This week's Perl 6 Summary

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The Perl 6 Summarizer

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May 25, 2005, 1:26:30 PM5/25/05
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The Perl 6 Summary for the week ending 2005-05-24
Note to self: It's generally not a good idea to go installing Tiger on
the day you return from holiday. It's especially not a good idea to fail
to check that it didn't completely and utterly radish your Postfix
configuration. And your emacs. And the backing store for your website.
And a bunch of other stuff. It's an especially bad idea not to have
backups of things like your aliases file...

Nor is it a good idea to get preoccupied with all these joys and
completely forget that you're supposed to be writ ting the Perl 6
summary.

Ahem.

I'm very, very sorry.

So, on with the show.

This week in perl6-compiler
Inline::Pugs
Autrijus announced the availability of Inline::Pugs. If you've ever been
moved to mix up Perls 5 and 6 in one program, your prayers have been
answered. Just grab Pugs and Inline and you're set. Brian Ingerson made
things even more delightfully evil:

#!perl
use pugs;
sub postfix:<!> { [*] 1..$_ }
sub sum_factorial { [+] 0..$_! }
no pugs;
print sum_factorial(3); # 21

<http://xrl.us/f73s>

Experimental Coroutine support
Autrijus announced that Pugs now has an experimental implementation of
coroutines. It's almost certainly not final, but it's good enough for
exploration and feedback purposes.

<http://xrl.us/f73t>

Graphing tool for PerlGuts Illustrated
Yuval Kogman asked what tool was used to generate the 'pretty diagrams'
in PerlGuts Illustrated because he wanted to use it for diagrams in a
forthcoming PugsGuts Illustrated. Ingy said that Gisle had hand hacked
postscript based on initial diagrams drawn on graph paper. After some
discussion, the plan seems to be that Yuval will just draw diagrams,
scan them and bung them into the pugs repository. He'll rely on the
LazyWeb to turn them into beautiful scalable graphics.

<http://www.lazyweb.org/>

<http://xrl.us/f73u>

Perl Development Server
Okay everyone, repeat after me: "Juerd is a star!"

You may ask me why, and I shall tell you.

Juerd and his cosponsors, Twistspace will making a Perl 6 development
server available over the internet to any Perl 6 developers who are
working on 'everything that improves Perl 6 development'. So, if you've
been put off working on Pugs by the hassles of getting Haskell working
on your machine, or if you have the kind of bandwidth that makes svn
updates a painful prospect, worry no longer. Just sign up for a
development account.

There was much rejoicing and suggesting of hostnames. Rather bizarrely,
there was also discussion of the etymology of 'sipuli' (Finnish for
'onion' in case you were wondering).

<http://xrl.us/f73v>

Two releases in one day
Autrijus announced the release of Pugs 6.2.4. About half an hour later
he announced the release of Pugs 6.2.5.

<http://xrl.us/f73w>

Undef issues
Adrian Taylor thought he'd found some issues with Perl 6's understanding
of "undef". It turned out that he'd found some issues with his own
understanding of same.

<http://xrl.us/f73x>

Method/attribute chaining
Alex Gutteridge found some weirdness with the chaining of autogenerated
attribute methods (I wonder if the same weirdness occurs with hand
rolled attribute methods). So far it remains unfixed, but given the
speed of Pugs development I doubt it'll stay that way for long.

<http://xrl.us/f73y>

Meanwhile, in perl6-internals
Parrot as an extension language
Colin Adams continued to have problems using Parrot as an extension
language for Eiffel. It turns out that interfacing between statically
strongly typed languages and Parrot isn't easy.

<http://xrl.us/f73z>

Fixing t/src/manifest.t
Dino Morelli reported problems with t/src/manifest.t and wondered how
some of the failures came about. Jürgen Bömmels thought that the problem
was an overzealous test -- the original version of which simply ensured
that version control and the MANIFEST were in sync. He provided his
suggested version of a less eager, but still svn compatible test.
Further discussion thrashed out the various difference use cases for
manifest checking.

