flush-lines and regexp problems with emacs 22.0.x

flush-lines and regexp problems with emacs 22.0.x

[Vincent Lefevre]

Hi,

I get strange results with flush-lines. The first one may be due to
a lack of clear documentation, but I'm pretty sure the second one is
a bug.

The following tests have been done with GNU Emacs 22.0.50.1 under
Mac OS X (MacPorts) and with GNU Emacs 22.0.92.1 under GNU/Linux
(Debian package emacs-snapshot).

1. Consider the following file:

--------------------
> test 1
> foo
  
blah
> test 2
> foo
> foobar

blah
--------------------

where the cursor is a the top. I evaluate (with "M-:") the following:

  (flush-lines "^\\(> \n\\)*> foo\n\\(\n?> .*\\)*")

and I get:

--------------------
> test 1
blah
> test 2

blah
--------------------

instead of

--------------------
> test 1

blah
> test 2

blah
--------------------

I'd say that the blank line shouldn't be deleted because nothing is
matched on it. But the end point is on this line, so I'm not sure.
The flush-lines documentation is not clear about that.

2. Now consider the following file:

--------------------
> test 1
> foo

blah
> test 2
> foo
> bar
> foobar

blah
> test 3
> foobar

blah
--------------------

(flush-lines "^\\(> \n\\)*> foo$\\(\n> .*\\)*") has no effect on it.
(flush-lines "^\\(> \n\\)*> foo\\($\\|\\(\n> .*\\)+\\)") doesn't have
any effect either, but if I permute the both sides of the "|", i.e.

  (flush-lines "^\\(> \n\\)*> foo\\(\\(\n> .*\\)+\\|$\\)")

then I get:

--------------------
> test 1

blah
> test 2

blah
> test 3
> foobar

blah
--------------------

as expected.

Regards,

-- 
Vincent Lefèvre <vincent@vinc17.org> - Web: <http://www.vinc17.org/>
100% accessible validated (X)HTML - Blog: <http://www.vinc17.org/blog/>
Work: CR INRIA - computer arithmetic / Arenaire project (LIP, ENS-Lyon)

Re: flush-lines and regexp problems with emacs 22.0.x

[Richard Stallman]

I don't think these are bugs.  $ is only special in certain contexts;
in other contexts it matches a $ character.  That may be the case of
your second puzzler.

Re: flush-lines and regexp problems with emacs 22.0.x

[Vincent Lefevre]

On 2007-01-16 21:18:08 -0500, Richard Stallman wrote:
> I don't think these are bugs.  $ is only special in certain contexts;
> in other contexts it matches a $ character.  That may be the case of
> your second puzzler.

Does this mean that the context changes when one swaps the both sides
of a "\|" in a regexp?

If $ depends on the context, it should be clearly documented.

-- 
Vincent Lefèvre <vincent@vinc17.org> - Web: <http://www.vinc17.org/>
100% accessible validated (X)HTML - Blog: <http://www.vinc17.org/blog/>
Work: CR INRIA - computer arithmetic / Arenaire project (LIP, ENS-Lyon)

Re: flush-lines and regexp problems with emacs 22.0.x

[martin rudalics]

 > I'd say that the blank line shouldn't be deleted because nothing is
 > matched on it. But the end point is on this line, so I'm not sure.
 > The flush-lines documentation is not clear about that.

`flush-lines' deletes everything from the beginning of the line where
the match starts to the beginning of the line following the end of the
match.  I think the documentation of `flush-lines' should be improved in
this regard.

 > (flush-lines "^\\(> \n\\)*> foo$\\(\n> .*\\)*") has no effect on it.

This is explained in the manuals:

      For historical compatibility reasons, `$' can be used only at the
      end of the regular expression, or before `\)' or `\|'.

 > (flush-lines "^\\(> \n\\)*> foo\\($\\|\\(\n> .*\\)+\\)") doesn't have
 > any effect either,

This is strange, it does match

 > foo

on my system, hence it should flush that line.  Please recheck.

Re: flush-lines and regexp problems with emacs 22.0.x

[Vincent Lefevre]

On 2007-01-17 09:01:04 +0100, martin rudalics wrote:
> > (flush-lines "^\\(> \n\\)*> foo\\($\\|\\(\n> .*\\)+\\)") doesn't have
> > any effect either,
> 
> This is strange, it does match
> 
> > foo
> 
> on my system, hence it should flush that line.  Please recheck.

Yes, you're right, I mixed up with another regexp.

-- 
Vincent Lefèvre <vincent@vinc17.org> - Web: <http://www.vinc17.org/>
100% accessible validated (X)HTML - Blog: <http://www.vinc17.org/blog/>
Work: CR INRIA - computer arithmetic / Arenaire project (LIP, ENS-Lyon)