Warning: This is the manual of the legacy Guile 2.2 series. You may want to read the manual of the current stable series instead.

6.17 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.