Re: regexp and strings you don't want

[Oliver Scholz <alkibiades@gmx.de>]

kai.grossjohann@gmx.net (Kai Großjohann) writes:

> chaz2@thedoghousemail.com (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?

    Oliver
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