not be
      given without the pragma_argument_identifier unless the argument for
      External_Name is given.}


                            Name Resolution Rules

10    The expected type for a string_expression in an interfacing pragma or in
pragma Linker_Options is String.


                               Legality Rules

11    The convention_identifier of an interfacing pragma shall be the name of
a convention. The convention names are implementation defined, except for
certain language-defined ones, such as Ada and Intrinsic, as explained in
6.3.1, ``Conformance Rules''. Additional convention names generally represent
the calling conventions of foreign languages, language implementations, or
specific run-time models. The convention of a callable entity is its calling
convention.

12    If L is a convention_identifier for a language, then a type T is said to
be compatible with convention L, (alternatively, is said to be an L-compatible
type) if any of the following conditions are met:

13    T is declared in a language interface package corresponding to L and is
      defined to be L-compatible (see B.3, B.3.1, B.3.2, B.4, B.5),

14    Convention L has been specified for T in a pragma Convention, and T is
      eligible for convention L; that is:

    15    T is an array type with either an unconstrained or
          statically-constrained first subtype, and its component type is
          L-compatible,

    16    T is a record type that has no discriminants and that only has
          components with statically-constrained subtypes, and each component
          type is L-compatible,

    17    T is an access-to-object type, and its designated type is
          L-compatible,

    18    T is an access-to-subprogram type, and its designated profile's
          parameter and result types are all L-compatible.

19    T is derived from an L-compatible type,

20    The implementation permits T as an L-compatible type.

21    If pragma Convention applies to a type, then the type shall either be
compatible with or eligible for the convention specified in the pragma.

22    A pragma Import shall be the completion of a declaration.
Notwithstanding any rule to the contrary, a pragma Import may serve as the
completion of any kind of (explicit) declaration if supported by an
implementation for that kind of declaration. If a completion is a pragma
Import, then it shall appear in the same declarative_part,
package_specification, task_definition or protected_definition as the
declaration. For a library unit, it shall appear in the same compilation,
before any subsequent compilation_units other than pragmas. If the local_name
denotes more than one entity, then the pragma Import is the completion of all
of them.

23     An entity specified as the Entity argument to a pragma Import (or
pragma Export) is said to be imported (respectively, exported).

24    The declaration of an imported object shall not include an explicit
initialization expression. Default initializations are not performed.

25    The type of an imported or exported object shall be compatible with the
convention specified in the corresponding pragma.

26    For an imported or exported subprogram, the result and parameter types
shall each be compatible with the convention specified in the corresponding
pragma.

27    The external name and link name string_expressions of a pragma Import or
Export, and the string_expression of a pragma Linker_Options, shall be static.


                              Static Semantics

28    Import, Export, and Convention pragmas are representation pragmas that
specify the convention aspect of representation. In addition, Import and
Export pragmas specify the imported and exported aspects of representation,
respectively.

29    An interfacing pragma is a program unit pragma when applied to a program
unit (see 10.1.5).

30    An interfacing pragma defines the convention of the entity denoted by
the local_name. The convention represents the calling convention or
representation convention of the entity. For an access-to-subprogram type, it
represents the calling convention of designated subprograms. In addition:

31    A pragma Import specifies that the entity is defined externally (that
      is, outside the Ada program).

32    A pragma Export specifies that the entity is used externally.

33    A pragma Import or Export optionally specifies an entity's external
      name, link name, or both.

34    An external name is a string value for the name used by a foreign
language program either for an entity that an Ada program imports, or for
referring to an entity that an Ada program exports.

35    A link name is a string value for the name of an exported or imported
entity, based on the conventions of the foreign language's compiler in
interfacing with the system's linker tool.

36    The meaning of link names is implementation defined. If neither a link
name nor the Address attribute of an imported or exported entity is specified,
then a link name is chosen in an implementation-defined manner, based on the
external name if one is specified.

37    Pragma Linker_Options has the effect of passing its string argument as a
parameter to the system linker (if one exists), if the immediately enclosing
compilation unit is included in the partition being linked. The interpretation
of the string argument, and the way in which the string arguments from
multiple Linker_Options pragmas are combined, is implementation defined.


                              Dynamic Semantics

38    Notwithstanding what this International Standard says elsewhere, the
elaboration of a declaration denoted by the local_name of a pragma Import does
not create the entity. Such an elaboration has no other effect than to allow
the defining name to denote the external entity.


                            Implementation Advice

39    If an implementation supports pragma Export to a given language, then it
should also allow the main subprogram to be written in that language. It
should support some mechanism for invoking the elaboration of the Ada library
units included in the system, and for invoking the finalization of the
environment task. On typical systems, the recommended mechanism is to provide
two subprograms whose link names are "adainit" and "adafinal". Adainit should
contain the elaboration code for library units. Adafinal should contain the
finalization code. These subprograms should have no effect the second and
subsequent time they are called. {}

40    Automatic elaboration of preelaborated packages should be provided when
pragma Export is supported.

41    For each supported convention L other than Intrinsic, an implementation
should support Import and Export pragmas for objects of L-compatible types and
for subprograms, and pragma Convention for L-eligible types and for
subprograms, presuming the other language has corresponding features. Pragma
Convention need not be supported for scalar types.

      NOTES

42    1  Implementations may place restrictions on interfacing pragmas; for
      example, requiring each exported entity to be declared at the library
      level.

43    2  A pragma Import specifies the conventions for accessing external
      entities. It is possible that the actual entity is written in assembly
      language, but reflects the conventions of a particular language. For
      example, pragma Import(Ada, ...) can be used to interface to an assembly
      language routine that obeys the Ada compiler's calling conventions.

44    3  To obtain ``call-back'' to an Ada subprogram from a foreign language
      environment, pragma Convention should be specified both for the
      access-to-subprogram type and the specific subprogram(s) to which
      'Access is applied.

45    4  It is illegal to specify more than one of Import, Export, or
      Convention for a given entity.

46    5  The local_name in an interfacing pragma can denote more than one
      entity in the case of overloading. Such a pragma applies to all of the
      denoted entities.

47    6  See also 13.8, ``Machine Code Insertions''.

48    7  If both External_Name and Link_Name are specified for an Import or
      Export pragma, then the External_Name is ignored.

49    8  An interfacing pragma might result in an effect that violates Ada
      semantics.


                                  Examples

50    Example of interfacing pragmas:

51    package Fortran_Library is
        function Sqrt (X : Float) return Float;
        function Exp  (X : Float) return Float;
      private
        pragma Import(Fortran, Sqrt);
        pragma Import(Fortran, Exp);
      end Fortran_Library;


B.2 The Package Interfaces


1     Package Interfaces is the parent of several library packages that
declare types and other entities useful for interfacing to foreign languages.
It also contains some implementation-defined types that are useful across more
than one language (in particular for interfacing to assembly language).


                              Static Semantics

2     The library package Interfaces has the following skeletal declaration:

3     
      package Interfaces is
         pragma Pure(Interfaces);

4        type Integer_n is range -2**(n-1) .. 2**(n-1) - 1;  --2's complement

5        type Unsigned_n is mod 2**n;

6        function Shift_Left  (Value : Unsigned_n; Amount : Natural)
            return Unsigned_n;
         function Shift_Right (Value : Unsigned_n; Amount : Natural)
            return Unsigned_n;
         function Shift_Right_Arithmetic (Value : Unsigned_n; Amount : Natural)
            return Unsigned_n;
         function Rotate_Left  (Value : Unsigned_n; Amount : Natural)
            return Unsigned_n;
         function Rotate_Right (Value : Unsigned_n; Amount : Natural)
            return Unsigned_n;
         ...
      end Interfaces;


                         Implementation Requirements

7     An implementation shall provide the following declarations in the
visible part of package Interfaces:

8     Signed and modular integer types of n bits, if supported by the target
      architecture, for each n that is at least the size of a storage element
      and that is a factor of the word size. The names of these types are of
      the form Integer_n for the signed types, and Unsigned_n for the modular
      types;

9     For each such modular type in Interfaces, shifting and rotating
      subprograms as specified in the declaration of Interfaces above. These
      subprograms are Intrinsic. They operate on a bit-by-bit basis, using the
      binary representation of the value of the operands to yield a binary
      representation for the result. The Amount parameter gives the number of
      bits by which to shift or rotate. For shifting, zero bits are shifted
      in, except in the case of Shift_Right_Arithmetic, where one bits are
      shifted in if Value is at least half the modulus.

10    Floating point types corresponding to each floating point format fully
      supported by the hardware.


                         Implementation Permissions

11    An implementation may provide implementation-defined library units that
are children of Interfaces, and may add declarations to the visible part of
Interfaces in addition to the ones defined above.


                            Implementation Advice

12    For each implementation-defined convention identifier, there should be a
child package of package Interfaces with the corresponding name. This package
should contain any declarations that would be useful for interfacing to the
language (implementation) represented by the convention. Any declarations
useful for interfacing to any language on the given hardware architecture
should be provided directly in Interfaces.

13    An implementation supporting an interface to C, COBOL, or Fortran should
provide the corresponding package or packages described in the following
clauses.


B.3 Interfacing with C


1/1   The facilities relevant to interfacing with the C language are the
package Interfaces.C and its children; [and ]support for the Import, Export,
and Convention pragmas with convention_identifier C{; and support for the
Convention pragma with convention_identifier C_Pass_By_Copy}.

2     The package Interfaces.C contains the basic types, constants and
subprograms that allow an Ada program to pass scalars and strings to C
functions.


                              Static Semantics

3     The library package Interfaces.C has the following declaration:

4     package Interfaces.C is
         pragma Pure(C);

5        -- Declarations based on C's <limits.h>

6        CHAR_BIT  : constant := implementation-defined;  -- typically 8
         SCHAR_MIN : constant := implementation-defined;  -- typically -128
         SCHAR_MAX : constant := implementation-defined;  -- typically 127
         UCHAR_MAX : constant := implementation-defined;  -- typically 255

7        -- Signed and Unsigned Integers
         type int   is range implementation-defined;
         type short is range implementation-defined;
         type long  is range implementation-defined;

8        type signed_char is range SCHAR_MIN .. SCHAR_MAX;
         for signed_char'Size use CHAR_BIT;

9        type unsigned       is mod implementation-defined;
         type unsigned_short is mod implementation-defined;
         type unsigned_long  is mod implementation-defined;

10       type unsigned_char is mod (UCHAR_MAX+1);
         for unsigned_char'Size use CHAR_BIT;

11       subtype plain_char is implementation-defined;

12       type ptrdiff_t is range implementation-defined;

13       type size_t is mod implementation-defined;

14       -- Floating Point

15       type C_float     is digits implementation-defined;

16       type double      is digits implementation-defined;

17       type long_double is digits implementation-defined;

18       -- Characters and Strings 

19       type char is <implementation-defined character type>;

20/1     nul : constant char := {implementation-defined}[char'First];

21       function To_C   (Item : in Character) return char;

22       function To_Ada (Item : in char) return Character;

23       type char_array is array (size_t range <>) of aliased char;
         pragma Pack(char_array);
         for char_array'Component_Size use CHAR_BIT;

24       function Is_Nul_Terminated (Item : in char_array) return Boolean;

25       function To_C   (Item       : in String;
                          Append_Nul : in Boolean := True)
            return char_array;

26       function To_Ada (Item     : in char_array;
                          Trim_Nul : in Boolean := True)
            return String;

27       procedure To_C (Item       : in String;
                         Target     : out char_array;
                         Count      : out size_t;
                         Append_Nul : in Boolean := True);

28       procedure To_Ada (Item     : in char_array;
                           Target   : out String;
                           Count    : out Natural;
                           Trim_Nul : in Boolean := True);

29       -- Wide Character and Wide String

30/1     type wchar_t
       is {<implementation-defined character type>}[implementation-defined];

31/1     wide_nul
       : constant wchar_t := {implementation-defined}[wchar_t'First];

32       function To_C   (Item : in Wide_Character) return wchar_t;
         function To_Ada (Item : in wchar_t       ) return Wide_Character;

33       type wchar_array is array (size_t range <>) of aliased wchar_t;

34       pragma Pack(wchar_array);

35       function Is_Nul_Terminated (Item : in wchar_array) return Boolean;

36       function To_C   (Item       : in Wide_String;
                          Append_Nul : in Boolean := True)
            return wchar_array;

37       function To_Ada (Item     : in wchar_array;
                          Trim_Nul : in Boolean := True)
            return Wide_String;

38       procedure To_C (Item       : in  Wide_String;
                         Target     : out wchar_array;
                         Count      : out size_t;
                         Append_Nul : in  Boolean := True);

39       procedure To_Ada (Item     : in  wchar_array;
                           Target   : out Wide_String;
                           Count    : out Natural;
                           Trim_Nul : in  Boolean := True);

40       Terminator_Error : exception;

41    end Interfaces.C;

42    Each of the types declared in Interfaces.C is C-compatible.

43    The types int, short, long, unsigned, ptrdiff_t, size_t, double, char,
and wchar_t correspond respectively to the C types having the same names. The
types signed_char, unsigned_short, unsigned_long, unsigned_char, C_float, and
long_double correspond respectively to the C types signed char, unsigned
short, unsigned long, unsigned char, float, and long double.

44    The type of the subtype plain_char is either signed_char or
unsigned_char, depending on the C implementation.

45    function To_C   (Item : in Character) return char;
      function To_Ada (Item : in char     ) return Character;

    46    The functions To_C and To_Ada map between the Ada type Character and
          the C type char.

47    function Is_Nul_Terminated (Item : in char_array) return Boolean;

    48    The result of Is_Nul_Terminated is True if Item contains nul, and is
          False otherwise.

49    function To_C   (Item : in String;     Append_Nul : in Boolean := True)
         return char_array;
      
      function To_Ada (Item : in char_array; Trim_Nul   : in Boolean := True)
         return String;

    50    The result of To_C is a char_array value of length Item'Length (if
          Append_Nul is False) or Item'Length+1 (if Append_Nul is True). The
          lower bound is 0. For each component Item(I), the corresponding
          component in the result is To_C applied to Item(I). The value nul is
          appended if Append_Nul is True.

    51    The result of To_Ada is a String whose length is Item'Length (if
          Trim_Nul is False) or the length of the slice of Item preceding the
          first nul (if Trim_Nul is True). The lower bound of the result is 1.
          If Trim_Nul is False, then for each component Item(I) the
          corresponding component in the result is To_Ada applied to Item(I).
          If Trim_Nul is True, then for each component Item(I) before the
          first nul the corresponding component in the result is To_Ada
          applied to Item(I). The function propagates Terminator_Error if
          Trim_Nul is True and Item does not contain nul.

52    procedure To_C (Item       : in String;
                      Target     : out char_array;
                      Count      : out size_t;
                      Append_Nul : in Boolean := True);
      
      procedure To_Ada (Item     : in char_array;
                        Target   : out String;
                        Count    : out Natural;
                        Trim_Nul : in Boolean := True);

    53    For procedure To_C, each element of Item is converted (via the To_C
          function) to a char, which is assigned to the corresponding element
          of Target. If Append_Nul is True, nul is then assigned to the next
          element of Target. In either case, Count is set to the number of
          Target elements assigned. If Target is not long enough,
          Constraint_Error is propagated.

    54    For procedure To_Ada, each element of Item (if Trim_Nul is False) or
          each element of Item preceding the first nul (if Trim_Nul is True)
          is converted (via the To_Ada function) to a Character, which is
          assigned to the corresponding element of Target. Count is set to the
          number of Target elements assigned. If Target is not long enough,
          Constraint_Error is propagated. If Trim_Nul is True and Item does
          not contain nul, then Terminator_Error is propagated.

55    function Is_Nul_Terminated (Item : in wchar_array) return Boolean;

    56    The result of Is_Nul_Terminated is True if Item contains wide_nul,
          and is False otherwise.

57    function To_C   (Item : in Wide_Character) return wchar_t;
      function To_Ada (Item : in wchar_t       ) return Wide_Character;

    58    To_C and To_Ada provide the mappings between the Ada and C wide
          character types.

59    function To_C   (Item       : in Wide_String;
                       Append_Nul : in Boolean := True)
         return wchar_array;
      
      function To_Ada (Item     : in wchar_array;
                       Trim_Nul : in Boolean := True)
         return Wide_String;
      
      procedure To_C (Item       : in Wide_String;
                      Target     : out wchar_array;
                      Count      : out size_t;
                      Append_Nul : in Boolean := True);
      
      procedure To_Ada (Item     : in wchar_array;
                        Target   : out Wide_String;
                        Count    : out Natural;
                        Trim_Nul : in Boolean := True);

    60    The To_C and To_Ada subprograms that convert between Wide_String and
          wchar_array have analogous effects to the To_C and To_Ada
          subprograms that convert between String and char_array, except that
          wide_nul is used instead of nul.

60.1/1 {A Convention pragma with convention_identifier C_Pass_By_Copy shall
only be applied to a type.}

60.2/1 {The eligibility rules in B.1 do not apply to convention
C_Pass_By_Copy. Instead, a type T is eligible for convention C_Pass_By_Copy if
T is a record type that has no discriminants and that only has components with
statically constrained subtypes, and each component is C-compatible.}

60.3/1 {If a type is C_Pass_By_Copy-compatible then it is also C-compatible.}


                         Implementation Requirements

61/1  An implementation shall support pragma Convention with a C
convention_identifier for a C-eligible type (see B.1){. An implementation
shall support pragma Convention with a C_Pass_By_Copy convention_identifier
for a C_Pass_By_Copy-eligible type.}


                         Implementation Permissions

62    An implementation may provide additional declarations in the C interface
packages.


                            Implementation Advice

62.1/1 {The constants nul and wide_nul should have a representation of zero.}

63    An implementation should support the following interface correspondences
between Ada and C.

64    An Ada procedure corresponds to a void-returning C function.

65    An Ada function corresponds to a non-void C function.

66    An Ada in scalar parameter is passed as a scalar argument to a C
      function.

67    An Ada in parameter of an access-to-object type with designated type T
      is passed as a t* argument to a C function, where t is the C type
      corresponding to the Ada type T.

68    An Ada access T parameter, or an Ada out or in out parameter of an
      elementary type T, is passed as a t* argument to a C function, where t
      is the C type corresponding to the Ada type T. In the case of an
      elementary out or in out parameter, a pointer to a temporary copy is
      used to preserve by-copy semantics.

68.1/1 {An Ada parameter of a C_Pass_By_Copy-compatible (record) type T, of
      mode in, is passed as a t argument to a C function, where t is the C
      struct corresponding to the Ada type T.}

69/1  An Ada parameter of a record type T, of any mode, {other than an in
      parameter of a C_Pass_By_Copy-compatible type,} is passed as a t*
      argument to a C function, where t is the C struct corresponding to the
      Ada type T.

70    An Ada parameter of an array type with component type T, of any mode, is
      passed as a t* argument to a C function, where t is the C type
      corresponding to the Ada type T.

71    An Ada parameter of an access-to-subprogram type is passed as a pointer
      to a C function whose prototype corresponds to the designated
      subprogram's specification.

      NOTES

72    9  Values of type char_array are not implicitly terminated with nul. If
      a char_array is to be passed as a parameter to an imported C function
      requiring nul termination, it is the programmer's responsibility to
      obtain this effect.

73    10  To obtain the effect of C's sizeof(item_type), where Item_Type is
      the corresponding Ada type, evaluate the expression:
      size_t(Item_Type'Size/CHAR_BIT).

74    11  There is no explicit support for C's union types. Unchecked
      conversions can be used to obtain the effect of C unions.

75    12  A C function that takes a variable number of arguments can
      correspond to several Ada subprograms, taking various specific numbers
      and types of parameters.


                                  Examples

76    Example of using the Interfaces.C package:

77    --Calling the C Library Function strcpy
      with Interfaces.C;
      procedure Test is
         package C renames Interfaces.C;
         use type C.char_array;
         -- Call <string.h>strcpy:
         -- C definition of strcpy:  char *strcpy(char *s1, const char *s2);
         --    This function copies the string pointed to by s2 (including the terminating null character)
         --     into the array pointed to by s1. If copying takes place between objects that overlap, 
         --     the behavior is undefined. The strcpy function returns the value of s1.

78       -- Note: since the C function's return value is of no interest, the Ada interface is a procedure
         procedure Strcpy (Target : out C.char_array;
                           Source : in  C.char_array);

79       pragma Import(C, Strcpy, "strcpy");

80       Chars1 :  C.char_array(1..20);
         Chars2 :  C.char_array(1..20);

81    begin
         Chars2(1..6) := "qwert" & C.nul;

82       Strcpy(Chars1, Chars2);

83    -- Now Chars1(1..6) = "qwert" & C.Nul

84    end Test;


B.3.1 The Package Interfaces.C.Strings


1     The package Interfaces.C.Strings declares types and subprograms allowing
an Ada program to allocate, reference, update, and free C-style strings. In
particular, the private type chars_ptr corresponds to a common use of ``char
*'' in C programs, and an object of this type can be passed to a subprogram to
which pragma Import(C,...) has been applied, and for which ``char *'' is the
type of the argument of the C function.


                              Static Semantics

2     The library package Interfaces.C.Strings has the following declaration:

3     package Interfaces.C.Strings is
         pragma Preelaborate(Strings);

4        type char_array_access is access all char_array;

5        type chars_ptr is private;

6        type chars_ptr_array is array (size_t range <>) of chars_ptr;

7        Null_Ptr : constant chars_ptr;

8        function To_Chars_Ptr (Item      : in char_array_access;
                                Nul_Check : in Boolean := False)
            return chars_ptr;

9        function New_Char_Array (Chars   : in char_array) return chars_ptr;

10       function New_String (Str : in String) return chars_ptr;

11       procedure Free (Item : in out chars_ptr);

12       Dereference_Error : exception;

13       function Value (Item : in chars_ptr) return char_array;

14       function Value (Item : in chars_ptr; Length : in size_t)
            return char_array;

15       function Value (Item : in chars_ptr) return String;

16       function Value (Item : in chars_ptr; Length : in size_t)
            return String;

17       function Strlen (Item : in chars_ptr) return size_t;

18       procedure Update (Item   : in chars_ptr;
                           Offset : in size_t;
                           Chars  : in char_array;
                           Check  : in Boolean := True);

19       procedure Update (Item   : in chars_ptr;
                           Offset : in size_t;
                           Str    : in String;
                           Check  : in Boolean := True);

20       Update_Error : exception;

21    private
         ... -- not specified by the language
      end Interfaces.C.Strings;

22    The type chars_ptr is C-compatible and corresponds to the use of C's `
`char *'' for a pointer to the first char in a char array terminated by nul.
When an object of type chars_ptr is declared, its value is by default set to
Null_Ptr, unless the object is imported (see B.1).

23    function To_Chars_Ptr (Item      : in char_array_access;
                             Nul_Check : in Boolean := False)
         return chars_ptr;

    24/1  If Item is null, then To_Chars_Ptr returns Null_Ptr. {If Item is not
          null,}[Otherwise, if ]Nul_Check is True{,} and Item.all does not
          contain nul, then the function propagates Terminator_Error;
          {otherwise}[if Nul_Check is True and Item.all does contain nul,]
          To_Chars_Ptr performs a pointer conversion with no allocation of
          memory.

25    function New_Char_Array (Chars   : in char_array) return chars_ptr;

    26    This function returns a pointer to an allocated object initialized
          to Chars(Chars'First .. Index) & nul, where

        27    Index = Chars'Last if Chars does not contain nul, or

        28    Index is the smallest size_t value I such that Chars(I+1) = nul.

    28.1  []Storage_Error is propagated if the allocation fails.

29    function New_String (Str : in String) return chars_ptr;

    30    This function is equivalent to New_Char_Array(To_C(Str)).

31    procedure Free (Item : in out chars_ptr);

    32    If Item is Null_Ptr, then Free has no effect. Otherwise, Free
          releases the storage occupied by Value(Item), and resets Item to
          Null_Ptr.

33    function Value (Item : in chars_ptr) return char_array;

    34    If Item = Null_Ptr then Value propagates Dereference_Error.
          Otherwise Value returns the prefix of the array of chars pointed to
          by Item, up to and including the first nul. The lower bound of the
          result is 0. If Item does not point to a nul-terminated string, then
          execution of Value is erroneous.

35    function Value (Item : in chars_ptr; Length : in size_t)
         return char_array;

    36/1  If Item = Null_Ptr then Value[(Item)] propagates Dereference_Error.
          Otherwise Value returns the shorter of two arrays{, either}[:] the
          first Length chars pointed to by Item, {or}[and] Value(Item). The
          lower bound of the result is 0. {If Length is 0, then Value
          propagates Constraint_Error.}

37    function Value (Item : in chars_ptr) return String;

    38    Equivalent to To_Ada(Value(Item), Trim_Nul=>True).

39    function Value (Item : in chars_ptr; Length : in size_t)
         return String;

    40/1  Equivalent to To_Ada(Value(Item, Length){ & nul}, Trim_Nul=>True).

41    function Strlen (Item : in chars_ptr) return size_t;

    42    Returns Val'Length-1 where Val = Value(Item); propagates
          Dereference_Error if Item = Null_Ptr.

43    procedure Update (Item   : in chars_ptr;
                        Offset : in size_t;
                        Chars  : in char_array;
                        Check  : Boolean := True);

    44/1  {If Item = Null_Ptr, then Update propagates Dereference_Error.
          Otherwise, t}[T]his procedure updates the value pointed to by Item,
          starting at position Offset, using Chars as the data to be copied
          into the array. Overwriting the nul terminator, and skipping with
          the Offset past the nul terminator, are both prevented if Check is
          True, as follows:

        45    Let N = Strlen(Item). If Check is True, then:

            46    If Offset+Chars'Length>N, propagate Update_Error.

            47    Otherwise, overwrite the data in the array pointed to by
                  Item, starting at the char at position Offset, with the data
                  in Chars.

        48    If Check is False, then processing is as above, but with no
              check that Offset+Chars'Length>N.

49    procedure Update (Item   : in chars_ptr;
                        Offset : in size_t;
                        Str    : in String;
                        Check  : in Boolean := True);

    50    Equivalent to Update(Item, Offset, To_C(Str), Check).


                             Erroneous Execution

51    Execution of any of the following is erroneous if the Item parameter is
not null_ptr and Item does not point to a nul-terminated array of chars.

52    a Value function not taking a Length parameter,

53    the Free procedure,

54    the Strlen function.

55    Execution of Free(X) is also erroneous if the chars_ptr X was not
returned by New_Char_Array or New_String.

56    Reading or updating a freed char_array is erroneous.

57    Execution of Update is erroneous if Check is False and a call with Check
equal to True would have propagated Update_Error.

      NOTES

58    13  New_Char_Array and New_String might be implemented either through
      the allocation function from the C environment (``malloc'') or through
      Ada dynamic memory allocation (``new''). The key points are

    59    the returned value (a chars_ptr) is represented as a C ``char *'' so
          that it may be passed to C functions;

    60    the allocated object should be freed by the programmer via a call of
          Free, not by a called C function.


B.3.2 The Generic Package Interfaces.C.Pointers


1     The generic package Interfaces.C.Pointers allows the Ada programmer to
perform C-style operations on pointers. It includes an access type Pointer,
Value functions that dereference a Pointer and deliver the designated array,
several pointer arithmetic operations, and ``copy'' procedures that copy the
contents of a source pointer into the array designated by a destination
pointer. As in C, it treats an object Ptr of type Pointer as a pointer to the
first element of an array, so that for example, adding 1 to Ptr yields a
pointer to the second element of the array.

2     The generic allows two styles of usage: one in which the array is
terminated by a special terminator element; and another in which the
programmer needs to keep track of the length.


                              Static Semantics

3     The generic library package Interfaces.C.Pointers has the following
declaration:

4     generic
         type Index is (<>);
         type Element is private;
         type Element_Array is array (Index range <>) of aliased Element;
         Default_Terminator : Element;
      package Interfaces.C.Pointers is
         pragma Preelaborate(Pointers);

5        type Pointer is access all Element;

6        function Value(Ref        : in Pointer;
                        Terminator : in Element := Default_Terminator)
            return Element_Array;

7        function Value(Ref    : in Pointer;
                        Length : in ptrdiff_t)
            return Element_Array;

8        Pointer_Error : exception;

9        -- C-style Pointer arithmetic

10       function "+" (Left : in Pointer;   Right : in ptrdiff_t) return Pointer;
         function "+" (Left : in ptrdiff_t; Right : in Pointer)   return Pointer;
         function "-" (Left : in Pointer;   Right : in ptrdiff_t) return Pointer;
         function "-" (Left : in Pointer;   Right : in Pointer) return ptrdiff_t;

11       procedure Increment (Ref : in out Pointer);
         procedure Decrement (Ref : in out Pointer);

12       pragma Convention (Intrinsic, "+");
         pragma Convention (Intrinsic, "-");
         pragma Convention (Intrinsic, Increment);
         pragma Convention (Intrinsic, Decrement);

13       function Virtual_Length (Ref        : in Pointer;
                                  Terminator : in Element := Default_Terminator)
            return ptrdiff_t;

14       procedure Copy_Terminated_Array
            (Source     : in Pointer;
             Target     : in Pointer;
             Limit      : in ptrdiff_t := ptrdiff_t'Last;
             Terminator : in Element :=  Default_Terminator);

15       procedure Copy_Array (Source  : in Pointer;
                               Target  : in Pointer;
                               Length  : in ptrdiff_t);

16    end Interfaces.C.Pointers;

17    The type Pointer is C-compatible and corresponds to one use of C's ``
Element *''. An object of type Pointer is interpreted as a pointer to the
initial Element in an Element_Array. Two styles are supported:

18    Explicit termination of an array value with Default_Terminator (a
      special terminator value);

19    Programmer-managed length, with Default_Terminator treated simply as a
      data element.

20    function Value(Ref        : in Pointer;
                     Terminator : in Element := Default_Terminator)
         return Element_Array;

    21    This function returns an Element_Array whose value is the array
          pointed to by Ref, up to and including the first Terminator; the
          lower bound of the array is Index'First.
          Interfaces.C.Strings.Dereference_Error is propagated if Ref is null.

22    function Value(Ref    : in Pointer;
                     Length : in ptrdiff_t)
         return Element_Array;

    23    This function returns an Element_Array comprising the first Length
          elements pointed to by Ref. The exception
          Interfaces.C.Strings.Dereference_Error is propagated if Ref is null.

24    The "+" and "-" functions perform arithmetic on Pointer values, based on
the Size of the array elements. In each of these functions, Pointer_Error is
propagated if a Pointer parameter is null.

25    procedure Increment (Ref : in out Pointer);

    26    Equivalent to Ref := Ref+1.

27    procedure Decrement (Ref : in out Pointer);

    28    Equivalent to Ref := Ref-1.

29    function Virtual_Length (Ref        : in Pointer;
                               Terminator : in Element := Default_Terminator)
         return ptrdiff_t;

    30    Returns the number of Elements, up to the one just before the first
          Terminator, in Value(Ref, Terminator).

31    procedure Copy_Terminated_Array
         (Source     : in Pointer;
          Target     : in Pointer;
          Limit      : in ptrdiff_t := ptrdiff_t'Last;
          Terminator : in Element := Default_Terminator);

    32    This procedure copies Value(Source, Terminator) into the array
          pointed to by Target; it stops either after Terminator has been
          copied, or the number of elements copied is Limit, whichever occurs
          first. Dereference_Error is propagated if either Source or Target is
          null.

33    procedure Copy_Array (Source  : in Pointer;
                            Target  : in Pointer;
                            Length  : in ptrdiff_t);

    34    This procedure copies the first Length elements from the array
          pointed to by Source, into the array pointed to by Target.
          Dereference_Error is propagated if either Source or Target is null.


                             Erroneous Execution

35    It is erroneous to dereference a Pointer that does not designate an
aliased Element.

36    Execution of Value(Ref, Terminator) is erroneous if Ref does not
designate an aliased Element in an Element_Array terminated by Terminator.

37    Execution of Value(Ref, Length) is erroneous if Ref does not designate
an aliased Element in an Element_Array containing at least Length Elements
between the designated Element and the end of the array, inclusive.

38    Execution of Virtual_Length(Ref, Terminator) is erroneous if Ref does
not designate an aliased Element in an Element_Array terminated by Terminator.

39    Execution of Copy_Terminated_Array(Source, Target, Limit, Terminator) is
erroneous in either of the following situations:

40    Execution of both Value(Source,Terminator) and Value(Source,Limit) are
      erroneous, or

41    Copying writes past the end of the array containing the Element
      designated by Target.

42    Execution of Copy_Array(Source, Target, Length) is erroneous if either
Value(Source, Length) is erroneous, or copying writes past the end of the
array containing the Element designated by Target.

      NOTES

43    14  To compose a Pointer from an Element_Array, use 'Access on the first
      element. For example (assuming appropriate instantiations):

44    Some_Array   : Element_Array(0..5) ;
      Some_Pointer : Pointer := Some_Array(0)'Access;


                                  Examples

45    Example of Interfaces.C.Pointers:

46    with Interfaces.C.Pointers;
      with Interfaces.C.Strings;
      procedure Test_Pointers is
         package C renames Interfaces.C;
         package Char_Ptrs is
            new C.Pointers (Index              => C.size_t,
                            Element            => C.char,
                            Element_Array      => C.char_array,
                            Default_Terminator => C.nul);

47       use type Char_Ptrs.Pointer;
         subtype Char_Star is Char_Ptrs.Pointer;

48       procedure Strcpy (Target_Ptr, Source_Ptr : Char_Star) is
            Target_Temp_Ptr : Char_Star := Target_Ptr;
            Source_Temp_Ptr : Char_Star := Source_Ptr;
            Element : C.char;
         begin
            if Target_Temp_Ptr = null or Source_Temp_Ptr = null then
               raise C.Strings.Dereference_Error;
            end if;

49/1        loop
               Element             := Source_Temp_Ptr.all;
               Target_Temp_Ptr.all := Element;
               exit when {C."="(Element, C.nul)}[Element = C.nul];
               Char_Ptrs.Increment(Target_Temp_Ptr);
               Char_Ptrs.Increment(Source_Temp_Ptr);
            end loop;
         end Strcpy;
      begin
         ...
      end Test_Pointers;


B.4 Interfacing with COBOL


1     The facilities relevant to interfacing with the COBOL language are the
package Interfaces.COBOL and support for the Import, Export and Convention
pragmas with convention_identifier COBOL.

2     The COBOL interface package supplies several sets of facilities:

3     A set of types corresponding to the native COBOL types of the supported
      COBOL implementation (so-called ``internal COBOL representations''),
      allowing Ada data to be passed as parameters to COBOL programs

4     A set of types and constants reflecting external data representations
      such as might be found in files or databases, allowing COBOL-generated
      data to be read by an Ada program, and Ada-generated data to be read by
      COBOL programs

5     A generic package for converting between an Ada decimal type value and
      either an internal or external COBOL representation


                              Static Semantics

6     The library package Interfaces.COBOL has the following declaration:

7     package Interfaces.COBOL is
         pragma Preelaborate(COBOL);

8     -- Types and operations for internal data representations

9        type Floating      is digits implementation-defined;
         type Long_Floating is digits implementation-defined;

10       type Binary      is range implementation-defined;
         type Long_Binary is range implementation-defined;

11       Max_Digits_Binary      : constant := implementation-defined;
         Max_Digits_Long_Binary : constant := implementation-defined;

12       type Decimal_Element  is mod implementation-defined;
         type Packed_Decimal is array (Positive range <>) of Decimal_Element;
         pragma Pack(Packed_Decimal);

13       type COBOL_Character is implementation-defined character type;

14       Ada_To_COBOL
       : array (Character) of COBOL_Character := implementation-defined;

15       COBOL_To_Ada
       : array (COBOL_Character) of Character := implementation-defined;

16       type Alphanumeric is array (Positive range <>) of COBOL_Character;
         pragma Pack(Alphanumeric);

17       function To_COBOL (Item : in String) return Alphanumeric;
         function To_Ada   (Item : in Alphanumeric) return String;

18       procedure To_COBOL (Item       : in String;
                             Target     : out Alphanumeric;
                             Last       : out Natural);

19       procedure To_Ada (Item     : in Alphanumeric;
                           Target   : out String;
                           Last     : out Natural);

20       type Numeric is array (Positive range <>) of COBOL_Character;
         pragma Pack(Numeric);

21    -- Formats for COBOL data representations

22       type Display_Format is private;

23       Unsigned             : constant Display_Format;
         Leading_Separate     : constant Display_Format;
         Trailing_Separate    : constant Display_Format;
         Leading_Nonseparate  : constant Display_Format;
         Trailing_Nonseparate : constant Display_Format;

24       type Binary_Format is private;

25       High_Order_First  : constant Binary_Format;
         Low_Order_First   : constant Binary_Format;
         Native_Binary     : constant Binary_Format;

26       type Packed_Format is private;

27       Packed_Unsigned   : constant Packed_Format;
         Packed_Signed     : constant Packed_Format;

28    -- Types for external representation of COBOL binary data

29       type Byte is mod 2**COBOL_Character'Size;
         type Byte_Array is array (Positive range <>) of Byte;
         pragma Pack (Byte_Array);

30       Conversion_Error : exception;

31       generic
            type Num is delta <> digits <>;
         package Decimal_Conversions is

32          -- Display Formats: data values are represented as Numeric

33          function Valid (Item   : in Numeric;
                            Format : in Display_Format) return Boolean;

34          function Length (Format : in Display_Format) return Natural;

35          function To_Decimal (Item   : in Numeric;
                                 Format : in Display_Format) return Num;

36          function To_Display (Item   : in Num;
                                 Format : in Display_Format) return Numeric;

37          -- Packed Formats: data values are represented as Packed_Decimal

38          function Valid (Item   : in Packed_Decimal;
                            Format : in Packed_Format) return Boolean;

39          function Length (Format : in Packed_Format) return Natural;

40          function To_Decimal (Item   : in Packed_Decimal;
                                 Format : in Packed_Format) return Num;

41          function To_Packed (Item   : in Num;
                                Format : in Packed_Format) return Packed_Decimal;

42          -- Binary Formats: external data values are represented as Byte_Array

43          function Valid (Item   : in Byte_Array;
                            Format : in Binary_Format) return Boolean;

44          function Length (Format : in Binary_Format) return Natural;
            function To_Decimal (Item   : in Byte_Array;
                                 Format : in Binary_Format) return Num;

45          function To_Binary (Item   : in Num;
                              Format : in Binary_Format) return Byte_Array;

46          -- Internal Binary formats: data values are of type Binary or Long_Binary

47          function To_Decimal (Item : in Binary)      return Num;
            function To_Decimal (Item : in Long_Binary) return Num;

48          function To_Binary      (Item : in Num)  return Binary;
            function To_Long_Binary (Item : in Num)  return Long_Binary;

49       end Decimal_Conversions;

50    private
         ... -- not specified by the language
      end Interfaces.COBOL;

51    Each of the types in Interfaces.COBOL is COBOL-compatible.

52    The types Floating and Long_Floating correspond to the native types in
COBOL for data items with computational usage implemented by floating point.
The types Binary and Long_Binary correspond to the native types in COBOL for
data items with binary usage, or with computational usage implemented by
binary.

53    Max_Digits_Binary is the largest number of decimal digits in a numeric
value that is represented as Binary. Max_Digits_Long_Binary is the largest
number of decimal digits in a numeric value that is represented as Long_Binary.

54    The type Packed_Decimal corresponds to COBOL's packed-decimal usage.

55    The type COBOL_Character defines the run-time character set used in the
COBOL implementation. Ada_To_COBOL and COBOL_To_Ada are the mappings between
the Ada and COBOL run-time character sets.

56    Type Alphanumeric corresponds to COBOL's alphanumeric data category.

57    Each of the functions To_COBOL and To_Ada converts its parameter based
on the mappings Ada_To_COBOL and COBOL_To_Ada, respectively. The length of the
result for each is the length of the parameter, and the lower bound of the
result is 1. Each component of the result is obtained by applying the relevant
mapping to the corresponding component of the parameter.

58    Each of the procedures To_COBOL and To_Ada copies converted elements
from Item to Target, using the appropriate mapping (Ada_To_COBOL or
COBOL_To_Ada, respectively). The index in Target of the last element assigned
is returned in Last (0 if Item is a null array). If Item'Length exceeds
Target'Length, Constraint_Error is propagated.

59    Type Numeric corresponds to COBOL's numeric data category with display
usage.

60    The types Display_Format, Binary_Format, and Packed_Format are used in
conversions between Ada decimal type values and COBOL internal or external
data representations. The value of the constant Native_Binary is either
High_Order_First or Low_Order_First, depending on the implementation.

61    function Valid (Item   : in Numeric;
                      Format : in Display_Format) return Boolean;

    62    The function Valid checks that the Item parameter has a value
          consistent with the value of Format. If the value of Format is other
          than Unsigned, Leading_Separate, and Trailing_Separate, the effect
          is implementation defined. If Format does have one of these values,
          the following rules apply:

        63/1  Format=Unsigned: if Item comprises [zero or more leading space
              characters followed by ]one or more decimal digit characters
              then Valid returns True, else it returns False.

        64/1  Format=Leading_Separate: if Item comprises [zero or more leading
              space characters, followed by ]a single occurrence of the plus
              or minus sign character, and then one or more decimal digit
              characters, then Valid returns True, else it returns False.

        65/1  Format=Trailing_Separate: if Item comprises [zero or more
              leading space characters, followed by ]one or more decimal digit
              characters and finally a plus or minus sign character, then
              Valid returns True, else it returns False.

66    function Length (Format : in Display_Format) return Natural;

    67    The Length function returns the minimal length of a Numeric value
          sufficient to hold any value of type Num when represented as Format.

68    function To_Decimal (Item   : in Numeric;
                           Format : in Display_Format) return Num;

    69    Produces a value of type Num corresponding to Item as represented by
          Format. The number of digits after the assumed radix point in Item
          is Num'Scale. Conversion_Error is propagated if the value
          represented by Item is outside the range of Num.

70    function To_Display (Item   : in Num;
                           Format : in Display_Format) return Numeric;

    71/1  This function returns the Numeric value for Item, represented in
          accordance with Format. {The length of the returned value is
          Length(Format), and the lower bound is 1. }Conversion_Error is
          propagated if Num is negative and Format is Unsigned.

72    function Valid (Item   : in Packed_Decimal;
                      Format : in Packed_Format) return Boolean;

    73    This function returns True if Item has a value consistent with
          Format, and False otherwise. The rules for the formation of
          Packed_Decimal values are implementation defined.

74    function Length (Format : in Packed_Format) return Natural;

    75    This function returns the minimal length of a Packed_Decimal value
          sufficient to hold any value of type Num when represented as Format.

76    function To_Decimal (Item   : in Packed_Decimal;
                           Format : in Packed_Format) return Num;

    77    Produces a value of type Num corresponding to Item as represented by
          Format. Num'Scale is the number of digits after the assumed radix
          point in Item. Conversion_Error is propagated if the value
          represented by Item is outside the range of Num.

78    function To_Packed (Item   : in Num;
                          Format : in Packed_Format) return Packed_Decimal;

    79/1  This function returns the Packed_Decimal value for Item, represented
          in accordance with Format. {The length of the returned value is
          Length(Format), and the lower bound is 1. }Conversion_Error is
          propagated if Num is negative and Format is Packed_Unsigned.

80    function Valid (Item   : in Byte_Array;
                      Format : in Binary_Format) return Boolean;

    81    This function returns True if Item has a value consistent with
          Format, and False otherwise.

82    function Length (Format : in Binary_Format) return Natural;

    83    This function returns the minimal length of a Byte_Array value
          sufficient to hold any value of type Num when represented as Format.

84    function To_Decimal (Item   : in Byte_Array;
                           Format : in Binary_Format) return Num;

    85    Produces a value of type Num corresponding to Item as represented by
          Format. Num'Scale is the number of digits after the assumed radix
          point in Item. Conversion_Error is propagated if the value
          represented by Item is outside the range of Num.

86    function To_Binary (Item   : in Num;
                          Format : in Binary_Format) return Byte_Array;

    87/1  This function returns the Byte_Array value for Item, represented in
          accordance with Format. {The length of the returned value is
          Length(Format), and the lower bound is 1.}

88    function To_Decimal (Item : in Binary)      return Num;
      
      function To_Decimal (Item : in Long_Binary) return Num;

    89    These functions convert from COBOL binary format to a corresponding
          value of the decimal type Num. Conversion_Error is propagated if
          Item is too large for Num.

90    function To_Binary      (Item : in Num)  return Binary;
      
      function To_Long_Binary (Item : in Num)  return Long_Binary;

    91    These functions convert from Ada decimal to COBOL binary format.
          Conversion_Error is propagated if the value of Item is too large to
          be represented in the result type.


                         Implementation Requirements

92    An implementation shall support pragma Convention with a COBOL
convention_identifier for a COBOL-eligible type (see B.1).


                         Implementation Permissions

93    An implementation may provide additional constants of the private types
Display_Format, Binary_Format, or Packed_Format.

94    An implementation may provide further floating point and integer types
in Interfaces.COBOL to match additional native COBOL types, and may also
supply corresponding conversion functions in the generic package
Decimal_Conversions.


                            Implementation Advice

95    An Ada implementation should support the following interface
correspondences between Ada and COBOL.

96    An Ada access T parameter is passed as a ``BY REFERENCE'' data item of
      the COBOL type corresponding to T.

97    An Ada in scalar parameter is passed as a ``BY CONTENT'' data item of
      the corresponding COBOL type.

98    Any other Ada parameter is passed as a ``BY REFERENCE'' data item of the
      COBOL type corresponding to the Ada parameter type; for scalars, a local
      copy is used if necessary to ensure by-copy semantics.

      NOTES

99    15  An implementation is not required to support pragma Convention for
      access types, nor is it required to support pragma Import, Export or
      Convention for functions.

100   16  If an Ada subprogram is exported to COBOL, then a call from COBOL
      call may specify either ``BY CONTENT'' or ``BY REFERENCE''.


                                  Examples

101   Examples of Interfaces.COBOL:

102   with Interfaces.COBOL;
      procedure Test_Call is

103      -- Calling a foreign COBOL program
         -- Assume that a COBOL program PROG has the following declaration
         --  in its LINKAGE section:
         --  01 Parameter-Area
         --     05 NAME   PIC X(20).
         --     05 SSN    PIC X(9).
         --     05 SALARY PIC 99999V99 USAGE COMP.
         -- The effect of PROG is to update SALARY based on some algorithm

104      package COBOL renames Interfaces.COBOL;

105      type Salary_Type is delta 0.01 digits 7;

106      type COBOL_Record is
            record
               Name   : COBOL.Numeric(1..20);
               SSN    : COBOL.Numeric(1..9);
               Salary : COBOL.Binary;  -- Assume Binary = 32 bits
            end record;
         pragma Convention (COBOL, COBOL_Record);

107      procedure Prog (Item : in out COBOL_Record);
         pragma Import (COBOL, Prog, "PROG");

108      package Salary_Conversions is
            new COBOL.Decimal_Conversions(Salary_Type);

109      Some_Salary : Salary_Type := 12_345.67;
         Some_Record : COBOL_Record :=
            (Name   => "Johnson, John       ",
             SSN    => "111223333",
             Salary => Salary_Conversions.To_Binary(Some_Salary));

110   begin
         Prog (Some_Record);
         ...
      end Test_Call;

111   with Interfaces.COBOL;
      with COBOL_Sequential_IO; -- Assumed to be supplied by implementation
      procedure Test_External_Formats is

112      -- Using data created by a COBOL program
         -- Assume that a COBOL program has created a sequential file with
         --  the following record structure, and that we need to
         --  process the records in an Ada program
         --  01 EMPLOYEE-RECORD
         --     05 NAME    PIC X(20).
         --     05 SSN     PIC X(9).
         --     05 SALARY  PIC 99999V99 USAGE COMP.
         --     05 ADJUST  PIC S999V999 SIGN LEADING SEPARATE.
         -- The COMP data is binary (32 bits), high-order byte first

113      package COBOL renames Interfaces.COBOL;

114      type Salary_Type      is delta 0.01  digits 7;
         type Adjustments_Type is delta 0.001 digits 6;

115      type COBOL_Employee_Record_Type is  -- External representation
            record
               Name    : COBOL.Alphanumeric(1..20);
               SSN     : COBOL.Alphanumeric(1..9);
               Salary  : COBOL.Byte_Array(1..4);
               Adjust  : COBOL.Numeric(1..7);  -- Sign and 6 digits
            end record;
         pragma Convention (COBOL, COBOL_Employee_Record_Type);

116      package COBOL_Employee_IO is
            new COBOL_Sequential_IO(COBOL_Employee_Record_Type);
         use COBOL_Employee_IO;

117      COBOL_File : File_Type;

118      type Ada_Employee_Record_Type is  -- Internal representation
            record
               Name    : String(1..20);
               SSN     : String(1..9);
               Salary  : Salary_Type;
               Adjust  : Adjustments_Type;
            end record;

119      COBOL_Record : COBOL_Employee_Record_Type;
         Ada_Record   : Ada_Employee_Record_Type;

120      package Salary_Conversions is
            new COBOL.Decimal_Conversions(Salary_Type);
         use Salary_Conversions;

121      package Adjustments_Conversions is
            new COBOL.Decimal_Conversions(Adjustments_Type);
         use Adjustments_Conversions;

122   begin
         Open (COBOL_File, Name => "Some_File");

123      loop
           Read (COBOL_File, COBOL_Record);

124        Ada_Record.Name := To_Ada(COBOL_Record.Name);
           Ada_Record.SSN  := To_Ada(COBOL_Record.SSN);
           Ada_Record.Salary :=
              To_Decimal(COBOL_Record.Salary, COBOL.High_Order_First);
           Ada_Record.Adjust :=
              To_Decimal(COBOL_Record.Adjust, COBOL.Leading_Separate);
           ... -- Process Ada_Record
         end loop;
      exception
         when End_Error => ...
      end Test_External_Formats;


B.5 Interfacing with Fortran


1     The facilities relevant to interfacing with the Fortran language are the
package Interfaces.Fortran and support for the Import, Export and Convention
pragmas with convention_identifier Fortran.

2     The package Interfaces.Fortran defines Ada types whose representations
are identical to the default representations of the Fortran intrinsic types
Integer, Real, Double Precision, Complex, Logical, and Character in a
supported Fortran implementation. These Ada types can therefore be used to
pass objects between Ada and Fortran programs.


                              Static Semantics

3     The library package Interfaces.Fortran has the following declaration:

4     with Ada.Numerics.Generic_Complex_Types;  -- see G.1.1
      pragma Elaborate_All(Ada.Numerics.Generic_Complex_Types);
      package Interfaces.Fortran is
         pragma Pure(Fortran);

5        type Fortran_Integer is range implementation-defined;

6        type Real             is digits implementation-defined;
         type Double_Precision is digits implementation-defined;

7        type Logical is new Boolean;

8        package Single_Precision_Complex_Types is
            new Ada.Numerics.Generic_Complex_Types (Real);

9        type Complex is new Single_Precision_Complex_Types.Complex;

10       subtype Imaginary is Single_Precision_Complex_Types.Imaginary;
         i : Imaginary renames Single_Precision_Complex_Types.i;
         j : Imaginary renames Single_Precision_Complex_Types.j;

11       type Character_Set is implementation-defined character type;

12       type Fortran_Character is array (Positive range <>) of Character_Set;
         pragma Pack (Fortran_Character);

13       function To_Fortran (Item : in Character) return Character_Set;
         function To_Ada (Item : in Character_Set) return Character;

14       function To_Fortran (Item : in String) return Fortran_Character;
         function To_Ada     (Item : in Fortran_Character) return String;

15       procedure To_Fortran (Item       : in String;
                               Target     : out Fortran_Character;
                               Last       : out Natural);

16       procedure To_Ada (Item     : in Fortran_Character;
                           Target   : out String;
                           Last     : out Natural);

17    end Interfaces.Fortran;

18    The types Fortran_Integer, Real, Double_Precision, Logical, Complex, and
Fortran_Character are Fortran-compatible.

19    The To_Fortran and To_Ada functions map between the Ada type Character
and the Fortran type Character_Set, and also between the Ada type String and
the Fortran type Fortran_Character. The To_Fortran and To_Ada procedures have
analogous effects to the string conversion subprograms found in
Interfaces.COBOL.


                         Implementation Requirements

20    An implementation shall support pragma Convention with a Fortran
convention_identifier for a Fortran-eligible type (see B.1).


                         Implementation Permissions

21    An implementation may add additional declarations to the Fortran
interface packages. For example, the Fortran interface package for an
implementation of Fortran 77 (ANSI X3.9-1978) that defines types like
Integer*n, Real*n, Logical*n, and Complex*n may contain the declarations of
types named Integer_Star_n, Real_Star_n, Logical_Star_n, and Complex_Star_n.
(This convention should not apply to Character*n, for which the Ada analog is
the constrained array subtype Fortran_Character (1..n).) Similarly, the
Fortran interface package for an implementation of Fortran 90 that provides
multiple kinds of intrinsic types, e.g. Integer (Kind=n), Real (Kind=n),
Logical (Kind=n), Complex (Kind=n), and Character (Kind=n), may contain the
declarations of types with the recommended names Integer_Kind_n, Real_Kind_n,
Logical_Kind_n, Complex_Kind_n, and Character_Kind_n.


                            Implementation Advice

22    An Ada implementation should support the following interface
correspondences between Ada and Fortran:

23    An Ada procedure corresponds to a Fortran subroutine.

24    An Ada function corresponds to a Fortran function.

25    An Ada parameter of an elementary, array, or record type T is passed as
      a T(F) argument to a Fortran procedure, where T(F) is the Fortran type
      corresponding to the Ada type T, and where the INTENT attribute of the
      corresponding dummy argument matches the Ada formal parameter mode; the
      Fortran implementation's parameter passing conventions are used. For
      elementary types, a local copy is used if necessary to ensure by-copy
      semantics.

26    An Ada parameter of an access-to-subprogram type is passed as a
      reference to a Fortran procedure whose interface corresponds to the
      designated subprogram's specification.

      NOTES

27    17  An object of a Fortran-compatible record type, declared in a library
      package or subprogram, can correspond to a Fortran common block; the
      type also corresponds to a Fortran ``derived type''.


                                  Examples

28    Example of Interfaces.Fortran:

29    with Interfaces.Fortran;
      use Interfaces.Fortran;
      procedure Ada_Application is

30       type Fortran_Matrix is array (Integer range <>,
                                       Integer range <>) of Double_Precision;
         pragma Convention (Fortran, Fortran_Matrix);    -- stored in Fortran's
                                                         -- column-major order
         procedure Invert (Rank : in Fortran_Integer; X : in out Fortran_Matrix);
         pragma Import (Fortran, Invert);                -- a Fortran subroutine

31       Rank      : constant Fortran_Integer := 100;
         My_Matrix : Fortran_Matrix (1 .. Rank, 1 .. Rank);

32    begin

33       ...
         My_Matrix := ...;
         ...
         Invert (Rank, My_Matrix);
         ...

34    end Ada_Application;



                                   Annex C
                                 (normative)

                             Systems Programming


1     The Systems Programming Annex specifies additional capabilities provided
for low-level programming. These capabilities are also required in many
real-time, embedded, distributed, and information systems.


C.1 Access to Machine Operations


1     This clause specifies rules regarding access to machine instructions
from within an Ada program.


                         Implementation Requirements

2     The implementation shall support machine code insertions (see 13.8) or
intrinsic subprograms (see 6.3.1) (or both). Implementation-defined attributes
shall be provided to allow the use of Ada entities as operands.


                            Implementation Advice

3     The machine code or intrinsics support should allow access to all
operations normally available to assembly language programmers for the target
environment, including privileged instructions, if any.

4     The interfacing pragmas (see Annex B) should support interface to
assembler; the default assembler should be associated with the convention
identifier Assembler.

5     If an entity is exported to assembly language, then the implementation
should allocate it at an addressable location, and should ensure that it is
retained by the linking process, even if not otherwise referenced from the Ada
code. The implementation should assume that any call to a machine code or
assembler subprogram is allowed to read or update every object that is
specified as exported.


                         Documentation Requirements

6     The implementation shall document the overhead associated with calling
machine-code or intrinsic subprograms, as compared to a fully-inlined call,
and to a regular out-of-line call.

7     The implementation shall document the types of the package
System.Machine_Code usable for machine code insertions, and the attributes to
be used in machine code insertions for references to Ada entities.

8     The implementation shall document the subprogram calling conventions
associated with the convention identifiers available for use with the
interfacing pragmas (Ada and Assembler, at a minimum), including register
saving, exception propagation, parameter passing, and function value returning.

9     For exported and imported subprograms, the implementation shall document
the mapping between the Link_Name string, if specified, or the Ada designator,
if not, and the external link name used for such a subprogram.


                            Implementation Advice

10    The implementation should ensure that little or no overhead is
associated with calling intrinsic and machine-code subprograms.

11    It is recommended that intrinsic subprograms be provided for convenient
access to any machine operations that provide special capabilities or
efficiency and that are not otherwise available through the language
constructs. Examples of such instructions include:

12    Atomic read-modify-write operations - e.g., test and set, compare and
      swap, decrement and test, enqueue/dequeue.

13    Standard numeric functions - e.g., sin, log.

14    String manipulation operations - e.g., translate and test.

15    Vector operations - e.g., compare vector against thresholds.

16    Direct operations on I/O ports.


C.2 Required Representation Support


1     This clause specifies minimal requirements on the implementation's
support for representation items and related features.


                         Implementation Requirements

2     The implementation shall support at least the functionality defined by
the recommended levels of support in Section 13.


C.3 Interrupt Support


1     This clause specifies the language-defined model for hardware interrupts
in addition to mechanisms for handling interrupts.


                              Dynamic Semantics

2     An interrupt represents a class of events that are detected by the
hardware or the system software. Interrupts are said to occur. An occurrence
of an interrupt is separable into generation and delivery. Generation of an
interrupt is the event in the underlying hardware or system that makes the
interrupt available to the program. Delivery is the action that invokes part
of the program as response to the interrupt occurrence. Between generation and
delivery, the interrupt occurrence (or interrupt) is pending. Some or all
interrupts may be blocked. When an interrupt is blocked, all occurrences of
that interrupt are prevented from being delivered. Certain interrupts are
reserved. The set of reserved interrupts is implementation defined. A reserved
interrupt is either an interrupt for which user-defined handlers are not
supported, or one which already has an attached handler by some other
implementation-defined means. Program units can be connected to non-reserved
interrupts. While connected, the program unit is said to be attached to that
interrupt. The execution of that program unit, the interrupt handler, is
invoked upon delivery of the interrupt occurrence.

3     While a handler is attached to an interrupt, it is called once for each
delivered occurrence of that interrupt. While the handler executes, the
corresponding interrupt is blocked.

4     While an interrupt is blocked, all occurrences of that interrupt are
prevented from being delivered. Whether such occurrences remain pending or are
lost is implementation defined.

5     Each interrupt has a default treatment which determines the system's
response to an occurrence of that interrupt when no user-defined handler is
attached. The set of possible default treatments is implementation defined, as
is the method (if one exists) for configuring the default treatments for
interrupts.

6     An interrupt is delivered to the handler (or default treatment) that is
in effect for that interrupt at the time of delivery.

7     An exception propagated from a handler that is invoked by an interrupt
has no effect.

8     If the Ceiling_Locking policy (see D.3) is in effect, the interrupt
handler executes with the active priority that is the ceiling priority of the
corresponding protected object.


                         Implementation Requirements

9     The implementation shall provide a mechanism to determine the minimum
stack space that is needed for each interrupt handler and to reserve that
space for the execution of the handler. This space should accommodate nested
invocations of the handler where the system permits this.

10    If the hardware or the underlying system holds pending interrupt
occurrences, the implementation shall provide for later delivery of these
occurrences to the program.

11    If the Ceiling_Locking policy is not in effect, the implementation shall
provide means for the application to specify whether interrupts are to be
blocked during protected actions.


                         Documentation Requirements

12    The implementation shall document the following items:

13    1.  For each interrupt, which interrupts are blocked from delivery when
          a handler attached to that interrupt executes (either as a result of
          an interrupt delivery or of an ordinary call on a procedure of the
          corresponding protected object).

14    2.  Any interrupts that cannot be blocked, and the effect of attaching
          handlers to such interrupts, if this is permitted.

15    3.  Which run-time stack an interrupt handler uses when it executes as a
          result of an interrupt delivery; if this is configurable, what is
          the mechanism to do so; how to specify how much space to reserve on
          that stack.

16    4.  Any implementation- or hardware-specific activity that happens
          before a user-defined interrupt handler gets control (e.g., reading
          device registers, acknowledging devices).

17    5.  Any timing or other limitations imposed on the execution of
          interrupt handlers.

18    6.  The state (blocked/unblocked) of the non-reserved interrupts when
          the program starts; if some interrupts are unblocked, what is the
          mechanism a program can use to protect itself before it can attach
          the corresponding handlers.

19    7.  Whether the interrupted task is allowed to resume execution before
          the interrupt handler returns.

20    8.  The treatment of interrupt occurrences that are generated while the
          interrupt is blocked; i.e., whether one or more occurrences are held
          for later delivery, or all are lost.

21    9.  Whether predefined or implementation-defined exceptions are raised
          as a result of the occurrence of any interrupt, and the mapping
          between the machine interrupts (or traps) and the predefined
          exceptions.

22    10. On a multi-processor, the rules governing the delivery of an
          interrupt to a particular processor.


                         Implementation Permissions

23    If the underlying system or hardware does not allow interrupts to be
blocked, then no blocking is required as part of the execution of subprograms
of a protected object whose one of its subprograms is an interrupt handler.

24    In a multi-processor with more than one interrupt subsystem, it is
implementation defined whether (and how) interrupt sources from separate
subsystems share the same Interrupt_ID type (see C.3.2). In particular, the
meaning of a blocked or pending interrupt may then be applicable to one
processor only.

25    Implementations are allowed to impose timing or other limitations on the
execution of interrupt handlers.

26    Other forms of handlers are allowed to be supported, in which case, the
rules of this subclause should be adhered to.

27    The active priority of the execution of an interrupt handler is allowed
to vary from one occurrence of the same interrupt to another.


                            Implementation Advice

28    If the Ceiling_Locking policy is not in effect, the implementation
should provide means for the application to specify which interrupts are to be
blocked during protected actions, if the underlying system allows for a
finer-grain control of interrupt blocking.

      NOTES

29    1  The default treatment for an interrupt can be to keep the interrupt
      pending or to deliver it to an implementation-defined handler. Examples
      of actions that an implementation-defined handler is allowed to perform
      include aborting the partition, ignoring (i.e., discarding occurrences
      of) the interrupt, or queuing one or more occurrences of the interrupt
      for possible later delivery when a user-defined handler is attached to
      that interrupt.

30    2  It is a bounded error to call Task_Identification.Current_Task (see
      C.7.1) from an interrupt handler.

31    3  The rule that an exception propagated from an interrupt handler has
      no effect is modeled after the rule about exceptions propagated out of
      task bodies.


C.3.1 Protected Procedure Handlers



                                   Syntax

1     The form of a pragma Interrupt_Handler is as follows:

2       pragma Interrupt_Handler(handler_name);

3     The form of a pragma Attach_Handler is as follows:

4       pragma Attach_Handler(handler_name, expression);


                            Name Resolution Rules

5     For the Interrupt_Handler and Attach_Handler pragmas, the handler_name
shall resolve to denote a protected procedure with a parameterless profile.

6     For the Attach_Handler pragma, the expected type for the expression is
Interrupts.Interrupt_ID (see C.3.2).


                               Legality Rules

7     The Attach_Handler pragma is only allowed immediately within the
protected_definition where the corresponding subprogram is declared. The
corresponding protected_type_declaration or single_protected_declaration shall
be a library level declaration.

8     The Interrupt_Handler pragma is only allowed immediately within a
protected_definition. The corresponding protected_type_declaration shall be a
library level declaration. In addition, any object_declaration of such a type
shall be a library level declaration.


                              Dynamic Semantics

9     If the pragma Interrupt_Handler appears in a protected_definition, then
the corresponding procedure can be attached dynamically, as a handler, to
interrupts (see C.3.2). Such procedures are allowed to be attached to multiple
interrupts.

10    The expression in the Attach_Handler pragma as evaluated at object
creation time specifies an interrupt. As part of the initialization of that
object, if the Attach_Handler pragma is specified, the handler procedure is
attached to the specified interrupt. A check is made that the corresponding
interrupt is not reserved. Program_Error is raised if the check fails, and the
existing treatment for the interrupt is not affected.

11    If the Ceiling_Locking policy (see D.3) is in effect then upon the
initialization of a protected object that either an Attach_Handler or
Interrupt_Handler pragma applies to one of its procedures, a check is made
that the ceiling priority defined in the protected_definition is in the range
of System.Interrupt_Priority. If the check fails, Program_Error is raised.

12/1  When a protected object is finalized, for any of its procedures that are
attached to interrupts, the handler is detached. If the handler was attached
by a procedure in the Interrupts package or if no user handler was previously
attached to the interrupt, the default treatment is restored. {If an Attach_-
Handler pragma was used and the most recently attached handler for the same
interrupt is the same as the one that was attached at the time the protected
object was initialized}[Otherwise, that is, if an Attach_Handler pragma was
used], the previous handler is restored.

13    When a handler is attached to an interrupt, the interrupt is blocked
(subject to the Implementation Permission in C.3) during the execution of
every protected action on the protected object containing the handler.


                             Erroneous Execution

14    If the Ceiling_Locking policy (see D.3) is in effect and an interrupt is
delivered to a handler, and the interrupt hardware priority is higher than the
ceiling priority of the corresponding protected object, the execution of the
program is erroneous.

14.1/1 {If the handlers for a given interrupt attached via pragma
Attach_Handler are not attached and detached in a stack-like (LIFO) order,
program execution is erroneous. In particular, when a protected object is
finalized, the execution is erroneous if any of the procedures of the
protected object are attached to interrupts via pragma Attach_Handler and the
most recently attached handler for the same interrupt is not the same as the
one that was attached at the time the protected object was initialized.}


                                   Metrics

15    The following metric shall be documented by the implementation:

16    1.  The worst case overhead for an interrupt handler that is a
          parameterless protected procedure, in clock cycles. This is the
          execution time not directly attributable to the handler procedure or
          the interrupted execution. It is estimated as C - (A+B), where A is
          how long it takes to complete a given sequence of instructions
          without any interrupt, B is how long it takes to complete a normal
          call to a given protected procedure, and C is how long it takes to
          complete the same sequence of instructions when it is interrupted by
          one execution of the same procedure called via an interrupt.


                         Implementation Permissions

17    When the pragmas Attach_Handler or Interrupt_Handler apply to a
protected procedure, the implementation is allowed to impose
implementation-defined restrictions on the corresponding protected_type_-
declaration and protected_body.

18    An implementation may use a different mechanism for invoking a protected
procedure in response to a hardware interrupt than is used for a call to that
protected procedure from a task.

19    Notwithstanding what this subclause says elsewhere, the Attach_Handler
and Interrupt_Handler pragmas are allowed to be used for other, implementation
defined, forms of interrupt handlers.


                            Implementation Advice

20    Whenever possible, the implementation should allow interrupt handlers to
be called directly by the hardware.

21    Whenever practical, the implementation should detect violations of any
implementation-defined restrictions before run time.

      NOTES

22    4  The Attach_Handler pragma can provide static attachment of handlers
      to interrupts if the implementation supports preelaboration of protected
      objects. (See C.4.)

23    5  The ceiling priority of a protected object that one of its procedures
      is attached to an interrupt should be at least as high as the highest
      processor priority at which that interrupt will ever be delivered.

24    6  Protected procedures can also be attached dynamically to interrupts
      via operations declared in the predefined package Interrupts.

25    7  An example of a possible implementation-defined restriction is
      disallowing the use of the standard storage pools within the body of a
      protected procedure that is an interrupt handler.


C.3.2 The Package Interrupts



                              Static Semantics

1     The following language-defined packages exist:

2     with System;
      package Ada.Interrupts is
         type Interrupt_ID is implementation-defined;
         type Parameterless_Handler is
            access protected procedure;

3/1   This paragraph was deleted.[ ]

4        function Is_Reserved (Interrupt : Interrupt_ID)
            return Boolean;

5        function Is_Attached (Interrupt : Interrupt_ID)
            return Boolean;

6        function Current_Handler (Interrupt : Interrupt_ID)
            return Parameterless_Handler;

7        procedure Attach_Handler
            (New_Handler : in Parameterless_Handler;
             Interrupt   : in Interrupt_ID);

8        procedure Exchange_Handler
            (Old_Handler : out Parameterless_Handler;
             New_Handler : in Parameterless_Handler;
             Interrupt   : in Interrupt_ID);

9        procedure Detach_Handler
            (Interrupt : in Interrupt_ID);

10       function Reference(Interrupt : Interrupt_ID)
            return System.Address;

11    private
         ... -- not specified by the language
      end Ada.Interrupts;

12    package Ada.Interrupts.Names is
         implementation-defined : constant Interrupt_ID :=
           implementation-defined;
            . . .
         implementation-defined : constant Interrupt_ID :=
           implementation-defined;
      end Ada.Interrupts.Names;


                              Dynamic Semantics

13    The Interrupt_ID type is an implementation-defined discrete type used to
identify interrupts.

14    The Is_Reserved function returns True if and only if the specified
interrupt is reserved.

15    The Is_Attached function returns True if and only if a user-specified
interrupt handler is attached to the interrupt.

16/1  The Current_Handler function returns a value that represents the
attached handler of the interrupt. If no user-defined handler is attached to
the interrupt, Current_Handler returns {null}[a value that designates the
default treatment; calling Attach_Handler or Exchange_Handler with this value
restores the default treatment].

17    The Attach_Handler procedure attaches the specified handler to the
interrupt, overriding any existing treatment (including a user handler) in
effect for that interrupt. If New_Handler is null, the default treatment is
restored. If New_Handler designates a protected procedure to which the pragma
Interrupt_Handler does not apply, Program_Error is raised. In this case, the
operation does not modify the existing interrupt treatment.

18/1  The Exchange_Handler procedure operates in the same manner as
Attach_Handler with the addition that the value returned in Old_Handler
designates the previous treatment for the specified interrupt.{ If the
previous treatment is not a user-defined handler, null is returned.}

19    The Detach_Handler procedure restores the default treatment for the
specified interrupt.

20    For all operations defined in this package that take a parameter of type
Interrupt_ID, with the exception of Is_Reserved and Reference, a check is made
that the specified interrupt is not reserved. Program_Error is raised if this
check fails.

21    If, by using the Attach_Handler, Detach_Handler, or Exchange_Handler
procedures, an attempt is made to detach a handler that was attached
statically (using the pragma Attach_Handler), the handler is not detached and
Program_Error is raised.

22    The Reference function returns a value of type System.Address that can
be used to attach a task entry, via an address clause (see J.7.1) to the
interrupt specified by Interrupt. This function raises Program_Error if
attaching task entries to interrupts (or to this particular interrupt) is not
supported.


                         Implementation Requirements

23    At no time during attachment or exchange of handlers shall the current
handler of the corresponding interrupt be undefined.


                         Documentation Requirements

24    If the Ceiling_Locking policy (see D.3) is in effect the implementation
shall document the default ceiling priority assigned to a protected object
that contains either the Attach_Handler or Interrupt_Handler pragmas, but not
the Interrupt_Priority pragma. This default need not be the same for all
interrupts.


                            Implementation Advice

25    If implementation-defined forms of interrupt handler procedures are
supported, such as protected procedures with parameters, then for each such
form of a handler, a type analogous to Parameterless_Handler should be
specified in a child package of Interrupts, with the same operations as in the
predefined package Interrupts.

      NOTES

26    8  The package Interrupts.Names contains implementation-defined names
      (and constant values) for the interrupts that are supported by the
      implementation.


                                  Examples

27    Example of interrupt handlers:

28    Device_Priority : constant
        array (1..5) of System.Interrupt_Priority := ( ... );
      protected type Device_Interface
        (Int_ID : Ada.Interrupts.Interrupt_ID) is
        procedure Handler;
        pragma Attach_Handler(Handler, Int_ID);
        ...
        pragma Interrupt_Priority(Device_Priority(Int_ID));
      end Device_Interface;
        ...
      Device_1_Driver : Device_Interface(1);
        ...
      Device_5_Driver : Device_Interface(5);
        ...


C.4 Preelaboration Requirements


1     This clause specifies additional implementation and documentation
requirements for the Preelaborate pragma (see 10.2.1).


                         Implementation Requirements

2     The implementation shall not incur any run-time overhead for the
elaboration checks of subprograms and protected_bodies declared in
preelaborated library units.

3     The implementation shall not execute any memory write operations after
load time for the elaboration of constant objects declared immediately within
the declarative region of a preelaborated library package, so long as the
subtype and initial expression (or default initial expressions if initialized
by default) of the object_declaration satisfy the following restrictions. The
meaning of load time is implementation defined.

4     Any subtype_mark denotes a statically constrained subtype, with
      statically constrained subcomponents, if any;

5     any constraint is a static constraint;

6     any allocator is for an access-to-constant type;

7     any uses of predefined operators appear only within static expressions;

8     any primaries that are names, other than attribute_references for the
      Access or Address attributes, appear only within static expressions;

9     any name that is not part of a static expression is an expanded name or
      direct_name that statically denotes some entity;

10    any discrete_choice of an array_aggregate is static;

11    no language-defined check associated with the elaboration of the
      object_declaration can fail.


                         Documentation Requirements

12    The implementation shall document any circumstances under which the
elaboration of a preelaborated package causes code to be executed at run time.

13    The implementation shall document whether the method used for
initialization of preelaborated variables allows a partition to be restarted
without reloading.


                            Implementation Advice

14    It is recommended that preelaborated packages be implemented in such a
way that there should be little or no code executed at run time for the
elaboration of entities not already covered by the
Implementation Requirements.


C.5 Pragma Discard_Names


1     A pragma Discard_Names may be used to request a reduction in storage
used for the names of certain entities.


                                   Syntax

2     The form of a pragma Discard_Names is as follows:

3       pragma Discard_Names[([On => ] local_name)];

4     A pragma Discard_Names is allowed only immediately within a
      declarative_part, immediately within a package_specification, or as a
      configuration pragma.


                               Legality Rules

5     The local_name (if present) shall denote a non-derived enumeration first
subtype, a tagged first subtype, or an exception. The pragma applies to the
type or exception. Without a local_name, the pragma applies to all such
entities declared after the pragma, within the same declarative region.
Alternatively, the pragma can be used as a configuration pragma. If the pragma
applies to a type, then it applies also to all descendants of the type.


                              Static Semantics

6     If a local_name is given, then a pragma Discard_Names is a
representation pragma.

7     If the pragma applies to an enumeration type, then the semantics of the
Wide_Image and Wide_Value attributes are implementation defined for that type;
the semantics of Image and Value are still defined in terms of Wide_Image and
Wide_Value. In addition, the semantics of Text_IO.Enumeration_IO are
implementation defined. If the pragma applies to a tagged type, then the
semantics of the Tags.Expanded_Name function are implementation defined for
that type. If the pragma applies to an exception, then the semantics of the
Exceptions.Exception_Name function are implementation defined for that
exception.


                            Implementation Advice

8     If the pragma applies to an entity, then the implementation should
reduce the amount of storage used for storing names associated with that
entity.


C.6 Shared Variable Control


1     This clause specifies representation pragmas that control the use of
shared variables.


                                   Syntax

2     The form for pragmas Atomic, Volatile, Atomic_Components, and
      Volatile_Components is as follows:

3       pragma Atomic(local_name);

4       pragma Volatile(local_name);

5       pragma Atomic_Components(array_local_name);

6       pragma Volatile_Components(array_local_name);

7     An atomic type is one to which a pragma Atomic applies. An atomic object
(including a component) is one to which a pragma Atomic applies, or a
component of an array to which a pragma Atomic_Components applies, or any
object of an atomic type.

8     A volatile type is one to which a pragma Volatile applies. A volatile
object (including a component) is one to which a pragma Volatile applies, or a
component of an array to which a pragma Volatile_Components applies, or any
object of a volatile type. In addition, every atomic type or object is also
defined to be volatile. Finally, if an object is volatile, then so are all of
its subcomponents (the same does not apply to atomic).


                            Name Resolution Rules

9     The local_name in an Atomic or Volatile pragma shall resolve to denote
either an object_declaration, a non-inherited component_declaration, or a
full_type_declaration. The array_local_name in an Atomic_Components or
Volatile_Components pragma shall resolve to denote the declaration of an array
type or an array object of an anonymous type.


                               Legality Rules

10    It is illegal to apply either an Atomic or Atomic_Components pragma to
an object or type if the implementation cannot support the indivisible reads
and updates required by the pragma (see below).

11    It is illegal to specify the Size attribute of an atomic object, the
Component_Size attribute for an array type with atomic components, or the
layout attributes of an atomic component, in a way that prevents the
implementation from performing the required indivisible reads and updates.

