sicp习题试解 (2.17)

; ======================================================================

;

; Structure and Interpretation of Computer Programs

; (trial answer to excercises)

;

; 计算机程序的构造和解释(习题试解)

;

; created: code17 07/14/05

; modified:

; (保持内容完整不变前提下，可以任意转载)

; ======================================================================

;; SICP No.2.17

(define (last-pair items)

(let ((len (length items)))

(cond ((= len 0) (error "empty list"))

((= len 1) items)

(else (last-pair (cdr items))))))

;; Test-it:

;; Welcome to MzScheme version 209, Copyright (c) 2004 PLT Scheme, Inc.

;; > (last-pair (list 23 72 149 34))

;; (34)

;; > (last-pair ())

;; empty list

;; > (last-pair (list 31))

;; (31)