<http://xrl.us/f733>

More t/p6rules tests
Dino Morelli posted a bunch of tests for the Perl 6 rules. Well, he did
once he'd done battling his mailer's somewhat bizarre choice of MIME
type for his test files. Remember, if you're about to attach a .t file
to a message you send to the list, make sure your mailer doesn't declare
it to be an "application/x-troff" file -- "text/plain" is your fiend.

Patches were applied.

<http://xrl.us/f734>

Stressing the hash
Leo asked for some stress and bench mark tests for hashes because he was
in the process of redoing src/hash.c. Bob Rogers provided one.

<http://xrl.us/f735>

In other news, PyPy gets an initial release
Leo crossposted the announcement of PyPy 0.6, a Python implementation
written in Python. It's not bootstrapping yet, but it's getting there...

<http://xrl.us/f736>

PIR compilers broken
Will Coleda had some problems with with his TCL in PIR implementation.
It turns Nick Glencross helped to track down the problems with the
snippet he posted. I'm not sure whether his fix can be extended to work
with the real ParTCL.

<http://xrl.us/f738>

MMD
While working on mod_parrot, Jeff Horwitz ran into an issue with Multi
Method Des patch (MMD). In particularly he didn't seem to be able to
declare a multimethod that accepted an arbitrary PMC. Leo asked for a .t
file so he could explore the issue further, which Jeff provided.

<http://xrl.us/f739>

State of ParTCL
Will Coleda posted a summary of the current state of ParTCL. By the
sound of things, it's getting there.

<http://xrl.us/f74a>

Meanwhile, in perl6-language
Virtual methods
Whilst noting that Perl 6 doesn't really need to be able to declare
methods as virtual in the same way as C++, since one can simply use the
handy "..." to do the job, Aaron Sherman noted that there was a case for
something similar when declaring 'stub' methods that could be overridden
by Roles. The idea being that you would implement an initial behaviour
that could be further decorated by a Role. Except, as Luke pointed out,
the Roles system as currently defined treats all such methods as
overridable.

Aaron wasn't sure that this was such a good idea, and produced code to
illustrate why.

<http://xrl.us/f74b>

Default precedence of user defined infix ops
Ingo Blechschmidt pointed out that user defined infix operators work in
Pugs now. He wondered what their default precedence should be and how to
explicitly define the precedence. Luke came forth with an answer, Sam
Vilain asked an evil question, and Damian Conway suggested that, given
how drastically precedence weirdness can mess with a programmer's head,
there shouldn't be a default precedence at all, and if there were, it
should be looser than "infix:<+>". I agree with Damian.

<http://xrl.us/f74c>

"1,(2,3),4)[2]"
Argh! My head hurts!

However, if you're not sure how context works in Perl 6, Juerd provides
a really good summary later in the thread

<http://xrl.us/f74e>

<http://xrl.us/f74f> -- Juerd explains context

Reduce metaoperator on an empty list
Matt Fowles wondered how the shiny new reduce metaoperator worked given
an empty list. Various suggestions were forthcoming, but I lean towards
Randal's "inject" solution -- but I'm a Smalltalk fan, so no surprise
there. Personally, I reckon that the metaoperator version should just
return undef given an empty list -- if you want anything clever you
should eschew the syntactic sugar and use "inject" or something like it.
It seems that the consensus is leaning towards using an "identity"
attribute on the infix operator.

BTW, what happens when you apply "[/]" to a list with one element?

<http://xrl.us/f74g>

Complex Arithmetic
Doing complex arithmetic right in a programming language is tricky.
Edward Cherlin wondered if Perl 6 should follow what seems to be the
consensus among programming languages that care about this sort of thing
and use the shared definitions used by APL, Common LISP and Ada. Luke
thought it might be best left to C6PAN. (The discerning language
designer's equivalent to paying no attention to the man behind the
curtain methinks).

<http://xrl.us/f74h>

Syntax for specifying role parameters
Ingo Blechschmidt wondered if the syntax for specifying role parameters
should be the same as the standard subroutine signature syntax (with a
slightly modified proposed meaning for ":"). Thomas Sandlaß had some
related suggestions to add. Nothing from any of the design team yet.

