[Fwd: Re: [cells-devel] observer design question]

[Ken Tilton]

[ooops--for the list]

-------- Original Message --------
Subject: Re: [cells-devel] observer design question
Date: Fri, 28 Mar 2008 10:44:15 -0400
From: Ken Tilton <kennytilton at optonline.net>
Organization: Theory Y Learning
To: achambers.home at gmail.com
References: 
<a70cc98c0803280617n161f774ek466efe371228d2bb at mail.gmail.com> 
<47ECF307.5000704 at optonline.net> 
<a70cc98c0803280730t27003f4dgbf5bc8d2fc22dbf2 at mail.gmail.com>

Andy Chambers wrote:
> On Fri, Mar 28, 2008 at 1:30 PM, Ken Tilton <kennytilton at optonline.net> wrote:
> 
>>Andy Chambers wrote:
>> > My model consists of a family tree of objects all of which have an
>> > xhtml ruled cell.  The client needs to
>> > be updated if the value of this slot has changed.  However, a change
>> > in one would cascade up
>> > the tree so if we were logging these changes, and sending them down to
>> > the client, one of the
>> > things we send would be the entire document which is not what we want.
>>
>> How did the entire document change (I mean in /precisely/ what way such
>> that your app wanted to send the whole thing?
> 
> 
> The xhtml rule (for an html div) looks almost like this (in the real
> one there's a line to
> put the attributes in too).
> 
> (c? (with-output-to-string (s)
>       (with-html-output (s)
>         (:div
>          (str (apply #'concatenate 'string
>                      (mapcar #'xhtml (^kids))))))))
> 
> So the value of it depends on its kids.  If any of the kids change,
> then the xhtml slot on the div object will also
> change.  If I was to put an observer on xhtml, it would fire all the
> way up the tree from each leaf that changed
> wouldn't it?

Yes. This is cool, this is like OpenGL display lists which are like
objects in that my parent does not need to be rebuilt on the OpenGL side
just because I have changed, my parent display list just runs and when
it calls me -- well, it is more like Lisp with changing a function
defintition while the application is running, my new display
instructions get executed.

So what I am hearing between the lines is that the kid can change and
push itself over to the DOM (if I have the jargon right) and the browser
  will Do the Right Thing in re getting everything rendered?

Get back to me to confirm, meanwhile I will refresh on the sleight of
hand I did to make display lists work. IIRC the trick will be to have
each rule turn off dependency tracking, sample each kid to get them up
to date, then turn dependency back on for the /assembly/ of the kids
into the current xhtml result.

kt