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Re: regexp and strings you don't want

From: Oliver Scholz
Subject: Re: regexp and strings you don't want
Date: Fri, 29 Aug 2003 18:14:24 +0200
User-agent: Gnus/5.1002 (Gnus v5.10.2) Emacs/21.3.50 (windows-nt)

address@hidden (Kai Großjohann) writes:

> address@hidden (Chaz) writes:
>> For example, how can I search for a paragraph beginning with "The"
>> that does NOT include the word "top"?
> It is possible to build a regexp that does this (disregarding the
> paragraph problem at the moment), but it is not pretty.
> Some regexp implementations have the feature you're looking for to
> make it convenient, but the Emacs implementation doesn't.
> Let me rephrase this in terms of lines instead of paragraphs.
> The idea is this: search for a line that begins with The and then
> does not have top after it, as follows: after The, we allow any
> characters that aren't t.  We also allow a t followed by something
> that's not o, and also a to that's followed by something that's not
> p.  And so on:
> "^The\\([^t]*\\($\\|t$\\|t[^o]\\|to$\\|to[^p]\\)\\)*$"

Hmm. This is not really human readable. Would it be hard and/or bad
to extend `rx' so that it allows for (not STRING)? A là:

(looking-at (rx (and line-start
                     "The "
                     (not "top"))))

Whereas `(not "top")' would compile to a normal regexp in the way you
described it. WDYT?

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