[cells-devel] Triple cells

[Ken Tilton]

Watt Poosanguansit wrote:
> Hi Ken,
> 
> I have got a hold of your slides at the European
> Common Lisp Meeting.  I also looked through Triple
> Cell code and I still do not know how to really use
> the code.  A few questions I have to start off.  It
> looks to me like the code stores only the slots and
> not the whole Clos object.
 >  Is that the case?

Actually triple-cells is an entirely new hack that just tries to work 
like CLOS Cells, with a little glue so a dynamic CLOS slot can depend on 
a Triple-cell /maintained by the same process/. (In a multi-user 
environment we would have to get into a whole protocol and IPC.)

This is good. RDF is more expressive than CLOS, so let's not cramp it. 
That said, the little bit I did do with Triple-cells did kinda follow an 
object-slot view of data, so it might seem as if I was thinking 
persistent CLOS, but if I were extending triple-cells I would not let 
CLOS drive what is possible.


>  If yes,
> how do I persist the whole Clos cell object? 

Well, I think you mean CLOS object. A cell is a defstruct. But I think I 
know what you mean.

Triple-cells is just a proof of concept to show how persistent data can 
be driven by something like Cells for CLOS. To do persistent CLOS would 
be a different, non-trivial project and might miss the coolness of RDF. 
I would suggest letting RDF be RDF and CLOS be CLOS. I know and 
appreciate the advantage of transparently making CLOS persistent, but I 
am strting to wonder if it should not be the other way around: should we 
forget CLOS and start working on a dynamic object model tailored after RDF?

> Also, if
> I have a cell object that is the composite of other
> cell objects - Document A has a number of Document B. 
> I want to state a rule saying A can not have more than
> 5 B associated with it.  How to simply state that in
> Clos and Cell?

If you want to allow the sixth B and raise an error, you would have an 
"errors" rule on A that simply says:

    (when (> (length (^A)) 5) (make-instance 'too-many-b))

If you want to prevent the sixth B from getting in, you would have to 
stop it via some add-b-to-a function that checks first of the maximum 
has been reached, ie, the old-fashioned way and not using Cells.

>  I am sorry for the newbie type
> questions.  I hope you can include more samples code
> so it will be easier for new comers to follow.  Thanks
> for your help.

I am afraid I am incredibly busy these days and won't have time for more 
than an occasional email. :(

kt