sicp exercise 2.30

;
;  Exercise 2.30. Define a procedure square-tree analogous to the square-list procedure of exercise 2.21.
;  That is, square-list should behave as follows:
;  (square-tree (list 1 (list 2 (list 3 4) 5) (list 6 7)))
;  (1 (4 (9 16) 25) (36 49))
;  Define square-tree both directly (i.e., without using any higher-order procedures) and also by using
;  map and recursion.
;

(define square-tree (lambda (tree)
  (cond ((null? tree) (list))
        ((pair? tree) (cons (square-tree (car tree)) (square-tree (cdr tree))))
        (else (* tree tree)))))


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

(define x (list (list 1 2 (list 3 4 (list 10 19)) 4 (list 10))))
(display (square-tree x)) (newline)
(display (square-tree-map x)) (newline)