Tentative step 2 de mieux gérer les erreurs et de faire un lookup

tentative_step_2+3a.rkt

+#lang r5rs
+; Authors : Nicolas Verbois - 1366 1600
+;           Nicolas Rosar   - 1443 1900
+;           Group F
+
+; In this step, we have added a new operator, whose name is "send".
+; It will allow us to improve the syntax of the code, by allowing to
+; send messages to objects in a clearer manner.
+
+; Defined below, the send operater first looks if the receiver object is indeed
+; an appropriate receiver object, else it returns a specific error.
+; Then, it will try to apply the message.s to the object.
+
+; A point object, constituted of two coordinates and returning a self function.
+(define (point x y)
+  (define (setx value)
+    (set! x value))
+  (define (add p)
+    (point (+ x (p 'getx)) (+ y (p 'gety))))
+  (define (self m)
+    (cond ((eq? m 'getx) x)
+          ((eq? m 'gety) y)
+          ((eq? m 'type) 'point)
+          ((eq? m 'info) (list (self 'type) (self 'getx) (self 'gety)) )
+          ((eq? m 'setx!) setx )
+          ((eq? m 'add) add)
+          (else (begin (display "Message not understood") #f))))
+  self)
+
+
+; The new send operator
+; It takes as argument a point and at least one message.
+
+; If send receives only a point and a message ( two parameters ),
+; then it will simply call the self function on this message.
+; Thus, (send p m) => (p m)
+
+; If send receives more than two arguments, it will assume that
+; it is a message with additional parameters, such as the add operator,
+; that should be translated as follow :
+; (send p m arg) => ((p m) arg)
+(define (send p m . args)
+  (if (procedure? p)
+      
+      (cond
+        ((null? args)
+         (if (lookup p m)
+             (p m)
+             (display "Message d'erreur redondant")
+         ))
+        (else ((p m) (car args))) ; We have to take the "car" of the args list
+        )
+      ; If the first parameter, p, is not a procedure, then we return a special error.
+      (display "Inappropriate receiver object") )
+  )
+
+(define (lookup p m)
+  (if (eq? #f (p m) )
+      #f
+      #t)
+  )
+
+; Sample code illustrating the execution of the step
+
+; We start by creating two points, p1 and p2
+
+(define p1 (point 1 2))
+(define p2 (point 3 4))
+
+(display (p1 'getx)) ; should display : 1
+(newline)
+
+(display (p1 'gety)) ; should display : 2
+(newline)
+
+(display '----------)
+(newline)
+
+(display (p2 'getx)) ; should display : 3
+(newline)
+
+(display (p2 'gety)) ; should display : 4
+(newline)
+
+(display '----------)
+(newline)
+
+(define p (send p1 'add p2))
+(display ( send p 'info )) ; should display : (point 4 6)
+(newline)
+
+(send p1 'setx! 5)
+(display (send p1 'getx )) ; should display : 5
+(newline)
+
+(display ( send 'not-a-point 'info )) ; should display : Inappropriate receiver object
+(newline)
+
+(display (send p 'foo)) ; should display : Message not understood
+(newline)
+
+;(display (send p 'bar 2)) ; should display : Message not understood, then crash
+(newline)
+