SCIP 练习集

2.2.7 deep-reverse

(define (next  x)
  (cond ((not (pair? x)) x)
    ((pair? (car x)) (cons (deep-reverse (car x)) (next (cdr x))))
    (else x)))
(define (deep-reverse x)
  (reverse (next x)))

一开始我想采用一个函数直接搞定的方法

如，这两个都是有错误的，主要问题在于null返回也会被加到list中去，导致最终结果和预期的有偏差

(define (deep-reverse1 x)
  (cond    ((pair? x) (cond ((null? (cdr x)) (deep-reverse1 (car x)))
             (else (list (deep-reverse1 (cdr x)) (deep-reverse1 (car x))))))
    (else x)))

(define (deep-reverse2 x)
  (cond    ((pair? x) (cond ((null? (cdr x)) (deep-reverse2 (car x)))
             (else (cons (deep-reverse2 (cdr x)) (deep-reverse2 (car x))))))
    (else x)))