方案的深度反转 [英] deep-reverse for scheme

问题描述

当进入((1 2) (3 4))的列表时，我想反转它，但不是这样的((3 4) (1 2))，这就是reverse的作用，所以我尝试编写一个深度反向过程:

When entering the list of ((1 2) (3 4)), I want to reverse it, but not so it's ((3 4) (1 2)), which is what reverse does, so I'm trying to write a deep-reverse procedure:

(define (deep-reverse l)
  (cond ((null? l) nil)
        (not (pair? (car l)) l)
        (else (append (deep-reverse (cdr l)) (list (car l))))))

但它只是返回 ((1 2) (3 4)).出了什么问题，我该如何让它发挥作用?

but it just throws back ((1 2) (3 4)). What's wrong and how do I get this to work?

推荐答案

尝试:

(define (deep-reverse l) (map reverse l))

以上是最简单的答案；真正的答案取决于您期望深度反向做什么.请参阅我对您的问题的评论.

The above is the simplest possible answer; a real answer depends on exactly what you expect deep-reverse to do. See my comment to your question.

如果你想要一切，一路向下:

If you want everything, all the way down:

(define (deep-reverse l)
  (if (list? l)
      (reverse (map deep-reverse l))
      l))

这是它的工作原理(正确):

Here is how it works (correctly):

> (deep-reverse '(1 2 ((3.1 3.2) (4) "abc")))
(("abc" (4) (3.2 3.1)) 2 1)

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