This week on Perl 6, week ending 2003-08-31

Welcome to this week’s Perl 6 summary. This week, for one week only I’m going to break with a long established summary tradition. No, that doesn’t mean I won’t be mentioning Leon Brocard this week. Nope, this week we’re going to start by discussing what’s been said on the perl6-language list this week.

Now that’s out of the way, we’ll continue with a summary of the internals list.

Continuation Passing is becoming the One True Calling Style

Jos Visser had some code that broke in an interesting fashion when find_lex through an exception, so he asked the list about it. Leo Tötsch explained that exceptions and old style subs don’t play at all well together. It seems to me that the total and utter deprecation of subs using the old style calling conventions is not far distant.

Embedding Parrot in Perl

Luke Palmer has started to learn XS in the service of his project to embed Parrot in Perl. Unsurprisingly, he had a few questions. He got a few answers.

Implementing ISA

Leo Tötsch has implemented isa. The unfashionably lowercased chromatic argued that what Leo had implemented should actually be called does. Chris Dutton thought does should be an alias for has. Piers Cawley thinks he might be missing something.

More on constant PMCs and classes

Leo Tötsch’s RFC on constant PMCs and classes from last week continued to attract comments about possible interfaces and implementations.

A miscellany of newbie questions

James Michael DuPont a bunch of questions and suggestions about bytecode emission, the JIT and about possibly extracting the Parrot object system into a separate library. Leo supplied answers.

What the heck is active data?

Dan clarified what he’d meant when he talked about Active Data. His one sentence definition being ‘``Active Data” is data that takes some active role in its use – reading, writing, modifying, deleting or using in some activity’. The consequences of such data are far reaching; even if your code has no active data in it, Dan points out that you still have to take the possibility into account, or solve the halting problem.

Benjamin Goldberg seemed to think that you didn’t need to solve the halting problem, you could just add scads of metadata to everything and do dataflow analysis at compile time. I look forward with interest to his implementation.

Matt Fowles wondered why active data necessitated keyed variants of all the ops, asking instead why we couldn’t have a prepkeyed op to return an appropriate specialized PMC to use in the next op. Dan agreed that such an approach was possible, but not necessarily very efficient. Leo Tötsch disagreed with him though.

TOGoS wondered if this meant that we wouldn’t know whether set Px, Py did binding or morphing until runtime. (It doesn’t. set always simply copies a pointer). In an IRC conversation with Dan we realised that some of this confusion arises from the fact that set_string and friends behave as if they were called assign_string; to get the expected set_string semantics you’d have to do:

    new Px, .PerlUndef
    set_string Px, "some string"

Hopefully this is going to get fixed.

Mission haiku

Nicholas Clark To make some kind of mark Committed haiku. Don’t you.

Yes, I know that’s not a haiku. It’s a Clerihew. I suggest that anyone else who feels tempted to perpetrate verse on list restrict themselves to a sestina or a villanelle, or maybe a sonnet.

I also note that POD is a lousy format for setting poetry in.

Jürgen gets De-Warnocked

Jürgen Bömmels had been caught on the horns of Warnock’s Dilemma over a patch he submitted a while back. It turns out that he’d been Warnocked in part because both Leo and Dan thought he already had commit rights. So that got fixed. Welcome to the ranks of Parrot committers Jürgen, you’ve deserved it for a while.

Parrot Z-machine

New face Amir Karger wants to write the Parrot Z-machine implementation and had a few questions about stuff. So far he’s been Warnocked.


Dan described how Parrot’s notification system would work, and what that means for weak references. Michael Schwern thought the outlined notification system would also be awfully useful for debugger watch expressions. Tim Bunce worried about some edge cases.

MSVC++ complaints

Vladimir Lipskiy (who’s been doing some stellar work recently on various build issues amongst other things) found some problems trying to build Parrot with MSVC++ and asked for help in working out how to fix them. Jürgen Bömmels suggested a fix, which Vladimir liked in principle, but noted that there were still some issues it didn’t quite fix.

exit opcode

Leo checked in a small change to Parrot, making exit throw an exception rather than simply quitting the program. Of course, unless the exception is caught, parrot will exit anyway. He also proposed changing the startup parameters by moving the ARGV array from P0 to P5 for consistency with the Parrot Calling conventions. For some reason this sparked off an enormous thread discussing how to return from the main function.

Dan liked the the idea, so Leo checked a patch in and fixed up as many of the examples and languages as he could find, but he expects that he hasn’t caught ‘em all.

Acknowledgements, Announcements, Apologies

I’m really, really sorry about the Clerihew. But not sorry enough to remove it.

Thanks to everyone involved in making sure I only got one and a half of last week’s predictions right. (The half prediction was to do with my writing real Perl code, I didn’t. But I did release the Paris code, you can find it on CPAN at Heritable::Types if you’re interested.)

Thanks to Gill for seven and 2 days (as I write this) of wedded bliss.

Check out for more of my writing (and thanks to those who have already popped by).

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