This file is part of the Perl 6 Archive

Note: these documents may be out of date. Do not use as reference!

To see what is currently happening visit

The Perl 6 Summary for the week ending 20021020

I'm sorry to have to inform you that I've returned from my holiday (no, base jumping and paragliding were not involved) and that this week's summary will not be written by the estimable Leon Brocard. Sorry about that. Leon is currently taking a rest cure.

So, with the customary mention of Mister Brocard out of the way good and early this week, it's time to take a look at what's been discussed on the internals list:

Regarding JVM - Parrot Compatibility

Newcomer Karthik Kumar is interested in writing a tool to convert java .class files to parrot .pbc files and asked for information on what had been done in this area. Leon Brocard says it's very easy to get the basics working because of the low number of JVM bytecodes. But getting the fundamentals (classes, objects) right is hard. Ramesh Ananthakrishnan commented that it might be a little early for anything more than proofs of concept at the moment as Parrot is a rapidly moving target. Ramesh also came up with the idea of compiling `real machine' assembly language to `virtual machine' parrot assembler.

Karthik commented that the real issue seems to be one of what level of support Parrot will offer for objects, and until that is known the class->parrot problem is almost pointless to solve. -- Ramesh clarifies his `Linux in Parrot' idea.

The Getting Started Guide

Erik Lechak is still not loving POD but, despite his distaste he posted version 0.4 of his getting started guide in POD format. Thanks a lot Erik. Marty Pauley suggested that Erik take a look at the Simple Document Format which may meet his needs better than POD

C# and Parrot

Rhys Weatherly, author of Portable.NET, part of the DotGNU project made a welcome appearance on the list. Apparently the DotGNU people are looking into compiling C# down to parrot bytecode and hoped that there might be parrot people who were interested in trying to complete their compiler and system library.

Rhys wanted to know how to make a user-defined class in Parrot; what the convention is for which registers must be saved across a call; the size of int and whether there was a way to store and access auxiliary data in a Parrot bytecode file.

Answers were provided. Sadly, the answer to Rhys's question about user-defined classes was "You don't, yet." Other answers were more immediately useful.

The DotGNU weekly IRC meeting discussed Parrot this week, Leon and Dan managed to cover both sessions between them, and there's a log available. -- Condensed summary of the meeting -- unedited logs available here

Variable/Value Split Prelims

Leopold Toetsch rather confused me when he replied to a two week old message (I thought I'd completely screwed up setting the `limit by date' values in my summary buffer) about the conceptual split between variables and values. Leo wanted some clarification which Dan provided.[] -- Dan's old message -- Leo's questions

PMC Initializers

Leon Brocard attempted to kick start discussion of Jonathan Sillito's patch to pass more information when creating new PMCs. Leopold Toetsch and Josef Höök both said they thought that something along those lines was a good idea, but the discussion seemed to die there. Later in the week, Dan introduced the new init_pmc function to PDD02, which works along the lines suggested.[]

PerlHash questions

Clinton A. Pierce wondered about how to do the equivalent of exists $hash{$key} in Parrot when one doesn't necessarily know the types of the things in the hash. Leo Toetsch pointed to exists_keyed and type_keyed. Jason Gloudon pointed out that the docs for type_keyed referred only to PMCs, with no mention of 'primitive' types. He wondered if PerlHash shouldn't just dictate that its contents were all PMCs.

Meanwhile in Perl6-language

The language group is trying to catch up with internals in number of posts. They managed 89 posts this week compared to internals' 96. If you discount attachments, language probably won on volume (and it certainly wins hands down on the `difficulty of summarization' metric).

Draft Proposal: Declaring Classwide Attributes

The discussion of how to declare classwide attributes rumbled on from last week; I'll just pick out a few nuggets.

  • HASH, <ARRAY> etc will likely become <Hash>, <Array> etc, and there's a good chance that UNIVERSAL will become Object
  • Implicit invocants can participate in multiple dispatch
  • It's worth taking a look at Smalltalk metaclasses, or Ruby's classes. Putting Metaclasses to To Work might also be worth a read -- Thread starts here -- the Metaclasses book

Perl6 Operator Precedence Table

The `Operator Precedence' thread kept on rolling from last week. The current game appears to be `working out how to free & and | to become superposition constructors', which means hanging the bitwise operators somewhere else. Various ideas have been proposed, but people really didn't like ||| and &&&. The current front runners appear to be:

  • $a b& $b
  • $a .& $b
  • my @a is bitmap($a); my @b is bitmap($b); my @c is bitmap($c); @a = @b ^|| @c; # Correcting what I assume is Larry's typo

It looks like this whole area is still somewhat fluid though.

untaintby property

Miko O'Sullivan proposed an untaintby property which `restricts which modules may untaint the data or data derived from that data.' The feedback wasn't that positive, but Larry came up with the idea of callbacks on properties which look rather cool. (`too cool!' according to Miko).

