move ufo and tank

ufo-tank.rkt

(require 2htdp/image)
(require 2htdp/universe)
(require lang/posn)

(struct world (ufo tank))

(define width 500)
(define height 500)

(define mtsn (empty-scene width height))


(define ufo (circle 10 "solid" "red"))

(define tank (overlay/xy
	      (overlay/xy (circle 5 "solid" "black") 20 0 (circle 5 "solid" "black"))
	      0
	      -8
	      (overlay/xy (rectangle 30 8 "solid" "red") 7 -4 (rectangle 15 4 "solid" "red"))))

(define (render w)
  (place-images
   (list ufo tank)
   (list (make-posn 50 (world-ufo w))
	 (make-posn (world-tank w) 200))
   mtsn))

(define (animate w)
  (world (+ 1 (world-ufo w))
	 (+ 1 (world-tank w))))

(define (main p0)
  (big-bang p0
	    [on-tick animate]
	    [to-draw render]))

(main (world 200 100))