Re: Issue: LIST-TYPE-SPECIFIER (Version 1)

[Rob.MacLachlan@WB1.CS.CMU.EDU]

I agree that it makes sense for a specialized LIST type specifier to be
analogous to ARRAY type specifiers.  But this would imply a dramatically
different semantics for LIST type discrimination than the one suggested in
the original proposal.

With array types, only the specalized types chosen by the implementation
are distinct.  TYPEP cannot distinguish (on the basis of element type)
between two arrays that were made with different types, but that specialize
to the same type.  If (as is probably the case) there is only one
specialized list type, then lists cannot be discriminated at all.

But (if you choose the right array type cleanup) specialized list types
would be useful for declaration, since an implementation *might* have
arbitrary specialized list types:
    (typep (elt (the (list number) foo) 3) 'number)  <=>  T

  Rob