[cells-devel] A question about the use of vectors in CELLS

[Kenneth Tilton]

FWIW: Probably the most elegant answer would be one in which one could 
rely on just one element of a vector, although I can also see how one 
would then need a way to have just one dependency if one was iterating 
over the whole vector. This would prolly mean a whole new entry point 
(md-slot-vector-value and (setf md-slot-vector-value)) and in the end 
not be all that hard, just some straightforward effort in the 
dependency-tracking code to keep it efficient.

This would not be transparent or foolproof -- if one forgets to use the 
slot-vector API the dependencies will mysteriously not work, but that is 
the kind of thing one recognizes after ten seconds of stunned 
astonishment (like CLOS methods whose signatures I change but neglect to 
expunge).

kt


Peder Chr. Nørgaard wrote:
> Larry, thanks for the answer.  Yes, a trick (OK, a technique) like this would 
> probably do the job for me.  I was kind of leaning in the same direction 
> myself, Kenneth Tilton's response pointing to Peter 
> Hildebrandt's "cells-store" extension which is actually a part of the Cells 
> package that I am using and using more or less the same hack (OK, same 
> technique) :-).
> 
> So, everybody, thanks for your help, Kenneth, Jakub, Larry.  And Peter 
> Hildebrandt, I found the Aug 2008 mail describing the rationale for 
> cells-store (not to be churlish, but that text ought to be in cells source 
> code package, not in a mail somewhere.  It is valuable!).
> 
> I have the answer to my problem now.  Just have to decide what to do.
> 
> best regards
> 				--peder chr.
> 
> 
> 
> On Monday 18 May 2009, Larry Clapp wrote:
>> On Sat, May 16, 2009 at 04:23:41PM +0200, Peder Chr. Nørgaard wrote:
>>> I am attempting to use a vector as the value in a slot.  It does not
>>> work well in first attempt:
>>>
>>> CL-USER> (use-package :cells)
>>> T
>>> CL-USER> (defparameter a1 (make-instance 'model :value (c-in #(1 2 3
>>> 4)))) A1
>>> CL-USER> (defparameter a2 (make-instance 'model :value (c? (apply #'+
>>> (map 'list #'identity (value a1))))))
>>> A2
>>> CL-USER> (value a2)
>>> 10
>>> CL-USER> (setf (elt (value a1) 1) 5)
>>> 5
>>> CL-USER> (value a1)
>>> #(1 5 3 4)
>>> CL-USER> (value a2)
>>> 10
>>>
>>> The VALUE slot of A2, depending on (VALUE A1) is not changing when
>>> (VALUE A1) is, shall we call it "changed in place".
>>>
>>> The cells version is
>>> from 
>>> :pserver:anonymous:anonymous at common-lisp.net:/project/cells/cvsroot.
>>>
>>> The Lisp system is SBCL is 1.0.18.0-2.
>>>
>>> I would like to enquire whether I am simply doing something
>>> trivially wrong, or whether this is something that simply cannot be
>>> done without a major CELLS extension for support of vector values
>>> (like, FAMILY, can be viewed as a kind of support for list values).
>>> The latter answer may force me to reconsider an implementation that
>>> I had in mind.
>> I asked a similar question almost exactly a year ago.  Hmmm.  :)
>> Anyway, see
>> http://common-lisp.net/pipermail/cells-devel/2008-May/002035.html .
>> The general answer hasn't changed since then: either don't do that, or
>> recons the sequence, or make the cell formula depend on something else
>> that changes directly in addition to the stuff it actually depends on.
>> (In last year's thread, Peter Hildebrandt noted that this last option
>> is how cells-store works.)
>>
>> I played with the last option a bit today, and came up with this
>> (which may or may not work very well in real usage, but the toy
>> example below works):
>>
>>   (defmodel change-counter ()
>>     ((count :initform (c-in 0) :accessor count-of)))
>>
>>   (defmethod kick ((self change-counter))
>>     (incf (count-of self)))
>>
>>   (defmacro change-watcher ((model) &body body)
>>     `(progn
>>        (count-of ,model)
>>        , at body))
>>
>>   (defmacro with-changes ((&rest models) &body body)
>>     `(unwind-protect
>> 	 (progn , at body)
>>        (with-integrity (:change)
>> 	 (dolist (model (list , at models))
>> 	   (kick model)))))
>>
>> Example (Lispworks, if it matters):
>>
>>   CELLS-PLAY 217 > (defmodel test (change-counter)
>> 		     ((slot :initarg :slot :accessor slot-of)))
>>   NIL
>>
>>   CELLS-PLAY 218 > (defparameter a1 (make-instance 'test :slot (c-in #(1 2
>> 3 4)))) A1
>>
>>   CELLS-PLAY 219 > (defparameter a2 (make-instance 'test :slot (c?
>> 								 (change-watcher (a1)
>> 								   (format t "recalc a2's s~%")
>> 								   (apply '+ (coerce (slot-of a1) 'list))))))
>>   recalc a2's s
>>   A2
>>
>>   CELLS-PLAY 220 > (slot-of a2)
>>   10
>>
>>   CELLS-PLAY 221 > (with-changes (a1)
>> 		     (setf (aref (slot-of a1) 1) 5))
>>   recalc a2's s
>>   5
>>
>>   CELLS-PLAY 222 > (slot-of a2)
>>   13
>>
>>   CELLS-PLAY 223 > (slot-of a1)
>>   #(1 5 3 4)
>>
>> Hope that's helpful.
>>
>> -- Larry
> 
> 
> 
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