frown

LALR(k) parser generator

Latest on Hackage:0.6.2.3

This package is not currently in any snapshots. If you're interested in using it, we recommend adding it to Stackage Nightly. Doing so will make builds more reliable, and allow stackage.org to host generated Haddocks.

GPL licensed by Ralf Hinze
Maintained by strake888@gmail.com

Frown is an LALR(k) parser generator for Haskell 98 written in Haskell 98. Its salient features are: • The generated parsers are time and space efficient. On the downside, the parsers are quite large. • Frown generates four different types of parsers. as a common characteristic, the parsers are genuinely functional (ie ‘table-free’); the states of the underlying LR automaton are encoded as mutually recursive functions. Three output formats use a typed stack representation, and one format due to Ross Paterson (code=stackless) works even without a stack. • Encoding states as functions means that each state can be treated individually as opposed to a table-driven approach, which necessitates a uniform treatment of states. For instance, look-ahead is only used when necessary to resolve conflicts. • Frown comes with debugging and tracing facilities; the standard output format due to Doaitse Swierstra (code=standard) may be useful for teaching LR parsing. • Common grammatical patterns such as repetition of symbols can be captured using rule schemata. There are several predefined rule schemata. • Terminal symbols are arbitrary variable-free Haskell patterns or guards. Both terminal and nonterminal symbols may have an arbitrary number of synthesized attributes. • Frown comes with extensive documentation; several example grammars are included. Furthermore, Frown supports the use of monadic lexers, monadic semantic actions, precedences, and associativity, the generation of backtracking parsers, multiple start symbols, error reporting, and a weak form of error correction.

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