| PackageDescription | LALR(k) parser generator
Frown is an LALR(k) parser generator for Haskell 98 written in Haskell 98.
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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. |