12    If an atomic object is passed as a parameter, then the type of the
formal parameter shall either be atomic or allow pass by copy (that is, not be
a nonatomic by-reference type). If an atomic object is used as an actual for a
generic formal object of mode in out, then the type of the generic formal
object shall be atomic. If the prefix of an attribute_reference for an Access
attribute denotes an atomic object (including a component), then the
designated type of the resulting access type shall be atomic. If an atomic
type is used as an actual for a generic formal derived type, then the ancestor
of the formal type shall be atomic or allow pass by copy. Corresponding rules
apply to volatile objects and types.

13    If a pragma Volatile, Volatile_Components, Atomic, or Atomic_Components
applies to a stand-alone constant object, then a pragma Import shall also
apply to it.


                              Static Semantics

14    These pragmas are representation pragmas (see 13.1).


                              Dynamic Semantics

15    For an atomic object (including an atomic component) all reads and
updates of the object as a whole are indivisible.

16    For a volatile object all reads and updates of the object as a whole are
performed directly to memory.

17    Two actions are sequential (see 9.10) if each is the read or update of
the same atomic object.

18    If a type is atomic or volatile and it is not a by-copy type, then the
type is defined to be a by-reference type. If any subcomponent of a type is
atomic or volatile, then the type is defined to be a by-reference type.

19    If an actual parameter is atomic or volatile, and the corresponding
formal parameter is not, then the parameter is passed by copy.


                         Implementation Requirements

20    The external effect of a program (see 1.1.3) is defined to include each
read and update of a volatile or atomic object. The implementation shall not
generate any memory reads or updates of atomic or volatile objects other than
those specified by the program.

21    If a pragma Pack applies to a type any of whose subcomponents are
atomic, the implementation shall not pack the atomic subcomponents more
tightly than that for which it can support indivisible reads and updates.

      NOTES

22    9  An imported volatile or atomic constant behaves as a constant (i.e.
      read-only) with respect to other parts of the Ada program, but can still
      be modified by an ``external source.''


C.7 Task Identification and Attributes


1     This clause describes operations and attributes that can be used to
obtain the identity of a task. In addition, a package that associates
user-defined information with a task is defined.


C.7.1 The Package Task_Identification



                              Static Semantics

1     The following language-defined library package exists:

2     package Ada.Task_Identification is
         type Task_ID is private;
         Null_Task_ID : constant Task_ID;
         function  "=" (Left, Right : Task_ID) return Boolean;

3/1      function  Image        (T : Task_ID) return String;
         function  Current_Task return Task_ID;
         procedure Abort_Task   (T : in [out ]Task_ID);

4        function  Is_Terminated(T : Task_ID) return Boolean;
         function  Is_Callable  (T : Task_ID) return Boolean;
      private
         ... -- not specified by the language
      end Ada.Task_Identification;


                              Dynamic Semantics

5     A value of the type Task_ID identifies an existent task. The constant
Null_Task_ID does not identify any task. Each object of the type Task_ID is
default initialized to the value of Null_Task_ID.

6     The function "=" returns True if and only if Left and Right identify the
same task or both have the value Null_Task_ID.

7     The function Image returns an implementation-defined string that
identifies T. If T equals Null_Task_ID, Image returns an empty string.

8     The function Current_Task returns a value that identifies the calling
task.

9     The effect of Abort_Task is the same as the abort_statement for the task
identified by T. In addition, if T identifies the environment task, the entire
partition is aborted, See E.1.

10    The functions Is_Terminated and Is_Callable return the value of the
corresponding attribute of the task identified by T.

11    For a prefix T that is of a task type (after any implicit dereference),
the following attribute is defined:

12    T'Identity
              Yields a value of the type Task_ID that identifies the task
              denoted by T.

13    For a prefix E that denotes an entry_declaration, the following
attribute is defined:

14    E'Caller
              Yields a value of the type Task_ID that identifies the task
              whose call is now being serviced. Use of this attribute is
              allowed only inside an entry_body or accept_statement
              corresponding to the entry_declaration denoted by E.

15    Program_Error is raised if a value of Null_Task_ID is passed as a
parameter to Abort_Task, Is_Terminated, and Is_Callable.

16    Abort_Task is a potentially blocking operation (see 9.5.1).


                          Bounded (Run-Time) Errors

17    It is a bounded error to call the Current_Task function from an entry
body or an interrupt handler. Program_Error is raised, or an
implementation-defined value of the type Task_ID is returned.


                             Erroneous Execution

18    If a value of Task_ID is passed as a parameter to any of the operations
declared in this package (or any language-defined child of this package), and
the corresponding task object no longer exists, the execution of the program
is erroneous.


                         Documentation Requirements

19    The implementation shall document the effect of calling Current_Task
from an entry body or interrupt handler.

      NOTES

20    10  This package is intended for use in writing user-defined task
      scheduling packages and constructing server tasks. Current_Task can be
      used in conjunction with other operations requiring a task as an
      argument such as Set_Priority (see D.5).

21    11  The function Current_Task and the attribute Caller can return a
      Task_ID value that identifies the environment task.


C.7.2 The Package Task_Attributes



                              Static Semantics

1     The following language-defined generic library package exists:

2     with Ada.Task_Identification; use Ada.Task_Identification;
      generic
         type Attribute is private;
         Initial_Value : in Attribute;
      package Ada.Task_Attributes is

3        type Attribute_Handle is access all Attribute;

4        function Value(T : Task_ID := Current_Task)
           return Attribute;

5        function Reference(T : Task_ID := Current_Task)
           return Attribute_Handle;

6        procedure Set_Value(Val : in Attribute;
                                   T : in Task_ID := Current_Task);
         procedure Reinitialize(T : in Task_ID := Current_Task);

7     end Ada.Task_Attributes;


                              Dynamic Semantics

8     When an instance of Task_Attributes is elaborated in a given active
partition, an object of the actual type corresponding to the formal type
Attribute is implicitly created for each task (of that partition) that exists
and is not yet terminated. This object acts as a user-defined attribute of the
task. A task created previously in the partition and not yet terminated has
this attribute from that point on. Each task subsequently created in the
partition will have this attribute when created. In all these cases, the
initial value of the given attribute is Initial_Value.

9     The Value operation returns the value of the corresponding attribute of
T.

10    The Reference operation returns an access value that designates the
corresponding attribute of T.

11    The Set_Value operation performs any finalization on the old value of
the attribute of T and assigns Val to that attribute (see 5.2 and 7.6).

12    The effect of the Reinitialize operation is the same as Set_Value where
the Val parameter is replaced with Initial_Value.

13    For all the operations declared in this package, Tasking_Error is raised
if the task identified by T is terminated. Program_Error is raised if the
value of T is Null_Task_ID.


                          Bounded (Run-Time) Errors

13.1/1 {If the package Ada.Task_Attributes is instantiated with a controlled
type and the controlled type has user-defined Adjust or Finalize operations
that in turn access task attributes by any of the above operations, then a
call of Set_Value of the instantiated package constitutes a bounded error. The
call may perform as expected or may result in forever blocking the calling
task and subsequently some or all tasks of the partition.}


                             Erroneous Execution

14    It is erroneous to dereference the access value returned by a given call
on Reference after a subsequent call on Reinitialize for the same task
attribute, or after the associated task terminates.

15    If a value of Task_ID is passed as a parameter to any of the operations
declared in this package and the corresponding task object no longer exists,
the execution of the program is erroneous.

15.1/1 {Accesses to task attributes via a value of type Attribute_Handle are
erroneous if executed concurrently with each other or with calls of any of the
operations declared in package Task_Attributes.}


                         Implementation Requirements

16/1  {For a given attribute of a given task, t}[T]he implementation shall
perform {the operations declared in this package}[each of the above operations
for a given attribute of a given task] atomically with respect to any {of
these operations of}[other of the above operations for] the same attribute of
the same task. {The granularity of any locking mechanism necessary to achieve
such atomicity is implementation defined.}

17    When a task terminates, the implementation shall finalize all attributes
of the task, and reclaim any other storage associated with the attributes.


                         Documentation Requirements

18    The implementation shall document the limit on the number of attributes
per task, if any, and the limit on the total storage for attribute values per
task, if such a limit exists.

19    In addition, if these limits can be configured, the implementation shall
document how to configure them.


                                   Metrics

20    The implementation shall document the following metrics: A task calling
the following subprograms shall execute in a sufficiently high priority as to
not be preempted during the measurement period. This period shall start just
before issuing the call and end just after the call completes. If the
attributes of task T are accessed by the measurement tests, no other task
shall access attributes of that task during the measurement period. For all
measurements described here, the Attribute type shall be a scalar whose size
is equal to the size of the predefined integer size. For each measurement, two
cases shall be documented: one where the accessed attributes are of the
calling task (that is, the default value for the T parameter is used), and the
other, where T identifies another, non-terminated, task.

21    The following calls (to subprograms in the Task_Attributes package)
shall be measured:

22    a call to Value, where the return value is Initial_Value;

23    a call to Value, where the return value is not equal to Initial_Value;

24    a call to Reference, where the return value designates a value equal to
      Initial_Value;

25    a call to Reference, where the return value designates a value not equal
      to Initial_Value;

26    a call to Set_Value where the Val parameter is not equal to
      Initial_Value and the old attribute value is equal to Initial_Value.

27    a call to Set_Value where the Val parameter is not equal to
      Initial_Value and the old attribute value is not equal to Initial_Value.


                         Implementation Permissions

28    An implementation need not actually create the object corresponding to a
task attribute until its value is set to something other than that of
Initial_Value, or until Reference is called for the task attribute. Similarly,
when the value of the attribute is to be reinitialized to that of
Initial_Value, the object may instead be finalized and its storage reclaimed,
to be recreated when needed later. While the object does not exist, the
function Value may simply return Initial_Value, rather than implicitly
creating the object.

29    An implementation is allowed to place restrictions on the maximum number
of attributes a task may have, the maximum size of each attribute, and the
total storage size allocated for all the attributes of a task.


                            Implementation Advice

30    Some implementations are targeted to domains in which memory use at run
time must be completely deterministic. For such implementations, it is
recommended that the storage for task attributes will be pre-allocated
statically and not from the heap. This can be accomplished by either placing
restrictions on the number and the size of the task's attributes, or by using
the pre-allocated storage for the first N attribute objects, and the heap for
the others. In the latter case, N should be documented.

      NOTES

31    12  An attribute always exists (after instantiation), and has the
      initial value. It need not occupy memory until the first operation that
      potentially changes the attribute value. The same holds true after
      Reinitialize.

32    13  The result of the Reference function should be used with care; it is
      always safe to use that result in the task body whose attribute is being
      accessed. However, when the result is being used by another task, the
      programmer must make sure that the task whose attribute is being
      accessed is not yet terminated. Failing to do so could make the program
      execution erroneous.

33    14  As specified in C.7.1, if the parameter T (in a call on a subprogram
      of an instance of this package) identifies a nonexistent task, the
      execution of the program is erroneous.



                                   Annex D
                                 (normative)

                              Real-Time Systems


1     This Annex specifies additional characteristics of Ada implementations
intended for real-time systems software. To conform to this Annex, an
implementation shall also conform to the Systems Programming Annex.


                                   Metrics

2     The metrics are documentation requirements; an implementation shall
document the values of the language-defined metrics for at least one
configuration of hardware or an underlying system supported by the
implementation, and shall document the details of that configuration.

3     The metrics do not necessarily yield a simple number. For some, a range
is more suitable, for others a formula dependent on some parameter is
appropriate, and for others, it may be more suitable to break the metric into
several cases. Unless specified otherwise, the metrics in this annex are
expressed in processor clock cycles. For metrics that require documentation of
an upper bound, if there is no upper bound, the implementation shall report
that the metric is unbounded.

      NOTES

4     1  The specification of the metrics makes a distinction between upper
      bounds and simple execution times. Where something is just specified as
      ``the execution time of'' a piece of code, this leaves one the freedom
      to choose a nonpathological case. This kind of metric is of the form `
      `there exists a program such that the value of the metric is V''.
      Conversely, the meaning of upper bounds is ``there is no program such
      that the value of the metric is greater than V''. This kind of metric
      can only be partially tested, by finding the value of V for one or more
      test programs.

5     2  The metrics do not cover the whole language; they are limited to
      features that are specified in Annex C, ``Systems Programming'' and in
      this Annex. The metrics are intended to provide guidance to potential
      users as to whether a particular implementation of such a feature is
      going to be adequate for a particular real-time application. As such,
      the metrics are aimed at known implementation choices that can result in
      significant performance differences.

6     3  The purpose of the metrics is not necessarily to provide fine-grained
      quantitative results or to serve as a comparison between different
      implementations on the same or different platforms. Instead, their goal
      is rather qualitative; to define a standard set of approximate values
      that can be measured and used to estimate the general suitability of an
      implementation, or to evaluate the comparative utility of certain
      features of an implementation for a particular real-time application.


D.1 Task Priorities


1     This clause specifies the priority model for real-time systems. In
addition, the methods for specifying priorities are defined.


                                   Syntax

2     The form of a pragma Priority is as follows:

3       pragma Priority(expression);

4     The form of a pragma Interrupt_Priority is as follows:

5       pragma Interrupt_Priority[(expression)];


                            Name Resolution Rules

6     The expected type for the expression in a Priority or Interrupt_Priority
pragma is Integer.


                               Legality Rules

7     A Priority pragma is allowed only immediately within a task_definition,
a protected_definition, or the declarative_part of a subprogram_body. An
Interrupt_Priority pragma is allowed only immediately within a task_definition
or a protected_definition. At most one such pragma shall appear within a given
construct.

8     For a Priority pragma that appears in the declarative_part of a
subprogram_body, the expression shall be static, and its value shall be in the
range of System.Priority.


                              Static Semantics

9     The following declarations exist in package System:

10    subtype Any_Priority is Integer range implementation-defined;
      subtype Priority is Any_Priority
         range Any_Priority'First .. implementation-defined;
      subtype Interrupt_Priority is Any_Priority
         range Priority'Last+1 .. Any_Priority'Last;

11    Default_Priority : constant Priority := (Priority'First + Priority'Last)/2;

12    The full range of priority values supported by an implementation is
specified by the subtype Any_Priority. The subrange of priority values that
are high enough to require the blocking of one or more interrupts is specified
by the subtype Interrupt_Priority. The subrange of priority values below
System.Interrupt_Priority'First is specified by the subtype System.Priority.

13    The priority specified by a Priority or Interrupt_Priority pragma is the
value of the expression in the pragma, if any. If there is no expression in an
Interrupt_Priority pragma, the priority value is Interrupt_Priority'Last.


                              Dynamic Semantics

14    A Priority pragma has no effect if it occurs in the declarative_part of
the subprogram_body of a subprogram other than the main subprogram.

15    A task priority is an integer value that indicates a degree of urgency
and is the basis for resolving competing demands of tasks for resources.
Unless otherwise specified, whenever tasks compete for processors or other
implementation-defined resources, the resources are allocated to the task with
the highest priority value. The base priority of a task is the priority with
which it was created, or to which it was later set by
Dynamic_Priorities.Set_Priority (see D.5). At all times, a task also has an
active priority, which generally reflects its base priority as well as any
priority it inherits from other sources. Priority inheritance is the process
by which the priority of a task or other entity (e.g. a protected object; see
D.3) is used in the evaluation of another task's active priority.

16    The effect of specifying such a pragma in a protected_definition is
discussed in D.3.

17    The expression in a Priority or Interrupt_Priority pragma that appears
in a task_definition is evaluated for each task object (see 9.1). For a
Priority pragma, the value of the expression is converted to the subtype
Priority; for an Interrupt_Priority pragma, this value is converted to the
subtype Any_Priority. The priority value is then associated with the task
object whose task_definition contains the pragma.

18    Likewise, the priority value is associated with the environment task if
the pragma appears in the declarative_part of the main subprogram.

19    The initial value of a task's base priority is specified by default or
by means of a Priority or Interrupt_Priority pragma. After a task is created,
its base priority can be changed only by a call to
Dynamic_Priorities.Set_Priority (see D.5). The initial base priority of a task
in the absence of a pragma is the base priority of the task that creates it at
the time of creation (see 9.1). If a pragma Priority does not apply to the
main subprogram, the initial base priority of the environment task is
System.Default_Priority. The task's active priority is used when the task
competes for processors. Similarly, the task's active priority is used to
determine the task's position in any queue when Priority_Queuing is specified
(see D.4).

20    At any time, the active priority of a task is the maximum of all the
priorities the task is inheriting at that instant. For a task that is not held
(see D.11), its base priority is always a source of priority inheritance.
Other sources of priority inheritance are specified under the following
conditions:

21/1  During activation, a task being activated inherits the active priority
      {that}[of the] its activator (see 9.2){ had at the time the activation
      was initiated}.

22/1  During rendezvous, the task accepting the entry call inherits the
      [active ]priority of the {entry call}[caller] (see 9.5.3{ and D.4}).

23    During a protected action on a protected object, a task inherits the
      ceiling priority of the protected object (see 9.5 and D.3).

24    In all of these cases, the priority ceases to be inherited as soon as
the condition calling for the inheritance no longer exists.


                         Implementation Requirements

25    The range of System.Interrupt_Priority shall include at least one value.

26    The range of System.Priority shall include at least 30 values.

      NOTES

27    4  The priority expression can include references to discriminants of
      the enclosing type.

28    5  It is a consequence of the active priority rules that at the point
      when a task stops inheriting a priority from another source, its active
      priority is re-evaluated. This is in addition to other instances
      described in this Annex for such re-evaluation.

29    6  An implementation may provide a non-standard mode in which tasks
      inherit priorities under conditions other than those specified above.


D.2 Priority Scheduling


1     This clause describes the rules that determine which task is selected
for execution when more than one task is ready (see 9.2). The rules have two
parts: the task dispatching model (see D.2.1), and a specific task dispatching
policy (see D.2.2).


D.2.1 The Task Dispatching Model


1     The task dispatching model specifies preemptive scheduling, based on
conceptual priority-ordered ready queues.


                              Dynamic Semantics

2     A task runs (that is, it becomes a running task) only when it is ready
(see 9.2) and the execution resources required by that task are available.
Processors are allocated to tasks based on each task's active priority.

3     It is implementation defined whether, on a multiprocessor, a task that
is waiting for access to a protected object keeps its processor busy.

4     Task dispatching is the process by which one ready task is selected for
execution on a processor. This selection is done at certain points during the
execution of a task called task dispatching points. A task reaches a task
dispatching point whenever it becomes blocked, and whenever it becomes ready.
In addition, the completion of an accept_statement (see 9.5.2), and task
termination are task dispatching points for the executing task. Other task
dispatching points are defined throughout this Annex.

5     Task dispatching policies are specified in terms of conceptual ready
queues, task states, and task preemption. A ready queue is an ordered list of
ready tasks. The first position in a queue is called the head of the queue,
and the last position is called the tail of the queue. A task is ready if it
is in a ready queue, or if it is running. Each processor has one ready queue
for each priority value. At any instant, each ready queue of a processor
contains exactly the set of tasks of that priority that are ready for
execution on that processor, but are not running on any processor; that is,
those tasks that are ready, are not running on any processor, and can be
executed using that processor and other available resources. A task can be on
the ready queues of more than one processor.

6     Each processor also has one running task, which is the task currently
being executed by that processor. Whenever a task running on a processor
reaches a task dispatching point, one task is selected to run on that
processor. The task selected is the one at the head of the highest priority
nonempty ready queue; this task is then removed from all ready queues to which
it belongs.

7     A preemptible resource is a resource that while allocated to one task
can be allocated (temporarily) to another instead. Processors are preemptible
resources. Access to a protected object (see 9.5.1) is a nonpreemptible
resource. When a higher-priority task is dispatched to the processor, and the
previously running task is placed on the appropriate ready queue, the latter
task is said to be preempted.

8     A new running task is also selected whenever there is a nonempty ready
queue with a higher priority than the priority of the running task, or when
the task dispatching policy requires a running task to go back to a ready
queue. These are also task dispatching points.


                         Implementation Permissions

9     An implementation is allowed to define additional resources as execution
resources, and to define the corresponding allocation policies for them. Such
resources may have an implementation defined effect on task dispatching (see
D.2.2).

10    An implementation may place implementation-defined restrictions on tasks
whose active priority is in the Interrupt_Priority range.

      NOTES

11    7  Section 9 specifies under which circumstances a task becomes ready.
      The ready state is affected by the rules for task activation and
      termination, delay statements, and entry calls. When a task is not
      ready, it is said to be blocked.

12    8  An example of a possible implementation-defined execution resource is
      a page of physical memory, which needs to be loaded with a particular
      page of virtual memory before a task can continue execution.

13    9  The ready queues are purely conceptual; there is no requirement that
      such lists physically exist in an implementation.

14    10  While a task is running, it is not on any ready queue. Any time the
      task that is running on a processor is added to a ready queue, a new
      running task is selected for that processor.

15    11  In a multiprocessor system, a task can be on the ready queues of
      more than one processor. At the extreme, if several processors share the
      same set of ready tasks, the contents of their ready queues is
      identical, and so they can be viewed as sharing one ready queue, and can
      be implemented that way. Thus, the dispatching model covers
      multiprocessors where dispatching is implemented using a single ready
      queue, as well as those with separate dispatching domains.

16    12  The priority of a task is determined by rules specified in this
      subclause, and under D.1, ``Task Priorities'', D.3, ``
      Priority Ceiling Locking'', and D.5, ``Dynamic Priorities''.


D.2.2 The Standard Task Dispatching Policy



                                   Syntax

1     The form of a pragma Task_Dispatching_Policy is as follows:

2       pragma Task_Dispatching_Policy(policy_identifier );


                               Legality Rules

3     The policy_identifier shall either be FIFO_Within_Priorities or an
implementation-defined identifier.


                           Post-Compilation Rules

4     A Task_Dispatching_Policy pragma is a configuration pragma.

5     If the FIFO_Within_Priorities policy is specified for a partition, then
the Ceiling_Locking policy (see D.3) shall also be specified for the
partition.


                              Dynamic Semantics

6     A task dispatching policy specifies the details of task dispatching that
are not covered by the basic task dispatching model. These rules govern when
tasks are inserted into and deleted from the ready queues, and whether a task
is inserted at the head or the tail of the queue for its active priority. The
task dispatching policy is specified by a Task_Dispatching_Policy
configuration pragma. If no such pragma appears in any of the program units
comprising a partition, the task dispatching policy for that partition is
unspecified.

7     The language defines only one task dispatching policy,
FIFO_Within_Priorities; when this policy is in effect, modifications to the
ready queues occur only as follows:

8     When a blocked task becomes ready, it is added at the tail of the ready
      queue for its active priority.

9     When the active priority of a ready task that is not running changes, or
      the setting of its base priority takes effect, the task is removed from
      the ready queue for its old active priority and is added at the tail of
      the ready queue for its new active priority, except in the case where
      the active priority is lowered due to the loss of inherited priority, in
      which case the task is added at the head of the ready queue for its new
      active priority.

10    When the setting of the base priority of a running task takes effect,
      the task is added to the tail of the ready queue for its active priority.

11    When a task executes a delay_statement that does not result in blocking,
      it is added to the tail of the ready queue for its active priority.

12    Each of the events specified above is a task dispatching point (see
D.2.1).

13    In addition, when a task is preempted, it is added at the head of the
ready queue for its active priority.


                         Documentation Requirements

14    Priority inversion is the duration for which a task remains at the head
of the highest priority ready queue while the processor executes a lower
priority task. The implementation shall document:

15    The maximum priority inversion a user task can experience due to
      activity of the implementation (on behalf of lower priority tasks), and

16    whether execution of a task can be preempted by the implementation
      processing of delay expirations for lower priority tasks, and if so, for
      how long.


                         Implementation Permissions

17    Implementations are allowed to define other task dispatching policies,
but need not support more than one such policy per partition.

18    For optimization purposes, an implementation may alter the points at
which task dispatching occurs, in an implementation defined manner. However, a
delay_statement always corresponds to at least one task dispatching point.

      NOTES

19    13  If the active priority of a running task is lowered due to loss of
      inherited priority (as it is on completion of a protected operation) and
      there is a ready task of the same active priority that is not running,
      the running task continues to run (provided that there is no higher
      priority task).

20    14  The setting of a task's base priority as a result of a call to
      Set_Priority does not always take effect immediately when Set_Priority
      is called. The effect of setting the task's base priority is deferred
      while the affected task performs a protected action.

21    15  Setting the base priority of a ready task causes the task to move to
      the end of the queue for its active priority, regardless of whether the
      active priority of the task actually changes.


D.3 Priority Ceiling Locking


1     This clause specifies the interactions between priority task scheduling
and protected object ceilings. This interaction is based on the concept of the
ceiling priority of a protected object.


                                   Syntax

2     The form of a pragma Locking_Policy is as follows:

3       pragma Locking_Policy(policy_identifier);


                               Legality Rules

4     The policy_identifier shall either be Ceiling_Locking or an
implementation-defined identifier.


                           Post-Compilation Rules

5     A Locking_Policy pragma is a configuration pragma.


                              Dynamic Semantics

6/1   A locking policy specifies the details of protected object locking.
These rules specify whether or not protected objects have priorities, and the
relationships between these priorities and task priorities. In addition, the
policy specifies the state of a task when it executes a protected action, and
how its active priority is affected by the locking. The locking policy is
specified by a Locking_Policy pragma. For implementation-defined locking
policies, the effect of a Priority or Interrupt_Priority pragma on a protected
object is implementation defined. If no Locking_Policy pragma {applies
to}[appears in] any of the program units comprising a partition, the locking
policy for that partition, as well as the effect of specifying either a
Priority or Interrupt_Priority pragma for a protected object, are
implementation defined.

7     There is one predefined locking policy, Ceiling_Locking; this policy is
defined as follows:

8     Every protected object has a ceiling priority, which is determined by
      either a Priority or Interrupt_Priority pragma as defined in D.1. The
      ceiling priority of a protected object (or ceiling, for short) is an
      upper bound on the active priority a task can have when it calls
      protected operations of that protected object.

9     The expression of a Priority or Interrupt_Priority pragma is evaluated
      as part of the creation of the corresponding protected object and
      converted to the subtype System.Any_Priority or
      System.Interrupt_Priority, respectively. The value of the expression is
      the ceiling priority of the corresponding protected object.

10    If an Interrupt_Handler or Attach_Handler pragma (see C.3.1) appears in
      a protected_definition without an Interrupt_Priority pragma, the ceiling
      priority of protected objects of that type is implementation defined,
      but in the range of the subtype System.Interrupt_Priority.

11    If no pragma Priority, Interrupt_Priority, Interrupt_Handler, or
      Attach_Handler is specified in the protected_definition, then the
      ceiling priority of the corresponding protected object is
      System.Priority'Last.

12    While a task executes a protected action, it inherits the ceiling
      priority of the corresponding protected object.

13    When a task calls a protected operation, a check is made that its active
      priority is not higher than the ceiling of the corresponding protected
      object; Program_Error is raised if this check fails.


                         Implementation Permissions

14    The implementation is allowed to round all ceilings in a certain
subrange of System.Priority or System.Interrupt_Priority up to the top of that
subrange, uniformly.

15    Implementations are allowed to define other locking policies, but need
not support more than one such policy per partition.

16    Since implementations are allowed to place restrictions on code that
runs at an interrupt-level active priority (see C.3.1 and D.2.1), the
implementation may implement a language feature in terms of a protected object
with an implementation-defined ceiling, but the ceiling shall be no less than
Priority'Last.


                            Implementation Advice

17    The implementation should use names that end with ``_Locking'' for
implementation-defined locking policies.

      NOTES

18    16  While a task executes in a protected action, it can be preempted
      only by tasks whose active priorities are higher than the ceiling
      priority of the protected object.

19    17  If a protected object has a ceiling priority in the range of
      Interrupt_Priority, certain interrupts are blocked while protected
      actions of that object execute. In the extreme, if the ceiling is
      Interrupt_Priority'Last, all blockable interrupts are blocked during
      that time.

20    18  The ceiling priority of a protected object has to be in the
      Interrupt_Priority range if one of its procedures is to be used as an
      interrupt handler (see C.3).

21    19  When specifying the ceiling of a protected object, one should choose
      a value that is at least as high as the highest active priority at which
      tasks can be executing when they call protected operations of that
      object. In determining this value the following factors, which can
      affect active priority, should be considered: the effect of
      Set_Priority, nested protected operations, entry calls, task activation,
      and other implementation-defined factors.

22    20  Attaching a protected procedure whose ceiling is below the interrupt
      hardware priority to an interrupt causes the execution of the program to
      be erroneous (see C.3.1).

23    21  On a single processor implementation, the ceiling priority rules
      guarantee that there is no possibility of deadlock involving only
      protected subprograms (excluding the case where a protected operation
      calls another protected operation on the same protected object).




D.4 Entry Queuing Policies


1/1   This clause specifies a mechanism for a user to choose an entry queuing
policy. It also defines {two}[one] such polic{ies}[y]. Other policies are
implementation defined.


                                   Syntax

2     The form of a pragma Queuing_Policy is as follows:

3       pragma Queuing_Policy(policy_identifier);


                               Legality Rules

4     The policy_identifier shall be either FIFO_Queuing, Priority_Queuing or
an implementation-defined identifier.


                           Post-Compilation Rules

5     A Queuing_Policy pragma is a configuration pragma.


                              Dynamic Semantics

6     A queuing policy governs the order in which tasks are queued for entry
service, and the order in which different entry queues are considered for
service. The queuing policy is specified by a Queuing_Policy pragma.

7     Two queuing policies, FIFO_Queuing and Priority_Queuing, are language
defined. If no Queuing_Policy pragma appears in any of the program units
comprising the partition, the queuing policy for that partition is
FIFO_Queuing. The rules for this policy are specified in 9.5.3 and 9.7.1.

8     The Priority_Queuing policy is defined as follows:

9     The calls to an entry (including a member of an entry family) are queued
      in an order consistent with the priorities of the calls. The priority of
      an entry call is initialized from the active priority of the calling
      task at the time the call is made, but can change later. Within the same
      priority, the order is consistent with the calling (or requeuing, or
      priority setting) time (that is, a FIFO order).

10/1  After a call is first queued, changes to the active priority of a task
      do not affect the priority of the call, unless the base priority of the
      task is set{ while the task is blocked on an entry call}.

11    When the base priority of a task is set (see D.5), if the task is
      blocked on an entry call, and the call is queued, the priority of the
      call is updated to the new active priority of the calling task. This
      causes the call to be removed from and then reinserted in the queue at
      the new active priority.

12    When more than one condition of an entry_barrier of a protected object
      becomes True, and more than one of the respective queues is nonempty,
      the call with the highest priority is selected. If more than one such
      call has the same priority, the call that is queued on the entry whose
      declaration is first in textual order in the protected_definition is
      selected. For members of the same entry family, the one with the lower
      family index is selected.

13    If the expiration time of two or more open delay_alternatives is the
      same and no other accept_alternatives are open, the
      sequence_of_statements of the delay_alternative that is first in textual
      order in the selective_accept is executed.

14    When more than one alternative of a selective_accept is open and has
      queued calls, an alternative whose queue has the highest-priority call
      at its head is selected. If two or more open alternatives have
      equal-priority queued calls, then a call on the entry in the
      accept_alternative that is first in textual order in the
      selective_accept is selected.


                         Implementation Permissions

15    Implementations are allowed to define other queuing policies, but need
not support more than one such policy per partition.


                            Implementation Advice

16    The implementation should use names that end with ``_Queuing'' for
implementation-defined queuing policies.


D.5 Dynamic Priorities


1     This clause specifies how the base priority of a task can be modified or
queried at run time.


                              Static Semantics

2     The following language-defined library package exists:

3     with System;
      with Ada.Task_Identification; -- See C.7.1
      package Ada.Dynamic_Priorities is

4         procedure Set_Priority(Priority : in System.Any_Priority;
                                 T : in Ada.Task_Identification.Task_ID :=
                                 Ada.Task_Identification.Current_Task);

5         function Get_Priority (T : Ada.Task_Identification.Task_ID :=
                                 Ada.Task_Identification.Current_Task)
                                 return System.Any_Priority;

6     end Ada.Dynamic_Priorities;


                              Dynamic Semantics

7     The procedure Set_Priority sets the base priority of the specified task
to the specified Priority value. Set_Priority has no effect if the task is
terminated.

8     The function Get_Priority returns T's current base priority.
Tasking_Error is raised if the task is terminated.

9     Program_Error is raised by Set_Priority and Get_Priority if T is equal
to Null_Task_ID.

10    Setting the task's base priority to the new value takes place as soon as
is practical but not while the task is performing a protected action. This
setting occurs no later then the next abort completion point of the task T
(see 9.8).


                          Bounded (Run-Time) Errors

11    If a task is blocked on a protected entry call, and the call is queued,
it is a bounded error to raise its base priority above the ceiling priority of
the corresponding protected object. When an entry call is cancelled, it is a
bounded error if the priority of the calling task is higher than the ceiling
priority of the corresponding protected object. In either of these cases,
either Program_Error is raised in the task that called the entry, or its
priority is temporarily lowered, or both, or neither.


                             Erroneous Execution

12    If any subprogram in this package is called with a parameter T that
specifies a task object that no longer exists, the execution of the program is
erroneous.


                                   Metrics

13    The implementation shall document the following metric:

14    The execution time of a call to Set_Priority, for the nonpreempting
      case, in processor clock cycles. This is measured for a call that
      modifies the priority of a ready task that is not running (which cannot
      be the calling one), where the new base priority of the affected task is
      lower than the active priority of the calling task, and the affected
      task is not on any entry queue and is not executing a protected
      operation.

      NOTES

15    22  Setting a task's base priority affects task dispatching. First, it
      can change the task's active priority. Second, under the standard task
      dispatching policy it always causes the task to move to the tail of the
      ready queue corresponding to its active priority, even if the new base
      priority is unchanged.

16    23  Under the priority queuing policy, setting a task's base priority
      has an effect on a queued entry call if the task is blocked waiting for
      the call. That is, setting the base priority of a task causes the
      priority of a queued entry call from that task to be updated and the
      call to be removed and then reinserted in the entry queue at the new
      priority (see D.4), unless the call originated from the
      triggering_statement of an asynchronous_select.

17    24  The effect of two or more Set_Priority calls executed in parallel on
      the same task is defined as executing these calls in some serial order.

18    25  The rule for when Tasking_Error is raised for Set_Priority or
      Get_Priority is different from the rule for when Tasking_Error is raised
      on an entry call (see 9.5.3). In particular, setting or querying the
      priority of a completed or an abnormal task is allowed, so long as the
      task is not yet terminated.

19    26  Changing the priorities of a set of tasks can be performed by a
      series of calls to Set_Priority for each task separately. For this to
      work reliably, it should be done within a protected operation that has
      high enough ceiling priority to guarantee that the operation completes
      without being preempted by any of the affected tasks.


D.6 Preemptive Abort


1     This clause specifies requirements on the immediacy with which an
aborted construct is completed.


                              Dynamic Semantics

2     On a system with a single processor, an aborted construct is completed
immediately at the first point that is outside the execution of an
abort-deferred operation.


                         Documentation Requirements

3     On a multiprocessor, the implementation shall document any conditions
that cause the completion of an aborted construct to be delayed later than
what is specified for a single processor.


                                   Metrics

4     The implementation shall document the following metrics:

5     The execution time, in processor clock cycles, that it takes for an
      abort_statement to cause the completion of the aborted task. This is
      measured in a situation where a task T2 preempts task T1 and aborts T1.
      T1 does not have any finalization code. T2 shall verify that T1 has
      terminated, by means of the Terminated attribute.

6     On a multiprocessor, an upper bound in seconds, on the time that the
      completion of an aborted task can be delayed beyond the point that it is
      required for a single processor.

7     An upper bound on the execution time of an asynchronous_select, in
      processor clock cycles. This is measured between a point immediately
      before a task T1 executes a protected operation Pr.Set that makes the
      condition of an entry_barrier Pr.Wait true, and the point where task T2
      resumes execution immediately after an entry call to Pr.Wait in an
      asynchronous_select. T1 preempts T2 while T2 is executing the abortable
      part, and then blocks itself so that T2 can execute. The execution time
      of T1 is measured separately, and subtracted.

8     An upper bound on the execution time of an asynchronous_select, in the
      case that no asynchronous transfer of control takes place. This is
      measured between a point immediately before a task executes the
      asynchronous_select with a nonnull abortable part, and the point where
      the task continues execution immediately after it. The execution time of
      the abortable part is subtracted.


                            Implementation Advice

9     Even though the abort_statement is included in the list of potentially
blocking operations (see 9.5.1), it is recommended that this statement be
implemented in a way that never requires the task executing the
abort_statement to block.

10    On a multi-processor, the delay associated with aborting a task on
another processor should be bounded; the implementation should use periodic
polling, if necessary, to achieve this.

      NOTES

11    27  Abortion does not change the active or base priority of the aborted
      task.

12    28  Abortion cannot be more immediate than is allowed by the rules for
      deferral of abortion during finalization and in protected actions.


D.7 Tasking Restrictions


1     This clause defines restrictions that can be used with a pragma
Restrictions (see 13.12) to facilitate the construction of highly efficient
tasking run-time systems.


                              Static Semantics

2     The following restriction_identifiers are language defined:

3     No_Task_Hierarchy
              All (nonenvironment) tasks depend directly on the environment
              task of the partition.

4/1   No_Nested_Finalization
              Objects with controlled{, protected, or task} parts and access
              types that designate such objects{,} shall be declared only at
              library level.

5     No_Abort_Statements
              There are no abort_statements, and there are no calls on
              Task_Identification.Abort_Task.

6     No_Terminate_Alternatives
              There are no selective_accepts with terminate_alternatives.

7     No_Task_Allocators
              There are no allocators for task types or types containing task
              subcomponents.

8     No_Implicit_Heap_Allocations
              There are no operations that implicitly require heap storage
              allocation to be performed by the implementation. The operations
              that implicitly require heap storage allocation are
              implementation defined.

9     No_Dynamic_Priorities
              There are no semantic dependences on the package
              Dynamic_Priorities.

10    No_Asynchronous_Control
              There are no semantic dependences on the package
              Asynchronous_Task_Control.

11    The following restriction_parameter_identifiers are language defined:

12    Max_Select_Alternatives
              Specifies the maximum number of alternatives in a
              selective_accept.

13    Max_Task_Entries
              Specifies the maximum number of entries per task. The bounds of
              every entry family of a task unit shall be static, or shall be
              defined by a discriminant of a subtype whose corresponding bound
              is static. A value of zero indicates that no rendezvous are
              possible.

14    Max_Protected_Entries
              Specifies the maximum number of entries per protected type. The
              bounds of every entry family of a protected unit shall be
              static, or shall be defined by a discriminant of a subtype whose
              corresponding bound is static.


                              Dynamic Semantics

15/1  This paragraph was deleted.[If the following restrictions are violated,
the behavior is implementation defined. If an implementation chooses to detect
such a violation, Storage_Error should be raised.]

16    The following restriction_parameter_identifiers are language defined:

17/1  Max_Storage_At_Blocking
              Specifies the maximum portion (in storage elements) of a task's
              Storage_Size that can be retained by a blocked task{. If an
              implementation chooses to detect a violation of this
              restriction, Storage_Error should be raised; otherwise, the
              behavior is implementation defined}.

18/1  Max_Asynchronous_Select_Nesting
              Specifies the maximum dynamic nesting level of
              asynchronous_selects. A value of zero prevents the use of any
              asynchronous_select{ and, if a program contains an asynchronous_-
              select, it is illegal. If an implementation chooses to detect a
              violation of this restriction for values other than zero,
              Storage_Error should be raised; otherwise, the behavior is
              implementation defined}.

19/1  Max_Tasks
              Specifies the maximum number of task creations that may be
              executed over the lifetime of a partition, not counting the
              creation of the environment task{. A value of zero prevents any
              task creation and, if a program contains a task creation, it is
              illegal. If an implementation chooses to detect a violation of
              this restriction, Storage_Error should be raised; otherwise, the
              behavior is implementation defined}.

20    It is implementation defined whether the use of pragma Restrictions
results in a reduction in executable program size, storage requirements, or
execution time. If possible, the implementation should provide quantitative
descriptions of such effects for each restriction.


                            Implementation Advice

21    When feasible, the implementation should take advantage of the specified
restrictions to produce a more efficient implementation.

      NOTES

22    29  The above Storage_Checks can be suppressed with pragma Suppress.


D.8 Monotonic Time


1     This clause specifies a high-resolution, monotonic clock package.


                              Static Semantics

2     The following language-defined library package exists:

3     package Ada.Real_Time is

4       type Time is private;
        Time_First : constant Time;
        Time_Last : constant Time;
        Time_Unit : constant := implementation-defined-real-number;

5       type Time_Span is private;
        Time_Span_First : constant Time_Span;
        Time_Span_Last : constant Time_Span;
        Time_Span_Zero : constant Time_Span;
        Time_Span_Unit : constant Time_Span;

6       Tick : constant Time_Span;
        function Clock return Time;

7       function "+" (Left : Time; Right : Time_Span) return Time;
        function "+" (Left : Time_Span; Right : Time) return Time;
        function "-" (Left : Time; Right : Time_Span) return Time;
        function "-" (Left : Time; Right : Time) return Time_Span;

8       function "<" (Left, Right : Time) return Boolean;
        function "<="(Left, Right : Time) return Boolean;
        function ">" (Left, Right : Time) return Boolean;
        function ">="(Left, Right : Time) return Boolean;

9       function "+" (Left, Right : Time_Span) return Time_Span;
        function "-" (Left, Right : Time_Span) return Time_Span;
        function "-" (Right : Time_Span) return Time_Span;
        function "*" (Left : Time_Span; Right : Integer) return Time_Span;
        function "*" (Left : Integer; Right : Time_Span) return Time_Span;
        function "/" (Left, Right : Time_Span) return Integer;
        function "/" (Left : Time_Span; Right : Integer) return Time_Span;

10      function "abs"(Right : Time_Span) return Time_Span;

11/1  This paragraph was deleted.[ ]

12      function "<" (Left, Right : Time_Span) return Boolean;
        function "<="(Left, Right : Time_Span) return Boolean;
        function ">" (Left, Right : Time_Span) return Boolean;
        function ">="(Left, Right : Time_Span) return Boolean;

13      function To_Duration (TS : Time_Span) return Duration;
        function To_Time_Span (D : Duration) return Time_Span;

14      function Nanoseconds  (NS : Integer) return Time_Span;
        function Microseconds (US : Integer) return Time_Span;
        function Milliseconds (MS : Integer) return Time_Span;

15      type Seconds_Count is range implementation-defined;

16      procedure Split
      (T : in Time; SC : out Seconds_Count; TS : out Time_Span);
        function Time_Of(SC : Seconds_Count; TS : Time_Span) return Time;

17    private
         ... -- not specified by the language
      end Ada.Real_Time;

18    In this Annex, real time is defined to be the physical time as observed
in the external environment. The type Time is a time type as defined by 9.6;
values of this type may be used in a delay_until_statement. Values of this
type represent segments of an ideal time line. The set of values of the type
Time corresponds one-to-one with an implementation-defined range of
mathematical integers.

19    The Time value I represents the half-open real time interval that starts
with E+I*Time_Unit and is limited by E+(I+1)*Time_Unit, where Time_Unit is an
implementation-defined real number and E is an unspecified origin point, the
epoch, that is the same for all values of the type Time. It is not specified
by the language whether the time values are synchronized with any standard
time reference. For example, E can correspond to the time of system
initialization or it can correspond to the epoch of some time standard.

20    Values of the type Time_Span represent length of real time duration. The
set of values of this type corresponds one-to-one with an
implementation-defined range of mathematical integers. The Time_Span value
corresponding to the integer I represents the real-time duration I*Time_Unit.

21    Time_First and Time_Last are the smallest and largest values of the Time
type, respectively. Similarly, Time_Span_First and Time_Span_Last are the
smallest and largest values of the Time_Span type, respectively.

22    A value of type Seconds_Count represents an elapsed time, measured in
seconds, since the epoch.


                              Dynamic Semantics

23    Time_Unit is the smallest amount of real time representable by the Time
type; it is expressed in seconds. Time_Span_Unit is the difference between two
successive values of the Time type. It is also the smallest positive value of
type Time_Span. Time_Unit and Time_Span_Unit represent the same real time
duration. A clock tick is a real time interval during which the clock value
(as observed by calling the Clock function) remains constant. Tick is the
average length of such intervals.

24    The function To_Duration converts the value TS to a value of type
Duration. Similarly, the function To_Time_Span converts the value D to a value
of type Time_Span. For both operations, the result is rounded to the nearest
exactly representable value (away from zero if exactly halfway between two
exactly representable values).

25    To_Duration(Time_Span_Zero) returns 0.0, and To_Time_Span(0.0) returns
Time_Span_Zero.

26    The functions Nanoseconds, Microseconds, and Milliseconds convert the
input parameter to a value of the type Time_Span. NS, US, and MS are
interpreted as a number of nanoseconds, microseconds, and milliseconds
respectively. The result is rounded to the nearest exactly representable value
(away from zero if exactly halfway between two exactly representable values).

27    The effects of the operators on Time and Time_Span are as for the
operators defined for integer types.

28    The function Clock returns the amount of time since the epoch.

29    The effects of the Split and Time_Of operations are defined as follows,
treating values of type Time, Time_Span, and Seconds_Count as mathematical
integers. The effect of Split(T,SC,TS) is to set SC and TS to values such that
T*Time_Unit = SC*1.0 + TS*Time_Unit, and 0.0 <= TS*Time_Unit < 1.0. The value
returned by Time_Of(SC,TS) is the value T such that T*Time_Unit = SC*1.0 +
TS*Time_Unit.


                         Implementation Requirements

30    The range of Time values shall be sufficient to uniquely represent the
range of real times from program start-up to 50 years later. Tick shall be no
greater than 1 millisecond. Time_Unit shall be less than or equal to 20
microseconds.

31    Time_Span_First shall be no greater than -3600 seconds, and
Time_Span_Last shall be no less than 3600 seconds.

32    A clock jump is the difference between two successive distinct values of
the clock (as observed by calling the Clock function). There shall be no
backward clock jumps.


                         Documentation Requirements

33    The implementation shall document the values of Time_First, Time_Last,
Time_Span_First, Time_Span_Last, Time_Span_Unit, and Tick.

34    The implementation shall document the properties of the underlying time
base used for the clock and for type Time, such as the range of values
supported and any relevant aspects of the underlying hardware or operating
system facilities used.

35    The implementation shall document whether or not there is any
synchronization with external time references, and if such synchronization
exists, the sources of synchronization information, the frequency of
synchronization, and the synchronization method applied.

36/1  The implementation shall document any aspects of the [the] external
environment that could interfere with the clock behavior as defined in this
clause.


                                   Metrics

37    For the purpose of the metrics defined in this clause, real time is
defined to be the International Atomic Time (TAI).

38    The implementation shall document the following metrics:

39    An upper bound on the real-time duration of a clock tick. This is a
      value D such that if t1 and t2 are any real times such that t1 < t2 and
      Clock(t1) = Clock(t2) then t2 - t1 <= D.

40    An upper bound on the size of a clock jump.

41    An upper bound on the drift rate of Clock with respect to real time.
      This is a real number D such that

    42    E*(1-D) <= (Clock(t+E) - Clock(t)) <= E*(1+D)
                  provided that: Clock(t) + E*(1+D) <= Time_Last.

43    where Clock(t) is the value of Clock at time t, and E is a real time
      duration not less than 24 hours. The value of E used for this metric
      shall be reported.

44    An upper bound on the execution time of a call to the Clock function, in
      processor clock cycles.

45    Upper bounds on the execution times of the operators of the types Time
      and Time_Span, in processor clock cycles.


                         Implementation Permissions

46    Implementations targeted to machines with word size smaller than 32 bits
need not support the full range and granularity of the Time and Time_Span
types.


                            Implementation Advice

47    When appropriate, implementations should provide configuration
mechanisms to change the value of Tick.

48    It is recommended that Calendar.Clock and Real_Time.Clock be implemented
as transformations of the same time base.

49    It is recommended that the ``best'' time base which exists in the
underlying system be available to the application through Clock. ``Best'' may
mean highest accuracy or largest range.

      NOTES

50    30  The rules in this clause do not imply that the implementation can
      protect the user from operator or installation errors which could result
      in the clock being set incorrectly.

51    31  Time_Unit is the granularity of the Time type. In contrast, Tick
      represents the granularity of Real_Time.Clock. There is no requirement
      that these be the same.


D.9 Delay Accuracy


1     This clause specifies performance requirements for the delay_statement.
The rules apply both to delay_relative_statement and to delay_until_statement.
Similarly, they apply equally to a simple delay_statement and to one which
appears in a delay_alternative.


                              Dynamic Semantics

2     The effect of the delay_statement for Real_Time.Time is defined in terms
of Real_Time.Clock:

3     If C(1) is a value of Clock read before a task executes a
      delay_relative_statement with duration D, and C(2) is a value of Clock
      read after the task resumes execution following that delay_statement,
      then C(2) - C(1) >= D.

4     If C is a value of Clock read after a task resumes execution following a
      delay_until_statement with Real_Time.Time value T, then C >= T.

5     A simple delay_statement with a negative or zero value for the
expiration time does not cause the calling task to be blocked; it is
nevertheless a potentially blocking operation (see 9.5.1).

6     When a delay_statement appears in a delay_alternative of a
timed_entry_call the selection of the entry call is attempted, regardless of
the specified expiration time. When a delay_statement appears in a
selective_accept_alternative, and a call is queued on one of the open entries,
the selection of that entry call proceeds, regardless of the value of the
delay expression.


                         Documentation Requirements

7     The implementation shall document the minimum value of the delay
expression of a delay_relative_statement that causes the task to actually be
blocked.

8     The implementation shall document the minimum difference between the
value of the delay expression of a delay_until_statement and the value of
Real_Time.Clock, that causes the task to actually be blocked.


                                   Metrics

9     The implementation shall document the following metrics:

10    An upper bound on the execution time, in processor clock cycles, of a
      delay_relative_statement whose requested value of the delay expression
      is less than or equal to zero.

11    An upper bound on the execution time, in processor clock cycles, of a
      delay_until_statement whose requested value of the delay expression is
      less than or equal to the value of Real_Time.Clock at the time of
      executing the statement. Similarly, for Calendar.Clock.

12    An upper bound on the lateness of a delay_relative_statement, for a
      positive value of the delay expression, in a situation where the task
      has sufficient priority to preempt the processor as soon as it becomes
      ready, and does not need to wait for any other execution resources. The
      upper bound is expressed as a function of the value of the delay
      expression. The lateness is obtained by subtracting the value of the
      delay expression from the actual duration. The actual duration is
      measured from a point immediately before a task executes the
      delay_statement to a point immediately after the task resumes execution
      following this statement.

13    An upper bound on the lateness of a delay_until_statement, in a
      situation where the value of the requested expiration time is after the
      time the task begins executing the statement, the task has sufficient
      priority to preempt the processor as soon as it becomes ready, and it
      does not need to wait for any other execution resources. The upper bound
      is expressed as a function of the difference between the requested
      expiration time and the clock value at the time the statement begins
      execution. The lateness of a delay_until_statement is obtained by
      subtracting the requested expiration time from the real time that the
      task resumes execution following this statement.

      NOTES

14    32  The execution time of a delay_statement that does not cause the task
      to be blocked (e.g. ``delay 0.0;'' ) is of interest in situations where
      delays are used to achieve voluntary round-robin task dispatching among
      equal-priority tasks.


D.10 Synchronous Task Control


1     This clause describes a language-defined private semaphore (suspension
object), which can be used for two-stage suspend operations and as a simple
building block for implementing higher-level queues.


                              Static Semantics

2     The following language-defined package exists:

3     package Ada.Synchronous_Task_Control is

4       type Suspension_Object is limited private;
        procedure Set_True(S : in out Suspension_Object);
        procedure Set_False(S : in out Suspension_Object);
        function Current_State(S : Suspension_Object) return Boolean;
        procedure Suspend_Until_True(S : in out Suspension_Object);
      private
           ... -- not specified by the language
      end Ada.Synchronous_Task_Control;

5     The type Suspension_Object is a by-reference type.


                              Dynamic Semantics

6     An object of the type Suspension_Object has two visible states: true and
false. Upon initialization, its value is set to false.

7     The operations Set_True and Set_False are atomic with respect to each
other and with respect to Suspend_Until_True; they set the state to true and
false respectively.

8     Current_State returns the current state of the object.

9     The procedure Suspend_Until_True blocks the calling task until the state
of the object S is true; at that point the task becomes ready and the state of
the object becomes false.

10    Program_Error is raised upon calling Suspend_Until_True if another task
is already waiting on that suspension object. Suspend_Until_True is a
potentially blocking operation (see 9.5.1).


                         Implementation Requirements

11    The implementation is required to allow the calling of Set_False and
Set_True during any protected action, even one that has its ceiling priority
in the Interrupt_Priority range.


D.11 Asynchronous Task Control


1     This clause introduces a language-defined package to do asynchronous
suspend/resume on tasks. It uses a conceptual held priority value to represent
the task's held state.


                              Static Semantics

2     The following language-defined library package exists:

3     with Ada.Task_Identification;
      package Ada.Asynchronous_Task_Control is
        procedure Hold(T : in Ada.Task_Identification.Task_ID);
        procedure Continue(T : in Ada.Task_Identification.Task_ID);
        function Is_Held(T : Ada.Task_Identification.Task_ID)
         return Boolean;
      end Ada.Asynchronous_Task_Control;


                              Dynamic Semantics

4     After the Hold operation has been applied to a task, the task becomes
held. For each processor there is a conceptual idle task, which is always
ready. The base priority of the idle task is below System.Any_Priority'First.
The held priority is a constant of the type integer whose value is below the
base priority of the idle task.

5     The Hold operation sets the state of T to held. For a held task: the
task's own base priority does not constitute an inheritance source (see D.1),
and the value of the held priority is defined to be such a source instead.

6     The Continue operation resets the state of T to not-held; T's active
priority is then reevaluated as described in D.1. This time, T's base priority
is taken into account.

7     The Is_Held function returns True if and only if T is in the held state.

8     As part of these operations, a check is made that the task identified by
T is not terminated. Tasking_Error is raised if the check fails. Program_Error
is raised if the value of T is Null_Task_ID.


                             Erroneous Execution

9     If any operation in this package is called with a parameter T that
specifies a task object that no longer exists, the execution of the program is
erroneous.


                         Implementation Permissions

10    An implementation need not support Asynchronous_Task_Control if it is
infeasible to support it in the target environment.

      NOTES

11    33  It is a consequence of the priority rules that held tasks cannot be
      dispatched on any processor in a partition (unless they are inheriting
      priorities) since their priorities are defined to be below the priority
      of any idle task.

12    34  The effect of calling Get_Priority and Set_Priority on a Held task
      is the same as on any other task.

13    35  Calling Hold on a held task or Continue on a non-held task has no
      effect.

14    36  The rules affecting queuing are derived from the above rules, in
      addition to the normal priority rules:

    15    When a held task is on the ready queue, its priority is so low as to
          never reach the top of the queue as long as there are other tasks on
          that queue.

    16    If a task is executing in a protected action, inside a rendezvous,
          or is inheriting priorities from other sources (e.g. when
          activated), it continues to execute until it is no longer executing
          the corresponding construct.

    17    If a task becomes held while waiting (as a caller) for a rendezvous
          to complete, the active priority of the accepting task is not
          affected.

    18/1  If a task becomes held while waiting in a selective_accept, and a{n}
          entry call is issued to one of the open entries, the corresponding
          {accept_alternative}[accept body] executes. When the rendezvous
          completes, the active priority of the accepting task is lowered to
          the held priority (unless it is still inheriting from other
          sources), and the task does not execute until another Continue.

    19    The same holds if the held task is the only task on a protected
          entry queue whose barrier becomes open. The corresponding entry body
          executes.


D.12 Other Optimizations and Determinism Rules


1     This clause describes various requirements for improving the response
and determinism in a real-time system.


                         Implementation Requirements

2     If the implementation blocks interrupts (see C.3) not as a result of
direct user action (e.g. an execution of a protected action) there shall be an
upper bound on the duration of this blocking.

3     The implementation shall recognize entry-less protected types. The
overhead of acquiring the execution resource of an object of such a type (see
9.5.1) shall be minimized. In particular, there should not be any overhead due
to evaluating entry_barrier conditions.

4     Unchecked_Deallocation shall be supported for terminated tasks that are
designated by access types, and shall have the effect of releasing all the
storage associated with the task. This includes any run-time system or heap
storage that has been implicitly allocated for the task by the implementation.


                         Documentation Requirements

5     The implementation shall document the upper bound on the duration of
interrupt blocking caused by the implementation. If this is different for
different interrupts or interrupt priority levels, it should be documented for
each case.


                                   Metrics

6     The implementation shall document the following metric:

7     The overhead associated with obtaining a mutual-exclusive access to an
      entry-less protected object. This shall be measured in the following way:

8     For a protected object of the form:

9     protected Lock is
         procedure Set;
         function Read return Boolean;
      private
         Flag : Boolean := False;
      end Lock;

10    protected body Lock is
         procedure Set is
         begin
            Flag := True;
         end Set;
         function Read return Boolean
         Begin
            return Flag;
         end Read;
      end Lock;

11    The execution time, in processor clock cycles, of a call to Set. This
      shall be measured between the point just before issuing the call, and
      the point just after the call completes. The function Read shall be
      called later to verify that Set was indeed called (and not optimized
      away). The calling task shall have sufficiently high priority as to not
      be preempted during the measurement period. The protected object shall
      have sufficiently high ceiling priority to allow the task to call Set.

12    For a multiprocessor, if supported, the metric shall be reported for the
      case where no contention (on the execution resource) exists from tasks
      executing on other processors.



                                   Annex E
                                 (normative)

                             Distributed Systems


1     This Annex defines facilities for supporting the implementation of
distributed systems using multiple partitions working cooperatively as part of
a single Ada program.


                           Post-Compilation Rules

2     A distributed system is an interconnection of one or more processing
nodes (a system resource that has both computational and storage
capabilities), and zero or more storage nodes (a system resource that has only
storage capabilities, with the storage addressable by one or more processing
nodes).

3     A distributed program comprises one or more partitions that execute
independently (except when they communicate) in a distributed system.

4     The process of mapping the partitions of a program to the nodes in a
distributed system is called configuring the partitions of the program.


                         Implementation Requirements

5     The implementation shall provide means for explicitly assigning library
units to a partition and for the configuring and execution of a program
consisting of multiple partitions on a distributed system; the means are
implementation defined.


                         Implementation Permissions

6     An implementation may require that the set of processing nodes of a
distributed system be homogeneous.

      NOTES

7     1  The partitions comprising a program may be executed on differently
      configured distributed systems or on a non-distributed system without
      requiring recompilation. A distributed program may be partitioned
      differently from the same set of library units without recompilation.
      The resulting execution is semantically equivalent.

8     2  A distributed program retains the same type safety as the equivalent
      single partition program.


E.1 Partitions


1     The partitions of a distributed program are classified as either active
or passive.


                           Post-Compilation Rules

2     An active partition is a partition as defined in 10.2. A passive
partition is a partition that has no thread of control of its own, whose
library units are all preelaborated, and whose data and subprograms are
accessible to one or more active partitions.

3     A passive partition shall include only library_items that either are
declared pure or are shared passive (see 10.2.1 and E.2.1).

4     An active partition shall be configured on a processing node. A passive
partition shall be configured either on a storage node or on a processing node.

5     The configuration of the partitions of a program onto a distributed
system shall be consistent with the possibility for data references or calls
between the partitions implied by their semantic dependences. Any reference to
data or call of a subprogram across partitions is called a remote access.


                              Dynamic Semantics

6     A library_item is elaborated as part of the elaboration of each
partition that includes it. If a normal library unit (see E.2) has state, then
a separate copy of the state exists in each active partition that elaborates
it. The state evolves independently in each such partition.

7     An active partition terminates when its environment task terminates. A
partition becomes inaccessible if it terminates or if it is aborted. An active
partition is aborted when its environment task is aborted. In addition, if a
partition fails during its elaboration, it becomes inaccessible to other
partitions. Other implementation-defined events can also result in a partition
becoming inaccessible.

8/1   For a {prefix}[prefix] D that denotes a library-level declaration,
excepting a declaration of or within a declared-pure library unit, the
following attribute is defined:

9     D'Partition_ID
              Denotes a value of the type universal_integer that identifies
              the partition in which D was elaborated. If D denotes the
              declaration of a remote call interface library unit (see E.2.3)
              the given partition is the one where the body of D was
              elaborated.


                          Bounded (Run-Time) Errors

10    It is a bounded error for there to be cyclic elaboration dependences
between the active partitions of a single distributed program. The possible
effects are deadlock during elaboration, or the raising of Program_Error in
one or all of the active partitions involved.


                         Implementation Permissions

11    An implementation may allow multiple active or passive partitions to be
configured on a single processing node, and multiple passive partitions to be
configured on a single storage node. In these cases, the scheduling policies,
treatment of priorities, and management of shared resources between these
partitions are implementation defined.

12    An implementation may allow separate copies of an active partition to be
configured on different processing nodes, and to provide appropriate
interactions between the copies to present a consistent state of the partition
to other active partitions.

13    In an implementation, the partitions of a distributed program need not
be loaded and elaborated all at the same time; they may be loaded and
elaborated one at a time over an extended period of time. An implementation
may provide facilities to abort and reload a partition during the execution of
a distributed program.

14    An implementation may allow the state of some of the partitions of a
distributed program to persist while other partitions of the program terminate
and are later reinvoked.

      NOTES

15    3  Library units are grouped into partitions after compile time, but
      before run time. At compile time, only the relevant library unit
      properties are identified using categorization pragmas.

16    4  The value returned by the Partition_ID attribute can be used as a
      parameter to implementation-provided subprograms in order to query
      information about the partition.


E.2 Categorization of Library Units


1     Library units can be categorized according to the role they play in a
distributed program. Certain restrictions are associated with each category to
ensure that the semantics of a distributed program remain close to the
semantics for a nondistributed program.

2     A categorization pragma is a library unit pragma (see 10.1.5) that
restricts the declarations, child units, or semantic dependences of the
library unit to which it applies. A categorized library unit is a library unit
to which a categorization pragma applies.

3     The pragmas Shared_Passive, Remote_Types, and Remote_Call_Interface are
categorization pragmas. In addition, for the purposes of this Annex, the
pragma Pure (see 10.2.1) is considered a categorization pragma.

4/1   A library package or generic library package is called a shared passive
library unit if a Shared_Passive pragma applies to it. A library package or
generic library package is called a remote types library unit if a
Remote_Types pragma applies to it. A library {unit}[package or generic library
package] is called a remote call interface if a Remote_Call_Interface pragma
applies to it. A normal library unit is one to which no categorization pragma
applies.

5     The various categories of library units and the associated restrictions
are described in this clause and its subclauses. The categories are related
hierarchically in that the library units of one category can depend
semantically only on library units of that category or an earlier one, except
that the body of a remote types or remote call interface library unit is
unrestricted.

6     The overall hierarchy (including declared pure) is as follows:

7     Declared Pure
              Can depend only on other declared pure library units;

8     Shared Passive
              Can depend only on other shared passive or declared pure library
              units;

9     Remote Types
              The declaration of the library unit can depend only on other
              remote types library units, or one of the above; the body of the
              library unit is unrestricted;

10    Remote Call Interface
              The declaration of the library unit can depend only on other
              remote call interfaces, or one of the above; the body of the
              library unit is unrestricted;

11    Normal  Unrestricted.

12    Declared pure and shared passive library units are preelaborated. The
declaration of a remote types or remote call interface library unit is
required to be preelaborable.


                         Implementation Requirements

13/1  This paragraph was deleted.[For a given library-level type declared in a
preelaborated library unit or in the declaration of a remote types or remote
call interface library unit, the implementation shall choose the same
representation for the type upon each elaboration of the type's declaration
for different partitions of the same program.]


                         Implementation Permissions

14    Implementations are allowed to define other categorization pragmas.


E.2.1 Shared Passive Library Units


1     A shared passive library unit is used for managing global data shared
between active partitions. The restrictions on shared passive library units
prevent the data or tasks of one active partition from being accessible to
another active partition through references implicit in objects declared in
the shared passive library unit.


                                   Syntax

2     The form of a pragma Shared_Passive is as follows:

3       pragma Shared_Passive[(library_unit_name)];


                               Legality Rules

4     A shared passive library unit is a library unit to which a
Shared_Passive pragma applies. The following restrictions apply to such a
library unit:

5     it shall be preelaborable (see 10.2.1);

6     it shall depend semantically only upon declared pure or shared passive
      library units;

7/1   it shall not contain a library-level declaration of an access type that
      designates a class-wide type, task type, or protected type with
      entry_declarations[; if the shared passive library unit is generic, it
      shall not contain a declaration for such an access type unless the
      declaration is nested within a body other than a package_body].

8     Notwithstanding the definition of accessibility given in 3.10.2, the
declaration of a library unit P1 is not accessible from within the declarative
region of a shared passive library unit P2, unless the shared passive library
unit P2 depends semantically on P1.


                              Static Semantics

9     A shared passive library unit is preelaborated.


                           Post-Compilation Rules

10    A shared passive library unit shall be assigned to at most one partition
within a given program.

11    Notwithstanding the rule given in 10.2, a compilation unit in a given
partition does not need (in the sense of 10.2) the shared passive library
units on which it depends semantically to be included in that same partition;
they will typically reside in separate passive partitions.


E.2.2 Remote Types Library Units


1     A remote types library unit supports the definition of types intended
for use in communication between active partitions.


                                   Syntax

2     The form of a pragma Remote_Types is as follows:

3       pragma Remote_Types[(library_unit_name)];


                               Legality Rules

4     A remote types library unit is a library unit to which the pragma
Remote_Types applies. The following restrictions apply to the declaration of
such a library unit:

5     it shall be preelaborable;

6     it shall depend semantically only on declared pure, shared passive, or
      other remote types library units;

7     it shall not contain the declaration of any variable within the visible
      part of the library unit;

8     if the full view of a type declared in the visible part of the library
      unit has a part that is of a non-remote access type, then that access
      type, or the type of some part that includes the access type
      subcomponent, shall have user-specified Read and Write attributes.

9/1   {}An access type declared in the visible part of a remote types or
remote call interface library unit is called a remote access type. Such a type
shall be{:}[ either an access-to-subprogram type or a general access type that
designates a class-wide limited private type.]

9.1/1 {an access-to-subprogram type, or}

9.2/1 {a general access type that designates a class-wide limited private type
      or a class-wide private type extension all of whose ancestors are either
      private type extensions or limited private types.}

9.3/1 {A type that is derived from a remote access type is also a remote
access type.}

10    The following restrictions apply to the use of a remote
access-to-subprogram type:

11    A value of a remote access-to-subprogram type shall be converted only to
      another (subtype-conformant) remote access-to-subprogram type;

12    The prefix of an Access attribute_reference that yields a value of a
      remote access-to-subprogram type shall statically denote a
      (subtype-conformant) remote subprogram.

13    The following restrictions apply to the use of a remote
access-to-class-wide type:

14/1  The primitive subprograms of the corresponding specific limited private
      type shall only have access parameters if they are controlling formal
      parameters; {each non-controlling formal parameter shall have either a
      nonlimited type or a type with}[the types of all the non-controlling
      formal parameters shall have] Read and Write attributes{ specified via
      an attribute_definition_clause;}[.]

15    A value of a remote access-to-class-wide type shall be explicitly
      converted only to another remote access-to-class-wide type;

16/1  A value of a remote access-to-class-wide type shall be dereferenced (or
      implicitly converted to an anonymous access type) only as part of a
      dispatching call where the value designates a controlling operand of the
      call (see E.4, ``Remote Subprogram Calls''){.}[;]

17/1  The Storage_Pool and Storage_Size attributes are not defined for remote
      access-to-class-wide types; the expected type for an allocator shall not
      be a remote access-to-class-wide type; a remote access-to-class-wide
      type shall not be an actual parameter for a generic formal access
      type{.}[;]

      NOTES

18    5  A remote types library unit need not be pure, and the types it
      defines may include levels of indirection implemented by using access
      types. User-specified Read and Write attributes (see 13.13.2) provide
      for sending values of such a type between active partitions, with Write
      marshalling the representation, and Read unmarshalling any levels of
      indirection.


E.2.3 Remote Call Interface Library Units


1     A remote call interface library unit can be used as an interface for
remote procedure calls (RPCs) (or remote function calls) between active
partitions.


                                   Syntax

2     The form of a pragma Remote_Call_Interface is as follows:

3       pragma Remote_Call_Interface[(library_unit_name)];

4     The form of a pragma All_Calls_Remote is as follows:

5       pragma All_Calls_Remote[(library_unit_name)];

6     A pragma All_Calls_Remote is a library unit pragma.


                               Legality Rules

7/1   A remote call interface (RCI) is a library unit to which the pragma
Remote_Call_Interface applies. A subprogram declared in the visible part of
such a library unit{, or declared by such a library unit,} is called a remote
subprogram.

8     The declaration of an RCI library unit shall be preelaborable (see
10.2.1), and shall depend semantically only upon declared pure, shared
passive, remote types, or other remote call interface library units.

9/1   In addition, the following restrictions apply to [the visible part of
]an RCI library unit:

10/1  it{s visible part} shall not contain the declaration of a variable;

11/1  it{s visible part} shall not contain the declaration of a limited type;

12/1  it{s visible part} shall not contain a nested generic_declaration;

13/1  it shall not {be, nor shall its visible part} contain{,} the declaration
      of a subprogram to which a pragma Inline applies;

14/1  it shall not {be, nor shall its visible part} contain{,} a subprogram
      (or access-to-subprogram) declaration whose profile has an access
      parameter, or a formal parameter of a limited type unless that limited
      type has user-specified Read and Write attributes;

15    any public child of the library unit shall be a remote call interface
      library unit.

16    If a pragma All_Calls_Remote applies to a library unit, the library unit
shall be a remote call interface.


                           Post-Compilation Rules

17    A remote call interface library unit shall be assigned to at most one
partition of a given program. A remote call interface library unit whose
parent is also an RCI library unit shall be assigned only to the same
partition as its parent.

18    Notwithstanding the rule given in 10.2, a compilation unit in a given
partition that semantically depends on the declaration of an RCI library unit,
needs (in the sense of 10.2) only the declaration of the RCI library unit, not
the body, to be included in that same partition. Therefore, the body of an RCI
library unit is included only in the partition to which the RCI library unit
is explicitly assigned.


                         Implementation Requirements

19/1  If a pragma All_Calls_Remote applies to a given RCI library
{unit}[package], then the implementation shall route any call to a subprogram
of the RCI {unit}[package] from outside the declarative region of the
{unit}[package] through the Partition Communication Subsystem (PCS); see E.5.
Calls to such subprograms from within the declarative region of the
{unit}[package] are defined to be local and shall not go through the PCS.


                         Implementation Permissions

20    An implementation need not support the Remote_Call_Interface pragma nor
the All_Calls_Remote pragma. Explicit message-based communication between
active partitions can be supported as an alternative to RPC.


E.3 Consistency of a Distributed System


1     This clause defines attributes and rules associated with verifying the
consistency of a distributed program.


                              Static Semantics

2/1   For a {prefix}[prefix] P that statically denotes a program unit, the
following attributes are defined:

3     P'Version
              Yields a value of the predefined type String that identifies the
              version of the compilation unit that contains the declaration of
              the program unit.

4     P'Body_Version
              Yields a value of the predefined type String that identifies the
              version of the compilation unit that contains the body (but not
              any subunits) of the program unit.

5/1   The version of a compilation unit changes whenever the [version changes
for any ]compilation unit {changes in a semantically significant way. This
International Standard does not define the exact meaning of "semantically
significant"}[on which it depends semantically. The version also changes
whenever the compilation unit itself changes in a semantically significant
way]. It is {unspecified}[implementation defined] whether there are other
events (such as recompilation) that result in the version of a compilation
unit changing. {}

5.1/1 {If P is not a library unit, and P has no completion, then
P'Body_Version returns the Body_Version of the innermost program unit
enclosing the declaration of P. If P is a library unit, and P has no
completion, then P'Body_Version returns a value that is different from
Body_Version of any version of P that has a completion.}


                          Bounded (Run-Time) Errors

6     In a distributed program, a library unit is consistent if the same
version of its declaration is used throughout. It is a bounded error to
elaborate a partition of a distributed program that contains a compilation
unit that depends on a different version of the declaration of a shared
passive or RCI library unit than that included in the partition to which the
shared passive or RCI library unit was assigned. As a result of this error,
Program_Error can be raised in one or both partitions during elaboration; in
any case, the partitions become inaccessible to one another.


E.4 Remote Subprogram Calls


1     A remote subprogram call is a subprogram call that invokes the execution
of a subprogram in another partition. The partition that originates the remote
subprogram call is the calling partition, and the partition that executes the
corresponding subprogram body is the called partition. Some remote procedure
calls are allowed to return prior to the completion of subprogram execution.
These are called asynchronous remote procedure calls.

2     There are three different ways of performing a remote subprogram call:

3     As a direct call on a (remote) subprogram explicitly declared in a
      remote call interface;

4     As an indirect call through a value of a remote access-to-subprogram
      type;

5     As a dispatching call with a controlling operand designated by a value
      of a remote access-to-class-wide type.

6     The first way of calling corresponds to a static binding between the
calling and the called partition. The latter two ways correspond to a dynamic
binding between the calling and the called partition.

7     A remote call interface library unit (see E.2.3) defines the remote
subprograms or remote access types used for remote subprogram calls.


                               Legality Rules

8     In a dispatching call with two or more controlling operands, if one
controlling operand is designated by a value of a remote access-to-class-wide
type, then all shall be.


                              Dynamic Semantics

9     For the execution of a remote subprogram call, subprogram parameters
(and later the results, if any) are passed using a stream-oriented
representation (see 13.13.1) which is suitable for transmission between
partitions. This action is called marshalling. Unmarshalling is the reverse
action of reconstructing the parameters or results from the stream-oriented
representation. Marshalling is performed initially as part of the remote
subprogram call in the calling partition; unmarshalling is done in the called
partition. After the remote subprogram completes, marshalling is performed in
the called partition, and finally unmarshalling is done in the calling
partition.

10    A calling stub is the sequence of code that replaces the subprogram body
of a remotely called subprogram in the calling partition. A receiving stub is
the sequence of code (the ``wrapper'') that receives a remote subprogram call
on the called partition and invokes the appropriate subprogram body.

11    Remote subprogram calls are executed at most once, that is, if the
subprogram call returns normally, then the called subprogram's body was
executed exactly once.

12    The task executing a remote subprogram call blocks until the subprogram
in the called partition returns, unless the call is asynchronous. For an
asynchronous remote procedure call, the calling task can become ready before
the procedure in the called partition returns.

13    If a construct containing a remote call is aborted, the remote
subprogram call is cancelled. Whether the execution of the remote subprogram
is immediately aborted as a result of the cancellation is implementation
defined.

14    If a remote subprogram call is received by a called partition before the
partition has completed its elaboration, the call is kept pending until the
called partition completes its elaboration (unless the call is cancelled by
the calling partition prior to that).

15    If an exception is propagated by a remotely called subprogram, and the
call is not an asynchronous call, the corresponding exception is reraised at
the point of the remote subprogram call. For an asynchronous call, if the
remote procedure call returns prior to the completion of the remotely called
subprogram, any exception is lost.

16    The exception Communication_Error (see E.5) is raised if a remote call
cannot be completed due to difficulties in communicating with the called
partition.

17    All forms of remote subprogram calls are potentially blocking operations
(see 9.5.1).

18/1  In a remote subprogram call with a formal parameter of a class-wide
type, a check is made that the tag of the actual parameter identifies a tagged
type declared in a declared-pure or shared passive library unit, or in the
visible part of a remote types or remote call interface library unit.
Program_Error is raised if this check fails. {In a remote function call which
returns a class-wide type, the same check is made on the function result.}

19    In a dispatching call with two or more controlling operands that are
designated by values of a remote access-to-class-wide type, a check is made
(in addition to the normal Tag_Check - see 11.5) that all the remote
access-to-class-wide values originated from Access attribute_references that
were evaluated by tasks of the same active partition. Constraint_Error is
raised if this check fails.


                         Implementation Requirements

20    The implementation of remote subprogram calls shall conform to the PCS
interface as defined by the specification of the language-defined package
System.RPC (see E.5). The calling stub shall use the Do_RPC procedure unless
the remote procedure call is asynchronous in which case Do_APC shall be used.
On the receiving side, the corresponding receiving stub shall be invoked by
the RPC-receiver.

