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)))