Scheme 生成一个函数，使线段坐标以斜率m为中心，位于点（x y）处

我正在构建一个绘图库，想要绘制坡度线。我有一个函数draw seg list device color lst，其中lst arg是一个列表，包含x0 y0 x1 y1线的起始线和终止线的列表。我想创建一个函数make slope seg x y m，然后返回以x，y为中心的线段的点列表，该线段的斜率为m

示例：使坡度分段为0 0->-.05 0.05 0，并使坡度分段为1.1 1->.05.05.15.15

我的非工作功能是：

(define (make-slope-cords x y m)
  (list (- x .05)
        (* y m -1)
        (+ x .05)
        (* y m)))

返回不正确的行。如果我使用：

;makes graphics window
(define window (make-graphics-device 'win32))

;plots blue line for function y = x^2 with black axis
(make-plot window 'simple-plot (list "white" "black" "blue" (list (range -1 1 .01) square)))

;makes list of lists containing the slope and x y cords that the slope lines
;are supposed to be centered at
(define cords (map (lambda (s x y)
                     (list s x y))
                   (map (lambda (x) (* 2 x)) (range -1 1 .1))
                   (range -1 1 .1)
                   (map square (range -1 1 .1))))

;plots the line segments generated by mapping make-slope-cords to the coordinate list
(draw-seg-list window "red"
               (map (lambda (lst)
                      (make-slope-cords (car lst) (cadr lst) (caddr lst)))
                    cords))

它的输出如下：

但我希望它在图像中的网格上输出宽度为.1平方的红线，斜率是蓝线λx平方x在沿x轴的每个点上的斜率，间隔为.1

---

注意：假设draw seg list有效。我只是需要帮助，使函数生成一个正确的cordinate列表

经过周密的实验，我能够确定答案

(define (make-sloped-seg x y m)
  (define b (- y (* m x)))
  (list (- x .03)
        (+ (* m (- x .03)) b)
        (+ x .03)
        (+ (* m (+ x .03)) b)))

它在计算开始时确定y截距b，然后使用正确的截距生成点

例如：

;makes graphics window
(define window (make-graphics-device 'win32))

;plots blue line for function y = x^2 with black axis
(make-plot window 'simple-plot (list "white" "black" "blue" (list (range -1 1 .01) square)))

;makes list of lists containing the slope and x y cords that the slope lines
;are supposed to be centered at
(define cords (map (lambda (s x y)
                     (list s x y))
                   (map (lambda (x) (* 2 x)) (range -1 1 .1))
                   (range -1 1 .1)
                   (map square (range -1 1 .1))))

;plots the line segments generated by mapping make-slope-cords to the coordinate list
(draw-seg-list window "red"
               (map (lambda (lst)
                      (make-slope-cords (car lst) (cadr lst) (caddr lst)))
                    cords))

产出如下：