frown

LALR(k) parser generator for Haskell 98

Install

All systems
curl cmd.cat/frown.sh
Debian Debian
apt-get install frown
Ubuntu
apt-get install frown
Raspbian
apt-get install frown

frown

LALR(k) parser generator for Haskell 98

Frown is inspired by the parser generator Happy and uses a syntax quite simular as the syntax used by Happy. Happy only handles LALR(1) grammars while Frown can use more extensive LALR(k) grammars and the parsers generated by Frown are also faster than the parsers generated by Happy. The salient features of Frown 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, 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.