4.6 BNF Grammars

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▼ | 4 | Scribbling Documentation

4.1 | Getting Started with Documentation
4.2 | Manual Forms
4.3 | Racket
4.4 | Evaluation and Examples
4.5 | In-Source Documentation
4.6 | BNF Grammars
4.7 | Compatibility Libraries

On this page:

BNF
nonterm
BNF-seq
BNF-seq-lines
BNF-group
optional
kleenestar
kleeneplus
kleenerange
BNF-alt
BNF-etc

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#### 4.6`` BNF Grammars🔗ℹ

(require scribble/bnf) | package: scribble-lib

The scribble/bnf library provides utilities for typesetting grammars.

For example,

@(let ([open @litchar{(}]
[close @litchar{)}])
@BNF[(list @nonterm{expr}
@nonterm{id}
@BNF-seq[open @kleeneplus[@nonterm{expr}] close]
@BNF-seq[open @litchar{lambda}
open @kleenestar[@nonterm{id}] close
@nonterm{expr} close]
@nonterm{val})
(list @nonterm{val}
@BNF-alt[@nonterm{number} @nonterm{primop}])
(list @nonterm{id}
@elem{any name except for @litchar{lambda}})])

produces the output

| ‹expr› | ::= | ‹id›
|  | | | ( ‹expr›+ )
|  | | | ( lambda ( ‹id›* ) ‹expr› )
|  | | | ‹val›
| ‹val› | ::= | ‹number› | ‹primop›
| ‹id› | ::= | any name except for lambda

See also racketgrammar.

> procedure (BNF prod ...) → table?
> | prod |  | : |  |
> (cons/c (or/c block? content?)
> (non-empty-listof (or/c block? content?)))

Typesets a grammar table. Each production starts with an element (typically constructed with nonterm) for the non-terminal being defined, and then a list of possibilities (typically constructed with BNF-seq, etc.) to show on separate lines.

> procedure (nonterm pre-content ...) → element?
> pre-content : pre-content?

Typesets a non-terminal: italic in angle brackets.

> procedure (BNF-seq elem ...) → (or/c element? "")
> elem : content?

Typesets a sequence.

> procedure (BNF-seq-lines elems ...) → block?
> elems : (listof content?)

Typesets a sequence that is broken into multiple lines, where each elems is one line.

> procedure (BNF-group pre-content ...) → element?
> pre-content : pre-content?

Typesets a group surrounded by curly braces (so the entire group can be repeated, for example).

> procedure (optional pre-content ...) → element?
> pre-content : pre-content?

Typesets an optional element: in square brackets.

> procedure (kleenestar pre-content ...) → element?
> pre-content : pre-content?

Typesets a 0-or-more repetition.

> procedure (kleeneplus pre-content ...) → element?
> pre-content : pre-content?

Typesets a 1-or-more repetition.

> procedure (kleenerange n m pre-content ...) → element?
> n : any/c
> m : any/c
> pre-content : pre-content?

Typesets a n-to-m repetition. The n and m arguments are converted to a string using (format "~a" n) and (format "~a" m).

> procedure (BNF-alt elem ...) → element?
> elem : element?

Typesets alternatives for a production’s right-hand side to appear on a single line. The result is normally used as a single possibility in a production list for BNF.

> value BNF-etc : element?

An element to use for omitted productions or content. Renders as: ...
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