Update step_2.rkt : added more comments to explain the code, and reorganized a bit of code

step_2.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))
@@ -15,30 +27,69 @@
           (else (display "Message not understood"))))
   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) (p m))
-        ; Checker length args
-        ;((eq? m 'add) (p 'add
-        (else ((p m) (car args) ) )
+        (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") )
   )
 
 
+; 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 p1 ( point 1 2 ) )
-( define p2 ( point 3 4 ) )
-(display ( send p1 'getx )) ; 1
-(display ( send p1 'gety )) ; 2
-(display ( send p2 'getx )) ; 3
-(display ( send p2 'gety )) ; 4
-;(display ( send p1 'add p2)) ;(4 6)
 (define p (send p1 'add p2))
-(display ( send p 'info )) ; ( p o i n t 4 6)
+(display ( send p 'info )) ; should display : (point 4 6)
+(newline)
 
 (send p1 'setx! 5)
-(display (send p1 'getx )) ; r e t u r n s 5
-(display (send 'add 'getx))
\ No newline at end of file
+(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)
+