presentation flavors

[Paul Vaughan <vaughan@MCC.COM>]

In a previous message, I wrote

        	I'm also wondering why Symbolics doesn't seem to allow for
        creating derived flavors of presentations.  It is possible to do
        
        (defflavor 1my-graphic-presentation
0              (my-slot)
              (dw:displayed-presentation)
          )
        
        but then there isn't any mechanism for getting the things made by the
        system.  That is, the macros 
        
        (graphics:with-output-as-graphics-presentation 
        (dw:with-output-as-presentation 
        
        don't allow you to specify the flavor of presentation that is
	created.


And you replied:

;I have a flavor called screen-point that I specify when presented in the
;following manner:
;        
;(graphics:with-output-as-graphics-presentation (screen :type 'screen-point
;								     :object self)
;	    (graphics:draw-circle x y 5
;				    :stream screen))

But, 
	This doesn't accomplish what I was referring to.  This mechanism
allows you to specify the type of the object for which the presentation
is created.  The presentation that is created is an instance of the
flavor dw:displayed-presentation.  Your example lets me create
presentations that may accepted by (accept 'screen-point), but it
doesn't let me add slots to the presentation itself.  Of course, I'm not
absolutely sure that I want to do that, but it has seemed like a good
idea on several occassions.

	The main trouble I have with the documentation is determining
how things were meant to be used.  They generally do a good job of
explaining what things do, it's just what do you do with them that's
hard.  I suppose that's the price of flexibility.  The other trouble I
have with the documentation is the things that aren't documented.  When
I find out about something useful that isn't documented, I never know if
there is some good reason that it's not documented.  Usually a few
experiments suffice to find out what it does.

  -- Paul Vaughan