20.1/1 {With respect to shared variables in shared passive library units, the
execution of the corresponding subprogram body of a synchronous remote
procedure call is considered to be part of the execution of the calling task.
The execution of the corresponding subprogram body of an asynchronous remote
procedure call proceeds in parallel with the calling task and does not signal
the next action of the calling task (see 9.10).}

      NOTES

21    6  A given active partition can both make and receive remote subprogram
      calls. Thus, an active partition can act as both a client and a server.

22    7  If a given exception is propagated by a remote subprogram call, but
      the exception does not exist in the calling partition, the exception can
      be handled by an others choice or be propagated to and handled by a
      third partition.


E.4.1 Pragma Asynchronous


1     This subclause introduces the pragma Asynchronous which allows a remote
subprogram call to return prior to completion of the execution of the
corresponding remote subprogram body.


                                   Syntax

2     The form of a pragma Asynchronous is as follows:

3       pragma Asynchronous(local_name);


                               Legality Rules

4     The local_name of a pragma Asynchronous shall denote either:

5     One or more remote procedures; the formal parameters of the procedure(s)
      shall all be of mode in;

6     The first subtype of a remote access-to-procedure type; the formal
      parameters of the designated profile of the type shall all be of mode in;

7     The first subtype of a remote access-to-class-wide type.


                              Static Semantics

8     A pragma Asynchronous is a representation pragma. When applied to a
type, it specifies the type-related asynchronous aspect of the type.


                              Dynamic Semantics

9     A remote call is asynchronous if it is a call to a procedure, or a call
through a value of an access-to-procedure type, to which a pragma Asynchronous
applies. In addition, if a pragma Asynchronous applies to a remote
access-to-class-wide type, then a dispatching call on a procedure with a
controlling operand designated by a value of the type is asynchronous if the
formal parameters of the procedure are all of mode in.


                         Implementation Requirements

10    Asynchronous remote procedure calls shall be implemented such that the
corresponding body executes at most once as a result of the call.


E.4.2 Example of Use of a Remote Access-to-Class-Wide Type



                                  Examples

1     Example of using a remote access-to-class-wide type to achieve dynamic
binding across active partitions:

2     package Tapes is
         pragma Pure(Tapes);
         type Tape is abstract tagged limited private;
         -- Primitive dispatching operations where
         -- Tape is controlling operand
         procedure Copy (From, To : access Tape; Num_Recs : in Natural) is abstract;
         procedure Rewind (T : access Tape) is abstract;
         -- More operations
      private
         type Tape is ...
      end Tapes;

3     with Tapes;
      package Name_Server is
         pragma Remote_Call_Interface;
         -- Dynamic binding to remote operations is achieved
         -- using the access-to-limited-class-wide type Tape_Ptr
         type Tape_Ptr is access all Tapes.Tape'Class;
         -- The following statically bound remote operations
         -- allow for a name-server capability in this example
         function  Find     (Name : String) return Tape_Ptr;
         procedure Register (Name : in String; T : in Tape_Ptr);
         procedure Remove   (T : in Tape_Ptr);
         -- More operations
      end Name_Server;

4     package Tape_Driver is
        -- Declarations are not shown, they are irrelevant here
      end Tape_Driver;

5     with Tapes, Name_Server;
      package body Tape_Driver is
         type New_Tape is new Tapes.Tape with ...
         procedure Copy
          (From, To : access New_Tape; Num_Recs: in Natural) is
         begin
           . . .
         end Copy;
         procedure Rewind (T : access New_Tape) is
         begin
            . . .
         end Rewind;
         -- Objects remotely accessible through use
         -- of Name_Server operations
         Tape1, Tape2 : aliased New_Tape;
      begin
         Name_Server.Register ("NINE-TRACK",  Tape1'Access);
         Name_Server.Register ("SEVEN-TRACK", Tape2'Access);
      end Tape_Driver;

6     with Tapes, Name_Server;
      -- Tape_Driver is not needed and thus not mentioned in the with_clause
      procedure Tape_Client is
         T1, T2 : Name_Server.Tape_Ptr;
      begin
         T1 := Name_Server.Find ("NINE-TRACK");
         T2 := Name_Server.Find ("SEVEN-TRACK");
         Tapes.Rewind (T1);
         Tapes.Rewind (T2);
         Tapes.Copy (T1, T2, 3);
      end Tape_Client;

7     Notes on the example:

8/1   This paragraph was deleted.[ ]

9     The package Tapes provides the necessary declarations of the type and
      its primitive operations.

10    Name_Server is a remote call interface package and is elaborated in a
      separate active partition to provide the necessary naming services (such
      as Register and Find) to the entire distributed program through remote
      subprogram calls.

11    Tape_Driver is a normal package that is elaborated in a partition
      configured on the processing node that is connected to the tape
      device(s). The abstract operations are overridden to support the locally
      declared tape devices (Tape1, Tape2). The package is not visible to its
      clients, but it exports the tape devices (as remote objects) through the
      services of the Name_Server. This allows for tape devices to be
      dynamically added, removed or replaced without requiring the
      modification of the clients' code.

12    The Tape_Client procedure references only declarations in the Tapes and
      Name_Server packages. Before using a tape for the first time, it needs
      to query the Name_Server for a system-wide identity for that tape. From
      then on, it can use that identity to access the tape device.

13    Values of remote access type Tape_Ptr include the necessary information
      to complete the remote dispatching operations that result from
      dereferencing the controlling operands T1 and T2.


E.5 Partition Communication Subsystem


1     The Partition Communication Subsystem (PCS) provides facilities for
supporting communication between the active partitions of a distributed
program. The package System.RPC is a language-defined interface to the PCS. An
implementation conforming to this Annex shall use the RPC interface to
implement remote subprogram calls.


                              Static Semantics

2     The following language-defined library package exists:

3     with Ada.Streams; -- see 13.13.1
      package System.RPC is

4        type Partition_ID is range 0 .. implementation-defined;

5        Communication_Error : exception;

6        type Params_Stream_Type (
            Initial_Size : Ada.Streams.Stream_Element_Count) is new
            Ada.Streams.Root_Stream_Type with private;

7        procedure Read(
            Stream : in out Params_Stream_Type;
            Item : out Ada.Streams.Stream_Element_Array;
            Last : out Ada.Streams.Stream_Element_Offset);

8        procedure Write(
            Stream : in out Params_Stream_Type;
            Item : in Ada.Streams.Stream_Element_Array);

9        -- Synchronous call
         procedure Do_RPC(
            Partition  : in Partition_ID;
            Params     : access Params_Stream_Type;
            Result     : access Params_Stream_Type);

10       -- Asynchronous call
         procedure Do_APC(
            Partition  : in Partition_ID;
            Params     : access Params_Stream_Type);

11       -- The handler for incoming RPCs
         type RPC_Receiver is access procedure(
            Params     : access Params_Stream_Type;
            Result     : access Params_Stream_Type);

12       procedure Establish_RPC_Receiver(
            Partition : in Partition_ID;
            Receiver  : in RPC_Receiver);

13    private
         ... -- not specified by the language
      end System.RPC;

14    A value of the type Partition_ID is used to identify a partition.

15    An object of the type Params_Stream_Type is used for identifying the
particular remote subprogram that is being called, as well as marshalling and
unmarshalling the parameters or result of a remote subprogram call, as part of
sending them between partitions.

16    The Read and Write procedures override the corresponding abstract
operations for the type Params_Stream_Type.


                              Dynamic Semantics

17    The Do_RPC and Do_APC procedures send a message to the active partition
identified by the Partition parameter.

18    After sending the message, Do_RPC blocks the calling task until a reply
message comes back from the called partition or some error is detected by the
underlying communication system in which case Communication_Error is raised at
the point of the call to Do_RPC.

19    Do_APC operates in the same way as Do_RPC except that it is allowed to
return immediately after sending the message.

20    Upon normal return, the stream designated by the Result parameter of
Do_RPC contains the reply message.

21    The procedure System.RPC.Establish_RPC_Receiver is called once,
immediately after elaborating the library units of an active partition (that
is, right after the elaboration of the partition) if the partition includes an
RCI library unit, but prior to invoking the main subprogram, if any. The
Partition parameter is the Partition_ID of the active partition being
elaborated. The Receiver parameter designates an implementation-provided
procedure called the RPC-receiver which will handle all RPCs received by the
partition from the PCS. Establish_RPC_Receiver saves a reference to the
RPC-receiver; when a message is received at the called partition, the
RPC-receiver is called with the Params stream containing the message. When the
RPC-receiver returns, the contents of the stream designated by Result is
placed in a message and sent back to the calling partition.

22    If a call on Do_RPC is aborted, a cancellation message is sent to the
called partition, to request that the execution of the remotely called
subprogram be aborted.

23    The subprograms declared in System.RPC are potentially blocking
operations.


                         Implementation Requirements

24    The implementation of the RPC-receiver shall be reentrant, thereby
allowing concurrent calls on it from the PCS to service concurrent remote
subprogram calls into the partition.

24.1/1 {An implementation shall not restrict the replacement of the body of
System.RPC. An implementation shall not restrict children of System.RPC. The
related implementation permissions in the introduction to Annex A do not
apply.}

24.2/1 {If the implementation of System.RPC is provided by the user, an
implementation shall support remote subprogram calls as specified.}


                         Documentation Requirements

25    The implementation of the PCS shall document whether the RPC-receiver is
invoked from concurrent tasks. If there is an upper limit on the number of
such tasks, this limit shall be documented as well, together with the
mechanisms to configure it (if this is supported).


                         Implementation Permissions

26    The PCS is allowed to contain implementation-defined interfaces for
explicit message passing, broadcasting, etc. Similarly, it is allowed to
provide additional interfaces to query the state of some remote partition
(given its partition ID) or of the PCS itself, to set timeouts and retry
parameters, to get more detailed error status, etc. These additional
interfaces should be provided in child packages of System.RPC.

27    A body for the package System.RPC need not be supplied by the
implementation.


                            Implementation Advice

28    Whenever possible, the PCS on the called partition should allow for
multiple tasks to call the RPC-receiver with different messages and should
allow them to block until the corresponding subprogram body returns.

29    The Write operation on a stream of type Params_Stream_Type should raise
Storage_Error if it runs out of space trying to write the Item into the
stream.

      NOTES

30    8  The package System.RPC is not designed for direct calls by user
      programs. It is instead designed for use in the implementation of remote
      subprograms calls, being called by the calling stubs generated for a
      remote call interface library unit to initiate a remote call, and in
      turn calling back to an RPC-receiver that dispatches to the receiving
      stubs generated for the body of a remote call interface, to handle a
      remote call received from elsewhere.



                                   Annex F
                                 (normative)

                             Information Systems


1     This Annex provides a set of facilities relevant to Information Systems
programming. These fall into several categories:

2     an attribute definition clause specifying Machine_Radix for a decimal
      subtype;

3     the package Decimal, which declares a set of constants defining the
      implementation's capacity for decimal types, and a generic procedure for
      decimal division; and

4     the child packages Text_IO.Editing and Wide_Text_IO.Editing, which
      support formatted and localized output of decimal data, based on ``
      picture String'' values.

5     See also: 3.5.9, ``Fixed Point Types''; 3.5.10, ``
Operations of Fixed Point Types''; 4.6, ``Type Conversions''; 13.3, ``
Operational and Representation Attributes''; A.10.9, ``
Input-Output for Real Types''; B.4, ``Interfacing with COBOL''; B.3, ``
Interfacing with C''; Annex G, ``Numerics''.

6     The character and string handling packages in Annex A, ``
Predefined Language Environment'' are also relevant for Information Systems.


                            Implementation Advice

7     If COBOL (respectively, C) is widely supported in the target
environment, implementations supporting the Information Systems Annex should
provide the child package Interfaces.COBOL (respectively, Interfaces.C)
specified in Annex B and should support a convention_identifier of COBOL
(respectively, C) in the interfacing pragmas (see Annex B), thus allowing Ada
programs to interface with programs written in that language.


F.1 Machine_Radix Attribute Definition Clause



                              Static Semantics

1     Machine_Radix may be specified for a decimal first subtype (see 3.5.9)
via an attribute_definition_clause; the expression of such a clause shall be
static, and its value shall be 2 or 10. A value of 2 implies a binary base
range; a value of 10 implies a decimal base range.


                            Implementation Advice

2     Packed decimal should be used as the internal representation for objects
of subtype S when S'Machine_Radix = 10.


                                  Examples

3     Example of Machine_Radix attribute definition clause:

4     type Money is delta 0.01 digits 15;
      for Money'Machine_Radix use 10;


F.2 The Package Decimal



                              Static Semantics

1     The library package Decimal has the following declaration:

2     package Ada.Decimal is
         pragma Pure(Decimal);

3        Max_Scale : constant := implementation-defined;
         Min_Scale : constant := implementation-defined;

4        Min_Delta : constant := 10.0**(-Max_Scale);
         Max_Delta : constant := 10.0**(-Min_Scale);

5        Max_Decimal_Digits : constant := implementation-defined;

6        generic
            type Dividend_Type  is delta <> digits <>;
            type Divisor_Type   is delta <> digits <>;
            type Quotient_Type  is delta <> digits <>;
            type Remainder_Type is delta <> digits <>;
         procedure Divide (Dividend  : in Dividend_Type;
                           Divisor   : in Divisor_Type;
                           Quotient  : out Quotient_Type;
                           Remainder : out Remainder_Type);
         pragma Convention(Intrinsic, Divide);

7     end Ada.Decimal;

8     Max_Scale is the largest N such that 10.0**(-N) is allowed as a decimal
type's delta. Its type is universal_integer.

9     Min_Scale is the smallest N such that 10.0**(-N) is allowed as a decimal
type's delta. Its type is universal_integer.

10    Min_Delta is the smallest value allowed for delta in a
decimal_fixed_point_definition. Its type is universal_real.

11    Max_Delta is the largest value allowed for delta in a
decimal_fixed_point_definition. Its type is universal_real.

12    Max_Decimal_Digits is the largest value allowed for digits in a
decimal_fixed_point_definition. Its type is universal_integer.


                              Static Semantics

13    The effect of Divide is as follows. The value of Quotient is
Quotient_Type(Dividend/Divisor). The value of Remainder is
Remainder_Type(Intermediate), where Intermediate is the difference between
Dividend and the product of Divisor and Quotient; this result is computed
exactly.


                         Implementation Requirements

14    Decimal.Max_Decimal_Digits shall be at least 18.

15    Decimal.Max_Scale shall be at least 18.

16    Decimal.Min_Scale shall be at most 0.

      NOTES

17    1  The effect of division yielding a quotient with control over rounding
      versus truncation is obtained by applying either the function attribute
      Quotient_Type'Round or the conversion Quotient_Type to the expression
      Dividend/Divisor.


F.3 Edited Output for Decimal Types


1     The child packages Text_IO.Editing and Wide_Text_IO.Editing provide
localizable formatted text output, known as edited output , for decimal types.
An edited output string is a function of a numeric value, program-specifiable
locale elements, and a format control value. The numeric value is of some
decimal type. The locale elements are:

2     the currency string;

3     the digits group separator character;

4     the radix mark character; and

5     the fill character that replaces leading zeros of the numeric value.

6     For Text_IO.Editing the edited output and currency strings are of type
String, and the locale characters are of type Character. For
Wide_Text_IO.Editing their types are Wide_String and Wide_Character,
respectively.

7     Each of the locale elements has a default value that can be replaced or
explicitly overridden.

8     A format-control value is of the private type Picture; it determines the
composition of the edited output string and controls the form and placement of
the sign, the position of the locale elements and the decimal digits, the
presence or absence of a radix mark, suppression of leading zeros, and
insertion of particular character values.

9     A Picture object is composed from a String value, known as a picture
String, that serves as a template for the edited output string, and a Boolean
value that controls whether a string of all space characters is produced when
the number's value is zero. A picture String comprises a sequence of one- or
two-Character symbols, each serving as a placeholder for a character or string
at a corresponding position in the edited output string. The picture String
symbols fall into several categories based on their effect on the edited
output string:

10      Decimal Digit:    '9'
        Radix Control:    '.'   'V'
        Sign Control:     '+'   '-'   '<'   '>'   "CR"  "DB"
        Currency Control:       '$'   '#'
        Zero Suppression:       'Z'   '*'
        Simple Insertion:       '_'   'B'   '0'   '/'

11    The entries are not case-sensitive. Mixed- or lower-case forms for "CR"
and "DB", and lower-case forms for 'V', 'Z', and 'B', have the same effect as
the upper-case symbols shown.

12    An occurrence of a '9' Character in the picture String represents a
decimal digit position in the edited output string.

13    A radix control Character in the picture String indicates the position
of the radix mark in the edited output string: an actual character position
for '.', or an assumed position for 'V'.

14    A sign control Character in the picture String affects the form of the
sign in the edited output string. The '<' and '>' Character values indicate
parentheses for negative values. A Character '+', '-', or '<' appears either
singly, signifying a fixed-position sign in the edited output, or repeated,
signifying a floating-position sign that is preceded by zero or more space
characters and that replaces a leading 0.

15    A currency control Character in the picture String indicates an
occurrence of the currency string in the edited output string. The '$'
Character represents the complete currency string; the '#' Character
represents one character of the currency string. A '$' Character appears
either singly, indicating a fixed-position currency string in the edited
output, or repeated, indicating a floating-position currency string that
occurs in place of a leading 0. A sequence of '#' Character values indicates
either a fixed- or floating-position currency string, depending on context.

16    A zero suppression Character in the picture String allows a leading zero
to be replaced by either the space character (for 'Z') or the fill character
(for '*').

17    A simple insertion Character in the picture String represents, in
general, either itself (if '/' or '0'), the space character (if 'B'), or the
digits group separator character (if '_'). In some contexts it is treated as
part of a floating sign, floating currency, or zero suppression string.

18    An example of a picture String is "<###Z_ZZ9.99>". If the currency
string is "FF", the separator character is ',', and the radix mark is '.' then
the edited output string values for the decimal values 32.10 and -5432.10 are
"bbFFbbb32.10b" and "(bFF5,432.10)", respectively, where 'b' indicates the
space character.

19    The generic packages Text_IO.Decimal_IO and Wide_Text_IO.Decimal_IO (see
A.10.9, ``Input-Output for Real Types'') provide text input and non-edited
text output for decimal types.

      NOTES

20    2  A picture String is of type Standard.String, both for Text_IO.Editing
      and Wide_Text_IO.Editing.


F.3.1 Picture String Formation


1     A well-formed picture String, or simply picture String, is a String
value that conforms to the syntactic rules, composition constraints, and
character replication conventions specified in this clause.


                              Dynamic Semantics

2/1   This paragraph was deleted.[ ]

3     picture_string ::=
         fixed_$_picture_string
       | fixed_#_picture_string
       | floating_currency_picture_string
       | non_currency_picture_string
      

4     fixed_$_picture_string ::=
         [fixed_LHS_sign] fixed_$_char {direct_insertion} [zero_suppression]
           number [RHS_sign]
      
       | [fixed_LHS_sign {direct_insertion}] [zero_suppression]
           number fixed_$_char {direct_insertion} [RHS_sign]
      
       | floating_LHS_sign number fixed_$_char {direct_insertion} [RHS_sign]
      
       | [fixed_LHS_sign] fixed_$_char {direct_insertion}
           all_zero_suppression_number {direct_insertion}  [RHS_sign]
      
       | [fixed_LHS_sign {direct_insertion}] all_zero_suppression_number {direct_insertion}
           fixed_$_char {direct_insertion} [RHS_sign]
      
       | all_sign_number {direct_insertion} fixed_$_char {direct_insertion} [RHS_sign]
      

5     fixed_#_picture_string ::=
         [fixed_LHS_sign] single_#_currency {direct_insertion}
           [zero_suppression] number [RHS_sign]
      
       | [fixed_LHS_sign] multiple_#_currency {direct_insertion}
           zero_suppression number [RHS_sign]
      
       | [fixed_LHS_sign {direct_insertion}] [zero_suppression]
           number fixed_#_currency {direct_insertion} [RHS_sign]
      
       | floating_LHS_sign number fixed_#_currency {direct_insertion} [RHS_sign]
      
       | [fixed_LHS_sign] single_#_currency {direct_insertion}
           all_zero_suppression_number {direct_insertion} [RHS_sign]
      
       | [fixed_LHS_sign] multiple_#_currency {direct_insertion}
           all_zero_suppression_number {direct_insertion} [RHS_sign]
      
       | [fixed_LHS_sign {direct_insertion}] all_zero_suppression_number {direct_insertion}
           fixed_#_currency {direct_insertion} [RHS_sign]
      
       | all_sign_number {direct_insertion} fixed_#_currency {direct_insertion} [RHS_sign]
      

6     floating_currency_picture_string ::=
         [fixed_LHS_sign] {direct_insertion} floating_$_currency number [RHS_sign]
       | [fixed_LHS_sign] {direct_insertion} floating_#_currency number [RHS_sign]
       | [fixed_LHS_sign] {direct_insertion} all_currency_number {direct_insertion} [RHS_sign]
      

7     non_currency_picture_string ::=
         [fixed_LHS_sign {direct_insertion}] zero_suppression number [RHS_sign]
       | [floating_LHS_sign] number [RHS_sign]
       | [fixed_LHS_sign {direct_insertion}] all_zero_suppression_number {direct_insertion}
           [RHS_sign]
       | all_sign_number {direct_insertion}
       | fixed_LHS_sign direct_insertion {direct_insertion} number [RHS_sign]
      

8     fixed_LHS_sign ::=  LHS_Sign

9     LHS_Sign ::=  + | - | <
      

10    fixed_$_char ::= $
      

11    direct_insertion ::=  simple_insertion

12    simple_insertion ::=  _ | B | 0 | /
      

13    zero_suppression ::=  Z {Z | context_sensitive_insertion} | fill_string

14    context_sensitive_insertion ::=  simple_insertion
      

15    fill_string ::=  * {* | context_sensitive_insertion}
      

16    number ::=
         fore_digits [radix [aft_digits] {direct_insertion}]
       | radix aft_digits {direct_insertion}

17    fore_digits ::= 9 {9 | direct_insertion}

18    aft_digits ::=  {9 | direct_insertion} 9

19    radix ::= . | V
      

20    RHS_sign ::= + | - | > | CR | DB
      

21    floating_LHS_sign ::=
         LHS_Sign {context_sensitive_insertion} LHS_Sign {LHS_Sign | context_sensitive_insertion}
      

22    single_#_currency ::= #

23    multiple_#_currency ::= ## {#}
      

24    fixed_#_currency ::= single_#_currency | multiple_#_currency
      

25    floating_$_currency ::=
         $ {context_sensitive_insertion} $ {$ | context_sensitive_insertion}
      

26    floating_#_currency ::=
         # {context_sensitive_insertion} # {# | context_sensitive_insertion}
      

27    all_sign_number ::=  all_sign_fore [radix [all_sign_aft]] [>]

28    all_sign_fore ::=
         sign_char {context_sensitive_insertion} sign_char {sign_char | context_sensitive_insertion}

29    all_sign_aft ::= {all_sign_aft_char} sign_char
      
      all_sign_aft_char ::=  sign_char | context_sensitive_insertion

30    sign_char ::= + | - | <
      

31    all_currency_number ::=  all_currency_fore [radix [all_currency_aft]]

32    all_currency_fore ::=
         currency_char {context_sensitive_insertion}
           currency_char {currency_char | context_sensitive_insertion}

33    all_currency_aft ::= {all_currency_aft_char} currency_char
      
      all_currency_aft_char ::= currency_char | context_sensitive_insertion

34    currency_char ::= $ | #
      

35    all_zero_suppression_number ::=  all_zero_suppression_fore [ radix [all_zero_suppression_aft]]

36    all_zero_suppression_fore ::=
         zero_suppression_char {zero_suppression_char | context_sensitive_insertion}

37    all_zero_suppression_aft ::= {all_zero_suppression_aft_char} zero_suppression_char
      
      all_zero_suppression_aft_char ::=  zero_suppression_char | context_sensitive_insertion

38    zero_suppression_char ::= Z | *

39    The following composition constraints apply to a picture String:

40    A floating_LHS_sign does not have occurrences of different LHS_Sign
      Character values.

41    If a picture String has '<' as fixed_LHS_sign, then it has '>' as
      RHS_sign.

42    If a picture String has '<' in a floating_LHS_sign or in an
      all_sign_number, then it has an occurrence of '>'.

43/1  If a picture String has '+' or '-' as fixed_LHS_sign, in a
      floating_LHS_sign, or in an all_sign_number, then it has no RHS_sign{ or
      '>' character}.

44    An instance of all_sign_number does not have occurrences of different
      sign_char Character values.

45    An instance of all_currency_number does not have occurrences of
      different currency_char Character values.

46    An instance of all_zero_suppression_number does not have occurrences of
      different zero_suppression_char Character values, except for possible
      case differences between 'Z' and 'z'.

47    A replicable Character is a Character that, by the above rules, can
occur in two consecutive positions in a picture String.

48    A Character replication is a String

49    char & '(' & spaces & count_string & ')'

50    where char is a replicable Character, spaces is a String (possibly
empty) comprising only space Character values, and count_string is a String of
one or more decimal digit Character values. A Character replication in a
picture String has the same effect as (and is said to be equivalent to) a
String comprising n consecutive occurrences of char, where
n=Integer'Value(count_string).

51    An expanded picture String is a picture String containing no Character
replications.

      NOTES

52    3  Although a sign to the left of the number can float, a sign to the
      right of the number is in a fixed position.


F.3.2 Edited Output Generation



                              Dynamic Semantics

1     The contents of an edited output string are based on:

2     A value, Item, of some decimal type Num,

3     An expanded picture String Pic_String,

4     A Boolean value, Blank_When_Zero,

5     A Currency string,

6     A Fill character,

7     A Separator character, and

8     A Radix_Mark character.

9     The combination of a True value for Blank_When_Zero and a '*' character
in Pic_String is inconsistent; no edited output string is defined.

10    A layout error is identified in the rules below if leading non-zero
digits of Item, character values of the Currency string, or a negative sign
would be truncated; in such cases no edited output string is defined.

11    The edited output string has lower bound 1 and upper bound N where N =
Pic_String'Length + Currency_Length_Adjustment - Radix_Adjustment, and

12    Currency_Length_Adjustment = Currency'Length - 1 if there is some
      occurrence of '$' in Pic_String, and 0 otherwise.

13    Radix_Adjustment = 1 if there is an occurrence of 'V' or 'v' in Pic_Str,
      and 0 otherwise.

14    Let the magnitude of Item be expressed as a base-10 number
I(p)···I(1).F(1)···F(q), called the displayed magnitude of Item, where:

15    q = Min(Max(Num'Scale, 0), n) where n is 0 if Pic_String has no radix
      and is otherwise the number of digit positions following radix in
      Pic_String, where a digit position corresponds to an occurrence of '9',
      a zero_suppression_char (for an all_zero_suppression_number), a
      currency_char (for an all_currency_number), or a sign_char (for an
      all_sign_number).

16    I(p) /= 0 if p>0.

17    If n < Num'Scale, then the above number is the result of rounding (away
from 0 if exactly midway between values).

18    If Blank_When_Zero = True and the displayed magnitude of Item is zero,
then the edited output string comprises all space character values. Otherwise,
the picture String is treated as a sequence of instances of syntactic
categories based on the rules in F.3.1, and the edited output string is the
concatenation of string values derived from these categories according to the
following mapping rules.

19    Table F-1 shows the mapping from a sign control symbol to a
corresponding character or string in the edited output. In the columns showing
the edited output, a lower-case 'b' represents the space character. If there
is no sign control symbol but the value of Item is negative, a layout error
occurs and no edited output string is produced.

          Table F-1: Edited Output for Sign Control Symbols

          Sign Control Symbol 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          Edited Output for
          Non-Negative Number 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          Edited Output for
          Negative Number

          '+' 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
'+' 

          '-'
          '-' 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
'b' 

          '-'
          '<' 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
'b' 

          '('
          '>' 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
'b' 

          ')'
          "CR" 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          "bb" 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          "CR"
          "DB" 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          "bb" 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          "DB"
20    An instance of fixed_LHS_sign maps to a character as shown in Table F-1.

21    An instance of fixed_$_char maps to Currency.

22    An instance of direct_insertion maps to Separator if direct_insertion =
'_', and to the direct_insertion Character otherwise.

23    An instance of number maps to a string integer_part & radix_part &
fraction_part where:

24    The string for integer_part is obtained as follows:

    25    1.  Occurrences of '9' in fore_digits of number are replaced from
              right to left with the decimal digit character values for I(1),
              ..., I(p), respectively.

    26    2.  Each occurrence of '9' in fore_digits to the left of the
              leftmost '9' replaced according to rule 1 is replaced with '0'.

    27    3.  If p exceeds the number of occurrences of '9' in fore_digits of
              number, then the excess leftmost digits are eligible for use in
              the mapping of an instance of zero_suppression,
              floating_LHS_sign, floating_$_currency, or floating_#_currency
              to the left of number; if there is no such instance, then a
              layout error occurs and no edited output string is produced.

28    The radix_part is:

    29    "" if number does not include a radix, if radix = 'V', or if radix =
          'v'

    30    Radix_Mark if number includes '.' as radix

31    The string for fraction_part is obtained as follows:

    32    1.  Occurrences of '9' in aft_digits of number are replaced from
              left to right with the decimal digit character values for F(1),
              ... F(q).

    33    2.  Each occurrence of '9' in aft_digits to the right of the
              rightmost '9' replaced according to rule 1 is replaced by '0'.

34    An instance of zero_suppression maps to the string obtained as follows:

35    1.  The rightmost 'Z', 'z', or '*' Character values are replaced with
          the excess digits (if any) from the integer_part of the mapping of
          the number to the right of the zero_suppression instance,

36    2.  A context_sensitive_insertion Character is replaced as though it
          were a direct_insertion Character, if it occurs to the right of some
          'Z', 'z', or '*' in zero_suppression that has been mapped to an
          excess digit,

37    3.  Each Character to the left of the leftmost Character replaced
          according to rule 1 above is replaced by:

    38    the space character if the zero suppression Character is 'Z' or 'z',
          or

    39    the Fill character if the zero suppression Character is '*'.

40    4.  A layout error occurs if some excess digits remain after all 'Z',
          'z', and '*' Character values in zero_suppression have been replaced
          via rule 1; no edited output string is produced.

41    An instance of RHS_sign maps to a character or string as shown in Table
F-1.

42    An instance of floating_LHS_sign maps to the string obtained as follows.

43    1.  Up to all but one of the rightmost LHS_Sign Character values are
          replaced by the excess digits (if any) from the integer_part of the
          mapping of the number to the right of the floating_LHS_sign instance.

44    2.  The next Character to the left is replaced with the character given
          by the entry in Table F-1 corresponding to the LHS_Sign Character.

45    3.  A context_sensitive_insertion Character is replaced as though it
          were a direct_insertion Character, if it occurs to the right of the
          leftmost LHS_Sign character replaced according to rule 1.

46    4.  Any other Character is replaced by the space character..

47    5.  A layout error occurs if some excess digits remain after replacement
          via rule 1; no edited output string is produced.

48    An instance of fixed_#_currency maps to the Currency string with n space
character values concatenated on the left (if the instance does not follow a
radix) or on the right (if the instance does follow a radix), where n is the
difference between the length of the fixed_#_currency instance and
Currency'Length. A layout error occurs if Currency'Length exceeds the length
of the fixed_#_currency instance; no edited output string is produced.

49    An instance of floating_$_currency maps to the string obtained as
follows:

50    1.  Up to all but one of the rightmost '$' Character values are replaced
          with the excess digits (if any) from the integer_part of the mapping
          of the number to the right of the floating_$_currency instance.

51    2.  The next Character to the left is replaced by the Currency string.

52    3.  A context_sensitive_insertion Character is replaced as though it
          were a direct_insertion Character, if it occurs to the right of the
          leftmost '$' Character replaced via rule 1.

53    4.  Each other Character is replaced by the space character.

54    5.  A layout error occurs if some excess digits remain after replacement
          by rule 1; no edited output string is produced.

55    An instance of floating_#_currency maps to the string obtained as
follows:

56    1.  Up to all but one of the rightmost '#' Character values are replaced
          with the excess digits (if any) from the integer_part of the mapping
          of the number to the right of the floating_#_currency instance.

57    2.  The substring whose last Character occurs at the position
          immediately preceding the leftmost Character replaced via rule 1,
          and whose length is Currency'Length, is replaced by the Currency
          string.

58    3.  A context_sensitive_insertion Character is replaced as though it
          were a direct_insertion Character, if it occurs to the right of the
          leftmost '#' replaced via rule 1.

59    4.  Any other Character is replaced by the space character.

60    5.  A layout error occurs if some excess digits remain after replacement
          rule 1, or if there is no substring with the required length for
          replacement rule 2; no edited output string is produced.

61    An instance of all_zero_suppression_number maps to:

62    a string of all spaces if the displayed magnitude of Item is zero, the
      zero_suppression_char is 'Z' or 'z', and the instance of
      all_zero_suppression_number does not have a radix at its last character
      position;

63    a string containing the Fill character in each position except for the
      character (if any) corresponding to radix, if zero_suppression_char =
      '*' and the displayed magnitude of Item is zero;

64    otherwise, the same result as if each zero_suppression_char in
      all_zero_suppression_aft were '9', interpreting the instance of
      all_zero_suppression_number as either zero_suppression number (if a
      radix and all_zero_suppression_aft are present), or as zero_suppression
      otherwise.

65    An instance of all_sign_number maps to:

66    a string of all spaces if the displayed magnitude of Item is zero and
      the instance of all_sign_number does not have a radix at its last
      character position;

67    otherwise, the same result as if each sign_char in all_sign_number_aft
      were '9', interpreting the instance of all_sign_number as either
      floating_LHS_sign number (if a radix and all_sign_number_aft are
      present), or as floating_LHS_sign otherwise.

68    An instance of all_currency_number maps to:

69    a string of all spaces if the displayed magnitude of Item is zero and
      the instance of all_currency_number does not have a radix at its last
      character position;

70    otherwise, the same result as if each currency_char in
      all_currency_number_aft were '9', interpreting the instance of
      all_currency_number as floating_$_currency number or floating_#_currency
      number (if a radix and all_currency_number_aft are present), or as
      floating_$_currency or floating_#_currency otherwise.


                                  Examples

71    In the result string values shown below, 'b' represents the space
character.

72    Item:         Picture and Result Strings:

73    123456.78     Picture:  "-###**_***_**9.99"
                              "bbb$***123,456.78"
                              "bbFF***123.456,78" (currency = "FF",
                                                   separator = '.',
                                                   radix mark = ',')

74/1  123456.78     Picture:  "-[$$]$**_***_**9.99"
                    Result:   "[bb]b$***123,456.78"
                             "b[bb]FF***123.456,78" (currency = "FF",
                               [  ]                  separator = '.',
                               [  ]                  radix mark = ',')

75    0.0          Picture: "-$$$$$$.$$"
                   Result:  "bbbbbbbbbb"

76    0.20         Picture: "-$$$$$$.$$"
                   Result:  "bbbbbb$.20"

77    -1234.565    Picture: "<<<<_<<<.<<###>"
                   Result:  "bb(1,234.57DMb)"  (currency = "DM")

78    12345.67     Picture: "###_###_##9.99"
                   Result:  "bbCHF12,345.67"   (currency = "CHF")


F.3.3 The Package Text_IO.Editing


1     The package Text_IO.Editing provides a private type Picture with
associated operations, and a generic package Decimal_Output. An object of type
Picture is composed from a well-formed picture String (see F.3.1) and a
Boolean item indicating whether a zero numeric value will result in an edited
output string of all space characters. The package Decimal_Output contains
edited output subprograms implementing the effects defined in F.3.2.


                              Static Semantics

2     The library package Text_IO.Editing has the following declaration:

3     package Ada.Text_IO.Editing is

4        type Picture is private;

5        function Valid (Pic_String      : in String;
                         Blank_When_Zero : in Boolean := False) return Boolean;

6        function To_Picture (Pic_String      : in String;
                              Blank_When_Zero : in Boolean := False)
            return Picture;

7        function Pic_String      (Pic : in Picture) return String;
         function Blank_When_Zero (Pic : in Picture) return Boolean;

8        Max_Picture_Length  : constant := implementation_defined;

9        Picture_Error       : exception;

10       Default_Currency    : constant String    := "$";
         Default_Fill        : constant Character := '*';
         Default_Separator   : constant Character := ',';
         Default_Radix_Mark  : constant Character := '.';

11       generic
            type Num is delta <> digits <>;
            Default_Currency   : in String    := Text_IO.Editing.Default_Currency;
            Default_Fill       : in Character := Text_IO.Editing.Default_Fill;
            Default_Separator  : in Character :=
                                    Text_IO.Editing.Default_Separator;
            Default_Radix_Mark : in Character :=
                                    Text_IO.Editing.Default_Radix_Mark;
         package Decimal_Output is
            function Length (Pic      : in Picture;
                             Currency : in String := Default_Currency)
               return Natural;

12          function Valid (Item     : in Num;
                            Pic      : in Picture;
                            Currency : in String := Default_Currency)
               return Boolean;

13          function Image (Item       : in Num;
                            Pic        : in Picture;
                            Currency   : in String    := Default_Currency;
                            Fill       : in Character := Default_Fill;
                            Separator  : in Character := Default_Separator;
                            Radix_Mark : in Character := Default_Radix_Mark)
               return String;

14          procedure Put (File       : in File_Type;
                           Item       : in Num;
                           Pic        : in Picture;
                           Currency   : in String    := Default_Currency;
                           Fill       : in Character := Default_Fill;
                           Separator  : in Character := Default_Separator;
                           Radix_Mark : in Character := Default_Radix_Mark);

15          procedure Put (Item       : in Num;
                           Pic        : in Picture;
                           Currency   : in String    := Default_Currency;
                           Fill       : in Character := Default_Fill;
                           Separator  : in Character := Default_Separator;
                           Radix_Mark : in Character := Default_Radix_Mark);

16          procedure Put (To         : out String;
                           Item       : in Num;
                           Pic        : in Picture;
                           Currency   : in String    := Default_Currency;
                           Fill       : in Character := Default_Fill;
                           Separator  : in Character := Default_Separator;
                           Radix_Mark : in Character := Default_Radix_Mark);
         end Decimal_Output;
      private
         ... -- not specified by the language
      end Ada.Text_IO.Editing;

17    The exception Constraint_Error is raised if the Image function or any of
the Put procedures is invoked with a null string for Currency.

18    function Valid (Pic_String      : in String;
                      Blank_When_Zero : in Boolean := False) return Boolean;

    19    Valid returns True if Pic_String is a well-formed picture String
          (see F.3.1) the length of whose expansion does not exceed
          Max_Picture_Length, and if either Blank_When_Zero is False or
          Pic_String contains no '*'.

20    function To_Picture (Pic_String      : in String;
                           Blank_When_Zero : in Boolean := False)
         return Picture;

    21    To_Picture returns a result Picture such that the application of the
          function Pic_String to this result yields an expanded picture String
          equivalent to Pic_String, and such that Blank_When_Zero applied to
          the result Picture is the same value as the parameter
          Blank_When_Zero. Picture_Error is raised if not Valid(Pic_String,
          Blank_When_Zero).

22    function Pic_String      (Pic : in Picture) return String;
      
      function Blank_When_Zero (Pic : in Picture) return Boolean;

    23    If Pic is To_Picture(String_Item, Boolean_Item) for some String_Item
          and Boolean_Item, then:

        24    Pic_String(Pic) returns an expanded picture String equivalent to
              String_Item and with any lower-case letter replaced with its
              corresponding upper-case form, and

        25    Blank_When_Zero(Pic) returns Boolean_Item.

    26    If Pic_1 and Pic_2 are objects of type Picture, then "="(Pic_1,
          Pic_2) is True when

        27    Pic_String(Pic_1) = Pic_String(Pic_2), and

        28    Blank_When_Zero(Pic_1) = Blank_When_Zero(Pic_2).

29    function Length (Pic      : in Picture;
                       Currency : in String := Default_Currency)
         return Natural;

    30    Length returns Pic_String(Pic)'Length + Currency_Length_Adjustment -
          Radix_Adjustment where

        31    Currency_Length_Adjustment =

            32    Currency'Length - 1 if there is some occurrence of '$' in
                  Pic_String(Pic), and

            33    0 otherwise.

        34    Radix_Adjustment =

            35    1 if there is an occurrence of 'V' or 'v' in Pic_Str(Pic),
                  and

            36    0 otherwise.

37    function Valid (Item     : in Num;
                      Pic      : in Picture;
                      Currency : in String := Default_Currency)
         return Boolean;

    38    Valid returns True if Image(Item, Pic, Currency) does not raise
          Layout_Error, and returns False otherwise.

39    function Image (Item       : in Num;
                      Pic        : in Picture;
                      Currency   : in String    := Default_Currency;
                      Fill       : in Character := Default_Fill;
                      Separator  : in Character := Default_Separator;
                      Radix_Mark : in Character := Default_Radix_Mark)
         return String;

    40    Image returns the edited output String as defined in F.3.2 for Item,
          Pic_String(Pic), Blank_When_Zero(Pic), Currency, Fill, Separator,
          and Radix_Mark. If these rules identify a layout error, then Image
          raises the exception Layout_Error.

41    procedure Put (File       : in File_Type;
                     Item       : in Num;
                     Pic        : in Picture;
                     Currency   : in String    := Default_Currency;
                     Fill       : in Character := Default_Fill;
                     Separator  : in Character := Default_Separator;
                     Radix_Mark : in Character := Default_Radix_Mark);
      
      procedure Put (Item       : in Num;
                     Pic        : in Picture;
                     Currency   : in String    := Default_Currency;
                     Fill       : in Character := Default_Fill;
                     Separator  : in Character := Default_Separator;
                     Radix_Mark : in Character := Default_Radix_Mark);

    42    Each of these Put procedures outputs Image(Item, Pic, Currency,
          Fill, Separator, Radix_Mark) consistent with the conventions for Put
          for other real types in case of bounded line length (see A.10.6, 
          ``Get and Put Procedures'').

43    procedure Put (To         : out String;
                     Item       : in Num;
                     Pic        : in Picture;
                     Currency   : in String    := Default_Currency;
                     Fill       : in Character := Default_Fill;
                     Separator  : in Character := Default_Separator;
                     Radix_Mark : in Character := Default_Radix_Mark);

    44    Put copies Image(Item, Pic, Currency, Fill, Separator, Radix_Mark)
          to the given string, right justified. Otherwise unassigned Character
          values in To are assigned the space character. If To'Length is less
          than the length of the string resulting from Image, then
          Layout_Error is raised.


                         Implementation Requirements

45    Max_Picture_Length shall be at least 30. The implementation shall
support currency strings of length up to at least 10, both for
Default_Currency in an instantiation of Decimal_Output, and for Currency in an
invocation of Image or any of the Put procedures.

      NOTES

46    4  The rules for edited output are based on COBOL (ANSI X3.23:1985,
      endorsed by ISO as ISO 1989-1985), with the following differences:

    47    The COBOL provisions for picture string localization and for 'P'
          format are absent from Ada.

    48    The following Ada facilities are not in COBOL:

        49    currency symbol placement after the number,

        50    localization of edited output string for multi-character
              currency string values, including support for both
              length-preserving and length-expanding currency symbols in
              picture strings

        51    localization of the radix mark, digits separator, and fill
              character, and

        52    parenthesization of negative values.

52.1  []The value of 30 for Max_Picture_Length is the same limit as in COBOL.


F.3.4 The Package Wide_Text_IO.Editing



                              Static Semantics

1     The child package Wide_Text_IO.Editing has the same contents as
Text_IO.Editing, except that:

2     each occurrence of Character is replaced by Wide_Character,

3     each occurrence of Text_IO is replaced by Wide_Text_IO,

4     the subtype of Default_Currency is Wide_String rather than String, and

5     each occurrence of String in the generic package Decimal_Output is
      replaced by Wide_String.

      NOTES

6     5  Each of the functions Wide_Text_IO.Editing.Valid, To_Picture, and
      Pic_String has String (versus Wide_String) as its parameter or result
      subtype, since a picture String is not localizable.



                                   Annex G
                                 (normative)

                                  Numerics


1     The Numerics Annex specifies

2     features for complex arithmetic, including complex I/O;

3     a mode (``strict mode''), in which the predefined arithmetic operations
      of floating point and fixed point types and the functions and operations
      of various predefined packages have to provide guaranteed accuracy or
      conform to other numeric performance requirements, which the Numerics
      Annex also specifies;

4     a mode (``relaxed mode''), in which no accuracy or other numeric
      performance requirements need be satisfied, as for implementations not
      conforming to the Numerics Annex;

5     models of floating point and fixed point arithmetic on which the
      accuracy requirements of strict mode are based; and

6     the definitions of the model-oriented attributes of floating point types
      that apply in the strict mode.


                            Implementation Advice

7     If Fortran (respectively, C) is widely supported in the target
environment, implementations supporting the Numerics Annex should provide the
child package Interfaces.Fortran (respectively, Interfaces.C) specified in
Annex B and should support a convention_identifier of Fortran (respectively,
C) in the interfacing pragmas (see Annex B), thus allowing Ada programs to
interface with programs written in that language.


G.1 Complex Arithmetic


1     Types and arithmetic operations for complex arithmetic are provided in
Generic_Complex_Types, which is defined in G.1.1. Implementation-defined
approximations to the complex analogs of the mathematical functions known as
the ``elementary functions'' are provided by the subprograms in Generic_-
Complex_Elementary_Functions, which is defined in G.1.2. Both of these library
units are generic children of the predefined package Numerics (see A.5).
Nongeneric equivalents of these generic packages for each of the predefined
floating point types are also provided as children of Numerics.


G.1.1 Complex Types



                              Static Semantics

1     The generic library package Numerics.Generic_Complex_Types has the
following declaration:

2/1   generic
         type Real is digits <>;
      package Ada.Numerics.Generic_Complex_Types is
         {pragma}[pragma] Pure(Generic_Complex_Types);

3        type Complex is
            record
               Re, Im : Real'Base;
            end record;

4        type Imaginary is private;

5        i : constant Imaginary;
         j : constant Imaginary;

6        function Re (X : Complex)   return Real'Base;
         function Im (X : Complex)   return Real'Base;
         function Im (X : Imaginary) return Real'Base;

7        procedure Set_Re (X  : in out Complex;
                           Re : in     Real'Base);
         procedure Set_Im (X  : in out Complex;
                           Im : in     Real'Base);
         procedure Set_Im (X  :    out Imaginary;
                           Im : in     Real'Base);

8        function Compose_From_Cartesian (Re, Im : Real'Base) return Complex;
         function Compose_From_Cartesian (Re     : Real'Base) return Complex;
         function Compose_From_Cartesian (Im     : Imaginary) return Complex;

9        function Modulus (X     : Complex) return Real'Base;
         function "abs"   (Right : Complex) return Real'Base renames Modulus;

10       function Argument (X     : Complex)   return Real'Base;
         function Argument (X     : Complex;
                            Cycle : Real'Base) return Real'Base;

11       function Compose_From_Polar (Modulus, Argument        : Real'Base)
            return Complex;
         function Compose_From_Polar (Modulus, Argument, Cycle : Real'Base)
            return Complex;

12       function "+"       (Right : Complex) return Complex;
         function "-"       (Right : Complex) return Complex;
         function Conjugate (X     : Complex) return Complex;

13       function "+" (Left, Right : Complex) return Complex;
         function "-" (Left, Right : Complex) return Complex;
         function "*" (Left, Right : Complex) return Complex;
         function "/" (Left, Right : Complex) return Complex;

14       function "**" (Left : Complex; Right : Integer) return Complex;

15       function "+"       (Right : Imaginary) return Imaginary;
         function "-"       (Right : Imaginary) return Imaginary;
         function Conjugate (X     : Imaginary) return Imaginary renames "-";
         function "abs"     (Right : Imaginary) return Real'Base;

16       function "+" (Left, Right : Imaginary) return Imaginary;
         function "-" (Left, Right : Imaginary) return Imaginary;
         function "*" (Left, Right : Imaginary) return Real'Base;
         function "/" (Left, Right : Imaginary) return Real'Base;

17       function "**" (Left : Imaginary; Right : Integer) return Complex;

18       function "<"  (Left, Right : Imaginary) return Boolean;
         function "<=" (Left, Right : Imaginary) return Boolean;
         function ">"  (Left, Right : Imaginary) return Boolean;
         function ">=" (Left, Right : Imaginary) return Boolean;

19       function "+" (Left : Complex;   Right : Real'Base) return Complex;
         function "+" (Left : Real'Base; Right : Complex)   return Complex;
         function "-" (Left : Complex;   Right : Real'Base) return Complex;
         function "-" (Left : Real'Base; Right : Complex)   return Complex;
         function "*" (Left : Complex;   Right : Real'Base) return Complex;
         function "*" (Left : Real'Base; Right : Complex)   return Complex;
         function "/" (Left : Complex;   Right : Real'Base) return Complex;
         function "/" (Left : Real'Base; Right : Complex)   return Complex;

20       function "+" (Left : Complex;   Right : Imaginary) return Complex;
         function "+" (Left : Imaginary; Right : Complex)   return Complex;
         function "-" (Left : Complex;   Right : Imaginary) return Complex;
         function "-" (Left : Imaginary; Right : Complex)   return Complex;
         function "*" (Left : Complex;   Right : Imaginary) return Complex;
         function "*" (Left : Imaginary; Right : Complex)   return Complex;
         function "/" (Left : Complex;   Right : Imaginary) return Complex;
         function "/" (Left : Imaginary; Right : Complex)   return Complex;

21       function "+" (Left : Imaginary; Right : Real'Base) return Complex;
         function "+" (Left : Real'Base; Right : Imaginary) return Complex;
         function "-" (Left : Imaginary; Right : Real'Base) return Complex;
         function "-" (Left : Real'Base; Right : Imaginary) return Complex;
         function "*" (Left : Imaginary; Right : Real'Base) return Imaginary;
         function "*" (Left : Real'Base; Right : Imaginary) return Imaginary;
         function "/" (Left : Imaginary; Right : Real'Base) return Imaginary;
         function "/" (Left : Real'Base; Right : Imaginary) return Imaginary;

22    private

23       type Imaginary is new Real'Base;
         i : constant Imaginary := 1.0;
         j : constant Imaginary := 1.0;

24    end Ada.Numerics.Generic_Complex_Types;

25/1  The library package Numerics.Complex_Types {is declared pure and
}defines the same types, constants, and subprograms as
Numerics.Generic_Complex_Types, except that the predefined type Float is
systematically substituted for Real'Base throughout. Nongeneric equivalents of
Numerics.Generic_Complex_Types for each of the other predefined floating point
types are defined similarly, with the names Numerics.Short_Complex_Types,
Numerics.Long_Complex_Types, etc.

26    Complex is a visible type with cartesian components.

27    Imaginary is a private type; its full type is derived from Real'Base.

28    The arithmetic operations and the Re, Im, Modulus, Argument, and
Conjugate functions have their usual mathematical meanings. When applied to a
parameter of pure-imaginary type, the ``imaginary-part'' function Im yields
the value of its parameter, as the corresponding real value. The remaining
subprograms have the following meanings:

29    The Set_Re and Set_Im procedures replace the designated component of a
      complex parameter with the given real value; applied to a parameter of
      pure-imaginary type, the Set_Im procedure replaces the value of that
      parameter with the imaginary value corresponding to the given real value.

30    The Compose_From_Cartesian function constructs a complex value from the
      given real and imaginary components. If only one component is given, the
      other component is implicitly zero.

31    The Compose_From_Polar function constructs a complex value from the
      given modulus (radius) and argument (angle). When the value of the
      parameter Modulus is positive (resp., negative), the result is the
      complex value represented by the point in the complex plane lying at a
      distance from the origin given by the absolute value of Modulus and
      forming an angle measured counterclockwise from the positive (resp.,
      negative) real axis given by the value of the parameter Argument.

32    When the Cycle parameter is specified, the result of the Argument
function and the parameter Argument of the Compose_From_Polar function are
measured in units such that a full cycle of revolution has the given value;
otherwise, they are measured in radians.

33    The computed results of the mathematically multivalued functions are
rendered single-valued by the following conventions, which are meant to imply
the principal branch:

34    The result of the Modulus function is nonnegative.

35    The result of the Argument function is in the quadrant containing the
      point in the complex plane represented by the parameter X. This may be
      any quadrant (I through IV); thus, the range of the Argument function is
      approximately -PI to PI (-Cycle/2.0 to Cycle/2.0, if the parameter Cycle
      is specified). When the point represented by the parameter X lies on the
      negative real axis, the result approximates

    36    PI (resp., -PI) when the sign of the imaginary component of X is
          positive (resp., negative), if Real'Signed_Zeros is True;

    37    PI, if Real'Signed_Zeros is False.

38    Because a result lying on or near one of the axes may not be exactly
      representable, the approximation inherent in computing the result may
      place it in an adjacent quadrant, close to but on the wrong side of the
      axis.


                              Dynamic Semantics

39    The exception Numerics.Argument_Error is raised by the Argument and
Compose_From_Polar functions with specified cycle, signaling a parameter value
outside the domain of the corresponding mathematical function, when the value
of the parameter Cycle is zero or negative.

40    The exception Constraint_Error is raised by the division operator when
the value of the right operand is zero, and by the exponentiation operator
when the value of the left operand is zero and the value of the exponent is
negative, provided that Real'Machine_Overflows is True; when
Real'Machine_Overflows is False, the result is unspecified. Constraint_Error
can also be raised when a finite result overflows (see G.2.6).


                         Implementation Requirements

41    In the implementation of Numerics.Generic_Complex_Types, the range of
intermediate values allowed during the calculation of a final result shall not
be affected by any range constraint of the subtype Real.

42    In the following cases, evaluation of a complex arithmetic operation
shall yield the prescribed result, provided that the preceding rules do not
call for an exception to be raised:

43    The results of the Re, Im, and Compose_From_Cartesian functions are
      exact.

44    The real (resp., imaginary) component of the result of a binary addition
      operator that yields a result of complex type is exact when either of
      its operands is of pure-imaginary (resp., real) type.

45    The real (resp., imaginary) component of the result of a binary
      subtraction operator that yields a result of complex type is exact when
      its right operand is of pure-imaginary (resp., real) type.

46    The real component of the result of the Conjugate function for the
      complex type is exact.

47    When the point in the complex plane represented by the parameter X lies
      on the nonnegative real axis, the Argument function yields a result of
      zero.

48    When the value of the parameter Modulus is zero, the Compose_From_Polar
      function yields a result of zero.

49    When the value of the parameter Argument is equal to a multiple of the
      quarter cycle, the result of the Compose_From_Polar function with
      specified cycle lies on one of the axes. In this case, one of its
      components is zero, and the other has the magnitude of the parameter
      Modulus.

50    Exponentiation by a zero exponent yields the value one. Exponentiation
      by a unit exponent yields the value of the left operand. Exponentiation
      of the value one yields the value one. Exponentiation of the value zero
      yields the value zero, provided that the exponent is nonzero. When the
      left operand is of pure-imaginary type, one component of the result of
      the exponentiation operator is zero.

51    When the result, or a result component, of any operator of
Numerics.Generic_Complex_Types has a mathematical definition in terms of a
single arithmetic or relational operation, that result or result component
exhibits the accuracy of the corresponding operation of the type Real.

52    Other accuracy requirements for the Modulus, Argument, and
Compose_From_Polar functions, and accuracy requirements for the multiplication
of a pair of complex operands or for division by a complex operand, all of
which apply only in the strict mode, are given in G.2.6.

53    The sign of a zero result or zero result component yielded by a complex
arithmetic operation or function is implementation defined when
Real'Signed_Zeros is True.


                         Implementation Permissions

54    The nongeneric equivalent packages may, but need not, be actual
instantiations of the generic package for the appropriate predefined type.

55/1  Implementations may obtain the result of exponentiation of a complex or
pure-imaginary operand by repeated complex multiplication, with arbitrary
association of the factors and with a possible final complex reciprocation
(when the exponent is negative). Implementations are also permitted to obtain
the result of exponentiation of a complex operand, but not of a pure-imaginary
operand, by converting the left operand to a polar representation;
exponentiating the modulus by the given exponent; multiplying the argument by
the given exponent[, when the exponent is positive, or dividing the argument
by the absolute value of the given exponent, when the exponent is negative];
and reconverting to a cartesian representation. Because of this implementation
freedom, no accuracy requirement is imposed on complex exponentiation (except
for the prescribed results given above, which apply regardless of the
implementation method chosen).


                            Implementation Advice

56    Because the usual mathematical meaning of multiplication of a complex
operand and a real operand is that of the scaling of both components of the
former by the latter, an implementation should not perform this operation by
first promoting the real operand to complex type and then performing a full
complex multiplication. In systems that, in the future, support an Ada binding
to IEC 559:1989, the latter technique will not generate the required result
when one of the components of the complex operand is infinite. (Explicit
multiplication of the infinite component by the zero component obtained during
promotion yields a NaN that propagates into the final result.) Analogous
advice applies in the case of multiplication of a complex operand and a
pure-imaginary operand, and in the case of division of a complex operand by a
real or pure-imaginary operand.

57    Likewise, because the usual mathematical meaning of addition of a
complex operand and a real operand is that the imaginary operand remains
unchanged, an implementation should not perform this operation by first
promoting the real operand to complex type and then performing a full complex
addition. In implementations in which the Signed_Zeros attribute of the
component type is True (and which therefore conform to IEC 559:1989 in regard
to the handling of the sign of zero in predefined arithmetic operations), the
latter technique will not generate the required result when the imaginary
component of the complex operand is a negatively signed zero. (Explicit
addition of the negative zero to the zero obtained during promotion yields a
positive zero.) Analogous advice applies in the case of addition of a complex
operand and a pure-imaginary operand, and in the case of subtraction of a
complex operand and a real or pure-imaginary operand.

58    Implementations in which Real'Signed_Zeros is True should attempt to
provide a rational treatment of the signs of zero results and result
components. As one example, the result of the Argument function should have
the sign of the imaginary component of the parameter X when the point
represented by that parameter lies on the positive real axis; as another, the
sign of the imaginary component of the Compose_From_Polar function should be
the same as (resp., the opposite of) that of the Argument parameter when that
parameter has a value of zero and the Modulus parameter has a nonnegative
(resp., negative) value.


G.1.2 Complex Elementary Functions



                              Static Semantics

1     The generic library package
Numerics.Generic_Complex_Elementary_Functions has the following declaration:

2     with Ada.Numerics.Generic_Complex_Types;
      generic
         with package Complex_Types is
               new Ada.Numerics.Generic_Complex_Types (<>);
         use Complex_Types;
      package Ada.Numerics.Generic_Complex_Elementary_Functions is
         pragma Pure(Generic_Complex_Elementary_Functions);

3        function Sqrt (X : Complex)   return Complex;
         function Log  (X : Complex)   return Complex;
         function Exp  (X : Complex)   return Complex;
         function Exp  (X : Imaginary) return Complex;
         function "**" (Left : Complex;   Right : Complex)   return Complex;
         function "**" (Left : Complex;   Right : Real'Base) return Complex;
         function "**" (Left : Real'Base; Right : Complex)   return Complex;

4        function Sin (X : Complex) return Complex;
         function Cos (X : Complex) return Complex;
         function Tan (X : Complex) return Complex;
         function Cot (X : Complex) return Complex;

5        function Arcsin (X : Complex) return Complex;
         function Arccos (X : Complex) return Complex;
         function Arctan (X : Complex) return Complex;
         function Arccot (X : Complex) return Complex;

6        function Sinh (X : Complex) return Complex;
         function Cosh (X : Complex) return Complex;
         function Tanh (X : Complex) return Complex;
         function Coth (X : Complex) return Complex;

7        function Arcsinh (X : Complex) return Complex;
         function Arccosh (X : Complex) return Complex;
         function Arctanh (X : Complex) return Complex;
         function Arccoth (X : Complex) return Complex;

8     end Ada.Numerics.Generic_Complex_Elementary_Functions;

9/1   The library package Numerics.Complex_Elementary_Functions {is declared
pure and }defines the same subprograms as Numerics.Generic_Complex_Elementary_-
Functions, except that the predefined type Float is systematically substituted
for Real'Base, and the Complex and Imaginary types exported by Numerics.-
Complex_Types are systematically substituted for Complex and Imaginary,
throughout. Nongeneric equivalents of Numerics.Generic_Complex_Elementary_-
Functions corresponding to each of the other predefined floating point types
are defined similarly, with the names Numerics.Short_Complex_Elementary_-
Functions, Numerics.Long_Complex_Elementary_Functions, etc.

10    The overloading of the Exp function for the pure-imaginary type is
provided to give the user an alternate way to compose a complex value from a
given modulus and argument. In addition to Compose_From_Polar(Rho, Theta) (see
G.1.1), the programmer may write Rho * Exp(i * Theta).

11    The imaginary (resp., real) component of the parameter X of the forward
hyperbolic (resp., trigonometric) functions and of the Exp function (and the
parameter X, itself, in the case of the overloading of the Exp function for
the pure-imaginary type) represents an angle measured in radians, as does the
imaginary (resp., real) component of the result of the Log and inverse
hyperbolic (resp., trigonometric) functions.

12    The functions have their usual mathematical meanings. However, the
arbitrariness inherent in the placement of branch cuts, across which some of
the complex elementary functions exhibit discontinuities, is eliminated by the
following conventions:

13    The imaginary component of the result of the Sqrt and Log functions is
      discontinuous as the parameter X crosses the negative real axis.

14    The result of the exponentiation operator when the left operand is of
      complex type is discontinuous as that operand crosses the negative real
      axis.

15    The real (resp., imaginary) component of the result of the Arcsin and
      Arccos (resp., Arctanh) functions is discontinuous as the parameter X
      crosses the real axis to the left of -1.0 or the right of 1.0.

16    The real (resp., imaginary) component of the result of the Arctan
      (resp., Arcsinh) function is discontinuous as the parameter X crosses
      the imaginary axis below -i or above i.

17    The real component of the result of the Arccot function is discontinuous
      as the parameter X crosses the imaginary axis between -i and i.

18    The imaginary component of the Arccosh function is discontinuous as the
      parameter X crosses the real axis to the left of 1.0.

19    The imaginary component of the result of the Arccoth function is
      discontinuous as the parameter X crosses the real axis between -1.0 and
      1.0.

20    The computed results of the mathematically multivalued functions are
rendered single-valued by the following conventions, which are meant to imply
the principal branch:

21    The real component of the result of the Sqrt and Arccosh functions is
      nonnegative.

22    The same convention applies to the imaginary component of the result of
      the Log function as applies to the result of the natural-cycle version
      of the Argument function of Numerics.Generic_Complex_Types (see G.1.1).

23    The range of the real (resp., imaginary) component of the result of the
      Arcsin and Arctan (resp., Arcsinh and Arctanh) functions is
      approximately -PI/2.0 to PI/2.0.

24    The real (resp., imaginary) component of the result of the Arccos and
      Arccot (resp., Arccoth) functions ranges from 0.0 to approximately PI.

25    The range of the imaginary component of the result of the Arccosh
      function is approximately -PI to PI.

26    In addition, the exponentiation operator inherits the single-valuedness
of the Log function.


                              Dynamic Semantics

27    The exception Numerics.Argument_Error is raised by the exponentiation
operator, signaling a parameter value outside the domain of the corresponding
mathematical function, when the value of the left operand is zero and the real
component of the exponent (or the exponent itself, when it is of real type) is
zero.

28    The exception Constraint_Error is raised, signaling a pole of the
mathematical function (analogous to dividing by zero), in the following cases,
provided that Complex_Types.Real'Machine_Overflows is True:

29    by the Log, Cot, and Coth functions, when the value of the parameter X
      is zero;

30    by the exponentiation operator, when the value of the left operand is
      zero and the real component of the exponent (or the exponent itself,
      when it is of real type) is negative;

31    by the Arctan and Arccot functions, when the value of the parameter X is
      ± i;

32    by the Arctanh and Arccoth functions, when the value of the parameter X
      is ± 1.0.

33    Constraint_Error can also be raised when a finite result overflows (see
G.2.6); this may occur for parameter values sufficiently near poles, and, in
the case of some of the functions, for parameter values having components of
sufficiently large magnitude. When Complex_Types.Real'Machine_Overflows is
False, the result at poles is unspecified.


                         Implementation Requirements

34    In the implementation of Numerics.Generic_Complex_Elementary_Functions,
the range of intermediate values allowed during the calculation of a final
result shall not be affected by any range constraint of the subtype
Complex_Types.Real.

35    In the following cases, evaluation of a complex elementary function
shall yield the prescribed result (or a result having the prescribed
component), provided that the preceding rules do not call for an exception to
be raised:

36    When the parameter X has the value zero, the Sqrt, Sin, Arcsin, Tan,
      Arctan, Sinh, Arcsinh, Tanh, and Arctanh functions yield a result of
      zero; the Exp, Cos, and Cosh functions yield a result of one; the Arccos
      and Arccot functions yield a real result; and the Arccoth function
      yields an imaginary result.

37    When the parameter X has the value one, the Sqrt function yields a
      result of one; the Log, Arccos, and Arccosh functions yield a result of
      zero; and the Arcsin function yields a real result.

38    When the parameter X has the value -1.0, the Sqrt function yields the
      result

    39    i (resp., -i), when the sign of the imaginary component of X is
          positive (resp., negative), if Complex_Types.Real'Signed_Zeros is
          True;

    40    i, if Complex_Types.Real'Signed_Zeros is False;

41    the Log function yields an imaginary result; and the Arcsin and Arccos
      functions yield a real result.

42    When the parameter X has the value ± i, the Log function yields an
      imaginary result.

43    Exponentiation by a zero exponent yields the value one. Exponentiation
      by a unit exponent yields the value of the left operand (as a complex
      value). Exponentiation of the value one yields the value one.
      Exponentiation of the value zero yields the value zero.

44    Other accuracy requirements for the complex elementary functions, which
apply only in the strict mode, are given in G.2.6.

45    The sign of a zero result or zero result component yielded by a complex
elementary function is implementation defined when
Complex_Types.Real'Signed_Zeros is True.


                         Implementation Permissions

46    The nongeneric equivalent packages may, but need not, be actual
instantiations of the generic package with the appropriate predefined
nongeneric equivalent of Numerics.Generic_Complex_Types; if they are, then the
latter shall have been obtained by actual instantiation of
Numerics.Generic_Complex_Types.

47    The exponentiation operator may be implemented in terms of the Exp and
Log functions. Because this implementation yields poor accuracy in some parts
of the domain, no accuracy requirement is imposed on complex exponentiation.

48    The implementation of the Exp function of a complex parameter X is
allowed to raise the exception Constraint_Error, signaling overflow, when the
real component of X exceeds an unspecified threshold that is approximately
log(Complex_Types.Real'Safe_Last). This permission recognizes the
impracticality of avoiding overflow in the marginal case that the exponential
of the real component of X exceeds the safe range of Complex_Types.Real but
both components of the final result do not. Similarly, the Sin and Cos (resp.,
Sinh and Cosh) functions are allowed to raise the exception Constraint_Error,
signaling overflow, when the absolute value of the imaginary (resp., real)
component of the parameter X exceeds an unspecified threshold that is
approximately log(Complex_Types.Real'Safe_Last) + log(2.0). This permission
recognizes the impracticality of avoiding overflow in the marginal case that
the hyperbolic sine or cosine of the imaginary (resp., real) component of X
exceeds the safe range of Complex_Types.Real but both components of the final
result do not.


                            Implementation Advice

49    Implementations in which Complex_Types.Real'Signed_Zeros is True should
attempt to provide a rational treatment of the signs of zero results and
result components. For example, many of the complex elementary functions have
components that are odd functions of one of the parameter components; in these
cases, the result component should have the sign of the parameter component at
the origin. Other complex elementary functions have zero components whose sign
is opposite that of a parameter component at the origin, or is always positive
or always negative.


G.1.3 Complex Input-Output


1     The generic package Text_IO.Complex_IO defines procedures for the
formatted input and output of complex values. The generic actual parameter in
an instantiation of Text_IO.Complex_IO is an instance of
Numerics.Generic_Complex_Types for some floating point subtype. Exceptional
conditions are reported by raising the appropriate exception defined in
Text_IO.


                              Static Semantics

2     The generic library package Text_IO.Complex_IO has the following
declaration:

3     with Ada.Numerics.Generic_Complex_Types;
      generic
         with package Complex_Types is
               new Ada.Numerics.Generic_Complex_Types (<>);
      package Ada.Text_IO.Complex_IO is

4        use Complex_Types;

5        Default_Fore : Field := 2;
         Default_Aft  : Field := Real'Digits - 1;
         Default_Exp  : Field := 3;

6        procedure Get (File  : in  File_Type;
                        Item  : out Complex;
                        Width : in  Field := 0);
         procedure Get (Item  : out Complex;
                        Width : in  Field := 0);

7        procedure Put (File : in File_Type;
                        Item : in Complex;
                        Fore : in Field := Default_Fore;
                        Aft  : in Field := Default_Aft;
                        Exp  : in Field := Default_Exp);
         procedure Put (Item : in Complex;
                        Fore : in Field := Default_Fore;
                        Aft  : in Field := Default_Aft;
                        Exp  : in Field := Default_Exp);

8        procedure Get (From : in  String;
                        Item : out Complex;
                        Last : out Positive);
         procedure Put (To   : out String;
                        Item : in  Complex;
                        Aft  : in  Field := Default_Aft;
                        Exp  : in  Field := Default_Exp);

9     end Ada.Text_IO.Complex_IO;

10    The semantics of the Get and Put procedures are as follows:

11    procedure Get (File  : in  File_Type;
                     Item  : out Complex;
                     Width : in  Field := 0);
      procedure Get (Item  : out Complex;
                     Width : in  Field := 0);

    12/1  The input sequence is a pair of optionally signed real literals
          representing the real and imaginary components of a complex value{
          These components have the format defined for the corresponding Get
          procedure of an instance of Text_IO.Float_IO (see A.10.9) for the
          base subtype of Complex_Types.Real. T}[; optionally, t]he pair of
          components may be separated by a comma [and/]or surrounded by a pair
          of parentheses{ or both}. Blanks are freely allowed before each of
          the components and before the parentheses and comma, if either is
          used. If the value of the parameter Width is zero, then

        13    line and page terminators are also allowed in these places;

        14    the components shall be separated by at least one blank or line
              terminator if the comma is omitted; and

        15    reading stops when the right parenthesis has been read, if the
              input sequence includes a left parenthesis, or when the
              imaginary component has been read, otherwise.

    15.1  []If a nonzero value of Width is supplied, then

        16    the components shall be separated by at least one blank if the
              comma is omitted; and

        17    exactly Width characters are read, or the characters (possibly
              none) up to a line terminator, whichever comes first (blanks are
              included in the count).

    18    Returns, in the parameter Item, the value of type Complex that
          corresponds to the input sequence.

    19    The exception Text_IO.Data_Error is raised if the input sequence
          does not have the required syntax or if the components of the
          complex value obtained are not of the base subtype of
          Complex_Types.Real.

20    procedure Put (File : in File_Type;
                     Item : in Complex;
                     Fore : in Field := Default_Fore;
                     Aft  : in Field := Default_Aft;
                     Exp  : in Field := Default_Exp);
      procedure Put (Item : in Complex;
                     Fore : in Field := Default_Fore;
                     Aft  : in Field := Default_Aft;
                     Exp  : in Field := Default_Exp);

    21    Outputs the value of the parameter Item as a pair of decimal
          literals representing the real and imaginary components of the
          complex value, using the syntax of an aggregate. More specifically,

        22    outputs a left parenthesis;

        23    outputs the value of the real component of the parameter Item
              with the format defined by the corresponding Put procedure of an
              instance of Text_IO.Float_IO for the base subtype of
              Complex_Types.Real, using the given values of Fore, Aft, and Exp;

        24    outputs a comma;

        25    outputs the value of the imaginary component of the parameter
              Item with the format defined by the corresponding Put procedure
              of an instance of Text_IO.Float_IO for the base subtype of
              Complex_Types.Real, using the given values of Fore, Aft, and Exp;

        26    outputs a right parenthesis.

27    procedure Get (From : in  String;
                     Item : out Complex;
                     Last : out Positive);

    28    Reads a complex value from the beginning of the given string,
          following the same rule as the Get procedure that reads a complex
          value from a file, but treating the end of the string as a line
          terminator. Returns, in the parameter Item, the value of type
          Complex that corresponds to the input sequence. Returns in Last the
          index value such that From(Last) is the last character read.

    29    The exception Text_IO.Data_Error is raised if the input sequence
          does not have the required syntax or if the components of the
          complex value obtained are not of the base subtype of
          Complex_Types.Real.

30    procedure Put (To   : out String;
                     Item : in  Complex;
                     Aft  : in  Field := Default_Aft;
                     Exp  : in  Field := Default_Exp);

    31    Outputs the value of the parameter Item to the given string as a
          pair of decimal literals representing the real and imaginary
          components of the complex value, using the syntax of an aggregate.
          More specifically,

        32    a left parenthesis, the real component, and a comma are left
              justified in the given string, with the real component having
              the format defined by the Put procedure (for output to a file)
              of an instance of Text_IO.Float_IO for the base subtype of
              Complex_Types.Real, using a value of zero for Fore and the given
              values of Aft and Exp;

        33    the imaginary component and a right parenthesis are right
              justified in the given string, with the imaginary component
              having the format defined by the Put procedure (for output to a
              file) of an instance of Text_IO.Float_IO for the base subtype of
              Complex_Types.Real, using a value for Fore that completely fills
              the remainder of the string, together with the given values of
              Aft and Exp.

    34    The exception Text_IO.Layout_Error is raised if the given string is
          too short to hold the formatted output.


                         Implementation Permissions

35    Other exceptions declared (by renaming) in Text_IO may be raised by the
preceding procedures in the appropriate circumstances, as for the
corresponding procedures of Text_IO.Float_IO.


G.1.4 The Package Wide_Text_IO.Complex_IO



                              Static Semantics

1     Implementations shall also provide the generic library package
Wide_Text_IO.Complex_IO. Its declaration is obtained from that of
Text_IO.Complex_IO by systematically replacing Text_IO by Wide_Text_IO and
String by Wide_String; the description of its behavior is obtained by
additionally replacing references to particular characters (commas,
parentheses, etc.) by those for the corresponding wide characters.


G.2 Numeric Performance Requirements



                         Implementation Requirements

1     Implementations shall provide a user-selectable mode in which the
accuracy and other numeric performance requirements detailed in the following
subclauses are observed. This mode, referred to as the strict mode, may or may
not be the default mode; it directly affects the results of the predefined
arithmetic operations of real types and the results of the subprograms in
children of the Numerics package, and indirectly affects the operations in
other language defined packages. Implementations shall also provide the
opposing mode, which is known as the relaxed mode.


                         Implementation Permissions

2     Either mode may be the default mode.

3     The two modes need not actually be different.


G.2.1 Model of Floating Point Arithmetic


1     In the strict mode, the predefined operations of a floating point type
shall satisfy the accuracy requirements specified here and shall avoid or
signal overflow in the situations described. This behavior is presented in
terms of a model of floating point arithmetic that builds on the concept of
the canonical form (see A.5.3).


                              Static Semantics

2     Associated with each floating point type is an infinite set of model
numbers. The model numbers of a type are used to define the accuracy
requirements that have to be satisfied by certain predefined operations of the
type; through certain attributes of the model numbers, they are also used to
explain the meaning of a user-declared floating point type declaration. The
model numbers of a derived type are those of the parent type; the model
numbers of a subtype are those of its type.

3     The model numbers of a floating point type T are zero and all the values
expressible in the canonical form (for the type T), in which mantissa has
T'Model_Mantissa digits and exponent has a value greater than or equal to
T'Model_Emin. (These attributes are defined in G.2.2.)

4     A model interval of a floating point type is any interval whose bounds
are model numbers of the type. The model interval of a type T associated with
a value v is the smallest model interval of T that includes v. (The model
interval associated with a model number of a type consists of that number
only.)


                         Implementation Requirements

5     The accuracy requirements for the evaluation of certain predefined
operations of floating point types are as follows.

6     An operand interval is the model interval, of the type specified for the
operand of an operation, associated with the value of the operand.

7     For any predefined arithmetic operation that yields a result of a
floating point type T, the required bounds on the result are given by a model
interval of T (called the result interval) defined in terms of the operand
values as follows:

8     The result interval is the smallest model interval of T that includes
      the minimum and the maximum of all the values obtained by applying the
      (exact) mathematical operation to values arbitrarily selected from the
      respective operand intervals.

9     The result interval of an exponentiation is obtained by applying the
above rule to the sequence of multiplications defined by the exponent,
assuming arbitrary association of the factors, and to the final division in
the case of a negative exponent.

10    The result interval of a conversion of a numeric value to a floating
point type T is the model interval of T associated with the operand value,
except when the source expression is of a fixed point type with a small that
is not a power of T'Machine_Radix or is a fixed point multiplication or
division either of whose operands has a small that is not a power of
T'Machine_Radix; in these cases, the result interval is implementation
defined.

