Perl 6 Grammars – not only for parsing

http://ttjjss.wordpress.com/2010/11/21/perl-6-grammars-–-not-only-for-parsing/

by draegtun • 16 years ago

48 13 16 years ago

ttjjss.wordpress.com

scott_s• 16 years ago

It would be wonderful if someone more familiar with Perl 6 could give a code break-down of what is going on.

Natsu• 16 years ago

I only know Perl 5, but I can figure out enough of it to give an educated guess. It seems like he's using the token returned by the grammar to select a method of the same name. So when he gets the token e404, he'll call the method e404 which does a make "404: Not found"

The grammar is something new in Perl 6, but it looks like there are a bunch of regexes that match different tokens. That makes me wonder how well it handles a buggy, ambiguous grammar, where the regexes overlap and something could be parsed as a token of two or more types. First rule wins?

Guess I should read some of chromatic's book over Thanksgiving so I'd understand more of this...

colomon• 16 years ago

Yes, using

    Mysite.parse($req, :actions(Mysite::Actions.new))

says "Parse $req using grammar Mysite and actions Mysite::Actions.new." When a token is found, the action method with the same name is called. As I understand it, the idea with separating token and action like that is one grammar can be associated with more than one set of actions.

python_padawan• 16 years ago

Congratulations, Perl 6 developers. You are beginning to catch up with Django. (See http://docs.djangoproject.com/en/dev/intro/tutorial03/ if you think I'm being sarcastic.)

Once upon a time, Perl was the de facto language for web development. Then there was a bit of falling out between the web-centric folks and the server-centric folks; resulting in PHP. Perl, as a language for web-development, never really recovered.

I find it kind of sad that it took over a decade and a half-hearted attempt at rewriting the language before the server-centric folks are even beginning to understand what the web-centric folks were talking about. :-/

hippich• 16 years ago

I can't say anything about Perl 6, I never really used it yet.

I can say about Perl 5 - check out Catalyst framework. I am pretty sure (if you throw away all prejudices) you will like it. Especially, check their chained actions.

This is web side. Can't say anything about server side, since I am using perl for web projects.

chromatic2• 16 years ago

Assume I'm barely competent at both Perl and Python. Can you explain how looping over repeated regular expressions is more powerful and useful than core language support for grammars and arbitrary tree transformations?

(I approve of Python's named captures, though even Perl 5 has had those for almost three years now.)

... over a decade and a half-hearted attempt at rewriting the language...

In truth, the Perl 6 redesign began a few months after Python 3000, in July 2000.

eru• 16 years ago

Oh, Python 3000 is now around ten years old? How time flies by..

cookietime2• 16 years ago

Perhaps you could provide an example of a situation where grammars and arbitrary tree transformations are more useful than looping over repeated regular expressions?

If you want others to see the utility of these Perl 6 features, they're going to need side-by-side syntax-highlighted clear-as-day examples. Otherwise it's just, "must be some weird Perl 6 feature -- the way I'm doing it in blub works fine for me".

davidw2• 16 years ago

PHP was its own, independent effort. It doesn't really have anything to do with Perl. People migrated to it because it was easier to deploy (just put it on the web server), and probably easier to write for many people.

whiskeyjack• 16 years ago

PHP was originally a layer over Perl. It's in the first paragraph of the history.

It doesn't NOW have anything to do with Perl... but it's pretty easy to see some of that history in the code.

Perl 6 Grammars – not only for parsing

Related Stories