yanfeng42

// mirror...
func cons<T0, T1>(_ x: T0, _ y: T1) -> (T0, T1) {
    return (x, y)
}

func car<T0, T1>(_ t:(T0, T1)) -> T0 {
    return t.0
}

func cdr<T0, T1>(_ t:(T0, T1)) -> T1 {

yanfeng42

; 迭代式改进. -- 哈哈哈. 最终的社区精简版, 竟然是我这种写法. --- 编程理念的差异. 在可读性和技巧性的取舍上, 我优先选择 可读性.
(define (iterative-improve good-enough? impove)
    (define (f x) 
        (if (good-enough? x)
            x
            (f (impove  x))
        )
    )
    f
)

yanfeng42

(define (png-size w h) (* w h 4.0 1/1024)) 

yanfeng42

(define (newton-transform g)
    (lambda (x)
        (- x (/ (g x) ((deriv g) x)))))

(define (deriv g)
    (lambda (x)
        (/ (- (g (+ x dx)) (g x))
            dx)
    )
)   

yanfeng42

; 我的答案:
; 递归写法.
(define (cont-frac-full n d k calculator)
    (define (iterator i)
        (if (< i k)
            (/ (n i) (calculator (d i) (iterator (+ i 1))))
            (/ (n i) (d i))
        )
    )

yanfeng42

(define (filtered-accumulate combiner null-value term a next b filter?)
    (if (> a b)
        null-value
         (combiner (if (filter? a) (term a) null-value)
                (filtered-accumulate combiner null-value term (next a) next b filter?)
            )
    )
)

(define (filtered-sum term a next b filter?)

yanfeng42

(define (accumulate combiner null-value term a next b)
    (if (> a b)
        null-value
        (combiner (term a)
           (accumulate combiner null-value term (next a) next b)
        )
    )
)

(define (accumulate combiner null-value term a next b)

yanfeng42

(define (product term a next b)
    (if (> a b)
        1
        (* (term a)
           (product term (next a) next b)
        )
    )
)

(define (product term a next b)

yanfeng42

(define (sum term a next b)
    (if (> a b)
        0
        (+ (term a)
           (sum term (next a) next b)
        )
    )
)

; 求立方.

yanfeng42

(define (sum term a next b)
    (if (> a b)
        0
        (+ (term a)
           (sum term (next a) next b)
        )
    )
)

; 结果逼近 Π/8