4.1 Backus-Naur Form (BNF) Grammars🔗ℹ

The scribble/bnf library provides functions for typesetting grammars in traditional BNF notation, as opposed to shrubbery grammars.

A BNFEntry for either the left-hand or right-hand of a production is either a FlowBlock or Content.

For example,

@(import scribble/bnf)

@(

block:

def open: @litchar{(}

def close: @litchar{)}

bnf.grammar([@bnf.nt{expr}, [@bnf.nt{id},

@bnf.seq(open, @bnf.plus(@bnf.nt{expr}), close),

bnf.seq(open, @litchar{lambda},

open, @bnf.star(@bnf.nt{id}), close,

@bnf.nt{expr}, close),

@bnf.nt{val}]],

[@bnf.nt{val}, [@bnf.alt(@bnf.nt{number}, @bnf.nt{primop})]],

[@bnf.nt{id}, [@elem{any name except for @litchar{lambda}}]])

)

renders as

• sequencing typeset as juxtaposition

• alternatives typeset with | separators

• a group typeset with parentheses

• a zero-or-one choice typeset in square brackets

• a zero-or-more choice typeset with a * suffix

• a one-or-more choice typeset with a + suffix

• a n-to-m choice typeset with a {} suffix