// example 8

<'
type size_t : [small, medium, large];
type color_t : [yellow, red, blue]; 

struct window {
   // All windows must have some response to a mouse click. The specific response: a sound, a change in color etc,
   // will be determined in the specific(inherited) windows. This method is defined as "empty"- the specific 
   // windows will provide the appropriate implementation

   draw() is empty;
   // All windows must draw something on the screen. The specific graphics of 
   // each window will be determined in the specific (inherited) windows. This
   // method is defined as "empty" and the specific windows will fill in the details
};


struct my_window like window { 
   // "size" and "background_color" are also fields of the inherited class "my_window" since they are
   // fields of the base class "window" therefore I can constrain them here.
   
   keep size == big;
   keep background color == blue;
   // "when_mouse_is_clicked" is defined in the base class since every window
   // has to do something when it is clicked. However, what is it that it should do exactly is different 
   // from window to window. Mine, for example, sounds a  bip, and then shows a pop up message.

   when_mouse_is_clicked() is {
      sound_a_bip();
      jump_a_pop_up("Come on and milk my cow");
   };
     
   // same for "draw"
   draw() is {
      draw_caw();
      draw_milk_bottle();
   };
};


struct her_window like window {

   keep size == small;
   keep background color == blue;

   when_mouse_is_clicked() is also {
       sound_a_wof();
       jump_a_pop_up("Come on and bite my dog");
   };

   draw() is also {
      draw_dog();
   };
};
'>