SICP Exercise 2.17
(define (last-pair items)
(let ((l (length items)))
(list-ref items (- l 1))))
(define (length items)
(if (null? items)
0
(+ 1 (length (cdr items)))))
(define (list-ref items n)
(if (= n 0)
(car items)
(list-ref (cdr items) (- n 1))))
There exists a better solution without using either list-ref or length:
(define (better-last-pair items)
(let ((rest (cdr items)))
(if (null? rest)
items
(last-pair rest))))