# class Racc::Parser

do_parse
  Parse entry point. This method is used with next_token. If Racc want to get token (and its value), call next_token.

      # example

      ---- inner
        def parse
          @q = [[1,1],
      	  [2,2],
      	  [3,3],
      	  [false, '$']]
          do_parse
        end

        def next_token
          @q.shift
        end

next_token [abstract]
  token getter method. If you use 'do_parse' method, you must also implement this method. The format of return value is [TOKEN-SYMBOL, VALUE]. token-symbol is represented by Ruby's symbol as default. For example, :IDENT for 'IDENT' in Racc. ";" (String) for ';'. Last symbol (EOF) must be false.
yyparse( recv, mid )
  parse entry point (2). If you use this method, you must also implement recv#mid method.

  recv#mid is token getter method. It must 'yield's token, which format is [TOKEN-SYMBOL, VALUE].

on_error( err_tok, err_val, _values )
  called when parse error is found. err_tok is an internal token number which makes error. err_val is its value. _values is a stack of symbol values. DO NOT EDIT this object.

  This method raises ParseError as default.

  If you override this method and make not raise exceptions, parser enters into "error recovering" mode.

yyerror
  If this method is called, racc enters error recovering mode.
yyerrok
  leave error recovering mode.
yyaccept
  return from parse routine (return value is Symbol-Value-Stack[0]).