1 (define (test-case actual expected)
2   (newline)
3   (display "Actual:   ")
4   (display actual)
5   (newline)
6   (display "Expected: ")
7   (display expected)
8   (newline))
9 
10 (define (scale-tree tree factor)
11   (cond ((null? tree) '())
12 	((not (pair? tree)) (* factor tree))
13 	(else (cons (scale-tree (car tree) factor)
14 		    (scale-tree (cdr tree) factor)))))
15 
16 (define (scale-tree tree factor)
17   (map (lambda (sub-tree)
18 	 (if (pair? sub-tree)
19 	     (scale-tree sub-tree factor)
20 	     (* factor sub-tree)))
21        tree))
22 
23 ;; 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:
24 
25 (define (square-tree tree)
26   (cond ((null? tree) '())
27 	((not (pair? tree)) (* tree tree))
28 	(else (cons (square-tree (car tree))
29 		    (square-tree (cdr tree))))))
30 
31 (test-case (square-tree
32 	    (list 1
33 		  (list 2 (list 3 4) 5)
34 		  (list 6 7)))
35 	   '(1 (4 (9 16) 25) (36 49)))
36 
37 ;; Define square-tree both directly (i.e., without using any higher-order procedures) and also by using map and recursion. 
38 
39 (define (square-tree-map tree)
40   (map (lambda (sub-tree)
41 	 (if (pair? sub-tree)
42 	     (square-tree-map sub-tree)
43 	     (* sub-tree sub-tree)))
44        tree))
45 
46 (test-case (square-tree-map
47 	    (list 1
48 		  (list 2 (list 3 4) 5)
49 		  (list 6 7)))
50 	   '(1 (4 (9 16) 25) (36 49)))