11    For any of the foregoing operations, the implementation shall deliver a
value that belongs to the result interval when both bounds of the result
interval are in the safe range of the result type T, as determined by the
values of T'Safe_First and T'Safe_Last; otherwise,

12    if T'Machine_Overflows is True, the implementation shall either deliver
      a value that belongs to the result interval or raise Constraint_Error;

13    if T'Machine_Overflows is False, the result is implementation defined.

14    For any predefined relation on operands of a floating point type T, the
implementation may deliver any value (i.e., either True or False) obtained by
applying the (exact) mathematical comparison to values arbitrarily chosen from
the respective operand intervals.

15    The result of a membership test is defined in terms of comparisons of
the operand value with the lower and upper bounds of the given range or type
mark (the usual rules apply to these comparisons).


                         Implementation Permissions

16    If the underlying floating point hardware implements division as
multiplication by a reciprocal, the result interval for division (and
exponentiation by a negative exponent) is implementation defined.


G.2.2 Model-Oriented Attributes of Floating Point Types


1     In implementations that support the Numerics Annex, the model-oriented
attributes of floating point types shall yield the values defined here, in
both the strict and the relaxed modes. These definitions add conditions to
those in A.5.3.


                              Static Semantics

2     For every subtype S of a floating point type T:

3     S'Model_Mantissa
              Yields the number of digits in the mantissa of the canonical
              form of the model numbers of T (see A.5.3). The value of this
              attribute shall be greater than or equal to Ceiling(d · log(10)
              / log(T'Machine_Radix)) + 1, where d is the requested decimal
              precision of T. In addition, it shall be less than or equal to
              the value of T'Machine_Mantissa. This attribute yields a value
              of the type universal_integer.

4     S'Model_Emin
              Yields the minimum exponent of the canonical form of the model
              numbers of T (see A.5.3). The value of this attribute shall be
              greater than or equal to the value of T'Machine_Emin. This
              attribute yields a value of the type universal_integer.

5     S'Safe_First
              Yields the lower bound of the safe range of T. The value of this
              attribute shall be a model number of T and greater than or equal
              to the lower bound of the base range of T. In addition, if T is
              declared by a floating_point_definition or is derived from such
              a type, and the floating_point_definition includes a
              real_range_specification specifying a lower bound of lb, then
              the value of this attribute shall be less than or equal to lb;
              otherwise, it shall be less than or equal to -10.0 (4 · d),
              where d is the requested decimal precision of T. This attribute
              yields a value of the type universal_real.

6     S'Safe_Last
              Yields the upper bound of the safe range of T. The value of this
              attribute shall be a model number of T and less than or equal to
              the upper bound of the base range of T. In addition, if T is
              declared by a floating_point_definition or is derived from such
              a type, and the floating_point_definition includes a
              real_range_specification specifying an upper bound of ub, then
              the value of this attribute shall be greater than or equal to
              ub; otherwise, it shall be greater than or equal to 10.0 (4 ·
              d), where d is the requested decimal precision of T. This
              attribute yields a value of the type universal_real.

7     S'Model Denotes a function (of a parameter X) whose specification is
              given in A.5.3. If X is a model number of T, the function yields
              X; otherwise, it yields the value obtained by rounding or
              truncating X to either one of the adjacent model numbers of T.
              Constraint_Error is raised if the resulting model number is
              outside the safe range of S. A zero result has the sign of X
              when S'Signed_Zeros is True.

8     Subject to the constraints given above, the values of S'Model_Mantissa
and S'Safe_Last are to be maximized, and the values of S'Model_Emin and
S'Safe_First minimized, by the implementation as follows:

9     First, S'Model_Mantissa is set to the largest value for which values of
      S'Model_Emin, S'Safe_First, and S'Safe_Last can be chosen so that the
      implementation satisfies the strict-mode requirements of G.2.1 in terms
      of the model numbers and safe range induced by these attributes.

10    Next, S'Model_Emin is set to the smallest value for which values of
      S'Safe_First and S'Safe_Last can be chosen so that the implementation
      satisfies the strict-mode requirements of G.2.1 in terms of the model
      numbers and safe range induced by these attributes and the previously
      determined value of S'Model_Mantissa.

11    Finally, S'Safe_First and S'Safe_last are set (in either order) to the
      smallest and largest values, respectively, for which the implementation
      satisfies the strict-mode requirements of G.2.1 in terms of the model
      numbers and safe range induced by these attributes and the previously
      determined values of S'Model_Mantissa and S'Model_Emin.


G.2.3 Model of Fixed Point Arithmetic


1     In the strict mode, the predefined arithmetic operations of a fixed
point type shall satisfy the accuracy requirements specified here and shall
avoid or signal overflow in the situations described.


                         Implementation Requirements

2     The accuracy requirements for the predefined fixed point arithmetic
operations and conversions, and the results of relations on fixed point
operands, are given below.

3     The operands of the fixed point adding operators, absolute value, and
comparisons have the same type. These operations are required to yield exact
results, unless they overflow.

4     Multiplications and divisions are allowed between operands of any two
fixed point types; the result has to be (implicitly or explicitly) converted
to some other numeric type. For purposes of defining the accuracy rules, the
multiplication or division and the conversion are treated as a single
operation whose accuracy depends on three types (those of the operands and the
result). For decimal fixed point types, the attribute T'Round may be used to
imply explicit conversion with rounding (see 3.5.10).

5     When the result type is a floating point type, the accuracy is as given
in G.2.1. For some combinations of the operand and result types in the
remaining cases, the result is required to belong to a small set of values
called the perfect result set; for other combinations, it is required merely
to belong to a generally larger and implementation-defined set of values
called the close result set. When the result type is a decimal fixed point
type, the perfect result set contains a single value; thus, operations on
decimal types are always fully specified.

6     When one operand of a fixed-fixed multiplication or division is of type
universal_real, that operand is not implicitly converted in the usual sense,
since the context does not determine a unique target type, but the accuracy of
the result of the multiplication or division (i.e., whether the result has to
belong to the perfect result set or merely the close result set) depends on
the value of the operand of type universal_real and on the types of the other
operand and of the result.

7     For a fixed point multiplication or division whose (exact) mathematical
result is v, and for the conversion of a value v to a fixed point type, the
perfect result set and close result set are defined as follows:

8     If the result type is an ordinary fixed point type with a small of s,

    9     if v is an integer multiple of s, then the perfect result set
          contains only the value v;

    10    otherwise, it contains the integer multiple of s just below v and
          the integer multiple of s just above v.

11    The close result set is an implementation-defined set of consecutive
      integer multiples of s containing the perfect result set as a subset.

12    If the result type is a decimal type with a small of s,

    13    if v is an integer multiple of s, then the perfect result set
          contains only the value v;

    14    otherwise, if truncation applies then it contains only the integer
          multiple of s in the direction toward zero, whereas if rounding
          applies then it contains only the nearest integer multiple of s
          (with ties broken by rounding away from zero).

15    The close result set is an implementation-defined set of consecutive
      integer multiples of s containing the perfect result set as a subset.

16    If the result type is an integer type,

    17    if v is an integer, then the perfect result set contains only the
          value v;

    18    otherwise, it contains the integer nearest to the value v (if v lies
          equally distant from two consecutive integers, the perfect result
          set contains the one that is further from zero).

19    The close result set is an implementation-defined set of consecutive
      integers containing the perfect result set as a subset.

20    The result of a fixed point multiplication or division shall belong
either to the perfect result set or to the close result set, as described
below, if overflow does not occur. In the following cases, if the result type
is a fixed point type, let s be its small; otherwise, i.e. when the result
type is an integer type, let s be 1.0.

21    For a multiplication or division neither of whose operands is of type
      universal_real, let l and r be the smalls of the left and right
      operands. For a multiplication, if (l · r) / s is an integer or the
      reciprocal of an integer (the smalls are said to be ``compatible'' in
      this case), the result shall belong to the perfect result set;
      otherwise, it belongs to the close result set. For a division, if l / (r
      · s) is an integer or the reciprocal of an integer (i.e., the smalls are
      compatible), the result shall belong to the perfect result set;
      otherwise, it belongs to the close result set.

22    For a multiplication or division having one universal_real operand with
      a value of v, note that it is always possible to factor v as an integer
      multiple of a ``compatible'' small, but the integer multiple may be `
      `too big.'' If there exists a factorization in which that multiple is
      less than some implementation-defined limit, the result shall belong to
      the perfect result set; otherwise, it belongs to the close result set.

23    A multiplication P * Q of an operand of a fixed point type F by an
operand of an integer type I, or vice-versa, and a division P / Q of an
operand of a fixed point type F by an operand of an integer type I, are also
allowed. In these cases, the result has a type of F; explicit conversion of
the result is never required. The accuracy required in these cases is the same
as that required for a multiplication F(P * Q) or a division F(P / Q) obtained
by interpreting the operand of the integer type to have a fixed point type
with a small of 1.0.

24    The accuracy of the result of a conversion from an integer or fixed
point type to a fixed point type, or from a fixed point type to an integer
type, is the same as that of a fixed point multiplication of the source value
by a fixed point operand having a small of 1.0 and a value of 1.0, as given by
the foregoing rules. The result of a conversion from a floating point type to
a fixed point type shall belong to the close result set. The result of a
conversion of a universal_real operand to a fixed point type shall belong to
the perfect result set.

25    The possibility of overflow in the result of a predefined arithmetic
operation or conversion yielding a result of a fixed point type T is analogous
to that for floating point types, except for being related to the base range
instead of the safe range. If all of the permitted results belong to the base
range of T, then the implementation shall deliver one of the permitted
results; otherwise,

26    if T'Machine_Overflows is True, the implementation shall either deliver
      one of the permitted results or raise Constraint_Error;

27    if T'Machine_Overflows is False, the result is implementation defined.


G.2.4 Accuracy Requirements for the Elementary Functions


1     In the strict mode, the performance of
Numerics.Generic_Elementary_Functions shall be as specified here.


                         Implementation Requirements

2     When an exception is not raised, the result of evaluating a function in
an instance EF of Numerics.Generic_Elementary_Functions belongs to a result
interval, defined as the smallest model interval of EF.Float_Type that
contains all the values of the form f · (1.0 + d), where f is the exact value
of the corresponding mathematical function at the given parameter values, d is
a real number, and |d| is less than or equal to the function's maximum
relative error. The function delivers a value that belongs to the result
interval when both of its bounds belong to the safe range of EF.Float_Type;
otherwise,

3     if EF.Float_Type'Machine_Overflows is True, the function either delivers
      a value that belongs to the result interval or raises Constraint_Error,
      signaling overflow;

4     if EF.Float_Type'Machine_Overflows is False, the result is
      implementation defined.

5     The maximum relative error exhibited by each function is as follows:

6     2.0 · EF.Float_Type'Model_Epsilon, in the case of the Sqrt, Sin, and Cos
      functions;

7     4.0 · EF.Float_Type'Model_Epsilon, in the case of the Log, Exp, Tan,
      Cot, and inverse trigonometric functions; and

8     8.0 · EF.Float_Type'Model_Epsilon, in the case of the forward and
      inverse hyperbolic functions.

9     The maximum relative error exhibited by the exponentiation operator,
which depends on the values of the operands, is (4.0   +   |Right · log(
Left)|   /   32.0) · EF.Float_Type'Model_Epsilon.

10    The maximum relative error given above applies throughout the domain of
the forward trigonometric functions when the Cycle parameter is specified.
When the Cycle parameter is omitted, the maximum relative error given above
applies only when the absolute value of the angle parameter X is less than or
equal to some implementation-defined angle threshold, which shall be at least
EF.Float_Type'Machine_Radix (Floor(EF.Float_Type'Machine_Mantissa/2)). Beyond
the angle threshold, the accuracy of the forward trigonometric functions is
implementation defined.

11    The prescribed results specified in A.5.1 for certain functions at
particular parameter values take precedence over the maximum relative error
bounds; effectively, they narrow to a single value the result interval allowed
by the maximum relative error bounds. Additional rules with a similar effect
are given by the table below for the inverse trigonometric functions, at
particular parameter values for which the mathematical result is possibly not
a model number of EF.Float_Type (or is, indeed, even transcendental). In each
table entry, the values of the parameters are such that the result lies on the
axis between two quadrants; the corresponding accuracy rule, which takes
precedence over the maximum relative error bounds, is that the result interval
is the model interval of EF.Float_Type associated with the exact mathematical
result given in the table.

12/1  This paragraph was deleted.[ ]

13    The last line of the table is meant to apply when
EF.Float_Type'Signed_Zeros is False; the two lines just above it, when
EF.Float_Type'Signed_Zeros is True and the parameter Y has a zero value with
the indicated sign.

14    The amount by which the result of an inverse trigonometric function is
allowed to spill over into a quadrant adjacent to the one corresponding to the
principal branch, as given in A.5.1, is limited. The rule is that the result
belongs to the smallest model interval of EF.Float_Type that contains both
boundaries of the quadrant corresponding to the principal branch. This rule
also takes precedence over the maximum relative error bounds, effectively
narrowing the result interval allowed by them.

          Tightly Approximated Elementary Function Results

          Function 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          Value of X 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          Value of Y 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          Exact Result
          when Cycle
          Specified 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          Exact Result
          when Cycle
          Omitted

          Arcsin 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          1.0 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          n.a. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          Cycle/4.0 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          PI/2.0
          Arcsin 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          -1.0 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          n.a. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          -Cycle/4.0 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          -PI/2.0
          Arccos 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          0.0 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          n.a. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          Cycle/4.0 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          PI/2.0
          Arccos 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          -1.0 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          n.a. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          Cycle/2.0 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          PI
          Arctan and Arccot 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          0.0 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          positive 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          Cycle/4.0 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          PI/2.0
          Arctan and Arccot 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          0.0 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          negative 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          -Cycle/4.0 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          -PI/2.0
          Arctan and Arccot 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          negative 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          +0.0 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          Cycle/2.0 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          PI
          Arctan and Arccot 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          negative 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          -0.0 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          -Cycle/2.0 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          -PI
          Arctan and Arccot 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          negative 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          0.0 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          Cycle/2.0 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          PI
15    Finally, the following specifications also take precedence over the
maximum relative error bounds:

16    The absolute value of the result of the Sin, Cos, and Tanh functions
      never exceeds one.

17    The absolute value of the result of the Coth function is never less than
      one.

18    The result of the Cosh function is never less than one.


                            Implementation Advice

19    The versions of the forward trigonometric functions without a Cycle
parameter should not be implemented by calling the corresponding version with
a Cycle parameter of 2.0*Numerics.Pi, since this will not provide the required
accuracy in some portions of the domain. For the same reason, the version of
Log without a Base parameter should not be implemented by calling the
corresponding version with a Base parameter of Numerics.e.


G.2.5 Performance Requirements for Random Number Generation


1     In the strict mode, the performance of Numerics.Float_Random and
Numerics.Discrete_Random shall be as specified here.


                         Implementation Requirements

2     Two different calls to the time-dependent Reset procedure shall reset
the generator to different states, provided that the calls are separated in
time by at least one second and not more than fifty years.

3     The implementation's representations of generator states and its
algorithms for generating random numbers shall yield a period of at least
2(31)-2; much longer periods are desirable but not required.

4     The implementations of Numerics.Float_Random.Random and
Numerics.Discrete_Random.Random shall pass at least 85% of the individual
trials in a suite of statistical tests. For Numerics.Float_Random, the tests
are applied directly to the floating point values generated (i.e., they are
not converted to integers first), while for Numerics.Discrete_Random they are
applied to the generated values of various discrete types. Each test suite
performs 6 different tests, with each test repeated 10 times, yielding a total
of 60 individual trials. An individual trial is deemed to pass if the
chi-square value (or other statistic) calculated for the observed counts or
distribution falls within the range of values corresponding to the 2.5 and
97.5 percentage points for the relevant degrees of freedom (i.e., it shall be
neither too high nor too low). For the purpose of determining the degrees of
freedom, measurement categories are combined whenever the expected counts are
fewer than 5.


G.2.6 Accuracy Requirements for Complex Arithmetic


1     In the strict mode, the performance of Numerics.Generic_Complex_Types
and Numerics.Generic_Complex_Elementary_Functions shall be as specified here.


                         Implementation Requirements

2     When an exception is not raised, the result of evaluating a real
function of an instance CT of Numerics.Generic_Complex_Types (i.e., a function
that yields a value of subtype CT.Real'Base or CT.Imaginary) belongs to a
result interval defined as for a real elementary function (see G.2.4).

3     When an exception is not raised, each component of the result of
evaluating a complex function of such an instance, or of an instance of
Numerics.Generic_Complex_Elementary_Functions obtained by instantiating the
latter with CT (i.e., a function that yields a value of subtype CT.Complex),
also belongs to a result interval. The result intervals for the components of
the result are either defined by a maximum relative error bound or by a
maximum box error bound. When the result interval for the real (resp.,
imaginary) component is defined by maximum relative error, it is defined as
for that of a real function, relative to the exact value of the real (resp.,
imaginary) part of the result of the corresponding mathematical function. When
defined by maximum box error, the result interval for a component of the
result is the smallest model interval of CT.Real that contains all the values
of the corresponding part of f · (1.0 + d), where f is the exact complex value
of the corresponding mathematical function at the given parameter values, d is
complex, and |d| is less than or equal to the given maximum box error. The
function delivers a value that belongs to the result interval (or a value both
of whose components belong to their respective result intervals) when both
bounds of the result interval(s) belong to the safe range of CT.Real;
otherwise,

4     if CT.Real'Machine_Overflows is True, the function either delivers a
      value that belongs to the result interval (or a value both of whose
      components belong to their respective result intervals) or raises
      Constraint_Error, signaling overflow;

5     if CT.Real'Machine_Overflows is False, the result is implementation
      defined.

6     The error bounds for particular complex functions are tabulated below.
In the table, the error bound is given as the coefficient of
CT.Real'Model_Epsilon.

7/1   This paragraph was deleted.[ ]

8     The maximum relative error given above applies throughout the domain of
the Compose_From_Polar function when the Cycle parameter is specified. When
the Cycle parameter is omitted, the maximum relative error applies only when
the absolute value of the parameter Argument is less than or equal to the
angle threshold (see G.2.4). For the Exp function, and for the forward
hyperbolic (resp., trigonometric) functions, the maximum relative error given
above likewise applies only when the absolute value of the imaginary (resp.,
real) component of the parameter X (or the absolute value of the parameter
itself, in the case of the Exp function with a parameter of pure-imaginary
type) is less than or equal to the angle threshold. For larger angles, the
accuracy is implementation defined.

           Error Bounds for Particular Complex Functions

          Function or Operator 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          Nature of
          Result 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          Nature of
          Bound 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          Error Bound

          Modulus 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          real 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          max. rel. error 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          3.0
          Argument 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          real 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          max. rel. error 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          4.0
          Compose_From_Polar 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          complex 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          max. rel. error 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          3.0
          "*" (both operands complex) 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          complex 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          max. box error 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          5.0
          "/" (right operand complex) 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          complex 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          max. box error 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          13.0
          Sqrt 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          complex 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          max. rel. error 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          6.0
          Log 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          complex 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          max. box error 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          13.0
          Exp (complex parameter) 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          complex 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          max. rel. error 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          7.0
          Exp (imaginary parameter) 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          complex 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          max. rel. error 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          2.0
          Sin, Cos, Sinh, and Cosh 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          complex 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          max. rel. error 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          11.0
          Tan, Cot, Tanh, and Coth 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          complex 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          max. rel. error 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          35.0
          inverse trigonometric 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          complex 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          max. rel. error 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          14.0
          inverse hyperbolic 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          complex 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          max. rel. error 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

          14.0
9     The prescribed results specified in G.1.2 for certain functions at
particular parameter values take precedence over the error bounds;
effectively, they narrow to a single value the result interval allowed by the
error bounds for a component of the result. Additional rules with a similar
effect are given below for certain inverse trigonometric and inverse
hyperbolic functions, at particular parameter values for which a component of
the mathematical result is transcendental. In each case, the accuracy rule,
which takes precedence over the error bounds, is that the result interval for
the stated result component is the model interval of CT.Real associated with
the component's exact mathematical value. The cases in question are as
follows:

10    When the parameter X has the value zero, the real (resp., imaginary)
      component of the result of the Arccot (resp., Arccoth) function is in
      the model interval of CT.Real associated with the value PI/2.0.

11    When the parameter X has the value one, the real component of the result
      of the Arcsin function is in the model interval of CT.Real associated
      with the value PI/2.0.

12    When the parameter X has the value -1.0, the real component of the
      result of the Arcsin (resp., Arccos) function is in the model interval
      of CT.Real associated with the value -PI/2.0 (resp., PI).

13    The amount by which a component of the result of an inverse
trigonometric or inverse hyperbolic function is allowed to spill over into a
quadrant adjacent to the one corresponding to the principal branch, as given
in G.1.2, is limited. The rule is that the result belongs to the smallest
model interval of CT.Real that contains both boundaries of the quadrant
corresponding to the principal branch. This rule also takes precedence to the
maximum error bounds, effectively narrowing the result interval allowed by
them.

14    Finally, the results allowed by the error bounds are narrowed by one
further rule: The absolute value of each component of the result of the Exp
function, for a pure-imaginary parameter, never exceeds one.


                            Implementation Advice

15    The version of the Compose_From_Polar function without a Cycle parameter
should not be implemented by calling the corresponding version with a Cycle
parameter of 2.0*Numerics.Pi, since this will not provide the required
accuracy in some portions of the domain.



                                   Annex H
                                 (normative)

                             Safety and Security


1     This Annex addresses requirements for systems that are safety critical
or have security constraints. It provides facilities and specifies
documentation requirements that relate to several needs:

2     Understanding program execution;

3     Reviewing object code;

4     Restricting language constructs whose usage might complicate the
      demonstration of program correctness

4.1   []Execution understandability is supported by pragma Normalize_Scalars,
and also by requirements for the implementation to document the effect of a
program in the presence of a bounded error or where the language rules leave
the effect unspecified.

5     The pragmas Reviewable and Restrictions relate to the other requirements
addressed by this Annex.

      NOTES

6     1  The Valid attribute (see 13.9.2) is also useful in addressing these
      needs, to avoid problems that could otherwise arise from scalars that
      have values outside their declared range constraints.


H.1 Pragma Normalize_Scalars


1     This pragma ensures that an otherwise uninitialized scalar object is set
to a predictable value, but out of range if possible.


                                   Syntax

2     The form of a pragma Normalize_Scalars is as follows:

3       pragma Normalize_Scalars;


                           Post-Compilation Rules

4     Pragma Normalize_Scalars is a configuration pragma. It applies to all
compilation_units included in a partition.


                         Documentation Requirements

5     If a pragma Normalize_Scalars applies, the implementation shall document
the implicit initial value for scalar subtypes, and shall identify each case
in which such a value is used and is not an invalid representation.


                            Implementation Advice

6     Whenever possible, the implicit initial value for a scalar subtype
should be an invalid representation (see 13.9.1).

      NOTES

7     2  The initialization requirement applies to uninitialized scalar
      objects that are subcomponents of composite objects, to allocated
      objects, and to stand-alone objects. It also applies to scalar out
      parameters. Scalar subcomponents of composite out parameters are
      initialized to the corresponding part of the actual, by virtue of
      6.4.1.

8     3  The initialization requirement does not apply to a scalar for which
      pragma Import has been specified, since initialization of an imported
      object is performed solely by the foreign language environment (see
      B.1).

9     4  The use of pragma Normalize_Scalars in conjunction with Pragma
      Restrictions(No_Exceptions) may result in erroneous execution (see H.4
      ).


H.2 Documentation of Implementation Decisions



                         Documentation Requirements

1     The implementation shall document the range of effects for each
situation that the language rules identify as either a bounded error or as
having an unspecified effect. If the implementation can constrain the effects
of erroneous execution for a given construct, then it shall document such
constraints. The documentation might be provided either independently of any
compilation unit or partition, or as part of an annotated listing for a given
unit or partition. See also 1.1.3, and 1.1.2.

      NOTES

2     5  Among the situations to be documented are the conventions chosen for
      parameter passing, the methods used for the management of run-time
      storage, and the method used to evaluate numeric expressions if this
      involves extended range or extra precision.


H.3 Reviewable Object Code


1     Object code review and validation are supported by pragmas Reviewable
and Inspection_Point.


H.3.1 Pragma Reviewable


1     This pragma directs the implementation to provide information to
facilitate analysis and review of a program's object code, in particular to
allow determination of execution time and storage usage and to identify the
correspondence between the source and object programs.


                                   Syntax

2     The form of a pragma Reviewable is as follows:

3       pragma Reviewable;


                           Post-Compilation Rules

4     Pragma Reviewable is a configuration pragma. It applies to all
compilation_units included in a partition.


                         Implementation Requirements

5     The implementation shall provide the following information for any
compilation unit to which such a pragma applies:

6     Where compiler-generated run-time checks remain;

7     An identification of any construct with a language-defined check that is
      recognized prior to run time as certain to fail if executed (even if the
      generation of run-time checks has been suppressed);

8     For each reference to a scalar object, an identification of the
      reference as either ``known to be initialized,'' or ``possibly
      uninitialized,'' independent of whether pragma Normalize_Scalars
      applies;

9     Where run-time support routines are implicitly invoked;

10    An object code listing, including:

    11    Machine instructions, with relative offsets;

    12    Where each data object is stored during its lifetime;

    13    Correspondence with the source program, including an identification
          of the code produced per declaration and per statement.

14    An identification of each construct for which the implementation detects
      the possibility of erroneous execution;

15    For each subprogram, block, task, or other construct implemented by
      reserving and subsequently freeing an area on a run-time stack, an
      identification of the length of the fixed-size portion of the area and
      an indication of whether the non-fixed size portion is reserved on the
      stack or in a dynamically-managed storage region.

16    The implementation shall provide the following information for any
partition to which the pragma applies:

17    An object code listing of the entire partition, including initialization
      and finalization code as well as run-time system components, and with an
      identification of those instructions and data that will be relocated at
      load time;

18    A description of the run-time model relevant to the partition.

18.1  []The implementation shall provide control- and data-flow information,
both within each compilation unit and across the compilation units of the
partition.


                            Implementation Advice

19    The implementation should provide the above information in both a
human-readable and machine-readable form, and should document the latter so as
to ease further processing by automated tools.

20    Object code listings should be provided both in a symbolic format and
also in an appropriate numeric format (such as hexadecimal or octal).

      NOTES

21    6  The order of elaboration of library units will be documented even in
      the absence of pragma Reviewable (see 10.2).


H.3.2 Pragma Inspection_Point


1     An occurrence of a pragma Inspection_Point identifies a set of objects
each of whose values is to be available at the point(s) during program
execution corresponding to the position of the pragma in the compilation unit.
The purpose of such a pragma is to facilitate code validation.


                                   Syntax

2     The form of a pragma Inspection_Point is as follows:

3       pragma Inspection_Point[(object_name {, object_name})];


                               Legality Rules

4     A pragma Inspection_Point is allowed wherever a declarative_item or
statement is allowed. Each object_name shall statically denote the declaration
of an object.


                              Static Semantics

5/1   An inspection point is a point in the object code corresponding to the
occurrence of a pragma Inspection_Point in the compilation unit. An object is
inspectable at an inspection point if the corresponding pragma
Inspection_Point either has an argument denoting that object, or has no
arguments{ and the object is visible at the inspection point}.


                              Dynamic Semantics

6     Execution of a pragma Inspection_Point has no effect.


                         Implementation Requirements

7     Reaching an inspection point is an external interaction with respect to
the values of the inspectable objects at that point (see 1.1.3).


                         Documentation Requirements

8     For each inspection point, the implementation shall identify a mapping
between each inspectable object and the machine resources (such as memory
locations or registers) from which the object's value can be obtained.

      NOTES

9     7  The implementation is not allowed to perform ``dead store
      elimination'' on the last assignment to a variable prior to a point where the
      variable is inspectable. Thus an inspection point has the effect of an
      implicit reference to each of its inspectable objects.

10    8  Inspection points are useful in maintaining a correspondence between
      the state of the program in source code terms, and the machine state
      during the program's execution. Assertions about the values of program
      objects can be tested in machine terms at inspection points. Object code
      between inspection points can be processed by automated tools to verify
      programs mechanically.

11    9  The identification of the mapping from source program objects to
      machine resources is allowed to be in the form of an annotated object
      listing, in human-readable or tool-processable form.


H.4 Safety and Security Restrictions


1     This clause defines restrictions that can be used with pragma
Restrictions (see 13.12); these facilitate the demonstration of program
correctness by allowing tailored versions of the run-time system.


                              Static Semantics

2     The following restrictions, the same as in D.7, apply in this Annex:
No_Task_Hierarchy, No_Abort_Statement, No_Implicit_Heap_Allocation, Max_-
Task_Entries is 0, Max_Asynchronous_Select_Nesting is 0, and Max_Tasks is 0.
The last three restrictions are checked prior to program execution.

3     The following additional restrictions apply in this Annex.

4     Tasking-related restriction:

5     No_Protected_Types
              There are no declarations of protected types or protected
              objects.

6     Memory-management related restrictions:

7     No_Allocators
              There are no occurrences of an allocator.

8/1   No_Local_Allocators
              Allocators are prohibited in subprograms, generic subprograms,
              tasks, and entry bodies[; instantiations of generic packages are
              also prohibited in these contexts].

9     No_Unchecked_Deallocation
              Semantic dependence on Unchecked_Deallocation is not allowed.

10    Immediate_Reclamation
              Except for storage occupied by objects created by allocators and
              not deallocated via unchecked deallocation, any storage reserved
              at run time for an object is immediately reclaimed when the
              object no longer exists.

11    Exception-related restriction:

12    No_Exceptions
              Raise_statements and exception_handlers are not allowed. No
              language-defined run-time checks are generated; however, a
              run-time check performed automatically by the hardware is
              permitted.

13    Other restrictions:

14    No_Floating_Point
              Uses of predefined floating point types and operations, and
              declarations of new floating point types, are not allowed.

15    No_Fixed_Point
              Uses of predefined fixed point types and operations, and
              declarations of new fixed point types, are not allowed.

16    No_Unchecked_Conversion
              Semantic dependence on the predefined generic
              Unchecked_Conversion is not allowed.

17    No_Access_Subprograms
              The declaration of access-to-subprogram types is not allowed.

18    No_Unchecked_Access
              The Unchecked_Access attribute is not allowed.

19    No_Dispatch
              Occurrences of T'Class are not allowed, for any (tagged) subtype
              T.

20    No_IO   Semantic dependence on any of the library units Sequential_IO,
              Direct_IO, Text_IO, Wide_Text_IO, or Stream_IO is not allowed.

21    No_Delay
              Delay_Statements and semantic dependence on package Calendar are
              not allowed.

22    No_Recursion
              As part of the execution of a subprogram, the same subprogram is
              not invoked.

23    No_Reentrancy
              During the execution of a subprogram by a task, no other task
              invokes the same subprogram.


                         Implementation Requirements

24    If an implementation supports pragma Restrictions for a particular
argument, then except for the restrictions No_Unchecked_Deallocation,
No_Unchecked_Conversion, No_Access_Subprograms, and No_Unchecked_Access, the
associated restriction applies to the run-time system.


                         Documentation Requirements

25    If a pragma Restrictions(No_Exceptions) is specified, the implementation
shall document the effects of all constructs where language-defined checks are
still performed automatically (for example, an overflow check performed by the
processor).


                             Erroneous Execution

26    Program execution is erroneous if pragma Restrictions(No_Exceptions) has
been specified and the conditions arise under which a generated
language-defined run-time check would fail.

27    Program execution is erroneous if pragma Restrictions(No_Recursion) has
been specified and a subprogram is invoked as part of its own execution, or if
pragma Restrictions(No_Reentrancy) has been specified and during the execution
of a subprogram by a task, another task invokes the same subprogram.



                                    Index


Index entries are given by paragraph number. A list of all language-defined library units may be found under Language-Defined Library Units. A list of all language-defined types may be found under Language-Defined Types.
{ A list of all language-defined subprograms may be found under Language-Defined Subprograms.}

 

& operator   4.4(1), 4.5.3(3)



* operator   4.4(1), 4.5.5(1)

** operator   4.4(1), 4.5.6(7)



+ operator   4.4(1), 4.5.3(1), 4.5.4(1)



- operator   4.4(1), 4.5.3(1), 4.5.4(1)



/ operator   4.4(1), 4.5.5(1)

/= operator   4.4(1), 4.5.2(1)



10646-1:1993, ISO/IEC standard   1.2(8/1)

1539:1991, ISO/IEC standard   1.2(3)

1989:1985, ISO standard   1.2(4)



6429:1992, ISO/IEC standard   1.2(5)

646:1991, ISO/IEC standard   1.2(2)



8859-1:1987, ISO/IEC standard   1.2(6)



9899:1990, ISO/IEC standard   1.2(7)



< operator   4.4(1), 4.5.2(1)

<= operator   4.4(1), 4.5.2(1)



= operator   4.4(1), 4.5.2(1)



> operator   4.4(1), 4.5.2(1)

>= operator   4.4(1), 4.5.2(1)


A


AARM   0.3(5)

abnormal completion   7.6.1(2)

abnormal state of an object   13.9.1(4)
   [partial]   9.8(21), 11.6(6), A.13(17)

abnormal task   9.8(4)

abort
   of a partition   E.1(7)
   of a task   9.8(4)
   of the execution of a construct   9.8(5)

abort completion point   9.8(15)

abort-deferred operation   9.8(5)

abort_statement   9.8(2)
   used   5.1(4), P

Abort_Task
   in Ada.Task_Identification   C.7.1(3/1)

abortable_part   9.7.4(5)
   used   9.7.4(2), P

abs operator   4.4(1), 4.5.6(1)

absolute value   4.4(1), 4.5.6(1)

abstract data type (ADT)
   See private types and private extensions   7.3(1)
   See also abstract type   3.9.3(1)

abstract subprogram   3.9.3(1), 3.9.3(3)

abstract type   3.9.3(1), 3.9.3(2)

abstract_subprogram_declaration   6.1(3)
   used   3.1(3), P

accept_alternative   9.7.1(5)
   used   9.7.1(4), P

accept_statement   9.5.2(3)
   used   5.1(5), 9.7.1(5), P

acceptable interpretation   8.6(14)

Access attribute   3.10.2(24/1), 3.10.2(32)
   See also Unchecked_Access attribute   13.10(3)

access discriminant   3.7(9)

access parameter   6.1(24)

access paths
   distinct   6.2(12)

access type   3.10(1)

access types
   input-output unspecified   A.7(6)

access value   3.10(1)

access-to-constant type   3.10(10)

access-to-object type   3.10(7/1)

access-to-subprogram type   3.10(7/1), 3.10(11)

access-to-variable type   3.10(10)

Access_Check   11.5(11/1)
   [partial]   4.1(13), 4.6(49)

access_definition   3.10(6)
   used   3.7(5), 6.1(15), P

access_to_object_definition   3.10(3)
   used   3.10(2), P

access_to_subprogram_definition   3.10(5)
   used   3.10(2), P

access_type_definition   3.10(2)
   used   3.2.1(4), 12.5.4(2), P

accessibility
   from shared passive library units   E.2.1(8)

accessibility level   3.10.2(3)

accessibility rule
   Access attribute   3.10.2(28), 3.10.2(32)
   record extension   3.9.1(3)
   requeue statement   9.5.4(6)
   type conversion   4.6(17), 4.6(20)

Accessibility_Check   11.5(21)
   [partial]   3.10.2(29), 4.6(48), 6.5(17), E.4(18/1)

accessible partition   E.1(7)

accuracy   4.6(32), G.2(1)

ACK
   in Ada.Characters.Latin_1   A.3.3(5)

acquire
   execution resource associated with protected object   9.5.1(5)

activation
   of a task   9.2(1)

activation failure   9.2(1)

activator
   of a task   9.2(5)

active partition   10.2(28), E.1(2)

active priority   D.1(15)

actual   12.3(7)

actual duration   D.9(12)

actual parameter
   for a formal parameter   6.4.1(3)

actual subtype   3.3(23), 12.5(4)
   of an object   3.3.1(9)

actual type   12.5(4)

actual_parameter_part   6.4(4)
   used   6.4(2), 6.4(3), 9.5.3(2), P

Acute
   in Ada.Characters.Latin_1   A.3.3(22)

Ada   A.2(2)

Ada calling convention   6.3.1(3)

Ada.Asynchronous_Task_Control   D.11(3)

Ada.Calendar   9.6(10)

Ada.Characters   A.3.1(2)

Ada.Characters.Handling   A.3.2(2)

Ada.Characters.Latin_1   A.3.3(3)

Ada.Command_Line   A.15(3)

Ada.Decimal   F.2(2)

Ada.Direct_IO   A.8.4(2)

Ada.Dynamic_Priorities   D.5(3)

Ada.Exceptions   11.4.1(2)

Ada.Finalization   7.6(4/1)

Ada.Float_Text_IO   A.10.9(33)

Ada.Float_Wide_Text_IO   A.11(3)

Ada.Integer_Text_IO   A.10.8(21)

Ada.Integer_Wide_Text_IO   A.11(3)

Ada.Interrupts   C.3.2(2)

Ada.Interrupts.Names   C.3.2(12)

Ada.IO_Exceptions   A.13(3)

Ada.Numerics   A.5(3)

Ada.Numerics.Complex_Elementary_Functions   G.1.2(9/1)

Ada.Numerics.Complex_Types   G.1.1(25/1)

Ada.Numerics.Complex_Elementary_Functions   G.1.2(9/1)

Ada.Numerics.Complex_Types   G.1.1(25/1)

Ada.Numerics.Discrete_Random   A.5.2(17)

Ada.Numerics.Elementary_Functions   A.5.1(9/1)

Ada.Numerics.Elementary_Functions   A.5.1(9/1)

Ada.Numerics.Float_Random   A.5.2(5)

Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(2)

Ada.Numerics.Generic_Complex_Types   G.1.1(2/1)

Ada.Numerics.Generic_Elementary_Functions   A.5.1(3)

Ada.Real_Time   D.8(3)

Ada.Sequential_IO   A.8.1(2)

Ada.Storage_IO   A.9(3)

Ada.Streams   13.13.1(2)

Ada.Streams.Stream_IO   A.12.1(3)

Ada.Strings   A.4.1(3)

Ada.Strings.Bounded   A.4.4(3)

Ada.Strings.Fixed   A.4.3(5)

Ada.Strings.Maps   A.4.2(3)

Ada.Strings.Maps.Constants   A.4.6(3)

Ada.Strings.Unbounded   A.4.5(3)

Ada.Strings.Wide_Bounded   A.4.7(1)

Ada.Strings.Wide_Fixed   A.4.7(1)

Ada.Strings.Wide_Maps.Wide_Constants   A.4.7(28)

Ada.Strings.Wide_Unbounded   A.4.7(1)

Ada.Strings.Wide_Maps   A.4.7(3)

Ada.Synchronous_Task_Control   D.10(3)

Ada.Tags   3.9(6)

Ada.Task_Attributes   C.7.2(2)

Ada.Task_Identification   C.7.1(2)

Ada.Text_IO   A.10.1(2)

Ada.Text_IO.Complex_IO   G.1.3(3)

Ada.Text_IO.Editing   F.3.3(3)

Ada.Text_IO.Text_Streams   A.12.2(3)

Ada.Unchecked_Conversion   13.9(3)

Ada.Unchecked_Deallocation   13.11.2(3)

Ada.Wide_Text_IO   A.11(2)

Ada.Wide_Text_IO.Complex_IO   G.1.4(1)

Ada.Wide_Text_IO.Editing   F.3.4(1)

Ada.Wide_Text_IO.Text_Streams   A.12.3(3)

Ada_To_COBOL
   in Interfaces.COBOL   B.4(14)

adafinal   B.1(39)

adainit   B.1(39)

address
   arithmetic   13.7.1(6)
   comparison   13.7(14)
   in System   13.7(12)

Address attribute   13.3(11)

Address clause   13.3(7), 13.3(12)

Address_To_Access_Conversions
   child of System   13.7.2(2)

Adjacent attribute   A.5.3(48)

Adjust   7.6(2)
   in Ada.Finalization   7.6(6)

adjusting the value of an object   7.6(15), 7.6(16)

adjustment   7.6(15), 7.6(16)
   as part of assignment   5.2(14)

ADT (abstract data type)
   See private types and private extensions   7.3(1)
   See also abstract type   3.9.3(1)

advice   1.1.2(37)

Aft attribute   3.5.10(5)

aggregate   4.3(1), 4.3(2)
   used   4.4(7), 4.7(2), P
   See also composite type   3.2(2)

aliased   3.10(9)

aliasing
   See distinct access paths   6.2(12)

Alignment
   in Ada.Strings   A.4.1(6)

Alignment attribute   13.3(23)

Alignment clause   13.3(7), 13.3(25)

All_Checks   11.5(25)

Allocate
   in System.Storage_Pools   13.11(7)

allocator   4.8(2)
   used   4.4(7), P

Alphanumeric
   in Interfaces.COBOL   B.4(16)

alphanumeric character
   a category of Character   A.3.2(31)

Alphanumeric_Set
   in Ada.Strings.Maps.Constants   A.4.6(4)

ambiguous   8.6(30)

ampersand   2.1(15)
   in Ada.Characters.Latin_1   A.3.3(8)

ampersand operator   4.4(1), 4.5.3(3)

ancestor
   of a library unit   10.1.1(11)
   of a type   3.4.1(10)
   ultimate   3.4.1(10)

ancestor subtype
   of a formal derived type   12.5.1(5)
   of a private_extension_declaration   7.3(8)

ancestor_part   4.3.2(3)
   used   4.3.2(2), P

and operator   4.4(1), 4.5.1(2)

and then (short-circuit control form)   4.4(1), 4.5.1(1)

angle threshold   G.2.4(10)

Annex
   informative   1.1.2(18)
   normative   1.1.2(14)
   Specialized Needs   1.1.2(7)

Annotated Ada Reference Manual   0.3(5)

anonymous access type   3.10(12)

anonymous array type   3.3.1(1)

anonymous protected type   3.3.1(1)

anonymous task type   3.3.1(1)

anonymous type   3.2.1(7)

Any_Priority
   in System   13.7(16)

APC
   in Ada.Characters.Latin_1   A.3.3(19)

apostrophe   2.1(15)
   in Ada.Characters.Latin_1   A.3.3(8)

Append
   in Ada.Strings.Bounded   A.4.4(13), A.4.4(14), A.4.4(15), A.4.4(16),
A.4.4(17), A.4.4(18), A.4.4(19), A.4.4(20)
   in Ada.Strings.Unbounded   A.4.5(12), A.4.5(13), A.4.5(14)

applicable index constraint   4.3.3(10)

application areas   1.1.2(7)

apply
   to a callable construct by a return_statement   6.5(4)
   to a loop_statement by an exit_statement   5.7(4)
   to a program unit by a program unit pragma   10.1.5(2)

arbitrary order   1.1.4(18)

Arccos
   in Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(5)
   in Ada.Numerics.Generic_Elementary_Functions   A.5.1(6)

Arccosh
   in Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(7)
   in Ada.Numerics.Generic_Elementary_Functions   A.5.1(7)

Arccot
   in Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(5)
   in Ada.Numerics.Generic_Elementary_Functions   A.5.1(6)

Arccoth
   in Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(7)
   in Ada.Numerics.Generic_Elementary_Functions   A.5.1(7)

Arcsin
   in Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(5)
   in Ada.Numerics.Generic_Elementary_Functions   A.5.1(6)

Arcsinh
   in Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(7)
   in Ada.Numerics.Generic_Elementary_Functions   A.5.1(7)

Arctan
   in Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(5)
   in Ada.Numerics.Generic_Elementary_Functions   A.5.1(6)

Arctanh
   in Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(7)
   in Ada.Numerics.Generic_Elementary_Functions   A.5.1(7)

Argument
   in Ada.Command_Line   A.15(5)
   in Ada.Numerics.Generic_Complex_Types   G.1.1(10)

argument of a pragma   2.8(9)

Argument_Count
   in Ada.Command_Line   A.15(4)

Argument_Error
   in Ada.Numerics   A.5(3)

array   3.6(1)

array component expression   4.3.3(6)

array indexing
   See indexed_component   4.1.1(1)

array slice   4.1.2(1)

array type   3.6(1)

array_aggregate   4.3.3(2)
   used   4.3(2), 13.4(3), P

array_component_association   4.3.3(5)
   used   4.3.3(4), P

array_type_definition   3.6(2)
   used   3.2.1(4), 3.3.1(2), 12.5.3(2), P

ASCII
   package physically nested within the declaration of Standard   A.1(36)

aspect of representation   13.1(8)
   coding   13.4(7)
   controlled   13.11.3(5)
   convention, calling convention   B.1(28)
   exported   B.1(28)
   imported   B.1(28)
   layout   13.5(1)
   packing   13.2(5)
   record layout   13.5(1)
   specifiable attributes   13.3(5/1)
   storage place   13.5(1)

aspect_clause   13.1(2/1)
   used   3.8(5/1), 3.11(4/1), 9.1(5/1), 9.4(5/1), 9.4(8/1), P

assembly language   C.1(4)

assign
   See assignment operation   5.2(3)

assigning back of parameters   6.4.1(17)

assignment
   user-defined   7.6(1)

assignment operation   5.2(3), 5.2(12), 7.6(13)
   during elaboration of an object_declaration   3.3.1(19)
   during evaluation of a generic_association for a formal object of mode in
   12.4(11)
   during evaluation of a parameter_association   6.4.1(11)
   during evaluation of an aggregate   4.3(5)
   during evaluation of an initialized allocator   4.8(7)
   during evaluation of an uninitialized allocator   4.8(9), 4.8(10/1)
   during evaluation of concatenation   4.5.3(10)
   during execution of a for loop   5.5(9)
   during execution of a return_statement   6.5(21)
   during execution of an assignment_statement   5.2(12)
   during parameter copy back   6.4.1(17)

assignment_statement   5.2(2)
   used   5.1(4), P

associated components
   of a record_component_association   4.3.1(10)

associated discriminants
   of a named discriminant_association   3.7.1(5)
   of a positional discriminant_association   3.7.1(5)

associated object
   of a value of a by-reference type   6.2(10)

asterisk   2.1(15)
   in Ada.Characters.Latin_1   A.3.3(8)

asynchronous
   remote procedure call   E.4.1(9)

asynchronous remote procedure call   E.4(1)

asynchronous_select   9.7.4(2)
   used   9.7(2), P

Asynchronous_Task_Control
   child of Ada   D.11(3)

at-most-once execution   E.4(11)

at_clause   J.7(1)
   used   13.1(2/1), P

atomic   C.6(7)

Attach_Handler
   in Ada.Interrupts   C.3.2(7)

attaching
   to an interrupt   C.3(2)

attribute   4.1.4(1), K(1)
   representation   13.3(1/1)
   specifiable   13.3(5/1)
   specifying   13.3(1/1)

attribute_definition_clause   13.3(2)
   used   13.1(2/1), P

attribute_designator   4.1.4(3)
   used   4.1.4(2), 13.1(3), 13.3(2), P

Attribute_Handle
   in Ada.Task_Attributes   C.7.2(3)

attribute_reference   4.1.4(2)
   used   4.1(2), P

attributes
   Access   3.10.2(24/1), 3.10.2(32)
   Address   13.3(11), J.7.1(5)
   Adjacent   A.5.3(48)
   Aft   3.5.10(5)
   Alignment   13.3(23)
   Base   3.5(15)
   Bit_Order   13.5.3(4)
   Body_Version   E.3(4)
   Callable   9.9(2)
   Caller   C.7.1(14)
   Ceiling   A.5.3(33)
   Class   3.9(14), 7.3.1(9)
   Component_Size   13.3(69)
   Compose   A.5.3(24)
   Constrained   3.7.2(3), J.4(2)
   Copy_Sign   A.5.3(51)
   Count   9.9(5)
   Definite   12.5.1(23)
   Delta   3.5.10(3)
   Denorm   A.5.3(9)
   Digits   3.5.8(2/1), 3.5.10(7)
   Exponent   A.5.3(18)
   External_Tag   13.3(75/1)
   First   3.5(12), 3.6.2(3)
   First(N)   3.6.2(4)
   First_Bit   13.5.2(3)
   Floor   A.5.3(30)
   Fore   3.5.10(4)
   Fraction   A.5.3(21)
   Identity   11.4.1(9), C.7.1(12)
   Image   3.5(35)
   Input   13.13.2(22), 13.13.2(32)
   Last   3.5(13), 3.6.2(5)
   Last(N)   3.6.2(6)
   Last_Bit   13.5.2(4)
   Leading_Part   A.5.3(54)
   Length   3.6.2(9)
   Length(N)   3.6.2(10)
   Machine   A.5.3(60)
   Machine_Emax   A.5.3(8)
   Machine_Emin   A.5.3(7)
   Machine_Mantissa   A.5.3(6)
   Machine_Overflows   A.5.3(12), A.5.4(4)
   Machine_Radix   A.5.3(2), A.5.4(2)
   Machine_Rounds   A.5.3(11), A.5.4(3)
   Max   3.5(19)
   Max_Size_In_Storage_Elements   13.11.1(3)
   Min   3.5(16)
   Model   A.5.3(68), G.2.2(7)
   Model_Emin   A.5.3(65), G.2.2(4)
   Model_Epsilon   A.5.3(66)
   Model_Mantissa   A.5.3(64), G.2.2(3)
   Model_Small   A.5.3(67)
   Modulus   3.5.4(17)
   Output   13.13.2(19), 13.13.2(29)
   Partition_ID   E.1(9)
   Pos   3.5.5(2)
   Position   13.5.2(2)
   Pred   3.5(25)
   Range   3.5(14), 3.6.2(7)
   Range(N)   3.6.2(8)
   Read   13.13.2(6), 13.13.2(14)
   Remainder   A.5.3(45)
   Round   3.5.10(12)
   Rounding   A.5.3(36)
   Safe_First   A.5.3(71), G.2.2(5)
   Safe_Last   A.5.3(72), G.2.2(6)
   Scale   3.5.10(11)
   Scaling   A.5.3(27)
   Signed_Zeros   A.5.3(13)
   Size   13.3(40), 13.3(45)
   Small   3.5.10(2/1)
   Storage_Pool   13.11(13)
   Storage_Size   13.3(60), 13.11(14), J.9(2)
   Succ   3.5(22)
   Tag   3.9(16), 3.9(18)
   Terminated   9.9(3)
   Truncation   A.5.3(42)
   Unbiased_Rounding   A.5.3(39)
   Unchecked_Access   13.10(3), H.4(18)
   Val   3.5.5(5)
   Valid   13.9.2(3), H(6)
   Value   3.5(52)
   Version   E.3(3)
   Wide_Image   3.5(28)
   Wide_Value   3.5(40)
   Wide_Width   3.5(38)
   Width   3.5(39)
   Write   13.13.2(3), 13.13.2(11)


B


Backus-Naur Form (BNF)
   complete listing   P
   cross reference   P
   notation   1.1.4(3)
   under Syntax heading   1.1.2(25)

base   2.4.2(3), 2.4.2(6)
   used   2.4.2(2), P

base 16 literal   2.4.2(1)

base 2 literal   2.4.2(1)

base 8 literal   2.4.2(1)

Base attribute   3.5(15)

base decimal precision
   of a floating point type   3.5.7(9)
   of a floating point type   3.5.7(10)

base priority   D.1(15)

base range
   of a decimal fixed point type   3.5.9(16)
   of a fixed point type   3.5.9(12)
   of a floating point type   3.5.7(8), 3.5.7(10)
   of a modular type   3.5.4(10)
   of a scalar type   3.5(6)
   of a signed integer type   3.5.4(9)
   of an ordinary fixed point type   3.5.9(13)

base subtype
   of a type   3.5(15)

based_literal   2.4.2(2)
   used   2.4(2), P

based_numeral   2.4.2(4)
   used   2.4.2(2), P

basic letter
   a category of Character   A.3.2(27)

basic_declaration   3.1(3)
   used   3.11(4/1), P

basic_declarative_item   3.11(4/1)
   used   3.11(3), 7.1(3), P

Basic_Map
   in Ada.Strings.Maps.Constants   A.4.6(5)

Basic_Set
   in Ada.Strings.Maps.Constants   A.4.6(4)

become nonlimited   7.3.1(5/1), 7.5(16)

BEL
   in Ada.Characters.Latin_1   A.3.3(5)

belong
   to a range   3.5(4)
   to a subtype   3.2(8)

bibliography   1.2(1)

big endian   13.5.3(2)

binary
   literal   2.4.2(1)
   in Interfaces.COBOL   B.4(10)

binary adding operator   4.5.3(1)

binary literal   2.4.2(1)

binary operator   4.5(9)

binary_adding_operator   4.5(4)
   used   4.4(4), P

Binary_Format
   in Interfaces.COBOL   B.4(24)

bit field
   See record_representation_clause   13.5.1(1)

bit ordering   13.5.3(2)

bit string
   See logical operators on boolean arrays   4.5.1(2)

Bit_Order
   in System   13.7(15)

Bit_Order attribute   13.5.3(4)

Bit_Order clause   13.3(7), 13.5.3(4)

blank
   in text input for enumeration and numeric types   A.10.6(5)

Blank_When_Zero
   in Ada.Text_IO.Editing   F.3.3(7)

block_statement   5.6(2)
   used   5.1(5), P

blocked
   [partial]   D.2.1(11)
   a task state   9(10)
   during an entry call   9.5.3(19)
   execution of a selective_accept   9.7.1(16)
   on a delay_statement   9.6(21)
   on an accept_statement   9.5.2(24)
   waiting for activations to complete   9.2(5)
   waiting for dependents to terminate   9.3(5)

blocked interrupt   C.3(2)

blocking, potentially   9.5.1(8)
   Abort_Task   C.7.1(16)
   delay_statement   9.6(34), D.9(5)
   remote subprogram call   E.4(17)
   RPC operations   E.5(23)
   Suspend_Until_True   D.10(10)

BMP   3.5.2(2), 3.5.2(3)

BNF (Backus-Naur Form)
   complete listing   P
   cross reference   P
   notation   1.1.4(3)
   under Syntax heading   1.1.2(25)

body   3.11(5), 3.11.1(1/1)
   used   3.11(3), P

body_stub   10.1.3(2)
   used   3.11(5), P

Body_Version attribute   E.3(4)

Boolean   3.5.3(1)
   in Standard   A.1(5)

boolean type   3.5.3(1)

Bounded
   child of Ada.Strings   A.4.4(3)

bounded error   1.1.2(31), 1.1.5(8)
   cause   6.2(12), 7.6.1(14/1), 9.5.1(8), 9.8(20), 10.2(26), 13.9.1(9),
13.11.2(11), C.7.1(17), C.7.2(13.1/1), D.5(11), E.1(10), E.3(6), J.7.1(11)

Bounded_String
   in Ada.Strings.Bounded   A.4.4(6)

bounds
   of a discrete_range   3.6.1(6)
   of an array   3.6(13)
   of the index range of an array_aggregate   4.3.3(24)

box
   compound delimiter   3.6(15)

BPH
   in Ada.Characters.Latin_1   A.3.3(17)

broadcast signal
   See protected object   9.4(1)
   See requeue   9.5.4(1)

Broken_Bar
   in Ada.Characters.Latin_1   A.3.3(21)

BS
   in Ada.Characters.Latin_1   A.3.3(5)

Buffer_Size
   in Ada.Storage_IO   A.9(4)

Buffer_Type
   in Ada.Storage_IO   A.9(4)

by copy parameter passing   6.2(2)

by reference parameter passing   6.2(2)

by-copy type   6.2(3)

by-reference type   6.2(4)
   atomic or volatile   C.6(18)

Byte
   in Interfaces.COBOL   B.4(29)
   See storage element   13.3(8)

byte sex
   See ordering of storage elements in a word   13.5.3(5)

Byte_Array
   in Interfaces.COBOL   B.4(29)


C


C
   child of Interfaces   B.3(4)

C interface   B.3(1/1)

C standard   1.2(7)

C_float
   in Interfaces.C   B.3(15)

Calendar
   child of Ada   9.6(10)

call   6(2)

call on a dispatching operation   3.9.2(2)

callable   9.9(2)

Callable attribute   9.9(2)

callable construct   6(2)

callable entity   6(2)

called partition   E.4(1)

Caller attribute   C.7.1(14)

calling convention   6.3.1(2/1), B.1(11)
   Ada   6.3.1(3)
   associated with a designated profile   3.10(11)
   entry   6.3.1(13)
   Intrinsic   6.3.1(4)
   protected   6.3.1(12)

calling partition   E.4(1)

calling stub   E.4(10)

CAN
   in Ada.Characters.Latin_1   A.3.3(6)

cancellation
   of a delay_statement   9.6(22)
   of an entry call   9.5.3(20)

cancellation of a remote subprogram call   E.4(13)

canonical form   A.5.3(3)

canonical semantics   11.6(2)

canonical-form representation   A.5.3(10)

case insensitive   2.3(5)

case_statement   5.4(2)
   used   5.1(5), P

case_statement_alternative   5.4(3)
   used   5.4(2), P

cast
   See type conversion   4.6(1)
   See unchecked type conversion   13.9(1)

catch (an exception)
   See handle   11(1)

categorization pragma   E.2(2)
   Remote_Call_Interface   E.2.3(2)
   Remote_Types   E.2.2(2)
   Shared_Passive   E.2.1(2)

categorized library unit   E.2(2)

catenation operator
   See concatenation operator   4.4(1)
   See concatenation operator   4.5.3(3)

CCH
   in Ada.Characters.Latin_1   A.3.3(18)

Cedilla
   in Ada.Characters.Latin_1   A.3.3(22)

Ceiling attribute   A.5.3(33)

ceiling priority
   of a protected object   D.3(8)

Ceiling_Check
   [partial]   C.3.1(11), D.3(13)

Cent_Sign
   in Ada.Characters.Latin_1   A.3.3(21)

change of representation   13.6(1)

char
   in Interfaces.C   B.3(19)

char_array
   in Interfaces.C   B.3(23)

char_array_access
   in Interfaces.C.Strings   B.3.1(4)

CHAR_BIT
   in Interfaces.C   B.3(6)

character   2.1(2), 3.5.2(2)
   used   2.7(2), P
   in Standard   A.1(35)

character set   2.1(1)

character set standard
   16-bit   1.2(8/1)
   7-bit   1.2(2)
   8-bit   1.2(6)
   control functions   1.2(5)

character type   3.5.2(1)

character_literal   2.5(2)
   used   3.5.1(4), 4.1(2), 4.1.3(3), P

Character_Mapping
   in Ada.Strings.Maps   A.4.2(20)

Character_Mapping_Function
   in Ada.Strings.Maps   A.4.2(25)

Character_Range
   in Ada.Strings.Maps   A.4.2(6)

Character_Ranges
   in Ada.Strings.Maps   A.4.2(7)

Character_Sequence
   in Ada.Strings.Maps   A.4.2(16)

Character_Set
   in Ada.Strings.Maps   A.4.2(4)
   in Ada.Strings.Wide_Maps.Wide_Constants   A.4.7(46)
   in Interfaces.Fortran   B.5(11)

characteristics   7.3(15)

Characters
   child of Ada   A.3.1(2)

chars_ptr
   in Interfaces.C.Strings   B.3.1(5)

chars_ptr_array
   in Interfaces.C.Strings   B.3.1(6)

check
   language-defined   11.5(2), 11.6(1)

check, language-defined
   Access_Check   4.1(13), 4.6(49)
   Accessibility_Check   3.10.2(29), 4.6(48), 6.5(17), E.4(18/1)
   Ceiling_Check   C.3.1(11), D.3(13)
   Discriminant_Check   4.1.3(15), 4.3(6), 4.3.2(8), 4.6(43), 4.6(45),
4.6(51), 4.6(52), 4.7(4), 4.8(10/1)
   Division_Check   3.5.4(20), 4.5.5(22), A.5.1(28), A.5.3(47), G.1.1(40),
G.1.2(28), K(202)
   Elaboration_Check   3.11(9)
   Index_Check   4.1.1(7), 4.1.2(7), 4.3.3(29), 4.3.3(30), 4.5.3(8), 4.6(51),
4.7(4), 4.8(10/1)
   Length_Check   4.5.1(8), 4.6(37), 4.6(52)
   Overflow_Check   3.5.4(20), 4.4(11), 5.4(13), G.2.1(11), G.2.2(7),
G.2.3(25), G.2.4(2), G.2.6(3)
   Partition_Check   E.4(19)
   Range_Check   3.2.2(11), 3.5(24), 3.5(27), 3.5(43), 3.5(44), 3.5(51),
3.5(55), 3.5.5(7), 3.5.9(19), 4.2(11), 4.3.3(28), 4.5.1(8), 4.5.6(6),
4.5.6(13), 4.6(28), 4.6(38), 4.6(46), 4.6(51), 4.7(4), 13.13.2(35),
A.5.2(39), A.5.2(40/1), A.5.3(26), A.5.3(29), A.5.3(50), A.5.3(53),
A.5.3(59), A.5.3(62), K(11), K(114), K(122), K(184), K(220), K(241), K(41),
K(47)
   Reserved_Check   C.3.1(10)
   Storage_Check   11.1(6), 13.3(67), 13.11(17), D.7(15/1), D.7(17/1),
D.7(18/1), D.7(19/1)
   Tag_Check   3.9.2(16), 4.6(42), 4.6(52), 5.2(10), 6.5(9)

child
   of a library unit   10.1.1(1)

choice parameter   11.2(9)

choice_parameter_specification   11.2(4)
   used   11.2(3), P

Circumflex
   in Ada.Characters.Latin_1   A.3.3(12)

class
   of types   3.2(2)
   See also package   7(1)
   See also tag   3.9(3)

Class attribute   3.9(14), 7.3.1(9)

class determined for a formal type   12.5(6)

class-wide type   3.4.1(4), 3.7(26)

cleanup
   See finalization   7.6.1(1)

clock   9.6(6)
   in Ada.Calendar   9.6(12)
   in Ada.Real_Time   D.8(6)

clock jump   D.8(32)

clock tick   D.8(23)

Close
   in Ada.Direct_IO   A.8.4(8)
   in Ada.Sequential_IO   A.8.1(8)
   in Ada.Streams.Stream_IO   A.12.1(10)
   in Ada.Text_IO   A.10.1(11)

close result set   G.2.3(5)

closed entry   9.5.3(5)
   of a protected object   9.5.3(7)
   of a task   9.5.3(6)

closed under derivation   3.4(28), N(6), N(41)

closure
   downward   3.10.2(37)

COBOL
   child of Interfaces   B.4(7)

COBOL interface   B.4(1)

COBOL standard   1.2(4)

COBOL_Character
   in Interfaces.COBOL   B.4(13)

COBOL_To_Ada
   in Interfaces.COBOL   B.4(15)

code_statement   13.8(2)
   used   5.1(4), P

coding
   aspect of representation   13.4(7)

Col
   in Ada.Text_IO   A.10.1(37)

colon   2.1(15)
   in Ada.Characters.Latin_1   A.3.3(10)

column number   A.10(9)

comma   2.1(15)
   in Ada.Characters.Latin_1   A.3.3(8)

Command_Line
   child of Ada   A.15(3)

Command_Name
   in Ada.Command_Line   A.15(6)

comment   2.7(2)

comments, instructions for submission   0.3(58/1)

Commercial_At
   in Ada.Characters.Latin_1   A.3.3(10)

Communication_Error
   in System.RPC   E.5(5)

comparison operator
   See relational operator   4.5.2(1)

compatibility
   composite_constraint with an access subtype   3.10(15)
   constraint with a subtype   3.2.2(12)
   delta_constraint with an ordinary fixed point subtype   J.3(9)
   digits_constraint with a decimal fixed point subtype   3.5.9(18)
   digits_constraint with a floating point subtype   J.3(10)
   discriminant constraint with a subtype   3.7.1(10)
   index constraint with a subtype   3.6.1(7)
   range with a scalar subtype   3.5(8)
   range_constraint with a scalar subtype   3.5(8)

compatible
   a type, with a convention   B.1(12)

compilation   10.1.1(2)
   separate   10.1(1)

Compilation unit   10.1(2), 10.1.1(9)

compilation units needed
   by a compilation unit   10.2(2)
   remote call interface   E.2.3(18)
   shared passive library unit   E.2.1(11)

compilation_unit   10.1.1(3)
   used   10.1.1(2), P

compile-time error   1.1.2(27), 1.1.5(4)

compile-time semantics   1.1.2(28)

complete context   8.6(4)

completely defined   3.11.1(8)

completion
   abnormal   7.6.1(2)
   compile-time concept   3.11.1(1/1)
   normal   7.6.1(2)
   run-time concept   7.6.1(2)

completion and leaving (completed and left)   7.6.1(2)

completion legality
   [partial]   3.10.1(13)
   entry_body   9.5.2(16)

Complex
   in Ada.Numerics.Generic_Complex_Types   G.1.1(3)
   in Interfaces.Fortran   B.5(9)

Complex_Elementary_Functions
   child of Ada.Numerics   G.1.2(9/1)

Complex_Types
   child of Ada.Numerics   G.1.1(25/1)

Complex_IO
   child of Ada.Text_IO   G.1.3(3)
   child of Ada.Wide_Text_IO   G.1.4(1)

component   3.2(2)

component subtype   3.6(10)

component_choice_list   4.3.1(5)
   used   4.3.1(4), P

component_clause   13.5.1(3)
   used   13.5.1(2), P

component_declaration   3.8(6)
   used   3.8(5/1), 9.4(6), P

component_definition   3.6(7)
   used   3.6(3), 3.6(5), 3.8(6), P

component_item   3.8(5/1)
   used   3.8(4), P

component_list   3.8(4)
   used   3.8(3), 3.8.1(3), P

Component_Size attribute   13.3(69)

Component_Size clause   13.3(7), 13.3(70)

components
   of a record type   3.8(9)

Compose attribute   A.5.3(24)

Compose_From_Cartesian
   in Ada.Numerics.Generic_Complex_Types   G.1.1(8)

Compose_From_Polar
   in Ada.Numerics.Generic_Complex_Types   G.1.1(11)

composite type   3.2(2)

composite_constraint   3.2.2(7)
   used   3.2.2(5), P

compound delimiter   2.2(10)

compound_statement   5.1(5)
   used   5.1(3), P

concatenation operator   4.4(1), 4.5.3(3)

concrete subprogram
   See nonabstract subprogram   3.9.3(1)

concrete type
   See nonabstract type   3.9.3(1)

concurrent processing
   See task   9(1)

condition   5.3(3)
   used   5.3(2), 5.5(3), 5.7(2), 9.5.2(7), 9.7.1(3), P
   See also exception   11(1)

conditional_entry_call   9.7.3(2)
   used   9.7(2), P

configuration
   of the partitions of a program   E(4)

configuration pragma   10.1.5(8)
   Locking_Policy   D.3(5)
   Normalize_Scalars   H.1(4)
   Queuing_Policy   D.4(5)
   Restrictions   13.12(8)
   Reviewable   H.3.1(4)
   Suppress   11.5(5)
   Task_Dispatching_Policy   D.2.2(4)

conformance   6.3.1(1)
   of an implementation with the Standard   1.1.3(1)
   See also full conformance, mode conformance, subtype conformance,
type conformance

Conjugate
   in Ada.Numerics.Generic_Complex_Types   G.1.1(12), G.1.1(15)

consistency
   among compilation units   10.1.4(5)

constant   3.3(13)
   result of a function_call   6.4(12)
   See also literal   4.2(1)
   See also static   4.9(1)

constant object   3.3(13)

constant view   3.3(13)

Constants
   child of Ada.Strings.Maps   A.4.6(3)

constituent
   of a construct   1.1.4(17)

constrained   3.2(9)
   object   3.3.1(9), 3.10(9)
   object   6.4.1(16)
   subtype   3.2(9), 3.4(6), 3.5(7), 3.5.1(10), 3.5.4(9), 3.5.4(10),
3.5.7(11), 3.5.9(13), 3.5.9(16), 3.6(15), 3.6(16), 3.7(26), 3.9(15)
   subtype   3.10(14/1)
   subtype   K(35)

Constrained attribute   3.7.2(3)

constrained by its initial value   3.3.1(9), 3.10(9)
   [partial]   4.8(6)

constrained_array_definition   3.6(5)
   used   3.6(2), P

constraint   3.2.2(5)
   [partial]   3.2(7)
   of a first array subtype   3.6(16)
   of an object   3.3.1(9)
   used   3.2.2(3), P

Constraint_Error
   raised by failure of run-time check   3.2.2(12), 3.5(24), 3.5(27),
3.5(43), 3.5(44), 3.5(51), 3.5(55), 3.5.4(20), 3.5.5(7), 3.5.9(19),
3.9.2(16), 4.1(13), 4.1.1(7), 4.1.2(7), 4.1.3(15), 4.2(11), 4.3(6), 4.3.2(8),
4.3.3(31), 4.4(11), 4.5(10), 4.5(11), 4.5(12), 4.5.1(8), 4.5.3(8), 4.5.5(22),
4.5.6(6), 4.5.6(12), 4.5.6(13), 4.6(28), 4.6(57), 4.6(60), 4.7(4), 4.8(10/1),
5.2(10), 5.4(13), 6.5(9), 11.1(4), 11.4.1(14), 11.5(10), 13.9.1(9),
13.13.2(35), A.4.3(109), A.4.3(68/1), A.4.7(47), A.5.1(28), A.5.1(34),
A.5.2(39), A.5.2(40.1/1), A.5.2(40/1), A.5.3(26), A.5.3(29), A.5.3(47),
A.5.3(50), A.5.3(53), A.5.3(59), A.5.3(62), A.15(14), B.3(53), B.3(54),
B.4(58), E.4(19), G.1.1(40), G.1.2(28), G.2.1(12), G.2.2(7), G.2.3(26),
G.2.4(3), G.2.6(4), K(11), K(114), K(122), K(184), K(202), K(220), K(241),
K(261), K(41), K(47)
   in Standard   A.1(46)

Construct   1.1.4(16), N(2)

constructor
   See initialization   3.3.1(19)
   See initialization   7.6(1)
   See initialization expression   3.3.1(4)
   See Initialize   7.6(1)
   See initialized allocator   4.8(4)

context free grammar
   complete listing   P
   cross reference   P
   notation   1.1.4(3)
   under Syntax heading   1.1.2(25)

context_clause   10.1.2(2)
   used   10.1.1(3), P

context_item   10.1.2(3)
   used   10.1.2(2), P

contiguous representation
   [partial]   13.5.2(5), 13.7.1(12), 13.9(9), 13.9(17), 13.11(16)

Continue
   in Ada.Asynchronous_Task_Control   D.11(3)

control character
   a category of Character   A.3.2(22)
   a category of Character   A.3.3(4), A.3.3(15)
   See also format_effector   2.1(13)
   See also other_control_function   2.1(14)

Control_Set
   in Ada.Strings.Maps.Constants   A.4.6(4)

controlled
   aspect of representation   13.11.3(5)
   in Ada.Finalization   7.6(5)

controlled type   7.6(2), 7.6(9)

controlling formal parameter   3.9.2(2)

controlling operand   3.9.2(2)

controlling result   3.9.2(2)

controlling tag
   for a call on a dispatching operation   3.9.2(1)

controlling tag value   3.9.2(14)
   for the expression     in an assignment_statement   5.2(9)

convention   6.3.1(2/1), B.1(11)
   aspect of representation   B.1(28)

conversion   4.6(1), 4.6(28)
   access   4.6(13), 4.6(18), 4.6(47)
   arbitrary order   1.1.4(18)
   array   4.6(9), 4.6(36)
   composite (non-array)   4.6(21), 4.6(40)
   enumeration   4.6(21), 4.6(34)
   numeric   4.6(8), 4.6(29)
   unchecked   13.9(1)
   value   4.6(5/1)
   view   4.6(5/1)

Conversion_Error
   in Interfaces.COBOL   B.4(30)

convertible   4.6(4)
   required   3.7(16), 3.7.1(9), 4.6(11/1), 4.6(15), 6.4.1(6)

copy back of parameters   6.4.1(17)

copy parameter passing   6.2(2)

Copy_Array
   in Interfaces.C.Pointers   B.3.2(15)

Copy_Sign attribute   A.5.3(51)

Copy_Terminated_Array
   in Interfaces.C.Pointers   B.3.2(14)

Copyright_Sign
   in Ada.Characters.Latin_1   A.3.3(21)

core language   1.1.2(2)

corresponding constraint   3.4(6)

corresponding discriminants   3.7(18)

corresponding index
   for an array_aggregate   4.3.3(8)

corresponding subtype   3.4(18)

corresponding value
   of the target type of a conversion   4.6(28)

Cos
   in Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(4)
   in Ada.Numerics.Generic_Elementary_Functions   A.5.1(5)

Cosh
   in Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(6)
   in Ada.Numerics.Generic_Elementary_Functions   A.5.1(7)

Cot
   in Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(4)
   in Ada.Numerics.Generic_Elementary_Functions   A.5.1(5)

Coth
   in Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(6)
   in Ada.Numerics.Generic_Elementary_Functions   A.5.1(7)

Count
   in Ada.Direct_IO   A.8.4(4)
   in Ada.Streams.Stream_IO   A.12.1(7)
   in Ada.Strings.Bounded   A.4.4(48), A.4.4(49), A.4.4(50)
   in Ada.Strings.Fixed   A.4.3(13), A.4.3(14), A.4.3(15)
   in Ada.Strings.Unbounded   A.4.5(43), A.4.5(44), A.4.5(45)
   in Ada.Text_IO   A.10.1(5)

Count attribute   9.9(5)

cover
   a type   3.4.1(9)
   of a choice and an exception   11.2(6)

cover a value
   by a discrete_choice   3.8.1(9)
   by a discrete_choice_list   3.8.1(13)

CR
   in Ada.Characters.Latin_1   A.3.3(5)

create   3.1(12)
   in Ada.Direct_IO   A.8.4(6)
   in Ada.Sequential_IO   A.8.1(6)
   in Ada.Streams.Stream_IO   A.12.1(8)
   in Ada.Text_IO   A.10.1(9)

creation
   of a protected object   C.3.1(10)
   of a task object   D.1(17)
   of an object   3.3(1)

critical section
   See intertask communication   9.5(1)

CSI
   in Ada.Characters.Latin_1   A.3.3(19)

Currency_Sign
   in Ada.Characters.Latin_1   A.3.3(21)

current column number   A.10(9)

current index
   of an open direct file   A.8(4)
   of an open stream file   A.12.1(1.1/1)

current instance
   of a generic unit   8.6(18)
   of a type   8.6(17)

current line number   A.10(9)

current mode
   of an open file   A.7(7)

current page number   A.10(9)

Current size
   of a stream file   A.12.1(1.1/1)
   of an external file   A.8(3)

Current_Error
   in Ada.Text_IO   A.10.1(17), A.10.1(20)

Current_Handler
   in Ada.Interrupts   C.3.2(6)

Current_Input
   in Ada.Text_IO   A.10.1(17), A.10.1(20)

Current_Output
   in Ada.Text_IO   A.10.1(17), A.10.1(20)

Current_State
   in Ada.Synchronous_Task_Control   D.10(4)

Current_Task
   in Ada.Task_Identification   C.7.1(3/1)


D


dangling references
   prevention via accessibility rules   3.10.2(3)

Data_Error
   in Ada.Direct_IO   A.8.4(18)
   in Ada.IO_Exceptions   A.13(4)
   in Ada.Sequential_IO   A.8.1(15)
   in Ada.Storage_IO   A.9(9)
   in Ada.Streams.Stream_IO   A.12.1(26)
   in Ada.Text_IO   A.10.1(85)

Day
   in Ada.Calendar   9.6(13)

Day_Duration
   in Ada.Calendar   9.6(11)

Day_Number
   in Ada.Calendar   9.6(11)

DC1
   in Ada.Characters.Latin_1   A.3.3(6)

DC2
   in Ada.Characters.Latin_1   A.3.3(6)

DC3
   in Ada.Characters.Latin_1   A.3.3(6)

DC4
   in Ada.Characters.Latin_1   A.3.3(6)

DCS
   in Ada.Characters.Latin_1   A.3.3(18)

Deallocate
   in System.Storage_Pools   13.11(8)

deallocation of storage   13.11.2(1)

Decimal
   child of Ada   F.2(2)

decimal digit
   a category of Character   A.3.2(28)

decimal fixed point type   3.5.9(1), 3.5.9(6)

Decimal_Digit_Set
   in Ada.Strings.Maps.Constants   A.4.6(4)

Decimal_Element
   in Interfaces.COBOL   B.4(12)

decimal_fixed_point_definition   3.5.9(4)
   used   3.5.9(2), P

Decimal_IO
   in Ada.Text_IO   A.10.1(73)

decimal_literal   2.4.1(2)
   used   2.4(2), P

Decimal_Output
   in Ada.Text_IO.Editing   F.3.3(11)

