Abstract: Frown is an LALR(k) parser generator for Haskell 98 written in Haskell 98.
Its salient features are: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.
- 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, 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.
This document was translated from LATEX by HEVEA.