def p_postfix_expression_2(self, p):
    ' postfix_expression : postfix_expression ARROW ID'
    p[0] = FieldSymbol(p[1], p[3])
postfix_expression : postfix_expression ARROW ID
def p_postfix_expression_2(self, p):
    ' '
    p[0] = FieldSymbol(p[1], p[3])