Chapter 2, Building Abstractions with Data
Section - 2.1 - Introduction to Data Abstraction
Exercise 2.12
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#lang sicp
(#%require (only racket/base error))
(define (make-center-percent c p)
(let ((width (/ (* c p) 100)))
(make-interval (- c width) (+ c width))
)
)
(define (percent-tolerance x)
(let (
(center (/ (+ (upper-bound x) (lower-bound x)) 2.0))
(width (/ (- (upper-bound x) (lower-bound x)) 2.0))
)
(* (/ width center) 100)
)
)
(define (make-center-width c w)
(make-interval (- c w) (+ c w)))
(define (center i)
(/ (+ (lower-bound i) (upper-bound i)) 2))
(define (width i)
(/ (- (upper-bound i) (lower-bound i)) 2))
(define (make-interval a b) (cons a b))
(define (lower-bound x) (min (car x) (cdr x)))
(define (upper-bound x) (max (car x) (cdr x)))
(define (display-interval x)
(display "[")
(display (lower-bound x))
(display ",")
(display (upper-bound x))
(display "]")
(newline)
)
Output:
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> (define intvl (make-center-percent 100 10))
> (display-interval intvl)
[90,110]
> (percent-tolerance intvl)
10.0
> (define intvl (make-center-percent 500 15))
> (display-interval intvl)
[425,575]