Exercise 2.17. Define a procedure last-pair that returns the list that contains only the last element of a given (nonempty) list:
(last-pair (list 23 72 149 34))
(34)
(define (last-pair lst)
(cond ((null? (cdr lst)) lst)
(else (last-pair (cdr lst)))))
;;; tests begin
(load "../testframe.scm")
(assertequal? (last-pair '(1)) '(1))
(assertequal? (last-pair '(a b c d)) '(d))