def p_postfix_expression4(self, p):
    ' postfix_expression : postfix_expression LPAREN argument_list RPAREN '
    p[0] = CallSymbol(p[1], p[3])
postfix_expression : postfix_expression LPAREN argument_list RPAREN
def p_postfix_expression4(self, p):
    '  '
    p[0] = CallSymbol(p[1], p[3])