[cells-devel] Re: [cello-devel] Unbound cells

[Kenny Tilton]

Thomas F. Burdick wrote:

>Kenny Tilton writes:
> > On the other hand, Cells should not change Lisp unnecessarily.
> > 
> > It would be easy enough to do something such as (cv +unbound+) or just 
> > (cv) and then have the internal sm-install function invoke 
> > slot-makunbound instead of forcing the slot to be bound. Then one does 
> > not need a special test for cell-boundp (which sounds wrong anyway in re 
> > transparency).
> > 
> > But what about a rule that runs across an unbound cell/slot? I should 
> > think that does not generate an unbound error, rather the slot mediated 
> > by the rule should in turn be made unbound.
> > 
> > I guess echoing works OK, tho anyway doing this on the GUI slots will 
> > not get far since existing echos are not testing for unbounditude.
>
>... I like this, because if you have rules that ultimately depend on
>an uncalculated value, you'll get an error when you try to ask for it.
>
Yes, I am thinking we throw a c-slot-unbound condition from the 
generated cell slot accessor. The internals code that kicks off a rule 
can trap for just that condition, so other non-cell unbound errors go 
splat normally. and user-level slot accesses would backtrace on 
c-slot-unbound. too bad there is no Lisp condition to be subclassed 
(guessing).

kt

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