1 (define (map proc items)
2   (if (null? items)
3       '()
4       (cons (proc (car items))
5 	    (map proc (cdr items)))))
6 
7 (define (scale-list items factor)
8   (map (lambda (x) (* x factor))
9        items))
10 
11 ;; Exercise 2.21.  The procedure square-list takes a list of numbers as argument and returns a list of the squares of those numbers.
12 
13 (define (square-list-map nums)
14   (map (lambda (x) (* x x)) nums))
15 
16 (define (square-list-recurse nums)
17   (if (null? nums)
18       '()
19       (cons (* (car nums) (car nums))
20 	    (square-list-recurse (cdr nums)))))
21 
22 (define (test-case actual expected)
23   (load-option 'format)
24   (newline)
25   (format #t "Actual: ~A Expected: ~A" actual expected))
26 
27 (test-case (square-list-recurse (list 1 2 3 4)) '(1 4 9 16))
28 (test-case (square-list-map (list 1 2 3 4)) '(1 4 9 16))
29