Perl 6 <-> Perl 5 bridges (was Re^2: Capturing parenthesis and grouping square brackets)

Edited to clarify. Added another couple examples of support for transition.

TL;DR Perl 6 accords Perl 5 special status, with many elements specifically designed to make P5/P6 interop straightforward. And, for those who want it, transition.

There is no evolutionary transition-plan here; not does one appear to be possible, let alone economical, let alone particularly beneficial.

Imo the ways in which P6 design and implementation bridges with P5 demonstrate great care about interop and evolutionary transition at both a big picture and tiny detail level.

First, sticking to just regex:

The P5 regex modifier allows Perl 5 regex syntax to be used. This marries Perl 5 regex syntax and semantics to the power and elegance of Perl 6 match objects. Hence the ability to visually debug Perl 5 regex using the Rakudo Perl 6 debugger.
Some P6 features exist partly/mostly to make things easier for a P5 programmer. For example, the ability to reset the numbering of regex captures will help P5 coders used to consecutive subpattern numbering in alternations and unnested numbering in nested subpatterns.
Compiler messages help P5 programmers pick up P6. For example, the Perl 6 parser defines an infix =~ operator, which fails at compile time with a message helping P5 coders.

It's not just regex either:

Mixing P6 and "pure" P5. Last year Larry Wall wrote a Perl 6 grammar (parser) for a substantial subset of Perl 5. Enough that it parsed (but did not compile) viv, a utility written in Perl 5 (4K LOC). This year FROGGS turned that grammar into a v5 module for rakudo, a pure Perl 5 compiler. (He is working his way through a P5 testsuite based on the #p5p perl testsuite.)
Mixing P6 and Perl 5 with XS. blizkost embedded libperl in Parrot, so Rakudo could eval Perl 5 code using #p5p perl. It didn't do much and Rakudo needed to focus on other things. Fast forward to today. Libperl is due to be embedded in MoarVM, a new VM for NQP/Rakudo. The architecture is such that Rakudo Perl 6 will be able to use #p5p perl, including XS, and vice-versa.

Please visit the IRC channel #perl6 on freenode and help improve it by constructively discussing things you think will improve transition or interop between P5 and P6. Thanks go to Larry, jnthn, and all who try to help. Illegitimi non carborundum! :)

Comment on Perl 6 <-> Perl 5 bridges (was Re^2: Capturing parenthesis and grouping square brackets)

