1 Aug
2020
1 Aug
'20
10:31 a.m.
I have a 30k+ character regex that I used to parse US street addresses from a single line
of input into component pieces. That’s the largest ( and yes it was crazy... but it just
grew and grew...and made sense to me as I decomposed the problem ). That’s the largest
one I ever saw.... and it was the fastest way I could solve the problem.. both mentally
and processing wise.
( there was some post processing to deal with soundex matching and data base matching of
the pieces to confirm the right answer. But it solved the problem with 95%+ accuracy...
that I got into the high 99%’s with the post processing. )
So that’s at least an example of an arbitrary problem that was solved with regex.
Earl
Sent from my iPhone
On Jul 31, 2020, at 11:08 PM, Will Senn
<will.senn(a)gmail.com> wrote:
Oh, and one good google over another, I also found this:
https://www.drdobbs.com/architecture-and-design/regular-expressions/1844109…
Which is also great and simple to follow :).
Will
On 7/31/20 7:36 PM, Rob Pike wrote:
I think this link - https://swtch.com/~rsc/regexp/regexp1.html i- s the best place to
start. Superb exposition on the background, theory, and implementation as well as a bit of
history of how the industry lost its way with regular expressions.
Regular expressions are beautiful, simple, and widely misunderstood.
-rob
On Sat, Aug 1, 2020 at 10:03 AM Bakul Shah <bakul(a)iitbombay.org> wrote:
> On Jul 31, 2020, at 3:57 PM, Will Senn <will.senn(a)gmail.com> wrote:
> >
> > I've always been intrigued with regexes. When I was first exposed to them,
I was mystified and lost in the greediness of matches. Now, I use them regularly, but
still have trouble using them. I think it is because I don't really understand how
they work.
> > ...
> > 1. What's the provenance of regex in unix (when did it appear, in what
form, etc)?
> > 2. What are the 'best' implementations throughout unix (keep it pre
1980s)?
> > 3. What are some of the milestones along the way (major changes, forks,
disagreements)?
> > 4. Where, in the source, or in a paper, would you point someone to wanting to
better understand the mechanics of regex?
>
> Start here: https://en.wikipedia.org/wiki/Thompson%27s_construction
>
> [I learned about regular expressions in an automata theory class,
> before I knew anything about Unix. What helped me was learning
> about finite state machines. You won't need more than paper and
> pencil to construct one. Reading source code would make more
> sense once you grasp how to construct a FSM corresponding to a RE.]
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