Declaration   3.1(5), 3.1(6)

declarative region
   of a construct   8.1(1)

declarative_item   3.11(3)
   used   3.11(2), P

declarative_part   3.11(2)
   used   5.6(2), 6.3(2), 7.2(2), 9.1(6), 9.5.2(5), P

declare   3.1(8), 3.1(12)

declared pure   10.2.1(17)

Decrement
   in Interfaces.C.Pointers   B.3.2(11)

deeper
   accessibility level   3.10.2(3)
   statically   3.10.2(4), 3.10.2(17)

default entry queuing policy   9.5.3(17)

default treatment   C.3(5)

Default_Aft
   in Ada.Text_IO   A.10.1(64), A.10.1(69), A.10.1(74)
   in Ada.Text_IO.Complex_IO   G.1.3(5)

Default_Base
   in Ada.Text_IO   A.10.1(53), A.10.1(58)

Default_Bit_Order
   in System   13.7(15)

Default_Currency
   in Ada.Text_IO.Editing   F.3.3(10)

Default_Exp
   in Ada.Text_IO   A.10.1(64), A.10.1(69), A.10.1(74)
   in Ada.Text_IO.Complex_IO   G.1.3(5)

default_expression   3.7(6)
   used   3.7(5), 3.8(6), 6.1(15), 12.4(2), P

Default_Fill
   in Ada.Text_IO.Editing   F.3.3(10)

Default_Fore
   in Ada.Text_IO   A.10.1(64), A.10.1(69), A.10.1(74)
   in Ada.Text_IO.Complex_IO   G.1.3(5)

default_name   12.6(4)
   used   12.6(3), P

Default_Priority
   in System   13.7(17)

Default_Radix_Mark
   in Ada.Text_IO.Editing   F.3.3(10)

Default_Separator
   in Ada.Text_IO.Editing   F.3.3(10)

Default_Setting
   in Ada.Text_IO   A.10.1(80)

Default_Width
   in Ada.Text_IO   A.10.1(53), A.10.1(58), A.10.1(80)

deferred constant   7.4(2)

deferred constant declaration   3.3.1(6), 7.4(2)

defining name   3.1(10)

defining_character_literal   3.5.1(4)
   used   3.5.1(3), P

defining_designator   6.1(6)
   used   6.1(4), 12.3(2), P

defining_identifier   3.1(4)
   used   3.2.1(3), 3.2.2(2), 3.3.1(3), 3.5.1(3), 3.10.1(2), 5.5(4), 6.1(7),
7.3(2), 7.3(3), 8.5.1(2), 8.5.2(2), 9.1(2), 9.1(3), 9.1(6), 9.4(2), 9.4(3),
9.4(7), 9.5.2(2), 9.5.2(5), 9.5.2(8), 10.1.3(4), 10.1.3(5), 10.1.3(6),
11.2(4), 12.5(2), 12.7(2), P

defining_identifier_list   3.3.1(3)
   used   3.3.1(2), 3.3.2(2), 3.7(5), 3.8(6), 6.1(15), 11.1(2), 12.4(2), P

defining_operator_symbol   6.1(11)
   used   6.1(6), P

defining_program_unit_name   6.1(7)
   used   6.1(4), 6.1(6), 7.1(3), 7.2(2), 8.5.3(2), 8.5.5(2), 12.3(2), P

Definite attribute   12.5.1(23)

definite subtype   3.3(23)

Definition   3.1(7)

Degree_Sign
   in Ada.Characters.Latin_1   A.3.3(22)

DEL
   in Ada.Characters.Latin_1   A.3.3(14)

delay_alternative   9.7.1(6)
   used   9.7.1(4), 9.7.2(2), P

delay_relative_statement   9.6(4)
   used   9.6(2), P

delay_statement   9.6(2)
   used   5.1(4), 9.7.1(6), 9.7.4(4), P

delay_until_statement   9.6(3)
   used   9.6(2), P

Delete
   in Ada.Direct_IO   A.8.4(8)
   in Ada.Sequential_IO   A.8.1(8)
   in Ada.Streams.Stream_IO   A.12.1(10)
   in Ada.Strings.Bounded   A.4.4(64), A.4.4(65)
   in Ada.Strings.Fixed   A.4.3(29), A.4.3(30)
   in Ada.Strings.Unbounded   A.4.5(59), A.4.5(60)
   in Ada.Text_IO   A.10.1(11)

delimiter   2.2(8)

delivery
   of an interrupt   C.3(2)

delta
   of a fixed point type   3.5.9(1)

Delta attribute   3.5.10(3)

delta_constraint   J.3(2)
   used   3.2.2(6), P

Denorm attribute   A.5.3(9)

denormalized number   A.5.3(10)

denote   8.6(16)
   informal definition   3.1(8)
   name used as a pragma argument   8.6(32)

depend on a discriminant
   for a component   3.7(20)
   for a constraint or component_definition   3.7(19)

dependence
   elaboration   10.2(9)
   of a task on a master   9.3(1)
   of a task on another task   9.3(4)
   semantic   10.1.1(26)

depth
   accessibility level   3.10.2(3)

dereference   4.1(8)

Dereference_Error
   in Interfaces.C.Strings   B.3.1(12)

derivation class
   for a type   3.4.1(2)

derived from
   directly or indirectly   3.4.1(2)

derived type   3.4(1)
   [partial]   3.4(24)

derived_type_definition   3.4(2)
   used   3.2.1(4), P

descendant   10.1.1(11)
   of a type   3.4.1(10)
   relationship with scope   8.2(4)

designate   3.10(1)

designated profile
   of an access-to-subprogram type   3.10(11)

designated subtype
   of a named access type   3.10(10)
   of an anonymous access type   3.10(12)

designated type
   of a named access type   3.10(10)
   of an anonymous access type   3.10(12)

designator   6.1(5)
   used   6.3(2), P

destructor
   See finalization   7.6(1)
   See finalization   7.6.1(1)

Detach_Handler
   in Ada.Interrupts   C.3.2(9)

determined class for a formal type   12.5(6)

determines
   a type by a subtype_mark   3.2.2(8)

Device_Error
   in Ada.Direct_IO   A.8.4(18)
   in Ada.IO_Exceptions   A.13(4)
   in Ada.Sequential_IO   A.8.1(15)
   in Ada.Streams.Stream_IO   A.12.1(26)
   in Ada.Text_IO   A.10.1(85)

Diaeresis
   in Ada.Characters.Latin_1   A.3.3(21)

digit   2.1(10)
   used   2.1(3), 2.3(3), 2.4.1(3), 2.4.2(5), P

digits
   of a decimal fixed point subtype   3.5.9(6), 3.5.10(7)

Digits attribute   3.5.8(2/1), 3.5.10(7)

digits_constraint   3.5.9(5)
   used   3.2.2(6), P

dimensionality
   of an array   3.6(12)

direct access   A.8(3)

direct file   A.8(1)

Direct_IO
   child of Ada   A.8.4(2)

direct_name   4.1(3)
   used   3.8.1(2), 4.1(2), 5.1(8), 9.5.2(3), 13.1(3), J.7(1), P

Direction
   in Ada.Strings   A.4.1(6)

directly specified
   of an aspect of representation of an entity   13.1(8)
   of an operational aspect of an entity   13.1(8.1/1)

directly visible   8.3(2), 8.3(21)
   within a pragma in a   context_clause   10.1.6(3)
   within a pragma that appears at the place of a compilation unit  
10.1.6(5)
   within a use_clause in a   context_clause   10.1.6(3)
   within a with_clause   10.1.6(2)
   within the parent_unit_name of a library unit   10.1.6(2)
   within the parent_unit_name of a subunit   10.1.6(4)

discontiguous representation
   [partial]   13.5.2(5), 13.7.1(12), 13.9(9), 13.9(17), 13.11(16)

discrete array type   4.5.2(1)

discrete type   3.2(3), 3.5(1)

Discrete_Random
   child of Ada.Numerics   A.5.2(17)

discrete_choice   3.8.1(5)
   used   3.8.1(4), P

discrete_choice_list   3.8.1(4)
   used   3.8.1(3), 4.3.3(5), 5.4(3), P

discrete_range   3.6.1(3)
   used   3.6.1(2), 3.8.1(5), 4.1.2(2), P

discrete_subtype_definition   3.6(6)
   used   3.6(5), 5.5(4), 9.5.2(2), 9.5.2(8), P

discriminant   3.2(5), 3.7(1)
   of a variant_part   3.8.1(6)

discriminant_association   3.7.1(3)
   used   3.7.1(2), P

Discriminant_Check   11.5(12)
   [partial]   4.1.3(15), 4.3(6), 4.3.2(8), 4.6(43), 4.6(45), 4.6(51),
4.6(52), 4.7(4), 4.8(10/1)

discriminant_constraint   3.7.1(2)
   used   3.2.2(7), P

discriminant_part   3.7(2)
   used   3.10.1(2), 7.3(2), 7.3(3), 12.5(2), P

discriminant_specification   3.7(5)
   used   3.7(4), P

discriminants
   known   3.7(26)
   unknown   3.7(26)

discriminated type   3.7(8/1)

dispatching   3.9(3)

dispatching call
   on a dispatching operation   3.9.2(1)

dispatching operation   3.9.2(1), 3.9.2(2)
   [partial]   3.9(1)

dispatching point   D.2.1(4)
   [partial]   D.2.1(8), D.2.2(12)

dispatching policy for tasks
   [partial]   D.2.1(5)

dispatching, task   D.2.1(4)

Display_Format
   in Interfaces.COBOL   B.4(22)

displayed magnitude (of a decimal value)   F.3.2(14)

disruption of an assignment   9.8(21), 13.9.1(5)
   [partial]   11.6(6)

distinct access paths   6.2(12)

distributed program   E(3)

distributed system   E(2)

distributed systems   C(1)

divide   2.1(15)
   in Ada.Decimal   F.2(6)

divide operator   4.4(1), 4.5.5(1)

Division_Check   11.5(13)
   [partial]   3.5.4(20), 4.5.5(22), A.5.1(28), A.5.3(47), G.1.1(40),
G.1.2(28), K(202)

Division_Sign
   in Ada.Characters.Latin_1   A.3.3(26)

DLE
   in Ada.Characters.Latin_1   A.3.3(6)

Do_APC
   in System.RPC   E.5(10)

Do_RPC
   in System.RPC   E.5(9)

documentation (required of an implementation)   1.1.3(18), M(1)

documentation requirements   1.1.2(34)

Dollar_Sign
   in Ada.Characters.Latin_1   A.3.3(8)

dot   2.1(15)

dot selection
   See selected_component   4.1.3(1)

double
   in Interfaces.C   B.3(16)

Double_Precision
   in Interfaces.Fortran   B.5(6)

downward closure   3.10.2(37)

drift rate   D.8(41)

Duration
   in Standard   A.1(43)

dynamic binding
   See dispatching operation   3.9(1)

dynamic semantics   1.1.2(30)

Dynamic_Priorities
   child of Ada   D.5(3)

dynamically determined tag   3.9.2(1)

dynamically enclosing
   of one execution by another   11.4(2)

dynamically tagged   3.9.2(5)


E


e
   in Ada.Numerics   A.5(3)

edited output   F.3(1)

Editing
   child of Ada.Text_IO   F.3.3(3)
   child of Ada.Wide_Text_IO   F.3.4(1)

effect
   external   1.1.3(8)

efficiency   11.5(29), 11.6(1)

elaborated   3.11(8)

elaboration   3.1(11), N(19)
   abstract_subprogram_declaration   6.1(31)
   access_definition   3.10(17)
   access_type_definition   3.10(16)
   array_type_definition   3.6(21)
   aspect_clause   13.1(19/1)
   choice_parameter_specification   11.4(7)
   component_declaration   3.8(17)
   component_definition   3.6(22/1), 3.8(18/1)
   component_list   3.8(17)
   declaration named by a pragma Import   B.1(38)
   declarative_part   3.11(7)
   deferred constant declaration   7.4(10)
   delta_constraint   J.3(11)
   derived_type_definition   3.4(26)
   digits_constraint   3.5.9(19)
   discrete_subtype_definition   3.6(22/1)
   discriminant_constraint   3.7.1(12)
   entry_declaration   9.5.2(22/1)
   enumeration_type_definition   3.5.1(10)
   exception_declaration   11.1(5)
   fixed_point_definition   3.5.9(17)
   floating_point_definition   3.5.7(13)
   full type definition   3.2.1(11)
   full_type_declaration   3.2.1(11)
   generic body   12.2(2)
   generic_declaration   12.1(10)
   generic_instantiation   12.3(20)
   incomplete_type_declaration   3.10.1(12)
   index_constraint   3.6.1(8)
   integer_type_definition   3.5.4(18)
   loop_parameter_specification   5.5(9)
   non-generic subprogram_body   6.3(6)
   nongeneric package_body   7.2(6)
   number_declaration   3.3.2(7)
   object_declaration   3.3.1(15), 7.6(10)
   of library units for a foreign language main subprogram   B.1(39)
   package_body of Standard   A.1(50)
   package_declaration   7.1(8)
   partition   E.1(6)
   partition   E.5(21)
   per-object constraint   3.8(18.1/1)
   pragma   2.8(12)
   private_extension_declaration   7.3(17)
   private_type_declaration   7.3(17)
   protected declaration   9.4(12)
   protected_body   9.4(15)
   protected_definition   9.4(13)
   range_constraint   3.5(9)
   real_type_definition   3.5.6(5)
   record_definition   3.8(16)
   record_extension_part   3.9.1(5)
   record_type_definition   3.8(16)
   renaming_declaration   8.5(3)
   representation_clause   13.1(19/1)
   single_protected_declaration   9.4(12)
   single_task_declaration   9.1(10)
   Storage_Size pragma   13.3(66)
   subprogram_declaration   6.1(31)
   subtype_declaration   3.2.2(9)
   subtype_indication   3.2.2(9)
   task declaration   9.1(10)
   task_body   9.1(13)
   task_definition   9.1(11)
   use_clause   8.4(12)
   variant_part   3.8.1(22)

elaboration control   10.2.1(1)

elaboration dependence
   library_item on another   10.2(9)

Elaboration_Check   11.5(20)
   [partial]   3.11(9)

element
   of a storage pool   13.11(11)
   in Ada.Strings.Bounded   A.4.4(26)
   in Ada.Strings.Unbounded   A.4.5(20)

elementary type   3.2(2)

Elementary_Functions
   child of Ada.Numerics   A.5.1(9/1)

eligible
   a type, for a convention   B.1(14)

else part
   of a selective_accept   9.7.1(11)

EM
   in Ada.Characters.Latin_1   A.3.3(6)

embedded systems   C(1), D(1)

encapsulation
   See package   7(1)

enclosing
   immediately   8.1(13)

end of a line   2.2(2)

End_Error
   raised by failure of run-time check   13.13.2(35.1/1)
   in Ada.Direct_IO   A.8.4(18)
   in Ada.IO_Exceptions   A.13(4)
   in Ada.Sequential_IO   A.8.1(15)
   in Ada.Streams.Stream_IO   A.12.1(26)
   in Ada.Text_IO   A.10.1(85)

End_Of_File
   in Ada.Direct_IO   A.8.4(16)
   in Ada.Sequential_IO   A.8.1(13)
   in Ada.Streams.Stream_IO   A.12.1(12)
   in Ada.Text_IO   A.10.1(34)

End_Of_Line
   in Ada.Text_IO   A.10.1(30)

End_Of_Page
   in Ada.Text_IO   A.10.1(33)

endian
   big   13.5.3(2)
   little   13.5.3(2)

ENQ
   in Ada.Characters.Latin_1   A.3.3(5)

entity
   [partial]   3.1(1)

entry
   closed   9.5.3(5)
   open   9.5.3(5)
   single   9.5.2(20)

entry call   9.5.3(1)
   simple   9.5.3(1)

entry calling convention   6.3.1(13)

entry family   9.5.2(20)

entry index subtype   3.8(18/1), 9.5.2(20)

entry queue   9.5.3(12)

entry queuing policy   9.5.3(17)
   default policy   9.5.3(17)

entry_barrier   9.5.2(7)
   used   9.5.2(5), P

entry_body   9.5.2(5)
   used   9.4(8/1), P

entry_body_formal_part   9.5.2(6)
   used   9.5.2(5), P

entry_call_alternative   9.7.2(3)
   used   9.7.2(2), 9.7.3(2), P

entry_call_statement   9.5.3(2)
   used   5.1(4), 9.7.2(3), 9.7.4(4), P

entry_declaration   9.5.2(2)
   used   9.1(5/1), 9.4(5/1), P

entry_index   9.5.2(4)
   used   9.5.2(3), P

entry_index_specification   9.5.2(8)
   used   9.5.2(6), P

enumeration literal   3.5.1(6)

enumeration type   3.2(3), 3.5.1(1)

enumeration_aggregate   13.4(3)
   used   13.4(2), P

Enumeration_IO
   in Ada.Text_IO   A.10.1(79)

enumeration_literal_specification   3.5.1(3)
   used   3.5.1(2), P

enumeration_representation_clause   13.4(2)
   used   13.1(2/1), P

enumeration_type_definition   3.5.1(2)
   used   3.2.1(4), P

environment   10.1.4(1)

environment declarative_part   10.1.4(1)
   for the environment task of a partition   10.2(13)

environment task   10.2(8)

EOT
   in Ada.Characters.Latin_1   A.3.3(5)

EPA
   in Ada.Characters.Latin_1   A.3.3(18)

epoch   D.8(19)

equal operator   4.4(1), 4.5.2(1)

equality operator   4.5.2(1)
   special inheritance rule for tagged types   3.4(17), 4.5.2(14)

equals sign   2.1(15)

Equals_Sign
   in Ada.Characters.Latin_1   A.3.3(10)

erroneous execution   1.1.2(32), 1.1.5(10)
   cause   3.7.2(4), 9.8(21), 9.10(11), 11.5(26), 13.3(13), 13.3(27),
13.3(28), 13.9.1(8), 13.9.1(12), 13.9.1(13), 13.11(21), 13.11.2(16),
A.10.3(22/1), A.12.1(36.1/1), A.13(17), B.3.1(51), B.3.1(55), B.3.1(56),
B.3.1(57), B.3.2(35), B.3.2(36), B.3.2(37), B.3.2(38), B.3.2(39), B.3.2(42),
C.3.1(14), C.3.1(14.1/1), C.7.1(18), C.7.2(14), C.7.2(15), C.7.2(15.1/1),
D.5(12), D.11(9), H.4(26), H.4(27)

error
   compile-time   1.1.2(27), 1.1.5(4)
   link-time   1.1.2(29), 1.1.5(4)
   run-time   1.1.2(30), 1.1.5(6), 11.5(2), 11.6(1)
   See also bounded error, erroneous execution

ESA
   in Ada.Characters.Latin_1   A.3.3(17)

ESC
   in Ada.Characters.Latin_1   A.3.3(6)

Establish_RPC_Receiver
   in System.RPC   E.5(12)

ETB
   in Ada.Characters.Latin_1   A.3.3(6)

ETX
   in Ada.Characters.Latin_1   A.3.3(5)

evaluation   3.1(11), N(19)
   aggregate   4.3(5)
   allocator   4.8(7)
   array_aggregate   4.3.3(21)
   attribute_reference   4.1.4(11)
   concatenation   4.5.3(5)
   dereference   4.1(13)
   discrete_range   3.6.1(8)
   extension_aggregate   4.3.2(7)
   generic_association   12.3(21)
   generic_association for a formal object of mode in   12.4(11)
   indexed_component   4.1.1(7)
   initialized allocator   4.8(7)
   membership test   4.5.2(27)
   name   4.1(11)
   name that has a prefix   4.1(12)
   null literal   4.2(9)
   numeric literal   4.2(9)
   parameter_association   6.4.1(7)
   prefix   4.1(12)
   primary that is a name   4.4(10)
   qualified_expression   4.7(4)
   range   3.5(9)
   range_attribute_reference   4.1.4(11)
   record_aggregate   4.3.1(18)
   record_component_association_list   4.3.1(19)
   selected_component   4.1.3(14)
   short-circuit control form   4.5.1(7)
   slice   4.1.2(7)
   string_literal   4.2(10)
   uninitialized allocator   4.8(8)
   Val   3.5.5(7), K(261)
   Value   3.5(55)
   value conversion   4.6(28)
   view conversion   4.6(52)
   Wide_Value   3.5(43)

Exception   11(1), 11.1(1)

exception occurrence   11(1)

exception_choice   11.2(5)
   used   11.2(3), P

exception_declaration   11.1(2)
   used   3.1(3), P

exception_handler   11.2(3)
   used   11.2(2), P

Exception_Id
   in Ada.Exceptions   11.4.1(2)

Exception_Identity
   in Ada.Exceptions   11.4.1(5)

Exception_Information
   in Ada.Exceptions   11.4.1(5)

Exception_Message
   in Ada.Exceptions   11.4.1(4)

Exception_Name
   in Ada.Exceptions   11.4.1(2), 11.4.1(5)

Exception_Occurrence
   in Ada.Exceptions   11.4.1(3)

Exception_Occurrence_Access
   in Ada.Exceptions   11.4.1(3)

exception_renaming_declaration   8.5.2(2)
   used   8.5(2), P

Exceptions
   child of Ada   11.4.1(2)

Exchange_Handler
   in Ada.Interrupts   C.3.2(8)

Exclamation
   in Ada.Characters.Latin_1   A.3.3(8)

execution   3.1(11)
   abort_statement   9.8(4)
   aborting the execution of a construct   9.8(5)
   accept_statement   9.5.2(24)
   Ada program   9(1)
   assignment_statement   5.2(7), 7.6(17), 7.6.1(12)
   asynchronous_select with a delay_statement trigger   9.7.4(7)
   asynchronous_select with an entry call trigger   9.7.4(6)
   block_statement   5.6(5)
   call on a dispatching operation   3.9.2(14)
   call on an inherited subprogram   3.4(27)
   case_statement   5.4(11)
   conditional_entry_call   9.7.3(3)
   delay_statement   9.6(20)
   dynamically enclosing   11.4(2)
   entry_body   9.5.2(26)
   entry_call_statement   9.5.3(8)
   exit_statement   5.7(5)
   goto_statement   5.8(5)
   handled_sequence_of_statements   11.2(10)
   handler   11.4(7)
   if_statement   5.3(5)
   instance of Unchecked_Deallocation   7.6.1(10)
   loop_statement   5.5(7)
   loop_statement with a for iteration_scheme   5.5(9)
   loop_statement with a while iteration_scheme   5.5(8)
   null_statement   5.1(13)
   partition   10.2(25)
   pragma   2.8(12)
   program   10.2(25)
   protected subprogram call   9.5.1(3)
   raise_statement with an exception_name   11.3(4)
   re-raise statement   11.3(4)
   remote subprogram call   E.4(9)
   requeue protected entry   9.5.4(9)
   requeue task entry   9.5.4(8)
   requeue_statement   9.5.4(7)
   return_statement   6.5(6)
   selective_accept   9.7.1(15)
   sequence_of_statements   5.1(15)
   subprogram call   6.4(10)
   subprogram_body   6.3(7)
   task   9.2(1)
   task_body   9.2(1)
   timed_entry_call   9.7.2(4)

execution resource
   associated with a protected object   9.4(18)
   required for a task to run   9(10)

exit_statement   5.7(2)
   used   5.1(4), P

Exit_Status
   in Ada.Command_Line   A.15(7), A.15(16.1/1)

Exp
   in Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(3)
   in Ada.Numerics.Generic_Elementary_Functions   A.5.1(4)

expanded name   4.1.3(4)

Expanded_Name
   in Ada.Tags   3.9(7)

expected profile   8.6(26)
   accept_statement entry_direct_name   9.5.2(11)
   Access attribute_reference prefix   3.10.2(2)
   attribute_definition_clause name   13.3(4)
   character_literal   4.2(3)
   formal subprogram actual   12.6(6)
   formal subprogram default_name   12.6(5)
   subprogram_renaming_declaration   8.5.4(3)

expected type   8.6(20)
   abort_statement task_name   9.8(3)
   access attribute_reference   3.10.2(2)
   actual parameter   6.4.1(3)
   aggregate   4.3(3)
   allocator   4.8(3/1)
   array_aggregate   4.3.3(7)
   array_aggregate component expression   4.3.3(7)
   array_aggregate discrete_choice   4.3.3(8)
   assignment_statement expression   5.2(4)
   assignment_statement variable_name   5.2(4)
   attribute_definition_clause expression or name   13.3(4)
   attribute_designator expression   4.1.4(7)
   case expression   5.4(4)
   case_statement_alternative discrete_choice   5.4(4)
   character_literal   4.2(3)
   code_statement   13.8(4)
   component_clause expressions   13.5.1(7)
   component_declaration default_expression   3.8(7)
   condition   5.3(4)
   decimal fixed point type digits   3.5.9(6)
   delay_relative_statement expression   9.6(5)
   delay_until_statement expression   9.6(5)
   delta_constraint expression   J.3(3)
   dereference name   4.1(8)
   discrete_subtype_definition range   3.6(8)
   discriminant default_expression   3.7(7)
   discriminant_association expression   3.7.1(6)
   entry_index   9.5.2(11)
   enumeration_representation_clause expressions   13.4(4)
   extension_aggregate   4.3.2(4)
   extension_aggregate ancestor expression   4.3.2(4)
   first_bit   13.5.1(7)
   fixed point type delta   3.5.9(6)
   generic formal in object actual   12.4(4)
   generic formal object default_expression   12.4(3)
   index_constraint discrete_range   3.6.1(4)
   indexed_component expression   4.1.1(4)
   Interrupt_Priority pragma argument   D.1(6)
   last_bit   13.5.1(7)
   link name   B.1(10)
   membership test simple_expression   4.5.2(3)
   modular_type_definition expression   3.5.4(5)
   null literal   4.2(2)
   number_declaration expression   3.3.2(3)
   object_declaration initialization expression   3.3.1(4)
   parameter default_expression   6.1(17)
   position   13.5.1(7)
   Priority pragma argument   D.1(6)
   range simple_expressions   3.5(5)
   range_attribute_designator expression   4.1.4(7)
   range_constraint range   3.5(5)
   real_range_specification bounds   3.5.7(5)
   record_aggregate   4.3.1(8)
   record_component_association expression   4.3.1(10)
   requested decimal precision   3.5.7(4)
   restriction parameter expression   13.12(5)
   return expression   6.5(3)
   short-circuit control form relation   4.5.1(1)
   signed_integer_type_definition simple_expression   3.5.4(5)
   slice discrete_range   4.1.2(4)
   Storage_Size pragma argument   13.3(65)
   string_literal   4.2(4)
   type_conversion operand   4.6(6)
   variant_part discrete_choice   3.8.1(6)

expiration time
   [partial]   9.6(1)
   for a delay_relative_statement   9.6(20)
   for a delay_until_statement   9.6(20)

explicit declaration   3.1(5), N(11)

explicit initial value   3.3.1(1)

explicit_actual_parameter   6.4(6)
   used   6.4(5), P

explicit_dereference   4.1(5)
   used   4.1(2), P

explicit_generic_actual_parameter   12.3(5)
   used   12.3(4), P

explicitly assign   10.2(2)

exponent   2.4.1(4), 4.5.6(11)
   used   2.4.1(2), 2.4.2(2), P

Exponent attribute   A.5.3(18)

exponentiation operator   4.4(1), 4.5.6(7)

exported
   aspect of representation   B.1(28)

exported entity   B.1(23)

expression   4.4(1), 4.4(2)
   used   2.8(3), 3.3.1(2), 3.3.2(2), 3.5.4(4), 3.5.7(2), 3.5.9(3), 3.5.9(4),
3.5.9(5), 3.7(6), 3.7.1(3), 3.8.1(5), 4.1.1(2), 4.1.4(3), 4.1.4(5), 4.3.1(4),
4.3.2(3), 4.3.3(3), 4.3.3(5), 4.4(7), 4.6(2), 4.7(2), 5.2(2), 5.3(3), 5.4(2),
6.4(6), 6.5(2), 9.5.2(4), 9.6(3), 9.6(4), 12.3(5), 13.3(2), 13.3(63),
13.5.1(4), 13.12(4), B.1(5), B.1(6), B.1(8), B.1(10), C.3.1(4), D.1(3),
D.1(5), J.3(2), J.7(1), J.8(1), L(6), L(13), L(14), L(18), L(19), L(27),
L(35), P

extended_digit   2.4.2(5)
   used   2.4.2(4), P

extension
   of a private type   3.9(2), 3.9.1(1)
   of a record type   3.9(2), 3.9.1(1)
   of a type   3.9(2), 3.9.1(1)

extension_aggregate   4.3.2(2)
   used   4.3(2), P

external call   9.5(4)

external effect
   of the execution of an Ada program   1.1.3(8)
   volatile/atomic objects   C.6(20)

external file   A.7(1)

external interaction   1.1.3(8)

external name   B.1(34)

external requeue   9.5(7)

External_Tag
   in Ada.Tags   3.9(7)

External_Tag attribute   13.3(75/1)

External_Tag clause   13.3(7), 13.3(75/1), K(65)

extra permission to avoid raising exceptions   11.6(5)

extra permission to reorder actions   11.6(6)


F


factor   4.4(6)
   used   4.4(5), P

failure
   of a language-defined check   11.5(2)
   in Ada.Command_Line   A.15(8)

False   3.5.3(1)

family
   entry   9.5.2(20)

Feminine_Ordinal_Indicator
   in Ada.Characters.Latin_1   A.3.3(21)

FF
   in Ada.Characters.Latin_1   A.3.3(5)

Field
   in Ada.Text_IO   A.10.1(6)

file
   as file object   A.7(2)

file terminator   A.10(7)

File_Access
   in Ada.Text_IO   A.10.1(18)

File_Mode
   in Ada.Direct_IO   A.8.4(4)
   in Ada.Sequential_IO   A.8.1(4)
   in Ada.Streams.Stream_IO   A.12.1(6)
   in Ada.Text_IO   A.10.1(4)

File_Type
   in Ada.Direct_IO   A.8.4(3)
   in Ada.Sequential_IO   A.8.1(3)
   in Ada.Streams.Stream_IO   A.12.1(5)
   in Ada.Text_IO   A.10.1(3)

finalization
   of a master   7.6.1(4)
   of a protected object   9.4(20)
   of a protected object   C.3.1(12/1)
   of a task object   J.7.1(8)
   of an object   7.6.1(5)
   of environment task for a foreign language main subprogram   B.1(39)
   child of Ada   7.6(4/1)

Finalize   7.6(2)
   in Ada.Finalization   7.6(6), 7.6(8)

Find_Token
   in Ada.Strings.Bounded   A.4.4(51)
   in Ada.Strings.Fixed   A.4.3(16)
   in Ada.Strings.Unbounded   A.4.5(46)

Fine_Delta
   in System   13.7(9)

First attribute   3.5(12), 3.6.2(3)

first subtype   3.2.1(6), 3.4.1(5)

First(N) attribute   3.6.2(4)

first_bit   13.5.1(5)
   used   13.5.1(3), P

First_Bit attribute   13.5.2(3)

Fixed
   child of Ada.Strings   A.4.3(5)

fixed point type   3.5.9(1)

Fixed_IO
   in Ada.Text_IO   A.10.1(68)

fixed_point_definition   3.5.9(2)
   used   3.5.6(2), P

Float   3.5.7(12), 3.5.7(14)
   in Standard   A.1(21)

Float_Random
   child of Ada.Numerics   A.5.2(5)

Float_Text_IO
   child of Ada   A.10.9(33)

Float_Wide_Text_IO
   child of Ada   A.11(3)

Float_IO
   in Ada.Text_IO   A.10.1(63)

Floating
   in Interfaces.COBOL   B.4(9)

floating point type   3.5.7(1)

floating_point_definition   3.5.7(2)
   used   3.5.6(2), P

Floor attribute   A.5.3(30)

Flush
   in Ada.Streams.Stream_IO   A.12.1(25/1)
   in Ada.Text_IO   A.10.1(21/1)

Fore attribute   3.5.10(4)

form
   of an external file   A.7(1)
   in Ada.Direct_IO   A.8.4(9)
   in Ada.Sequential_IO   A.8.1(9)
   in Ada.Streams.Stream_IO   A.12.1(11)
   in Ada.Text_IO   A.10.1(12)

formal object, generic   12.4(1)

formal package, generic   12.7(1)

formal parameter
   of a subprogram   6.1(17)

formal subprogram, generic   12.6(1)

formal subtype   12.5(5)

formal type   12.5(5)

formal_access_type_definition   12.5.4(2)
   used   12.5(3), P

formal_array_type_definition   12.5.3(2)
   used   12.5(3), P

formal_decimal_fixed_point_definition   12.5.2(7)
   used   12.5(3), P

formal_derived_type_definition   12.5.1(3)
   used   12.5(3), P

formal_discrete_type_definition   12.5.2(2)
   used   12.5(3), P

formal_floating_point_definition   12.5.2(5)
   used   12.5(3), P

formal_modular_type_definition   12.5.2(4)
   used   12.5(3), P

formal_object_declaration   12.4(2)
   used   12.1(6), P

formal_ordinary_fixed_point_definition   12.5.2(6)
   used   12.5(3), P

formal_package_actual_part   12.7(3)
   used   12.7(2), P

formal_package_declaration   12.7(2)
   used   12.1(6), P

formal_part   6.1(14)
   used   6.1(12), 6.1(13), P

formal_private_type_definition   12.5.1(2)
   used   12.5(3), P

formal_signed_integer_type_definition   12.5.2(3)
   used   12.5(3), P

formal_subprogram_declaration   12.6(2)
   used   12.1(6), P

formal_type_declaration   12.5(2)
   used   12.1(6), P

formal_type_definition   12.5(3)
   used   12.5(2), P

format_effector   2.1(13)
   used   2.1(2), P

Fortran
   child of Interfaces   B.5(4)

Fortran interface   B.5(1)

FORTRAN standard   1.2(3)

Fortran_Character
   in Interfaces.Fortran   B.5(12)

Fortran_Integer
   in Interfaces.Fortran   B.5(5)

Fraction attribute   A.5.3(21)

Fraction_One_Half
   in Ada.Characters.Latin_1   A.3.3(22)

Fraction_One_Quarter
   in Ada.Characters.Latin_1   A.3.3(22)

Fraction_Three_Quarters
   in Ada.Characters.Latin_1   A.3.3(22)

Free
   in Ada.Strings.Unbounded   A.4.5(7)
   in Interfaces.C.Strings   B.3.1(11)

freed
   See nonexistent   13.11.2(10)

freeing storage   13.11.2(1)

freezing
   by a constituent of a construct   13.14(4/1)
   by an expression   13.14(8/1)
   by an implicit call   13.14(8.1/1)
   by an object name   13.14(8/1)
   class-wide type caused by the freezing of the specific type   13.14(15)
   constituents of a full type definition   13.14(15)
   designated subtype caused by an allocator   13.14(13)
   entity   13.14(2)
   entity caused by a body   13.14(3/1)
   entity caused by a construct   13.14(4/1)
   entity caused by a name   13.14(11)
   entity caused by the end of an enclosing construct   13.14(3/1)
   first subtype caused by the freezing of the type   13.14(15)
   function call   13.14(14)
   generic_instantiation   13.14(5)
   nominal subtype caused by a name   13.14(11)
   object_declaration   13.14(6)
   specific type caused by the freezing of the class-wide type   13.14(15)
   subtype caused by a record extension   13.14(7)
   subtype caused by an implicit conversion   13.14(8.2/1)
   subtype caused by an implicit dereference   13.14(11.1/1)
   subtypes of the profile of a callable entity   13.14(14)
   type caused by a range   13.14(12)
   type caused by an expression   13.14(10)
   type caused by the freezing of a subtype   13.14(15)

freezing points
   entity   13.14(2)

FS
   in Ada.Characters.Latin_1   A.3.3(6)

full conformance
   for discrete_subtype_definitions   6.3.1(24)
   for expressions   6.3.1(19)
   for known_discriminant_parts   6.3.1(23)
   for profiles   6.3.1(18)
   required   3.10.1(4), 6.3(4), 7.3(9), 8.5.4(5/1), 9.5.2(14), 9.5.2(16),
9.5.2(17), 10.1.3(11), 10.1.3(12)

full constant declaration   3.3.1(6)

full declaration   7.4(2)

full stop   2.1(15)

full type   3.2.1(8)

full type definition   3.2.1(8)

full view
   of a type   7.3(4)

Full_Stop
   in Ada.Characters.Latin_1   A.3.3(8)

full_type_declaration   3.2.1(3)
   used   3.2.1(2), P

function   6(1)

function instance   12.3(13)

function_call   6.4(3)
   used   4.1(2), P


G


gaps   13.1(7)

garbage collection   13.11.3(6)

general access type   3.10(7/1), 3.10(8)

general_access_modifier   3.10(4)
   used   3.10(3), P

generation
   of an interrupt   C.3(2)

Generator
   in Ada.Numerics.Discrete_Random   A.5.2(19)
   in Ada.Numerics.Float_Random   A.5.2(7)

generic actual   12.3(7)

generic actual parameter   12.3(7)

generic actual subtype   12.5(4)

generic actual type   12.5(4)

generic body   12.2(1)

generic contract issue   10.2.1(10)
   [partial]   3.9.1(3), 3.10.2(28), 3.10.2(32), 4.6(17), 4.6(20), 8.3(26/1),
10.2.1(11/1)

generic formal   12.1(9)

generic formal object   12.4(1)

generic formal package   12.7(1)

generic formal subprogram   12.6(1)

generic formal subtype   12.5(5)

generic formal type   12.5(5)

generic function   12.1(8)

generic package   12.1(8)

generic procedure   12.1(8)

generic subprogram   12.1(8)

generic unit   12(1)
   See also dispatching operation   3.9(1)

Generic_Complex_Elementary_Functions
   child of Ada.Numerics   G.1.2(2)

Generic_Complex_Types
   child of Ada.Numerics   G.1.1(2/1)

Generic_Elementary_Functions
   child of Ada.Numerics   A.5.1(3)

generic_actual_part   12.3(3)
   used   12.3(2), 12.7(3), P

generic_association   12.3(4)
   used   12.3(3), P

Generic_Bounded_Length
   in Ada.Strings.Bounded   A.4.4(4)

generic_declaration   12.1(2)
   used   3.1(3), 10.1.1(5), P

generic_formal_parameter_declaration   12.1(6)
   used   12.1(5), P

generic_formal_part   12.1(5)
   used   12.1(3), 12.1(4), P

generic_instantiation   12.3(2)
   used   3.1(3), 10.1.1(5), P

generic_package_declaration   12.1(4)
   used   12.1(2), P

generic_renaming_declaration   8.5.5(2)
   used   8.5(2), 10.1.1(6), P

generic_subprogram_declaration   12.1(3)
   used   12.1(2), P

Get
   in Ada.Text_IO   A.10.1(41), A.10.1(47), A.10.1(54), A.10.1(55),
A.10.1(59), A.10.1(60), A.10.1(65), A.10.1(67), A.10.1(70), A.10.1(72),
A.10.1(75), A.10.1(77), A.10.1(81), A.10.1(83)
   in Ada.Text_IO.Complex_IO   G.1.3(6), G.1.3(8)

Get_Immediate
   in Ada.Text_IO   A.10.1(44), A.10.1(45)

Get_Line
   in Ada.Text_IO   A.10.1(49)

Get_Priority
   in Ada.Dynamic_Priorities   D.5(5)

global to   8.1(15)

Glossary   N(1)

goto_statement   5.8(2)
   used   5.1(4), P

govern a variant   3.8.1(20)

govern a variant_part   3.8.1(20)

grammar
   complete listing   P
   cross reference   P
   notation   1.1.4(3)
   resolution of ambiguity   8.6(3)
   under Syntax heading   1.1.2(25)

graphic character
   a category of Character   A.3.2(23)

graphic_character   2.1(3)
   used   2.1(2), 2.5(2), 2.6(3), P

Graphic_Set
   in Ada.Strings.Maps.Constants   A.4.6(4)

Grave
   in Ada.Characters.Latin_1   A.3.3(13)

greater than operator   4.4(1), 4.5.2(1)

greater than or equal operator   4.4(1), 4.5.2(1)

greater-than sign   2.1(15)

Greater_Than_Sign
   in Ada.Characters.Latin_1   A.3.3(10)

GS
   in Ada.Characters.Latin_1   A.3.3(6)

guard   9.7.1(3)
   used   9.7.1(2), P


H


handle
   an exception   11(1), N(18)
   an exception occurrence   11.4(1), 11.4(7)

handled_sequence_of_statements   11.2(2)
   used   5.6(2), 6.3(2), 7.2(2), 9.1(6), 9.5.2(3), 9.5.2(5), P

Handling
   child of Ada.Characters   A.3.2(2)

Head
   in Ada.Strings.Bounded   A.4.4(70), A.4.4(71)
   in Ada.Strings.Fixed   A.4.3(35), A.4.3(36)
   in Ada.Strings.Unbounded   A.4.5(65), A.4.5(66)

head (of a queue)   D.2.1(5)

heap management
   user-defined   13.11(1)
   See also allocator   4.8(1)

held priority   D.11(4)

heterogeneous input-output   A.12.1(1)

hexadecimal
   literal   2.4.2(1)

hexadecimal digit
   a category of Character   A.3.2(30)

hexadecimal literal   2.4.2(1)

Hexadecimal_Digit_Set
   in Ada.Strings.Maps.Constants   A.4.6(4)

hidden from all visibility   8.3(5), 8.3(14)
   by lack of a with_clause   8.3(20)
   for a declaration completed   by a subsequent declaration   8.3(19)
   for overridden declaration   8.3(15)
   within the declaration itself   8.3(16)

hidden from direct visibility   8.3(5), 8.3(21)
   by an inner homograph   8.3(22)
   where hidden from all visibility   8.3(23)

hiding   8.3(5)

High_Order_First   13.5.3(2)
   in Interfaces.COBOL   B.4(25)

highest precedence operator   4.5.6(1)

highest_precedence_operator   4.5(7)

Hold
   in Ada.Asynchronous_Task_Control   D.11(3)

homograph   8.3(8)

HT
   in Ada.Characters.Latin_1   A.3.3(5)

HTJ
   in Ada.Characters.Latin_1   A.3.3(17)

HTS
   in Ada.Characters.Latin_1   A.3.3(17)

Hyphen
   in Ada.Characters.Latin_1   A.3.3(8)

hyphen-minus   2.1(15)


I


i
   in Ada.Numerics.Generic_Complex_Types   G.1.1(5)
   in Interfaces.Fortran   B.5(10)

identifier   2.3(2)
   used   2.8(2), 2.8(3), 2.8(21), 2.8(23), 3.1(4), 4.1(3), 4.1.3(3),
4.1.4(3), 5.5(2), 5.6(2), 6.1(5), 7.1(3), 7.2(2), 9.1(4), 9.1(6), 9.4(4),
9.4(7), 9.5.2(3), 9.5.2(5), 11.5(4), 13.12(4), B.1(5), B.1(6), B.1(7),
D.2.2(2), D.2.2(3), D.3(3), D.3(4), D.4(3), D.4(4), L(8), L(13), L(14),
L(20), L(21), L(23), L(29), L(36), L(37), M(95), M(98), P

identifier specific to a pragma   2.8(10)

identifier_letter   2.1(7)
   used   2.1(3), 2.3(2), 2.3(3), P

Identity
   in Ada.Strings.Maps   A.4.2(22)
   in Ada.Strings.Wide_Maps   A.4.7(22)

Identity attribute   11.4.1(9), C.7.1(12)

idle task   D.11(4)

if_statement   5.3(2)
   used   5.1(5), P

illegal
   construct   1.1.2(27)
   partition   1.1.2(29)

Im
   in Ada.Numerics.Generic_Complex_Types   G.1.1(6)

image
   of a value   3.5(30), K(273)
   in Ada.Numerics.Discrete_Random   A.5.2(26)
   in Ada.Numerics.Float_Random   A.5.2(14)
   in Ada.Task_Identification   C.7.1(3/1)
   in Ada.Text_IO.Editing   F.3.3(13)

Image attribute   3.5(35)

Imaginary
   in Ada.Numerics.Generic_Complex_Types   G.1.1(4)
   in Interfaces.Fortran   B.5(10)

immediate scope
   of (a view of) an entity   8.2(11)
   of a declaration   8.2(2)

immediately enclosing   8.1(13)

immediately visible   8.3(4), 8.3(21)

immediately within   8.1(13)

implementation advice   1.1.2(37)

implementation defined   1.1.3(18)
   summary of characteristics   M(1)

implementation permissions   1.1.2(36)

implementation requirements   1.1.2(33)

implementation-dependent
   See unspecified   1.1.3(18)

implicit declaration   3.1(5), N(11)

implicit initial values
   for a subtype   3.3.1(10)

implicit subtype conversion   4.6(59), 4.6(60)
   Access attribute   3.10.2(30)
   access discriminant   3.7(27)
   array bounds   4.6(38)
   array index   4.1.1(7)
   assignment to view conversion   4.6(55)
   assignment_statement   5.2(11)
   bounds of a decimal fixed point type   3.5.9(16)
   bounds of a fixed point type   3.5.9(14)
   bounds of a range   3.5(9), 3.6(18)
   choices of aggregate   4.3.3(22)
   component defaults   3.3.1(13)
   delay expression   9.6(20)
   derived type discriminants   3.4(21)
   discriminant values   3.7.1(12)
   entry index   9.5.2(24)
   expressions in aggregate   4.3.1(19)
   expressions of aggregate   4.3.3(23)
   function return   6.5(6)
   generic formal object of mode in   12.4(11)
   inherited enumeration literal   3.4(29)
   initialization expression   3.3.1(17)
   initialization expression of allocator   4.8(7)
   named number value   3.3.2(6)
   operand of concatenation   4.5.3(9)
   parameter passing   6.4.1(10), 6.4.1(11), 6.4.1(17)
   pragma Interrupt_Priority   D.1(17), D.3(9)
   pragma Priority   D.1(17), D.3(9)
   qualified_expression   4.7(4)
   reading a view conversion   4.6(56)
   result of inherited function   3.4(27)

implicit_dereference   4.1(6)
   used   4.1(4), P

imported
   aspect of representation   B.1(28)

imported entity   B.1(23)

in (membership test)   4.4(1), 4.5.2(2)

inaccessible partition   E.1(7)

inactive
   a task state   9(10)

included
   one range in another   3.5(4)

incomplete type   3.10.1(11)

incomplete_type_declaration   3.10.1(2)
   used   3.2.1(2), P

Increment
   in Interfaces.C.Pointers   B.3.2(11)

indefinite subtype   3.3(23), 3.7(26)

independent subprogram   11.6(6)

independently addressable   9.10(1)

index
   of an element of an open direct file   A.8(3)
   in Ada.Direct_IO   A.8.4(15)
   in Ada.Streams.Stream_IO   A.12.1(23)
   in Ada.Strings.Bounded   A.4.4(44), A.4.4(45), A.4.4(46)
   in Ada.Strings.Fixed   A.4.3(9), A.4.3(10), A.4.3(11)
   in Ada.Strings.Unbounded   A.4.5(39), A.4.5(40), A.4.5(41)

index range   3.6(13)

index subtype   3.6(9)

index type   3.6(9)

Index_Check   11.5(14)
   [partial]   4.1.1(7), 4.1.2(7), 4.3.3(29), 4.3.3(30), 4.5.3(8), 4.6(51),
4.7(4), 4.8(10/1)

index_constraint   3.6.1(2)
   used   3.2.2(7), P

Index_Error
   in Ada.Strings   A.4.1(5)

Index_Non_Blank
   in Ada.Strings.Bounded   A.4.4(47)
   in Ada.Strings.Fixed   A.4.3(12)
   in Ada.Strings.Unbounded   A.4.5(42)

index_subtype_definition   3.6(4)
   used   3.6(3), P

indexed_component   4.1.1(2)
   used   4.1(2), P

indivisible   C.6(10)

information hiding
   See package   7(1)
   See private types and private extensions   7.3(1)

information systems   C(1), F(1)

informative   1.1.2(18)

inheritance
   See derived types and classes   3.4(1)
   See also tagged types and type extension   3.9(1)

inherited
   from an ancestor type   3.4.1(11)

inherited component   3.4(11), 3.4(12)

inherited discriminant   3.4(11)

inherited entry   3.4(12)

inherited protected subprogram   3.4(12)

inherited subprogram   3.4(17)

initialization
   of a protected object   9.4(14)
   of a protected object   C.3.1(10), C.3.1(11)
   of a task object   9.1(12/1), J.7.1(7)
   of an object   3.3.1(19)

initialization expression   3.3.1(1), 3.3.1(4)

Initialize   7.6(2)
   in Ada.Finalization   7.6(6), 7.6(8)

initialized allocator   4.8(4)

innermost dynamically enclosing   11.4(2)

input   A.6(1)

Input attribute   13.13.2(22), 13.13.2(32)

Input clause   13.3(7), 13.13.2(36/1)

input-output
   unspecified for access types   A.7(6)

Insert
   in Ada.Strings.Bounded   A.4.4(60), A.4.4(61)
   in Ada.Strings.Fixed   A.4.3(25), A.4.3(26)
   in Ada.Strings.Unbounded   A.4.5(55), A.4.5(56)

inspectable object   H.3.2(5/1)

inspection point   H.3.2(5/1)

instance
   of a generic function   12.3(13)
   of a generic package   12.3(13)
   of a generic procedure   12.3(13)
   of a generic subprogram   12.3(13)
   of a generic unit   12.3(1)

instructions for comment submission   0.3(58/1)

int
   in Interfaces.C   B.3(7)

Integer   3.5.4(11), 3.5.4(21)
   in Standard   A.1(12)

integer literal   2.4(1)

integer literals   3.5.4(14), 3.5.4(30)

integer type   3.5.4(1)

Integer_Text_IO
   child of Ada   A.10.8(21)

Integer_Wide_Text_IO
   child of Ada   A.11(3)

Integer_Address
   in System.Storage_Elements   13.7.1(10)

Integer_IO
   in Ada.Text_IO   A.10.1(52)

integer_type_definition   3.5.4(2)
   used   3.2.1(4), P

interaction
   between tasks   9(1)

interface to assembly language   C.1(4)

interface to C   B.3(1/1)

interface to COBOL   B.4(1)

interface to Fortran   B.5(1)

interface to other languages   B(1)

Interfaces   B.2(3)

Interfaces.C   B.3(4)

Interfaces.C.Pointers   B.3.2(4)

Interfaces.C.Strings   B.3.1(3)

Interfaces.COBOL   B.4(7)

Interfaces.Fortran   B.5(4)

interfacing pragma   B.1(4)
   Convention   B.1(4)
   Export   B.1(4)
   Import   B.1(4)

internal call   9.5(3)

internal code   13.4(7)

internal requeue   9.5(7)

Internal_Tag
   in Ada.Tags   3.9(7)

interpretation
   of a complete context   8.6(10)
   of a constituent of a complete context   8.6(15)
   overload resolution   8.6(14)

interrupt   C.3(2)
   example using asynchronous_select   9.7.4(10), 9.7.4(12)

interrupt entry   J.7.1(5)

interrupt handler   C.3(2)

Interrupt_ID
   in Ada.Interrupts   C.3.2(2)

Interrupt_Priority
   in System   13.7(16)

Interrupts
   child of Ada   C.3.2(2)

intertask communication   9.5(1)
   See also task   9(1)

Intrinsic calling convention   6.3.1(4)

invalid representation   13.9.1(9)

Inverted_Exclamation
   in Ada.Characters.Latin_1   A.3.3(21)

Inverted_Question
   in Ada.Characters.Latin_1   A.3.3(22)

IO_Exceptions
   child of Ada   A.13(3)

IS1
   in Ada.Characters.Latin_1   A.3.3(16)

IS2
   in Ada.Characters.Latin_1   A.3.3(16)

IS3
   in Ada.Characters.Latin_1   A.3.3(16)

IS4
   in Ada.Characters.Latin_1   A.3.3(16)

Is_Alphanumeric
   in Ada.Characters.Handling   A.3.2(4)

Is_Attached
   in Ada.Interrupts   C.3.2(5)

Is_Basic
   in Ada.Characters.Handling   A.3.2(4)

Is_Callable
   in Ada.Task_Identification   C.7.1(4)

Is_Character
   in Ada.Characters.Handling   A.3.2(14)

Is_Control
   in Ada.Characters.Handling   A.3.2(4)

Is_Decimal_Digit
   in Ada.Characters.Handling   A.3.2(4)

Is_Digit
   in Ada.Characters.Handling   A.3.2(4)

Is_Graphic
   in Ada.Characters.Handling   A.3.2(4)

Is_Held
   in Ada.Asynchronous_Task_Control   D.11(3)

Is_Hexadecimal_Digit
   in Ada.Characters.Handling   A.3.2(4)

Is_In
   in Ada.Strings.Maps   A.4.2(13)
   in Ada.Strings.Wide_Maps   A.4.7(13)

Is_ISO_646
   in Ada.Characters.Handling   A.3.2(10)

Is_Letter
   in Ada.Characters.Handling   A.3.2(4)

Is_Lower
   in Ada.Characters.Handling   A.3.2(4)

Is_Nul_Terminated
   in Interfaces.C   B.3(24), B.3(35)

Is_Open
   in Ada.Direct_IO   A.8.4(10)
   in Ada.Sequential_IO   A.8.1(10)
   in Ada.Streams.Stream_IO   A.12.1(12)
   in Ada.Text_IO   A.10.1(13)

Is_Reserved
   in Ada.Interrupts   C.3.2(4)

Is_Special
   in Ada.Characters.Handling   A.3.2(4)

Is_String
   in Ada.Characters.Handling   A.3.2(14)

Is_Subset
   in Ada.Strings.Maps   A.4.2(14)
   in Ada.Strings.Wide_Maps   A.4.7(14)

Is_Terminated
   in Ada.Task_Identification   C.7.1(4)

Is_Upper
   in Ada.Characters.Handling   A.3.2(4)

ISO 10646   3.5.2(2), 3.5.2(3)

ISO 1989:1985   1.2(4)

ISO/IEC 10646-1:1993   1.2(8/1)

ISO/IEC 1539:1991   1.2(3)

ISO/IEC 6429:1992   1.2(5)

ISO/IEC 646:1991   1.2(2)

ISO/IEC 8859-1:1987   1.2(6)

ISO/IEC 9899:1990   1.2(7)

ISO_646
   in Ada.Characters.Handling   A.3.2(9)

ISO_646_Set
   in Ada.Strings.Maps.Constants   A.4.6(4)

issue
   an entry call   9.5.3(8)

italics
   nongraphic characters   3.5.2(2)
   pseudo-names of anonymous types   3.2.1(7), A.1(2)
   syntax rules   1.1.4(14)
   terms introduced or defined   1.3(1)

iteration_scheme   5.5(3)
   used   5.5(2), P


J


j
   in Ada.Numerics.Generic_Complex_Types   G.1.1(5)
   in Interfaces.Fortran   B.5(10)


K


known discriminants   3.7(26)

known_discriminant_part   3.7(4)
   used   3.2.1(3), 3.7(2), 9.1(2), 9.4(2), P


L


label   5.1(7)
   used   5.1(3), P

language
   interface to assembly   C.1(4)
   interface to non-Ada   B(1)

language-defined check   11.5(2), 11.6(1)

language-defined class
   [partial]   3.2(10)
   of types   3.2(2)

Language-Defined Library Units   A(1)
   Ada   A.2(2)
   Ada.Asynchronous_Task_Control   D.11(3)
   Ada.Calendar   9.6(10)
   Ada.Characters   A.3.1(2)
   Ada.Characters.Handling   A.3.2(2)
   Ada.Characters.Latin_1   A.3.3(3)
   Ada.Command_Line   A.15(3)
   Ada.Decimal   F.2(2)
   Ada.Direct_IO   A.8.4(2)
   Ada.Dynamic_Priorities   D.5(3)
   Ada.Exceptions   11.4.1(2)
   Ada.Finalization   7.6(4/1)
   Ada.Float_Text_IO   A.10.9(33)
   Ada.Float_Wide_Text_IO   A.11(3)
   Ada.Integer_Text_IO   A.10.8(21)
   Ada.Integer_Wide_Text_IO   A.11(3)
   Ada.Interrupts   C.3.2(2)
   Ada.Interrupts.Names   C.3.2(12)
   Ada.IO_Exceptions   A.13(3)
   Ada.Numerics   A.5(3)
   Ada.Numerics.Complex_Elementary_Functions   G.1.2(9/1)
   Ada.Numerics.Complex_Types   G.1.1(25/1)
   Ada.Numerics.Discrete_Random   A.5.2(17)
   Ada.Numerics.Elementary_Functions   A.5.1(9/1)
   Ada.Numerics.Float_Random   A.5.2(5)
   Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(2)
   Ada.Numerics.Generic_Complex_Types   G.1.1(2/1)
   Ada.Numerics.Generic_Elementary_Functions   A.5.1(3)
   Ada.Real_Time   D.8(3)
   Ada.Sequential_IO   A.8.1(2)
   Ada.Storage_IO   A.9(3)
   Ada.Streams   13.13.1(2)
   Ada.Streams.Stream_IO   A.12.1(3)
   Ada.Strings   A.4.1(3)
   Ada.Strings.Bounded   A.4.4(3)
   Ada.Strings.Fixed   A.4.3(5)
   Ada.Strings.Maps   A.4.2(3)
   Ada.Strings.Maps.Constants   A.4.6(3)
   Ada.Strings.Unbounded   A.4.5(3)
   Ada.Strings.Wide_Bounded   A.4.7(1)
   Ada.Strings.Wide_Fixed   A.4.7(1)
   Ada.Strings.Wide_Maps.Wide_Constants   A.4.7(28)
   Ada.Strings.Wide_Unbounded   A.4.7(1)
   Ada.Strings.Wide_Maps   A.4.7(3)
   Ada.Synchronous_Task_Control   D.10(3)
   Ada.Tags   3.9(6)
   Ada.Task_Attributes   C.7.2(2)
   Ada.Task_Identification   C.7.1(2)
   Ada.Text_IO   A.10.1(2)
   Ada.Text_IO.Complex_IO   G.1.3(3)
   Ada.Text_IO.Editing   F.3.3(3)
   Ada.Text_IO.Text_Streams   A.12.2(3)
   Ada.Unchecked_Conversion   13.9(3)
   Ada.Unchecked_Deallocation   13.11.2(3)
   Ada.Wide_Text_IO   A.11(2)
   Ada.Wide_Text_IO.Complex_IO   G.1.4(1)
   Ada.Wide_Text_IO.Editing   F.3.4(1)
   Ada.Wide_Text_IO.Text_Streams   A.12.3(3)
   Interfaces   B.2(3)
   Interfaces.C   B.3(4)
   Interfaces.C.Pointers   B.3.2(4)
   Interfaces.C.Strings   B.3.1(3)
   Interfaces.COBOL   B.4(7)
   Interfaces.Fortran   B.5(4)
   Standard   A.1(4)
   System   13.7(3)
   System.Address_To_Access_Conversions   13.7.2(2)
   System.Machine_Code   13.8(7)
   System.RPC   E.5(3)
   System.Storage_Elements   13.7.1(2)
   System.Storage_Pools   13.11(5)

Language-Defined Subprogram
   Abort_Task in Ada.Task_Identification   C.7.1(3/1)
   Adjust in Ada.Finalization   7.6(6)
   Allocate in System.Storage_Pools   13.11(7)
   Append in Ada.Strings.Bounded   A.4.4(13), A.4.4(14), A.4.4(15),
A.4.4(16), A.4.4(17), A.4.4(18), A.4.4(19), A.4.4(20)
   Append in Ada.Strings.Unbounded   A.4.5(12), A.4.5(13), A.4.5(14)
   Arccos in Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(5)
   Arccos in Ada.Numerics.Generic_Elementary_Functions   A.5.1(6)
   Arccosh in Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(7)
   Arccosh in Ada.Numerics.Generic_Elementary_Functions   A.5.1(7)
   Arccot in Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(5)
   Arccot in Ada.Numerics.Generic_Elementary_Functions   A.5.1(6)
   Arccoth in Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(7)
   Arccoth in Ada.Numerics.Generic_Elementary_Functions   A.5.1(7)
   Arcsin in Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(5)
   Arcsin in Ada.Numerics.Generic_Elementary_Functions   A.5.1(6)
   Arcsinh in Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(7)
   Arcsinh in Ada.Numerics.Generic_Elementary_Functions   A.5.1(7)
   Arctan in Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(5)
   Arctan in Ada.Numerics.Generic_Elementary_Functions   A.5.1(6)
   Arctanh in Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(7)
   Arctanh in Ada.Numerics.Generic_Elementary_Functions   A.5.1(7)
   Argument in Ada.Command_Line   A.15(5)
   Argument in Ada.Numerics.Generic_Complex_Types   G.1.1(10)
   Argument_Count in Ada.Command_Line   A.15(4)
   Attach_Handler in Ada.Interrupts   C.3.2(7)
   Blank_When_Zero in Ada.Text_IO.Editing   F.3.3(7)
   Clock in Ada.Calendar   9.6(12)
   Clock in Ada.Real_Time   D.8(6)
   Close in Ada.Direct_IO   A.8.4(8)
   Close in Ada.Sequential_IO   A.8.1(8)
   Close in Ada.Streams.Stream_IO   A.12.1(10)
   Close in Ada.Text_IO   A.10.1(11)
   Col in Ada.Text_IO   A.10.1(37)
   Command_Name in Ada.Command_Line   A.15(6)
   Compose_From_Cartesian in Ada.Numerics.Generic_Complex_Types   G.1.1(8)
   Compose_From_Polar in Ada.Numerics.Generic_Complex_Types   G.1.1(11)
   Conjugate in Ada.Numerics.Generic_Complex_Types   G.1.1(12), G.1.1(15)
   Continue in Ada.Asynchronous_Task_Control   D.11(3)
   Copy_Array in Interfaces.C.Pointers   B.3.2(15)
   Copy_Terminated_Array in Interfaces.C.Pointers   B.3.2(14)
   Cos in Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(4)
   Cos in Ada.Numerics.Generic_Elementary_Functions   A.5.1(5)
   Cosh in Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(6)
   Cosh in Ada.Numerics.Generic_Elementary_Functions   A.5.1(7)
   Cot in Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(4)
   Cot in Ada.Numerics.Generic_Elementary_Functions   A.5.1(5)
   Coth in Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(6)
   Coth in Ada.Numerics.Generic_Elementary_Functions   A.5.1(7)
   Count in Ada.Strings.Bounded   A.4.4(48), A.4.4(49), A.4.4(50)
   Count in Ada.Strings.Fixed   A.4.3(13), A.4.3(14), A.4.3(15)
   Count in Ada.Strings.Unbounded   A.4.5(43), A.4.5(44), A.4.5(45)
   Create in Ada.Direct_IO   A.8.4(6)
   Create in Ada.Sequential_IO   A.8.1(6)
   Create in Ada.Streams.Stream_IO   A.12.1(8)
   Create in Ada.Text_IO   A.10.1(9)
   Current_Error in Ada.Text_IO   A.10.1(17), A.10.1(20)
   Current_Handler in Ada.Interrupts   C.3.2(6)
   Current_Input in Ada.Text_IO   A.10.1(17), A.10.1(20)
   Current_Output in Ada.Text_IO   A.10.1(17), A.10.1(20)
   Current_State in Ada.Synchronous_Task_Control   D.10(4)
   Current_Task in Ada.Task_Identification   C.7.1(3/1)
   Day in Ada.Calendar   9.6(13)
   Deallocate in System.Storage_Pools   13.11(8)
   Decrement in Interfaces.C.Pointers   B.3.2(11)
   Delete in Ada.Direct_IO   A.8.4(8)
   Delete in Ada.Sequential_IO   A.8.1(8)
   Delete in Ada.Streams.Stream_IO   A.12.1(10)
   Delete in Ada.Strings.Bounded   A.4.4(64), A.4.4(65)
   Delete in Ada.Strings.Fixed   A.4.3(29), A.4.3(30)
   Delete in Ada.Strings.Unbounded   A.4.5(59), A.4.5(60)
   Delete in Ada.Text_IO   A.10.1(11)
   Dereference_Error in Interfaces.C.Strings   B.3.1(12)
   Detach_Handler in Ada.Interrupts   C.3.2(9)
   Divide in Ada.Decimal   F.2(6)
   Do_APC in System.RPC   E.5(10)
   Do_RPC in System.RPC   E.5(9)
   Element in Ada.Strings.Bounded   A.4.4(26)
   Element in Ada.Strings.Unbounded   A.4.5(20)
   End_Of_File in Ada.Direct_IO   A.8.4(16)
   End_Of_File in Ada.Sequential_IO   A.8.1(13)
   End_Of_File in Ada.Streams.Stream_IO   A.12.1(12)
   End_Of_File in Ada.Text_IO   A.10.1(34)
   End_Of_Line in Ada.Text_IO   A.10.1(30)
   End_Of_Page in Ada.Text_IO   A.10.1(33)
   Establish_RPC_Receiver in System.RPC   E.5(12)
   Exception_Identity in Ada.Exceptions   11.4.1(5)
   Exception_Information in Ada.Exceptions   11.4.1(5)
   Exception_Message in Ada.Exceptions   11.4.1(4)
   Exception_Name in Ada.Exceptions   11.4.1(2), 11.4.1(5)
   Exchange_Handler in Ada.Interrupts   C.3.2(8)
   Exp in Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(3)
   Exp in Ada.Numerics.Generic_Elementary_Functions   A.5.1(4)
   Expanded_Name in Ada.Tags   3.9(7)
   External_Tag in Ada.Tags   3.9(7)
   Finalize in Ada.Finalization   7.6(6), 7.6(8)
   Find_Token in Ada.Strings.Bounded   A.4.4(51)
   Find_Token in Ada.Strings.Fixed   A.4.3(16)
   Find_Token in Ada.Strings.Unbounded   A.4.5(46)
   Flush in Ada.Streams.Stream_IO   A.12.1(25/1)
   Flush in Ada.Text_IO   A.10.1(21/1)
   Form in Ada.Direct_IO   A.8.4(9)
   Form in Ada.Sequential_IO   A.8.1(9)
   Form in Ada.Streams.Stream_IO   A.12.1(11)
   Form in Ada.Text_IO   A.10.1(12)
   Free in Ada.Strings.Unbounded   A.4.5(7)
   Free in Interfaces.C.Strings   B.3.1(11)
   Get in Ada.Text_IO   A.10.1(41), A.10.1(47), A.10.1(54), A.10.1(55),
A.10.1(59), A.10.1(60), A.10.1(65), A.10.1(67), A.10.1(70), A.10.1(72),
A.10.1(75), A.10.1(77), A.10.1(81), A.10.1(83)
   Get in Ada.Text_IO.Complex_IO   G.1.3(6), G.1.3(8)
   Get_Immediate in Ada.Text_IO   A.10.1(44), A.10.1(45)
   Get_Line in Ada.Text_IO   A.10.1(49)
   Get_Priority in Ada.Dynamic_Priorities   D.5(5)
   Head in Ada.Strings.Bounded   A.4.4(70), A.4.4(71)
   Head in Ada.Strings.Fixed   A.4.3(35), A.4.3(36)
   Head in Ada.Strings.Unbounded   A.4.5(65), A.4.5(66)
   Hold in Ada.Asynchronous_Task_Control   D.11(3)
   Im in Ada.Numerics.Generic_Complex_Types   G.1.1(6)
   Image in Ada.Numerics.Discrete_Random   A.5.2(26)
   Image in Ada.Numerics.Float_Random   A.5.2(14)
   Image in Ada.Task_Identification   C.7.1(3/1)
   Image in Ada.Text_IO.Editing   F.3.3(13)
   Increment in Interfaces.C.Pointers   B.3.2(11)
   Index in Ada.Direct_IO   A.8.4(15)
   Index in Ada.Streams.Stream_IO   A.12.1(23)
   Index in Ada.Strings.Bounded   A.4.4(44), A.4.4(45), A.4.4(46)
   Index in Ada.Strings.Fixed   A.4.3(9), A.4.3(10), A.4.3(11)
   Index in Ada.Strings.Unbounded   A.4.5(39), A.4.5(40), A.4.5(41)
   Index_Non_Blank in Ada.Strings.Bounded   A.4.4(47)
   Index_Non_Blank in Ada.Strings.Fixed   A.4.3(12)
   Index_Non_Blank in Ada.Strings.Unbounded   A.4.5(42)
   Initialize in Ada.Finalization   7.6(6), 7.6(8)
   Insert in Ada.Strings.Bounded   A.4.4(60), A.4.4(61)
   Insert in Ada.Strings.Fixed   A.4.3(25), A.4.3(26)
   Insert in Ada.Strings.Unbounded   A.4.5(55), A.4.5(56)
   Internal_Tag in Ada.Tags   3.9(7)
   Is_Alphanumeric in Ada.Characters.Handling   A.3.2(4)
   Is_Attached in Ada.Interrupts   C.3.2(5)
   Is_Basic in Ada.Characters.Handling   A.3.2(4)
   Is_Callable in Ada.Task_Identification   C.7.1(4)
   Is_Character in Ada.Characters.Handling   A.3.2(14)
   Is_Control in Ada.Characters.Handling   A.3.2(4)
   Is_Decimal_Digit in Ada.Characters.Handling   A.3.2(4)
   Is_Digit in Ada.Characters.Handling   A.3.2(4)
   Is_Graphic in Ada.Characters.Handling   A.3.2(4)
   Is_Held in Ada.Asynchronous_Task_Control   D.11(3)
   Is_Hexadecimal_Digit in Ada.Characters.Handling   A.3.2(4)
   Is_In in Ada.Strings.Maps   A.4.2(13)
   Is_In in Ada.Strings.Wide_Maps   A.4.7(13)
   Is_ISO_646 in Ada.Characters.Handling   A.3.2(10)
   Is_Letter in Ada.Characters.Handling   A.3.2(4)
   Is_Lower in Ada.Characters.Handling   A.3.2(4)
   Is_Nul_Terminated in Interfaces.C   B.3(24), B.3(35)
   Is_Open in Ada.Direct_IO   A.8.4(10)
   Is_Open in Ada.Sequential_IO   A.8.1(10)
   Is_Open in Ada.Streams.Stream_IO   A.12.1(12)
   Is_Open in Ada.Text_IO   A.10.1(13)
   Is_Reserved in Ada.Interrupts   C.3.2(4)
   Is_Special in Ada.Characters.Handling   A.3.2(4)
   Is_String in Ada.Characters.Handling   A.3.2(14)
   Is_Subset in Ada.Strings.Maps   A.4.2(14)
   Is_Subset in Ada.Strings.Wide_Maps   A.4.7(14)
   Is_Terminated in Ada.Task_Identification   C.7.1(4)
   Is_Upper in Ada.Characters.Handling   A.3.2(4)
   Length in Ada.Strings.Bounded   A.4.4(9)
   Length in Ada.Strings.Unbounded   A.4.5(6)
   Length in Ada.Text_IO.Editing   F.3.3(11)
   Length in Interfaces.COBOL   B.4(34), B.4(39), B.4(44)
   Line in Ada.Text_IO   A.10.1(38)
   Line_Length in Ada.Text_IO   A.10.1(25)
   Log in Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(3)
   Log in Ada.Numerics.Generic_Elementary_Functions   A.5.1(4)
   Look_Ahead in Ada.Text_IO   A.10.1(43)
   Microseconds in Ada.Real_Time   D.8(14)
   Milliseconds in Ada.Real_Time   D.8(14)
   Mode in Ada.Direct_IO   A.8.4(9)
   Mode in Ada.Sequential_IO   A.8.1(9)
   Mode in Ada.Streams.Stream_IO   A.12.1(11)
   Mode in Ada.Text_IO   A.10.1(12)
   Modulus in Ada.Numerics.Generic_Complex_Types   G.1.1(9)
   Month in Ada.Calendar   9.6(13)
   Move in Ada.Strings.Fixed   A.4.3(7)
   Name in Ada.Direct_IO   A.8.4(9)
   Name in Ada.Sequential_IO   A.8.1(9)
   Name in Ada.Streams.Stream_IO   A.12.1(11)
   Name in Ada.Text_IO   A.10.1(12)
   Nanoseconds in Ada.Real_Time   D.8(14)
   New_Char_Array in Interfaces.C.Strings   B.3.1(9)
   New_Line in Ada.Text_IO   A.10.1(28)
   New_Page in Ada.Text_IO   A.10.1(31)
   New_String in Interfaces.C.Strings   B.3.1(10)
   Null_Task_ID in Ada.Task_Identification   C.7.1(2)
   Open in Ada.Direct_IO   A.8.4(7)
   Open in Ada.Sequential_IO   A.8.1(7)
   Open in Ada.Streams.Stream_IO   A.12.1(9)
   Open in Ada.Text_IO   A.10.1(10)
   Overwrite in Ada.Strings.Bounded   A.4.4(62), A.4.4(63)
   Overwrite in Ada.Strings.Fixed   A.4.3(27), A.4.3(28)
   Overwrite in Ada.Strings.Unbounded   A.4.5(57), A.4.5(58)
   Page in Ada.Text_IO   A.10.1(39)
   Page_Length in Ada.Text_IO   A.10.1(26)
   Pic_String in Ada.Text_IO.Editing   F.3.3(7)
   Put in Ada.Text_IO   A.10.1(42), A.10.1(48), A.10.1(55), A.10.1(60),
A.10.1(66), A.10.1(67), A.10.1(71), A.10.1(72), A.10.1(76), A.10.1(77),
A.10.1(82), A.10.1(83)
   Put in Ada.Text_IO.Complex_IO   G.1.3(7), G.1.3(8)
   Put in Ada.Text_IO.Editing   F.3.3(14), F.3.3(15), F.3.3(16)
   Put_Line in Ada.Text_IO   A.10.1(50)
   Raise_Exception in Ada.Exceptions   11.4.1(4)
   Random in Ada.Numerics.Discrete_Random   A.5.2(20)
   Random in Ada.Numerics.Float_Random   A.5.2(8)
   Re in Ada.Numerics.Generic_Complex_Types   G.1.1(6)
   Read in Ada.Direct_IO   A.8.4(12)
   Read in Ada.Sequential_IO   A.8.1(12)
   Read in Ada.Storage_IO   A.9(6)
   Read in Ada.Streams   13.13.1(5)
   Read in Ada.Streams.Stream_IO   A.12.1(15), A.12.1(16)
   Read in System.RPC   E.5(7)
   Reference in Ada.Interrupts   C.3.2(10)
   Reference in Ada.Task_Attributes   C.7.2(5)
   Reinitialize in Ada.Task_Attributes   C.7.2(6)
   Replace_Element in Ada.Strings.Bounded   A.4.4(27)
   Replace_Element in Ada.Strings.Unbounded   A.4.5(21)
   Replace_Slice in Ada.Strings.Bounded   A.4.4(58), A.4.4(59)
   Replace_Slice in Ada.Strings.Fixed   A.4.3(23), A.4.3(24)
   Replace_Slice in Ada.Strings.Unbounded   A.4.5(53), A.4.5(54)
   Replicate in Ada.Strings.Bounded   A.4.4(78), A.4.4(79), A.4.4(80)
   Reraise_Occurrence in Ada.Exceptions   11.4.1(4)
   Reset in Ada.Direct_IO   A.8.4(8)
   Reset in Ada.Numerics.Discrete_Random   A.5.2(21), A.5.2(24)
   Reset in Ada.Numerics.Float_Random   A.5.2(9), A.5.2(12)
   Reset in Ada.Sequential_IO   A.8.1(8)
   Reset in Ada.Streams.Stream_IO   A.12.1(10)
   Reset in Ada.Text_IO   A.10.1(11)
   Save in Ada.Numerics.Discrete_Random   A.5.2(24)
   Save in Ada.Numerics.Float_Random   A.5.2(12)
   Save_Occurrence in Ada.Exceptions   11.4.1(6)
   Seconds in Ada.Calendar   9.6(13)
   Set_Col in Ada.Text_IO   A.10.1(35)
   Set_Error in Ada.Text_IO   A.10.1(15)
   Set_Exit_Status in Ada.Command_Line   A.15(9)
   Set_False in Ada.Synchronous_Task_Control   D.10(4)
   Set_Im in Ada.Numerics.Generic_Complex_Types   G.1.1(7)
   Set_Index in Ada.Direct_IO   A.8.4(14)
   Set_Index in Ada.Streams.Stream_IO   A.12.1(22)
   Set_Input in Ada.Text_IO   A.10.1(15)
   Set_Line in Ada.Text_IO   A.10.1(36)
   Set_Line_Length in Ada.Text_IO   A.10.1(23)
   Set_Mode in Ada.Streams.Stream_IO   A.12.1(24)
   Set_Output in Ada.Text_IO   A.10.1(15)
   Set_Page_Length in Ada.Text_IO   A.10.1(24)
   Set_Priority in Ada.Dynamic_Priorities   D.5(4)
   Set_Re in Ada.Numerics.Generic_Complex_Types   G.1.1(7)
   Set_True in Ada.Synchronous_Task_Control   D.10(4)
   Set_Value in Ada.Task_Attributes   C.7.2(6)
   Sin in Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(4)
   Sin in Ada.Numerics.Generic_Elementary_Functions   A.5.1(5)
   Sinh in Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(6)
   Sinh in Ada.Numerics.Generic_Elementary_Functions   A.5.1(7)
   Size in Ada.Direct_IO   A.8.4(15)
   Size in Ada.Streams.Stream_IO   A.12.1(23)
   Skip_Line in Ada.Text_IO   A.10.1(29)
   Skip_Page in Ada.Text_IO   A.10.1(32)
   Slice in Ada.Strings.Bounded   A.4.4(28)
   Slice in Ada.Strings.Unbounded   A.4.5(22)
   Split in Ada.Calendar   9.6(14)
   Split in Ada.Real_Time   D.8(16)
   Sqrt in Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(3)
   Sqrt in Ada.Numerics.Generic_Elementary_Functions   A.5.1(4)
   Standard_Error in Ada.Text_IO   A.10.1(16), A.10.1(19)
   Standard_Input in Ada.Text_IO   A.10.1(16), A.10.1(19)
   Standard_Output in Ada.Text_IO   A.10.1(16), A.10.1(19)
   Storage_Size in System.Storage_Pools   13.11(9)
   Stream in Ada.Streams.Stream_IO   A.12.1(13)
   Stream in Ada.Text_IO.Text_Streams   A.12.2(4)
   Stream in Ada.Wide_Text_IO.Text_Streams   A.12.3(4)
   Strlen in Interfaces.C.Strings   B.3.1(17)
   Suspend_Until_True in Ada.Synchronous_Task_Control   D.10(4)
   Tail in Ada.Strings.Bounded   A.4.4(72), A.4.4(73)
   Tail in Ada.Strings.Fixed   A.4.3(37), A.4.3(38)
   Tail in Ada.Strings.Unbounded   A.4.5(67), A.4.5(68)
   Tan in Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(4)
   Tan in Ada.Numerics.Generic_Elementary_Functions   A.5.1(5)
   Tanh in Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(6)
   Tanh in Ada.Numerics.Generic_Elementary_Functions   A.5.1(7)
   Time_Of in Ada.Calendar   9.6(15)
   Time_Of in Ada.Real_Time   D.8(16)
   To_Ada in Interfaces.C   B.3(22), B.3(26), B.3(28), B.3(32), B.3(37),
B.3(39)
   To_Ada in Interfaces.COBOL   B.4(17), B.4(19)
   To_Ada in Interfaces.Fortran   B.5(13), B.5(14), B.5(16)
   To_Address in System.Address_To_Access_Conversions   13.7.2(3)
   To_Address in System.Storage_Elements   13.7.1(10)
   To_Basic in Ada.Characters.Handling   A.3.2(6), A.3.2(7)
   To_Binary in Interfaces.COBOL   B.4(45), B.4(48)
   To_Bounded_String in Ada.Strings.Bounded   A.4.4(11)
   To_C in Interfaces.C   B.3(21), B.3(25), B.3(27), B.3(32), B.3(36),
B.3(38)
   To_Character in Ada.Characters.Handling   A.3.2(15)
   To_Chars_Ptr in Interfaces.C.Strings   B.3.1(8)
   To_COBOL in Interfaces.COBOL   B.4(17), B.4(18)
   To_Decimal in Interfaces.COBOL   B.4(35), B.4(40), B.4(44), B.4(47)
   To_Display in Interfaces.COBOL   B.4(36)
   To_Domain in Ada.Strings.Maps   A.4.2(24)
   To_Domain in Ada.Strings.Wide_Maps   A.4.7(24)
   To_Duration in Ada.Real_Time   D.8(13)
   To_Fortran in Interfaces.Fortran   B.5(13), B.5(14), B.5(15)
   To_Integer in System.Storage_Elements   13.7.1(10)
   To_ISO_646 in Ada.Characters.Handling   A.3.2(11), A.3.2(12)
   To_Long_Binary in Interfaces.COBOL   B.4(48)
   To_Lower in Ada.Characters.Handling   A.3.2(6), A.3.2(7)
   To_Mapping in Ada.Strings.Maps   A.4.2(23)
   To_Mapping in Ada.Strings.Wide_Maps   A.4.7(23)
   To_Packed in Interfaces.COBOL   B.4(41)
   To_Picture in Ada.Text_IO.Editing   F.3.3(6)
   To_Pointer in System.Address_To_Access_Conversions   13.7.2(3)
   To_Range in Ada.Strings.Maps   A.4.2(24)
   To_Range in Ada.Strings.Wide_Maps   A.4.7(25)
   To_Ranges in Ada.Strings.Maps   A.4.2(10)
   To_Ranges in Ada.Strings.Wide_Maps   A.4.7(10)
   To_Sequence in Ada.Strings.Maps   A.4.2(19)
   To_Sequence in Ada.Strings.Wide_Maps   A.4.7(19)
   To_Set in Ada.Strings.Maps   A.4.2(8), A.4.2(9), A.4.2(17), A.4.2(18)
   To_Set in Ada.Strings.Wide_Maps   A.4.7(8), A.4.7(9), A.4.7(17),
A.4.7(18)
   To_String in Ada.Characters.Handling   A.3.2(16)
   To_String in Ada.Strings.Bounded   A.4.4(12)
   To_String in Ada.Strings.Unbounded   A.4.5(11)
   To_Time_Span in Ada.Real_Time   D.8(13)
   To_Unbounded_String in Ada.Strings.Unbounded   A.4.5(9), A.4.5(10)
   To_Upper in Ada.Characters.Handling   A.3.2(6), A.3.2(7)
   To_Wide_Character in Ada.Characters.Handling   A.3.2(17)
   To_Wide_String in Ada.Characters.Handling   A.3.2(18)
   Translate in Ada.Strings.Bounded   A.4.4(53), A.4.4(54), A.4.4(55),
A.4.4(56)
   Translate in Ada.Strings.Fixed   A.4.3(18), A.4.3(19), A.4.3(20),
A.4.3(21)
   Translate in Ada.Strings.Unbounded   A.4.5(48), A.4.5(49), A.4.5(50),
A.4.5(51)
   Trim in Ada.Strings.Bounded   A.4.4(67), A.4.4(68), A.4.4(69)
   Trim in Ada.Strings.Fixed   A.4.3(31), A.4.3(32), A.4.3(33), A.4.3(34)
   Trim in Ada.Strings.Unbounded   A.4.5(61), A.4.5(62), A.4.5(63),
A.4.5(64)
   Update in Interfaces.C.Strings   B.3.1(18), B.3.1(19)
   Update_Error in Interfaces.C.Strings   B.3.1(20)
   Valid in Ada.Text_IO.Editing   F.3.3(5), F.3.3(12)
   Valid in Interfaces.COBOL   B.4(33), B.4(38), B.4(43)
   Value in Ada.Numerics.Discrete_Random   A.5.2(26)
   Value in Ada.Numerics.Float_Random   A.5.2(14)
   Value in Ada.Strings.Maps   A.4.2(21)
   Value in Ada.Strings.Wide_Maps   A.4.7(21)
   Value in Ada.Task_Attributes   C.7.2(4)
   Value in Interfaces.C.Pointers   B.3.2(6), B.3.2(7)
   Value in Interfaces.C.Strings   B.3.1(13), B.3.1(14), B.3.1(15),
B.3.1(16)
   Virtual_Length in Interfaces.C.Pointers   B.3.2(13)
   Write in Ada.Direct_IO   A.8.4(13)
   Write in Ada.Sequential_IO   A.8.1(12)
   Write in Ada.Storage_IO   A.9(7)
   Write in Ada.Streams   13.13.1(6)
   Write in Ada.Streams.Stream_IO   A.12.1(18), A.12.1(19)
   Write in System.RPC   E.5(8)
   Year in Ada.Calendar   9.6(13)

