GNU bug report logs - #5689
looking-back-p

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Devon Sean McCullough <Emacs-hacker <at> Jovi.Net>
To: emacs-pretest-bug <at> gnu.org
Subject: looking-back-p
Date: Sat, 6 Mar 2010 13:29:46 -0500 (EST)

Please include the missing looking-back-p
either as a subst like looking-at-p and string-match-p

--- lisp/subr.el.~1.667.~	2009-11-24 22:59:23.000000000 -0500
+++ lisp/subr.el	2010-03-06 12:52:30.000000000 -0500
@@ -2984,6 +2984,12 @@
   (let ((inhibit-changing-match-data t))
     (looking-at regexp)))
 
+(defsubst looking-back-p (regexp &optional limit greedy)
+  "\
+Same as `looking-back' except this saves the match data."
+  (save-match-data
+    (looking-back regexp limit greedy)))
+
 (defsubst string-match-p (regexp string &optional start)
   "\
 Same as `string-match' except this function does not change the match data."

or as a macro like

--- lisp/subr.el.~1.667.~	2009-11-24 22:59:23.000000000 -0500
+++ lisp/subr.el	2010-03-06 13:18:53.000000000 -0500
@@ -2984,6 +2984,14 @@
   (let ((inhibit-changing-match-data t))
     (looking-at regexp)))
 
+(defmacro looking-back-p (&rest args)
+  "\
+Same as `looking-back' except this saves the match data.
+
+\(fn REGEXP &optional LIMIT GREEDY)"
+  `(save-match-data
+     (looking-back .,args)))
+
 (defsubst string-match-p (regexp string &optional start)
   "\
 Same as `string-match' except this function does not change the match data."

Message #8 received at 5689 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: Devon Sean McCullough <Emacs-hacker <at> Jovi.Net>
Cc: 5689 <at> debbugs.gnu.org
Subject: Re: bug#5689: looking-back-p
Date: Sat, 06 Mar 2010 16:21:54 -0500

> Please include the missing looking-back-p

looking-back is a function that people should generally try to avoid,
because it's very costly and its behavior is not always as people
might expect.  So if anything, I'd rename it to
do-something-like-looking-at-but-going-backward and would definitely
refrain from providing a "-p" alternative that would make it sound like
"it's more lightweight" even tho it's actually even worse (tho
unnoticeably so).



        Stefan

Message #11 received at 5689 <at> debbugs.gnu.org (full text, mbox):

From: Andreas Röhler <andreas.roehler <at> easy-emacs.de>
To: Devon Sean McCullough <Emacs-hacker <at> Jovi.Net>
Cc: 5689 <at> debbugs.gnu.org
Subject: Re: bug#5689: looking-back-p
Date: Sun, 07 Mar 2010 13:17:03 +0100

Devon Sean McCullough wrote:
> Please include the missing looking-back-p
> either as a subst like looking-at-p and string-match-p
> 
> --- lisp/subr.el.~1.667.~	2009-11-24 22:59:23.000000000 -0500
> +++ lisp/subr.el	2010-03-06 12:52:30.000000000 -0500
> @@ -2984,6 +2984,12 @@
>    (let ((inhibit-changing-match-data t))
>      (looking-at regexp)))
>  
> +(defsubst looking-back-p (regexp &optional limit greedy)
> +  "\
> +Same as `looking-back' except this saves the match data."
> +  (save-match-data
> +    (looking-back regexp limit greedy)))
> +
>  (defsubst string-match-p (regexp string &optional start)
>    "\
>  Same as `string-match' except this function does not change the match data."
> 
> or as a macro like
> 
> --- lisp/subr.el.~1.667.~	2009-11-24 22:59:23.000000000 -0500
> +++ lisp/subr.el	2010-03-06 13:18:53.000000000 -0500
> @@ -2984,6 +2984,14 @@
>    (let ((inhibit-changing-match-data t))
>      (looking-at regexp)))
>  
> +(defmacro looking-back-p (&rest args)
> +  "\
> +Same as `looking-back' except this saves the match data.
> +
> +\(fn REGEXP &optional LIMIT GREEDY)"
> +  `(save-match-data
> +     (looking-back .,args)))
> +
>  (defsubst string-match-p (regexp string &optional start)
>    "\
>  Same as `string-match' except this function does not change the match data."
> 
> 
> 
> 


Hi Devon,

thanks a lot.

As a change usually has pros and cons, just my personal
view:

`save-match-data' changes the way of execution, I'd
like to see it expressingly.

Think code is pretty good readable as it's now.

Andreas

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