Update step_0.rkt : adding comments and more tests

step_0.rkt

 #lang r5rs
+; Authors : Nicolas Verbois - 1366 1600
+;           Nicolas Rosar   - 1443 1900
+;           Group F
+
+; This acts as the first step in building objects in Scheme
+; The object, here a point, is defined as a dispacther returning values.
+; We thus emulate a point class as a constructor function that creates
+; an object through a dispacter function.
+
+; A point will be defined as an object containing two coordinates, x and y.
+; Once the object is created using the constructor, the dispacther will be
+; able to respond to messages, concerning those two coordinates as well as
+; characteristics of the point object, like the type of object, or printing
+; a "string-like" representation using the "info" message.
+
+; In case of a message that the dispatcher cannot handle, it will return a
+; simple error message through a display.
 
 (define (point  x y)
   (define (dispatch m)
@@ -9,11 +26,38 @@
           (else (display "ERROR"))))
   dispatch)
 
+
+
+; Sample code illustrating the execution of the step
+
+; We start by trying to create a new point p
 (define p (point 1 2))
-(display (p 'getx))
+
+(display (p 'getx)) ; should display : 1
 (newline)
-(display (p 'gety))
+
+(display (p 'gety)) ; should display : 2
 (newline)
-(display (p 'type))
+
+(display (p 'type)) ; should display : point
+(newline)
+
+(display (p 'info)) ; should display : (point 1 2)
 (newline)
-(display (p 'info))
+
+(display '------------)
+(newline)
+
+; We then create a second point p
+(define p2 (point 4 -1))
+
+(display (p2 'getx)) ; should display : 4
+(newline)
+
+(display (p2 'gety)) ; should display : -1
+(newline)
+
+(display (p2 'type)) ; should display : point
+(newline)
+
+(display (p2 'info)) ; should display : (point 4 -1)