1 665c255d 2023-08-04 jrmu ;; Devise a correct version of the count-pairs procedure of exercise 3.16 that returns the number of distinct pairs in any structure. (Hint: Traverse the structure, maintaining an auxiliary data structure that is used to keep track of which pairs have already been counted.) 
 2 665c255d 2023-08-04 jrmu 
 3 665c255d 2023-08-04 jrmu (define (test-case actual expected)
 4 665c255d 2023-08-04 jrmu   (newline)
 5 665c255d 2023-08-04 jrmu   (display "Actual:   ")
 6 665c255d 2023-08-04 jrmu   (display actual)
 7 665c255d 2023-08-04 jrmu   (newline)
 8 665c255d 2023-08-04 jrmu   (display "Expected: ")
 9 665c255d 2023-08-04 jrmu   (display expected)
10 665c255d 2023-08-04 jrmu   (newline))
11 665c255d 2023-08-04 jrmu 
12 665c255d 2023-08-04 jrmu (define (count-pairs x)
13 665c255d 2023-08-04 jrmu   (if (not (pair? x))
14 665c255d 2023-08-04 jrmu       0
15 665c255d 2023-08-04 jrmu       (+ (count-pairs (car x))
16 665c255d 2023-08-04 jrmu          (count-pairs (cdr x))
17 665c255d 2023-08-04 jrmu          1)))
18 665c255d 2023-08-04 jrmu 
19 665c255d 2023-08-04 jrmu (define three '(a b c))
20 665c255d 2023-08-04 jrmu (define four )
21 665c255d 2023-08-04 jrmu (define seven )
22 665c255d 2023-08-04 jrmu (define circular )
23 665c255d 2023-08-04 jrmu