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Re: Improving regexp-opt

From: Stefan Monnier
Subject: Re: Improving regexp-opt
Date: Fri, 12 Apr 2019 12:53:06 -0400
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/27.0.50 (gnu/linux)

> The pros:
> If the resulting strings "came from" a regexp that is splittable, the
> FA implementation always simplifies to it.  In pratice, these are
> uncommun, and in most cases, the results are equivalent.
> The cons:
> The algorithm for FA seams to have greater computation complexity,
> takes about 20 times to compute in average.

Furthermore, even when the result is noticeably shorter, have you
compared the performance of the regexp-matcher?  I expect that you won't
be able to see a measurable difference there.

IOW it's just not a good deal.

As I said, if you really want to improve on regexp-opt, you have to go
through a *real* DFA and that means not returning a regexp but a DFA, so
it's a completely different beast from `regexp-opt`.


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