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Re: Perl 6 <-> Perl 5 bridges (was Re^2: Capturing parenthesis and grouping square brackets) by Jenda (Abbot) on Jun 20, 2013 at 23:43 UTC
"Perl 6 match objects"? OK, not that I think Perl6 actually matters, but still ... having experience with the insanely overcomplicated Match/Matches/etc./etc./etc./etc. objects of the .Net regular expressions ... this sounds scary. So I asked uncle Google, ended up in per6-regex-intro and ... I did not like what I saw. OK. So the matches are in the object named $/ (OK, so $/ meant something in Perl5, let's change that!) and you can access them as `$/[0], $/[1], ...` (hey, wasn't we supposed to use @ for arrays. Oh, right, this is an object, you just index it as if it was an array, but ...) ... and there are shortcuts in the form $0, $1, $2, ... WHAT?!? Yeah, the sortcuts start with $0! Yeah, what used to be $1 is now $0, what used to be $2 is now $1 etc. Just lovely! Imagine you got yourself into the situation when you have to write Perl6 code while still maintaining Perl5 code. I'd love to have a penny for every full hour lost because of the confusion caused by this change! Even with the number of people using Perl6 now, I'm sure it'd pay a few beers. The more I know about Perl6, the more I hope it's gonna disappear almost without a trace as a failed experiment. It uses the name, it looks deceptively similar, yet it is full of changes carefuly designed to cause as much confusion as possible. Jenda Enoch was right! Enjoy the last years of Rome.	[reply] [d/l]
Re^2: Perl 6 <-> Perl 5 bridges (was Re^2: Capturing parenthesis and grouping square brackets) by raiph (Deacon) on Jun 21, 2013 at 08:32 UTC
Perl 6 is many things. For one, it includes a language I'll call STD. STD is specifically designed to host other languages including ones I'll call Pure Perl 5 (a new Perl 5 parser) and #p5p perl (Pumpkin Perl). In your comment you explore STD but then reject everything, which means you've thrown the babies (Pure Perl 5 and #p5p perl hosted alongside Pure Perl 5) out with the bathwater. Maybe you can reconsider the bathtub so you can at least look forward to using Pure Perl 5 (which supports $/ as input record separator, $0 as the executable name, and so on) running on android or in a browser and supporting parallel processing and so on. So the matches are in the object named $/ (OK, so $/ meant something in Perl5, let's change that!) If you want $/ as the input separator, use a Perl 5. I agree with @Larry (the team who designed the Perl 6 STD language) that constraining the Perl 6 STD language to back compat with Perl 5 syntax and semantics would have been a big mistake and a big missed opportunity. The end result is still much more friendly to the average Perl 5 user than, say, lisp, haskell, or scala. you can access them as $/[0], $/1, ... (hey, wasn't we supposed to use @ for arrays. Oh, right, this is an object, you just index it as if it was an array, but ...) You can use @ for arrays in the STD language of Perl 6, but you don't have to: `my $array; $array[3] = True; my @array; @array[3] = True;` [download] ... and there are shortcuts in the form $0, $1, $2, ... WHAT?!? Yeah, the sortcuts start with $0! I agree this sounds particularly disturbing. In practice it doesn't trip folk up. Note that you can do this: `say "bar" ~~ /$1=(\w)(\w)(\w)/; say $2; # a` [download] The more I know about Perl6, the more I hope it's gonna disappear almost without a trace as a failed experiment. The community is sustainable, vibrant, and growing. The contributor base, family of languages, Rakudo compiler, Rakudo debugger, toolchain, modules, doc, and intrastructure are all maturing nicely. The team has figured out the path to speeding Rakudo up by orders of magnitude. Larry's writing a Camel equivalent. There's still $100k left of the Hague grant. Sorry, but it ain't going away. :) Perl 6 is already attracting curious hackers that have never touched Perl 5 and will I predict begin to attract Perl 5 users next year that want to be able to write in a Perl (5ish or 6ish) on new platforms (eg android via the jvm or browsers via javascript), and/or use new capabilities (eg automatic parallelizing) and/or gain expressivity (grammars, lispish macros, etc.). You are free to ignore it but I'm confident it is here to stay and is inevitably going to help usefully address many of the long standing problems Perl 5 has.	[reply] [d/l] [select]
Re^3: Perl 6 <-> Perl 5 bridges (was Re^2: Capturing parenthesis and grouping square brackets) by Jenda (Abbot) on Jun 21, 2013 at 08:57 UTC
It's one thing to not constrain Perl6 to back compat and another to create unnecessary confusion by arbitrary operator and sigil changes. No the result is not more friendly, the result is more confusing. It's like Russian to a Czech. Yeah the languages have lots of similarities, part of the vocabulary, the declination system ... which means that Czechs use Slovak words with Russian accents in cases where the Russian word is completely different, they use word that sound similar, but mean something completely different, waste time trying to remember a word when pronouncing the Czech one in Russian accent would be correct, they decline all wrong, because while the declinations are deceptively similar they are also different etc. etc. etc. All this doesn't matter that much when speaking to a human being (unless that being is a teacher), communication with a compiler is much less forgiving and when combined with your hailed two kindaPerl5s this just creates an insane mess. You can use @ for arrays in the STD language of Perl 6, but you don't have to So what's the difference between `$array` and `@array` then? Sigils are a perfect example of an absolutely pointless and confusion generating change. Imagine you are new to all this and you ask uncle Google what the heck do those $s and @s and %s mean ... you get contradicting answers! The toolchain eventually created by this project may end up being used for something, but so far it has hurt rather then helped Perl. Jenda Enoch was right! Enjoy the last years of Rome.	[reply] [d/l] [select]
Re^4: Perl 6 <-> Perl 5 bridges (was Re^2: Capturing parenthesis and grouping square brackets) by raiph (Deacon) on Jun 21, 2013 at 11:50 UTC
Re^4: Perl 6 <-> Perl 5 bridges (was Re^2: Capturing parenthesis and grouping square brackets) by raiph (Deacon) on Jun 28, 2013 at 02:23 UTC
Re^5: Perl 6 <-> Perl 5 bridges (was Re^2: Capturing parenthesis and grouping square brackets) by Jenda (Abbot) on Jun 28, 2013 at 10:16 UTC
Some notes below your chosen depth have not been shown here
Re: Perl 6 <-> Perl 5 bridges (was Re^2: Capturing parenthesis and grouping square brackets) by Anonymous Monk on Jun 19, 2013 at 19:27 UTC
Horray! Keep telling people how good it's gonna be when one of these projects finally gets finished!! Everybody is on the edge of their seats, except I was holding my breath but then I turned blue! So other than Perl-6 causing cyanosis it sounds really good!	[reply]
Re^2: Perl 6 <-> Perl 5 bridges (was Re^2: Capturing parenthesis and grouping square brackets) by raiph (Deacon) on Jun 20, 2013 at 23:06 UTC
To clarify, all the regex stuff I discussed is already implemented in the Rakudo compiler, modulo bugs. I did not intend to comment on whether any of the remaining stuff was going to be any good, just that it was at last happening, which is probably news to many monks.	[reply]
Re^3: Perl 6 <-> Perl 5 bridges (was Re^2: Capturing parenthesis and grouping square brackets) by Anonymous Monk on Jun 20, 2013 at 23:47 UTC
Blah blah blah! Keep on congratulating the Perl-6 cult for talking about doing things! If anything did happen that would be news.	[reply]