Complete Program from Figure 13

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

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

(define Union-Shape
  (unit (import Shape)
        (export Union)

    (define Union
      (class* object% (Shape) (left right)
	  [draw (lambda (dc x y)
		  (send left draw dc x y)
		  (send right draw dc x y))])
        (sequence (super-init))))))

(define Basic+Union-Shapes 
   (link [S (Basic-Shapes)]
	 [US (Union-Shape (S Shape))])
   (export(S Shape)
	  (S Rectangle)
	  (S Circle)
	  (S Translated)
	  (US Union))))

(define BB-Shapes
  (unit (import Shape Rectangle Circle Translated Union) 
	(export BB-Shape BB-Rectangle BB-Circle 
		BB-Translated BB-Union
		make-BB BB-left BB-top BB-right BB-bottom)

    (define BB-Shape (interface (Shape) bounding-box))

    (define-struct BB (left top right bottom))
    (define BB-Rectangle
      (class* Rectangle (BB-Shape) (width height)
	   (lambda () (make-BB 0 0 width height))])
	(sequence (super-init width height))))
    (define BB-Circle
      (class* Circle (BB-Shape) (r)
	   (lambda () (make-BB (- r) (- r) r r))])
	(sequence (super-init r))))
    (define BB-Translated
      (class* Translated (BB-Shape) (shape dx dy)
	   (lambda ()
	     (let ([pre-bb (send shape bounding-box)])
	       (make-BB (+ (BB-left pre-bb) dx)
			(+ (BB-top pre-bb) dy)
			(+ (BB-right pre-bb) dx)
			(+ (BB-bottom pre-bb) dy))))])
	(sequence (super-init shape dx dy))))
    (define BB-Union
      (class* Union (BB-Shape) (left right)
	   (lambda ()
	     (let ([left-bb (send left bounding-box)]
		   [right-bb (send right bounding-box)])
	       (make-BB (min (BB-left left-bb) (BB-left right-bb))
			(min (BB-top left-bb) (BB-top right-bb))
			(max (BB-right left-bb) (BB-right right-bb))
			(max (BB-bottom left-bb) (BB-bottom right-bb)))))])
	(sequence (super-init left right))))))

(define Basic+Union+BB-Shapes 
   (link [S (Basic+Union-Shapes)] 
	 [BS (BB-Shapes (S Shape) 
			(S Rectangle) 
			(S Circle) 
			(S Translated) 
			(S Union))]) 
   (export (S Shape) 
	   (BS BB-Shape)

	   ;rename BS's BB-Rectangle to Rectangle, etc.:
	   (BS (BB-Rectangle Rectangle)) 
	   (BS (BB-Circle Circle)) 
	   (BS (BB-Translated Translated)) 
	   (BS (BB-Union Union))

	   (BS make-BB)
	   (BS BB-left)
	   (BS BB-top)
	   (BS BB-right)
	   (BS BB-bottom))))

(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)))

(define Union-Picture
  (unit (import Rectangle Circle Translated Union
		shape1 shape2

    (define shape3 (make-object Union shape1 shape2))
    (display-shape shape3)))

;; the graphics library (mred@) is defaultly a signed unit.
;; see mzscheme manual for details of signed units.
(define MrEd-Toolkit (unit/sig->unit mred@))

(define BB-Gui
  (unit (import BB-Shape
		BB-left BB-top BB-right BB-bottom
		canvas% frame%)
        (export display-shape) 

    (define shape-canvas%
      (class canvas% (parent shape)
	(inherit get-dc get-client-size)
	   (lambda ()
             (let-values ([(win-width win-height) (get-client-size)])
               (let* ([bb (send shape bounding-box)]
		       (lambda (left1 right1 left2 right2)
			 (- (/ (- (- right2 left2)
				  (- right1 left1))
		      [x (size (BB-left bb) (BB-right bb) 0 win-width)]
		      [y (size (BB-top bb) (BB-bottom bb) 0 win-height)])
                 (send shape draw (get-dc) x y))))])
	(sequence (super-init parent))))
    (define display-shape
      (lambda (a-shape)
	(unless (is-a? a-shape BB-Shape)
	  (error 'display-shape "expected a BB-Shape, got: ~e" a-shape))
	(let* ([frame (make-object frame% "Centered Shapes" #F 150 150)]
	       [canvas (make-object shape-canvas% frame a-shape)])
	  (send frame show #t))))))

(define BB-Program 
   (link [S (Basic+Union+BB-Shapes)] 
	 [M (MrEd-Toolkit)]
	 [BG (BB-Gui (S BB-Shape)
		     (S BB-left) (S BB-top) (S BB-right) (S BB-bottom)
		     (M canvas%) (M frame%))]
	 [P (Picture (S Rectangle)
		     (S Circle)
		     (S Translated) 
		     (BG display-shape))]
	 [UP (Union-Picture (S Rectangle)
			    (S Circle) 
			    (S Translated)
			    (S Union)
			    (P shape1)
			    (P shape2)
			    (BG display-shape))])

(invoke-unit BB-Program)

in context