Re: Types in CL

[Jeff Barnett <jbarnett@nrtc.northrop.com>]

Your claim that the compiler should inhibit (SETF (AREF A 0) A) is only valid 
if A is declared of type T1.  It may not be.  What you are pointing out is
that there is a problem if one tries to determine the type of an object (or
its type membership status) *after* the object is created.  In fact, the
runtime package and compiler can offer you more protection if an object is
marked with a type when it is created; only then can modifications and so on
be checked locally.  However this loses something that may not be obvious: an
object can not be referenced by a register unless its marked type entails ALL
type restrictions imposed by the reference.  It is not sufficient that its
current configuration passes muster.
	Jeff
P.S.  The barber is an old friend.