presentation flavors

[Donald Leo Kaiser <dlk%bas-seatac.dialnet.symbolics.com@RELAY.CS.NET>]

    Date: Wed, 22 Feb 89 10:40 CST
    From: vaughan@MCC.COM (Paul Vaughan)

    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
----------------------------------------------------------------------------------------

Sorry, I did not fully understance the question. You are right.