GNU bug report logs - #15296
24.3.50; A macro object does not necessarily have `lambda' as its cadr

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Drew Adams <drew.adams <at> oracle.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 24.3.50; A macro object does not necessarily have `lambda' as its cadr
Date: Fri, 6 Sep 2013 22:39:58 -0700 (PDT)

AFAICT, (elisp) `Defining Macros' is the closest thing we have to doc
telling you how to test whether a Lisp object is a macro.  There is no
`macro-p' predicate or similar in Emacs Lisp, unless I'm missing
something.  (Shouldn't there be?)

Anyway, this Elisp manual node says that a macro is a list whose car is
`macro' and whose `cdr' is a lambda expression.  That's not true if the
`defmacro' was byte-compiled.  The macro is then a list whose car is `macro'
but whose cdr is byte code, AFAICT.  So this will not work, for example:

(defun macro-p (obj)
  (and (fboundp obj)
       (let ((def  (symbol-function obj)))
         (and (consp def)
              (eq (car def) 'macro)
              (eq (cadr def) 'lambda)))))

In GNU Emacs 24.3.50.1 (i686-pc-mingw32)
 of 2013-08-23 on ODIEONE
Bzr revision: 113986 rgm <at> gnu.org-20130823185841-zoy6h1qk433ibrlf
Windowing system distributor `Microsoft Corp.', version 6.1.7601
Configured using:
 `configure --prefix=/c/Devel/emacs/binary --enable-checking=yes,glyphs
 'CFLAGS=-O0 -g3' LDFLAGS=-Lc:/Devel/emacs/lib
 CPPFLAGS=-Ic:/Devel/emacs/include'

Message #8 received at 15296 <at> debbugs.gnu.org (full text, mbox):

From: Michael Heerdegen <michael_heerdegen <at> web.de>
To: Drew Adams <drew.adams <at> oracle.com>
Cc: 15296 <at> debbugs.gnu.org
Subject: Re: bug#15296: 24.3.50;
 A macro object does not necessarily have `lambda' as its cadr
Date: Sat, 07 Sep 2013 13:34:27 +0200

Drew Adams <drew.adams <at> oracle.com> writes:

> AFAICT, (elisp) `Defining Macros' is the closest thing we have to doc
> telling you how to test whether a Lisp object is a macro.  There is no
> `macro-p' predicate or similar in Emacs Lisp, unless I'm missing
> something.  (Shouldn't there be?)

There is `macrop' in subr.el (since some months ago, I think).

> Anyway, this Elisp manual node says that a macro is a list whose car
> is `macro' and whose `cdr' is a lambda expression.  That's not true if
> the `defmacro' was byte-compiled.

Confusing, indeed.


Michael.

Message #11 received at 15296 <at> debbugs.gnu.org (full text, mbox):

From: Drew Adams <drew.adams <at> oracle.com>
To: Michael Heerdegen <michael_heerdegen <at> web.de>
Cc: 15296 <at> debbugs.gnu.org
Subject: RE: bug#15296: 24.3.50; A macro object does not necessarily have
 `lambda' as its cadr
Date: Sat, 7 Sep 2013 07:23:39 -0700 (PDT)

> > AFAICT, (elisp) `Defining Macros' is the closest thing we have to doc
> > telling you how to test whether a Lisp object is a macro.  There is no
> > `macro-p' predicate or similar in Emacs Lisp, unless I'm missing
> > something.  (Shouldn't there be?)
> 
> There is `macrop' in subr.el (since some months ago, I think).

Wow, that's weird.  And thank you.  That was the first thing I looked for
(the second was `macro-p'), and for some reason I didn't find it (and I'm
using only a recent Emacs 24 build for this testing).

But you are right.  I must have somehow checked for that in a different
Emacs version.  Anyway, that solves my problem wrt testing the type.

> > Anyway, this Elisp manual node says that a macro is a list whose car
> > is `macro' and whose `cdr' is a lambda expression.  That's not true if
> > the `defmacro' was byte-compiled.
> 
> Confusing, indeed.

Not confusing, actually.  It's quite clear.  And wrong, unfortunately.
So AFAICT this should remain open for now, as a doc bug.

Message #16 received at 15296-done <at> debbugs.gnu.org (full text, mbox):

From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: Drew Adams <drew.adams <at> oracle.com>
Cc: 15296-done <at> debbugs.gnu.org
Subject: Re: bug#15296: 24.3.50;
 A macro object does not necessarily have `lambda' as its cadr
Date: Sun, 08 Sep 2013 14:01:53 -0400

> `macro' and whose `cdr' is a lambda expression.  That's not true if the

I changed it to say "function" instead.


        Stefan

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