bug#7267: 23.1; regexp backslash-B matches word

bug#7267: 23.1; regexp backslash-B matches word

[Thibault Kruse]

Please write in English if possible, because the Emacs maintainers
usually do not have translators to read other languages for them.

Your bug report will be posted to the bug-gnu-emacs@gnu.org mailing list,
and to the gnu.emacs.bug news group.

Please describe exactly what actions triggered the bug
and the precise symptoms of the bug:

According to emacs manual, \B matches the empty string, but it does not.

start emacs with emacs -q --no-site-file
move point over word in the splash screen.
M-:
(looking-at "\\B")
minibuffer says: T, should say nil

If Emacs crashed, and you have the Emacs process in the gdb debugger,
please include the output from the following gdb commands:
    `bt full' and `xbacktrace'.
If you would like to further debug the crash, please read the file
/usr/share/emacs/23.1/etc/DEBUG for instructions.


In GNU Emacs 23.1.1 (i486-pc-linux-gnu, GTK+ Version 2.20.0)
 of 2010-03-29 on rothera, modified by Debian
Windowing system distributor `The X.Org Foundation', version 11.0.10706000
configured using `configure  '--build=i486-linux-gnu' '--host=i486-linux-gnu' '--prefix=/usr' '--sharedstatedir=/var/lib' '--libexecdir=/usr/lib' '--localstatedir=/var/lib' '--infodir=/usr/share/info' '--mandir=/usr/share/man' '--with-pop=yes' '--enable-locallisppath=/etc/emacs23:/etc/emacs:/usr/local/share/emacs/23.1/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/23.1/site-lisp:/usr/share/emacs/site-lisp:/usr/share/emacs/23.1/leim' '--with-x=yes' '--with-x-toolkit=gtk' '--with-toolkit-scroll-bars' 'build_alias=i486-linux-gnu' 'host_alias=i486-linux-gnu' 'CFLAGS=-DDEBIAN -g -O2' 'LDFLAGS=-g' 'CPPFLAGS=''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: en_US.utf8
  value of $XMODIFIERS: nil
  locale-coding-system: utf-8-unix
  default-enable-multibyte-characters: t

Major mode: Fundamental

Minor modes in effect:
  tooltip-mode: t
  tool-bar-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  blink-cursor-mode: t
  global-auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
<right> M-: <up> ( l o o k i n g - a t SPC " " <left> 
\ \ B <right> ) <return> <left> M-: <up> <return> <right> 
<help-echo> M-x r e p o <tab> r t - e <tab> <retur
n>

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
goto-history-element: Beginning of history; no preceding item
t
nil
Making completion list...
-- 
GRATIS! Movie-FLAT mit über 300 Videos. 
Jetzt freischalten unter http://portal.gmx.net/de/go/maxdome

bug#7267: 23.1; regexp backslash-B matches word

[Glenn Morris]

"Thibault Kruse" wrote:

> According to emacs manual, \B matches the empty string, but it does not.

The elisp manual says:

Backslash Constructs in Regular Expressions
[...]

`\B'
     matches the empty string, but _not_ at the beginning or end of a
     word, nor at the beginning or end of the buffer (or string).

> start emacs with emacs -q --no-site-file
> move point over word in the splash screen.
> M-:
> (looking-at "\\B")
> minibuffer says: T, should say nil

Why do you think it should return nil?

This construct matches the empty string inside words.
It only returns nil at word boundaries. Try

(looking-at "\\B")

with point at the start, middle, and end of a word.
It returns nil, t, nil, as it should.

The empty string is _empty_, ie length zero, not whitespace or
anything like that.

bug#7267: 23.1; regexp backslash-B matches word

[Thibault Kruse]

sorry, I misunderstood. But I now understand it means it always returns t except for the noted cases, as any string contains the empty string.

-------- Original-Nachricht --------
> Datum: Fri, 22 Oct 2010 22:49:27 -0400
> Von: Glenn Morris <rgm@gnu.org>
> An: "Thibault Kruse" <thibault.kruse@gmx.de>
> CC: 7267@debbugs.gnu.org
> Betreff: Re: bug#7267: 23.1; regexp backslash-B matches word

> "Thibault Kruse" wrote:
> 
> > According to emacs manual, \B matches the empty string, but it does not.
> 
> The elisp manual says:
> 
> Backslash Constructs in Regular Expressions
> [...]
> 
> `\B'
>      matches the empty string, but _not_ at the beginning or end of a
>      word, nor at the beginning or end of the buffer (or string).
> 
> > start emacs with emacs -q --no-site-file
> > move point over word in the splash screen.
> > M-:
> > (looking-at "\\B")
> > minibuffer says: T, should say nil
> 
> Why do you think it should return nil?
> 
> This construct matches the empty string inside words.
> It only returns nil at word boundaries. Try
> 
> (looking-at "\\B")
> 
> with point at the start, middle, and end of a word.
> It returns nil, t, nil, as it should.
> 
> The empty string is _empty_, ie length zero, not whitespace or
> anything like that.
> 

-- 
GRATIS! Movie-FLAT mit über 300 Videos. 
Jetzt freischalten unter http://portal.gmx.net/de/go/maxdome