Lemon (parser generator)

Lemon is a parser generator, maintained as part of the SQLite project, that generates a look-ahead LR parser (LALR parser) in the programming language C from an input context-free grammar. The generator is quite simple, implemented in one C source file with another file used as a template for output. Lexical analysis is performed externally.

Lemon

Developer(s)	D. Richard Hipp
Written in	C
Operating system	Cross-platform
Type	Parser generator
License	Public domain
Website	www.hwaci.com/sw/lemon/

Lemon is similar to the programs Bison and Yacc, but is incompatible with both. The grammar input format is different, to help prevent common coding errors. Other distinctive features include a reentrant, thread-safe output parser, and the concept of non-terminal destructors that try to make it easier to avoid memory leaks.

SQLite uses Lemon with a hand-coded tokenizer to parse SQL strings.

Lemon, together with re2c and a re2c wrapper named Perplex, are used^[1][2][3] in BRL-CAD as platform-agnostic and easily compilable alternatives to Flex and Bison. This combination is also used with STEPcode.^[4]

OpenFOAM expression evaluation^[5] uses a combination of ragel and a version of lemon that has been minimally modified^[6] to ease C++ integration without affecting C integration.^[7] The parser grammars are augmented with m4 macros.