Ejemplo Universe

(define circulo (circle 20 "solid" "red"))
(define rectangulo (rectangle 80 10 "solid" "orange"))
(define fondo (rectangle 300 300 "solid" "blue"))
(define cuadrado (rectangle 50 50 "solid" "pink"))
(define nave
  (underlay/align
   "center"
   "bottom"
   circulo
   rectangulo)
  )
(define (mover n)
  (underlay/align
   "center"
   "top"
   fondo
   (underlay/xy
    circulo
    20
    n
    rectangulo)
   )
  )

;;vamos a utilizar la función bigbang


(define (terminar n)
  (cond
    [(= 100 n) #t]
    [else #f]
    ))

(define (juego n)
  (big-bang n
            [to-draw mover]
            [on-tick add1]
            [stop-when terminar]
            )
  )

(define (animacion n)
  (underlay/align
   "center"
   "bottom"
   (underlay/xy
    fondo
    120
    n
    nave)
   cuadrado)
  )

(define (tecla estado k)
  (cond
    [(key=? "d" k) (/ estado 2)]
    [(key=? "w" k) (* estado 2)]
    [else estado]
    )
  )

(define (juego2 n)
  (big-bang n
            [on-tick add1]
            [to-draw animacion]
            [stop-when terminar]
            [on-key tecla]
            )
  )