<http://xrl.us/f74i>

"./method"
Martin Kuel can't make himself like "./method" as a shortcut for
"$whatever_you_call_self_this_week.method". Frankly, I can't blame him.
But then I continue to think that the originally specified semantics of
".method" (calls method on $_, whether in a method or a sub, or anywhere
else for that matter) are fine.

<http://xrl.us/f74j>

"uniq"
Ingo wondered why "uniq" wasn't in the current draft of Synopsis 29. He
also wondered if its default comparator should be "=:=". It turns out
that there's rather more to the semantics of "uniq" than you'd expect;
Damian's 'hyper correct' implementation blew my mind.

<http://xrl.us/f74k>

"s/.../{ $junction }/"
Junctions? In substitutions? What is Ingo thinking? Warnock applies.

<http://xrl.us/f74m>

Argument type checking
Joshua Gatcomb sought reassurance that

sub foo (Int $bar) { say $bar }
foo 'hello';

would do the right thing, namely throw an exception. Luke reassured him.

<http://xrl.us/f74o>

How to create a new meta operator
Ingo's obviously been in a very wondering mood this week. This time he
wondered if he could create a new meta operator in the obvious (to
anyone who's read Apocalypse 12 carefully) way. What? You've not read
Apocalypse 12 carefully? Shame on you! Like this:

sub infix_circumfix_meta_operator:{'->', '<-'} (Code &op, $left, $right)
{ op $left + 1, $right + 1 }

say 2 ->+<- 3; # 7

Luke thought so, but threw in his own question about how we'd specify
meta operators that only work on particular classes of operators.

<http://xrl.us/f74p>

How to invoke a method reference
Continuing to mine his wondering vein, Ingo asked how to invoke method
references. Juerd thought it'd work pretty much as it does in Perl 5.

<http://xrl.us/f74r>

Junctive and Higher order Types
Sam Vilain's question about converting a Haskellish chunk of code into
Perl 6 was Warnocked.

<http://xrl.us/f74s>

"foo(1: 2: 3: 4:)"
I was *so* tempted to use 'Multimethod colonoscopy' as the heading for
this section. Aren't you glad I resisted?

Autrijus has started to implement multi-level invocants in MMDs. He
asked a bunch of sanity check questions before proceeding. Luke and
Damian provided the sanity.

<http://xrl.us/f74t>

Lazy context
Borrowing Ingo's wondering hat, Yuval Kogman had questions about the
semantics of laziness. Laziness is one of many features of Perl 6 that's
reasonably easy to understand from the point of view of the user, but
which is a big old can of worms from the point of view of the
implementer. I think I understood Yuval's proposed
semantics/implementation, but I'm stumped when it comes to summarizing
it. People seemed to like it though.

<http://xrl.us/f74u>

Declaration of "my()" variables using symbolic referentiation
Snatching back his wondering hat, Ingo asked a question I didn't
understand about declaring "my" variables using symbolic referentiation.
Frankly, I don't even understand the subject. The consensus of those
responding seemed to be that what Ingo wanted to do was pretty silly in
the first place.

<http://xrl.us/f74v>

Explicit laws about white space in rules
Jeff 'japhy' Pinyan wanted to know what the rules were about where white
space is permitted in rules. In particular, was it legal to write "\c
[CHARACTER NAME]", or must he write "\c[CHARACTER NAME]". Damian reckons
only the second is legal.

<http://xrl.us/f74w>

And we're done
That's it for another week. Tune in at the same time next week when Mr
Fowles will entertain you all with his interpretation of the coming
week's events. I'll be back here the week after that.

If you find these summaries useful or enjoyable, please consider
contributing to the Perl Foundation to help support the development of
Perl.

<http://donate.perl-foundation.org/> -- The Perl Foundation

<http://dev.perl.org/perl6/> -- Perl 6 Development site

Or, you can check out my website. Maybe now I'm back writing stuff I'll
start updating it.

<http://www.bofh.org.uk/>

Vaguely pretty photos by me can be found at:

<http://xrl.us/f74x>

Fayland Lam

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May 26, 2005, 5:49:31 AM5/26/05
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