Language-Defined Type
   Address in System   13.7(12)
   Alignment in Ada.Strings   A.4.1(6)
   Alphanumeric in Interfaces.COBOL   B.4(16)
   Attribute_Handle in Ada.Task_Attributes   C.7.2(3)
   Binary in Interfaces.COBOL   B.4(10)
   Binary_Format in Interfaces.COBOL   B.4(24)
   Bit_Order in System   13.7(15)
   Boolean in Standard   A.1(5)
   Bounded_String in Ada.Strings.Bounded   A.4.4(6)
   Byte in Interfaces.COBOL   B.4(29)
   Byte_Array in Interfaces.COBOL   B.4(29)
   C_float in Interfaces.C   B.3(15)
   char in Interfaces.C   B.3(19)
   char_array in Interfaces.C   B.3(23)
   char_array_access in Interfaces.C.Strings   B.3.1(4)
   Character in Standard   A.1(35)
   Character_Mapping in Ada.Strings.Maps   A.4.2(20)
   Character_Mapping_Function in Ada.Strings.Maps   A.4.2(25)
   Character_Range in Ada.Strings.Maps   A.4.2(6)
   Character_Ranges in Ada.Strings.Maps   A.4.2(7)
   Character_Set in Ada.Strings.Maps   A.4.2(4)
   Character_Set in Interfaces.Fortran   B.5(11)
   chars_ptr in Interfaces.C.Strings   B.3.1(5)
   chars_ptr_array in Interfaces.C.Strings   B.3.1(6)
   COBOL_Character in Interfaces.COBOL   B.4(13)
   Complex in Ada.Numerics.Generic_Complex_Types   G.1.1(3)
   Complex in Interfaces.Fortran   B.5(9)
   Controlled in Ada.Finalization   7.6(5)
   Count in Ada.Direct_IO   A.8.4(4)
   Count in Ada.Streams.Stream_IO   A.12.1(7)
   Count in Ada.Text_IO   A.10.1(5)
   Decimal_Element in Interfaces.COBOL   B.4(12)
   Direction in Ada.Strings   A.4.1(6)
   Display_Format in Interfaces.COBOL   B.4(22)
   double in Interfaces.C   B.3(16)
   Double_Precision in Interfaces.Fortran   B.5(6)
   Duration in Standard   A.1(43)
   Exception_Id in Ada.Exceptions   11.4.1(2)
   Exception_Occurrence in Ada.Exceptions   11.4.1(3)
   Exception_Occurrence_Access in Ada.Exceptions   11.4.1(3)
   Exit_Status in Ada.Command_Line   A.15(7), A.15(16.1/1)
   File_Access in Ada.Text_IO   A.10.1(18)
   File_Mode in Ada.Direct_IO   A.8.4(4)
   File_Mode in Ada.Sequential_IO   A.8.1(4)
   File_Mode in Ada.Streams.Stream_IO   A.12.1(6)
   File_Mode in Ada.Text_IO   A.10.1(4)
   File_Type in Ada.Direct_IO   A.8.4(3)
   File_Type in Ada.Sequential_IO   A.8.1(3)
   File_Type in Ada.Streams.Stream_IO   A.12.1(5)
   File_Type in Ada.Text_IO   A.10.1(3)
   Float in Standard   A.1(21)
   Floating in Interfaces.COBOL   B.4(9)
   Fortran_Character in Interfaces.Fortran   B.5(12)
   Fortran_Integer in Interfaces.Fortran   B.5(5)
   Generator in Ada.Numerics.Discrete_Random   A.5.2(19)
   Generator in Ada.Numerics.Float_Random   A.5.2(7)
   Imaginary in Ada.Numerics.Generic_Complex_Types   G.1.1(4)
   int in Interfaces.C   B.3(7)
   Integer in Standard   A.1(12)
   Integer_Address in System.Storage_Elements   13.7.1(10)
   Interrupt_ID in Ada.Interrupts   C.3.2(2)
   Limited_Controlled in Ada.Finalization   7.6(7)
   Logical in Interfaces.Fortran   B.5(7)
   long in Interfaces.C   B.3(7)
   Long_Binary in Interfaces.COBOL   B.4(10)
   long_double in Interfaces.C   B.3(17)
   Long_Floating in Interfaces.COBOL   B.4(9)
   Membership in Ada.Strings   A.4.1(6)
   Name in System   13.7(4)
   Numeric in Interfaces.COBOL   B.4(20)
   Packed_Decimal in Interfaces.COBOL   B.4(12)
   Packed_Format in Interfaces.COBOL   B.4(26)
   Parameterless_Handler in Ada.Interrupts   C.3.2(2)
   Params_Stream_Type in System.RPC   E.5(6)
   Partition_ID in System.RPC   E.5(4)
   Picture in Ada.Text_IO.Editing   F.3.3(4)
   plain_char in Interfaces.C   B.3(11)
   Pointer in Interfaces.C.Pointers   B.3.2(5)
   ptrdiff_t in Interfaces.C   B.3(12)
   Real in Interfaces.Fortran   B.5(6)
   Root_Storage_Pool in System.Storage_Pools   13.11(6)
   Root_Stream_Type in Ada.Streams   13.13.1(3)
   RPC_Receiver in System.RPC   E.5(11)
   Seconds_Count in Ada.Real_Time   D.8(15)
   short in Interfaces.C   B.3(7)
   signed_char in Interfaces.C   B.3(8)
   size_t in Interfaces.C   B.3(13)
   State in Ada.Numerics.Discrete_Random   A.5.2(23)
   State in Ada.Numerics.Float_Random   A.5.2(11)
   Storage_Array in System.Storage_Elements   13.7.1(5)
   Storage_Element in System.Storage_Elements   13.7.1(5)
   Storage_Offset in System.Storage_Elements   13.7.1(3)
   Stream_Access in Ada.Streams.Stream_IO   A.12.1(4)
   Stream_Access in Ada.Text_IO.Text_Streams   A.12.2(3)
   Stream_Access in Ada.Wide_Text_IO.Text_Streams   A.12.3(3)
   Stream_Element in Ada.Streams   13.13.1(4/1)
   Stream_Element_Array in Ada.Streams   13.13.1(4/1)
   Stream_Element_Offset in Ada.Streams   13.13.1(4/1)
   String in Standard   A.1(37)
   String_Access in Ada.Strings.Unbounded   A.4.5(7)
   Suspension_Object in Ada.Synchronous_Task_Control   D.10(4)
   Tag in Ada.Tags   3.9(6)
   Task_ID in Ada.Task_Identification   C.7.1(2)
   Time in Ada.Calendar   9.6(10)
   Time in Ada.Real_Time   D.8(4)
   Time_Span in Ada.Real_Time   D.8(5)
   Trim_End in Ada.Strings   A.4.1(6)
   Truncation in Ada.Strings   A.4.1(6)
   Type_Set in Ada.Text_IO   A.10.1(7)
   Unbounded_String in Ada.Strings.Unbounded   A.4.5(4)
   unsigned in Interfaces.C   B.3(9)
   unsigned_char in Interfaces.C   B.3(10)
   unsigned_long in Interfaces.C   B.3(9)
   unsigned_short in Interfaces.C   B.3(9)
   wchar_array in Interfaces.C   B.3(33)
   wchar_t in Interfaces.C   B.3(30/1)
   Wide_Character in Standard   A.1(36)
   Wide_Character_Mapping in Ada.Strings.Wide_Maps   A.4.7(20)
   Wide_Character_Mapping_Function in Ada.Strings.Wide_Maps   A.4.7(26)
   Wide_Character_Range in Ada.Strings.Wide_Maps   A.4.7(6)
   Wide_Character_Ranges in Ada.Strings.Wide_Maps   A.4.7(7)
   Wide_Character_Set in Ada.Strings.Wide_Maps   A.4.7(4)
   Wide_String in Standard   A.1(41)

Last attribute   3.5(13), 3.6.2(5)

Last(N) attribute   3.6.2(6)

last_bit   13.5.1(6)
   used   13.5.1(3), P

Last_Bit attribute   13.5.2(4)

lateness   D.9(12)

Latin-1   3.5.2(2)

Latin_1
   child of Ada.Characters   A.3.3(3)

layout
   aspect of representation   13.5(1)

Layout_Error
   in Ada.IO_Exceptions   A.13(4)
   in Ada.Text_IO   A.10.1(85)

LC_A
   in Ada.Characters.Latin_1   A.3.3(13)

LC_A_Acute
   in Ada.Characters.Latin_1   A.3.3(25)

LC_A_Circumflex
   in Ada.Characters.Latin_1   A.3.3(25)

LC_A_Diaeresis
   in Ada.Characters.Latin_1   A.3.3(25)

LC_A_Grave
   in Ada.Characters.Latin_1   A.3.3(25)

LC_A_Ring
   in Ada.Characters.Latin_1   A.3.3(25)

LC_A_Tilde
   in Ada.Characters.Latin_1   A.3.3(25)

LC_AE_Diphthong
   in Ada.Characters.Latin_1   A.3.3(25)

LC_B
   in Ada.Characters.Latin_1   A.3.3(13)

LC_C
   in Ada.Characters.Latin_1   A.3.3(13)

LC_C_Cedilla
   in Ada.Characters.Latin_1   A.3.3(25)

LC_D
   in Ada.Characters.Latin_1   A.3.3(13)

LC_E
   in Ada.Characters.Latin_1   A.3.3(13)

LC_E_Acute
   in Ada.Characters.Latin_1   A.3.3(25)

LC_E_Circumflex
   in Ada.Characters.Latin_1   A.3.3(25)

LC_E_Diaeresis
   in Ada.Characters.Latin_1   A.3.3(25)

LC_E_Grave
   in Ada.Characters.Latin_1   A.3.3(25)

LC_F
   in Ada.Characters.Latin_1   A.3.3(13)

LC_G
   in Ada.Characters.Latin_1   A.3.3(13)

LC_German_Sharp_S
   in Ada.Characters.Latin_1   A.3.3(24)

LC_H
   in Ada.Characters.Latin_1   A.3.3(13)

LC_I
   in Ada.Characters.Latin_1   A.3.3(13)

LC_I_Acute
   in Ada.Characters.Latin_1   A.3.3(25)

LC_I_Circumflex
   in Ada.Characters.Latin_1   A.3.3(25)

LC_I_Diaeresis
   in Ada.Characters.Latin_1   A.3.3(25)

LC_I_Grave
   in Ada.Characters.Latin_1   A.3.3(25)

LC_Icelandic_Eth
   in Ada.Characters.Latin_1   A.3.3(26)

LC_Icelandic_Thorn
   in Ada.Characters.Latin_1   A.3.3(26)

LC_J
   in Ada.Characters.Latin_1   A.3.3(13)

LC_K
   in Ada.Characters.Latin_1   A.3.3(13)

LC_L
   in Ada.Characters.Latin_1   A.3.3(13)

LC_M
   in Ada.Characters.Latin_1   A.3.3(13)

LC_N
   in Ada.Characters.Latin_1   A.3.3(13)

LC_N_Tilde
   in Ada.Characters.Latin_1   A.3.3(26)

LC_O
   in Ada.Characters.Latin_1   A.3.3(13)

LC_O_Acute
   in Ada.Characters.Latin_1   A.3.3(26)

LC_O_Circumflex
   in Ada.Characters.Latin_1   A.3.3(26)

LC_O_Diaeresis
   in Ada.Characters.Latin_1   A.3.3(26)

LC_O_Grave
   in Ada.Characters.Latin_1   A.3.3(26)

LC_O_Oblique_Stroke
   in Ada.Characters.Latin_1   A.3.3(26)

LC_O_Tilde
   in Ada.Characters.Latin_1   A.3.3(26)

LC_P
   in Ada.Characters.Latin_1   A.3.3(14)

LC_Q
   in Ada.Characters.Latin_1   A.3.3(14)

LC_R
   in Ada.Characters.Latin_1   A.3.3(14)

LC_S
   in Ada.Characters.Latin_1   A.3.3(14)

LC_T
   in Ada.Characters.Latin_1   A.3.3(14)

LC_U
   in Ada.Characters.Latin_1   A.3.3(14)

LC_U_Acute
   in Ada.Characters.Latin_1   A.3.3(26)

LC_U_Circumflex
   in Ada.Characters.Latin_1   A.3.3(26)

LC_U_Diaeresis
   in Ada.Characters.Latin_1   A.3.3(26)

LC_U_Grave
   in Ada.Characters.Latin_1   A.3.3(26)

LC_V
   in Ada.Characters.Latin_1   A.3.3(14)

LC_W
   in Ada.Characters.Latin_1   A.3.3(14)

LC_X
   in Ada.Characters.Latin_1   A.3.3(14)

LC_Y
   in Ada.Characters.Latin_1   A.3.3(14)

LC_Y_Acute
   in Ada.Characters.Latin_1   A.3.3(26)

LC_Y_Diaeresis
   in Ada.Characters.Latin_1   A.3.3(26)

LC_Z
   in Ada.Characters.Latin_1   A.3.3(14)

Leading_Nonseparate
   in Interfaces.COBOL   B.4(23)

Leading_Part attribute   A.5.3(54)

Leading_Separate
   in Interfaces.COBOL   B.4(23)

leaving   7.6.1(3)

left   7.6.1(3)

left curly bracket   2.1(15)

left parenthesis   2.1(15)

left square bracket   2.1(15)

Left_Angle_Quotation
   in Ada.Characters.Latin_1   A.3.3(21)

Left_Curly_Bracket
   in Ada.Characters.Latin_1   A.3.3(14)

Left_Parenthesis
   in Ada.Characters.Latin_1   A.3.3(8)

Left_Square_Bracket
   in Ada.Characters.Latin_1   A.3.3(12)

legal
   construct   1.1.2(27)
   partition   1.1.2(29)

legality rules   1.1.2(27)

length
   of a dimension of an array   3.6(13)
   of a one-dimensional array   3.6(13)
   in Ada.Strings.Bounded   A.4.4(9)
   in Ada.Strings.Unbounded   A.4.5(6)
   in Ada.Text_IO.Editing   F.3.3(11)
   in Interfaces.COBOL   B.4(34), B.4(39), B.4(44)

Length attribute   3.6.2(9)

Length(N) attribute   3.6.2(10)

Length_Check   11.5(15)
   [partial]   4.5.1(8), 4.6(37), 4.6(52)

Length_Error
   in Ada.Strings   A.4.1(5)

Length_Range
   in Ada.Strings.Bounded   A.4.4(8)

less than operator   4.4(1), 4.5.2(1)

less than or equal operator   4.4(1), 4.5.2(1)

less-than sign   2.1(15)

Less_Than_Sign
   in Ada.Characters.Latin_1   A.3.3(10)

letter
   a category of Character   A.3.2(24)

letter_or_digit   2.3(3)
   used   2.3(2), P

Letter_Set
   in Ada.Strings.Maps.Constants   A.4.6(4)

level
   accessibility   3.10.2(3)
   library   3.10.2(22)

lexical element   2.2(1)

lexicographic order   4.5.2(26)

LF
   in Ada.Characters.Latin_1   A.3.3(5)

library   10.1.4(9)
   informal introduction   10(2)

library level   3.10.2(22)

Library unit   10.1(3), 10.1.1(9)
   informal introduction   10(2)
   See also language-defined library units

library unit pragma   10.1.5(7)
   All_Calls_Remote   E.2.3(6)
   categorization pragmas   E.2(2)
   Elaborate_Body   10.2.1(24)
   Preelaborate   10.2.1(4)
   Pure   10.2.1(15)

library_item   10.1.1(4)
   informal introduction   10(2)
   used   10.1.1(3), P

library_unit_body   10.1.1(7)
   used   10.1.1(4), P

library_unit_declaration   10.1.1(5)
   used   10.1.1(4), P

library_unit_renaming_declaration   10.1.1(6)
   used   10.1.1(4), P

lifetime   3.10.2(3)

Limited type   7.5(1), 7.5(3)
   becoming nonlimited   7.3.1(5/1), 7.5(16)

Limited_Controlled
   in Ada.Finalization   7.6(7)

line   2.2(2)
   in Ada.Text_IO   A.10.1(38)

line terminator   A.10(7)

Line_Length
   in Ada.Text_IO   A.10.1(25)

link name   B.1(35)

link-time error
   See post-compilation error   1.1.2(29)
   See post-compilation error   1.1.5(4)

linking
   See partition building   10.2(2)

literal   4.2(1)
   based   2.4.2(1)
   decimal   2.4.1(1)
   numeric   2.4(1)
   See also aggregate   4.3(1)

little endian   13.5.3(2)

load time   C.4(3)

local to   8.1(14)

local_name   13.1(3)
   used   13.2(3), 13.3(2), 13.4(2), 13.5.1(2), 13.5.1(3), 13.11.3(3),
B.1(5), B.1(6), B.1(7), C.5(3), C.6(3), C.6(4), C.6(5), C.6(6), E.4.1(3),
L(3), L(4), L(5), L(7), L(8), L(9), L(13), L(14), L(24), L(38), L(39), P

localization   3.5.2(4), 3.5.2(5)

locking policy   D.3(6/1)

Log
   in Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(3)
   in Ada.Numerics.Generic_Elementary_Functions   A.5.1(4)

Logical
   in Interfaces.Fortran   B.5(7)

logical operator   4.5.1(2)
   See also not operator   4.5.6(3)

logical_operator   4.5(2)

long
   in Interfaces.C   B.3(7)

Long_Binary
   in Interfaces.COBOL   B.4(10)

long_double
   in Interfaces.C   B.3(17)

Long_Float   3.5.7(15), 3.5.7(16), 3.5.7(17)

Long_Floating
   in Interfaces.COBOL   B.4(9)

Long_Integer   3.5.4(22), 3.5.4(25), 3.5.4(28)

Look_Ahead
   in Ada.Text_IO   A.10.1(43)

loop parameter   5.5(6)

loop_parameter_specification   5.5(4)
   used   5.5(3), P

loop_statement   5.5(2)
   used   5.1(5), P

low line   2.1(15)

low-level programming   C(1)

Low_Line
   in Ada.Characters.Latin_1   A.3.3(12)

Low_Order_First   13.5.3(2)
   in Interfaces.COBOL   B.4(25)

lower bound
   of a range   3.5(4)

lower-case letter
   a category of Character   A.3.2(25)

lower_case_identifier_letter   2.1(9)

Lower_Case_Map
   in Ada.Strings.Maps.Constants   A.4.6(5)

Lower_Set
   in Ada.Strings.Maps.Constants   A.4.6(4)


M


Machine attribute   A.5.3(60)

machine code insertion   13.8(1), C.1(2)

machine numbers
   of a floating point type   3.5.7(8)

Machine_Code
   child of System   13.8(7)

Machine_Emax attribute   A.5.3(8)

Machine_Emin attribute   A.5.3(7)

Machine_Mantissa attribute   A.5.3(6)

Machine_Overflows attribute   A.5.3(12), A.5.4(4)

Machine_Radix attribute   A.5.3(2), A.5.4(2)

Machine_Radix clause   13.3(7), F.1(1)

Machine_Rounds attribute   A.5.3(11), A.5.4(3)

macro
   See generic unit   12(1)

Macron
   in Ada.Characters.Latin_1   A.3.3(21)

main subprogram
   for a partition   10.2(7)

malloc
   See allocator   4.8(1)

Maps
   child of Ada.Strings   A.4.2(3)

marshalling   E.4(9)

Masculine_Ordinal_Indicator
   in Ada.Characters.Latin_1   A.3.3(22)

master   7.6.1(3)

match
   a character to a pattern character   A.4.2(54)
   a character to a pattern character, with respect to a character mapping function
   A.4.2(64)
   a string to a pattern string   A.4.2(54)

matching components   4.5.2(16)

Max attribute   3.5(19)

Max_Base_Digits   3.5.7(6)
   in System   13.7(8)

Max_Binary_Modulus   3.5.4(7)
   in System   13.7(7)

Max_Decimal_Digits
   in Ada.Decimal   F.2(5)

Max_Delta
   in Ada.Decimal   F.2(4)

Max_Digits   3.5.7(6)
   in System   13.7(8)

Max_Digits_Binary
   in Interfaces.COBOL   B.4(11)

Max_Digits_Long_Binary
   in Interfaces.COBOL   B.4(11)

Max_Image_Width
   in Ada.Numerics.Discrete_Random   A.5.2(25)
   in Ada.Numerics.Float_Random   A.5.2(13)

Max_Int   3.5.4(14)
   in System   13.7(6)

Max_Length
   in Ada.Strings.Bounded   A.4.4(5)

Max_Mantissa
   in System   13.7(9)

Max_Nonbinary_Modulus   3.5.4(7)
   in System   13.7(7)

Max_Picture_Length
   in Ada.Text_IO.Editing   F.3.3(8)

Max_Scale
   in Ada.Decimal   F.2(3)

Max_Size_In_Storage_Elements attribute   13.11.1(3)

maximum box error
   for a component of the result of evaluating a complex function   G.2.6(3)

maximum line length   A.10(11)

maximum page length   A.10(11)

maximum relative error
   for a component of the result of evaluating a complex function   G.2.6(3)
   for the evaluation of an elementary function   G.2.4(2)

Membership
   in Ada.Strings   A.4.1(6)

membership test   4.5.2(2)

Memory_Size
   in System   13.7(13)

mentioned in a with_clause   10.1.2(6)

message
   See dispatching call   3.9.2(1)

method
   See dispatching subprogram   3.9.2(1)

metrics   1.1.2(35)

Micro_Sign
   in Ada.Characters.Latin_1   A.3.3(22)

Microseconds
   in Ada.Real_Time   D.8(14)

Middle_Dot
   in Ada.Characters.Latin_1   A.3.3(22)

Milliseconds
   in Ada.Real_Time   D.8(14)

Min attribute   3.5(16)

Min_Delta
   in Ada.Decimal   F.2(4)

Min_Int   3.5.4(14)
   in System   13.7(6)

Min_Scale
   in Ada.Decimal   F.2(3)

minus   2.1(15)

minus operator   4.4(1), 4.5.3(1), 4.5.4(1)

Minus_Sign
   in Ada.Characters.Latin_1   A.3.3(8)

mixed-language programs   B(1), C.1(4)

mod operator   4.4(1), 4.5.5(1)

mod_clause   J.8(1)
   used   13.5.1(2), P

mode   6.1(16)
   used   6.1(15), 12.4(2), P
   in Ada.Direct_IO   A.8.4(9)
   in Ada.Sequential_IO   A.8.1(9)
   in Ada.Streams.Stream_IO   A.12.1(11)
   in Ada.Text_IO   A.10.1(12)

mode conformance   6.3.1(16)
   required   8.5.4(4), 8.5.4(5/1), 12.5.4(5), 12.6(7), 12.6(8)

mode of operation
   nonstandard   1.1.5(11)
   standard   1.1.5(11)

Mode_Error
   in Ada.Direct_IO   A.8.4(18)
   in Ada.IO_Exceptions   A.13(4)
   in Ada.Sequential_IO   A.8.1(15)
   in Ada.Streams.Stream_IO   A.12.1(26)
   in Ada.Text_IO   A.10.1(85)

Model attribute   A.5.3(68)

model interval   G.2.1(4)
   associated with a value   G.2.1(4)

model number   G.2.1(3)

model-oriented attributes
   of a floating point subtype   A.5.3(63)

Model_Emin attribute   A.5.3(65)

Model_Epsilon attribute   A.5.3(66)

Model_Mantissa attribute   A.5.3(64)

Model_Small attribute   A.5.3(67)

modular type   3.5.4(1)

Modular_IO
   in Ada.Text_IO   A.10.1(57)

modular_type_definition   3.5.4(4)
   used   3.5.4(2), P

module
   See package   7(1)

modulus
   of a modular type   3.5.4(7)
   in Ada.Numerics.Generic_Complex_Types   G.1.1(9)

Modulus attribute   3.5.4(17)

Month
   in Ada.Calendar   9.6(13)

Month_Number
   in Ada.Calendar   9.6(11)

Move
   in Ada.Strings.Fixed   A.4.3(7)

multi-dimensional array   3.6(12)

Multiplication_Sign
   in Ada.Characters.Latin_1   A.3.3(24)

multiply   2.1(15)

multiply operator   4.4(1), 4.5.5(1)

multiplying operator   4.5.5(1)

multiplying_operator   4.5(6)
   used   4.4(5), P

MW
   in Ada.Characters.Latin_1   A.3.3(18)


N


n-dimensional array_aggregate   4.3.3(6)

NAK
   in Ada.Characters.Latin_1   A.3.3(6)

name   4.1(2)
   [partial]   3.1(1)
   of (a view of) an entity   3.1(8)
   of a pragma   2.8(9)
   of an external file   A.7(1)
   used   2.8(3), 3.2.2(4), 4.1(4), 4.1(5), 4.1(6), 4.4(7), 4.6(2), 5.2(2),
5.7(2), 5.8(2), 6.3.2(3), 6.4(2), 6.4(3), 6.4(6), 8.4(3), 8.5.1(2), 8.5.2(2),
8.5.3(2), 8.5.4(2), 8.5.5(2), 9.5.3(2), 9.5.4(2), 9.8(2), 10.1.1(8),
10.1.2(4), 10.2.1(3), 10.2.1(14), 10.2.1(20), 10.2.1(21), 10.2.1(22),
11.2(5), 11.3(2), 11.5(4), 12.3(2), 12.3(5), 12.6(4), 12.7(2), 13.1(3),
13.3(2), C.3.1(2), C.3.1(4), E.2.1(3), E.2.2(3), E.2.3(3), E.2.3(5),
H.3.2(3), L(2), L(6), L(10), L(11), L(12), L(15), L(16), L(17), L(26), L(28),
L(30), L(31), L(34), L(36), P
   in Ada.Direct_IO   A.8.4(9)
   in Ada.Sequential_IO   A.8.1(9)
   in Ada.Streams.Stream_IO   A.12.1(11)
   in Ada.Text_IO   A.10.1(12)
   in System   13.7(4)

name resolution rules   1.1.2(26)

Name_Error
   in Ada.Direct_IO   A.8.4(18)
   in Ada.IO_Exceptions   A.13(4)
   in Ada.Sequential_IO   A.8.1(15)
   in Ada.Streams.Stream_IO   A.12.1(26)
   in Ada.Text_IO   A.10.1(85)

named association   6.4(7), 12.3(6)

named component association   4.3.1(6)

named discriminant association   3.7.1(4)

named entry index   9.5.2(21)

named number   3.3(24)

named type   3.2.1(7)

named_array_aggregate   4.3.3(4)
   used   4.3.3(2), P

Names
   child of Ada.Interrupts   C.3.2(12)

names of special_characters   2.1(15)

Nanoseconds
   in Ada.Real_Time   D.8(14)

Native_Binary
   in Interfaces.COBOL   B.4(25)

Natural   3.5.4(12)
   in Standard   A.1(13)

NBH
   in Ada.Characters.Latin_1   A.3.3(17)

NBSP
   in Ada.Characters.Latin_1   A.3.3(21)

needed
   of a compilation unit by another   10.2(2)
   remote call interface   E.2.3(18)
   shared passive library unit   E.2.1(11)

needed component
   extension_aggregate record_component_association_list   4.3.2(6)
   record_aggregate record_component_association_list   4.3.1(9)

NEL
   in Ada.Characters.Latin_1   A.3.3(17)

new
   See allocator   4.8(1)

New_Char_Array
   in Interfaces.C.Strings   B.3.1(9)

New_Line
   in Ada.Text_IO   A.10.1(28)

New_Page
   in Ada.Text_IO   A.10.1(31)

New_String
   in Interfaces.C.Strings   B.3.1(10)

No_Break_Space
   in Ada.Characters.Latin_1   A.3.3(21)

nominal subtype   3.3(23), 3.3.1(8)
   associated with a dereference   4.1(9)
   associated with a type_conversion   4.6(27)
   associated with an indexed_component   4.1.1(5)
   of a component   3.6(20)
   of a formal parameter   6.1(23)
   of a generic formal object   12.4(9)
   of a record component   3.8(14)
   of the result of a function_call   6.4(12)

non-normative
   See informative   1.1.2(18)

nondispatching call
   on a dispatching operation   3.9.2(1)

nonexistent   13.11.2(10), 13.11.2(16)

nongraphic character   3.5(32)

nonlimited type   7.5(7)
   becoming nonlimited   7.3.1(5/1), 7.5(16)

nonstandard integer type   3.5.4(26)

nonstandard mode   1.1.5(11)

nonstandard real type   3.5.6(8)

normal completion   7.6.1(2)

normal library unit   E.2(4/1)

normal state of an object   11.6(6), 13.9.1(4)
   [partial]   9.8(21), A.13(17)

normalized exponent   A.5.3(14)

normalized number   A.5.3(10)

normative   1.1.2(14)

not equal operator   4.4(1), 4.5.2(1)

not in (membership test)   4.4(1), 4.5.2(2)

not operator   4.4(1), 4.5.6(3)

Not_Sign
   in Ada.Characters.Latin_1   A.3.3(21)

notes   1.1.2(38)

notwithstanding   10.1.6(2), B.1(22), B.1(38), C.3.1(19), E.2.1(8),
E.2.1(11), E.2.3(18), J.3(6)

NUL
   in Ada.Characters.Latin_1   A.3.3(5)
   in Interfaces.C   B.3(20/1)

null access value   4.2(9)

null array   3.6.1(7)

null constraint   3.2(7)

null pointer
   See null access value   4.2(9)

null range   3.5(4)

null record   3.8(15)

null slice   4.1.2(7)

null string literal   2.6(6)

null value
   of an access type   3.10(13)

Null_Address
   in System   13.7(12)

Null_Bounded_String
   in Ada.Strings.Bounded   A.4.4(7)

Null_Id
   in Ada.Exceptions   11.4.1(2)

Null_Occurrence
   in Ada.Exceptions   11.4.1(3)

Null_Ptr
   in Interfaces.C.Strings   B.3.1(7)

Null_Set
   in Ada.Strings.Maps   A.4.2(5)
   in Ada.Strings.Wide_Maps   A.4.7(5)

null_statement   5.1(6)
   used   5.1(4), P

Null_Task_ID
   in Ada.Task_Identification   C.7.1(2)

Null_Unbounded_String
   in Ada.Strings.Unbounded   A.4.5(5)

number sign   2.1(15)

Number_Base
   in Ada.Text_IO   A.10.1(6)

number_declaration   3.3.2(2)
   used   3.1(3), P

Number_Sign
   in Ada.Characters.Latin_1   A.3.3(8)

numeral   2.4.1(3)
   used   2.4.1(2), 2.4.1(4), 2.4.2(3), P

Numeric
   in Interfaces.COBOL   B.4(20)

numeric type   3.5(1)

numeric_literal   2.4(2)
   used   4.4(7), P

numerics   G(1)
   child of Ada   A.5(3)


O


object   3.3(2)
   [partial]   3.2(1)

object-oriented programming (OOP)
   See dispatching operations of tagged types   3.9.2(1)
   See tagged types and type extensions   3.9(1)

object_declaration   3.3.1(2)
   used   3.1(3), P

object_renaming_declaration   8.5.1(2)
   used   8.5(2), P

obsolescent feature   J(1)

occur immediately within   8.1(13)

occurrence
   of an interrupt   C.3(2)

octal
   literal   2.4.2(1)

octal literal   2.4.2(1)

one's complement
   modular types   3.5.4(27)

one-dimensional array   3.6(12)

only as a completion
   entry_body   9.5.2(16)

OOP (object-oriented programming)
   See dispatching operations of tagged types   3.9.2(1)
   See tagged types and type extensions   3.9(1)

opaque type
   See private types and private extensions   7.3(1)

Open
   in Ada.Direct_IO   A.8.4(7)
   in Ada.Sequential_IO   A.8.1(7)
   in Ada.Streams.Stream_IO   A.12.1(9)
   in Ada.Text_IO   A.10.1(10)

open alternative   9.7.1(14)

open entry   9.5.3(5)
   of a protected object   9.5.3(7)
   of a task   9.5.3(6)

operand
   of a qualified_expression   4.7(3)
   of a type_conversion   4.6(3)

operand interval   G.2.1(6)

operand type
   of a type_conversion   4.6(3)

operates on a type   3.2.3(1)

operational aspect   13.1(8.1/1)
   specifiable attributes   13.3(5/1)

operational item   13.1(1.1/1)

operator   6.6(1)
   &   4.4(1), 4.5.3(3)
   *   4.4(1), 4.5.5(1)
   **   4.4(1), 4.5.6(7)
   +   4.4(1), 4.5.3(1), 4.5.4(1)
   -   4.4(1), 4.5.3(1), 4.5.4(1)
   /   4.4(1), 4.5.5(1)
   /=   4.4(1), 4.5.2(1)
   <   4.4(1), 4.5.2(1)
   <=   4.4(1), 4.5.2(1)
   =   4.4(1), 4.5.2(1)
   >   4.4(1), 4.5.2(1)
   >=   4.4(1), 4.5.2(1)
   abs   4.4(1), 4.5.6(1)
   ampersand   4.4(1), 4.5.3(3)
   and   4.4(1), 4.5.1(2)
   binary   4.5(9)
   binary adding   4.5.3(1)
   concatenation   4.4(1), 4.5.3(3)
   divide   4.4(1), 4.5.5(1)
   equal   4.4(1), 4.5.2(1)
   equality   4.5.2(1)
   exponentiation   4.4(1), 4.5.6(7)
   greater than   4.4(1), 4.5.2(1)
   greater than or equal   4.4(1), 4.5.2(1)
   highest precedence   4.5.6(1)
   less than   4.4(1), 4.5.2(1)
   less than or equal   4.4(1), 4.5.2(1)
   logical   4.5.1(2)
   minus   4.4(1), 4.5.3(1), 4.5.4(1)
   mod   4.4(1), 4.5.5(1)
   multiply   4.4(1), 4.5.5(1)
   multiplying   4.5.5(1)
   not   4.4(1), 4.5.6(3)
   not equal   4.4(1), 4.5.2(1)
   or   4.4(1), 4.5.1(2)
   ordering   4.5.2(1)
   plus   4.4(1), 4.5.3(1), 4.5.4(1)
   predefined   4.5(9)
   relational   4.5.2(1)
   rem   4.4(1), 4.5.5(1)
   times   4.4(1), 4.5.5(1)
   unary   4.5(9)
   unary adding   4.5.4(1)
   user-defined   6.6(1)
   xor   4.4(1), 4.5.1(2)

operator precedence   4.5(1)

operator_symbol   6.1(9)
   used   4.1(3), 4.1.3(3), 6.1(5), 6.1(11), P

optimization   11.5(29), 11.6(1)

or else (short-circuit control form)   4.4(1), 4.5.1(1)

or operator   4.4(1), 4.5.1(2)

ordering operator   4.5.2(1)

ordinary fixed point type   3.5.9(1), 3.5.9(8)

ordinary_fixed_point_definition   3.5.9(3)
   used   3.5.9(2), P

OSC
   in Ada.Characters.Latin_1   A.3.3(19)

other_control_function   2.1(14)
   used   2.1(2), P

output   A.6(1)

Output attribute   13.13.2(19), 13.13.2(29)

Output clause   13.3(7), 13.13.2(36/1)

overall interpretation
   of a complete context   8.6(10)

Overflow_Check   11.5(16)
   [partial]   3.5.4(20), 4.4(11), 5.4(13), G.2.1(11), G.2.2(7), G.2.3(25),
G.2.4(2), G.2.6(3)

overload resolution   8.6(1)

overloadable   8.3(7)

overloaded   8.3(6)
   enumeration literal   3.5.1(9)

overloading rules   1.1.2(26), 8.6(2)

overridable   8.3(9/1)

override   8.3(9/1), 12.3(17)
   a primitive subprogram   3.2.3(7)

Overwrite
   in Ada.Strings.Bounded   A.4.4(62), A.4.4(63)
   in Ada.Strings.Fixed   A.4.3(27), A.4.3(28)
   in Ada.Strings.Unbounded   A.4.5(57), A.4.5(58)


P


Package   7(1)

package instance   12.3(13)

package_body   7.2(2)
   used   3.11(6), 10.1.1(7), P

package_body_stub   10.1.3(4)
   used   10.1.3(2), P

package_declaration   7.1(2)
   used   3.1(3), 10.1.1(5), P

package_renaming_declaration   8.5.3(2)
   used   8.5(2), 10.1.1(6), P

package_specification   7.1(3)
   used   7.1(2), 12.1(4), P

packed   13.2(5)

Packed_Decimal
   in Interfaces.COBOL   B.4(12)

Packed_Format
   in Interfaces.COBOL   B.4(26)

Packed_Signed
   in Interfaces.COBOL   B.4(27)

Packed_Unsigned
   in Interfaces.COBOL   B.4(27)

packing
   aspect of representation   13.2(5)

padding bits   13.1(7)

Page
   in Ada.Text_IO   A.10.1(39)

page terminator   A.10(7)

Page_Length
   in Ada.Text_IO   A.10.1(26)

Paragraph_Sign
   in Ada.Characters.Latin_1   A.3.3(22)

parallel processing
   See task   9(1)

parameter
   See formal parameter   6.1(17)
   See generic formal parameter   12(1)
   See also discriminant   3.7(1)
   See also loop parameter   5.5(6)

parameter assigning back   6.4.1(17)

parameter copy back   6.4.1(17)

parameter mode   6.1(18)

parameter passing   6.4.1(1)

parameter_and_result_profile   6.1(13)
   used   3.10(5), 6.1(4), P

parameter_association   6.4(5)
   used   6.4(4), P

parameter_profile   6.1(12)
   used   3.10(5), 6.1(4), 9.5.2(2), 9.5.2(3), 9.5.2(6), P

parameter_specification   6.1(15)
   used   6.1(14), P

Parameterless_Handler
   in Ada.Interrupts   C.3.2(2)

Params_Stream_Type
   in System.RPC   E.5(6)

parent body
   of a subunit   10.1.3(8)

parent declaration
   of a library unit   10.1.1(10)
   of a library_item   10.1.1(10)

parent subtype   3.4(3)

parent type   3.4(3)

parent unit
   of a library unit   10.1.1(10)

parent_unit_name   10.1.1(8)
   used   6.1(5), 6.1(7), 7.1(3), 7.2(2), 10.1.3(7), P

part
   of an object or value   3.2(6)

partial view
   of a type   7.3(4)

partition   10.2(2)

partition building   10.2(2)

partition communication subsystem (PCS)   E.5(1)

Partition_Check
   [partial]   E.4(19)

Partition_ID
   in System.RPC   E.5(4)

Partition_ID attribute   E.1(9)

pass by copy   6.2(2)

pass by reference   6.2(2)

passive partition   E.1(2)

Pattern_Error
   in Ada.Strings   A.4.1(5)

PCS (partition communication subsystem)   E.5(1)

pending interrupt occurrence   C.3(2)

per-object constraint   3.8(18/1)

per-object expression   3.8(18/1)

Percent_Sign
   in Ada.Characters.Latin_1   A.3.3(8)

perfect result set   G.2.3(5)

periodic task
   example   9.6(39)
   See delay_until_statement   9.6(39)

Pi
   in Ada.Numerics   A.5(3)

Pic_String
   in Ada.Text_IO.Editing   F.3.3(7)

Picture
   in Ada.Text_IO.Editing   F.3.3(4)

picture String
   for edited output   F.3.1(1)

Picture_Error
   in Ada.Text_IO.Editing   F.3.3(9)

Pilcrow_Sign
   in Ada.Characters.Latin_1   A.3.3(22)

plain_char
   in Interfaces.C   B.3(11)

PLD
   in Ada.Characters.Latin_1   A.3.3(17)

PLU
   in Ada.Characters.Latin_1   A.3.3(17)

plus operator   4.4(1), 4.5.3(1), 4.5.4(1)

plus sign   2.1(15)

Plus_Minus_Sign
   in Ada.Characters.Latin_1   A.3.3(22)

Plus_Sign
   in Ada.Characters.Latin_1   A.3.3(8)

PM
   in Ada.Characters.Latin_1   A.3.3(19)

point   2.1(15)

Pointer
   in Interfaces.C.Pointers   B.3.2(5)
   See access value   3.10(1)
   See type System.Address   13.7(34)

pointer type
   See access type   3.10(1)

Pointer_Error
   in Interfaces.C.Pointers   B.3.2(8)

Pointers
   child of Interfaces.C   B.3.2(4)

polymorphism   3.9(1), 3.9.2(1)

pool element   3.10(7/1), 13.11(11)

pool type   13.11(11)

pool-specific access type   3.10(7/1), 3.10(8)

Pos attribute   3.5.5(2)

position   13.5.1(4)
   used   13.5.1(3), P

Position attribute   13.5.2(2)

position number   3.5(1)
   of an enumeration value   3.5.1(7)
   of an integer value   3.5.4(15)

positional association   6.4(7), 12.3(6)

positional component association   4.3.1(6)

positional discriminant association   3.7.1(4)

positional_array_aggregate   4.3.3(3)
   used   4.3.3(2), P

Positive   3.5.4(12)
   in Standard   A.1(13)

Positive_Count
   in Ada.Direct_IO   A.8.4(4)
   in Ada.Streams.Stream_IO   A.12.1(7)
   in Ada.Text_IO   A.10.1(5)

possible interpretation   8.6(14)
   for direct_names   8.3(24)
   for selector_names   8.3(24)

post-compilation error   1.1.2(29)

post-compilation rules   1.1.2(29)

potentially blocking operation   9.5.1(8)
   Abort_Task   C.7.1(16)
   delay_statement   9.6(34), D.9(5)
   remote subprogram call   E.4(17)
   RPC operations   E.5(23)
   Suspend_Until_True   D.10(10)

potentially use-visible   8.4(8)

Pound_Sign
   in Ada.Characters.Latin_1   A.3.3(21)

Pragma   2.8(1), 2.8(2), L(1)

pragma argument   2.8(9)

pragma name   2.8(9)

pragma, categorization   E.2(2)
   Remote_Call_Interface   E.2.3(2)
   Remote_Types   E.2.2(2)
   Shared_Passive   E.2.1(2)

pragma, configuration   10.1.5(8)
   Locking_Policy   D.3(5)
   Normalize_Scalars   H.1(4)
   Queuing_Policy   D.4(5)
   Restrictions   13.12(8)
   Reviewable   H.3.1(4)
   Suppress   11.5(5)
   Task_Dispatching_Policy   D.2.2(4)

pragma, identifier specific to   2.8(10)

pragma, interfacing
   Convention   B.1(4)
   Export   B.1(4)
   Import   B.1(4)
   Linker_Options   B.1(4)

pragma, library unit   10.1.5(7)
   All_Calls_Remote   E.2.3(6)
   categorization pragmas   E.2(2)
   Elaborate_Body   10.2.1(24)
   Preelaborate   10.2.1(4)
   Pure   10.2.1(15)

pragma, program unit   10.1.5(2)
   Convention   B.1(29)
   Export   B.1(29)
   Import   B.1(29)
   Inline   6.3.2(2)
   library unit pragmas   10.1.5(7)

pragma, representation   13.1(1/1)
   Asynchronous   E.4.1(8)
   Atomic   C.6(14)
   Atomic_Components   C.6(14)
   Controlled   13.11.3(5)
   Convention   B.1(28)
   Discard_Names   C.5(6)
   Export   B.1(28)
   Import   B.1(28)
   Pack   13.2(5)
   Volatile   C.6(14)
   Volatile_Components   C.6(14)

pragma_argument_association   2.8(3)
   used   2.8(2), P

pragmas
   All_Calls_Remote   E.2.3(5), L(2)
   Asynchronous   E.4.1(3), L(3)
   Atomic   C.6(3), L(4)
   Atomic_Components   C.6(5), L(5)
   Attach_Handler   C.3.1(4), L(6)
   Controlled   13.11.3(3), L(7)
   Convention   B.1(7), L(8)
   Discard_Names   C.5(3), L(9)
   Elaborate   10.2.1(20), L(10)
   Elaborate_All   10.2.1(21), L(11)
   Elaborate_Body   10.2.1(22), L(12)
   Export   B.1(6), L(13)
   Import   B.1(5), L(14)
   Inline   6.3.2(3), L(15)
   Inspection_Point   H.3.2(3), L(16)
   Interrupt_Handler   C.3.1(2), L(17)
   Interrupt_Priority   D.1(5), L(18)
   Linker_Options   B.1(8), L(19)
   List   2.8(21), L(20)
   Locking_Policy   D.3(3), L(21)
   Normalize_Scalars   H.1(3), L(22)
   Optimize   2.8(23), L(23)
   Pack   13.2(3), L(24)
   Page   2.8(22), L(25)
   Preelaborate   10.2.1(3), L(26)
   Priority   D.1(3), L(27)
   Pure   10.2.1(14), L(28)
   Queuing_Policy   D.4(3), L(29)
   Remote_Call_Interface   E.2.3(3), L(30)
   Remote_Types   E.2.2(3), L(31)
   Restrictions   13.12(3), L(32)
   Reviewable   H.3.1(3), L(33)
   Shared_Passive   E.2.1(3), L(34)
   Storage_Size   13.3(63), L(35)
   Suppress   11.5(4), L(36)
   Task_Dispatching_Policy   D.2.2(2), L(37)
   Volatile   C.6(4), L(38)
   Volatile_Components   C.6(6), L(39)

precedence of operators   4.5(1)

Pred attribute   3.5(25)

predefined environment   A(1)

predefined exception   11.1(4)

predefined library unit
   See language-defined library units

predefined operation
   of a type   3.2.3(1)

predefined operations
   of a discrete type   3.5.5(10)
   of a fixed point type   3.5.10(17)
   of a floating point type   3.5.8(3)
   of a record type   3.8(24)
   of an access type   3.10.2(34)
   of an array type   3.6.2(15)

predefined operator   4.5(9)
   [partial]   3.2.1(9)

predefined type   3.2.1(10)
   See language-defined types

preelaborable
   of an elaborable construct   10.2.1(5)

preelaborated   10.2.1(11/1)
   [partial]   10.2.1(11/1), E.2.1(9)

preempted task   D.2.1(7)

preemptible resource   D.2.1(7)

preference
   for root numeric operators and ranges   8.6(29)

preference control
   See requeue   9.5.4(1)

prefix   4.1(4)
   used   4.1.1(2), 4.1.2(2), 4.1.3(2), 4.1.4(2), 4.1.4(4), 6.4(2), 6.4(3),
P

prescribed result
   for the evaluation of a complex arithmetic operation   G.1.1(42)
   for the evaluation of a complex elementary function   G.1.2(35)
   for the evaluation of an elementary function   A.5.1(37)

primary   4.4(7)
   used   4.4(6), P

primitive function   A.5.3(17)

primitive operation
   [partial]   3.2(1)

primitive operations
   of a type   3.2.3(1)

primitive operator
   of a type   3.2.3(8)

primitive subprograms
   of a type   3.2.3(2)

priority   D.1(15)
   in System   13.7(16)

priority inheritance   D.1(15)

priority inversion   D.2.2(14)

priority of an entry call   D.4(9)

private declaration of a library unit   10.1.1(12)

private descendant
   of a library unit   10.1.1(12)

private extension   3.2(4), 3.9(2), 3.9.1(1)
   [partial]   7.3(14)

private library unit   10.1.1(12)

private operations   7.3.1(1)

private part   8.2(5)
   of a package   7.1(6)
   of a protected unit   9.4(11)
   of a task unit   9.1(9)

private type   3.2(4)
   [partial]   7.3(14)

private types and private extensions   7.3(1)

private_extension_declaration   7.3(3)
   used   3.2.1(2), P

private_type_declaration   7.3(2)
   used   3.2.1(2), P

procedure   6(1)

procedure instance   12.3(13)

procedure_call_statement   6.4(2)
   used   5.1(4), P

processing node   E(2)

profile   6.1(22)
   associated with a dereference   4.1(10)
   fully conformant   6.3.1(18)
   mode conformant   6.3.1(16)
   subtype conformant   6.3.1(17)
   type conformant   6.3.1(15)

profile resolution rule
   name with a given expected profile   8.6(26)

program   10.2(1)

program execution   10.2(1)

program library
   See library   10(2)
   See library   10.1.4(9)

Program unit   10.1(1)

program unit pragma   10.1.5(2)
   Convention   B.1(29)
   Export   B.1(29)
   Import   B.1(29)
   Inline   6.3.2(2)
   library unit pragmas   10.1.5(7)

Program_Error
   raised by failure of run-time check   1.1.3(20), 1.1.5(8), 1.1.5(12),
3.5.5(8), 3.10.2(29), 3.11(14), 4.6(57), 6.2(12), 6.4(11), 6.5(20),
7.6.1(15), 7.6.1(16/1), 7.6.1(17), 7.6.1(17.1/1), 7.6.1(17.2/1), 7.6.1(18),
8.5.4(8.1/1), 9.4(20), 9.5.1(17), 9.5.3(7), 9.7.1(21), 9.8(20), 10.2(26),
11.1(4), 11.5(19), 13.7.1(16), 13.9.1(9), 13.11.2(13), 13.11.2(14),
A.5.2(40.1/1), A.7(14), C.3.1(10), C.3.1(11), C.3.2(17), C.3.2(20),
C.3.2(21), C.3.2(22), C.7.1(15), C.7.1(17), C.7.2(13), D.3(13), D.5(9),
D.5(11), D.10(10), D.11(8), E.1(10), E.3(6), E.4(18/1), J.7.1(7)
   in Standard   A.1(46)

propagate   11.4(1)
   an exception occurrence by an execution, to a dynamically enclosing execution
   11.4(6)

proper_body   3.11(6)
   used   3.11(5), 10.1.3(7), P

protected action   9.5.1(4)
   complete   9.5.1(6)
   start   9.5.1(5)

protected calling convention   6.3.1(12)

protected declaration   9.4(1)

protected entry   9.4(1)

protected function   9.5.1(1)

protected object   9(3), 9.4(1)

protected operation   9.4(1)

protected procedure   9.5.1(1)

protected subprogram   9.4(1), 9.5.1(1)

protected unit   9.4(1)

protected_body   9.4(7)
   used   3.11(6), P

protected_body_stub   10.1.3(6)
   used   10.1.3(2), P

protected_definition   9.4(4)
   used   9.4(2), 9.4(3), P

protected_element_declaration   9.4(6)
   used   9.4(4), P

protected_operation_declaration   9.4(5/1)
   used   9.4(4), 9.4(6), P

protected_operation_item   9.4(8/1)
   used   9.4(7), P

protected_type_declaration   9.4(2)
   used   3.2.1(3), P

ptrdiff_t
   in Interfaces.C   B.3(12)

PU1
   in Ada.Characters.Latin_1   A.3.3(18)

PU2
   in Ada.Characters.Latin_1   A.3.3(18)

public declaration of a library unit   10.1.1(12)

public descendant
   of a library unit   10.1.1(12)

public library unit   10.1.1(12)

pure   10.2.1(16)

Put
   in Ada.Text_IO   A.10.1(42), A.10.1(48), A.10.1(55), A.10.1(60),
A.10.1(66), A.10.1(67), A.10.1(71), A.10.1(72), A.10.1(76), A.10.1(77),
A.10.1(82), A.10.1(83)
   in Ada.Text_IO.Complex_IO   G.1.3(7), G.1.3(8)
   in Ada.Text_IO.Editing   F.3.3(14), F.3.3(15), F.3.3(16)

Put_Line
   in Ada.Text_IO   A.10.1(50)


Q


qualified_expression   4.7(2)
   used   4.4(7), 4.8(2), 13.8(2), P

Question
   in Ada.Characters.Latin_1   A.3.3(10)

queuing policy   D.4(1/1), D.4(6)

Quotation
   in Ada.Characters.Latin_1   A.3.3(8)

quotation mark   2.1(15)

quoted string
   See string_literal   2.6(1)


R


raise
   an exception   11(1)
   an exception   11.3(4)
   an exception   N(18)
   an exception occurrence   11.4(3)

Raise_Exception
   in Ada.Exceptions   11.4.1(4)

raise_statement   11.3(2)
   used   5.1(4), P

Random
   in Ada.Numerics.Discrete_Random   A.5.2(20)
   in Ada.Numerics.Float_Random   A.5.2(8)

random number   A.5.2(1)

range   3.5(3), 3.5(4)
   of a scalar subtype   3.5(7)
   used   3.5(2), 3.6(6), 3.6.1(3), 4.4(3), P

Range attribute   3.5(14), 3.6.2(7)

Range(N) attribute   3.6.2(8)

range_attribute_designator   4.1.4(5)
   used   4.1.4(4), P

range_attribute_reference   4.1.4(4)
   used   3.5(3), P

Range_Check   11.5(17)
   [partial]   3.2.2(11), 3.5(24), 3.5(27), 3.5(43), 3.5(44), 3.5(51),
3.5(55), 3.5.5(7), 3.5.9(19), 4.2(11), 4.3.3(28), 4.5.1(8), 4.5.6(6),
4.5.6(13), 4.6(28), 4.6(38), 4.6(46), 4.6(51), 4.7(4), 13.13.2(35),
A.5.2(39), A.5.2(40/1), A.5.3(26), A.5.3(29), A.5.3(50), A.5.3(53),
A.5.3(59), A.5.3(62), K(11), K(114), K(122), K(184), K(220), K(241), K(41),
K(47)

range_constraint   3.5(2)
   used   3.2.2(6), 3.5.9(5), J.3(2), P

RCI
   generic   E.2.3(7/1)
   library unit   E.2.3(7/1)
   package   E.2.3(7/1)

Re
   in Ada.Numerics.Generic_Complex_Types   G.1.1(6)

re-raise statement   11.3(3)

read
   the value of an object   3.3(14)
   in Ada.Direct_IO   A.8.4(12)
   in Ada.Sequential_IO   A.8.1(12)
   in Ada.Storage_IO   A.9(6)
   in Ada.Streams   13.13.1(5)
   in Ada.Streams.Stream_IO   A.12.1(15), A.12.1(16)
   in System.RPC   E.5(7)

Read attribute   13.13.2(6), 13.13.2(14)

Read clause   13.3(7), 13.13.2(36/1)

ready
   a task state   9(10)

ready queue   D.2.1(5)

ready task   D.2.1(5)

Real
   in Interfaces.Fortran   B.5(6)

real literal   2.4(1)

real literals   3.5.6(4)

real time   D.8(18)

real type   3.2(3), 3.5.6(1)

real-time systems   C(1), D(1)

real_range_specification   3.5.7(3)
   used   3.5.7(2), 3.5.9(3), 3.5.9(4), P

Real_Time
   child of Ada   D.8(3)

real_type_definition   3.5.6(2)
   used   3.2.1(4), P

receiving stub   E.4(10)

reclamation of storage   13.11.2(1)

recommended level of support   13.1(20)
   Address attribute   13.3(15)
   Alignment attribute for objects   13.3(33)
   Alignment attribute for subtypes   13.3(29)
   bit ordering   13.5.3(7)
   Component_Size attribute   13.3(71)
   enumeration_representation_clause   13.4(9)
   pragma Pack   13.2(7)
   record_representation_clause   13.5.1(17)
   required in Systems Programming Annex   C.2(2)
   Size attribute   13.3(42), 13.3(54)
   unchecked conversion   13.9(16)
   with respect to nonstatic expressions   13.1(21)

record   3.8(1)

record extension   3.4(5), 3.9.1(1)

record layout
   aspect of representation   13.5(1)

record type   3.8(1)

record_aggregate   4.3.1(2)
   used   4.3(2), P

record_component_association   4.3.1(4)
   used   4.3.1(3), P

record_component_association_list   4.3.1(3)
   used   4.3.1(2), 4.3.2(2), P

record_definition   3.8(3)
   used   3.8(2), 3.9.1(2), P

record_extension_part   3.9.1(2)
   used   3.4(2), P

record_representation_clause   13.5.1(2)
   used   13.1(2/1), P

record_type_definition   3.8(2)
   used   3.2.1(4), P

Reference
   in Ada.Interrupts   C.3.2(10)
   in Ada.Task_Attributes   C.7.2(5)

reference parameter passing   6.2(2)

references   1.2(1)

Registered_Trade_Mark_Sign
   in Ada.Characters.Latin_1   A.3.3(21)

Reinitialize
   in Ada.Task_Attributes   C.7.2(6)

relation   4.4(3)
   used   4.4(2), P

relational operator   4.5.2(1)

relational_operator   4.5(3)
   used   4.4(3), P

relaxed mode   G.2(1)

release
   execution resource associated with protected object   9.5.1(6)

rem operator   4.4(1), 4.5.5(1)

Remainder attribute   A.5.3(45)

remote access   E.1(5)

remote access type   E.2.2(9/1)

remote access-to-class-wide type   E.2.2(9/1)

remote access-to-subprogram type   E.2.2(9/1)

remote call interface   E.2(4/1), E.2.3(7/1)

remote procedure call
   asynchronous   E.4.1(9)

remote subprogram   E.2.3(7/1)

remote subprogram binding   E.4(1)

remote subprogram call   E.4(1)

remote types library unit   E.2(4/1), E.2.2(4)

renamed entity   8.5(3)

renamed view   8.5(3)

renaming-as-body   8.5.4(1)

renaming-as-declaration   8.5.4(1)

renaming_declaration   8.5(2)
   used   3.1(3), P

rendezvous   9.5.2(25)

Replace_Element
   in Ada.Strings.Bounded   A.4.4(27)
   in Ada.Strings.Unbounded   A.4.5(21)

Replace_Slice
   in Ada.Strings.Bounded   A.4.4(58), A.4.4(59)
   in Ada.Strings.Fixed   A.4.3(23), A.4.3(24)
   in Ada.Strings.Unbounded   A.4.5(53), A.4.5(54)

Replicate
   in Ada.Strings.Bounded   A.4.4(78), A.4.4(79), A.4.4(80)

representation
   change of   13.6(1)

representation aspect   13.1(8)

representation attribute   13.3(1/1)

representation item   13.1(1/1)

representation of an object   13.1(7)

representation pragma   13.1(1/1)
   Asynchronous   E.4.1(8)
   Atomic   C.6(14)
   Atomic_Components   C.6(14)
   Controlled   13.11.3(5)
   Convention   B.1(28)
   Discard_Names   C.5(6)
   Export   B.1(28)
   Import   B.1(28)
   Pack   13.2(5)
   Volatile   C.6(14)
   Volatile_Components   C.6(14)

representation-oriented attributes
   of a fixed point subtype   A.5.4(1)
   of a floating point subtype   A.5.3(1)

representation_clause
   used   3.8(5/1), 3.11(4/1), 9.1(5/1), 9.4(5/1), 9.4(8/1), P
   See aspect_clause   13.1(4/1)

represented in canonical form   A.5.3(10)

requested decimal precision
   of a floating point type   3.5.7(4)

requeue   9.5.4(1)

requeue-with-abort   9.5.4(13)

requeue_statement   9.5.4(2)
   used   5.1(4), P

requires a completion   3.11.1(1/1), 3.11.1(6)
   declaration of a partial view   7.3(4)
   declaration to which a pragma Elaborate_Body applies   10.2.1(25)
   deferred constant declaration   7.4(2)
   generic_package_declaration   7.1(5)
   generic_subprogram_declaration   6.1(20)
   incomplete_type_declaration   3.10.1(3)
   package_declaration   7.1(5)
   protected entry_declaration   9.5.2(16)
   protected_declaration}   9.4(10)
   subprogram_declaration   6.1(20)
   task_declaration}   9.1(8)

Reraise_Occurrence
   in Ada.Exceptions   11.4.1(4)

reserved interrupt   C.3(2)

reserved word   2.9(2)

Reserved_128
   in Ada.Characters.Latin_1   A.3.3(17)

Reserved_129
   in Ada.Characters.Latin_1   A.3.3(17)

Reserved_132
   in Ada.Characters.Latin_1   A.3.3(17)

Reserved_153
   in Ada.Characters.Latin_1   A.3.3(19)

Reserved_Check
   [partial]   C.3.1(10)

Reset
   in Ada.Direct_IO   A.8.4(8)
   in Ada.Numerics.Discrete_Random   A.5.2(21), A.5.2(24)
   in Ada.Numerics.Float_Random   A.5.2(9), A.5.2(12)
   in Ada.Sequential_IO   A.8.1(8)
   in Ada.Streams.Stream_IO   A.12.1(10)
   in Ada.Text_IO   A.10.1(11)

resolution rules   1.1.2(26)

resolve
   overload resolution   8.6(14)

restriction   13.12(4)
   used   13.12(3), L(32)

Restrictions
   Immediate_Reclamation   H.4(10)
   Max_Asynchronous_Select_Nesting   D.7(18/1)
   Max_Protected_Entries   D.7(14)
   Max_Select_Alternatives   D.7(12)
   Max_Storage_At_Blocking   D.7(17/1)
   Max_Task_Entries   D.7(13)
   Max_Tasks   D.7(19/1)
   No_Abort_Statements   D.7(5)
   No_Access_Subprograms   H.4(17)
   No_Allocators   H.4(7)
   No_Asynchronous_Control   D.7(10)
   No_Delay   H.4(21)
   No_Dispatch   H.4(19)
   No_Dynamic_Priorities   D.7(9)
   No_Exceptions   H.4(12)
   No_Fixed_Point   H.4(15)
   No_Floating_Point   H.4(14)
   No_Implicit_Heap_Allocations   D.7(8)
   No_IO   H.4(20)
   No_Local_Allocators   H.4(8/1)
   No_Nested_Finalization   D.7(4/1)
   No_Protected_Types   H.4(5)
   No_Recursion   H.4(22)
   No_Reentrancy   H.4(23)
   No_Task_Allocators   D.7(7)
   No_Task_Hierarchy   D.7(3)
   No_Terminate_Alternatives   D.7(6)
   No_Unchecked_Access   H.4(18)
   No_Unchecked_Conversion   H.4(16)
   No_Unchecked_Deallocation   H.4(9)

result interval
   for a component of the result of evaluating a complex function   G.2.6(3)
   for the evaluation of a predefined arithmetic operation   G.2.1(8)
   for the evaluation of an elementary function   G.2.4(2)

result subtype
   of a function   6.5(3)

return expression   6.5(3)

return-by-reference type   6.5(11)

return_statement   6.5(2)
   used   5.1(4), P

Reverse_Solidus
   in Ada.Characters.Latin_1   A.3.3(12)

RI
   in Ada.Characters.Latin_1   A.3.3(17)

right curly bracket   2.1(15)

right parenthesis   2.1(15)

right square bracket   2.1(15)

Right_Angle_Quotation
   in Ada.Characters.Latin_1   A.3.3(22)

Right_Curly_Bracket
   in Ada.Characters.Latin_1   A.3.3(14)

Right_Parenthesis
   in Ada.Characters.Latin_1   A.3.3(8)

Right_Square_Bracket
   in Ada.Characters.Latin_1   A.3.3(12)

Ring_Above
   in Ada.Characters.Latin_1   A.3.3(22)

root library unit   10.1.1(10)

root type
   of a class   3.4.1(2)

root_integer   3.5.4(14)
   [partial]   3.4.1(8)

root_real   3.5.6(3)
   [partial]   3.4.1(8)

Root_Storage_Pool
   in System.Storage_Pools   13.11(6)

Root_Stream_Type
   in Ada.Streams   13.13.1(3)

rooted at a type   3.4.1(2)

rotate   B.2(9)

Round attribute   3.5.10(12)

Rounding attribute   A.5.3(36)

RPC
   child of System   E.5(3)

RPC-receiver   E.5(21)

RPC_Receiver
   in System.RPC   E.5(11)

RS
   in Ada.Characters.Latin_1   A.3.3(6)

run-time check
   See language-defined check   11.5(2)

run-time error   1.1.2(30), 1.1.5(6), 11.5(2), 11.6(1)

run-time polymorphism   3.9.2(1)

run-time semantics   1.1.2(30)

run-time type
   See tag   3.9(3)

running a program
   See program execution   10.2(1)

running task   D.2.1(6)


S


safe range
   of a floating point type   3.5.7(9)
   of a floating point type   3.5.7(10)

Safe_First attribute   A.5.3(71)

Safe_Last attribute   A.5.3(72)

safety-critical systems   H(1)

satisfies
   a discriminant constraint   3.7.1(11)
   a range constraint   3.5(4)
   an index constraint   3.6.1(7)
   for an access value   3.10(15)

Save
   in Ada.Numerics.Discrete_Random   A.5.2(24)
   in Ada.Numerics.Float_Random   A.5.2(12)

Save_Occurrence
   in Ada.Exceptions   11.4.1(6)

scalar type   3.2(3), 3.5(1)

scalar_constraint   3.2.2(6)
   used   3.2.2(5), P

scale
   of a decimal fixed point subtype   3.5.10(11), K(216)

Scale attribute   3.5.10(11)

Scaling attribute   A.5.3(27)

SCHAR_MAX
   in Interfaces.C   B.3(6)

SCHAR_MIN
   in Interfaces.C   B.3(6)

SCI
   in Ada.Characters.Latin_1   A.3.3(19)

scope
   informal definition   3.1(8)
   of (a view of) an entity   8.2(11)
   of a declaration   8.2(10)
   of a use_clause   8.4(6)
   of a with_clause   10.1.2(5)

Seconds
   in Ada.Calendar   9.6(13)

Seconds_Count
   in Ada.Real_Time   D.8(15)

Section_Sign
   in Ada.Characters.Latin_1   A.3.3(21)

secure systems   H(1)

select an entry call
   from an entry queue   9.5.3(13), 9.5.3(16)
   immediately   9.5.3(8)

select_alternative   9.7.1(4)
   used   9.7.1(2), P

select_statement   9.7(2)
   used   5.1(5), P

selected_component   4.1.3(2)
   used   4.1(2), P

selection
   of an entry caller   9.5.2(24)

selective_accept   9.7.1(2)
   used   9.7(2), P

selector_name   4.1.3(3)
   used   3.7.1(3), 4.1.3(2), 4.3.1(5), 6.4(5), 12.3(4), P

semantic dependence
   of one compilation unit upon another   10.1.1(26)

semicolon   2.1(15)
   in Ada.Characters.Latin_1   A.3.3(10)

separate compilation   10.1(1)

separator   2.2(3)

sequence of characters
   of a string_literal   2.6(5)

sequence_of_statements   5.1(2)
   used   5.3(2), 5.4(3), 5.5(2), 9.7.1(2), 9.7.1(5), 9.7.1(6), 9.7.2(3),
9.7.3(2), 9.7.4(3), 9.7.4(5), 11.2(2), 11.2(3), P

sequential
   actions   9.10(11), C.6(17)

sequential access   A.8(2)

sequential file   A.8(1)

Sequential_IO
   child of Ada   A.8.1(2)

service
   an entry queue   9.5.3(13)

Set_Col
   in Ada.Text_IO   A.10.1(35)

Set_Error
   in Ada.Text_IO   A.10.1(15)

Set_Exit_Status
   in Ada.Command_Line   A.15(9)

Set_False
   in Ada.Synchronous_Task_Control   D.10(4)

Set_Im
   in Ada.Numerics.Generic_Complex_Types   G.1.1(7)

Set_Index
   in Ada.Direct_IO   A.8.4(14)
   in Ada.Streams.Stream_IO   A.12.1(22)

Set_Input
   in Ada.Text_IO   A.10.1(15)

Set_Line
   in Ada.Text_IO   A.10.1(36)

Set_Line_Length
   in Ada.Text_IO   A.10.1(23)

Set_Mode
   in Ada.Streams.Stream_IO   A.12.1(24)

Set_Output
   in Ada.Text_IO   A.10.1(15)

Set_Page_Length
   in Ada.Text_IO   A.10.1(24)

Set_Priority
   in Ada.Dynamic_Priorities   D.5(4)

Set_Re
   in Ada.Numerics.Generic_Complex_Types   G.1.1(7)

Set_True
   in Ada.Synchronous_Task_Control   D.10(4)

Set_Value
   in Ada.Task_Attributes   C.7.2(6)

shared passive library unit   E.2(4/1), E.2.1(4)

shared variable
   protection of   9.10(1)

shift   B.2(9)

short
   in Interfaces.C   B.3(7)

short-circuit control form   4.5.1(1)

Short_Float   3.5.7(16)

Short_Integer   3.5.4(25)

SI
   in Ada.Characters.Latin_1   A.3.3(5)

signal
   as defined between actions   9.10(2)
   See interrupt   C.3(1)

signal (an exception)
   See raise   11(1)

signal handling
   example   9.7.4(10)

signed integer type   3.5.4(1)

signed_char
   in Interfaces.C   B.3(8)

signed_integer_type_definition   3.5.4(3)
   used   3.5.4(2), P

Signed_Zeros attribute   A.5.3(13)

simple entry call   9.5.3(1)

simple_expression   4.4(4)
   used   3.5(3), 3.5.4(3), 3.5.7(3), 4.4(3), 13.5.1(5), 13.5.1(6), P

simple_statement   5.1(4)
   used   5.1(3), P

Sin
   in Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(4)
   in Ada.Numerics.Generic_Elementary_Functions   A.5.1(5)

single
   class expected type   8.6(27)

single entry   9.5.2(20)

Single_Precision_Complex_Types
   in Interfaces.Fortran   B.5(8)

single_protected_declaration   9.4(3)
   used   3.3.1(2), P

single_task_declaration   9.1(3)
   used   3.3.1(2), P

Sinh
   in Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(6)
   in Ada.Numerics.Generic_Elementary_Functions   A.5.1(7)

size
   of an object   13.1(7)
   in Ada.Direct_IO   A.8.4(15)
   in Ada.Streams.Stream_IO   A.12.1(23)

