From: pjb@informatimago.com (Pascal J. Bourguignon)
To: help-gnu-emacs@gnu.org
Subject: Re: Problem advising nreverse.
Date: Mon, 14 Dec 2009 16:23:52 +0100 [thread overview]
Message-ID: <873a3dmvef.fsf@galatea.local> (raw)
In-Reply-To: mailman.12940.1260803316.2239.help-gnu-emacs@gnu.org
Sergei Organov <osv@javad.com> writes:
> pjb@informatimago.com (Pascal J. Bourguignon) writes:
>
>> Sergei Organov <osv@javad.com> writes:
>>
>>> pjb@informatimago.com (Pascal J. Bourguignon) writes:
>>>> Sergei Organov <osv@javad.com> writes:
>>>>
>>>>> Hello,
>>>>>
>>>>> It seems that an advice set for `nreverse' function fails to be called
>>>>> when `nreverse' is called from a byte compiled function:
>>>
>>> [...]
>>>
>>>>> Is it bug or feature? What's going on here?
>>>>
>>>> Indeed, it is a feature.
>>>>
>>>> Advices are not available from several call points:
>>>>
>>>> 1- when the advised function is called from C code.
>>>>
>>>> 2- when the advised function is a an opcode of the virtual machine.
>>>> You can observe the difference between the two primitives nreverse
>>>> and buffer-name for example, with:
>>>>
>>>> (disassemble (byte-compile (lambda (x) (nreverse x))))
>>>> vs.:
>>>> (disassemble (byte-compile (lambda (x) (buffer-name x))))
>>>>
>>>> In the former case, nreverse is a byte code, and therefore no
>>>> advice applies. In the later case, buffer-name is called with the
>>>> call byte code, which will go thru the advice.
>>>>
>>>> Notice that if you really want to advice such a low level primitive
>>>> function as nreverse, you can replace it with a lisp function (and
>>>> recompile all the code that uses it).
>>>
>>> Thanks a lot for the explanations and suggestion.
>>>
>>> Unfortunately this is not an option as intention was to advise
>>> `nreverse' during calls to a possibly buggy `ewoc-collect' function that
>>> for a long time errorneously called `nreverse' at the end (fixed since
>>> 2008).
>>
>> Redefining nreverse and reloading the ewoc-collect function would help
>> as indicated...
>
> Yeah, but:
>
> 1. I don't really want `nreverse' to be always redefined.
Of course. You do that only while "debugging" ewoc-collect. Then you
can either put back the old nreverse, or reboot emacs.
(require 'cl)
(setf (symbol-function 'old-nreverse) (symbol-function 'nreverse))
(defun nreverse (&rest arguments)
(message "nreverse called with %S" arguments)
(funcall old-nreverse arguments))
;; possibly add an advice, but you can as well put the code in the
;; new definition of nreverse above.
(do-stuff-with-new-nreverse)
;; When done:
(setf (symbol-function 'nreverse) (symbol-function 'old-nreverse))
> 2. I don't know how to reload `ewoc-collect' (from elisp) provided it's
> already byte-compiled.
C-h f ewoc-collect RET C-x o TAB RET
should bring you to the file where ewoc-collect is defined. Then you
can load it, or just re-evaluate the ewoc-collect definition to have
it take into account the new nreverse. If you want to debug it while
compiled, you can byte-compile it too.
> Here what I've actually originally tried (that didn't work):
>
> (defadvice ewoc-collect (around fix-ewoc-collect activate)
> "Fix buggy `ewoc-collect' by reversing its result provided it
> was altered by `nreverse'."
> (let ((last-nreverse-result))
> (unwind-protect
> (progn
> (defadvice nreverse (after notice-nreverse activate)
> (setq last-nreverse-result ad-return-value))
> ad-do-it)
> (ad-unadvise 'nreverse))
> (if (eq last-nreverse-result ad-return-value)
> (setq ad-return-value (nreverse ad-return-value)))))
>
> This starts to work as soon as I re-evaluate the (defun ewoc-collect
> ...) in the ewoc.el file
Then you know where ewoc-collect is defined, you can load this ewoc.el
file!
> after the above defadvice is evaluated and
> continues to work even if I byte-compile the (defun ewoc-collect...)
> after that (though I still don't understand why it works after
> byte-compiling), but then it's both easier and cleaner to just re-define
> ewoc-collect to a correct version.
Indeed.
--
__Pascal Bourguignon__
next prev parent reply other threads:[~2009-12-14 15:23 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 [this message]
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
2009-12-11 13:22 Sergei Organov
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