lisp - 如何格式化嵌套的多值绑定(bind)？

Question

最近，我经常嵌套几个返回多个值的函数。然而，不像 let ，我允许将这些调用优雅地写成一个大语句，我总是以很多缩进结束。

我的 问题 是:具有多个多值函数，例如

(defun return-1-and-2 ()
  (values 1 2))

(defun return-3-and-4 ()
  (values 3 4))

是否有可能实现与

(multiple-value-bind (one two)
    (return-1-and-2)
  (multiple-value-bind (three four)
      (return-3-and-4)
    (list one two three four)))

但写得更简洁 let -方式，即，类似的东西

(multiple-let (((one two) (return-1-and-2))
               ((three four) (return-3-and-4)))
  (list one two three four))

?

Answer 1

库中可能有类似的结构。

请注意，它更类似于 let* ，而不是 let , 因为范围是嵌套的。

可以写一个宏。例如:

(defmacro multiple-value-let* ((&rest bindings) &body body)

  "Sets the scope for several ((var-0 ... var-n) form)
  binding clauses, using the multiple return values of the form."

  (if (null bindings)
      `(progn ,@body)
    (destructuring-bind (((&rest vars) form) &rest rest-bindings)
        bindings
      `(multiple-value-bind ,vars
           ,form
         (multiple-value-let* ,rest-bindings
           ,@body)))))

例子:

CL-USER 33 > (walker:walk-form
              '(multiple-value-let* (((one two)    (return-1-and-2))
                                     ((three four) (return-3-and-4)))
                 (list one two three four)))
(MULTIPLE-VALUE-BIND (ONE TWO)
    (RETURN-1-AND-2)
  (MULTIPLE-VALUE-BIND (THREE FOUR)
      (RETURN-3-AND-4)
    (PROGN (LIST ONE TWO THREE FOUR))))