exercise2-30.lisp

(define (square-tree tree)
  (cond ((null? tree) '())
        ((not (pair? tree)) (* tree tree))
        (else (cons (square-tree (car tree))
                    (square-tree (cdr tree))))))
(display (square-tree (list 1 (list 2 (list 3 4) 5) (list 6 7))))
(newline)

(define (square-tree tree)
  (map (lambda (sub-tree)
         (if (pair? sub-tree)
           (square-tree sub-tree)
           (* sub-tree sub-tree)))
       tree))
(display (square-tree (list 1 (list 2 (list 3 4) 5) (list 6 7))))
(newline)