Re: looking-back - looking-at
Am Sonntag, 3. Februar 2008 02:15 schrieb Stephen J. Turnbull:
Andreas Röhler writes:
> AFAIS `looking-back' as pendant to `looking-at' is not
> available at XEmacs. Would like to have it for
> compatibility reasons, should I'm being right so far.
Not every 3-line function needs to be a primitive. What does it do
(*exactly*, there are a number of possible semantics it could have)?
Quoting the whole defun, especially including the docstring, would
probably be the best idea.
from GNU's subr.el:
(defun looking-back (regexp &optional limit greedy)
"Return non-nil if text before point matches regular expression REGEXP.
Like `looking-at' except matches before point, and is slower.
LIMIT if non-nil speeds up the search by specifying a minimum
starting position, to avoid checking matches that would start
before LIMIT.
If GREEDY is non-nil, extend the match backwards as far as possible,
stopping when a single additional previous character cannot be part
of a match for REGEXP."
(let ((start (point))
(pos
(save-excursion
(and (re-search-backward (concat "\\(?:" regexp "\\)\\=") limit
t)
(point)))))
(if (and greedy pos)
(save-restriction
(narrow-to-region (point-min) start)
(while (and (> pos (point-min))
(save-excursion
(goto-char pos)
(backward-char 1)
(looking-at (concat "\\(?:" regexp "\\)\\'"))))
(setq pos (1- pos)))
(save-excursion
(goto-char pos)
(looking-at (concat "\\(?:" regexp "\\)\\'")))))
(not (null pos))))
BTW tried with `char-before' to write an alternative,
but that turned out much more complicated.
Andreas Röhler
_______________________________________________
XEmacs-Beta mailing list
XEmacs-Beta(a)xemacs.org
http://calypso.tux.org/cgi-bin/mailman/listinfo/xemacs-beta