(define plotter
  (lambda (f res x1 x2 y1 y2)
    (let* ((dx (- x2 x1)) (dy (- y2 y1)) (delta (/ dx res)))
      (letrec
	  ((scaled
	    (lambda (f x y) 
	      (f
	       (* res (/ (- x x1) dx))
	       (* res (/ (- y y1) dy)))))
	   (plotit
	    (lambda (x)
	      (scaled draw-line x (f x))
	      (if (< x x2) (plotit (+ x delta))))))
	(draw-color 0 0 0)
	(scaled draw-move 0 y1)
	(scaled draw-line 0 y2)
	(scaled draw-move x1 0)
	(scaled draw-line x2 0)
	(draw-color 255 0 0)
	(scaled draw-move x1 (f x1))
	(plotit x1)))))

(plotter (lambda (x) (* x x x)) 70 -5.0 5.0 -50.0 50.0)
(plotter sin 50 -5.0 5.0 -1.0 1.0)
(plotter (lambda (x) (* x (sin x))) 100 -25.0 25.0 -25.0 25.0)
(plotter (lambda (x) (+ (* x x) (* -5 x) 6)) 80 -1.0 5.0 -3.0 10.0)