From: Daniel Colascione <dancol@dancol.org>
To: Stefan Monnier <monnier@IRO.UMontreal.CA>
Cc: emacs-devel@gnu.org
Subject: Re: [Emacs-diffs] trunk r117002: Correctly treat progn contents as toplevel forms when byte compiling
Date: Mon, 21 Apr 2014 15:29:38 -0700 [thread overview]
Message-ID: <53559BD2.3000006@dancol.org> (raw)
In-Reply-To: <jwvioq2nxvp.fsf-monnier+emacsdiffs@gnu.org>
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On 04/21/2014 03:09 PM, Stefan Monnier wrote:
>>>> Correctly treat progn contents as toplevel forms when byte compiling
>>> Your commit messages should be copies of the ChangeLog entry.
>>> Could you describe the case(s) that this fixes?
>> See the testcases. Generally speaking, this change fixes situations
>> where the byte-compiler miscompiles code that contains (or generates)
>> top-level progns that define macros, then use them.
>
> Can you show an example of a macro that does that?
Any macro that expands to something like this:
(progn (defmacro abc (arg) 1) (defun def () (abc 2)))
Some of the iface stuff I was working on used this functionality. The
comments in bytecomp.el suggest that EIEIO has similar stuff. In any
case, it's a reasonable thing to want to do, so we should support it.
>>>> + ;; Macroexpand (not macroexpand-all!)
>>> That could be a problem.
>> Why? We macroexpand-all forms later when we actually compile or eval them.
>
> Not sure why, exactly. It just feels like it could be a problem.
> Usually, we assume it's safe to use macroexpand-all, and it's not 100%
> crystal clear why we could be sure that macroexpand-all won't be used.
We only want to expand the top-level macro to see whether it expands
into a progn. If it does, we treat each form in the progn as its own
top-level form, recursively. If we called macroexpand-all, we'd expand
the subforms too soon, before we'd compiled defmacro forms that might be
inside the progn body.
>> Unless there's a good reason to depart from CL, we should follow CL's
>> approach to things. CL in a good sane default, and in this case, CL
>> specifies exactly the right behavior.
>
> Yes. But Elisp's design constraints, especially w.r.t macro expansion,
> are slightly different, partly for historical reasons, partly for
> technical reasons. It might not be relevant here, but I just want to
> make double sure.
It's not relevant here. I also still want to make those macro-expansion
changes I proposed last year.
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next prev parent reply other threads:[~2014-04-21 22:29 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <E1WcAcP-0006zy-MJ@vcs.savannah.gnu.org>
2014-04-21 15:09 ` [Emacs-diffs] trunk r117002: Correctly treat progn contents as toplevel forms when byte compiling Stefan Monnier
2014-04-21 17:44 ` Daniel Colascione
2014-04-21 22:09 ` Stefan Monnier
2014-04-21 22:29 ` Daniel Colascione [this message]
2014-04-22 2:09 ` Stefan Monnier
2014-04-22 2:21 ` Daniel Colascione
2014-04-22 4:25 ` Stefan Monnier
2014-04-22 4:46 ` Daniel Colascione
2014-04-22 15:06 ` Stefan Monnier
2014-04-22 17:22 ` Daniel Colascione
2014-04-22 18:13 ` Daniel Colascione
2014-04-22 18:37 ` Stefan Monnier
2014-04-22 19:08 ` Daniel Colascione
2014-04-22 18:44 ` Drew Adams
2014-04-22 19:23 ` Daniel Colascione
2014-04-22 19:59 ` Drew Adams
2014-04-22 20:10 ` Daniel Colascione
2014-04-22 20:41 ` Drew Adams
2014-04-22 21:05 ` Daniel Colascione
2014-04-23 0:50 ` Stephen J. Turnbull
2014-04-22 18:29 ` Stefan Monnier
2014-04-22 15:20 ` Stefan Monnier
2014-04-22 17:04 ` Daniel Colascione
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