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An example of classes with inheritance
We sketch one of the favorite toy specializations of Point - ColorPoint
(define (color-point x y color)
 (let ((super (new-part point x y))
       (self 'nil))
   (let ((color color))
     (define (get-color)

     (define (type-of) 'color-point)
     (define (dispatch message)
       (cond ((eqv? message 'get-color) get-color)
             ((eqv? message 'type-of) type-of)
             (else (method-lookup super message))))
     (set! self dispatch))
All necessary stuff to play with ColorPoint.
A sample construction and sample dialogue with ColorPoint.
Go to exercise
Color Point Extension