Parse::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 sub-rules within productions
   * Late-bound (run-time dispatched) sub-rules
   * 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)
   * The ability to retrieve the generated parsing code