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The real problem with TYPE-OF is that Common Lisp types form a lattice,
not a simple hierarchy. So in addition to implementation-dependent
decisions about how much precision to return, there are fundamental
issues about which of many possible including classes to describe.
Moon's objection is an instance of this: he loooks at one way of cutting
up the super class, while you look at a different one. None of this
bothers TYPEP or SUBTYPEP, but TYPE-OF becomes less meaningful as the
complexity of the type hierarchy increases. We nearly threw TYPE-OF out
of the language last time around, but we were persuaded that we should
keep it because it is of some use to people trying to browse around the
system. Trying to extend it and make it "do the right thing" in all
cases is a mistake.