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Re: Painful retraction

Your arguments about not wanting to do in-line type checking on stock
hardware are valid in general, but one could probably special-case the
NIL case without much loss.  E.g. (ship-captain NIL) ==> exception
handling.   The real question is, would it be worth it just for NIL.  

If one implementation did it, there would be the strong temptation to
write non-portable code, i.e., depending on (ship-captain NIL) ==> NIL,
and such code couldn't be mechanically fixed.  In view of this, either
the standard should permit this exception case, or we should lobby hard
to prevent it from being implemented in Common Lisp "dialects".

-- JonL --