From: Barry Margolin <barmar@alum.mit.edu>
To: help-gnu-emacs@gnu.org
Subject: Re: Problem advising nreverse.
Date: Thu, 17 Dec 2009 11:52:02 -0500 [thread overview]
Message-ID: <barmar-D220AE.11520217122009@news.eternal-september.org> (raw)
In-Reply-To: mailman.13051.1260962896.2239.help-gnu-emacs@gnu.org
In article <mailman.13051.1260962896.2239.help-gnu-emacs@gnu.org>,
Sergei Organov <osv@javad.com> wrote:
> Barry Margolin <barmar@alum.mit.edu> writes:
>
> > In article <mailman.13027.1260909564.2239.help-gnu-emacs@gnu.org>,
> > Sergei Organov <osv@javad.com> wrote:
> >
> >> > pjb@informatimago.com (Pascal J. Bourguignon) writes:
> >> >
> >> >> Sergei Organov <osv@javad.com> writes:
> >> >>> I still wonder if it's documented somewhere in some manual when
> >> >>> defadvice doesn't actually work. It seems it is not there in the Elisp
> >> >>> manual, or did I miss it?
> >> >>
> >> >> See: (info "(elisp)Advising Primitives")
> >> >
> >> > Well, but I didn't find even single word there describing cases when
> >> > it does not work to advise a funciton.
> >>
> >> Sorry, my mistake. In fact, this topic does tell about when advice won't
> >> work, but it tells exactly opposite to what actually happens:
> >>
> >> "Calls to the primitive from Lisp code will take note of the advice, but
> >> calls from C code will ignore the advice."
> >>
> >> Now, in my case `nreverse' is called from Lisp code, not from C code, so
> >> according to the manual advice must work, right? And there is no single
> >> word about differences in behavior due to byte-compiling.
> >
> > Byte compiling effectively changes it to a call from C code, because the
> > byte code is a direct reference to the primitive. "Called from Lisp
> > code" means interpreting Lisp source code, since that indirects through
> > the function name, which is where advice is stored.
>
> I do understand what you are saying, but I can't persuade myself to
> believe that "calls from C code" include "calls from byte-compiled Lisp
> code" in general. As far as I understand, byte-compiled Lisp code is
> never seen by a C compiler and can't be compiled by a C compiler, so
> it's not C code, thus calls from byte-compiled code are not calls from C
> code. IMHO it should be explicitly specified in the documentation that
> calls to a primitive from byte-compiled Lisp code will ignore the
> advice, provided this is feature indeed.
I agree that the documentation should say this explicitly.
What's presumably going on is that nreverse is a primitive byte-code
operation. The code is presumably an index into a table of C function
pointers, so the byte code interpreter simply calls those function
directly. That's why it's equivalent to calling the function directly
from other C code.
--
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***
*** PLEASE don't copy me on replies, I'll read them in the group ***
next prev parent reply other threads:[~2009-12-17 16:52 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <mailman.12764.1260538816.2239.help-gnu-emacs@gnu.org>
2009-12-12 12:18 ` Problem advising nreverse Pascal J. Bourguignon
2009-12-14 11:07 ` Sergei Organov
[not found] ` <mailman.12932.1260788943.2239.help-gnu-emacs@gnu.org>
2009-12-14 13:01 ` Pascal J. Bourguignon
2009-12-14 15:05 ` Sergei Organov
2009-12-15 8:19 ` Kevin Rodgers
2009-12-15 12:02 ` Sergei Organov
[not found] ` <mailman.12940.1260803316.2239.help-gnu-emacs@gnu.org>
2009-12-14 15:23 ` Pascal J. Bourguignon
2009-12-14 16:01 ` Sergei Organov
[not found] ` <mailman.12941.1260806509.2239.help-gnu-emacs@gnu.org>
2009-12-14 17:56 ` Pascal J. Bourguignon
2009-12-14 19:59 ` Sergei Organov
[not found] ` <mailman.12952.1260820780.2239.help-gnu-emacs@gnu.org>
2009-12-15 1:47 ` Pascal J. Bourguignon
2009-12-15 12:06 ` Sergei Organov
[not found] ` <mailman.13009.1260879016.2239.help-gnu-emacs@gnu.org>
2009-12-15 19:54 ` Pascal J. Bourguignon
2009-12-15 20:38 ` Sergei Organov
[not found] ` <mailman.13027.1260909564.2239.help-gnu-emacs@gnu.org>
2009-12-15 21:12 ` Barry Margolin
2009-12-16 11:27 ` Sergei Organov
[not found] ` <mailman.13051.1260962896.2239.help-gnu-emacs@gnu.org>
2009-12-17 16:52 ` Barry Margolin [this message]
2009-12-11 13:22 Sergei Organov
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