Damian Conway Publishes Exegesis 5

prostoalex writes "Come gather round Mongers, whatever you code, And admit that your forehead's about to explode, 'Cos Perl patterns induce complete brain overload, If there's source code you should be maintainin', Then you better start learnin' Perl 6 patterns soon, For the regexes, they are a-changin'. This remix of Bob Dylan serves as an epigraph to Exegesis 5."

Comments

Perl6 FAQ

[ajs]

Perl 6 is a big scary beast that sets people off in a lot of ways. Let me try to answer some of the big questions:

• Why is Perl changing so much?!

  Because it needs to. Perl is the legacy of something like 15 years of development and evolution. It started as a simple text processing system, and is now used in every field of endevor where computers are used. There are some old things that needed to go, some new things that were needed and generally a need to re-examine the way "stuff" was done.

• But what about my programs? Why break them?!

  Perl 6 is two things (at least): a parser for Perl 6 and a back-end virtual machine, much like Java or C#. One of the design criteria for the release of Perl 6 is a Perl 5 compatible parser front-end that outputs Perl 6 virtual machine bytecode. This means that your Perl 5 programs will run with no modification in a Perl 6 environment (or at most a path change to the interpreter, that much is still under some debate).

• Why would you want to break compatibility with other regular expression engines?

  Remember that Perl has been leading the pack in terms of regular expression handling for a long time. Now Perl is moving beyond regular expressions to grammar specification. This is a good thing, as long as the benefits of regular expressions are preserved.

Some of this will be good for everyone. Some of it some of you won't like, but a lot of it you will. Give Perl 6 a chance, and don't react as if we've shot your pet.

Re:skimmed the article

[twoshortplanks]

1. A regular expression is, and always will be, a way of creating a rule engine/fine-state machine. It's a type three grammer. There are simple maths proofs that can demonstrate this
2. A finate state machine cannot match XML. XML requires you to have the ability to match the right number of opening and closing brackets (and to do that you need to be able to store the number you've seen somewhere.) This requires a push down automina - a stack machine - a type two grammer.
3. Perl's "Regular Expressions" have been beond a true regular expression for quite a while now (see backreferences)
4. Perl 6's rule system - let's dump the term regular expression now - is a further step in this complicated matching.
5. Matching type two grammers - like Parse::RecDescent can - is a good thing.

Perl 6 will be largely backward compatible

[barries]

People--especially FUDchunkers--are missing the most important points:

Almost all of the most useful Perl5 code of today will be runnable by Perl6 tomorrow: the compiler will fall back to perl5 and the VM is language neutral (even moreso that .NET it would seem).

In addition to running most perl5 modules as-is, Perl6 matching rules will have a perl5 backwards compatability mode built in so you can continue using the Perl5 regular expressions you know and love from Perl, Java, and everywhere else that's adopted them as needed in Perl6 code.

Yes, Perl6 is a rewrite and introduces a lot of deep CS concepts and ew syntax, but some care is being taken to assure that most Perl5 code will be runnable as is, while people learn about the power of some of the advanced tools Perl6 will provide.

Please Don't Panic (or incite others to): the apocolypses and exegises are technical documents, they are not meant to be smooth, easy reading or to reassure today's perlers that their hard won skills will be useful. They're meant to describe what's new and different and usually why. Don't be scared by the new and different, just as with existing Perl, you should be able to adopt the powerful new concepts and syntax as you need to without having to swallow it whole or unlearn everything you already know.

Perl6 will be stunningly more powerful, expressive, and provide (optionally) the safety features required for average coders to implement large systems while letting experts use extremely powerful tools like closures, continuations, intricate pattern matching that have mostly been accessible in academic languages to this point. And it will still allow convenient scripts to be generated if that's what you need to do.

Remember folks, other languages can make shitty code smell nice, but it's still shitty code and you wouldn't want to eat^Wmaintain it.

- Barrie

Wow. A perl 4 geek's summary

[dschuetz]

[preface:
I first used perl back in version 3, something like 12 years ago. I first really learned perl, v4, about 9 years ago. It did everything I ever needed.

Then, perl 5 came out. I didn't bother "learning" it -- that is, I've been using it, and when I really need to, I've used some perl 5 features, but I've learned them as I go (by example), and I know I'm not really using the full capabilites. (plus, though I know what I'm doing, I don't always know what to call what I'm doing -- I got stumped the other day when someone asked me how to do pointers in perl. I drew a blank, not making the connection to all the weird hash magic I'd been doing lately. But I digress.)

Anyway, the bottom line of this is: Perl 5 looked interesting, but like more of the same, and wasn't really compelling for me to buckle down and learn all the new features. Perl 6, on the other hand, scares me. In a good way.

Here's a page-by-page description of how I read the article:

• Page 1: Hm. Looks like they're describing a grammar with regex. Cool.
  
• Page 2: I can intuitively match against a set of strings! Wild. These strings can be expressions themselves? Even better!
  
• Page 3: It's a grammar. A full, honkin, real, honest-to-goodness grammar. That I can match against. Are those angels I hear singing?
  
• Page 4: <head explodes>
  
• Page 5: <drools>
  

Seriously, though, I was concerned at first that I'd have to learn something new, crazy, and difficult (given how screwed-up much of perl 5 has seemed, at times). I'm impressed. I'm very impressed. Yes, I have to learn somthing new and crazy, but it's not at all difficult. In fact, I think I've already learned it.

The power that this new system holds, and, more importantly, the simplicity of it all, is amazing.

So, unlike some other posters, I can't wait for Perl 6. When does this come out, again? And, more importantly, when can I buy the new book?

(also, was I the only one who expected, after the demonstration of matching method invocations, to be told that the entire source code for perl6 was just one giant RegEx/Grammar?)

Re:Ugh

[jdavidb]

You might want to have a look at this article which highlights some of the ways in which Perl 6 is not changing.