Newton polinomial

(define (fact n)
    (if (eq? n 0)
        1
        (* (fact (- n 1)) n)
    )
)

(define (delta s y)
    (if (eq? s 0)    0)
    (if (eq? s 1)
        (- (car (cdr y)) (car y))
        (- (delta (- s 1) (cdr y))
           (delta (- s 1) y))
    )
)

(define (NewtonPolinomial sX sY lastX n x)
    ;; When called need increment n by 1.
    (define (compute_q q n)
        (if (eq? n 0)
            q
            (* (- q n) (compute_q q (- n 1)))
        )
    )

    ;; Main function.
    (define (NP sX sY lastX n h q i)
        (cond
            ((or (and (eq? (car sX) lastX)
                      (eq? (cdr sX) '()))
                 (eq? i 0))     (NP sX sY lastX n h q (+ i 1)))
            ((eq? i 1)       (+ (car sY) (* q (delta i sY))))
            (#t              (+ (* (/ (compute_q q (+ n 1))
                                      (fact (+ i 1)))
                                   (delta i sY))
                                (NP (cdr sX) sY lastX (- n 1) h q (+ i 1))))
        )
    )

    (let*
        (
            (h (/ (- lastX (car sX)) n))
            (q (/ (- x (car sX)) h))
        )

        (NP sX sY lastX n h q 0)
    )
)

;; (NewtonPolinomial sX sY lastX n)

(define (bust csX csY currX maxX n)
    (display currX)
    (display " ")
    (display (NewtonPolinomial csX csY maxX n currX))
    (display " ")

    (cond
        ((> currX maxX)  0)
        (#t              (bust csX csY (+ currX 0.2) maxX 11))
    )
)

(let
    (
        (sX '(1 2 3 4 5 6 7))
        (sY '(2 3 4 5 6 7 8))
    )

    (bust sX sY 0 15 11)
)