Step 3b: Object meta-class

project-2/step3b.rkt

@@ -0,0 +1,82 @@
+(define (object)
+	(define super 'nil)
+	(define (self m)
+		(cond
+			((eq? m 'type) (lambda () 'object))
+		  (else (lambda () (display (string-append "Message not understood: " (symbol->string m) "\n"))))
+		)
+	)
+	self
+)
+
+(define (point x y)
+	(define super (object))
+  (define (getx) (lambda () x))
+  (define (gety) (lambda () y))
+  (define (type) (lambda () 'point))
+  (define (setx!) (lambda (nx) (set! x nx)))
+  (define (sety!) (lambda (ny) (set! y ny)))
+  (define (info) (lambda () (list 'point x y)))
+  (define (add) (lambda (p)
+                  (let ((px ((p 'getx)))
+                        (py ((p 'gety))))
+                    (point (+ x px) (+ y py))
+                   )
+                 ))
+  (define (sub) (lambda (p)
+                  (let ((px ((p 'getx)))
+                        (py ((p 'gety))))
+                    (point (- x px) (- y py))
+                   )
+                 ))
+  (define (self m)
+    (cond ((eq? m 'getx) (getx))
+          ((eq? m 'gety) (gety))
+          ((eq? m 'type) (type))
+          ((eq? m 'setx!) (setx!))
+          ((eq? m 'sety!) (sety!))
+          ((eq? m 'info) (info))
+          ((eq? m 'add) (add))
+          ((eq? m 'sub) (sub))
+          (else (lambda () (method-lookup super (list m))))
+		)
+	)
+  self
+ )
+
+(define (send2 obj . args)
+  (if (procedure? obj)
+      (if (= (length args) 1)
+          ((obj (car args)))
+          ((obj (car args)) (car (cdr args))))  ; Extracting the second argument
+      (display (string-append "Inappropriate receiver object: " (symbol->string obj) "\n"))))
+
+(define (method-lookup reciever message)
+  (if (= (length message) 1)
+      ((reciever (car message)))
+      ((reciever (car message)) (car (cdr message)))
+  ))
+
+(define (send reciever . message)
+  (if (procedure? reciever)
+      (method-lookup reciever message)
+      (display (string-append "Inappropriate receiver object: " (symbol->string reciever) "\n"))
+  )
+ )
+
+
+(define p1 (point 1 2))
+(define p2 (point 3 4))
+(send p1 'getx) ; 1
+(send p1 'gety) ; 2
+(send p2 'getx) ; 3
+(send p2 'gety) ; 4
+(define p (send p1 'add p2))
+(send p 'test);
+(send p 'info) ; (point 4 6)
+(send 'not-a-point 'info) ; should display "Inappropriate receiver object"
+(send p 'foo) ; should display "Message not understood"
+; Same issue than step3
+;(send p 'bar 2) ; should display "Message not understood"
+(send p1 'setx! 5)
+(send p1 'getx) ; returns 5