From: Ted Zlatanov <tzz@lifelogs.com>
To: emacs-devel@gnu.org
Subject: add INVERT to re-search-{forward, backward} (was: occur API change proposal)
Date: Tue, 05 Aug 2008 13:49:52 -0500 [thread overview]
Message-ID: <86myjrl2jz.fsf_-_@lifelogs.com> (raw)
In-Reply-To: 87fxyni898.fsf@jurta.org
On Sat, 01 Dec 2007 02:34:35 +0200 Juri Linkov <juri@jurta.org> wrote:
>> I propose changing the occur API to allow an optional predicate
>> function. For example, this is useful to invert a regular expression so
>> you don't have to run occur on the whole buffer matching everything,
>> then limit the results.
JL> The occur engine currently hard-codes the function call of
JL> `re-search-forward'. Instead of this, we could do the same
JL> as is done already in isearch for customization of the search
JL> function using a variable `isearch-search-fun-function', and
JL> add a new analogous variable `occur-fun-function'.
JL> Even though such a variable will be useful for other purposes,
JL> no simple function will allow inverting a regular expression.
JL> Implementing this feature requires significant modification in
JL> the logic of the occur engine: either changing the algorithm to
JL> call `looking-at' at every line (very inefficient), or recording
JL> a position of the previous match and outputing lines between it
JL> and the current position (not easy to customize).
After thinking about this (yes, it sat in my TODO queue for a while) I
realize the problem is fundamental: Emacs doesn't have a way to invert
at the re-search-{forward,backward} API level. There's no way to
automatically invert a regular expression into another regular
expression, so this change must happen at the API level to avoid
unpleasant workarounds as Juri describes.
I propose simply adding an optional INVERT parameter to those two
functions. The API cost is small with an optional parameter, though I
don't know if performance will be affected by the extra check on every
search cycle.
Once this API is in place, making the change in occur-mode and other
places to use the new API is very easy.
Ted
next prev parent reply other threads:[~2008-08-05 18:49 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-11-29 16:02 occur API change proposal Ted Zlatanov
2007-12-01 0:34 ` Juri Linkov
2008-08-05 18:49 ` Ted Zlatanov [this message]
2008-08-25 15:45 ` add INVERT to re-search-{forward, backward} (was: occur API change proposal) Juri Linkov
2008-08-25 15:57 ` add INVERT to re-search-{forward, backward} Lennart Borgman (gmail)
2008-08-25 19:45 ` Juri Linkov
2008-08-25 20:07 ` Lennart Borgman (gmail)
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