1 665c255d 2023-08-04 jrmu (define (test-case actual expected)
 2 665c255d 2023-08-04 jrmu   (newline)
 3 665c255d 2023-08-04 jrmu   (display "Actual:   ")
 4 665c255d 2023-08-04 jrmu   (display actual)
 5 665c255d 2023-08-04 jrmu   (newline)
 6 665c255d 2023-08-04 jrmu   (display "Expected: ")
 7 665c255d 2023-08-04 jrmu   (display expected)
 8 665c255d 2023-08-04 jrmu   (newline))
 9 665c255d 2023-08-04 jrmu 
10 665c255d 2023-08-04 jrmu (define (last-pair x)
11 665c255d 2023-08-04 jrmu   (if (null? (cdr x))
12 665c255d 2023-08-04 jrmu       x
13 665c255d 2023-08-04 jrmu       (last-pair (cdr x))))
14 665c255d 2023-08-04 jrmu 
15 665c255d 2023-08-04 jrmu (define (make-cycle x)
16 665c255d 2023-08-04 jrmu   (set-cdr! (last-pair x) x)
17 665c255d 2023-08-04 jrmu   x)
18 665c255d 2023-08-04 jrmu 
19 665c255d 2023-08-04 jrmu (define (count-pairs x)
20 665c255d 2023-08-04 jrmu   (if (not (pair? x))
21 665c255d 2023-08-04 jrmu       0
22 665c255d 2023-08-04 jrmu       (+ (count-pairs (car x))
23 665c255d 2023-08-04 jrmu 	 (count-pairs (cdr x))
24 665c255d 2023-08-04 jrmu 	 1)))
25 665c255d 2023-08-04 jrmu 
26 665c255d 2023-08-04 jrmu (define three '(a b c))
27 665c255d 2023-08-04 jrmu (define a-pair (cons '() '()))
28 665c255d 2023-08-04 jrmu (define b-pair (cons a-pair a-pair))
29 665c255d 2023-08-04 jrmu (define four (cons 'a b-pair))
30 665c255d 2023-08-04 jrmu (define seven (cons b-pair b-pair))
31 665c255d 2023-08-04 jrmu (define circular (make-cycle '(a b c)))
32 665c255d 2023-08-04 jrmu 
33 665c255d 2023-08-04 jrmu (test-case (count-pairs three) 3)
34 665c255d 2023-08-04 jrmu (test-case (count-pairs four) 4)
35 665c255d 2023-08-04 jrmu (test-case (count-pairs seven) 7)
36 665c255d 2023-08-04 jrmu (test-case (count-pairs circular) 'infinite-loop)