Perl 6 Grammars and Regular Expressions

An anonymous reader writes "Perl 6 is finally coming within reach. This article gives you a tour of the grammars and regular expressions of the Perl 6 language, comparing them with the currently available Parse::RecDescent module for Perl 5. Find out what will be new with Perl 6 regular expressions and how to make use of the new, powerful incarnation of the Perl scripting language."

Comments

Perl goodness

[Zorilla]

HXGF*&#$()#P*&ULJKDFHV)(&*#$utrhk:jlhdsf(p*&#$OJDF >KLJDFP)(*$#&pyu:

Crap, I think I just accidentally programmed a web browser in Perl

Re:Perl goodness

[b12arr0]

Uh, that's not a web browser, it's clearly a web server.

Re:Perl goodness

[Zorilla]

It curls fries, too, you know.

Re:Perl goodness

[jandrese]

There are two things about regular expressions:

1. Perl chose a keystroke-efficent syntax that makes them unreadable to anybody who doesn't know how to read them. It also made them very compact and easy to write for anybody who does know how to read them. They look very intimidating, but underneath they are usually easier to understand than the C like perl code surrounding it.
2. They are amazingly useful. Seriously, if you have never learned about Regular Expressions you owe yourself a lesson in how they work and what they do. I've seen people spend days working on stuff that can be written (more efficently!) in a regular expression in a matter of minutes. Pattern matching is the sort of thing that every general purpose language should have, it is a shame that the basic Regular Expression libraries that comes with most Unixes is such a piece of crap. Who wants to deal with the arcance invocation method, the extremely limited syntax, or the syntatic sugar like: "[[:digit:]]{2}:[[:space:]][[:space:]]*[[:alpha:]] *" when you could write "\d{2}:\s+\w*"?

Re:Perl goodness

[Anonymous Coward]

A web browser? That's:

perl -MHTML::Strip -MIO::All -e 'print HTML::Strip->new->parse(io($ARGV[0])->scalar )'

A web server? That's:

perl -MIO::All -e 'io(":8080")->fork->accept->(sub { $_[0] < io(-x $1 ? "./$1 |" : $1) if /^GET \/(.*) / })'

Grammar

[dprust]

It is good to see PERL focussing on what makes it great. There is no other language, IMHO, that handles text input as well as PERL does. Adding this level of processing just makes it even more powerful.

Re:Grammar

[Mr. Muskrat]

Perl never was an acronym. It's a backronym.

Perl is the language and perl is the interpreter. Remember, "only perl can parse Perl" and it's easy to remember.

hrm...

[Anonymous Coward]

"...zztop-wants-a-perl-necklace dept."

i do not think that means what you think it means.

Why would a satisfied Perl5 user migrate?

[winkydink]

What does Perl6 offer a satisfied Perl5 user? Is it faster? Smaller?

To this user, the last several releases (5.x) have looked more like opportunities for continuing royalty streams for perl authors (new versions of old books) than significant releases.

Re:Why would a satisfied Perl5 user migrate?

[WWWWolf]

Yeah, Perl 5 hasn't changed that much over time. But it has been around for a while. Perl 6 is just different.

From what I have seen from the announcements, the Perl 6 syntax looks far cleaner, probably more consistent and less ugly. Some of the new tricks look genuinely handy. For example, if it seems like type checking would be a good idea, you can have it if you want it, even on compile time!

Especially the regular expressions side seems pretty interesting, as noted in this article. Regular expressions have always been a poor but effective replacement for grammar-based parsing, and now finally Perl is going to have both integrated. There's probably going to be less whining about line noise.

And then there's something that I find especially interesting, though it hasn't been explained in detail yet: Complete tuning of the object system. In case you haven't noticed, Perl 5's object system is a complete and utter mess that looks and smells like it has been added as an afterthought, and rest assured it's going to be changed radically for better in Perl 6. I'm definitely waiting eagerly to see what Perl 6's take is going to look like - I sure hope it's something like Ruby, only it smells like a camel =)

Re:Big problem

[Speare]

Um, ALL PERL CODE IS TREATED AS PERL5 CODE unless you use a specific Perl 6 keyword in your script. Perl 6 interpreters will not require you modify your scripts AT ALL to use Perl 5 scripts.

Therefore, it's just Perl 6 scripts which want to use Perl 5 regular expression syntax, which would want to use the :p5 modifier.

Don't get your knickers in a bunch.

aw hell

[The Unabageler]

I'm going to have to rewrite my sig.

Re:Ok, start the flame wars under this post

[TheFlyingGoat]

Those of us that use Perl as more than just system duct-tape know it's a programming language. Perl 6 will make that even more clear by being based on OO fundamentals rather than being a procedural language with OO tacked on top of it. This is just another debate that makes the OS community look like a bunch of freaks and zealots... just like the GNU/Linux thing. Get over it and start focusing on what the software does, not how to classify/name it.

