🚀 go-pugleaf

In article <DODD.92Dec11074209@mycenae.cchem.berkeley.edu> dodd@mycenae.cchem.berkeley.edu (Lawrence R. Dodd) writes:

> `looking-back' is not standard but probably can be constructed using
> `looking-at' although it seems interesting that it isn't in the standard
> distribution.  Can anyone out there explain this?

Probably because our heroes do not want to encourage backwards regexp
processing.  Emacs' regexp implementation works better forwards.  For
example, notice that (re-search-backward "x+") only finds the last x in
`xxx'.  Also, I suspect backwards is slower.


Anyway, here is a quick and dirty version:

(defun looking-back (regexp &optional span)
  "t if text before point matches regular expression PAT.
For simplicity, only the preceding SPAN chars (default 2000) are searched."
  (save-excursion
    (eq (point)
	(and (re-search-backward regexp (- (point) (or span 2000)) t)
	     (match-end 0)))))
--

Hallvard