sicp习题试解 (2.8)

王朝other·作者佚名 2006-01-09

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

;

; 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 04/25/05

; modified:

; (保持内容完整不变前提下，可以任意转载)

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

;; SICP No.2.8

;; 两个interval的差依然是interval。根据不等式原理，此interval的最小值可以达到

;; 减数的lower-bound减去被减数的upper-bound，其最大值最大可至减数的upper-bound

;; 减去被减数的lower-bound

(define (sub-interval x y)

(make-interval (- (lower-bound x) (upper-bound y))

(- (upper-bound x) (lower-bound y))))

;; Test-it:

;; > (define test1 (make-interval 3 5))

;; > (define test2 (make-interval 8 1))

;; > (add-interval test1 test2)

;; (4 . 13)

;; > (sub-interval test1 test2)

;; (-5 . 4)