;; The first three lines of this file were inserted by DrScheme. They record metadata
;; about the language level of this file in a form that our tools can easily process.
#reader(lib "htdp-beginner-reader.ss" "lang")((modname ring) (read-case-sensitive #t) (teachpacks ((lib "draw.ss" "teachpack" "htdp"))) (htdp-settings #(#t constructor repeating-decimal #f #t none #f ((lib "draw.ss" "teachpack" "htdp")))))
;; The structrure represents a ring; center is a position (posn)
;; of the center, inner-rad and outer-rad are the inner and the
;; oter raduius values, respectively, and color is a symbol 
;; that represents the color
(define-struct ring (center inner-rad outer-rad color))

(define (draw-ring a-ring) 
  (and 
   (draw-solid-disk (ring-center a-ring) (ring-outer-rad a-ring) (ring-color a-ring))
   (draw-solid-disk (ring-center a-ring) (ring-inner-rad a-ring) 'white)
  )
)

(start 300 300)

(define ring1 (make-ring (make-posn 150 150) 50 100 'red))

(draw-ring ring1)

(define (clear-ring a-ring)
   (clear-solid-disk (ring-center a-ring) (ring-outer-rad a-ring) (ring-color a-ring))
)

(sleep-for-a-while 1)

(clear-ring ring1)

(define ring2 (make-ring (make-posn 150 150) 40 90 'red))

(define (draw-and-clear-ring a-ring)
  (and (draw-ring a-ring)
       (sleep-for-a-while 1)
       (clear-ring a-ring)
  )
)

(draw-and-clear-ring ring2)

(define ring3 (make-ring (make-posn 150 150) 30 80 'red))

(draw-and-clear-ring ring3)

(define ring4 (make-ring (make-posn 150 150) 20 70 'red))

(draw-and-clear-ring ring4)

(define ring5 (make-ring (make-posn 150 150) 10 60 'red))

(draw-and-clear-ring ring5)