Re: will we ever have zero width assertions in regexps?

[Stefan Monnier <monnier@iro.umontreal.ca>]

>> similar to Lua's Lpeg.  I myself would also be more interested in
>> replacing the backtracking matcher with a non-backtracking one (for the
>> cases where backtracking is not required by backrefs).
> What for?  [After my final round of backtracking-optimizations for
> Perl REx engine, I do not recollect people (loudly) wanting anything
> like this for Perl anymore...]

To get rid of the occasional pathological case where matching takes
forever and Emacs appears to be frozen.  Programmers who are used to
backtracking matchers will usually intuitively stay away from regexps
that can show such behaviors, but not all programmers do, and even if
you're careful there are cases that are hard to avoid.

Another minor reason is that it can be handy to have an incremental
matching primitive, so you can match over a long string one chunk at
a time.  I'm not sure how often this would be useful, but I've come
across a few cases where it seemed like it could be put to good use
(tho, for lack of experience with it, I can't sweat that it would turn
out to be a good idea).


        Stefan