Chapter 3, Modularity, Objects, and State
Exercise 3.13
Clearly it creates a circle and when we call last-pair? it should get stuck in loop.
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#lang sicp
(define (append! x y)
(set-cdr! (last-pair x) y)
x)
(define (last-pair x)
(if (null? (cdr x))
x
(last-pair (cdr x))))
(define (make-cycle x)
(set-cdr! (last-pair x) x)
x)
Output:
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> (define z (make-cycle (list 'a 'b 'c)))
> (display z)
#0=(a b c . #0#)
> z
#0=(mcons 'a (mcons 'b (mcons 'c #0#)))
> (last-pair z)
. . user break
>