(www.gnu.org) PEG Parsing (Guile Reference Manual)

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* 6.15 PEG Parsing ¶

Parsing Expression Grammars (PEGs) are a way of specifying formal languages for text processing. They can be used either for matching (like regular expressions) or for building recursive descent parsers (like lex/yacc). Guile uses a superset of PEG syntax that allows more control over what information is preserved during parsing.

Wikipedia has a clear and concise introduction to PEGs if you want to familiarize yourself with the syntax: http://en.wikipedia.org/wiki/Parsing_expression_grammar.

The

(ice-9 peg)

module works by compiling PEGs down to lambda expressions. These can either be stored in variables at compile-time by the define macros (

define-peg-pattern

and

define-peg-string-patterns

) or calculated explicitly at runtime with the compile functions (

compile-peg-pattern

and

peg-string-compile

).

They can then be used for either parsing (

match-pattern

) or searching (

search-for-pattern

). For convenience,

search-for-pattern

also takes pattern literals in case you want to inline a simple search (people often use regular expressions this way).

The rest of this documentation consists of a syntax reference, an API reference, and a tutorial.