sicp习题试解 (2.30)

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

;

; 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)

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

;; SICP No.2.30

(require (lib "math.ss"))

(define (square-tree-basic tree)

(cond ((null? tree) ())

((not (pair? tree)) (sqr tree))

(else (cons (square-tree-basic (car tree))

(square-tree-basic (cdr tree))))))

(define (square-tree-with-map tree)

(map (lambda (sub-tree)

(if (pair? sub-tree)

(square-tree-with-map sub-tree)

(sqr sub-tree)))

tree))

;; Test-it:

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

;; > (define tree-1

;; (list 1

;; (list 2 (list 3 4) 5)

;; (list 6 7)))

;; > tree-1

;; (1 (2 (3 4) 5) (6 7))

;; > (square-tree-basic tree-1)

;; (1 (4 (9 16) 25) (36 49))

;; > (square-tree-with-map tree-1)

;; (1 (4 (9 16) 25) (36 49))