[elephant-devel] SBCL errors

[Alex Mizrahi]

>>> Unexpected Error: #<SB-INT:BUG "~@<failed AVER: ~2I~_~A~:>"
>>> {1002E81E41}>
>>> failed AVER: NSLOTDS

I've found source of this error -- SBCL's internal %UPDATE-CLASS assumes 
that slot-allocation is either :instance or :class (and we have 
:database for persistent slots), so it breaks when you drop a virtual 
slot (i.e. redefine class without this slot).

It is trivial to fix this particular problem, but I'm not sure that rest 
of %UPDATE-CLASS code is correct.

So I didn't submit a patch: it would be better if SBCL developers review 
%UPDATE-CLASS and related code assuming that some slots might be 
"virtual". I just don't understand SBCL internals very well.

You can probably ignore this bug and use latest version of SBCL anyway 
if you abstain from redefining classes with dropped slots :)