Adoption

[base_chakra]

Years ago, Eric Raymond wrote:

"Perl XS is acknowledged to be a nasty mess. My guess is the Perl guys would drop it like a hot rock for our [Python's] stuff -- that would be as clear a win for them as co-opting Perl-style regexps was for us." [emphasis added]

Maybe I misinterpreted ESR's intended message, but it would be disappointing if hypercompetition prevented Perl's already-influential regex extensions from exerting a positive influence on other platforms. Raymond seems to imply that the Python team only grudgingly included support for Perl-style regex. I understand that developement teams in similar niches each want to make a big splash in the industry, hopefully Python's great increase in popularity has softened the survivalist attitude that seems to characterize this Raymond quote from Python-Dev. Evolving regex can benefit everyone.

Note to those ready to mod me Troll/Flamebait: I'm not trying to pick on Python, I just happened to be acquainted with this candid quote.

Re:Adoption

[Black Perl]

Yes, you did misinterpret the message. Eric Raymond was a former Perl programmer, and is now a Python programmer. He was saying that Python's native-code-binding facility is superior than Perl's XS, and it would benefit Perl to adopt it. He mentions that Python benefitted from adopting Perl's regex syntax. Nowhere does he say or imply it was "grudgingly" done.

By the way, not long after he wrote that, Perl coders started using the Inline:: modules like Inline::C instead of XS, which is very easy to use. I do not know if this was an adoption of Python's technique, but I don't think so.

Complex grammars in Perl

[imnoteddy]

I can understand a desire for adding grammars that are more powerful than regular expressions in Perl 6 but it opens up a whole new can of worms.

The grammars appear to be in a class called "context free languages"(CFGs). Some CFGs are ambiguous in the sense that a given "sentence" can be derived from more than one set of rules. Traditional tools such as yacc/bison tell you where there is ambiguity in your rules - even then it isn't always easy to remove the ambiguity (trust me on this). If the Perl 6 system doesn't help the programmer debug the grammar he/she will not be happy when the parsing doesn't work as expected.

In addition, the article ends the description of features with "And much more...". It appears that Perl 6 grammars are more powerful than CFGs. If they can simulate a Turing machine...

Re:Big problem

[Zaak]

Meaning that it is not backward compatible without modifying your source code.

Thus spake Larry Wall in Apocalypse 5:

...we took several large steps in Perl 5 to enhance regex capabilities. We took one large step forwards with the /x option, which allowed whitespace between regex tokens. But we also took several large steps sideways with the (?...) extension syntax. I call them steps sideways, but they were simultaneously steps forward in terms of functionality and steps backwards in terms of readability. At the time, I rationalized it all in the name of backward compatibility, and perhaps that approach was correct for that time and place. It's not correct now, since the Perl 6 approach is to break everything that needs breaking all at once.

And unfortunately, there's a lot of regex culture that needs breaking.

And from Apocalypse 1:

It would be rather bad to suddenly give working code a brand new set of semantics. The answer, I believe, is that it has to be impossible by definition to accidentally feed Perl 5 code to Perl 6. That is, Perl 6 must assume it is being fed Perl 5 code until it knows otherwise.

In other words, it is backwards compatible, it isn't backwards compatible, and when you install Perl 6, you are installing both.

TTFN

Re:An anecdote and an opinion.

[adamruck]

I think you went about things the wrong way. Why would you ever look at the nitty gritty syntax rules first when trying to learn a language. First do some simple examples to get the general feel of the langauage. Then learn the nitty gritty stuff as required.

"IMO, "the right job" for perl is about 2% of all programming tasks out there."

76 percent of all statistics..... You get the point. You really dont have any valid point here, every language is designed to do certain things, and people will use it for those things and more. Trying to say whats the best langague out there is stupid. Trying to say what percent of projects perl should be used on is also stupid.

"It can accomplish this, but not without the reader having to go through the mental gyrations of what could be best called linguistic decompression."

Have you tried to program in a logical language lately? Have you tried to program in a functional language lately? Have you tried to program in anything but your standard imperical/oo language lately? There are tons of styles of languages, and each one required its own linguistic decompression. Which one feels more natural its a matter of opinion.

I can't remember all that!

[warrax_666]

... so when I need a webserver, I just

$ cat /dev/urandom | perl

It usually works in 3 tries or less.

Let me guess.... the usual Perl backlash

[Anonymous Coward]

I get sick of the 'standard' backlash every time a Perl article is posted. Why do people have such a problem with Perl? It's an excellent, high-level general purpose programming language with a huge range of extension modules available. I have personally used Perl for many projects, as do TicketMaster, ValueClick, Morgan Stanley and Ryanair and I've also learnt a lot about software engineering and computing through Perl.

Yes, it does include a lot of symbols, but there is payback to learning them, and really most programs won't use much beyond $ % # () [] {}. Unlike some languages, Perl is not what I would describe as a 'bondage' language. If you want to program sloppy, you can program sloppy. That's fine by Perl. And this generousity is what gives Perl its bad reputation. This is funny since I and most knowledgeable Perl programmers can write perfectly clear and maintainable code. The way we do this is no secret--it's just by commenting appropriately, using meaningful identifier names and following the Perl style guidelines.

People can mock Perl all they like, but it is still a widely used powerful programming language and I am more productive in it than any other language. As a parting comment, a Cisco employee once told me (off the record of course!) that "Cisco would fall apart without Perl".