4 ms·

This reduction is really cool. I love reductions like this. Is there a general consensus to use "regular expression" to refer to the actual regular ones and "r

by awirth 6y ago

This reduction is really cool. I love reductions like this. Is there a general consensus to use "regular expression" to refer to the actual regular ones and "regex" to refer to the non-regular variants?

praptak 6y ago
I don't think so. Usually you can tell from the context: # math and/or computer science texts? It's the regular ones. # pretty much elsewhere? It's the extended ones. # threads about parsing HTML with regular expressions? People using both and insisting their version is the only correct one.
zokier 6y ago
I think Raku (neé Perl 6) has been spearheading that distinction https://docs.raku.org/language/regexes https://docs.raku.org/language/regexes (see the intro paragraph)
chubot 6y ago
I wouldn't say so, but I use the term "regular language" if I mean the mathematical concept.
- robinhouston 6y ago
  I don’t think it’s pedantic to say that a regular language is not the same thing as a regular expression. The difference between syntax and semantics is real and important.
  - chubot 6y ago
    (late reply) Right that's what I'm saying. Who said it was pedantic? :)
- gnulinux 6y ago
  But a "regular language" is not the same as "regular expression" as mathematical concepts.
  - chubot 6y ago
    (late reply) Hm you've negelected to do the obvious thing and explain the difference. I don't think there's a difference, and if there is one, it's probably not relevant to programming. Whereas the one I'm highlighting is relevant to programming.
robinhouston 6y ago
This distinction was introduced by Jeffrey Friedl’s book _Mastering Regular Expressions_ (2006), and it seems to be fairly commonly used now.
stevefan1999 6y ago
Isn't it PCRE that we started to call it regex?
gbacon 6y ago
Yes, for at least ten years and likely much longer. https://cstheory.stackexchange.com/q/448/362 https://cstheory.stackexchange.com/q/448/362
- awirth 6y ago
  Interesting, I wasn't aware of the history. Personally I make the distinction, but I've noticed many many people do not, hence the question.
  - gbacon 6y ago
    People without theoretical CS background probably think of regular expressions (or regexes for short) as just text-matching thingies that sometimes give you two problems and would look at you blankly if you mention the Chomsky hierarchy. When we don’t know there’s a distinction to be made, we go for economy of expression.
awirth 6y ago
Too late to edit, but out of curiosity I re-implemented this to use the PCRE JIT (in PHP) to see what kind of speedup it would provide: https://gist.github.com/allanlw/69df509519335b88db886d48503a0f15 https://gist.github.com/allanlw/69df509519335b88db886d48503a... Timings for fred.cnf on my machine: python: 0m53.744s PHP (no PCRE JIT): (hits backtrack limit in 1m15.994s) PHP (PCRE JIT): 0m20.109s

by awirth 6y ago

praptak 6y ago

I don't think so. Usually you can tell from the context: # math and/or computer science texts? It's the regular ones. # pretty much elsewhere? It's the extended ones. # threads about parsing HTML with regular expressions? People using both and insisting their version is the only correct one.

zokier 6y ago

I think Raku (neé Perl 6) has been spearheading that distinction https://docs.raku.org/language/regexes https://docs.raku.org/language/regexes (see the intro paragraph)

chubot 6y ago

I wouldn't say so, but I use the term "regular language" if I mean the mathematical concept.

robinhouston 6y ago
I don’t think it’s pedantic to say that a regular language is not the same thing as a regular expression. The difference between syntax and semantics is real and important.
- chubot 6y ago
  (late reply) Right that's what I'm saying. Who said it was pedantic? :)
gnulinux 6y ago
But a "regular language" is not the same as "regular expression" as mathematical concepts.
- chubot 6y ago
  (late reply) Hm you've negelected to do the obvious thing and explain the difference. I don't think there's a difference, and if there is one, it's probably not relevant to programming. Whereas the one I'm highlighting is relevant to programming.

robinhouston 6y ago

This distinction was introduced by Jeffrey Friedl’s book _Mastering Regular Expressions_ (2006), and it seems to be fairly commonly used now.

stevefan1999 6y ago

Isn't it PCRE that we started to call it regex?

gbacon 6y ago

Yes, for at least ten years and likely much longer. https://cstheory.stackexchange.com/q/448/362 https://cstheory.stackexchange.com/q/448/362

awirth 6y ago
Interesting, I wasn't aware of the history. Personally I make the distinction, but I've noticed many many people do not, hence the question.
- gbacon 6y ago
  People without theoretical CS background probably think of regular expressions (or regexes for short) as just text-matching thingies that sometimes give you two problems and would look at you blankly if you mention the Chomsky hierarchy. When we don’t know there’s a distinction to be made, we go for economy of expression.

awirth 6y ago

Too late to edit, but out of curiosity I re-implemented this to use the PCRE JIT (in PHP) to see what kind of speedup it would provide: https://gist.github.com/allanlw/69df509519335b88db886d48503a0f15 https://gist.github.com/allanlw/69df509519335b88db886d48503a... Timings for fred.cnf on my machine: python: 0m53.744s PHP (no PCRE JIT): (hits backtrack limit in 1m15.994s) PHP (PCRE JIT): 0m20.109s