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Perl 6 and the Parrot Project

  • September 12, 2003
  • By Allison Randal, Dan Sugalski, & Leopold Tötsch
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The plan for Parrot was to build a language–neutral runtime environment. Itwould support all the features of dynamic languages such as Python, Ruby,Scheme, Befunge,and others. It would have threading and Unicode support(two of the most problematic features to add into Perl 5 code) built in fromthe start. It would support exceptions and compilation to bytecode, andhave clean extension and embedding mechanisms.

The language-neutral interpreter was originally just a side effect of gooddesign. Keeping the implementation independent of the syntax would makethe code cleaner and easier to maintain. One practical advantage of thisdesign was that Parrot development could begin even though the Perl 6 language specification was still in flux.

The bigger win in the long term, though, was that since Parrot would support the features of the major dynamic languages and wasn´t biased to a particular syntax, it could run all these languages with little additional effort.It´s generally acknowledged that different languages are suited to differenttasks. Picking which language will be used in a large software project is acommon planning problem. There´s never a perfect fit. It usually boils downto picking the language with the most advantages and the least noticeabledisadvantages. The ability to combine multiple languages within a projectcould be a huge benefit. Use well–tested libraries from one language for onetask. Take advantage of a clean way of expressing a particular problemdomain in a second, without being forced to use it in areas where it´s weak.

The modular design also benefits future language designers. Instead of targeting lex/yacc and reimplementing low-level features such as garbage collection and dynamic types, designers can write a parser that targets theParrot virtual machine.

The internals development for Perl 6 falls to the Parrot project. Dan Sugalski leads the project as internals designer, and Steve Fink is the currentpumpking. The Parrot project is largely autonomous. Dan coordinates withthe rest of the design team to ensure that Parrot will be able to support thesemantics Perl 6 will require, but the language designers have very littleinput into the details of implementation. Parrot isn´t developed solely forPerl, but Perl 6 is entirely dependent on Parrot–it is the only interpreter forPerl 6.

The core communication line for the Parrot project is the mailing list, perl6-internals@perl.org, otherwise known as “p6i.” It´s a much more business-like list than p6l. Workflow in Parrot takes the form of submitted patches.Anyone is free to submit a patch, and contributors who consistently submitvaluable patches over a long period of time are granted check-in access tothe CVS repository.

Documentation

Though adequate documentation has been a goal from the very beginning,the Perl 6 documentation project is a relatively recent addition. It operatesunder the guidance of Michael Lazzaro. The stated goal of the documentation project is to systematically walk through each Apocalypse and producefully specified documentation from it. The results of the project are eventually intended to be the documentation released with Perl 6.0.

The task of the documenters is a difficult one. The specification for Perl 6 isstill in development and constantly shifting, so they´re shooting at a moving target.The process is immensely valuable though,as it helps to identifyinconsistencies or problems in the design that the broad brushstrokes of theApocalypses miss. Sometimes it is the documentation process that causesthe shift in language specification, as identified problems lead to solutionsand the solutions, in turn, trigger changes throughout the system.

Supporting Structure

Last, but not least, is the glue that holds the project together. The highestpraise belongs to Ask Björn Hansen and Robert Spier, who manage theemail, revision control, and bug–tracking systems, as well as the web pagesfor Perl 6 and Parrot. Without these systems, the project would grind to ascreeching halt.

Nathan Torkington and Allison Randal share the load of project management.Nat tends to handle outside interfacing while Allison tends to handlethe nuts and bolts of the project, but neither role is set in stone. As is typicalof open source development projects, managing the Perl 6 project is quitedifferent from managing a commercial project of the same size and complexity.There are no schedules, no deadlines, no hiring and firing, and no salaries,bonuses, or stock options. There are no employees or bosses; there isvery little hierarchy whatsoever. Management in this context isnt about giving orders, it´s about making sure everyone has what they need to keep moving forward.

In the end, it is the developers themselves who hold the project together.Each individual bears their own share of the responsibility for finding a taskthat suits their skills, coordinating with others to keep duplicated effort minimal,and making sure the job gets done.

About the Authors

Allison Randal is the assistant project manager of the Perl 6 core development team. She has been working closely with Damian Conway and Larry Wall on Perl 6 and has co written the “synopses” of Perl 6. She is dedicated to the success of the project and is one of the very first to learn about anything new that's proposed for Perl 6.

Dan Sugalski is the chief architect for Parrot, the interpreter engine for Perl 6. He's been a Perl 5 core developer for years, writing more than a dozen modules in the process. He's been a contributor to The Perl Journal and The Perl Review, as well as the O´Reilly Network.

Leopold Tötsch hails from Austria where he first started working with computers in 1976. He is an independent software developer who has been exploring and developing open source software since 1991. He´s a frequent contributor to isdnlog (an open source project for monitoring ISDN lines and optimizing telephone costs) and spends the majority of his free time working on Parrot, the language-independent interpreter developed as part of the Perl 6 design strategy.

Source of this material

This is Chapter 1: Project Overview from the book Perl 6 Essentials (ISBN:0-596-00499-0) written by Allison Randal, Dan Sugalski, and Leopold Tötsch, published by O'Reilly & Associates.

To access the full Table of Contents for the book





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