Re: [9fans] non greedy regular expressions

[Uriel <uriel99@gmail.com>]

On Fri, Oct 24, 2008 at 6:11 PM, Rudolf Sykora <rudolf.sykora@gmail.com> wrote:
> Further, in R. Cox's text (http://swtch.com/~rsc/regexp/regexp1.html)
> he claims that all nice features except for backreferences can be
> implemented with Thomson's NFA algorithm. And even the backreferences
> can be handled gracefully somehow. That is: ALL: non-greedy operators,
> generalized assertions, counted repetitions, character classes CAN be
> processed using the fast algorithm. Why then we don't have it?

Just because something is possible doesn't mean that it is a good
idea. Implementing every possible feature is the GNU/way, if you want
to go down that path, you know where to find it.

> I once
> wrote a program in python and was pretty happy to have non-greedy
> operators and lookahead assertions on hand. Should I hadn't had those,
> I probably wouldn't have been able to write it (nicely).

Python uses the absolutely dreadful and unintelligible PCRE, which not
only have unpredictable performance as Russ points out, but are a
total mess so complex that I doubt anybody fully understands them,
they are to Plan 9 regexps what C++ is to C.

Maybe Plan 9 regexps are not as 'powerful', but at least I can understand them.

uriel