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Proposal #7 Status: TYPE-SPECIFIER-P

Several people have proposed that this be restricted to take only
symbols, since that is the most important use, and it becomes hard to
specify exactly what things must be checked for correctness in the
myriad of more complex cases.  (Speaking for myself, I favor this
change.)  This is proposed in 7A below.

If someone wants to argue in favor of handling the more complex
type-specifiers as well, I would ask you to provide a specific and
detailed proposal for exactly what things must be examined in each case.

It was also suggested that we do this by (TYPEP arg 'TYPE-SPECIFIER), but
some opposition to this idea has also been expressed, on the grounds
that TYPE-SPECIFIER is not really a type in the usual sense.  Also, if
we did this, it would be awkward to restrict the argument to being a

Proposed extension:

Add a new function (TYPE-SPECIFIER-P arg), where ARG must be a symbol.
If ARG is a valid type specifier, this returns T; else it returns NIL.
Note that the use of DEFSTRUCT and DEFTYPE can change the behavior of