TYPED-IDENTITY

[JONL at MIT-MC (Jon L White)]

There appears to be good reason for flushing the fsubr notion of this;
but since it makes little sense to have a changeable type argument,
how about accepting two new "numerical" subrs
  FIXNUM-IDENTITY  and FLONUM-IDENTITY
Thus (FIXNUM-IDENTITY (car l)) would require the interpreter to check
that "(car l)" evaluate to a fixnum, and the compiler would treat it
similarly to "(+ (car l))".  The reason why the latter will no longer
be satisfactory for this purpose is that (ho! ho!) the compiler will
"optimize" this into merely "(car l)", thereby losing the type-restriction
information that comes along with "+".   The need for these on the LISPM
is less urgent since there is not compilation advantage to be had, but
it would be a consistent way to get the argument type checking that 
goes along with compilation.