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    Date: Thu, 14 Feb 85 16:45:52 PST
    From: Scott Turner <srt at UCLA-LOCUS>

    Never mind.  I found STRUCTURE-TYPE (under "Debugging Primitives"), which
    means, however, that we aren't supposed to use it in normal programming.
    Is there a more acceptable way of getting this information?

As I believe it says in the manual, STRUCTURE-TYPE can't be a
non-"meta"-operation since it violates data abstraction.  E.g. a client
of a package could surreptitiously forge that package's structures, so
that a reimplementation of the package might screw such clients.

However, it would make sense to define generic operations on your
structures, if there were a released way to do that.  I think that the
next edition of the manual will have to document DEFINE-METHODS since
it's so difficult to live without it.  It is a pretty poor interface,
and that's why it hasn't been released before, but...

So you could do something like:

(define-methods handle-foo
  ((get-stype self) foo-stype)

and define GET-STYPE methods for any structure type which you wanted
clients to be able to concretize.