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Re: [Orgmode] proposal: defconst/defcustom org-tags-regexp
From: |
Adam Spiers |
Subject: |
Re: [Orgmode] proposal: defconst/defcustom org-tags-regexp |
Date: |
Sat, 1 Sep 2007 12:01:23 +0100 |
User-agent: |
Mutt/1.5.14 (2007-02-12) |
Carsten Dominik (address@hidden) wrote:
> On Jul 20, 2007, at 17:05, Adam Spiers wrote:
> >On Wed, Jul 18, 2007 at 11:24:40PM +0200, Carsten Dominik wrote:
> >>On Jul 16, 2007, at 15:21, Adam Spiers wrote:
> >>>There seem to be a number of hardcoded regexps currently used for
> >>>matching heading tags, all very similar looking, and typically
> >>>something like:
> >>>
> >>> [ \t]*\\(:[[:alnum:]_@:]+:\\)?[ \t]*\\($\\|\r\\)
> >>>
> >>>Is there any reason why these shouldn't be factored out into a new
> >>>defcustom org-tags-regexp?
> >>
> >>Well, one reason is efficiency. When a regular expression is a constant,
> >>Emacs is able to cache the compiled version of the regular expression,
> >>and this can speed up code that does a lot of matching quite a bit.
> >>The token you show above is usually part of a larger string, so the full
> >>regular expression would have to be make with concat and will therefore
> >>be recompiled all the time.
> >
> >Right, point taken - like m//o in Perl. To be honest, it doesn't
> >matter too much to me if it's defconst rather than defcustom. The
> >main thing is that I can have tags starting with '<' :-)
>
> Hi Adam,
>
> this is not about defcustom or defconst, but about the question
> of the regexp is built each time with concat, or not.
Ah, I was assuming that the elisp interpreter was intelligent enough
that if you did a concat of two or more constants, it would only build
the regexp the first time, similar to m//o in Perl. Is that not the
case? Or maybe it only performs this optimisation if you
byte-compile? I found this in the elisp manual:
-- Special Form: eval-when-compile body...
This form marks BODY to be evaluated at compile time but not when
the compiled program is loaded. The result of evaluation by the
compiler becomes a constant which appears in the compiled program.
If you load the source file, rather than compiling it, BODY is
evaluated normally.
If you have a constant that needs some calculation to produce,
`eval-when-compile' can do that at compile-time. For example,
(defvar my-regexp
(eval-when-compile (regexp-opt '("aaa" "aba" "abb"))))
Maybe I should practice what I preach and use mercurial to start an
experimental branch to look at the impact on performance of doing this
refactoring :-)
- Re: [Orgmode] proposal: defconst/defcustom org-tags-regexp,
Adam Spiers <=