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Re: Problem advising nreverse.


From: Sergei Organov
Subject: Re: Problem advising nreverse.
Date: Wed, 16 Dec 2009 14:27:43 +0300
User-agent: Gnus/5.11 (Gnus v5.11) Emacs/22.2 (gnu/linux)

Barry Margolin <address@hidden> writes:

> In article <address@hidden>,
>  Sergei Organov <address@hidden> wrote:
>
>> > address@hidden (Pascal J. Bourguignon) writes:
>> >
>> >> Sergei Organov <address@hidden> 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.

-- 
Sergei.





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