(define Basic-Shapes
  (unit (import) 
        (export Shape Rectangle Circle Translated)

    (define Shape (interface () draw))
    
    (define Rectangle
      (class* null (Shape) (width height)
	(public
	  [draw (lambda (dc x y)
		  (send dc draw-rectangle x y width height))])))
    
    (define Circle
      (class* null (Shape) (radius)
	(public
	  [draw (lambda (dc x y)
		  (send dc draw-ellipse
			(- x radius)
			(- y radius)
			(* 2 radius)
			(* 2 radius)))])))
    
    (define Translated
      (class* null (Shape) (orig-shape dx dy)
	(public
	  [draw (lambda (dc x y)
		  (send orig-shape draw 
			dc (+ x dx) (+ y dy)))])))))


(define Gui
  (unit (import Shape mred:canvas% mred:frame% mred:vertical-panel%)
        (export display-shape)
    
    (define shape-canvas%
      (class mred:canvas% (panel shape)
	(inherit get-dc)
	(public
	  [on-paint
	   (lambda ()
	     (send shape draw (get-dc) 0 0))])
	(sequence (super-init panel))))
    
    (define display-shape
      (lambda (shape)
	(unless (is-a? shape Shape)
	  (error 'display-shape "expected a Shape, got: ~e" shape))
	(let* ([frame (make-object mred:frame% null "Shapes" 0 0 150 150)]
	       [panel (make-object mred:vertical-panel% frame)]
	       [canvas (make-object shape-canvas% panel shape)])
	  (send frame show #t))))))

(define Picture 
  (unit (import Rectangle Circle Translated display-shape) 
        (export shape1 shape2)

    (define shape1 (make-object Rectangle 40 30))
    (define shape2 (make-object Translated 
		     (make-object Circle 20)
		     30 30))

    (display-shape shape1)
    (display-shape shape2)))