Lisp（Scheme）Newton方法

Question

我正在研究一个学术问题，我被卡住了。

我要实现的功能（使-NSTF F）。该函数应该返回一个函数，该函数通过使用牛顿方法来计算函数的零。

为了测试我的功能我用https://repl.it/BWbp/1您可以将代码复制到这个网站，如果你想测试它。

我（不工作）的代码。我写了一些评论，以便给大家一点帮助理解代码：

(define (abs x) 
    (if (< x 0) (- x) x) 
) 

;defines a function dif which returns another function (derivative) 
(define (dif fkt k) 
    (lambda (x) 
     (/ 
      (- 
       (fkt (+ x k)) 
       (fkt (- x k)) 
      ) 
      (* 2 k) 
     ) 
    ) 
) 

;Calculates next x for newton method 
(define (nextx f x) 
    (- 
     x 
     (/ 
      (f x) 
      ((dif f 1) x) 
     ) 
    ) 
) 

;Should return a function which does the newton method with function f 
(define (make-nstf f) 
    (lambda(guess) 
     ;Function checks whether the guess is good enough or not 
     ;good enoug if guess - next guess < 0.0001 ist 
     (define (good-enough? guess) 
      (< 
       (abs 
        (- 
         guess 
         (nextx f guess) 
        ) 
       ) 
      ) 
      0.0001 
     ) 
     ;calculates next guess 
     (define (improve guess) 
      (nextx f guess) 
     ) 
     ;checks whether guess is good enough and if not improve guess and try again 
     (define (sqrt-iter guess) 
      (if (good-enough? guess) 
       guess 
       (sqrt-iter (improve guess)) 
      ) 
     ) 
     ;Start with guess 
     (sqrt-iter guess) 
    ) 
) 

;defines a function: (3*x*x)-2 
(define (myfunc x) 
    (- 
     (* 
      3 
      x 
      x 
     ) 
     2 
    ) 
) 

;defines a function which calls mak-nstf with my func. 
(define nstf 
    (make-nstf myfunc) 
) 

能否请你帮我找到了这个错误？

问候， 海波

Answer 1

你有good-enough?放错了地方接近括号（那些偷偷摸摸的括号...）

(define (good-enough? guess) 
    (< 
     (abs 
      (- 
       guess 
       (nextx f guess) 
      ) 
     ) 
    ) 
    0.0001 ;this should be moved up a line 
)