Indeterminate Maths

Michael Schwern opened a can of worms when he wondered if 1/0 would throw an error or just return a value representing an indeterminate result. Leon wondered if it'd be possible to, for instance have a module which did all its arithmetic in, say, integers module prime P. Dan thought yes, with lots of overloading. Adam Lopresto thought 1/0 would be a good place for the new fail semantics. We ended up in a debate about the mathematical values of $n/0 (apparently x/0 is indeterminate when x is zero and undefined otherwise).

This thread also saw discussion of: the nature of Object Orientation and the benefits of instance based inheritance; the semantics of NaN. (Did you know that NaN != NaN; the use of exceptions; proofs that 1/0 is, necessarily, undefined; Lukasiewiczian logic (SQL type NULLs); Miko's `inner Larry Wall'; and the hypothetical Math::Perverse module, which sounds like a candidate for the Acme namespace to me.

Larry seems to think that a combination of pragmas and overloaded classes should be enough to do the job. -- complete with citation of

A concept for Exceptions

Miko O'Sullivan has been doing some serious thinking. After wowing us with his untaintby proposal, he came up with some proposals for exceptions which would allow for all sorts of cunning tricks. Dan pointed out that at least one of the cunning tricks wasn't actually possible, but that you could get something like it by throwing continuations with your exceptions.

In brief

The effort to fix the JIT core when compiled with optimizations on x86 boxes continues (with a certain amount of discussion of how to use the test modules).

Simon Glover sent a covey of patches, mostly adding tests (yay!) along with one to fix up and document the .include assembler macro. Applied.

Chromatic did some copy editing of the docs and sent in a patch with his fixes. Applied.

Leopold Toetsch has a large patch for the GC system which tries to deal with some of the problems. It's not a complete fix, but Leo thinks it's a start.

Simon Glover noticed that lib/Parrot/ is marked as autogenerated and therefore removed by a make clean, which would be okay, but there's no rule in the makefile to regenerate it. Steve Fink fixed it using Simon's suggested solution.

Dan's fixed the docs for the splice vtable entries in PDD2. Leopold Toetsch promised to implement it.

Michael Lazzaro offers a summary of variables and assignment at Thanks Michael.

Who's Who in Perl 6

  • Who are you?
  • Brent Dax

  • What do you do for/with Perl 6?
  • I manage Configure changes and occasionally work on embedding and extending, the regex engine, misc.c, or whatever catches my fancy.

  • Where are you coming from?
  • The end of a day in high school (or sometimes the middle of the day...) :^)

    Seriously, I think Perl 6 is an excellent idea. Perl is a great language, but it's been in need of a de-crufting for some time.

  • When do you think Perl 6 will be released?
  • Hmm...probably next year sometime. Not soon enough for me to like it, but not late enough to complain about it.

  • Why are you doing this?
  • Because it's fun and interesting. And I get paid to manage a Web site, so Perl eq money. And I'm actually taken seriously.

  • You have 5 words. Describe yourself.
  • Hubristic hacker who really knows_little.

  • Do you have anything to declare?
  • No, of course not. No need to search this suitcase. Nope, not a bit. The customs dogs must have smelled a doggy treat or something.


Thanks are, of course, due to Leon Brocard for ably filling my shoes for the past couple of weeks and making sure that the summaries got through.

I'd also like to thank Rhys Weatherly and Gopal V for popping up on the internals list. I think it's great to see good communication and cooperation between the different projects working in this field.

Thanks too to my army of crack proofreaders who help to turn the misspelled morass of bad grammar that is my first draft into something that's readable. This week's team was: Chris Ball

The Perl 6 Summary was produced with the aid of GNER tea, the distractions of MAME and 10 Yard Fight and with money from O'Reilly and Associates. If you liked it, please consider giving money to the Perl Foundation at and feedback and/or NeXTcubes to me, mailto:[email protected]

The fee paid for publication of this summary on has been donated directly to the Perl Foundation.