Size attribute   13.3(40), 13.3(45)

Size clause   13.3(7), 13.3(41), 13.3(48)

size_t
   in Interfaces.C   B.3(13)

Skip_Line
   in Ada.Text_IO   A.10.1(29)

Skip_Page
   in Ada.Text_IO   A.10.1(32)

slice   4.1.2(2)
   used   4.1(2), P
   in Ada.Strings.Bounded   A.4.4(28)
   in Ada.Strings.Unbounded   A.4.5(22)

small
   of a fixed point type   3.5.9(8)

Small attribute   3.5.10(2/1)

Small clause   3.5.10(2/1), 13.3(7)

SO
   in Ada.Characters.Latin_1   A.3.3(5)

Soft_Hyphen
   in Ada.Characters.Latin_1   A.3.3(21)

SOH
   in Ada.Characters.Latin_1   A.3.3(5)

solidus   2.1(15)
   in Ada.Characters.Latin_1   A.3.3(8)

SOS
   in Ada.Characters.Latin_1   A.3.3(19)

SPA
   in Ada.Characters.Latin_1   A.3.3(18)

Space
   in Ada.Characters.Latin_1   A.3.3(8)
   in Ada.Strings   A.4.1(4)

space_character   2.1(11)
   used   2.1(3), P

special graphic character
   a category of Character   A.3.2(32)

special_character   2.1(12)
   names   2.1(15)
   used   2.1(3), P

Special_Set
   in Ada.Strings.Maps.Constants   A.4.6(4)

Specialized Needs Annexes   1.1.2(7)

specifiable
   of Address for entries   J.7.1(6)
   of Address for stand-alone objects and for program units   13.3(12)
   of Alignment for first subtypes and objects   13.3(25)
   of Bit_Order for record types and record extensions   13.5.3(4)
   of Component_Size for array types   13.3(70)
   of External_Tag for a tagged type   13.3(75/1), K(65)
   of Input for a type   13.13.2(36/1)
   of Machine_Radix for decimal first subtypes   F.1(1)
   of Output for a type   13.13.2(36/1)
   of Read for a type   13.13.2(36/1)
   of Size for first subtypes   13.3(48)
   of Size for stand-alone objects   13.3(41)
   of Small for fixed point types   3.5.10(2/1)
   of Storage_Pool for a non-derived access-to-object type   13.11(15)
   of Storage_Size for a non-derived access-to-object type   13.11(15)
   of Storage_Size for a task first subtype   J.9(3)
   of Write for a type   13.13.2(36/1)

specifiable (of an attribute and for an entity)   13.3(5/1)

specific type   3.4.1(3)

specified
   of an aspect of representation of an entity   13.1(17)
   of an operational aspect of an entity   13.1(18.1/1)

specified (not!)   1.1.3(18)

specified discriminant   3.7(18)

Split
   in Ada.Calendar   9.6(14)
   in Ada.Real_Time   D.8(16)

Sqrt
   in Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(3)
   in Ada.Numerics.Generic_Elementary_Functions   A.5.1(4)

SS2
   in Ada.Characters.Latin_1   A.3.3(17)

SS3
   in Ada.Characters.Latin_1   A.3.3(17)

SSA
   in Ada.Characters.Latin_1   A.3.3(17)

ST
   in Ada.Characters.Latin_1   A.3.3(19)

stand-alone constant   3.3.1(23)
   corresponding to a formal object of mode in   12.4(10)

stand-alone object   3.3.1(1)

stand-alone variable   3.3.1(23)

Standard   A.1(4)

standard error file   A.10(6)

standard input file   A.10(5)

standard mode   1.1.5(11)

standard output file   A.10(5)

standard storage pool   13.11(17)

Standard_Error
   in Ada.Text_IO   A.10.1(16), A.10.1(19)

Standard_Input
   in Ada.Text_IO   A.10.1(16), A.10.1(19)

Standard_Output
   in Ada.Text_IO   A.10.1(16), A.10.1(19)

State
   in Ada.Numerics.Discrete_Random   A.5.2(23)
   in Ada.Numerics.Float_Random   A.5.2(11)

statement   5.1(3)
   used   5.1(2), P

statement_identifier   5.1(8)
   used   5.1(7), 5.5(2), 5.6(2), P

static   4.9(1)
   constant   4.9(24)
   constraint   4.9(27)
   delta constraint   4.9(29)
   digits constraint   4.9(29)
   discrete_range   4.9(25)
   discriminant constraint   4.9(31)
   expression   4.9(2)
   function   4.9(18)
   index constraint   4.9(30)
   range   4.9(25)
   range constraint   4.9(29)
   scalar subtype   4.9(26)
   string subtype   4.9(26)
   subtype   4.9(26)
   subtype   12.4(9)

static semantics   1.1.2(28)

statically
   constrained   4.9(32)
   denote   4.9(14)

statically compatible
   for a constraint and a scalar subtype   4.9.1(4)
   for a constraint and an access or composite subtype   4.9.1(4)
   for two subtypes   4.9.1(4)

statically deeper   3.10.2(4), 3.10.2(17)

statically determined tag   3.9.2(1)
   [partial]   3.9.2(15), 3.9.2(19)

statically matching
   effect on subtype-specific aspects   13.1(14)
   for constraints   4.9.1(1)
   for ranges   4.9.1(3)
   for subtypes   4.9.1(2)
   required   3.9.2(10/1), 3.10.2(27/1), 4.6(12/1), 4.6(16), 6.3.1(16),
6.3.1(17), 6.3.1(23), 7.3(13), 12.5.1(14), 12.5.3(6), 12.5.3(7), 12.5.4(3),
12.7(7)

statically tagged   3.9.2(4)

Status_Error
   in Ada.Direct_IO   A.8.4(18)
   in Ada.IO_Exceptions   A.13(4)
   in Ada.Sequential_IO   A.8.1(15)
   in Ada.Streams.Stream_IO   A.12.1(26)
   in Ada.Text_IO   A.10.1(85)

storage deallocation
   unchecked   13.11.2(1)

storage element   13.3(8)

storage management
   user-defined   13.11(1)

storage node   E(2)

storage place
   of a component   13.5(1)

storage place attributes
   of a component   13.5.2(1)

storage pool   3.10(7/1)

storage pool element   13.11(11)

storage pool type   13.11(11)

Storage_Array
   in System.Storage_Elements   13.7.1(5)

Storage_Check   11.5(23)
   [partial]   11.1(6), 13.3(67), 13.11(17), D.7(15/1), D.7(17/1), D.7(18/1),
D.7(19/1)

Storage_Count
   in System.Storage_Elements   13.7.1(4)

Storage_Element
   in System.Storage_Elements   13.7.1(5)

Storage_Elements
   child of System   13.7.1(2)

Storage_Error
   raised by failure of run-time check   4.8(14), 8.5.4(8.1/1), 11.1(4),
11.1(6), 11.5(23), 13.3(67), 13.11(17), 13.11(18), A.7(14), D.7(15/1),
D.7(17/1), D.7(18/1), D.7(19/1)
   in Standard   A.1(46)

Storage_IO
   child of Ada   A.9(3)

Storage_Offset
   in System.Storage_Elements   13.7.1(3)

Storage_Pool attribute   13.11(13)

Storage_Pool clause   13.3(7), 13.11(15)

Storage_Pools
   child of System   13.11(5)

Storage_Size
   in System.Storage_Pools   13.11(9)

Storage_Size attribute   13.3(60), 13.11(14)

Storage_Size clause   13.3(7), 13.11(15)
   See also pragma Storage_Size   13.3(61)

Storage_Unit
   in System   13.7(13)

stream   13.13(1)
   in Ada.Streams.Stream_IO   A.12.1(13)
   in Ada.Text_IO.Text_Streams   A.12.2(4)
   in Ada.Wide_Text_IO.Text_Streams   A.12.3(4)

stream type   13.13(1)

Stream_IO
   child of Ada.Streams   A.12.1(3)

Stream_Access
   in Ada.Streams.Stream_IO   A.12.1(4)
   in Ada.Text_IO.Text_Streams   A.12.2(3)
   in Ada.Wide_Text_IO.Text_Streams   A.12.3(3)

Stream_Element
   in Ada.Streams   13.13.1(4/1)

Stream_Element_Array
   in Ada.Streams   13.13.1(4/1)

Stream_Element_Count
   in Ada.Streams   13.13.1(4/1)

Stream_Element_Offset
   in Ada.Streams   13.13.1(4/1)

Streams
   child of Ada   13.13.1(2)

strict mode   G.2(1)

String
   in Standard   A.1(37)

string type   3.6.3(1)

String_Access
   in Ada.Strings.Unbounded   A.4.5(7)

string_element   2.6(3)
   used   2.6(2), P

string_literal   2.6(2)
   used   4.4(7), 6.1(9), P

Strings
   child of Ada   A.4.1(3)
   child of Interfaces.C   B.3.1(3)

Strlen
   in Interfaces.C.Strings   B.3.1(17)

structure
   See record type   3.8(1)

STS
   in Ada.Characters.Latin_1   A.3.3(18)

STX
   in Ada.Characters.Latin_1   A.3.3(5)

SUB
   in Ada.Characters.Latin_1   A.3.3(6)

subaggregate
   of an array_aggregate   4.3.3(6)

subcomponent   3.2(6)

subprogram   6(1)
   abstract   3.9.3(3)

subprogram call   6.4(1)

subprogram instance   12.3(13)

subprogram_body   6.3(2)
   used   3.11(6), 9.4(8/1), 10.1.1(7), P

subprogram_body_stub   10.1.3(3)
   used   10.1.3(2), P

subprogram_declaration   6.1(2)
   used   3.1(3), 9.4(5/1), 9.4(8/1), 10.1.1(5), P

subprogram_default   12.6(3)
   used   12.6(2), P

subprogram_renaming_declaration   8.5.4(2)
   used   8.5(2), 10.1.1(6), P

subprogram_specification   6.1(4)
   used   6.1(2), 6.1(3), 6.3(2), 8.5.4(2), 10.1.3(3), 12.1(3), 12.6(2), P

subsystem   10.1(3), N(22)

subtype   3.2(8)

subtype (of an object)
   See actual subtype of an object   3.3(23)
   See actual subtype of an object   3.3.1(9)

subtype conformance   6.3.1(17)
   [partial]   3.10.2(34), 9.5.4(17)
   required   3.9.2(10/1), 3.10.2(32), 4.6(19), 8.5.4(5/1), 9.5.4(5),
13.3(6)

subtype conversion
   See type conversion   4.6(1)
   See also implicit subtype conversion   4.6(1)

subtype-specific
   of a representation item   13.1(8)
   of an aspect   13.1(8)

subtype_declaration   3.2.2(2)
   used   3.1(3), P

subtype_indication   3.2.2(3)
   used   3.2.2(2), 3.3.1(2), 3.4(2), 3.6(6), 3.6(7), 3.6.1(3), 3.10(3),
4.8(2), 7.3(3), P

subtype_mark   3.2.2(4)
   used   3.2.2(3), 3.6(4), 3.7(5), 3.10(6), 4.3.2(3), 4.4(3), 4.6(2),
4.7(2), 6.1(13), 6.1(15), 8.4(4), 8.5.1(2), 12.3(5), 12.4(2), 12.5.1(3), P

subtypes
   of a profile   6.1(25)

subunit   10.1.3(7), 10.1.3(8)
   used   10.1.1(3), P

Succ attribute   3.5(22)

Success
   in Ada.Command_Line   A.15(8)

super
   See view conversion   4.6(5/1)

Superscript_One
   in Ada.Characters.Latin_1   A.3.3(22)

Superscript_Three
   in Ada.Characters.Latin_1   A.3.3(22)

Superscript_Two
   in Ada.Characters.Latin_1   A.3.3(22)

suppressed check   11.5(8)

Suspend_Until_True
   in Ada.Synchronous_Task_Control   D.10(4)

Suspension_Object
   in Ada.Synchronous_Task_Control   D.10(4)

SYN
   in Ada.Characters.Latin_1   A.3.3(6)

synchronization   9(1)

Synchronous_Task_Control
   child of Ada   D.10(3)

syntactic category   1.1.4(15)

syntax
   complete listing   P(1)
   cross reference   P(1)
   notation   1.1.4(3)
   under Syntax heading   1.1.2(25)

System   13.7(3)

System.Address_To_Access_Conversions   13.7.2(2)

System.Machine_Code   13.8(7)

System.RPC   E.5(3)

System.Storage_Elements   13.7.1(2)

System.Storage_Pools   13.11(5)

System_Name
   in System   13.7(4)

systems programming   C(1)


T


Tag
   in Ada.Tags   3.9(6)

Tag attribute   3.9(16), 3.9(18)

tag indeterminate   3.9.2(6)

tag of an object   3.9(3)
   class-wide object   3.9(22)
   object created by an allocator   3.9(21)
   preserved by type conversion and parameter passing   3.9(25)
   returned by a function   3.9(23), 3.9(24)
   stand-alone object,   component, or aggregate   3.9(20)

Tag_Check   11.5(18)
   [partial]   3.9.2(16), 4.6(42), 4.6(52), 5.2(10), 6.5(9)

Tag_Error
   in Ada.Tags   3.9(8)

tagged type   3.9(2)

Tags
   child of Ada   3.9(6)

Tail
   in Ada.Strings.Bounded   A.4.4(72), A.4.4(73)
   in Ada.Strings.Fixed   A.4.3(37), A.4.3(38)
   in Ada.Strings.Unbounded   A.4.5(67), A.4.5(68)

tail (of a queue)   D.2.1(5)

Tan
   in Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(4)
   in Ada.Numerics.Generic_Elementary_Functions   A.5.1(5)

Tanh
   in Ada.Numerics.Generic_Complex_Elementary_Functions   G.1.2(6)
   in Ada.Numerics.Generic_Elementary_Functions   A.5.1(7)

target
   of an assignment operation   5.2(3)
   of an assignment_statement   5.2(3)

target entry
   of a requeue_statement   9.5.4(3)

target object
   of a call on an entry or a protected subprogram   9.5(2)
   of a requeue_statement   9.5(7)

target statement
   of a goto_statement   5.8(3)

target subtype
   of a type_conversion   4.6(3)

task   9(1)
   activation   9.2(1)
   completion   9.3(1)
   dependence   9.3(1)
   execution   9.2(1)
   termination   9.3(1)

task declaration   9.1(1)

task dispatching   D.2.1(4)

task dispatching point   D.2.1(4)
   [partial]   D.2.1(8), D.2.2(12)

task dispatching policy   D.2.2(6)
   [partial]   D.2.1(5)

task priority   D.1(15)

task state
   abnormal   9.8(4)
   blocked   9(10)
   callable   9.9(2)
   held   D.11(4)
   inactive   9(10)
   ready   9(10)
   terminated   9(10)

task unit   9(9)

Task_Attributes
   child of Ada   C.7.2(2)

task_body   9.1(6)
   used   3.11(6), P

task_body_stub   10.1.3(5)
   used   10.1.3(2), P

task_definition   9.1(4)
   used   9.1(2), 9.1(3), P

Task_ID
   in Ada.Task_Identification   C.7.1(2)

Task_Identification
   child of Ada   C.7.1(2)

task_item   9.1(5/1)
   used   9.1(4), P

task_type_declaration   9.1(2)
   used   3.2.1(3), P

Tasking_Error
   raised by failure of run-time check   9.2(5), 9.5.3(21), 11.1(4),
13.11.2(13), 13.11.2(14), C.7.2(13), D.5(8), D.11(8)
   in Standard   A.1(46)

template   12(1)
   for a formal package   12.7(4)
   See generic unit   12(1)

term   4.4(5)
   used   4.4(4), P

terminal interrupt
   example   9.7.4(10)

terminate_alternative   9.7.1(7)
   used   9.7.1(4), P

terminated
   a task state   9(10)

Terminated attribute   9.9(3)

termination
   of a partition   E.1(7)

Terminator_Error
   in Interfaces.C   B.3(40)

tested type
   of a membership test   4.5.2(3)

text of a program   2.2(1)

Text_Streams
   child of Ada.Text_IO   A.12.2(3)
   child of Ada.Wide_Text_IO   A.12.3(3)

Text_IO
   child of Ada   A.10.1(2)

throw (an exception)
   See raise   11(1)

tick   2.1(15)
   in Ada.Real_Time   D.8(6)
   in System   13.7(10)

Tilde
   in Ada.Characters.Latin_1   A.3.3(14)

Time
   in Ada.Calendar   9.6(10)
   in Ada.Real_Time   D.8(4)

time base   9.6(6)

time limit
   example   9.7.4(12)

time type   9.6(6)

Time-dependent Reset procedure
   of the random number generator   A.5.2(34)

time-out
   example   9.7.4(12)
   See asynchronous_select   9.7.4(12)
   See selective_accept   9.7.1(1)
   See timed_entry_call   9.7.2(1)

Time_Error
   in Ada.Calendar   9.6(18)

Time_First
   in Ada.Real_Time   D.8(4)

Time_Last
   in Ada.Real_Time   D.8(4)

Time_Of
   in Ada.Calendar   9.6(15)
   in Ada.Real_Time   D.8(16)

Time_Span
   in Ada.Real_Time   D.8(5)

Time_Span_First
   in Ada.Real_Time   D.8(5)

Time_Span_Last
   in Ada.Real_Time   D.8(5)

Time_Span_Unit
   in Ada.Real_Time   D.8(5)

Time_Span_Zero
   in Ada.Real_Time   D.8(5)

Time_Unit
   in Ada.Real_Time   D.8(4)

timed_entry_call   9.7.2(2)
   used   9.7(2), P

timer interrupt
   example   9.7.4(12)

times operator   4.4(1), 4.5.5(1)

timing
   See delay_statement   9.6(1)

To_Ada
   in Interfaces.C   B.3(22), B.3(26), B.3(28), B.3(32), B.3(37), B.3(39)
   in Interfaces.COBOL   B.4(17), B.4(19)
   in Interfaces.Fortran   B.5(13), B.5(14), B.5(16)

To_Address
   in System.Address_To_Access_Conversions   13.7.2(3)
   in System.Storage_Elements   13.7.1(10)

To_Basic
   in Ada.Characters.Handling   A.3.2(6), A.3.2(7)

To_Binary
   in Interfaces.COBOL   B.4(45), B.4(48)

To_Bounded_String
   in Ada.Strings.Bounded   A.4.4(11)

To_C
   in Interfaces.C   B.3(21), B.3(25), B.3(27), B.3(32), B.3(36), B.3(38)

To_Character
   in Ada.Characters.Handling   A.3.2(15)

To_Chars_Ptr
   in Interfaces.C.Strings   B.3.1(8)

To_COBOL
   in Interfaces.COBOL   B.4(17), B.4(18)

To_Decimal
   in Interfaces.COBOL   B.4(35), B.4(40), B.4(44), B.4(47)

To_Display
   in Interfaces.COBOL   B.4(36)

To_Domain
   in Ada.Strings.Maps   A.4.2(24)
   in Ada.Strings.Wide_Maps   A.4.7(24)

To_Duration
   in Ada.Real_Time   D.8(13)

To_Fortran
   in Interfaces.Fortran   B.5(13), B.5(14), B.5(15)

To_Integer
   in System.Storage_Elements   13.7.1(10)

To_ISO_646
   in Ada.Characters.Handling   A.3.2(11), A.3.2(12)

To_Long_Binary
   in Interfaces.COBOL   B.4(48)

To_Lower
   in Ada.Characters.Handling   A.3.2(6), A.3.2(7)

To_Mapping
   in Ada.Strings.Maps   A.4.2(23)
   in Ada.Strings.Wide_Maps   A.4.7(23)

To_Packed
   in Interfaces.COBOL   B.4(41)

To_Picture
   in Ada.Text_IO.Editing   F.3.3(6)

To_Pointer
   in System.Address_To_Access_Conversions   13.7.2(3)

To_Range
   in Ada.Strings.Maps   A.4.2(24)
   in Ada.Strings.Wide_Maps   A.4.7(25)

To_Ranges
   in Ada.Strings.Maps   A.4.2(10)
   in Ada.Strings.Wide_Maps   A.4.7(10)

To_Sequence
   in Ada.Strings.Maps   A.4.2(19)
   in Ada.Strings.Wide_Maps   A.4.7(19)

To_Set
   in Ada.Strings.Maps   A.4.2(8), A.4.2(9), A.4.2(17), A.4.2(18)
   in Ada.Strings.Wide_Maps   A.4.7(8), A.4.7(9), A.4.7(17), A.4.7(18)

To_String
   in Ada.Characters.Handling   A.3.2(16)
   in Ada.Strings.Bounded   A.4.4(12)
   in Ada.Strings.Unbounded   A.4.5(11)

To_Time_Span
   in Ada.Real_Time   D.8(13)

To_Unbounded_String
   in Ada.Strings.Unbounded   A.4.5(9), A.4.5(10)

To_Upper
   in Ada.Characters.Handling   A.3.2(6), A.3.2(7)

To_Wide_Character
   in Ada.Characters.Handling   A.3.2(17)

To_Wide_String
   in Ada.Characters.Handling   A.3.2(18)

token
   See lexical element   2.2(1)

Trailing_Nonseparate
   in Interfaces.COBOL   B.4(23)

Trailing_Separate
   in Interfaces.COBOL   B.4(23)

transfer of control   5.1(14)

Translate
   in Ada.Strings.Bounded   A.4.4(53), A.4.4(54), A.4.4(55), A.4.4(56)
   in Ada.Strings.Fixed   A.4.3(18), A.4.3(19), A.4.3(20), A.4.3(21)
   in Ada.Strings.Unbounded   A.4.5(48), A.4.5(49), A.4.5(50), A.4.5(51)

Translation_Error
   in Ada.Strings   A.4.1(5)

triggering_alternative   9.7.4(3)
   used   9.7.4(2), P

triggering_statement   9.7.4(4)
   used   9.7.4(3), P

Trim
   in Ada.Strings.Bounded   A.4.4(67), A.4.4(68), A.4.4(69)
   in Ada.Strings.Fixed   A.4.3(31), A.4.3(32), A.4.3(33), A.4.3(34)
   in Ada.Strings.Unbounded   A.4.5(61), A.4.5(62), A.4.5(63), A.4.5(64)

Trim_End
   in Ada.Strings   A.4.1(6)

True   3.5.3(1)

Truncation
   in Ada.Strings   A.4.1(6)

Truncation attribute   A.5.3(42)

two's complement
   modular types   3.5.4(29)

type   3.2(1)
   abstract   3.9.3(2)
   See also tag   3.9(3)
   See also language-defined types

type conformance   6.3.1(15)
   [partial]   3.4(17), 8.3(8), 8.3(26/1), 10.1.4(4/1)
   required   3.11.1(5), 4.1.4(14/1), 8.6(26), 9.5.4(3)

type conversion   4.6(1)
   access   4.6(13), 4.6(18), 4.6(47)
   arbitrary order   1.1.4(18)
   array   4.6(9), 4.6(36)
   composite (non-array)   4.6(21), 4.6(40)
   enumeration   4.6(21), 4.6(34)
   numeric   4.6(8), 4.6(29)
   unchecked   13.9(1)
   See also qualified_expression   4.7(1)

type conversion, implicit
   See implicit subtype conversion   4.6(1)

type extension   3.9(2), 3.9.1(1)

type of a discrete_range   3.6.1(4)

type of a range   3.5(4)

type parameter
   See discriminant   3.7(1)

type profile
   See profile, type conformant   6.3.1(15)

type resolution rules   8.6(20)
   if any type in a specified class of types is expected   8.6(21)
   if expected type is specific   8.6(22)
   if expected type is universal or class-wide   8.6(21)

type tag
   See tag   3.9(3)

type-related
   aspect   13.1(8)
   aspect   13.1(8.1/1)
   operational item   13.1(8.1/1)
   representation item   13.1(8)

type_conversion   4.6(2)
   used   4.1(2), P
   See also unchecked type conversion   13.9(1)

type_declaration   3.2.1(2)
   used   3.1(3), P

type_definition   3.2.1(4)
   used   3.2.1(3), P

Type_Set
   in Ada.Text_IO   A.10.1(7)

types
   of a profile   6.1(29)


U


UC_A_Acute
   in Ada.Characters.Latin_1   A.3.3(23)

UC_A_Circumflex
   in Ada.Characters.Latin_1   A.3.3(23)

UC_A_Diaeresis
   in Ada.Characters.Latin_1   A.3.3(23)

UC_A_Grave
   in Ada.Characters.Latin_1   A.3.3(23)

UC_A_Ring
   in Ada.Characters.Latin_1   A.3.3(23)

UC_A_Tilde
   in Ada.Characters.Latin_1   A.3.3(23)

UC_AE_Diphthong
   in Ada.Characters.Latin_1   A.3.3(23)

UC_C_Cedilla
   in Ada.Characters.Latin_1   A.3.3(23)

UC_E_Acute
   in Ada.Characters.Latin_1   A.3.3(23)

UC_E_Circumflex
   in Ada.Characters.Latin_1   A.3.3(23)

UC_E_Diaeresis
   in Ada.Characters.Latin_1   A.3.3(23)

UC_E_Grave
   in Ada.Characters.Latin_1   A.3.3(23)

UC_I_Acute
   in Ada.Characters.Latin_1   A.3.3(23)

UC_I_Circumflex
   in Ada.Characters.Latin_1   A.3.3(23)

UC_I_Diaeresis
   in Ada.Characters.Latin_1   A.3.3(23)

UC_I_Grave
   in Ada.Characters.Latin_1   A.3.3(23)

UC_Icelandic_Eth
   in Ada.Characters.Latin_1   A.3.3(24)

UC_Icelandic_Thorn
   in Ada.Characters.Latin_1   A.3.3(24)

UC_N_Tilde
   in Ada.Characters.Latin_1   A.3.3(24)

UC_O_Acute
   in Ada.Characters.Latin_1   A.3.3(24)

UC_O_Circumflex
   in Ada.Characters.Latin_1   A.3.3(24)

UC_O_Diaeresis
   in Ada.Characters.Latin_1   A.3.3(24)

UC_O_Grave
   in Ada.Characters.Latin_1   A.3.3(24)

UC_O_Oblique_Stroke
   in Ada.Characters.Latin_1   A.3.3(24)

UC_O_Tilde
   in Ada.Characters.Latin_1   A.3.3(24)

UC_U_Acute
   in Ada.Characters.Latin_1   A.3.3(24)

UC_U_Circumflex
   in Ada.Characters.Latin_1   A.3.3(24)

UC_U_Diaeresis
   in Ada.Characters.Latin_1   A.3.3(24)

UC_U_Grave
   in Ada.Characters.Latin_1   A.3.3(24)

UC_Y_Acute
   in Ada.Characters.Latin_1   A.3.3(24)

UCHAR_MAX
   in Interfaces.C   B.3(6)

ultimate ancestor
   of a type   3.4.1(10)

unary adding operator   4.5.4(1)

unary operator   4.5(9)

unary_adding_operator   4.5(5)
   used   4.4(4), P

Unbiased_Rounding attribute   A.5.3(39)

Unbounded
   child of Ada.Strings   A.4.5(3)
   in Ada.Text_IO   A.10.1(5)

Unbounded_String
   in Ada.Strings.Unbounded   A.4.5(4)

unchecked storage deallocation   13.11.2(1)

unchecked type conversion   13.9(1)

Unchecked_Access attribute   13.10(3)
   See also Access attribute   3.10.2(24/1)

Unchecked_Conversion
   child of Ada   13.9(3)

Unchecked_Deallocation
   child of Ada   13.11.2(3)

unconstrained   3.2(9)
   object   3.3.1(9), 3.10(9)
   object   6.4.1(16)
   subtype   3.2(9), 3.4(6), 3.5(7), 3.5.1(10), 3.5.4(9), 3.5.4(10),
3.5.7(11), 3.5.9(13), 3.5.9(16), 3.6(15), 3.6(16), 3.7(26), 3.9(15)
   subtype   3.10(14/1)
   subtype   K(35)

unconstrained_array_definition   3.6(3)
   used   3.6(2), P

undefined result   11.6(5)

underline   2.1(15)
   used   2.3(2), 2.4.1(3), 2.4.2(4), P

Uniformly_Distributed
   in Ada.Numerics.Float_Random   A.5.2(8)

uninitialized allocator   4.8(4)

uninitialized variables   13.9.1(2)
   [partial]   3.3.1(21)

unit consistency   E.3(6)

universal type   3.4.1(6)

universal_fixed
   [partial]   3.5.6(4)

universal_integer   3.5.4(30)
   [partial]   3.5.4(14)

universal_real
   [partial]   3.5.6(4)

unknown discriminants   3.7(26)

unknown_discriminant_part   3.7(3)
   used   3.7(2), P

unmarshalling   E.4(9)

unpolluted   13.13.1(2)

unsigned
   in Interfaces.C   B.3(9)
   in Interfaces.COBOL   B.4(23)

unsigned type
   See modular type   3.5.4(1)

unsigned_char
   in Interfaces.C   B.3(10)

unsigned_long
   in Interfaces.C   B.3(9)

unsigned_short
   in Interfaces.C   B.3(9)

unspecified   1.1.3(18)
   [partial]   2.1(5), 4.5.2(13), 4.5.2(24.1/1), 4.5.5(21), 6.2(11), 7.2(5),
9.8(14), 10.2(26), 11.1(6), 11.5(27), 13.1(18), 13.7.2(5), 13.9.1(7),
13.11(20), A.1(1), A.5.1(34), A.5.2(28), A.5.2(34), A.7(6), A.10(8),
A.10.7(8/1), A.10.7(12), A.10.7(19), A.14(1), A.15(20), D.2.2(6), D.8(19),
E.3(5/1), G.1.1(40), G.1.2(33), G.1.2(48), H(4.1), H.2(1)

update
   the value of an object   3.3(14)
   in Interfaces.C.Strings   B.3.1(18), B.3.1(19)

Update_Error
   in Interfaces.C.Strings   B.3.1(20)

upper bound
   of a range   3.5(4)

upper-case letter
   a category of Character   A.3.2(26)

upper_case_identifier_letter   2.1(8)

Upper_Case_Map
   in Ada.Strings.Maps.Constants   A.4.6(5)

Upper_Set
   in Ada.Strings.Maps.Constants   A.4.6(4)

US
   in Ada.Characters.Latin_1   A.3.3(6)

usage name   3.1(10)

use-visible   8.3(4), 8.4(9)

use_clause   8.4(2)
   used   3.11(4/1), 10.1.2(3), 12.1(5), P

Use_Error
   in Ada.Direct_IO   A.8.4(18)
   in Ada.IO_Exceptions   A.13(4)
   in Ada.Sequential_IO   A.8.1(15)
   in Ada.Streams.Stream_IO   A.12.1(26)
   in Ada.Text_IO   A.10.1(85)

use_package_clause   8.4(3)
   used   8.4(2), P

use_type_clause   8.4(4)
   used   8.4(2), P

user-defined assignment   7.6(1)

user-defined heap management   13.11(1)

user-defined operator   6.6(1)

user-defined storage management   13.11(1)


V


Val attribute   3.5.5(5)

Valid
   in Ada.Text_IO.Editing   F.3.3(5), F.3.3(12)
   in Interfaces.COBOL   B.4(33), B.4(38), B.4(43)

Valid attribute   13.9.2(3)

Value
   in Ada.Numerics.Discrete_Random   A.5.2(26)
   in Ada.Numerics.Float_Random   A.5.2(14)
   in Ada.Strings.Maps   A.4.2(21)
   in Ada.Strings.Wide_Maps   A.4.7(21)
   in Ada.Task_Attributes   C.7.2(4)
   in Interfaces.C.Pointers   B.3.2(6), B.3.2(7)
   in Interfaces.C.Strings   B.3.1(13), B.3.1(14), B.3.1(15), B.3.1(16)

Value attribute   3.5(52)

value conversion   4.6(5/1)

variable   3.3(13)

variable object   3.3(13)

variable view   3.3(13)

variant   3.8.1(3)
   used   3.8.1(2), P
   See also tagged type   3.9(1)

variant_part   3.8.1(2)
   used   3.8(4), P

version
   of a compilation unit   E.3(5/1)

Version attribute   E.3(3)

vertical line   2.1(15)

Vertical_Line
   in Ada.Characters.Latin_1   A.3.3(14)

view   3.1(7), N(12)

view conversion   4.6(5/1)

virtual function
   See dispatching subprogram   3.9.2(1)

Virtual_Length
   in Interfaces.C.Pointers   B.3.2(13)

visibility
   direct   8.3(2), 8.3(21)
   immediate   8.3(4), 8.3(21)
   use clause   8.3(4), 8.4(9)

visibility rules   8.3(1)

visible   8.3(2), 8.3(14)
   within a   use_clause in a context_clause   10.1.6(3)
   within a pragma in a   context_clause   10.1.6(3)
   within a pragma that appears at the place of a compilation unit  
10.1.6(5)
   within a with_clause   10.1.6(2)
   within the parent_unit_name of a library unit   10.1.6(2)
   within the parent_unit_name of a subunit   10.1.6(4)

visible part   8.2(5)
   of a formal package   12.7(10)
   of a generic unit   8.2(8)
   of a package (other than a generic formal package)   7.1(6)
   of a protected unit   9.4(11)
   of a task unit   9.1(9)
   of a view of a callable entity   8.2(6)
   of a view of a composite type   8.2(7)

volatile   C.6(8)

VT
   in Ada.Characters.Latin_1   A.3.3(5)

VTS
   in Ada.Characters.Latin_1   A.3.3(17)


W


wchar_array
   in Interfaces.C   B.3(33)

wchar_t
   in Interfaces.C   B.3(30/1)

well-formed picture String
   for edited output   F.3.1(1)

Wide_Bounded
   child of Ada.Strings   A.4.7(1)

Wide_Constants
   child of Ada.Strings.Wide_Maps   A.4.7(28)

Wide_Fixed
   child of Ada.Strings   A.4.7(1)

Wide_Text_IO
   child of Ada   A.11(2)

Wide_Unbounded
   child of Ada.Strings   A.4.7(1)

Wide_Character   3.5.2(3)
   in Standard   A.1(36)

Wide_Character_Mapping
   in Ada.Strings.Wide_Maps   A.4.7(20)

Wide_Character_Mapping_Function
   in Ada.Strings.Wide_Maps   A.4.7(26)

Wide_Character_Range
   in Ada.Strings.Wide_Maps   A.4.7(6)

Wide_Character_Ranges
   in Ada.Strings.Wide_Maps   A.4.7(7)

Wide_Character_Sequence
   in Ada.Strings.Wide_Maps   A.4.7(16)

Wide_Character_Set
   in Ada.Strings.Wide_Maps   A.4.7(4)

Wide_Image attribute   3.5(28)

Wide_Maps
   child of Ada.Strings   A.4.7(3)

wide_nul
   in Interfaces.C   B.3(31/1)

Wide_Space
   in Ada.Strings   A.4.1(4)

Wide_String
   in Standard   A.1(41)

Wide_Value attribute   3.5(40)

Wide_Width attribute   3.5(38)

Width attribute   3.5(39)

with_clause   10.1.2(4)
   mentioned in   10.1.2(6)
   used   10.1.2(3), P

within
   immediately   8.1(13)

word   13.3(8)

Word_Size
   in System   13.7(13)

Write
   in Ada.Direct_IO   A.8.4(13)
   in Ada.Sequential_IO   A.8.1(12)
   in Ada.Storage_IO   A.9(7)
   in Ada.Streams   13.13.1(6)
   in Ada.Streams.Stream_IO   A.12.1(18), A.12.1(19)
   in System.RPC   E.5(8)

Write attribute   13.13.2(3), 13.13.2(11)

Write clause   13.3(7), 13.13.2(36/1)


X


xor operator   4.4(1), 4.5.1(2)


Y


Year
   in Ada.Calendar   9.6(13)

Year_Number
   in Ada.Calendar   9.6(11)

Yen_Sign
   in Ada.Characters.Latin_1   A.3.3(21)



                                   Annex J
                                 (normative)

                            Obsolescent Features


1     This Annex contains descriptions of features of the language whose
functionality is largely redundant with other features defined by this
International Standard. Use of these features is not recommended in newly
written programs.


J.1 Renamings of Ada 83 Library Units



                              Static Semantics

1     The following library_unit_renaming_declarations exist:

2     with Ada.Unchecked_Conversion;
      generic function Unchecked_Conversion renames Ada.Unchecked_Conversion;

3     with Ada.Unchecked_Deallocation;
      generic procedure Unchecked_Deallocation renames Ada.Unchecked_Deallocation;

4     with Ada.Sequential_IO;
      generic package Sequential_IO renames Ada.Sequential_IO;

5     with Ada.Direct_IO;
      generic package Direct_IO renames Ada.Direct_IO;

6     with Ada.Text_IO;
      package Text_IO renames Ada.Text_IO;

7     with Ada.IO_Exceptions;
      package IO_Exceptions renames Ada.IO_Exceptions;

8     with Ada.Calendar;
      package Calendar renames Ada.Calendar;

9     with System.Machine_Code;
      package Machine_Code renames System.Machine_Code; -- If supported.


                         Implementation Requirements

10    The implementation shall allow the user to replace these renamings.


J.2 Allowed Replacements of Characters



                                   Syntax

1     The following replacements are allowed for the vertical line, number
      sign, and quotation mark characters:

    2     A vertical line character (|) can be replaced by an exclamation mark
          (!) where used as a delimiter.

    3     The number sign characters (#) of a based_literal can be replaced by
          colons (:) provided that the replacement is done for both
          occurrences.

    4     The quotation marks (") used as string brackets at both ends of a
          string literal can be replaced by percent signs (%) provided that
          the enclosed sequence of characters contains no quotation mark, and
          provided that both string brackets are replaced. Any percent sign
          within the sequence of characters shall then be doubled and each
          such doubled percent sign is interpreted as a single percent sign
          character value.

5     These replacements do not change the meaning of the program.


J.3 Reduced Accuracy Subtypes


1     A digits_constraint may be used to define a floating point subtype with
a new value for its requested decimal precision, as reflected by its Digits
attribute. Similarly, a delta_constraint may be used to define an ordinary
fixed point subtype with a new value for its delta, as reflected by its Delta
attribute.


                                   Syntax

2     delta_constraint ::= delta static_expression [range_constraint]


                            Name Resolution Rules

3     The expression of a delta_constraint is expected to be of any real type.


                               Legality Rules

4     The expression of a delta_constraint shall be static.

5     For a subtype_indication with a delta_constraint, the subtype_mark shall
denote an ordinary fixed point subtype.

6     For a subtype_indication with a digits_constraint, the subtype_mark
shall denote either a decimal fixed point subtype or a floating point subtype
(notwithstanding the rule given in 3.5.9 that only allows a decimal fixed
point subtype).


                              Static Semantics

7     A subtype_indication with a subtype_mark that denotes an ordinary fixed
point subtype and a delta_constraint defines an ordinary fixed point subtype
with a delta given by the value of the expression of the delta_constraint. If
the delta_constraint includes a range_constraint, then the ordinary fixed
point subtype is constrained by the range_constraint.

8     A subtype_indication with a subtype_mark that denotes a floating point
subtype and a digits_constraint defines a floating point subtype with a
requested decimal precision (as reflected by its Digits attribute) given by
the value of the expression of the digits_constraint. If the digits_constraint
includes a range_constraint, then the floating point subtype is constrained by
the range_constraint.


                              Dynamic Semantics

9     A delta_constraint is compatible with an ordinary fixed point subtype if
the value of the expression is no less than the delta of the subtype, and the
range_constraint, if any, is compatible with the subtype.

10    A digits_constraint is compatible with a floating point subtype if the
value of the expression is no greater than the requested decimal precision of
the subtype, and the range_constraint, if any, is compatible with the subtype.

11    The elaboration of a delta_constraint consists of the elaboration of the
range_constraint, if any.


J.4 The Constrained Attribute



                              Static Semantics

1     For every private subtype S, the following attribute is defined:

2     S'Constrained
              Yields the value False if S denotes an unconstrained nonformal
              private subtype with discriminants; also yields the value False
              if S denotes a generic formal private subtype, and the
              associated actual subtype is either an unconstrained subtype
              with discriminants or an unconstrained array subtype; yields the
              value True otherwise. The value of this attribute is of the
              predefined subtype Boolean.


J.5 ASCII



                              Static Semantics

1     The following declaration exists in the declaration of package Standard:

2     package ASCII is

3       --  Control characters:

4       NUL   : constant Character := nul;                     
      SOH   : constant Character := soh;
        STX   : constant Character := stx;                     
      ETX   : constant Character := etx;
        EOT   : constant Character := eot;                     
      ENQ   : constant Character := enq;
        ACK   : constant Character := ack;                     
      BEL   : constant Character := bel;
        BS    : constant Character := bs;                      
      HT    : constant Character := ht;
        LF    : constant Character := lf;                      
      VT    : constant Character := vt;
        FF    : constant Character := ff;                      
      CR    : constant Character := cr;
        SO    : constant Character := so;                      
      SI    : constant Character := si;
        DLE   : constant Character := dle;                     
      DC1   : constant Character := dc1;
        DC2   : constant Character := dc2;                     
      DC3   : constant Character := dc3;
        DC4   : constant Character := dc4;                     
      NAK   : constant Character := nak;
        SYN   : constant Character := syn;                     
      ETB   : constant Character := etb;
        CAN   : constant Character := can;                     
      EM    : constant Character := em;
        SUB   : constant Character := sub;                     
      ESC   : constant Character := esc;
        FS    : constant Character := fs;                      
      GS    : constant Character := gs;
        RS    : constant Character := rs;                      
      US    : constant Character := us;
        DEL   : constant Character := del;

5       -- Other characters:

6       Exclam   : constant Character:= '!';                   
      Quotation : constant Character:= '"';
        Sharp    : constant Character:= '#';                   
      Dollar    : constant Character:= '$';
        Percent  : constant Character:= '%';                   
      Ampersand : constant Character:= '&';
        Colon    : constant Character:= ':';                   
      Semicolon : constant Character:= ';';
        Query    : constant Character:= '?';                   
      At_Sign   : constant Character:= '@';
        L_Bracket: constant Character:= '[';                   
      Back_Slash: constant Character:= '\';
        R_Bracket: constant Character:= ']';                   
      Circumflex: constant Character:= '^';
        Underline: constant Character:= '_';                   
      Grave     : constant Character:= '`';
        L_Brace  : constant Character:= '{';                   
      Bar       : constant Character:= '|';
        R_Brace  : constant Character:= '}';                   
      Tilde     : constant Character:= '~';

7       -- Lower case letters:

8       LC_A: constant Character:= 'a';
        ...
        LC_Z: constant Character:= 'z';

9     end ASCII;


J.6 Numeric_Error



                              Static Semantics

1     The following declaration exists in the declaration of package Standard:

2     Numeric_Error : exception renames Constraint_Error;


J.7 At Clauses



                                   Syntax

1     at_clause ::= for direct_name use at expression;


                              Static Semantics

2     An at_clause of the form ``for x use at y;'' is equivalent to an
attribute_definition_clause of the form ``for x'Address use y;''.


J.7.1 Interrupt Entries


1     Implementations are permitted to allow the attachment of task entries to
interrupts via the address clause. Such an entry is referred to as an
interrupt entry.

2     The address of the task entry corresponds to a hardware interrupt in an
implementation-defined manner. (See Ada.Interrupts.Reference in C.3.2.)


                              Static Semantics

3     The following attribute is defined:

4     For any task entry X:

5     X'Address
              For a task entry whose address is specified (an interrupt
              entry), the value refers to the corresponding hardware
              interrupt. For such an entry, as for any other task entry, the
              meaning of this value is implementation defined. The value of
              this attribute is of the type of the subtype System.Address.

        6     Address may be specified for single entries via an
              attribute_definition_clause.


                              Dynamic Semantics

7     As part of the initialization of a task object, the address clause for
an interrupt entry is elaborated, which evaluates the expression of the
address clause. A check is made that the address specified is associated with
some interrupt to which a task entry may be attached. If this check fails,
Program_Error is raised. Otherwise, the interrupt entry is attached to the
interrupt associated with the specified address.

8     Upon finalization of the task object, the interrupt entry, if any, is
detached from the corresponding interrupt and the default treatment is
restored.

9     While an interrupt entry is attached to an interrupt, the interrupt is
reserved (see C.3).

10    An interrupt delivered to a task entry acts as a call to the entry
issued by a hardware task whose priority is in the System.Interrupt_Priority
range. It is implementation defined whether the call is performed as an
ordinary entry call, a timed entry call, or a conditional entry call; which
kind of call is performed can depend on the specific interrupt.


                          Bounded (Run-Time) Errors

11    It is a bounded error to evaluate E'Caller (see C.7.1) in an
accept_statement for an interrupt entry. The possible effects are the same as
for calling Current_Task from an entry body.


                         Documentation Requirements

12    The implementation shall document to which interrupts a task entry may
be attached.

13    The implementation shall document whether the invocation of an interrupt
entry has the effect of an ordinary entry call, conditional call, or a timed
call, and whether the effect varies in the presence of pending interrupts.


                         Implementation Permissions

14    The support for this subclause is optional.

15    Interrupts to which the implementation allows a task entry to be
attached may be designated as reserved for the entire duration of program
execution; that is, not just when they have an interrupt entry attached to
them.

16/1  Interrupt entry calls may be implemented by having the hardware execute
directly the appropriate {accept_statement}[accept body]. Alternatively, the
implementation is allowed to provide an internal interrupt handler to simulate
the effect of a normal task calling the entry.

17    The implementation is allowed to impose restrictions on the
specifications and bodies of tasks that have interrupt entries.

18    It is implementation defined whether direct calls (from the program) to
interrupt entries are allowed.

19    If a select_statement contains both a terminate_alternative and an
accept_alternative for an interrupt entry, then an implementation is allowed
to impose further requirements for the selection of the terminate_alternative
in addition to those given in 9.3.

      NOTES

20/1  1  Queued interrupts correspond to ordinary entry calls. Interrupts that
      are lost if not immediately processed correspond to conditional entry
      calls. It is a consequence of the priority rules that an
      {accept_statement}[accept body] executed in response to an interrupt can
      be executed with the active priority at which the hardware generates the
      interrupt, taking precedence over lower priority tasks, without a
      scheduling action.

21    2  Control information that is supplied upon an interrupt can be passed
      to an associated interrupt entry as one or more parameters of mode in.


                                  Examples

22    Example of an interrupt entry:

23    task Interrupt_Handler is
        entry Done;
        for Done'Address use Ada.Interrupts.Reference(Ada.Interrupts.Names.Device_Done);
      end Interrupt_Handler;


J.8 Mod Clauses



                                   Syntax

1     mod_clause ::= at mod static_expression;


                              Static Semantics

2     A record_representation_clause of the form:

3     for r use
          record at mod a
              ...
          end record;

4     is equivalent to:

5     for r'Alignment use a;
      for r use
          record
              ...
          end record;


J.9 The Storage_Size Attribute



                              Static Semantics

1     For any task subtype T, the following attribute is defined:

2     T'Storage_Size
              Denotes an implementation-defined value of type
              universal_integer representing the number of storage elements
              reserved for a task of the subtype T.

3     Storage_Size may be specified for a task first subtype via an
              attribute_definition_clause.



                                   Annex K
                                (informative)

                         Language-Defined Attributes


1     This annex summarizes the definitions given elsewhere of the
language-defined attributes.

2     P'Access
              For a prefix P that denotes a subprogram:

        3     P'Access yields an access value that designates the subprogram
              denoted by P. The type of P'Access is an access-to-subprogram
              type (S), as determined by the expected type. See 3.10.2.

4     X'Access
              For a prefix X that denotes an aliased view of an object:

        5     X'Access yields an access value that designates the object
              denoted by X. The type of X'Access is an access-to-object type,
              as determined by the expected type. The expected type shall be a
              general access type. See 3.10.2.

6/1   X'Address
              For a {prefix}[prefix] X that denotes an object, program unit,
              or label:

        7     Denotes the address of the first of the storage elements
              allocated to X. For a program unit or label, this value refers
              to the machine code associated with the corresponding body or
              statement. The value of this attribute is of type
              System.Address. See 13.3.

8     S'Adjacent
              For every subtype S of a floating point type T:

        9     S'Adjacent denotes a function with the following specification:

            10    function S'Adjacent (X, Towards : T)
                    return T

        11    If Towards   =   X, the function yields X; otherwise, it yields
              the machine number of the type T adjacent to X in the direction
              of Towards, if that machine number exists. If the result would
              be outside the base range of S, Constraint_Error is raised. When
              T'Signed_Zeros is True, a zero result has the sign of X. When
              Towards is zero, its sign has no bearing on the result. See
              A.5.3.

12    S'Aft   For every fixed point subtype S:

        13    S'Aft yields the number of decimal digits needed after the
              decimal point to accommodate the delta of the subtype S, unless
              the delta of the subtype S is greater than 0.1, in which case
              the attribute yields the value one. (S'Aft is the smallest
              positive integer N for which (10**N)*S'Delta is greater than or
              equal to one.) The value of this attribute is of the type
              universal_integer. See 3.5.10.

14/1  X'Alignment
              For a {prefix}[prefix] X that denotes a subtype or object:

        15    The Address of an object that is allocated under control of the
              implementation is an integral multiple of the Alignment of the
              object (that is, the Address modulo the Alignment is zero). The
              offset of a record component is a multiple of the Alignment of
              the component. For an object that is not allocated under control
              of the implementation (that is, one that is imported, that is
              allocated by a user-defined allocator, whose Address has been
              specified, or is designated by an access value returned by an
              instance of Unchecked_Conversion), the implementation may assume
              that the Address is an integral multiple of its Alignment. The
              implementation shall not assume a stricter alignment.

        16    The value of this attribute is of type universal_integer, and
              nonnegative; zero means that the object is not necessarily
              aligned on a storage element boundary. See 13.3.

17    S'Base  For every scalar subtype S:

        18    S'Base denotes an unconstrained subtype of the type of S. This
              unconstrained subtype is called the base subtype of the type.
              See 3.5.

19    S'Bit_Order
              For every specific record subtype S:

        20    Denotes the bit ordering for the type of S. The value of this
              attribute is of type System.Bit_Order. See 13.5.3.

21/1  P'Body_Version
              For a {prefix}[prefix] P that statically denotes a program unit:

        22    Yields a value of the predefined type String that identifies the
              version of the compilation unit that contains the body (but not
              any subunits) of the program unit. See E.3.

23    T'Callable
              For a prefix T that is of a task type (after any implicit
              dereference):

        24    Yields the value True when the task denoted by T is callable,
              and False otherwise; See 9.9.

25    E'Caller
              For a prefix E that denotes an entry_declaration:

        26    Yields a value of the type Task_ID that identifies the task
              whose call is now being serviced. Use of this attribute is
              allowed only inside an entry_body or accept_statement
              corresponding to the entry_declaration denoted by E. See C.7.1.

27    S'Ceiling
              For every subtype S of a floating point type T:

        28    S'Ceiling denotes a function with the following specification:

            29    function S'Ceiling (X : T)
                    return T

        30    The function yields the value Ceiling(X), i.e., the smallest
              (most negative) integral value greater than or equal to X. When
              X is zero, the result has the sign of X; a zero result otherwise
              has a negative sign when S'Signed_Zeros is True. See A.5.3.

31    S'Class For every subtype S of an untagged private type whose full view
              is tagged:

        32    Denotes the class-wide subtype corresponding to the full view of
              S. This attribute is allowed only from the beginning of the
              private part in which the full view is declared, until the
              declaration of the full view. After the full view, the Class
              attribute of the full view can be used. See 7.3.1.

33    S'Class For every subtype S of a tagged type T (specific or class-wide):

        34    S'Class denotes a subtype of the class-wide type (called T'Class
              in this International Standard) for the class rooted at T (or if
              S already denotes a class-wide subtype, then S'Class is the same
              as S).

        35    S'Class is unconstrained. However, if S is constrained, then the
              values of S'Class are only those that when converted to the type
              T belong to S. See 3.9.

36/1  X'Component_Size
              For a {prefix}[prefix] X that denotes an array subtype or array
              object (after any implicit dereference):

        37    Denotes the size in bits of components of the type of X. The
              value of this attribute is of type universal_integer. See 13.3.

38    S'Compose
              For every subtype S of a floating point type T:

        39    S'Compose denotes a function with the following specification:

            40    function S'Compose (Fraction : T;
                                      Exponent : universal_integer)
                    return T

        41    Let v be the value Fraction · T'Machine_Radix(Exponent-k), where
              k is the normalized exponent of Fraction. If v is a machine
              number of the type T, or if |v| >= T'Model_Small, the function
              yields v; otherwise, it yields either one of the machine numbers
              of the type T adjacent to v. Constraint_Error is optionally
              raised if v is outside the base range of S. A zero result has
              the sign of Fraction when S'Signed_Zeros is True. See A.5.3.

42    A'Constrained
              For a prefix A that is of a discriminated type (after any
              implicit dereference):

        43    Yields the value True if A denotes a constant, a value, or a
              constrained variable, and False otherwise. See 3.7.2.

44    S'Copy_Sign
              For every subtype S of a floating point type T:

        45    S'Copy_Sign denotes a function with the following specification:

            46    function S'Copy_Sign (Value, Sign : T)
                    return T

        47    If the value of Value is nonzero, the function yields a result
              whose magnitude is that of Value and whose sign is that of Sign;
              otherwise, it yields the value zero. Constraint_Error is
              optionally raised if the result is outside the base range of S.
              A zero result has the sign of Sign when S'Signed_Zeros is True.
              See A.5.3.

48    E'Count For a prefix E that denotes an entry of a task or protected unit:

        49    Yields the number of calls presently queued on the entry E of
              the current instance of the unit. The value of this attribute is
              of the type universal_integer. See 9.9.

50/1  S'Definite
              For a {prefix}[prefix] S that denotes a formal indefinite
              subtype:

        51    S'Definite yields True if the actual subtype corresponding to S
              is definite; otherwise it yields False. The value of this
              attribute is of the predefined type Boolean. See 12.5.1.

52    S'Delta For every fixed point subtype S:

        53    S'Delta denotes the delta of the fixed point subtype S. The
              value of this attribute is of the type universal_real. See
              3.5.10.

54    S'Denorm
              For every subtype S of a floating point type T:

        55    Yields the value True if every value expressible in the form
                  ± mantissa · T'Machine_Radix(T'Machine_Emin)
              where mantissa is a nonzero T'Machine_Mantissa-digit fraction in
              the number base T'Machine_Radix, the first digit of which is
              zero, is a machine number (see 3.5.7) of the type T; yields the
              value False otherwise. The value of this attribute is of the
              predefined type Boolean. See A.5.3.

56    S'Digits
              For every decimal fixed point subtype S:

        57    S'Digits denotes the digits of the decimal fixed point subtype
              S, which corresponds to the number of decimal digits that are
              representable in objects of the subtype. The value of this
              attribute is of the type universal_integer. See 3.5.10.

58    S'Digits
              For every floating point subtype S:

        59    S'Digits denotes the requested decimal precision for the subtype
              S. The value of this attribute is of the type universal_integer.
              See 3.5.8.

60    S'Exponent
              For every subtype S of a floating point type T:

        61    S'Exponent denotes a function with the following specification:

            62    function S'Exponent (X : T)
                    return universal_integer

        63    The function yields the normalized exponent of X. See A.5.3.

64    S'External_Tag
              For every subtype S of a tagged type T (specific or class-wide):

        65    S'External_Tag denotes an external string representation for
              S'Tag; it is of the predefined type String. External_Tag may be
              specified for a specific tagged type via an
              attribute_definition_clause; the expression of such a clause
              shall be static. The default external tag representation is
              implementation defined. See 3.9.2 and 13.13.2. See 13.3.

66/1  A'First For a {prefix}[prefix] A that is of an array type (after any
              implicit dereference), or denotes a constrained array subtype:

        67    A'First denotes the lower bound of the first index range; its
              type is the corresponding index type. See 3.6.2.

68    S'First For every scalar subtype S:

        69    S'First denotes the lower bound of the range of S. The value of
              this attribute is of the type of S. See 3.5.

70/1  A'First(N)
              For a {prefix}[prefix] A that is of an array type (after any
              implicit dereference), or denotes a constrained array subtype:

        71    A'First(N) denotes the lower bound of the N-th index range; its
              type is the corresponding index type. See 3.6.2.

72    R.C'First_Bit
              For a component C of a composite, non-array object R:

        73    Denotes the offset, from the start of the first of the storage
              elements occupied by C, of the first bit occupied by C. This
              offset is measured in bits. The first bit of a storage element
              is numbered zero. The value of this attribute is of the type
              universal_integer. See 13.5.2.

74    S'Floor For every subtype S of a floating point type T:

        75    S'Floor denotes a function with the following specification:

            76    function S'Floor (X : T)
                    return T

        77    The function yields the value Floor(X), i.e., the largest (most
              positive) integral value less than or equal to X. When X is
              zero, the result has the sign of X; a zero result otherwise has
              a positive sign. See A.5.3.

78    S'Fore  For every fixed point subtype S:

        79    S'Fore yields the minimum number of characters needed before the
              decimal point for the decimal representation of any value of the
              subtype S, assuming that the representation does not include an
              exponent, but includes a one-character prefix that is either a
              minus sign or a space. (This minimum number does not include
              superfluous zeros or underlines, and is at least 2.) The value
              of this attribute is of the type universal_integer. See 3.5.10.

80    S'Fraction
              For every subtype S of a floating point type T:

        81    S'Fraction denotes a function with the following specification:

            82    function S'Fraction (X : T)
                    return T

        83    The function yields the value X · T'Machine_Radix(-k), where k
              is the normalized exponent of X. A zero result, which can only
              occur when X is zero, has the sign of X. See A.5.3.

84    T'Identity
              For a prefix T that is of a task type (after any implicit
              dereference):

        85    Yields a value of the type Task_ID that identifies the task
              denoted by T. See C.7.1.

86/1  E'Identity
              For a {prefix}[prefix] E that denotes an exception:

        87    E'Identity returns the unique identity of the exception. The
              type of this attribute is Exception_Id. See 11.4.1.

88    S'Image For every scalar subtype S:

        89    S'Image denotes a function with the following specification:

            90    function S'Image(Arg : S'Base)
                    return String

        91    The function returns an image of the value of Arg as a String.
              See 3.5.

92    S'Class'Input
              For every subtype S'Class of a class-wide type T'Class:

        93    S'Class'Input denotes a function with the following
              specification:

            94    function S'Class'Input(
                     Stream : access Ada.Streams.Root_Stream_Type'Class)
                     return T'Class

        95    First reads the external tag from Stream and determines the
              corresponding internal tag (by calling
              Tags.Internal_Tag(String'Input(Stream)) - see 3.9) and then
              dispatches to the subprogram denoted by the Input attribute of
              the specific type identified by the internal tag; returns that
              result. See 13.13.2.

96    S'Input For every subtype S of a specific type T:

        97    S'Input denotes a function with the following specification:

            98    function S'Input(
                     Stream : access Ada.Streams.Root_Stream_Type'Class)
                     return T

        99    S'Input reads and returns one value from Stream, using any
              bounds or discriminants written by a corresponding S'Output to
              determine how much to read. See 13.13.2.

100/1 A'Last  For a {prefix}[prefix] A that is of an array type (after any
              implicit dereference), or denotes a constrained array subtype:

        101   A'Last denotes the upper bound of the first index range; its
              type is the corresponding index type. See 3.6.2.

102   S'Last  For every scalar subtype S:

        103   S'Last denotes the upper bound of the range of S. The value of
              this attribute is of the type of S. See 3.5.

104/1 A'Last(N)
              For a {prefix}[prefix] A that is of an array type (after any
              implicit dereference), or denotes a constrained array subtype:

        105   A'Last(N) denotes the upper bound of the N-th index range; its
              type is the corresponding index type. See 3.6.2.

106   R.C'Last_Bit
              For a component C of a composite, non-array object R:

        107   Denotes the offset, from the start of the first of the storage
              elements occupied by C, of the last bit occupied by C. This
              offset is measured in bits. The value of this attribute is of
              the type universal_integer. See 13.5.2.

108   S'Leading_Part
              For every subtype S of a floating point type T:

        109   S'Leading_Part denotes a function with the following
              specification:

            110   function S'Leading_Part (X : T;
                                           Radix_Digits : universal_integer)
                    return T

        111   Let v be the value T'Machine_Radix(k-Radix_Digits), where k is
              the normalized exponent of X. The function yields the value

            112   Floor(X/v) · v, when X is nonnegative and Radix_Digits is
                  positive;

            113   Ceiling(X/v) · v, when X is negative and Radix_Digits is
                  positive.

        114   Constraint_Error is raised when Radix_Digits is zero or
              negative. A zero result, which can only occur when X is zero,
              has the sign of X. See A.5.3.

115/1 A'Length
              For a {prefix}[prefix] A that is of an array type (after any
              implicit dereference), or denotes a constrained array subtype:

        116   A'Length denotes the number of values of the first index range
              (zero for a null range); its type is universal_integer. See
              3.6.2.

117/1 A'Length(N)
              For a {prefix}[prefix] A that is of an array type (after any
              implicit dereference), or denotes a constrained array subtype:

        118   A'Length(N) denotes the number of values of the N-th index range
              (zero for a null range); its type is universal_integer. See
              3.6.2.

119   S'Machine
              For every subtype S of a floating point type T:

        120   S'Machine denotes a function with the following specification:

            121   function S'Machine (X : T)
                    return T

        122   If X is a machine number of the type T, the function yields X;
              otherwise, it yields the value obtained by rounding or
              truncating X to either one of the adjacent machine numbers of
              the type T. Constraint_Error is raised if rounding or truncating
              X to the precision of the machine numbers results in a value
              outside the base range of S. A zero result has the sign of X
              when S'Signed_Zeros is True. See A.5.3.

123   S'Machine_Emax
              For every subtype S of a floating point type T:

        124   Yields the largest (most positive) value of exponent such that
              every value expressible in the canonical form (for the type T),
              having a mantissa of T'Machine_Mantissa digits, is a machine
              number (see 3.5.7) of the type T. This attribute yields a value
              of the type universal_integer. See A.5.3.

125   S'Machine_Emin
              For every subtype S of a floating point type T:

        126   Yields the smallest (most negative) value of exponent such that
              every value expressible in the canonical form (for the type T),
              having a mantissa of T'Machine_Mantissa digits, is a machine
              number (see 3.5.7) of the type T. This attribute yields a value
              of the type universal_integer. See A.5.3.

127   S'Machine_Mantissa
              For every subtype S of a floating point type T:

        128   Yields the largest value of p such that every value expressible
              in the canonical form (for the type T), having a p-digit
              mantissa and an exponent between T'Machine_Emin and
              T'Machine_Emax, is a machine number (see 3.5.7) of the type T.
              This attribute yields a value of the type universal_integer. See
              A.5.3.

129   S'Machine_Overflows
              For every subtype S of a fixed point type T:

        130   Yields the value True if overflow and divide-by-zero are
              detected and reported by raising Constraint_Error for every
              predefined operation that yields a result of the type T; yields
              the value False otherwise. The value of this attribute is of the
              predefined type Boolean. See A.5.4.

131   S'Machine_Overflows
              For every subtype S of a floating point type T:

        132   Yields the value True if overflow and divide-by-zero are
              detected and reported by raising Constraint_Error for every
              predefined operation that yields a result of the type T; yields
              the value False otherwise. The value of this attribute is of the
              predefined type Boolean. See A.5.3.

133   S'Machine_Radix
              For every subtype S of a fixed point type T:

        134   Yields the radix of the hardware representation of the type T.
              The value of this attribute is of the type universal_integer.
              See A.5.4.

135   S'Machine_Radix
              For every subtype S of a floating point type T:

        136   Yields the radix of the hardware representation of the type T.
              The value of this attribute is of the type universal_integer.
              See A.5.3.

137   S'Machine_Rounds
              For every subtype S of a fixed point type T:

        138   Yields the value True if rounding is performed on inexact
              results of every predefined operation that yields a result of
              the type T; yields the value False otherwise. The value of this
              attribute is of the predefined type Boolean. See A.5.4.

139   S'Machine_Rounds
              For every subtype S of a floating point type T:

        140   Yields the value True if rounding is performed on inexact
              results of every predefined operation that yields a result of
              the type T; yields the value False otherwise. The value of this
              attribute is of the predefined type Boolean. See A.5.3.

141   S'Max   For every scalar subtype S:

        142   S'Max denotes a function with the following specification:

            143   function S'Max(Left, Right : S'Base)
                    return S'Base

        144   The function returns the greater of the values of the two
              parameters. See 3.5.

145   S'Max_Size_In_Storage_Elements
              For every subtype S:

        146   Denotes the maximum value for Size_In_Storage_Elements that will
              be requested via Allocate for an access type whose designated
              subtype is S. The value of this attribute is of type
              universal_integer. See 13.11.1.

147   S'Min   For every scalar subtype S:

        148   S'Min denotes a function with the following specification:

            149   function S'Min(Left, Right : S'Base)
                    return S'Base

        150   The function returns the lesser of the values of the two
              parameters. See 3.5.

151   S'Model For every subtype S of a floating point type T:

        152   S'Model denotes a function with the following specification:

            153   function S'Model (X : T)
                    return T

        154   If the Numerics Annex is not supported, the meaning of this
              attribute is implementation defined; see G.2.2 for the
              definition that applies to implementations supporting the
              Numerics Annex. See A.5.3.

155   S'Model_Emin
              For every subtype S of a floating point type T:

        156   If the Numerics Annex is not supported, this attribute yields an
              implementation defined value that is greater than or equal to
              the value of T'Machine_Emin. See G.2.2 for further requirements
              that apply to implementations supporting the Numerics Annex. The
              value of this attribute is of the type universal_integer. See
              A.5.3.

157   S'Model_Epsilon
              For every subtype S of a floating point type T:

        158   Yields the value T'Machine_Radix(1 - T'Model_Mantissa). The
              value of this attribute is of the type universal_real. See A.5.3.

159   S'Model_Mantissa
              For every subtype S of a floating point type T:

        160   If the Numerics Annex is not supported, this attribute yields an
              implementation defined value that is greater than or equal to
              Ceiling(d · log(10) / log(T'Machine_Radix)) + 1, where d is the
              requested decimal precision of T, and less than or equal to the
              value of T'Machine_Mantissa. See G.2.2 for further requirements
              that apply to implementations supporting the Numerics Annex. The
              value of this attribute is of the type universal_integer. See
              A.5.3.

161   S'Model_Small
              For every subtype S of a floating point type T:

        162   Yields the value T'Machine_Radix(T'Model_Emin - 1). The value of
              this attribute is of the type universal_real. See A.5.3.

163   S'Modulus
              For every modular subtype S:

        164   S'Modulus yields the modulus of the type of S, as a value of the
              type universal_integer. See 3.5.4.

165   S'Class'Output
              For every subtype S'Class of a class-wide type T'Class:

        166   S'Class'Output denotes a procedure with the following
              specification:

            167   procedure S'Class'Output(
                     Stream : access Ada.Streams.Root_Stream_Type'Class;
                     Item   : in T'Class)

        168   First writes the external tag of Item to Stream (by calling
              String'Output(Tags.External_Tag(Item'Tag) - see 3.9) and then
              dispatches to the subprogram denoted by the Output attribute of
              the specific type identified by the tag. See 13.13.2.

169   S'Output
              For every subtype S of a specific type T:

        170   S'Output denotes a procedure with the following specification:

            171   procedure S'Output(
                     Stream : access Ada.Streams.Root_Stream_Type'Class;
                     Item : in T)

        172   S'Output writes the value of Item to Stream, including any
              bounds or discriminants. See 13.13.2.

173/1 D'Partition_ID
              For a {prefix}[prefix] D that denotes a library-level
              declaration, excepting a declaration of or within a
              declared-pure library unit:

        174   Denotes a value of the type universal_integer that identifies
              the partition in which D was elaborated. If D denotes the
              declaration of a remote call interface library unit (see E.2.3)
              the given partition is the one where the body of D was
              elaborated. See E.1.

175   S'Pos   For every discrete subtype S:

        176   S'Pos denotes a function with the following specification:

            177   function S'Pos(Arg : S'Base)
                    return universal_integer

        178   This function returns the position number of the value of Arg,
              as a value of type universal_integer. See 3.5.5.

179   R.C'Position
              For a component C of a composite, non-array object R:

        180   Denotes the same value as R.C'Address - R'Address. The value of
              this attribute is of the type universal_integer. See 13.5.2.

181   S'Pred  For every scalar subtype S:

        182   S'Pred denotes a function with the following specification:

            183   function S'Pred(Arg : S'Base)
                    return S'Base

        184   For an enumeration type, the function returns the value whose
              position number is one less than that of the value of Arg;
              Constraint_Error is raised if there is no such value of the
              type. For an integer type, the function returns the result of
              subtracting one from the value of Arg. For a fixed point type,
              the function returns the result of subtracting small from the
              value of Arg. For a floating point type, the function returns
              the machine number (as defined in 3.5.7) immediately below the
              value of Arg; Constraint_Error is raised if there is no such
              machine number. See 3.5.

185/1 A'Range For a {prefix}[prefix] A that is of an array type (after any
              implicit dereference), or denotes a constrained array subtype:

        186   A'Range is equivalent to the range A'First .. A'Last, except
              that the prefix A is only evaluated once. See 3.6.2.

187   S'Range For every scalar subtype S:

        188   S'Range is equivalent to the range S'First .. S'Last. See 3.5.

189/1 A'Range(N)
              For a {prefix}[prefix] A that is of an array type (after any
              implicit dereference), or denotes a constrained array subtype:

        190   A'Range(N) is equivalent to the range A'First(N) .. A'Last(N),
              except that the prefix A is only evaluated once. See 3.6.2.

191   S'Class'Read
              For every subtype S'Class of a class-wide type T'Class:

        192   S'Class'Read denotes a procedure with the following
              specification:

            193   procedure S'Class'Read(
                     Stream : access Ada.Streams.Root_Stream_Type'Class;
                     Item : out T'Class)

        194   Dispatches to the subprogram denoted by the Read attribute of
              the specific type identified by the tag of Item. See 13.13.2.

195   S'Read  For every subtype S of a specific type T:

        196   S'Read denotes a procedure with the following specification:

            197   procedure S'Read(
                     Stream : access Ada.Streams.Root_Stream_Type'Class;
                     Item : out T)

        198   S'Read reads the value of Item from Stream. See 13.13.2.

199   S'Remainder
              For every subtype S of a floating point type T:

        200   S'Remainder denotes a function with the following specification:

            201   function S'Remainder (X, Y : T)
                    return T

        202   For nonzero Y, let v be the value X - n · Y, where n is the
              integer nearest to the exact value of X/Y; if |n - X/Y|   =  
              1/2, then n is chosen to be even. If v is a machine number of
              the type T, the function yields v; otherwise, it yields zero.
              Constraint_Error is raised if Y is zero. A zero result has the
              sign of X when S'Signed_Zeros is True. See A.5.3.

203   S'Round For every decimal fixed point subtype S:

        204   S'Round denotes a function with the following specification:

            205   function S'Round(X : universal_real)
                    return S'Base

        206   The function returns the value obtained by rounding X (away from
              0, if X is midway between two values of the type of S). See
              3.5.10.

207   S'Rounding
              For every subtype S of a floating point type T:

        208   S'Rounding denotes a function with the following specification:

            209   function S'Rounding (X : T)
                    return T

        210   The function yields the integral value nearest to X, rounding
              away from zero if X lies exactly halfway between two integers. A
              zero result has the sign of X when S'Signed_Zeros is True. See
              A.5.3.

211   S'Safe_First
              For every subtype S of a floating point type T:

        212   Yields the lower bound of the safe range (see 3.5.7) of the type
              T. If the Numerics Annex is not supported, the value of this
              attribute is implementation defined; see G.2.2 for the
              definition that applies to implementations supporting the
              Numerics Annex. The value of this attribute is of the type
              universal_real. See A.5.3.

213   S'Safe_Last
              For every subtype S of a floating point type T:

        214   Yields the upper bound of the safe range (see 3.5.7) of the type
              T. If the Numerics Annex is not supported, the value of this
              attribute is implementation defined; see G.2.2 for the
              definition that applies to implementations supporting the
              Numerics Annex. The value of this attribute is of the type
              universal_real. See A.5.3.

215   S'Scale For every decimal fixed point subtype S:

        216   S'Scale denotes the scale of the subtype S, defined as the value
              N such that S'Delta = 10.0**(-N). The scale indicates the
              position of the point relative to the rightmost significant
              digits of values of subtype S. The value of this attribute is of
              the type universal_integer. See 3.5.10.

217   S'Scaling
              For every subtype S of a floating point type T:

        218   S'Scaling denotes a function with the following specification:

            219   function S'Scaling (X : T;
                                      Adjustment : universal_integer)
                    return T

        220   Let v be the value X · T'Machine_Radix(Adjustment). If v is a
              machine number of the type T, or if |v| >= T'Model_Small, the
              function yields v; otherwise, it yields either one of the
              machine numbers of the type T adjacent to v. Constraint_Error is
              optionally raised if v is outside the base range of S. A zero
              result has the sign of X when S'Signed_Zeros is True. See A.5.3.

221   S'Signed_Zeros
              For every subtype S of a floating point type T:

        222   Yields the value True if the hardware representation for the
              type T has the capability of representing both positively and
              negatively signed zeros, these being generated and used by the
              predefined operations of the type T as specified in IEC
              559:1989; yields the value False otherwise. The value of this
              attribute is of the predefined type Boolean. See A.5.3.

223   S'Size  For every subtype S:

        224   If S is definite, denotes the size (in bits) that the
              implementation would choose for the following objects of subtype
              S:

            225   A record component of subtype S when the record type is
                  packed.

            226   The formal parameter of an instance of Unchecked_Conversion
                  that converts from subtype S to some other subtype.

        227   If S is indefinite, the meaning is implementation defined. The
              value of this attribute is of the type universal_integer. See
              13.3.

228/1 X'Size  For a {prefix}[prefix] X that denotes an object:

        229   Denotes the size in bits of the representation of the object.
              The value of this attribute is of the type universal_integer.
              See 13.3.

230   S'Small For every fixed point subtype S:

        231   S'Small denotes the small of the type of S. The value of this
              attribute is of the type universal_real. See 3.5.10.

232   S'Storage_Pool
              For every access subtype S:

        233   Denotes the storage pool of the type of S. The type of this
              attribute is Root_Storage_Pool'Class. See 13.11.

234   S'Storage_Size
              For every access subtype S:

        235   Yields the result of calling Storage_Size(S'Storage_Pool), which
              is intended to be a measure of the number of storage elements
              reserved for the pool. The type of this attribute is
              universal_integer. See 13.11.

236/1 T'Storage_Size
              For a {prefix}[prefix] T that denotes a task object (after any
              implicit dereference):

        237   Denotes the number of storage elements reserved for the task.
              The value of this attribute is of the type universal_integer.
              The Storage_Size includes the size of the task's stack, if any.
              The language does not specify whether or not it includes other
              storage associated with the task (such as the ``task control
              block'' used by some implementations.) See 13.3.

238   S'Succ  For every scalar subtype S:

        239   S'Succ denotes a function with the following specification:

            240   function S'Succ(Arg : S'Base)
                    return S'Base

        241   For an enumeration type, the function returns the value whose
              position number is one more than that of the value of Arg;
              Constraint_Error is raised if there is no such value of the
              type. For an integer type, the function returns the result of
              adding one to the value of Arg. For a fixed point type, the
              function returns the result of adding small to the value of Arg.
              For a floating point type, the function returns the machine
              number (as defined in 3.5.7) immediately above the value of Arg;
              Constraint_Error is raised if there is no such machine number.
              See 3.5.

242   X'Tag   For a prefix X that is of a class-wide tagged type (after any
              implicit dereference):

        243   X'Tag denotes the tag of X. The value of this attribute is of
              type Tag. See 3.9.

244   S'Tag   For every subtype S of a tagged type T (specific or class-wide):

        245   S'Tag denotes the tag of the type T (or if T is class-wide, the
              tag of the root type of the corresponding class). The value of
              this attribute is of type Tag. See 3.9.

246   T'Terminated
              For a prefix T that is of a task type (after any implicit
              dereference):

        247   Yields the value True if the task denoted by T is terminated,
              and False otherwise. The value of this attribute is of the
              predefined type Boolean. See 9.9.

248   S'Truncation
              For every subtype S of a floating point type T:

        249   S'Truncation denotes a function with the following
              specification:

            250   function S'Truncation (X : T)
                    return T

        251   The function yields the value Ceiling(X) when X is negative, and
              Floor(X) otherwise. A zero result has the sign of X when
              S'Signed_Zeros is True. See A.5.3.

