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Another (major) difference


	A major difference between the AAAI release of PCL and
previous releases of PCL is minimally documented in the release notes.
PCL now checks whether slots are "unbound", in other words, you can no
longer assume that fields within an object are initialized to NIL.
This is a major change to the sematics of PCL (and a major difference
from the semantics of CL structures).

	I also find the terminology of slots being "bound" to be
extremely confusing.  Binding has a clear fuzzy meaning in CL and
assignment to fields of objects is not related to this concept.  I had
a good deal of trouble understanding PCL's error message:

    Error: The slot OBJECT-MARK is unbound in the object #<MO 35160071>.

I would suggest that correct verb is "uninitialized", not "unbound".
Note that the keyword in DEFCLASS is :INITFORM, not :BINDFORM.  But,
this is probably the wrong mailing list for this flame.