How to Implement Perl 6 in '10

(Originally posted as a reply to chromatic++'s How to Implement Perl 6 in 10 Years on PerlMonks.)
(Also thanks to Limbic_Region++ for forwarding the original thread link to me. :-))

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Hi. This is 唐鳳, a.k.a. Audrey Tang.

For the record, I think what chromatic wrote above contains a fair and accurate assessment to Pugs.hs (Perl6-on-Haskell).

However, please note that it elided over our collective shift of focus to the Perl 5 runtime during 2006 on #perl6, which resulted in the first CPAN releases of Moose, Module::Compile, v6-alpha (now evolved into Perlito), Pugs::Compiler::Rule, etc.

So while Pugs.hs was indeed suddenly unmaintained due to my '07 hepatitis outbreak, already by '06 we have redirected our main efforts into coding Perl6-on-CPAN.

Concretely speaking, that means we took various Pugs.hs structures (Signatures, MetaObject logic, Grammar parser, etc) and coded counterparts for the Perl5 runtime.

I'm very happy with what turned out - indeed MooseX::Declare and Perl 5.12.0 went way far beyond our original vision, in a very good way.

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As for Pugs.hs, the 6.2.x series has already fulfilled its goals.

In order to code the 6.28.x series (compile-time gradual typing) without unreasonable pain, it required several significant changes in the host language (Haskell).

Some of them were codified into Haskell 2010 (then known as haskell-prime), such as PatternGuards; some were implemented in GHC, such as Type Families and Quasi-Quoting.

In addition to the language changes, a better theoretical understanding of GADTs (which was deep black magic when Pugs.hs 6.2.x first used them), of OO+Functional type inference (Martin Odersky et al), of sound STM semantics and gradual typing (Jeremy Siek et al), was also essential in coding the type system of Perl 6 as originally envisioned.

Also notable was basic groundworks for 6.28.x such as Parsec Transformers, Dynamic-linkable binaries and Data Parallelism (to name a few) has gradually materialized as of early 2010, so folks who'd like to tackle type systems now have a significantly easier compilation-environment support than even a year before.

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However, speaking for myself, though Haskell became sufficiently attractive to implement compile-time type analysis for Perl 6, the success of Moose and Pluggable Keywords in Perl 5.12.0 has convinced me that we can also fruitfully implement such analysis directly in Perl 6, or in Perl6-flavoured CPAN modules, which is a much more straightforward way to amass a developer ecosystem than coding it in Haskell.

As lambdamoose demonstrated, real programmers can write Perl 6 and/or Haskell in any language, particularly if that language is as polymorphically existentially recursive as Perl 5. :-)

Comments

[audreyt]

I'd like to thank chromatic++ for his swift and gracious reply:

Thanks for replying. I don't mean to minimize any of those projects by omission, and I apologize for not mentioning them. I'm glad to hear you consider my assessment of Pugs.hs accurate.

[Jed Harris]

Could you say more about actual work on gradual typing (in 6.28.x or elsewhere)? I've hoped for years to see some actual development on this and have been frustrated.

A pointer to docs on design of 6.28.x if they exist would be interesting.

[audreyt]

Jed, that's a great question.

For Perl-specific, runtime-verified gradual typing, Moose::Manual::Types is a pretty good start.

For a glance on compile-time verified gradual typing, please refer to Siek and Wadler's POPL 2010 paper and chase the references. :-)

Also, Siek's PEPM 2010 keynote, General Purpose Languages Should be Metalanguages, is a pretty good read on (one of the many) motivations of Perl 6 development...