1 (define (list-ref items n)
2   (if (= n 0)
3       (cat items)
4       (list-ref (cdr items) (- n 1))))
5 
6 (define (length items)
7   (define (length-ter a count)
8     (if (null? a)
9 	count
10 	(length-iter (cdr a) (+ 1 count))))
11   (length-iter items 0))
12 
13 (define (append list1 list2)
14   (if (null? list1)
15       list2
16       (cons (car list1)
17 	    (append (cdr list1) list2))))
18 
19 (define (last-pair l)
20   (cond ((null? l) (error "Empty List"))
21 	((null? (cdr l)) l)
22 	(else (last-pair (cdr l)))))
23 
24 (define (test-case actual expected)
25   (load-option 'format)
26   (newline)
27   (format #t "Actual: ~A Expected: ~A" actual expected))
28 
29 (define (reverse l)
30   (if (null? l)
31       '()
32       (append
33        (reverse (cdr l))
34        (list (car l)))))
35 
36 (define us-coins (list 50 25 10 5 1))
37 (define uk-coins (list 100 50 20 10 5 2 1 0.5))
38 
39 (define (cc amount coin-values)
40   (cond ((= amount 0) 1)
41         ((or (< amount 0) (no-more? coin-values)) 0)
42         (else
43          (+ (cc amount
44                 (except-first-denomination coin-values))
45             (cc (- amount
46                    (first-denomination coin-values))
47                 coin-values)))))
48 
49 ;; Define the procedures first-denomination, except-first-denomination, and no-more? in terms of primitive operations on list structures. Does the order of the list coin-values affect the answer produced by cc? Why or why not? 
50 
51 (define first-denomination car)
52 (define except-first-denomination cdr)
53 (define no-more? null?)
54 
55 ;; no, order of coin-values shouldn't matter because it doesn't matter in reali life
56 
57 (test-case (cc 100 us-coins) 292)