docs: def p_function_expr_1(self, p):
          """
          function_expr \
              : FUNCTION LPAREN RPAREN LBRACE function_body RBRACE
              | FUNCTION LPAREN formal_parameter_list RPAREN \
                  LBRACE function_body RBRACE
          """
          if len(p) == 7:
              p[0] = ast.FuncExpr(
                  identifier=None, parameters=None, elements=p[5])
          else:
              p[0] = ast.FuncExpr(
                  identifier=None, parameters=p[3], elements=p[6])