Expressions
Author: JTC1/SC22/WG9/ARG, by Randall Brukardt, ARG Editor

Ada Reference Manual — Legal Information

# 4.4 Expressions

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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

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expression ::=
relation {and relation} | relation {and then relation}
| relation {or relation} | relation {or else relation}
| relation {xor relation}
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relation ::=
simple_expression [relational_operator simple_expression]
| simple_expression [not] in range
| simple_expression [not] in subtype_mark
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simple_expression ::= [unary_adding_operator] term {binary_adding_operator term}
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term ::= factor {multiplying_operator factor}
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factor ::= primary [** primary] | abs primary | not primary
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primary ::=
numeric_literal | null | string_literal | aggregate
| name | qualified_expression | allocator | (expression)

#### Name Resolution Rules

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A name used as a primary shall resolve to denote an object or a value.

#### Static Semantics

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Each expression has a type; it specifies the computation or retrieval of a value of that type.

#### Dynamic Semantics

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The value of a primary that is a name denoting an object is the value of the object.

#### Implementation Permissions

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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

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Examples of primaries:
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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
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Examples of expressions:
15/2
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
R*Sin(θ)*Cos(φ) -- 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)

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