2-30.scm

#lang sicp

(define (square-tree tree)
  (map (lambda (sub-tree)
         (if (pair? sub-tree)
           (square-tree sub-tree)
           (* sub-tree sub-tree)))
       tree))

(define (sqr-tree tree)
  (cond ((null? tree) nil)
        ((not (pair? tree)) (* tree tree))
        (else (cons (sqr-tree (car tree))
                    (sqr-tree (cdr tree))))))

(square-tree
  (list 1
        (list 2 (list 3 4) 5)
        (list 6 7)))
(sqr-tree
  (list 1
        (list 2 (list 3 4) 5)
        (list 6 7)))