sicp习题试解 (2.28)

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

;

; 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 07/28/05

; modified:

; (保持内容完整不变前提下，可以任意转载)

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;; SICP No.2.28

(define (finger x)

(cond ((pair? x) (append (finger (car x)) (finger (cdr x))))

((null? x) x)

(else (list x))))

;; Test-it:

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

;; > (define x (list (list 1 2) (list 3 4)))

;; > x

;; ((1 2) (3 4))

;; > (finger x)

;; (1 2 3 4)