peg/leg — recursive-descent parser generators for C
peg and leg are tools for generating
recursive-descent parsers: programs that perform pattern matching on
text. They processes a Parsing Expression Grammar (PEG) [Ford 2004]
to produce a program that recognises legal sentences of that grammar.
peg processes PEGs written using the original syntax
described by Ford; leg processes PEGs written using slightly
different syntax and conventions that are intended to make it an
attractive replacement for parsers built with lex and
yacc. Unlike lex and yacc, peg
and leg support unlimited backtracking, provide ordered
choice as a means for disambiguation, and can combine scanning
(lexical analysis) and parsing (syntactic analysis) into a single
Download the source code: peg-0.1.14.tar.gz
peg is distributed under the MIT license. It will not infect
your project with a contagious
Browse the source code: peg-0.1.14
Read the manual page: peg.1.html
license disease if you
decide to modify it for your own use. The parser generators that
peg creates are unencumbered and you are free to use and/or
distribute them any way you like.
If you find bugs or have suggestions, please send them to Ian at the
domain name of this web site. Thanks!
- [Ford 2004] Bryan Ford, Parsing Expression Grammars: A
Recognition-Based Syntactic Foundation. ACM SIGPLAN Symposium on
Principles of Programming Languages (POPL), 2004.
- 2013-12-01 peg-0.1.14
Documentation typos fixed (thanks to Giulio Paci).
- 2013-08-16 peg-0.1.13
Predicate actions can refer to yytext (thanks to Grégory Pakosz).
Hexadecimal character escapes are supported by leg (thanks to Hugo Etchegoyen).
- 2013-07-20 peg-0.1.12
Use BSD-licensed getopt() in Windows build.
Verbose mode handles Variable nodes.
- 2013-06-03 peg-0.1.11
Add error actions via "~" operator.
Support declaration of local variables at the top level of semantic actions.
Dynamically grow data structures to remove artificial limits on rule recursion (thanks to Alex Klinkhamer).
Many small changes to better support C++.
Add build files for Win32 and MacOS (thanks to Fyodor Sheremetyev).
Update manual page to describe new features.
- 2012-04-29 peg-0.1.9
Move global state into a structure to facilitate reentrant and thread-safe parsers (thanks to Dmitry Lipovoi).
- 2012-03-29 peg-0.1.8
Allow nested, matched braces within actions.
- 2011-11-25 peg-0.1.7
Fix matching of 8-bit chars to allow utf-8 sequences in matching expressions (thanks to Grégory Pakosz).
- 2011-11-24 peg-0.1.6
Allow octal escapes in character classes.
- 2011-11-24 peg-0.1.5
Remove dwarf sym dirs when cleaning.
Fix size calculation when resizing text buffers.
Backslash can be escaped.
- 2009-08-26 peg-0.1.4
Fix match of a single single quote character.
Rename getline -> nextline to avoid C namespace conflict.
- 2007-09-13 peg-0.1.3
Allow matched braces inside leg actions.
Handle empty rules.
Handle empty grammars.
- 2007-08-31 peg-0.1.2
Grow buffers while (not if) they are too small.
Remove dependencies on grammar files.
Add more basic examples.
- 2007-05-15 peg-0.1.1
First public release.