Reporting errors at macro-expansion time

[Brad Miller <miller@ACORN.CS.ROCHESTER.EDU>]

Is there a good (read: appropriate) way to report errors to the user that
are detected at macro expansion time?

I'm thinking of something along the following lines:

(defmacro foo (x)
  (typecase x
    (keyword
      `(mumble ,x))
    (symbol
      `(mumble (eval ,x)))
    (t
      (ERROR))))

That is, the macro will detect an erronious argument (or some other problem)
at expansion time, and thus should do something appropriate, other than drop
into the debugger, maybe? I'm hoping there's something along the lines of
sys:read-error which I can't use here since I don't know the stream.

Thanks,
----
Brad Miller		U. Rochester Comp Sci Dept.
miller@cs.rochester.edu {...allegra!rochester!miller}