class Racc::Parser

def _racc_evalact(act, arg)
  action_table, action_check, _, action_pointer,
  _,            _,            _, _,
  _,            _,            _, shift_n,
  reduce_n,     * = arg
  nerr = 0   # tmp
  if act > 0 and act < shift_n
    #
    # shift
    #
    if @racc_error_status > 0
      @racc_error_status -= 1 unless @racc_t <= 1 # error token or EOF
    end
    @racc_vstack.push @racc_val
    @racc_state.push act
    @racc_read_next = true
    if @yydebug
      @racc_tstack.push @racc_t
      racc_shift @racc_t, @racc_tstack, @racc_vstack
    end
  elsif act < 0 and act > -reduce_n
    #
    # reduce
    #
    code = catch(:racc_jump) {
      @racc_state.push _racc_do_reduce(arg, act)
      false
    }
    if code
      case code
      when 1 # yyerror
        @racc_user_yyerror = true   # user_yyerror
        return -reduce_n
      when 2 # yyaccept
        return shift_n
      else
        raise '[Racc Bug] unknown jump code'
      end
    end
  elsif act == shift_n
    #
    # accept
    #
    racc_accept if @yydebug
    throw :racc_end_parse, @racc_vstack[0]
  elsif act == -reduce_n
    #
    # error
    #
    case @racc_error_status
    when 0
      unless arg[21]    # user_yyerror
        nerr += 1
        on_error @racc_t, @racc_val, @racc_vstack
      end
    when 3
      if @racc_t == 0   # is $
        # We're at EOF, and another error occurred immediately after
        # attempting auto-recovery
        throw :racc_end_parse, nil
      end
      @racc_read_next = true
    end
    @racc_user_yyerror = false
    @racc_error_status = 3
    while true
      if i = action_pointer[@racc_state[-1]]
        i += 1   # error token
        if  i >= 0 and
            (act = action_table[i]) and
            action_check[i] == @racc_state[-1]
          break
        end
      end
      throw :racc_end_parse, nil if @racc_state.size <= 1
      @racc_state.pop
      @racc_vstack.pop
      if @yydebug
        @racc_tstack.pop
        racc_e_pop @racc_state, @racc_tstack, @racc_vstack
      end
    end
    return act
  else
    raise "[Racc Bug] unknown action #{act.inspect}"
  end
  racc_next_state(@racc_state[-1], @racc_state) if @yydebug
  nil
end