def gen_basic(fail, scope = ParserScope.empty)
      case fail.attrs[:type]
      when :expr  then gen_fail_expr fail.message
      when :rule  then gen_fail_rule fail.message
      when :parse then gen_fail_parse fail.message
      end
    end
def gen_basic(fail, scope = ParserScope.empty)
      case fail.attrs[:type]
      when :expr  then gen_fail_expr fail.message
      when :rule  then gen_fail_rule fail.message
      when :parse then gen_fail_parse fail.message
      end
    end
:nodoc: