1 Aug
2020
1 Aug
'20
10:53 a.m.
kernighan did this one at a talk at udel in 1976: find all the words
in the dictionary that you can see on a calculator looking at it
upside down.
On Fri, Jul 31, 2020 at 9:32 PM Earl Baugh <earl.baugh(a)gmail.com> wrote:
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:
--
GPG Fingerprint: 68F4 B3BD 1730 555A 4462 7D45 3EAA 5B6D A982 BAAF
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.]