Lisp（方案）牛顿法

Question

我正在研究一个学术问题，但我陷入了困境。

我必须实现一个函数（make-nstf f）。该函数应返回一个函数，该函数使用牛顿方法计算函数的零。

为了测试我的功能，我使用https://repl.it/BWbp/1，如果您愿意，可以将代码复制到本网站进行测试。

我的（不工作的）代码。为了给大家理解代码提供一点帮助，我写了一些cmets：

(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)
)

你能帮我找出错误吗？

问候， 超离子

Answer 1

good-enough? 中有一个错误的右括号（那些鬼鬼祟祟的括号...）

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