Update step_4.rkt : adding comments and explanations

step_4.rkt

+#lang r5rs
+; Authors : Nicolas Verbois - 1366 1600
+;           Nicolas Rosar   - 1443 1900
+;           Group F
+
+; In this last step, we want to implement a way of executing the calls delegated to a method defined in the super class
+; in the context of the child class. This will be done using what we have called a "self_ref" value inside each class.
+; We have also created a new constructor procedure, that will handle the creation of any class instance, and will help
+; the achieve this dynamic binding of self.
+
+; The purpose of the self_ref value is linked to the special method named 'set-self! that we have added to each class.
+; It binds self_ref to a given instance and then recursively calls the same 'set-self! method on the superclass to bind
+; its self_ref to that same instance, solving the dynamic binding issue.
+
+; For the object class, we don't need a recursive call to the super class in the set_self! method since it is the root
+; of our inheritance hierarchy.
+; Thus, in this case, we do not propagate the set_self! method and instead only dynamically bind the local self_ref value.
 (define (object)
+  ; #f is the default value before any binding
   (define self_ref #f)
   (define (set-self! ref) (set! self_ref ref))
   (define (gettype) 'object)
@@ -8,7 +26,8 @@
           (else (display "Message not understood"))))
   self)
 
-; COLOR-POINT
+; For the color-point class, since it is a child class of point, we need to propagate the set-self! call to the super class.
+; Thus, we have an extra line in the definition of the set_self! procedure to propagate the dynamic binding upwards.
 (define (color-point x y color)
   (define self_ref #f)
   (define super (point x y))
@@ -31,7 +50,7 @@
           (else (super m))))
   self)
 
-;POINT
+; For the point class, as it is a child class of object, we also need to propagate the set-self! call to the super class.
 (define (point x y)
   (define self_ref #f)
   (define (set-self! ref)
@@ -61,6 +80,7 @@
           (else (super m))))
   self)
 
+
 (define (send p m . args)
   (if (procedure? p)
       (cond
@@ -73,6 +93,11 @@
  )
 
 
+; The new construtctor procedure.
+; It has to take as parameters one object-class, as well as a variable numbler of
+; class parameters.
+; It will then create the new object, and initiate the dynamic binding of self through
+; a 'set-self call.
 (define (new object-class . class-args)
   (let ((temp (apply object-class class-args)))
     (begin
@@ -82,10 +107,30 @@
     )
   )
 
-(eq? color-point point)
-( define cp ( new color-point 5 6 'red ) )
-( send cp 'type ) ; c o l o r - p o i n t
-( send cp 'getx ) ; 5
-( send cp 'gety ) ; 6
-( send cp 'get-color ) ; red
-( send cp 'info ) ; ( c o l o r - p o i n t 5 6 red )
+
+
+; Sample code illustrating the execution of the step
+
+; We can prove that the dynamic binding indeed worked with the followig piece of code.
+; Indeed, with the current implementation, if the dynamic binding were not to work,
+; then the 'info message sent to the color point would return something wrong.
+
+; It is because the way we build the return value of the 'info message in the color-point
+; class is done using informations retrieved by the parent class, and appending other informations
+; to this : (append (send super 'info) ... )).
+
+; Without dynamic binding, the parent point class would have no clue it is called by a color-point object,
+; and thus return the information of a point and not a color-point.
+
+
+(define cp (new color-point 5 6 'red))
+(display (send cp 'type)) ; should display : color-point
+(newline)
+(display (send cp 'getx)) ; should display : 5
+(newline)
+(display (send cp 'gety)) ; should display : 6
+(newline)
+(display (send cp 'get-color)) ; should display : red
+(newline)
+(display (send cp 'info )) ; should display : (color-point 5 6 red)
+(newline)