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

[Thomas F. Burdick]

Kenny Tilton writes:
 > 
 > 
 > 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).

Heh, you missed it in my first message: unbound-slot.