Reporting errors at macro-expansion time

["David L. Andre" <DLA@jasper.scrc.symbolics.com>]

    Date: Fri, 15 Jul 88 00:33:16 EDT
    From: barmar@Think.COM

       Date: Tue, 12 Jul 88 16:53 EDT
       From: DLA@jasper.scrc.symbolics.com (David L. Andre)

	   Date: Mon, 11 Jul 88 22:27 EDT
	   From: barmar@Think.COM (Barry Margolin)

	       Date: Mon, 11 Jul 88 13:34 EDT
	       From: cjl@wheaties.ai.mit.edu (Chris Lindblad)

	       What I do is use warn instead of error, and have the macro expand to something
	       safe, like nil.

	   NIL isn't safe.  Expand into (PROGN) or (VALUES) instead.  If the form
	   is in the body of a TAGBODY (or anything with an implicit tag body, such
	   as DO or PROG), NIL is treated as a tag, not a form, and if you have
	   multiple of them you will get a warning about duplicate tags.

       Sorry.  I was unaware that the body of a LET was an implicit tagbody.

    The body of a LET is not an implicit tagbody.  But who says that
    macros are only used in the bodies of LET? ...

Apparently you didn't receive the revocation of my reply.  My apologies;
I was getting my conversations mixed up.