SICP 习题1.46 iterative-improve

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原创最新推荐文章于 2026-06-25 12:05:30 发布 398 阅读 AI 写同款· GEO 优化 ›

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LISP的括号非常重要，括号打错，整个程序就错了。

(define (iterative-improve good-enough? improve)
    (define (iter x)
        ;(newline)
        ;(display x)
        ;(newline)
        ;(display "HELLO")
        (if (good-enough? x)
            x 
            (iter (improve x))))
    (lambda (guess) (iter guess)))

(define (sqrt x) 
    (define square 
        (lambda (a) (* a a)))
    (define average
        (lambda (a y) (/ (+ a y) 2.0)))
    (define good-enough? 

        (lambda (guess)
            ;(newline) 
            ;(display "GOOD")
            (< (abs (- (square guess) x)) 0.001)))
    (define improve 
        (lambda (guess)
            ;(newline)
            ;(display "IMPROVE")
            (average guess (/ x guess))))
    ((iterative-improve good-enough? improve) 1.0))

(newline)
(display (sqrt 9))

(define tolerance 0.0001)

(define fixed-point
    (lambda (f x)
        (define good-enough?
            (lambda (x)
                (< (abs (- (f x) x)) tolerance)))
        (define improve
            (lambda (x) 
                (f x)))
        ((iterative-improve good-enough? improve) 1.0)))

(newline)
(display (fixed-point cos 1.0))