【SICP练习】60 练习2.30

练习2.30

如果这道题感觉有点难度的话，可以回过头来看看75页定义的两个scale-tree。我的定义如下：

(define (square-tree tree)

   (cond ((null? tree) ‘())

         ((not (pair? tree)) (square tree))

            (else (cons (square-tree (car tree))

                    (square-tree (cdrtree))))))

(define (square-tree tree)

   (map (lambda (sub-tree)

            (if (pair? sub-tree)

               (square-tree sub-tree)

               (square sub-tree)))

         tree))