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Re: Question on re-search-forward and infinite loop
From: |
Barry Margolin |
Subject: |
Re: Question on re-search-forward and infinite loop |
Date: |
Thu, 26 Nov 2009 18:17:16 -0500 |
User-agent: |
MT-NewsWatcher/3.5.3b3 (Intel Mac OS X) |
In article <mailman.11588.1259269277.2239.help-gnu-emacs@gnu.org>,
David Maus <maus.david@gmail.com> wrote:
> Hi,
>
> By accident I stumpled on a way to force Emacs in a infinite loop with
> `re-search-forward'.
>
> If I create a shiny new buffer, insert something like this:
>
> ,----
> | (while (re-search-forward "^[ \t]*"))
> | Something else
> `----
>
> -- go back beyond the while-clause and evaluate it, Emacs enters an
> infinite loop. As far as I was able to find out
> `re-search-forward' with this regexp moves point to the beginning
> of the next line above the "S" of "Something else" and stays there
> forever so it never reaches end-of-buffer.
>
> As I dunno much (or better: anything) on Emacs' interiors my question
> is: Why does this happen?
Your regexp matches zero or more whitespace characters at the beginning
of a line. If there's an empty line at the end of the buffer, it will
match that. But since it's a zero-length match, point is left at that
position, and the next time around it again matches it.
In general, whenever a regexp can match a zero-length string, I think
that type of loop will go infinitely.
--
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
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