Parrot: May 2009 Archives

On Saturday, I wrote up a possible API for Parrot compilers to support loading libraries written in other languages and discussed some of the details with Jonathan++ and Allison++. It’s not perfect, and is missing a few parts, but should be extensible enough to support whatever else we need in the future. I still need to formalize it a bit and add it to the Parrot docs and the example language shell.

On Sunday, I implemented it on Rakudo (Perl 6) and Cardinal (Ruby; very incomplete).

This morning, after confirming the spec with pmicahud++, I merged the changes into Rakudo trunk.

The syntax for specifying the source language for Perl 6 is:

use Foo:lang<cardinal>;

I couldn’t quite figure out what an appropriate way to do this in Ruby would be, so I just added a function to cardinal:

foreign_load('perl6','Foo/Bar')

If you have a better suggestion for what it should look like in Ruby, please let me know! I don’t actually know much Ruby at all, so my Ruby compiler is fairly limited.

I’ll be adding support for this to pynie (Python) soon, and other languages after that.

Here’s a simple example of using a Perl library from Ruby:

[sweeks@kweh ~]$ cat Foo.pm
module Foo {
    sub greet($name) is export {
        say "Hello, $name!"
    }
}
[sweeks@kweh ~]$ cat perl6.rb
foreign_load 'perl6', 'Foo'
['Ruby', 'Perl', 'World'].each { |name| greet name }
[sweeks@kweh ~]$ cardinal perl6.rb
Hello, Ruby!
Hello, Perl!
Hello, World!

Here’s a similar example of using a Ruby library from Perl:

[sweeks@kweh ~]$ cat Foo.rb
module Foo
    def greet(name)
        puts "hello, " + name
    end
    def apply_people(cb)
        people = ['Dave', 'Bryan', 'Stuart', 'Dax']
        people.each { |name| cb(name) }
    end
end
[sweeks@kweh ~]$ cat ruby.pl
use Foo:lang<cardinal>;
greet("person $_") for 1..5;
apply_people( { say "hello from perl, $^name" } )
[sweeks@kweh ~]$ perl6 ruby.pl
hello, person 1
hello, person 2
hello, person 3
hello, person 4
hello, person 5
hello from perl, Dave
hello from perl, Bryan
hello from perl, Stuart
hello from perl, Dax

Thanks go to my employer (Guru Labs) for their support in my work on Rakudo and Parrot.

Rakudo is just starting to get support for adding custom operators to the grammar from user-level code. You can’t specify the precedence yet, but you can run the traditional examples:

multi sub infix:<±>(Int $a, Int $b) { return $a + $b | $a - $b }
multi sub postfix:<!>(Int $a where { $_ > 0 }) { return [*] 1..$a }

my $x = 5! ± 2;
say "hi dood" if $x > 121;
say "hello again" if $x < 119;

I was playing around today with defining operators for mathematical set operations (∩ ∪ ∖ ⊂ ⊃ ⊆ ⊇ etc.) and then decided that I wanted a fancy syntax for defining sets, so I added support to rakudo for circumfix operator definition, and i now have this running on rakudo:

say "subset" if ⦃ 1, 3, 5 ⦄ ⊆ ⦃ 1, 2, 3, 4, 5 ⦄;