Piirretään sektoreita

(require 2htdp/image)
(define SIZE 50)
(define (make-wedge color angle)
   (underlay/align
    "left" "top"
    (circle SIZE "solid" (make-color 255 255 255 0))
    (crop 0 0 (* 2 SIZE) SIZE
          (cond
            [(< angle 90)
             (underlay/align "left" "bottom"
                             (circle SIZE "solid" (make-color 255 255 255 0))
                             (rotate (- 180 angle)
                                     (crop 0 0 (* 2 SIZE) SIZE
                                           (circle SIZE "solid" color))))]
            [else
             (underlay/align "left" "top"
                             (circle SIZE "solid" (make-color 255 255 255 0))
                             (rotate (- 180 angle)
                                     (crop 0 0 (* 2 SIZE) SIZE
                                           (circle SIZE "solid" color))))]))))

(overlay
 (rotate 240 (make-wedge "red" 120))
 (rotate 120 (make-wedge "blue" 120))
 (make-wedge "green" 120))

(overlay
 (rotate 300 (make-wedge "red" 60))
 (rotate 240 (make-wedge "violet" 60))
 (rotate 180 (make-wedge "blue" 60))
 (rotate 120 (make-wedge "green" 60))
 (rotate 60 (make-wedge "yellow" 60))
 (make-wedge "orange" 120))

HSL.

(define (hue-to-color hue)
  (f1 (/ hue 60)))

(define (my-modulo a b)
  (cond
    [(< a b) a]
    [else (my-modulo (- a b) b)]))

(define (f1 H2)
  (f2 H2 (round (* 255 (- 1 (abs (- (my-modulo H2 2) 1)))))))

(define (f2 H2 X)
  (cond
    [(<= 0 H2 1) (make-color 255 X 0)]
    [(<= 1 H2 2) (make-color X 255 0)]
    [(<= 2 H2 3) (make-color 0 255 X)]
    [(<= 3 H2 4) (make-color 0 X 255)]
    [(<= 4 H2 5) (make-color X 0 255)]
    [(<= 5 H2 6) (make-color 255 0 X)]))

(define (lots-of-wedges number)
  (make-more-wedges number 0))

(define (make-more-wedges how-many angle)
  (cond
    [(>= angle 360) (make-wedge "white" 0)]
    [else
     (overlay
      (rotate angle (make-wedge (hue-to-color angle) (/ 360 how-many)))
      (make-more-wedges how-many (+ angle (/ 360 how-many))))]))

(lots-of-wedges 60)

Hieman toistettua koodia vähentämällä:

(require 2htdp/image)
(define SIZE 50)
(define alpha-circle
  (circle SIZE "solid" (make-color 255 255 255 0)))

(define (half image)
  (crop 0 0 (* 2 SIZE) SIZE image))

(define (make-wedge color angle)
   (underlay/align
    "left" "top"
    alpha-circle
    (half (underlay/align
           "left"
           (cond [(< angle 90) "bottom"]
                 [else "top"])
           alpha-circle
           (rotate (- 180 angle)
                   (half (circle SIZE "solid" color)))))))

(define (hue-to-color hue)
  (f1 (/ hue 60)))

(define (f1 H2)
  (f2 H2 (round (* 255 (- 1 (abs (- (my-modulo H2 2) 1)))))))

(define (my-modulo a b)
  (cond [(< a b) a]
        [else (my-modulo (- a b) b)]))

(define (f2 H2 X)
  (cond [(<= 0 H2 1) (make-color 255 X 0)]
        [(<= 1 H2 2) (make-color X 255 0)]
        [(<= 2 H2 3) (make-color 0 255 X)]
        [(<= 3 H2 4) (make-color 0 X 255)]
        [(<= 4 H2 5) (make-color X 0 255)]
        [(<= 5 H2 6) (make-color 255 0 X)]))