Description:

RecDescent incrementally generates top-down recursive-descent text
parsers from simple yacc-like grammar specifications. It provides:
* Regular expressions or literal strings as terminals (tokens),
* Multiple (non-contiguous) productions for any rule,
* Repeated, optional and alternate subrules within productions,
* Late-bound (run-time dispatched) subrules,
* Full access to Perl within actions specified as part of the
grammar,
* Simple automated error reporting during parser generation and
parsing,
* The ability to commit to, uncommit to, or reject particular
productions during a parse,
* Incremental extension of the parsing grammar (even during a
parse),
* Precompilation of parser objects,
* User-definable reduce-reduce conflict resolution via
"scoring" of matching productions.