Lecture 3 - slide 5 : 43

(define (new-instance class . parameters)
  (apply class parameters))

(define (send message object . args)
  (let ((method (method-lookup object message)))
    (cond ((procedure? method) (apply method args))
          (else (error "Error in method lookup " method)))))

(define (method-lookup object selector)
  (cond ((procedure? object) (object selector))
        (else
         (error "Inappropriate object in method-lookup: "
                object))))


(define (point x y)
 (let ((x x) 
       (y y)
      )
     
   (define (getx) x)

   (define (gety) y)

   (define (add p) 
    (point 
     (+ x (send 'getx p))
     (+ y (send 'gety p))))

   (define (type-of) 'point)
     
   (define (self message)
     (cond ((eqv? message 'getx) getx)
           ((eqv? message 'gety) gety)
           ((eqv? message 'add)  add)
           ((eqv? message 'type-of) type-of)
           (else (error "Message not understood" message))))
     
   self))