252   S'Unbiased_Rounding
              For every subtype S of a floating point type T:

        253   S'Unbiased_Rounding denotes a function with the following
              specification:

            254   function S'Unbiased_Rounding (X : T)
                    return T

        255   The function yields the integral value nearest to X, rounding
              toward the even integer if X lies exactly halfway between two
              integers. A zero result has the sign of X when S'Signed_Zeros is
              True. See A.5.3.

256   X'Unchecked_Access
              For a prefix X that denotes an aliased view of an object:

        257   All rules and semantics that apply to X'Access (see 3.10.2)
              apply also to X'Unchecked_Access, except that, for the purposes
              of accessibility rules and checks, it is as if X were declared
              immediately within a library package. See 13.10.

258   S'Val   For every discrete subtype S:

        259   S'Val denotes a function with the following specification:

            260   function S'Val(Arg : universal_integer)
                    return S'Base

        261   This function returns a value of the type of S whose position
              number equals the value of Arg. See 3.5.5.

262   X'Valid For a prefix X that denotes a scalar object (after any implicit
              dereference):

        263   Yields True if and only if the object denoted by X is normal and
              has a valid representation. The value of this attribute is of
              the predefined type Boolean. See 13.9.2.

264   S'Value For every scalar subtype S:

        265   S'Value denotes a function with the following specification:

            266   function S'Value(Arg : String)
                    return S'Base

        267   This function returns a value given an image of the value as a
              String, ignoring any leading or trailing spaces. See 3.5.

268/1 P'Version
              For a {prefix}[prefix] P that statically denotes a program unit:

        269   Yields a value of the predefined type String that identifies the
              version of the compilation unit that contains the declaration of
              the program unit. See E.3.

270   S'Wide_Image
              For every scalar subtype S:

        271   S'Wide_Image denotes a function with the following
              specification:

            272   function S'Wide_Image(Arg : S'Base)
                    return Wide_String

        273   The function returns an image of the value of Arg, that is, a
              sequence of characters representing the value in display form.
              See 3.5.

274   S'Wide_Value
              For every scalar subtype S:

        275   S'Wide_Value denotes a function with the following
              specification:

            276   function S'Wide_Value(Arg : Wide_String)
                    return S'Base

        277   This function returns a value given an image of the value as a
              Wide_String, ignoring any leading or trailing spaces. See 3.5.

278   S'Wide_Width
              For every scalar subtype S:

        279   S'Wide_Width denotes the maximum length of a Wide_String
              returned by S'Wide_Image over all values of the subtype S. It
              denotes zero for a subtype that has a null range. Its type is
              universal_integer. See 3.5.

280   S'Width For every scalar subtype S:

        281   S'Width denotes the maximum length of a String returned by
              S'Image over all values of the subtype S. It denotes zero for a
              subtype that has a null range. Its type is universal_integer.
              See 3.5.

282   S'Class'Write
              For every subtype S'Class of a class-wide type T'Class:

        283   S'Class'Write denotes a procedure with the following
              specification:

            284   procedure S'Class'Write(
                     Stream : access Ada.Streams.Root_Stream_Type'Class;
                     Item   : in T'Class)

        285   Dispatches to the subprogram denoted by the Write attribute of
              the specific type identified by the tag of Item. See 13.13.2.

286   S'Write For every subtype S of a specific type T:

        287   S'Write denotes a procedure with the following specification:

            288   procedure S'Write(
                     Stream : access Ada.Streams.Root_Stream_Type'Class;
                     Item : in T)

        289   S'Write writes the value of Item to Stream. See 13.13.2.



                                   Annex L
                                (informative)

                          Language-Defined Pragmas


1     This Annex summarizes the definitions given elsewhere of the
language-defined pragmas.

2     pragma All_Calls_Remote[(library_unit_name)]; - See E.2.3.

3     pragma Asynchronous(local_name); - See E.4.1.

4     pragma Atomic(local_name); - See C.6.

5     pragma Atomic_Components(array_local_name); - See C.6.

6     pragma Attach_Handler(handler_name, expression); - See C.3.1.

7     pragma Controlled(first_subtype_local_name); - See 13.11.3.

8     pragma Convention([Convention =>] convention_identifier,[Entity =>]
local_name); - See B.1.

9     pragma Discard_Names[([On => ] local_name)]; - See C.5.

10    pragma Elaborate(library_unit_name{, library_unit_name}); - See 10.2.1.

11    pragma Elaborate_All(library_unit_name{, library_unit_name}); - See
10.2.1.

12    pragma Elaborate_Body[(library_unit_name)]; - See 10.2.1.

13    pragma Export(
     [Convention =>] convention_identifier, [Entity =>] local_name
  [, [External_Name =>] string_expression] [, [Link_Name =>]
string_expression]); - See B.1.

14    pragma Import(
     [Convention =>] convention_identifier, [Entity =>] local_name
  [, [External_Name =>] string_expression] [, [Link_Name =>]
string_expression]); - See B.1.

15    pragma Inline(name {, name}); - See 6.3.2.

16    pragma Inspection_Point[(object_name {, object_name})]; - See H.3.2.

17    pragma Interrupt_Handler(handler_name); - See C.3.1.

18    pragma Interrupt_Priority[(expression)]; - See D.1.

19    pragma Linker_Options(string_expression); - See B.1.

20    pragma List(identifier); - See 2.8.

21    pragma Locking_Policy(policy_identifier); - See D.3.

22    pragma Normalize_Scalars; - See H.1.

23    pragma Optimize(identifier); - See 2.8.

24    pragma Pack(first_subtype_local_name); - See 13.2.

25    pragma Page; - See 2.8.

26    pragma Preelaborate[(library_unit_name)]; - See 10.2.1.

27    pragma Priority(expression); - See D.1.

28    pragma Pure[(library_unit_name)]; - See 10.2.1.

29    pragma Queuing_Policy(policy_identifier); - See D.4.

30    pragma Remote_Call_Interface[(library_unit_name)]; - See E.2.3.

31    pragma Remote_Types[(library_unit_name)]; - See E.2.2.

32    pragma Restrictions(restriction{, restriction}); - See 13.12.

33    pragma Reviewable; - See H.3.1.

34    pragma Shared_Passive[(library_unit_name)]; - See E.2.1.

35    pragma Storage_Size(expression); - See 13.3.

36    pragma Suppress(identifier [, [On =>] name]); - See 11.5.

37    pragma Task_Dispatching_Policy(policy_identifier ); - See D.2.2.

38    pragma Volatile(local_name); - See C.6.

39    pragma Volatile_Components(array_local_name); - See C.6.



                           The Standard Libraries




                                   Annex M
                                (informative)

                   Implementation-Defined Characteristics


1     The Ada language allows for certain machine dependences in a controlled
manner. Each Ada implementation must document all implementation-defined
characteristics:

2     Whether or not each recommendation given in Implementation Advice is
      followed. See 1.1.2(37).

3     Capacity limitations of the implementation. See 1.1.3(3).

4     Variations from the standard that are impractical to avoid given the
      implementation's execution environment. See 1.1.3(6).

5     Which code_statements cause external interactions. See 1.1.3(10).

6     The coded representation for the text of an Ada program. See 2.1(4).

7     The control functions allowed in comments. See 2.1(14).

8     The representation for an end of line. See 2.2(2).

9     Maximum supported line length and lexical element length. See 2.2(14).

10    Implementation-defined pragmas. See 2.8(14).

11    Effect of pragma Optimize. See 2.8(27).

12    The sequence of characters of the value returned by S'Image when some of
      the graphic characters of S'Wide_Image are not defined in Character. See
      3.5(37).

13    The predefined integer types declared in Standard. See 3.5.4(25).

14    Any nonstandard integer types and the operators defined for them. See
      3.5.4(26).

15    Any nonstandard real types and the operators defined for them. See
      3.5.6(8).

16    What combinations of requested decimal precision and range are supported
      for floating point types. See 3.5.7(7).

17    The predefined floating point types declared in Standard. See 3.5.7(16).

18    The small of an ordinary fixed point type. See 3.5.9(8).

19    What combinations of small, range, and digits are supported for fixed
      point types. See 3.5.9(10).

20    The result of Tags.Expanded_Name for types declared within an unnamed
      block_statement. See 3.9(10).

21    Implementation-defined attributes. See 4.1.4(12/1).

22    Any implementation-defined time types. See 9.6(6).

23    The time base associated with relative delays. See 9.6(20).

24    The time base of the type Calendar.Time. See 9.6(23).

25    The timezone used for package Calendar operations. See 9.6(24).

26    Any limit on delay_until_statements of select_statements. See 9.6(29).

27    Whether or not two nonoverlapping parts of a composite object are
      independently addressable, in the case where packing, record layout, or
      Component_Size is specified for the object. See 9.10(1).

28    The representation for a compilation. See 10.1(2).

29    Any restrictions on compilations that contain multiple
      compilation_units. See 10.1(4).

30    The mechanisms for creating an environment and for adding and replacing
      compilation units. See 10.1.4(3).

31    The implementation-defined means, if any, of specifying which
      compilation units are needed by a given compilation unit. See 10.2(2).

32    The manner of explicitly assigning library units to a partition. See
      10.2(2).

33    The manner of designating the main subprogram of a partition. See
      10.2(7).

34    The order of elaboration of library_items. See 10.2(18).

35    Parameter passing and function return for the main subprogram. See
      10.2(21).

36    The mechanisms for building and running partitions. See 10.2(24).

37    The details of program execution, including program termination. See
      10.2(25).

38    The semantics of any nonactive partitions supported by the
      implementation. See 10.2(28).

39    The information returned by Exception_Message. See 11.4.1(10).

40    The result of Exceptions.Exception_Name for types declared within an
      unnamed block_statement. See 11.4.1(12).

41    The information returned by Exception_Information. See 11.4.1(13).

42    Implementation-defined check names. See 11.5(27).

43    Any restrictions placed upon representation items. See 13.1(20).

44    The interpretation of each aspect of representation. See 13.1(20).

45    The meaning of Size for indefinite subtypes. See 13.3(48).

46    The default external representation for a type tag. See 13.3(75/1).

47    What determines whether a compilation unit is the same in two different
      partitions. See 13.3(76).

48    Implementation-defined components. See 13.5.1(15).

49    If Word_Size = Storage_Unit, the default bit ordering. See 13.5.3(5).

50    The contents of the visible part of package System and its
      language-defined children. See 13.7(2).

51    The contents of the visible part of package System.Machine_Code, and the
      meaning of code_statements. See 13.8(7).

52    The effect of unchecked conversion. See 13.9(11).

53    Whether or not the implementation provides user-accessible names for the
      standard pool type(s). See 13.11(17).

54    The manner of choosing a storage pool for an access type when
      Storage_Pool is not specified for the type. See 13.11(17).

55    The meaning of Storage_Size. See 13.11(18).

56    Implementation-defined aspects of storage pools. See 13.11(22).

57    The set of restrictions allowed in a pragma Restrictions. See 13.12(7).

58    The consequences of violating limitations on Restrictions pragmas. See
      13.12(9).

59    The representation used by the Read and Write attributes of elementary
      types in terms of stream elements. See 13.13.2(9).

60    The names and characteristics of the numeric subtypes declared in the
      visible part of package Standard. See A.1(3).

61    The accuracy actually achieved by the elementary functions. See A.5.1(1).

62    The sign of a zero result from some of the operators or functions in
      Numerics.Generic_Elementary_Functions, when Float_Type'Signed_Zeros is
      True. See A.5.1(46).

63    The value of Numerics.Discrete_Random.Max_Image_Width. See A.5.2(27).

64    The value of Numerics.Float_Random.Max_Image_Width. See A.5.2(27).

65    The algorithms for random number generation. See A.5.2(32).

66    The string representation of a random number generator's state. See
      A.5.2(38).

67    The minimum time interval between calls to the time-dependent Reset
      procedure that are guaranteed to initiate different random number
      sequences. See A.5.2(45).

68    The values of the Model_Mantissa, Model_Emin, Model_Epsilon, Model,
      Safe_First, and Safe_Last attributes, if the Numerics Annex is not
      supported. See A.5.3(72).

69    Any implementation-defined characteristics of the input-output packages.
      See A.7(14).

70    The value of Buffer_Size in Storage_IO. See A.9(10).

71    external files for standard input, standard output, and standard error
      See A.10(5).

72    The accuracy of the value produced by Put. See A.10.9(36).

72.1/1 {Current size for a stream file for which positioning is not
      supported.}{ See A.12.1(1.1/1).}

73    The meaning of Argument_Count, Argument, and Command_Name. See A.15(1).

74    Implementation-defined convention names. See B.1(11).

75    The manner of choosing link names when neither the link name nor the
      address of an imported or exported entity is specified. See B.1(36).

76    The meaning of link names. See B.1(36).

77    The effect of pragma Linker_Options. See B.1(37).

78    The contents of the visible part of package Interfaces and its
      language-defined descendants. See B.2(1).

79    Implementation-defined children of package Interfaces. The contents of
      the visible part of package Interfaces. See B.2(11).

79.1/1 {The definitions of types and constants in Interfaces.C.}{ See B.3(41).}

80/1  The types Floating, Long_Floating, Binary, Long_Binary, Decimal_Element,
      and COBOL_Character; and the initializations of the variables
      Ada_To_COBOL and COBOL_To_Ada, in Interfaces.COBOL{.} See B.4(50).

80.1/1 {The types Fortran_Integer, Real, Double_Precision, and Character_Set
      in Interfaces.Fortran.}{ See B.5(17).}

81    Support for access to machine instructions. See C.1(1).

82    Implementation-defined aspects of access to machine operations. See
      C.1(9).

83    Implementation-defined aspects of interrupts. See C.3(2).

84    Implementation-defined aspects of preelaboration. See C.4(13).

85    The semantics of pragma Discard_Names. See C.5(7).

86    The result of the Task_Identification.Image attribute. See C.7.1(7).

87    The value of Current_Task when in a protected entry or interrupt
      handler. See C.7.1(17).

88    The effect of calling Current_Task from an entry body or interrupt
      handler. See C.7.1(19).

88.1/1 {Granularity of locking for Task_Attributes.}{ See C.7.2(16/1).}

89/1  {Limits on the number and size of task attributes, and how to configure
      them.}[Implementation-defined aspects of Task_Attributes.] See C.7.2(19).

90    Values of all Metrics. See D(2).

91    The declarations of Any_Priority and Priority. See D.1(11).

92    Implementation-defined execution resources. See D.1(15).

93    Whether, on a multiprocessor, a task that is waiting for access to a
      protected object keeps its processor busy. See D.2.1(3).

94    The affect of implementation defined execution resources on task
      dispatching. See D.2.1(9).

95    Implementation-defined policy_identifiers allowed in a pragma
      Task_Dispatching_Policy. See D.2.2(3).

96    Implementation-defined aspects of priority inversion. See D.2.2(16).

97    Implementation defined task dispatching. See D.2.2(18).

98    Implementation-defined policy_identifiers allowed in a pragma
      Locking_Policy. See D.3(4).

99    Default ceiling priorities. See D.3(10).

100   The ceiling of any protected object used internally by the
      implementation. See D.3(16).

101   Implementation-defined queuing policies. See D.4(1/1).

102   On a multiprocessor, any conditions that cause the completion of an
      aborted construct to be delayed later than what is specified for a
      single processor. See D.6(3).

103   Any operations that implicitly require heap storage allocation. See
      D.7(8).

104   Implementation-defined aspects of pragma Restrictions. See D.7(20).

105   Implementation-defined aspects of package Real_Time. See D.8(17).

106   Implementation-defined aspects of delay_statements. See D.9(8).

107   The upper bound on the duration of interrupt blocking caused by the
      implementation. See D.12(5).

108   The means for creating and executing distributed programs. See E(5).

109   Any events that can result in a partition becoming inaccessible. See
      E.1(7).

110   The scheduling policies, treatment of priorities, and management of
      shared resources between partitions in certain cases. See E.1(11).

111/1 This paragraph was deleted.[Events that cause the version of a
      compilation unit to change.][ See E.3(5/1).]

112   Whether the execution of the remote subprogram is immediately aborted as
      a result of cancellation. See E.4(13).

113   Implementation-defined aspects of the PCS. See E.5(25).

114   Implementation-defined interfaces in the PCS. See E.5(26).

115   The values of named numbers in the package Decimal. See F.2(7).

116   The value of Max_Picture_Length in the package Text_IO.Editing See
      F.3.3(16).

117   The value of Max_Picture_Length in the package Wide_Text_IO.Editing See
      F.3.4(5).

118   The accuracy actually achieved by the complex elementary functions and
      by other complex arithmetic operations. See G.1(1).

119   The sign of a zero result (or a component thereof) from any operator or
      function in Numerics.Generic_Complex_Types, when Real'Signed_Zeros is
      True. See G.1.1(53).

120   The sign of a zero result (or a component thereof) from any operator or
      function in Numerics.Generic_Complex_Elementary_Functions, when
      Complex_Types.Real'Signed_Zeros is True. See G.1.2(45).

121   Whether the strict mode or the relaxed mode is the default. See G.2(2).

122   The result interval in certain cases of fixed-to-float conversion. See
      G.2.1(10).

123   The result of a floating point arithmetic operation in overflow
      situations, when the Machine_Overflows attribute of the result type is
      False. See G.2.1(13).

124   The result interval for division (or exponentiation by a negative
      exponent), when the floating point hardware implements division as
      multiplication by a reciprocal. See G.2.1(16).

125   The definition of close result set, which determines the accuracy of
      certain fixed point multiplications and divisions. See G.2.3(5).

126   Conditions on a universal_real operand of a fixed point multiplication
      or division for which the result shall be in the perfect result set. See
      G.2.3(22).

127   The result of a fixed point arithmetic operation in overflow situations,
      when the Machine_Overflows attribute of the result type is False. See
      G.2.3(27).

128   The result of an elementary function reference in overflow situations,
      when the Machine_Overflows attribute of the result type is False. See
      G.2.4(4).

129   The accuracy of certain elementary functions for parameters beyond the
      angle threshold. See G.2.4(10).

130   The value of the angle threshold, within which certain elementary
      functions, complex arithmetic operations, and complex elementary
      functions yield results conforming to a maximum relative error bound.
      See G.2.4(10).

131   The result of a complex arithmetic operation or complex elementary
      function reference in overflow situations, when the Machine_Overflows
      attribute of the corresponding real type is False. See G.2.6(5).

132   The accuracy of certain complex arithmetic operations and certain
      complex elementary functions for parameters (or components thereof)
      beyond the angle threshold. See G.2.6(8).

133   Information regarding bounded errors and erroneous execution. See H.2(1).

134   Implementation-defined aspects of pragma Inspection_Point. See H.3.2(8).

135   Implementation-defined aspects of pragma Restrictions. See H.4(25).

136   Any restrictions on pragma Restrictions. See H.4(27).



                                   Annex N
                                (informative)

                                  Glossary


1     This Annex contains informal descriptions of some terms used in this
International Standard. To find more formal definitions, look the term up in
the index.

2     Access type. An access type has values that designate aliased objects.
Access types correspond to ``pointer types'' or ``reference types'' in some
other languages.

3     Aliased. An aliased view of an object is one that can be designated by
an access value. Objects allocated by allocators are aliased. Objects can also
be explicitly declared as aliased with the reserved word aliased. The Access
attribute can be used to create an access value designating an aliased object.

4     Array type. An array type is a composite type whose components are all
of the same type. Components are selected by indexing.

5     Character type. A character type is an enumeration type whose values
include characters.

6     Class. A class is a set of types that is closed under derivation, which
means that if a given type is in the class, then all types derived from that
type are also in the class. The set of types of a class share common
properties, such as their primitive operations.

7     Compilation unit. The text of a program can be submitted to the compiler
in one or more compilations. Each compilation is a succession of
compilation_units. A compilation_unit contains either the declaration, the
body, or a renaming of a program unit.

8     Composite type. A composite type has components.

9     Construct. A construct is a piece of text (explicit or implicit) that is
an instance of a syntactic category defined under ``Syntax.''

10    Controlled type. A controlled type supports user-defined assignment and
finalization. Objects are always finalized before being destroyed.

11    Declaration. A declaration is a language construct that associates a
name with (a view of) an entity. A declaration may appear explicitly in the
program text (an explicit declaration), or may be supposed to occur at a given
place in the text as a consequence of the semantics of another construct (an
implicit declaration).

12    Definition. All declarations contain a definition for a view of an
entity. A view consists of an identification of the entity (the entity of the
view), plus view-specific characteristics that affect the use of the entity
through that view (such as mode of access to an object, formal parameter names
and defaults for a subprogram, or visibility to components of a type). In most
cases, a declaration also contains the definition for the entity itself (a
renaming_declaration is an example of a declaration that does not define a new
entity, but instead defines a view of an existing entity (see 8.5)).

13    Derived type. A derived type is a type defined in terms of another type,
which is the parent type of the derived type. Each class containing the parent
type also contains the derived type. The derived type inherits properties such
as components and primitive operations from the parent. A type together with
the types derived from it (directly or indirectly) form a derivation class.

14    Discrete type. A discrete type is either an integer type or an
enumeration type. Discrete types may be used, for example, in case_statements
and as array indices.

15    Discriminant. A discriminant is a parameter of a composite type. It can
control, for example, the bounds of a component of the type if that type is an
array type. A discriminant of a task type can be used to pass data to a task
of the type upon creation.

16    Elementary type. An elementary type does not have components.

17    Enumeration type. An enumeration type is defined by an enumeration of
its values, which may be named by identifiers or character literals.

18    Exception. An exception represents a kind of exceptional situation; an
occurrence of such a situation (at run time) is called an exception
occurrence. To raise an exception is to abandon normal program execution so as
to draw attention to the fact that the corresponding situation has arisen.
Performing some actions in response to the arising of an exception is called
handling the exception.

19    Execution. The process by which a construct achieves its run-time effect
is called execution. Execution of a declaration is also called elaboration.
Execution of an expression is also called evaluation.

20    Generic unit. A generic unit is a template for a (nongeneric) program
unit; the template can be parameterized by objects, types, subprograms, and
packages. An instance of a generic unit is created by a generic_instantiation.
The rules of the language are enforced when a generic unit is compiled, using
a generic contract model; additional checks are performed upon instantiation
to verify the contract is met. That is, the declaration of a generic unit
represents a contract between the body of the generic and instances of the
generic. Generic units can be used to perform the role that macros sometimes
play in other languages.

21    Integer type. Integer types comprise the signed integer types and the
modular types. A signed integer type has a base range that includes both
positive and negative numbers, and has operations that may raise an exception
when the result is outside the base range. A modular type has a base range
whose lower bound is zero, and has operations with ``wraparound'' semantics.
Modular types subsume what are called ``unsigned types'' in some other
languages.

22    Library unit. A library unit is a separately compiled program unit, and
is always a package, subprogram, or generic unit. Library units may have other
(logically nested) library units as children, and may have other program units
physically nested within them. A root library unit, together with its children
and grandchildren and so on, form a subsystem.

23    Limited type. A limited type is (a view of) a type for which the
assignment operation is not allowed. A nonlimited type is a (view of a) type
for which the assignment operation is allowed.

24    Object. An object is either a constant or a variable. An object contains
a value. An object is created by an object_declaration or by an allocator. A
formal parameter is (a view of) an object. A subcomponent of an object is an
object.

25    Package. Packages are program units that allow the specification of
groups of logically related entities. Typically, a package contains the
declaration of a type (often a private type or private extension) along with
the declarations of primitive subprograms of the type, which can be called
from outside the package, while their inner workings remain hidden from
outside users.

26    Partition. A partition is a part of a program. Each partition consists
of a set of library units. Each partition may run in a separate address space,
possibly on a separate computer. A program may contain just one partition. A
distributed program typically contains multiple partitions, which can execute
concurrently.

27    Pragma. A pragma is a compiler directive. There are language-defined
pragmas that give instructions for optimization, listing control, etc. An
implementation may support additional (implementation-defined) pragmas.

28    Primitive operations. The primitive operations of a type are the
operations (such as subprograms) declared together with the type declaration.
They are inherited by other types in the same class of types. For a tagged
type, the primitive subprograms are dispatching subprograms, providing
run-time polymorphism. A dispatching subprogram may be called with statically
tagged operands, in which case the subprogram body invoked is determined at
compile time. Alternatively, a dispatching subprogram may be called using a
dispatching call, in which case the subprogram body invoked is determined at
run time.

29    Private extension. A private extension is like a record extension,
except that the components of the extension part are hidden from its clients.

30    Private type. A private type is a partial view of a type whose full view
is hidden from its clients.

31    Program. A program is a set of partitions, each of which may execute in
a separate address space, possibly on a separate computer. A partition
consists of a set of library units.

32    Program unit. A program unit is either a package, a task unit, a
protected unit, a protected entry, a generic unit, or an explicitly declared
subprogram other than an enumeration literal. Certain kinds of program units
can be separately compiled. Alternatively, they can appear physically nested
within other program units.

33    Protected type. A protected type is a composite type whose components
are protected from concurrent access by multiple tasks.

34    Real type. A real type has values that are approximations of the real
numbers. Floating point and fixed point types are real types.

35    Record extension. A record extension is a type that extends another type
by adding additional components.

36    Record type. A record type is a composite type consisting of zero or
more named components, possibly of different types.

37    Scalar type. A scalar type is either a discrete type or a real type.

38    Subtype. A subtype is a type together with a constraint, which
constrains the values of the subtype to satisfy a certain condition. The
values of a subtype are a subset of the values of its type.

39    Tagged type. The objects of a tagged type have a run-time type tag,
which indicates the specific type with which the object was originally
created. An operand of a class-wide tagged type can be used in a dispatching
call; the tag indicates which subprogram body to invoke. Nondispatching calls,
in which the subprogram body to invoke is determined at compile time, are also
allowed. Tagged types may be extended with additional components.

40    Task type. A task type is a composite type whose values are tasks, which
are active entities that may execute concurrently with other tasks. The
top-level task of a partition is called the environment task.

41    Type. Each object has a type. A type has an associated set of values,
and a set of primitive operations which implement the fundamental aspects of
its semantics. Types are grouped into classes. The types of a given class
share a set of primitive operations. Classes are closed under derivation; that
is, if a type is in a class, then all of its derivatives are in that class.

42    View. (See Definition.)



                                   Annex P
                                (informative)

                               Syntax Summary


This Annex summarizes the complete syntax of the language. See 1.1.4 for a
description of the notation used.

      2.1:
      character::= graphic_character | format_effector
       | other_control_function

      2.1:
      graphic_character::= identifier_letter | digit | space_character
       | special_character

      2.3:
      identifier::= 
         identifier_letter {[underline] letter_or_digit}

      2.3:
      letter_or_digit::= identifier_letter | digit

      2.4:
      numeric_literal::= decimal_literal | based_literal

      2.4.1:
      decimal_literal::= numeral [.numeral] [exponent]

      2.4.1:
      numeral::= digit {[underline] digit}

      2.4.1:
      exponent::= E [+] numeral | E - numeral

      2.4.2:
      based_literal::= 
         base # based_numeral [.based_numeral] # [exponent]

      2.4.2:
      base::= numeral

      2.4.2:
      based_numeral::= 
         extended_digit {[underline] extended_digit}

      2.4.2:
      extended_digit::= digit | A | B | C | D | E | F

      2.5:
      character_literal::= 'graphic_character'

      2.6:
      string_literal::= "{string_element}"

      2.6:
      string_element::= "" | non_quotation_mark_graphic_character

      2.7:
      comment::= --{non_end_of_line_character}

      2.8:
      pragma::= 
         pragma identifier [(pragma_argument_association
       {, pragma_argument_association})];

      2.8:
      pragma_argument_association::= 
           [pragma_argument_identifier =>] name
         | [pragma_argument_identifier =>] expression

      3.1:
      basic_declaration::= 
           type_declaration           | subtype_declaration
         | object_declaration         | number_declaration
         | subprogram_declaration     | abstract_subprogram_declaration
         | package_declaration        | renaming_declaration
         | exception_declaration      | generic_declaration
         | generic_instantiation

      3.1:
      defining_identifier::= identifier

      3.2.1:
      type_declaration::=  full_type_declaration
         | incomplete_type_declaration
         | private_type_declaration
         | private_extension_declaration

      3.2.1:
      full_type_declaration::= 
           type defining_identifier [known_discriminant_part
      ] is type_definition;
         | task_type_declaration
         | protected_type_declaration

      3.2.1:
      type_definition::= 
           enumeration_type_definition   | integer_type_definition
         | real_type_definition          | array_type_definition
         | record_type_definition        | access_type_definition
         | derived_type_definition

      3.2.2:
      subtype_declaration::= 
         subtype defining_identifier is subtype_indication;

      3.2.2:
      subtype_indication::=  subtype_mark [constraint]

      3.2.2:
      subtype_mark::= subtype_name

      3.2.2:
      constraint::= scalar_constraint | composite_constraint

      3.2.2:
      scalar_constraint::= 
           range_constraint | digits_constraint | delta_constraint

      3.2.2:
      composite_constraint::= 
           index_constraint | discriminant_constraint

      3.3.1:
      object_declaration::= 
          defining_identifier_list
       : [aliased] [constant] subtype_indication [:= expression];
        | defining_identifier_list
       : [aliased] [constant] array_type_definition [:= expression];
        | single_task_declaration
        | single_protected_declaration

      3.3.1:
      defining_identifier_list::= 
        defining_identifier {, defining_identifier}

      3.3.2:
      number_declaration::= 
           defining_identifier_list : constant := static_expression;

      3.4:
      derived_type_definition::= [abstract] new parent_subtype_indication
       [record_extension_part]

      3.5:
      range_constraint::=  range range

      3.5:
      range::=  range_attribute_reference
         | simple_expression .. simple_expression

      3.5.1:
      enumeration_type_definition::= 
         (enumeration_literal_specification
       {, enumeration_literal_specification})

      3.5.1:
      enumeration_literal_specification::=  defining_identifier
       | defining_character_literal

      3.5.1:
      defining_character_literal::= character_literal

      3.5.4:
      integer_type_definition::= signed_integer_type_definition
       | modular_type_definition

      3.5.4:
      signed_integer_type_definition::= range static_simple_expression
       .. static_simple_expression

      3.5.4:
      modular_type_definition::= mod static_expression

      3.5.6:
      real_type_definition::= 
         floating_point_definition | fixed_point_definition

      3.5.7:
      floating_point_definition::= 
        digits static_expression [real_range_specification]

      3.5.7:
      real_range_specification::= 
        range static_simple_expression .. static_simple_expression

      3.5.9:
      fixed_point_definition::= ordinary_fixed_point_definition
       | decimal_fixed_point_definition

      3.5.9:
      ordinary_fixed_point_definition::= 
         delta static_expression  real_range_specification

      3.5.9:
      decimal_fixed_point_definition::= 
         delta static_expression digits static_expression
       [real_range_specification]

      3.5.9:
      digits_constraint::= 
         digits static_expression [range_constraint]

      3.6:
      array_type_definition::= 
         unconstrained_array_definition | constrained_array_definition

      3.6:
      unconstrained_array_definition::= 
         array(index_subtype_definition {, index_subtype_definition
      }) of component_definition

      3.6:
      index_subtype_definition::= subtype_mark range <>

      3.6:
      constrained_array_definition::= 
         array (discrete_subtype_definition {, discrete_subtype_definition
      }) of component_definition

      3.6:
      discrete_subtype_definition::= discrete_subtype_indication | range

      3.6:
      component_definition::= [aliased] subtype_indication

      3.6.1:
      index_constraint::=  (discrete_range {, discrete_range})

      3.6.1:
      discrete_range::= discrete_subtype_indication | range

      3.7:
      discriminant_part::= unknown_discriminant_part
       | known_discriminant_part

      3.7:
      unknown_discriminant_part::= (<>)

      3.7:
      known_discriminant_part::= 
         (discriminant_specification {; discriminant_specification})

      3.7:
      discriminant_specification::= 
         defining_identifier_list : subtype_mark [:= default_expression]
       | defining_identifier_list : access_definition
       [:= default_expression]

      3.7:
      default_expression::= expression

      3.7.1:
      discriminant_constraint::= 
         (discriminant_association {, discriminant_association})

      3.7.1:
      discriminant_association::= 
         [discriminant_selector_name {| discriminant_selector_name
      } =>] expression

      3.8:
      record_type_definition::= [[abstract] tagged] [limited] record_definition

      3.8:
      record_definition::= 
          record
             component_list
          end record
        | null record

      3.8:
      component_list::= 
            component_item {component_item}
         | {component_item} variant_part
         |  null;

      3.8:
      component_item::= component_declaration | {aspect_clause
      }[representation_clause]

      3.8:
      component_declaration::= 
         defining_identifier_list : component_definition
       [:= default_expression];

      3.8.1:
      variant_part::= 
         case discriminant_direct_name is
             variant
            {variant}
         end case;

      3.8.1:
      variant::= 
         when discrete_choice_list =>
            component_list

      3.8.1:
      discrete_choice_list::= discrete_choice {| discrete_choice}

      3.8.1:
      discrete_choice::= expression | discrete_range | others

      3.9.1:
      record_extension_part::= with record_definition

      3.10:
      access_type_definition::= 
          access_to_object_definition
        | access_to_subprogram_definition

      3.10:
      access_to_object_definition::= 
          access [general_access_modifier] subtype_indication

      3.10:
      general_access_modifier::= all | constant

      3.10:
      access_to_subprogram_definition::= 
          access [protected] procedure parameter_profile
        | access [protected] function  parameter_and_result_profile

      3.10:
      access_definition::= access subtype_mark

      3.10.1:
      incomplete_type_declaration::= type defining_identifier
       [discriminant_part];

      3.11:
      declarative_part::= {declarative_item}

      3.11:
      declarative_item::= 
          basic_declarative_item | body

      3.11:
      basic_declarative_item::= 
          basic_declaration | {aspect_clause}[representation_clause
      ] | use_clause

      3.11:
      body::= proper_body | body_stub

      3.11:
      proper_body::= 
          subprogram_body | package_body | task_body | protected_body

      4.1:
      name::= 
           direct_name          | explicit_dereference
         | indexed_component    | slice
         | selected_component   | attribute_reference
         | type_conversion      | function_call
         | character_literal

      4.1:
      direct_name::= identifier | operator_symbol

      4.1:
      prefix::= name | implicit_dereference

      4.1:
      explicit_dereference::= name.all

      4.1:
      implicit_dereference::= name

      4.1.1:
      indexed_component::= prefix(expression {, expression})

      4.1.2:
      slice::= prefix(discrete_range)

      4.1.3:
      selected_component::= prefix . selector_name

      4.1.3:
      selector_name::= identifier | character_literal | operator_symbol

      4.1.4:
      attribute_reference::= prefix'attribute_designator

      4.1.4:
      attribute_designator::= 
          identifier[(static_expression)]
        | Access | Delta | Digits

      4.1.4:
      range_attribute_reference::= prefix'range_attribute_designator

      4.1.4:
      range_attribute_designator::= Range[(static_expression)]

      4.3:
      aggregate::= record_aggregate | extension_aggregate | array_aggregate

      4.3.1:
      record_aggregate::= (record_component_association_list)

      4.3.1:
      record_component_association_list::= 
          record_component_association {, record_component_association}
        | null record

      4.3.1:
      record_component_association::= 
         [ component_choice_list => ] expression

      4.3.1:
      component_choice_list::= 
           component_selector_name {| component_selector_name}
         | others

      4.3.2:
      extension_aggregate::= 
          (ancestor_part with record_component_association_list)

      4.3.2:
      ancestor_part::= expression | subtype_mark

      4.3.3:
      array_aggregate::= 
        positional_array_aggregate | named_array_aggregate

      4.3.3:
      positional_array_aggregate::= 
          (expression, expression {, expression})
        | (expression {, expression}, others => expression)

      4.3.3:
      named_array_aggregate::= 
          (array_component_association {, array_component_association})

      4.3.3:
      array_component_association::= 
          discrete_choice_list => expression

      4.4:
      expression::= 
           relation {and relation}  | relation {and then relation}
         | relation {or relation}  | relation {or else relation}
         | relation {xor relation}

      4.4:
      relation::= 
           simple_expression [relational_operator simple_expression]
         | simple_expression [not] in range
         | simple_expression [not] in subtype_mark

      4.4:
      simple_expression::= [unary_adding_operator] term
       {binary_adding_operator term}

      4.4:
      term::= factor {multiplying_operator factor}

      4.4:
      factor::= primary [** primary] | abs primary | not primary

      4.4:
      primary::= 
         numeric_literal | null | string_literal | aggregate
       | name | qualified_expression | allocator | (expression)

      4.5:
      logical_operator::=                          and | or  | xor

      4.5:
      relational_operator::=                      
       =   | /=  | <   | <= | > | >=

      4.5:
      binary_adding_operator::=                    +   | -   | &

      4.5:
      unary_adding_operator::=                     +   | -

      4.5:
      multiplying_operator::=                      *   | /   | mod | rem

      4.5:
      highest_precedence_operator::=               **  | abs | not

      4.6:
      type_conversion::= 
          subtype_mark(expression)
        | subtype_mark(name)

      4.7:
      qualified_expression::= 
         subtype_mark'(expression) | subtype_mark'aggregate

      4.8:
      allocator::= 
         new subtype_indication | new qualified_expression

      5.1:
      sequence_of_statements::= statement {statement}

      5.1:
      statement::= 
         {label} simple_statement | {label} compound_statement

      5.1:
      simple_statement::= null_statement
         | assignment_statement            | exit_statement
         | goto_statement                  | procedure_call_statement
         | return_statement                | entry_call_statement
         | requeue_statement               | delay_statement
         | abort_statement                 | raise_statement
         | code_statement

      5.1:
      compound_statement::= 
           if_statement                    | case_statement
         | loop_statement                  | block_statement
         | accept_statement                | select_statement

      5.1:
      null_statement::= null;

      5.1:
      label::= <<label_statement_identifier>>

      5.1:
      statement_identifier::= direct_name

      5.2:
      assignment_statement::= 
         variable_name := expression;

      5.3:
      if_statement::= 
          if condition then
            sequence_of_statements
         {elsif condition then
            sequence_of_statements}
         [else
            sequence_of_statements]
          end if;

      5.3:
      condition::= boolean_expression

      5.4:
      case_statement::= 
         case expression is
             case_statement_alternative
            {case_statement_alternative}
         end case;

      5.4:
      case_statement_alternative::= 
         when discrete_choice_list =>
            sequence_of_statements

      5.5:
      loop_statement::= 
         [loop_statement_identifier:]
            [iteration_scheme] loop
               sequence_of_statements
             end loop [loop_identifier];

      5.5:
      iteration_scheme::= while condition
         | for loop_parameter_specification

      5.5:
      loop_parameter_specification::= 
         defining_identifier in [reverse] discrete_subtype_definition

      5.6:
      block_statement::= 
         [block_statement_identifier:]
             [declare
                  declarative_part]
              begin
                  handled_sequence_of_statements
              end [block_identifier];

      5.7:
      exit_statement::= 
         exit [loop_name] [when condition];

      5.8:
      goto_statement::= goto label_name;

      6.1:
      subprogram_declaration::= subprogram_specification;

      6.1:
      abstract_subprogram_declaration::= subprogram_specification is abstract;

      6.1:
      subprogram_specification::= 
           procedure defining_program_unit_name  parameter_profile
         | function defining_designator  parameter_and_result_profile

      6.1:
      designator::= [parent_unit_name . ]identifier | operator_symbol

      6.1:
      defining_designator::= defining_program_unit_name
       | defining_operator_symbol

      6.1:
      defining_program_unit_name::= [parent_unit_name
       . ]defining_identifier

      6.1:
      operator_symbol::= string_literal

      6.1:
      defining_operator_symbol::= operator_symbol

      6.1:
      parameter_profile::= [formal_part]

      6.1:
      parameter_and_result_profile::= [formal_part] return subtype_mark

      6.1:
      formal_part::= 
         (parameter_specification {; parameter_specification})

      6.1:
      parameter_specification::= 
          defining_identifier_list : mode  subtype_mark
       [:= default_expression]
        | defining_identifier_list : access_definition
       [:= default_expression]

      6.1:
      mode::= [in] | in out | out

      6.3:
      subprogram_body::= 
          subprogram_specification is
             declarative_part
          begin
              handled_sequence_of_statements
          end [designator];

      6.4:
      procedure_call_statement::= 
          procedure_name;
        | procedure_prefix actual_parameter_part;

      6.4:
      function_call::= 
          function_name
        | function_prefix actual_parameter_part

      6.4:
      actual_parameter_part::= 
          (parameter_association {, parameter_association})

      6.4:
      parameter_association::= 
         [formal_parameter_selector_name =>] explicit_actual_parameter

      6.4:
      explicit_actual_parameter::= expression | variable_name

      6.5:
      return_statement::= return [expression];

      7.1:
      package_declaration::= package_specification;

      7.1:
      package_specification::= 
          package defining_program_unit_name is
            {basic_declarative_item}
         [private
            {basic_declarative_item}]
          end [[parent_unit_name.]identifier]

      7.2:
      package_body::= 
          package body defining_program_unit_name is
             declarative_part
         [begin
              handled_sequence_of_statements]
          end [[parent_unit_name.]identifier];

      7.3:
      private_type_declaration::= 
         type defining_identifier [discriminant_part
      ] is [[abstract] tagged] [limited] private;

      7.3:
      private_extension_declaration::= 
         type defining_identifier [discriminant_part] is
           [abstract] new ancestor_subtype_indication with private;

      8.4:
      use_clause::= use_package_clause | use_type_clause

      8.4:
      use_package_clause::= use package_name {, package_name};

      8.4:
      use_type_clause::= use type subtype_mark {, subtype_mark};

      8.5:
      renaming_declaration::= 
            object_renaming_declaration
          | exception_renaming_declaration
          | package_renaming_declaration
          | subprogram_renaming_declaration
          | generic_renaming_declaration

      8.5.1:
      object_renaming_declaration::= defining_identifier : subtype_mark
       renames object_name;

      8.5.2:
      exception_renaming_declaration::= defining_identifier
       : exception renames exception_name;

      8.5.3:
      package_renaming_declaration::= package defining_program_unit_name
       renames package_name;

      8.5.4:
      subprogram_renaming_declaration::= subprogram_specification
       renames callable_entity_name;

      8.5.5:
      generic_renaming_declaration::= 
          generic package       defining_program_unit_name
       renames generic_package_name;
        | generic procedure     defining_program_unit_name
       renames generic_procedure_name;
        | generic function      defining_program_unit_name
       renames generic_function_name;

      9.1:
      task_type_declaration::= 
         task type defining_identifier [known_discriminant_part
      ] [is task_definition];

      9.1:
      single_task_declaration::= 
         task defining_identifier [is task_definition];

      9.1:
      task_definition::= 
           {task_item}
        [ private
           {task_item}]
        end [task_identifier]

      9.1:
      task_item::= entry_declaration | {aspect_clause
      }[representation_clause]

      9.1:
      task_body::= 
         task body defining_identifier is
           declarative_part
         begin
           handled_sequence_of_statements
         end [task_identifier];

      9.4:
      protected_type_declaration::= 
        protected type defining_identifier [known_discriminant_part
      ] is protected_definition;

      9.4:
      single_protected_declaration::= 
        protected defining_identifier is protected_definition;

      9.4:
      protected_definition::= 
          { protected_operation_declaration }
      [ private
          { protected_element_declaration } ]
        end [protected_identifier]

      9.4:
      protected_operation_declaration::= subprogram_declaration
           | entry_declaration
           | {aspect_clause}[representation_clause]

      9.4:
      protected_element_declaration::= protected_operation_declaration
           | component_declaration

      9.4:
      protected_body::= 
        protected body defining_identifier is
         { protected_operation_item }
        end [protected_identifier];

      9.4:
      protected_operation_item::= subprogram_declaration
           | subprogram_body
           | entry_body
           | {aspect_clause}[representation_clause]

      9.5.2:
      entry_declaration::= 
         entry defining_identifier [(discrete_subtype_definition
      )] parameter_profile;

      9.5.2:
      accept_statement::= 
         accept entry_direct_name [(entry_index)] parameter_profile [do
           handled_sequence_of_statements
         end [entry_identifier]];

      9.5.2:
      entry_index::= expression

      9.5.2:
      entry_body::= 
        entry defining_identifier  entry_body_formal_part  entry_barrier is
          declarative_part
        begin
          handled_sequence_of_statements
        end [entry_identifier];

      9.5.2:
      entry_body_formal_part::= [(entry_index_specification
      )] parameter_profile

      9.5.2:
      entry_barrier::= when condition

      9.5.2:
      entry_index_specification::= for defining_identifier
       in discrete_subtype_definition

      9.5.3:
      entry_call_statement::= entry_name [actual_parameter_part];

      9.5.4:
      requeue_statement::= requeue entry_name [with abort];

      9.6:
      delay_statement::= delay_until_statement | delay_relative_statement

      9.6:
      delay_until_statement::= delay until delay_expression;

      9.6:
      delay_relative_statement::= delay delay_expression;

      9.7:
      select_statement::= 
         selective_accept
        | timed_entry_call
        | conditional_entry_call
        | asynchronous_select

      9.7.1:
      selective_accept::= 
        select
         [guard]
           select_alternative
      { or
         [guard]
           select_alternative }
      [ else
         sequence_of_statements ]
        end select;

      9.7.1:
      guard::= when condition =>

      9.7.1:
      select_alternative::= 
         accept_alternative
        | delay_alternative
        | terminate_alternative

      9.7.1:
      accept_alternative::= 
        accept_statement [sequence_of_statements]

      9.7.1:
      delay_alternative::= 
        delay_statement [sequence_of_statements]

      9.7.1:
      terminate_alternative::= terminate;

      9.7.2:
      timed_entry_call::= 
        select
         entry_call_alternative
        or
         delay_alternative
        end select;

      9.7.2:
      entry_call_alternative::= 
        entry_call_statement [sequence_of_statements]

      9.7.3:
      conditional_entry_call::= 
        select
         entry_call_alternative
        else
         sequence_of_statements
        end select;

      9.7.4:
      asynchronous_select::= 
        select
         triggering_alternative
        then abort
         abortable_part
        end select;

      9.7.4:
      triggering_alternative::= triggering_statement
       [sequence_of_statements]

      9.7.4:
      triggering_statement::= entry_call_statement | delay_statement

      9.7.4:
      abortable_part::= sequence_of_statements

      9.8:
      abort_statement::= abort task_name {, task_name};

      10.1.1:
      compilation::= {compilation_unit}

      10.1.1:
      compilation_unit::= 
          context_clause library_item
        | context_clause subunit

      10.1.1:
      library_item::= [private] library_unit_declaration
        | library_unit_body
        | [private] library_unit_renaming_declaration

      10.1.1:
      library_unit_declaration::= 
           subprogram_declaration   | package_declaration
         | generic_declaration      | generic_instantiation

      10.1.1:
      library_unit_renaming_declaration::= 
         package_renaming_declaration
       | generic_renaming_declaration
       | subprogram_renaming_declaration

      10.1.1:
      library_unit_body::= subprogram_body | package_body

      10.1.1:
      parent_unit_name::= name

      10.1.2:
      context_clause::= {context_item}

      10.1.2:
      context_item::= with_clause | use_clause

      10.1.2:
      with_clause::= with library_unit_name {, library_unit_name};

      10.1.3:
      body_stub::= subprogram_body_stub | package_body_stub
       | task_body_stub | protected_body_stub

      10.1.3:
      subprogram_body_stub::= subprogram_specification is separate;

      10.1.3:
      package_body_stub::= package body defining_identifier is separate;

      10.1.3:
      task_body_stub::= task body defining_identifier is separate;

      10.1.3:
      protected_body_stub::= protected body defining_identifier is separate;

      10.1.3:
      subunit::= separate (parent_unit_name) proper_body

      11.1:
      exception_declaration::= defining_identifier_list : exception;

      11.2:
      handled_sequence_of_statements::= 
           sequence_of_statements
        [exception
           exception_handler
          {exception_handler}]

      11.2:
      exception_handler::= 
        when [choice_parameter_specification:] exception_choice
       {| exception_choice} =>
           sequence_of_statements

      11.2:
      choice_parameter_specification::= defining_identifier

      11.2:
      exception_choice::= exception_name | others

      11.3:
      raise_statement::= raise [exception_name];

      12.1:
      generic_declaration::= generic_subprogram_declaration
       | generic_package_declaration

      12.1:
      generic_subprogram_declaration::= 
           generic_formal_part  subprogram_specification;

      12.1:
      generic_package_declaration::= 
           generic_formal_part  package_specification;

      12.1:
      generic_formal_part::= generic {generic_formal_parameter_declaration
       | use_clause}

      12.1:
      generic_formal_parameter_declaration::= 
            formal_object_declaration
          | formal_type_declaration
          | formal_subprogram_declaration
          | formal_package_declaration

      12.3:
      generic_instantiation::= 
           package defining_program_unit_name is
               new generic_package_name [generic_actual_part];
         | procedure defining_program_unit_name is
               new generic_procedure_name [generic_actual_part];
         | function defining_designator is
               new generic_function_name [generic_actual_part];

      12.3:
      generic_actual_part::= 
         (generic_association {, generic_association})

      12.3:
      generic_association::= 
         [generic_formal_parameter_selector_name
       =>] explicit_generic_actual_parameter

      12.3:
      explicit_generic_actual_parameter::= expression | variable_name
         | subprogram_name | entry_name | subtype_mark
         | package_instance_name

      12.4:
      formal_object_declaration::= 
          defining_identifier_list : mode subtype_mark
       [:= default_expression];

      12.5:
      formal_type_declaration::= 
          type defining_identifier[discriminant_part
      ] is formal_type_definition;

      12.5:
      formal_type_definition::= 
            formal_private_type_definition
          | formal_derived_type_definition
          | formal_discrete_type_definition
          | formal_signed_integer_type_definition
          | formal_modular_type_definition
          | formal_floating_point_definition
          | formal_ordinary_fixed_point_definition
          | formal_decimal_fixed_point_definition
          | formal_array_type_definition
          | formal_access_type_definition

      12.5.1:
      formal_private_type_definition::= [[abstract] tagged] [limited] private

      12.5.1:
      formal_derived_type_definition::= [abstract] new subtype_mark
       [with private]

      12.5.2:
      formal_discrete_type_definition::= (<>)

      12.5.2:
      formal_signed_integer_type_definition::= range <>

      12.5.2:
      formal_modular_type_definition::= mod <>

      12.5.2:
      formal_floating_point_definition::= digits <>

      12.5.2:
      formal_ordinary_fixed_point_definition::= delta <>

      12.5.2:
      formal_decimal_fixed_point_definition::= delta <> digits <>

      12.5.3:
      formal_array_type_definition::= array_type_definition

      12.5.4:
      formal_access_type_definition::= access_type_definition

      12.6:
      formal_subprogram_declaration::= with subprogram_specification
       [is subprogram_default];

      12.6:
      subprogram_default::= default_name | <>

      12.6:
      default_name::= name

      12.7:
      formal_package_declaration::= 
          with package defining_identifier is new generic_package_name
        formal_package_actual_part;

      12.7:
      formal_package_actual_part::= 
          (<>) | [generic_actual_part]

      13.1:
      {aspect_clause}[representation_clause]::= attribute_definition_clause
            | enumeration_representation_clause
            | record_representation_clause
            | at_clause

      13.1:
      local_name::= direct_name
            | direct_name'attribute_designator
            | library_unit_name

      13.3:
      attribute_definition_clause::= 
            for local_name'attribute_designator use expression;
          | for local_name'attribute_designator use name;

      13.4:
      enumeration_representation_clause::= 
          for first_subtype_local_name use enumeration_aggregate;

      13.4:
      enumeration_aggregate::= array_aggregate

      13.5.1:
      record_representation_clause::= 
          for first_subtype_local_name use
            record [mod_clause]
              {component_clause}
            end record;

      13.5.1:
      component_clause::= 
          component_local_name at position range first_bit .. last_bit;

      13.5.1:
      position::= static_expression

      13.5.1:
      first_bit::= static_simple_expression

      13.5.1:
      last_bit::= static_simple_expression

      13.8:
      code_statement::= qualified_expression;

      13.12:
      restriction::= restriction_identifier
          | restriction_parameter_identifier => expression

      J.3:
      delta_constraint::= delta static_expression [range_constraint]

      J.7:
      at_clause::= for direct_name use at expression;

      J.8:
      mod_clause::= at mod static_expression;



Syntax Cross Reference



      abort_statement
          simple_statement                          5.1

      abortable_part
          asynchronous_select                       9.7.4

      abstract_subprogram_declaration
          basic_declaration                         3.1

      accept_alternative
          select_alternative                        9.7.1

      accept_statement
          accept_alternative                        9.7.1
          compound_statement                        5.1

      access_definition
          discriminant_specification                3.7
          parameter_specification                   6.1

      access_to_object_definition
          access_type_definition                    3.10

      access_to_subprogram_definition
          access_type_definition                    3.10

      access_type_definition
          formal_access_type_definition             12.5.4
          type_definition                           3.2.1

      actual_parameter_part
          entry_call_statement                      9.5.3
          function_call                             6.4
          procedure_call_statement                  6.4

      aggregate
          primary                                   4.4
          qualified_expression                      4.7

      allocator
          primary                                   4.4

      ancestor_part
          extension_aggregate                       4.3.2

      array_aggregate
          aggregate                                 4.3
          enumeration_aggregate                     13.4

      array_component_association
          named_array_aggregate                     4.3.3

      array_type_definition
          formal_array_type_definition              12.5.3
          object_declaration                        3.3.1
          type_definition                           3.2.1

      aspect_clause
          basic_declarative_item                    3.11
          component_item                            3.8
          protected_operation_declaration           9.4
          protected_operation_item                  9.4
          task_item                                 9.1

      assignment_statement
          simple_statement                          5.1

      asynchronous_select
          select_statement                          9.7

      at_clause
          aspect_clause                             13.1

      attribute_definition_clause
          aspect_clause                             13.1

      attribute_designator
          attribute_definition_clause               13.3
          attribute_reference                       4.1.4
          local_name                                13.1

      attribute_reference
          name                                      4.1

      base
          based_literal                             2.4.2

      based_literal
          numeric_literal                           2.4

      based_numeral
          based_literal                             2.4.2

      basic_declaration
          basic_declarative_item                    3.11

      basic_declarative_item
          declarative_item                          3.11
          package_specification                     7.1

      binary_adding_operator
          simple_expression                         4.4

      block_statement
          compound_statement                        5.1

      body
          declarative_item                          3.11

      body_stub
          body                                      3.11

      case_statement
          compound_statement                        5.1

      case_statement_alternative
          case_statement                            5.4

      character
          comment                                   2.7

      character_literal
          defining_character_literal                3.5.1
          name                                      4.1
          selector_name                             4.1.3

      choice_parameter_specification
          exception_handler                         11.2

      code_statement
          simple_statement                          5.1

      compilation_unit
          compilation                               10.1.1

      component_choice_list
          record_component_association              4.3.1

      component_clause
          record_representation_clause              13.5.1

      component_declaration
          component_item                            3.8
          protected_element_declaration             9.4

      component_definition
          component_declaration                     3.8
          constrained_array_definition              3.6
          unconstrained_array_definition            3.6

      component_item
          component_list                            3.8

      component_list
          record_definition                         3.8
          variant                                   3.8.1

      composite_constraint
          constraint                                3.2.2

      compound_statement
          statement                                 5.1

      condition
          entry_barrier                             9.5.2
          exit_statement                            5.7
          guard                                     9.7.1
          if_statement                              5.3
          iteration_scheme                          5.5

      conditional_entry_call
          select_statement                          9.7

      constrained_array_definition
          array_type_definition                     3.6

      constraint
          subtype_indication                        3.2.2

      context_clause
          compilation_unit                          10.1.1

      context_item
          context_clause                            10.1.2

      decimal_fixed_point_definition
          fixed_point_definition                    3.5.9

      decimal_literal
          numeric_literal                           2.4

      declarative_item
          declarative_part                          3.11

      declarative_part
          block_statement                           5.6
          entry_body                                9.5.2
          package_body                              7.2
          subprogram_body                           6.3
          task_body                                 9.1

      default_expression
          component_declaration                     3.8
          discriminant_specification                3.7
          formal_object_declaration                 12.4
          parameter_specification                   6.1

      default_name
          subprogram_default                        12.6

      defining_character_literal
          enumeration_literal_specification         3.5.1

      defining_designator
          generic_instantiation                     12.3
          subprogram_specification                  6.1

      defining_identifier
          choice_parameter_specification            11.2
          defining_identifier_list                  3.3.1
          defining_program_unit_name                6.1
          entry_body                                9.5.2
          entry_declaration                         9.5.2
          entry_index_specification                 9.5.2
          enumeration_literal_specification         3.5.1
          exception_renaming_declaration            8.5.2
          formal_package_declaration                12.7
          formal_type_declaration                   12.5
          full_type_declaration                     3.2.1
          incomplete_type_declaration               3.10.1
          loop_parameter_specification              5.5
          object_renaming_declaration               8.5.1
          package_body_stub                         10.1.3
          private_extension_declaration             7.3
          private_type_declaration                  7.3
          protected_body                            9.4
          protected_body_stub                       10.1.3
          protected_type_declaration                9.4
          single_protected_declaration              9.4
          single_task_declaration                   9.1
          subtype_declaration                       3.2.2
          task_body                                 9.1
          task_body_stub                            10.1.3
          task_type_declaration                     9.1

      defining_identifier_list
          component_declaration                     3.8
          discriminant_specification                3.7
          exception_declaration                     11.1
          formal_object_declaration                 12.4
          number_declaration                        3.3.2
          object_declaration                        3.3.1
          parameter_specification                   6.1

      defining_operator_symbol
          defining_designator                       6.1

      defining_program_unit_name
          defining_designator                       6.1
          generic_instantiation                     12.3
          generic_renaming_declaration              8.5.5
          package_body                              7.2
          package_renaming_declaration              8.5.3
          package_specification                     7.1
          subprogram_specification                  6.1

      delay_alternative
          select_alternative                        9.7.1
          timed_entry_call                          9.7.2

      delay_relative_statement
          delay_statement                           9.6

      delay_statement
          delay_alternative                         9.7.1
          simple_statement                          5.1
          triggering_statement                      9.7.4

      delay_until_statement
          delay_statement                           9.6

      delta_constraint
          scalar_constraint                         3.2.2

      derived_type_definition
          type_definition                           3.2.1

      designator
          subprogram_body                           6.3

      digit
          extended_digit                            2.4.2
          graphic_character                         2.1
          letter_or_digit                           2.3
          numeral                                   2.4.1

      digits_constraint
          scalar_constraint                         3.2.2

      direct_name
          accept_statement                          9.5.2
          at_clause                                 J.7
          local_name                                13.1
          name                                      4.1
          statement_identifier                      5.1
          variant_part                              3.8.1

      discrete_choice
          discrete_choice_list                      3.8.1

      discrete_choice_list
          array_component_association               4.3.3
          case_statement_alternative                5.4
          variant                                   3.8.1

      discrete_range
          discrete_choice                           3.8.1
          index_constraint                          3.6.1
          slice                                     4.1.2

      discrete_subtype_definition
          constrained_array_definition              3.6
          entry_declaration                         9.5.2
          entry_index_specification                 9.5.2
          loop_parameter_specification              5.5

      discriminant_association
          discriminant_constraint                   3.7.1

      discriminant_constraint
          composite_constraint                      3.2.2

      discriminant_part
          formal_type_declaration                   12.5
          incomplete_type_declaration               3.10.1
          private_extension_declaration             7.3
          private_type_declaration                  7.3

      discriminant_specification
          known_discriminant_part                   3.7

      entry_barrier
          entry_body                                9.5.2

      entry_body
          protected_operation_item                  9.4

      entry_body_formal_part
          entry_body                                9.5.2

      entry_call_alternative
          conditional_entry_call                    9.7.3
          timed_entry_call                          9.7.2

      entry_call_statement
          entry_call_alternative                    9.7.2
          simple_statement                          5.1
          triggering_statement                      9.7.4

      entry_declaration
          protected_operation_declaration           9.4
          task_item                                 9.1

      entry_index
          accept_statement                          9.5.2

      entry_index_specification
          entry_body_formal_part                    9.5.2

      enumeration_aggregate
          enumeration_representation_clause         13.4

      enumeration_literal_specification
          enumeration_type_definition               3.5.1

      enumeration_representation_clause
          aspect_clause                             13.1

      enumeration_type_definition
          type_definition                           3.2.1

      exception_choice
          exception_handler                         11.2

      exception_declaration
          basic_declaration                         3.1

      exception_handler
          handled_sequence_of_statements            11.2

      exception_renaming_declaration
          renaming_declaration                      8.5

      exit_statement
          simple_statement                          5.1

      explicit_actual_parameter
          parameter_association                     6.4

      explicit_dereference
          name                                      4.1

      explicit_generic_actual_parameter
          generic_association                       12.3

      exponent
          based_literal                             2.4.2
          decimal_literal                           2.4.1

      expression
          ancestor_part                             4.3.2
          array_component_association               4.3.3
          assignment_statement                      5.2
          at_clause                                 J.7
          attribute_definition_clause               13.3
          attribute_designator                      4.1.4
          case_statement                            5.4
          condition                                 5.3
          decimal_fixed_point_definition            3.5.9
          default_expression                        3.7
          delay_relative_statement                  9.6
          delay_until_statement                     9.6
          delta_constraint                          J.3
          digits_constraint                         3.5.9
          discrete_choice                           3.8.1
          discriminant_association                  3.7.1
          entry_index                               9.5.2
          explicit_actual_parameter                 6.4
          explicit_generic_actual_parameter         12.3
          floating_point_definition                 3.5.7
          indexed_component                         4.1.1
          mod_clause                                J.8
          modular_type_definition                   3.5.4
          number_declaration                        3.3.2
          object_declaration                        3.3.1
          ordinary_fixed_point_definition           3.5.9
          position                                  13.5.1
          positional_array_aggregate                4.3.3
          pragma_argument_association               2.8
          primary                                   4.4
          qualified_expression                      4.7
          range_attribute_designator                4.1.4
          record_component_association              4.3.1
          restriction                               13.12
          return_statement                          6.5
          type_conversion                           4.6

      extended_digit
          based_numeral                             2.4.2

      extension_aggregate
          aggregate                                 4.3

      factor
          term                                      4.4

      first_bit
          component_clause                          13.5.1

      fixed_point_definition
          real_type_definition                      3.5.6

      floating_point_definition
          real_type_definition                      3.5.6

      formal_access_type_definition
          formal_type_definition                    12.5

      formal_array_type_definition
          formal_type_definition                    12.5

      formal_decimal_fixed_point_definition
          formal_type_definition                    12.5

      formal_derived_type_definition
          formal_type_definition                    12.5

      formal_discrete_type_definition
          formal_type_definition                    12.5

      formal_floating_point_definition
          formal_type_definition                    12.5

      formal_modular_type_definition
          formal_type_definition                    12.5

      formal_object_declaration
          generic_formal_parameter_declaration      12.1

      formal_ordinary_fixed_point_definition
          formal_type_definition                    12.5

      formal_package_actual_part
          formal_package_declaration                12.7

      formal_package_declaration
          generic_formal_parameter_declaration      12.1

      formal_part
          parameter_and_result_profile              6.1
          parameter_profile                         6.1

      formal_private_type_definition
          formal_type_definition                    12.5

      formal_signed_integer_type_definition
          formal_type_definition                    12.5

      formal_subprogram_declaration
          generic_formal_parameter_declaration      12.1

      formal_type_declaration
          generic_formal_parameter_declaration      12.1

      formal_type_definition
          formal_type_declaration                   12.5

      format_effector
          character                                 2.1

      full_type_declaration
          type_declaration                          3.2.1

      function_call
          name                                      4.1

      general_access_modifier
          access_to_object_definition               3.10

      generic_actual_part
          formal_package_actual_part                12.7
          generic_instantiation                     12.3

      generic_association
          generic_actual_part                       12.3

      generic_declaration
          basic_declaration                         3.1
          library_unit_declaration                  10.1.1

      generic_formal_parameter_declaration
          generic_formal_part                       12.1

      generic_formal_part
          generic_package_declaration               12.1
          generic_subprogram_declaration            12.1

      generic_instantiation
          basic_declaration                         3.1
          library_unit_declaration                  10.1.1

      generic_package_declaration
          generic_declaration                       12.1

      generic_renaming_declaration
          library_unit_renaming_declaration         10.1.1
          renaming_declaration                      8.5

      generic_subprogram_declaration
          generic_declaration                       12.1

      goto_statement
          simple_statement                          5.1

      graphic_character
          character                                 2.1
          character_literal                         2.5
          string_element                            2.6

      guard
          selective_accept                          9.7.1

      handled_sequence_of_statements
          accept_statement                          9.5.2
          block_statement                           5.6
          entry_body                                9.5.2
          package_body                              7.2
          subprogram_body                           6.3
          task_body                                 9.1

      identifier
          accept_statement                          9.5.2
          attribute_designator                      4.1.4
          block_statement                           5.6
          defining_identifier                       3.1
          designator                                6.1
          direct_name                               4.1
          entry_body                                9.5.2
          loop_statement                            5.5
          package_body                              7.2
          package_specification                     7.1
          pragma                                    2.8
          pragma_argument_association               2.8
          protected_body                            9.4
          protected_definition                      9.4
          restriction                               13.12
          selector_name                             4.1.3
          task_body                                 9.1
          task_definition                           9.1

      identifier_letter
          graphic_character                         2.1
          identifier                                2.3
          letter_or_digit                           2.3

      if_statement
          compound_statement                        5.1

      implicit_dereference
          prefix                                    4.1

      incomplete_type_declaration
          type_declaration                          3.2.1

      index_constraint
          composite_constraint                      3.2.2

      index_subtype_definition
          unconstrained_array_definition            3.6

      indexed_component
          name                                      4.1

      integer_type_definition
          type_definition                           3.2.1

      iteration_scheme
          loop_statement                            5.5

      known_discriminant_part
          discriminant_part                         3.7
          full_type_declaration                     3.2.1
          protected_type_declaration                9.4
          task_type_declaration                     9.1

      label
          statement                                 5.1

      last_bit
          component_clause                          13.5.1

      letter_or_digit
          identifier                                2.3

      library_item
          compilation_unit                          10.1.1

      library_unit_body
          library_item                              10.1.1

      library_unit_declaration
          library_item                              10.1.1

      library_unit_renaming_declaration
          library_item                              10.1.1

      local_name
          attribute_definition_clause               13.3
          component_clause                          13.5.1
          enumeration_representation_clause         13.4
          record_representation_clause              13.5.1

      loop_parameter_specification
          iteration_scheme                          5.5

      loop_statement
          compound_statement                        5.1

      mod_clause
          record_representation_clause              13.5.1

      mode
          formal_object_declaration                 12.4
          parameter_specification                   6.1

      modular_type_definition
          integer_type_definition                   3.5.4

      multiplying_operator
          term                                      4.4

      name
          abort_statement                           9.8
          assignment_statement                      5.2
          attribute_definition_clause               13.3
          default_name                              12.6
          entry_call_statement                      9.5.3
          exception_choice                          11.2
          exception_renaming_declaration            8.5.2
          exit_statement                            5.7
          explicit_actual_parameter                 6.4
          explicit_dereference                      4.1
          explicit_generic_actual_parameter         12.3
          formal_package_declaration                12.7
          function_call                             6.4
          generic_instantiation                     12.3
          generic_renaming_declaration              8.5.5
          goto_statement                            5.8
          implicit_dereference                      4.1
          local_name                                13.1
          object_renaming_declaration               8.5.1
          package_renaming_declaration              8.5.3
          parent_unit_name                          10.1.1
          pragma_argument_association               2.8
          prefix                                    4.1
          primary                                   4.4
          procedure_call_statement                  6.4
          raise_statement                           11.3
          requeue_statement                         9.5.4
          subprogram_renaming_declaration           8.5.4
          subtype_mark                              3.2.2
          type_conversion                           4.6
          use_package_clause                        8.4
          with_clause                               10.1.2

      named_array_aggregate
          array_aggregate                           4.3.3

      null_statement
          simple_statement                          5.1

      number_declaration
          basic_declaration                         3.1

      numeral
          base                                      2.4.2
          decimal_literal                           2.4.1
          exponent                                  2.4.1

      numeric_literal
          primary                                   4.4

      object_declaration
          basic_declaration                         3.1

      object_renaming_declaration
          renaming_declaration                      8.5

      operator_symbol
          defining_operator_symbol                  6.1
          designator                                6.1
          direct_name                               4.1
          selector_name                             4.1.3

      ordinary_fixed_point_definition
          fixed_point_definition                    3.5.9

      other_control_function
          character                                 2.1

      package_body
          library_unit_body                         10.1.1
          proper_body                               3.11

      package_body_stub
          body_stub                                 10.1.3

      package_declaration
          basic_declaration                         3.1
          library_unit_declaration                  10.1.1

      package_renaming_declaration
          library_unit_renaming_declaration         10.1.1
          renaming_declaration                      8.5

      package_specification
          generic_package_declaration               12.1
          package_declaration                       7.1

      parameter_and_result_profile
          access_to_subprogram_definition           3.10
          subprogram_specification                  6.1

      parameter_association
          actual_parameter_part                     6.4

      parameter_profile
          accept_statement                          9.5.2
          access_to_subprogram_definition           3.10
          entry_body_formal_part                    9.5.2
          entry_declaration                         9.5.2
          subprogram_specification                  6.1

      parameter_specification
          formal_part                               6.1

      parent_unit_name
          defining_program_unit_name                6.1
          designator                                6.1
          package_body                              7.2
          package_specification                     7.1
          subunit                                   10.1.3

      position
          component_clause                          13.5.1

      positional_array_aggregate
          array_aggregate                           4.3.3

      pragma_argument_association
          pragma                                    2.8

      prefix
          attribute_reference                       4.1.4
          function_call                             6.4
          indexed_component                         4.1.1
          procedure_call_statement                  6.4
          range_attribute_reference                 4.1.4
          selected_component                        4.1.3
          slice                                     4.1.2

      primary
          factor                                    4.4

      private_extension_declaration
          type_declaration                          3.2.1

      private_type_declaration
          type_declaration                          3.2.1

      procedure_call_statement
          simple_statement                          5.1

      proper_body
          body                                      3.11
          subunit                                   10.1.3

      protected_body
          proper_body                               3.11

      protected_body_stub
          body_stub                                 10.1.3

      protected_definition
          protected_type_declaration                9.4
          single_protected_declaration              9.4

      protected_element_declaration
          protected_definition                      9.4

      protected_operation_declaration
          protected_definition                      9.4
          protected_element_declaration             9.4

      protected_operation_item
          protected_body                            9.4

      protected_type_declaration
          full_type_declaration                     3.2.1

      qualified_expression
          allocator                                 4.8
          code_statement                            13.8
          primary                                   4.4

      raise_statement
          simple_statement                          5.1

      range
          discrete_range                            3.6.1
          discrete_subtype_definition               3.6
          range_constraint                          3.5
          relation                                  4.4

      range_attribute_designator
          range_attribute_reference                 4.1.4

      range_attribute_reference
          range                                     3.5

      range_constraint
          delta_constraint                          J.3
          digits_constraint                         3.5.9
          scalar_constraint                         3.2.2

      real_range_specification
          decimal_fixed_point_definition            3.5.9
          floating_point_definition                 3.5.7
          ordinary_fixed_point_definition           3.5.9

      real_type_definition
          type_definition                           3.2.1

      record_aggregate
          aggregate                                 4.3

      record_component_association
          record_component_association_list         4.3.1

      record_component_association_list
          extension_aggregate                       4.3.2
          record_aggregate                          4.3.1

      record_definition
          record_extension_part                     3.9.1
          record_type_definition                    3.8

      record_extension_part
          derived_type_definition                   3.4

      record_representation_clause
          aspect_clause                             13.1

      record_type_definition
          type_definition                           3.2.1

      relation
          expression                                4.4

      relational_operator
          relation                                  4.4

      renaming_declaration
          basic_declaration                         3.1

      representation_clause
          basic_declarative_item                    3.11
          component_item                            3.8
          protected_operation_declaration           9.4
          protected_operation_item                  9.4
          task_item                                 9.1

      requeue_statement
          simple_statement                          5.1

      return_statement
          simple_statement                          5.1

      scalar_constraint
          constraint                                3.2.2

      select_alternative
          selective_accept                          9.7.1

      select_statement
          compound_statement                        5.1

      selected_component
          name                                      4.1

      selective_accept
          select_statement                          9.7

      selector_name
          component_choice_list                     4.3.1
          discriminant_association                  3.7.1
          generic_association                       12.3
          parameter_association                     6.4
          selected_component                        4.1.3

      sequence_of_statements
          abortable_part                            9.7.4
          accept_alternative                        9.7.1
          case_statement_alternative                5.4
          conditional_entry_call                    9.7.3
          delay_alternative                         9.7.1
          entry_call_alternative                    9.7.2
          exception_handler                         11.2
          handled_sequence_of_statements            11.2
          if_statement                              5.3
          loop_statement                            5.5
          selective_accept                          9.7.1
          triggering_alternative                    9.7.4

      signed_integer_type_definition
          integer_type_definition                   3.5.4

      simple_expression
          first_bit                                 13.5.1
          last_bit                                  13.5.1
          range                                     3.5
          real_range_specification                  3.5.7
          relation                                  4.4
          signed_integer_type_definition            3.5.4

      simple_statement
          statement                                 5.1

      single_protected_declaration
          object_declaration                        3.3.1

      single_task_declaration
          object_declaration                        3.3.1

      slice
          name                                      4.1

      space_character
          graphic_character                         2.1

      special_character
          graphic_character                         2.1

      statement
          sequence_of_statements                    5.1

      statement_identifier
          block_statement                           5.6
          label                                     5.1
          loop_statement                            5.5

      string_element
          string_literal                            2.6

      string_literal
          operator_symbol                           6.1
          primary                                   4.4

      subprogram_body
          library_unit_body                         10.1.1
          proper_body                               3.11
          protected_operation_item                  9.4

      subprogram_body_stub
          body_stub                                 10.1.3

      subprogram_declaration
          basic_declaration                         3.1
          library_unit_declaration                  10.1.1
          protected_operation_declaration           9.4
          protected_operation_item                  9.4

      subprogram_default
          formal_subprogram_declaration             12.6

      subprogram_renaming_declaration
          library_unit_renaming_declaration         10.1.1
          renaming_declaration                      8.5

      subprogram_specification
          abstract_subprogram_declaration           6.1
          formal_subprogram_declaration             12.6
          generic_subprogram_declaration            12.1
          subprogram_body                           6.3
          subprogram_body_stub                      10.1.3
          subprogram_declaration                    6.1
          subprogram_renaming_declaration           8.5.4

      subtype_declaration
          basic_declaration                         3.1

      subtype_indication
          access_to_object_definition               3.10
          allocator                                 4.8
          component_definition                      3.6
          derived_type_definition                   3.4
          discrete_range                            3.6.1
          discrete_subtype_definition               3.6
          object_declaration                        3.3.1
          private_extension_declaration             7.3
          subtype_declaration                       3.2.2

      subtype_mark
          access_definition                         3.10
          ancestor_part                             4.3.2
          discriminant_specification                3.7
          explicit_generic_actual_parameter         12.3
          formal_derived_type_definition            12.5.1
          formal_object_declaration                 12.4
          index_subtype_definition                  3.6
          object_renaming_declaration               8.5.1
          parameter_and_result_profile              6.1
          parameter_specification                   6.1
          qualified_expression                      4.7
          relation                                  4.4
          subtype_indication                        3.2.2
          type_conversion                           4.6
          use_type_clause                           8.4

      subunit
          compilation_unit                          10.1.1

      task_body
          proper_body                               3.11

      task_body_stub
          body_stub                                 10.1.3

      task_definition
          single_task_declaration                   9.1
          task_type_declaration                     9.1

      task_item
          task_definition                           9.1

      task_type_declaration
          full_type_declaration                     3.2.1

      term
          simple_expression                         4.4

      terminate_alternative
          select_alternative                        9.7.1

      timed_entry_call
          select_statement                          9.7

      triggering_alternative
          asynchronous_select                       9.7.4

      triggering_statement
          triggering_alternative                    9.7.4

      type_conversion
          name                                      4.1

      type_declaration
          basic_declaration                         3.1

      type_definition
          full_type_declaration                     3.2.1

      unary_adding_operator
          simple_expression                         4.4

      unconstrained_array_definition
          array_type_definition                     3.6

      underline
          based_numeral                             2.4.2
          identifier                                2.3
          numeral                                   2.4.1

      unknown_discriminant_part
          discriminant_part                         3.7

      use_clause
          basic_declarative_item                    3.11
          context_item                              10.1.2
          generic_formal_part                       12.1

      use_package_clause
          use_clause                                8.4

      use_type_clause
          use_clause                                8.4

      variant
          variant_part                              3.8.1

      variant_part
          component_list                            3.8

      with_clause
          context_item                              10.1.2

