The Perl 6 Summary for the week ending 2005-08-02
In case you were wondering, Darwin ports didn't work it's magic and I
still don't have a working Haskell compiler. Thank Juerd for feather,
even if I did have to turn my laptop upside down to read the MOTD.
Rot-180: oN hes +snf
This week in perl6-compiler
12 messages in the compiler list this week. Either everyone has decamped
to IRC or OSCON or the compiler's getting mature enough that most of the
interesting discussion about is happening in perl6-language as Autrijus
and others seek clarification.
Some Thoughts on PIL/Complete Type Inferencing
Autrijus has been doing some thinking on the next version of PIL (The
Pugs Intermediate Language) which will be a little less tightly coupled
with PIR/Parrot. He outlined his thinking (which seems to be directed
towards being able to do useful things and optimizations with Type
information) in this thread.
<http://xrl.us/gzbx>
Definition of containers
Autrijus announced that he'd checked in the first part of the new PIL
run core. In case you were wondering, containers are the things that
Perl variables have as values. They're where things like 'tie' magic
happens.
<http://xrl.us/gzby>
Hoisting Variable declarations
Hands up! How does the scoping of
{
$x = $x + my $x if $x;
#1 #2 #3 #4
}
work in Perl 6?
In Perl 5, all those $xs refer to the same thing. In Perl 6, #1 and #2
refer to $OUTER::x.
This behaviour (lexical scopes really are lexical) makes a compiler
writer's head hurt. Autrijus outlined a plan for making it work.
<http://xrl.us/gzbz>
Meanwhile, in perl6-internals
Dominance Frontier
Curtis Rawls had posted a patch adding 'dominance frontiers' to IMCC.
(I'm afraid I don't know what a dominance frontier is, but it sounds
like it might be fun.) This week he wondered if it could be applied any
time soon, because he had another patch that depended on it.
It turned out that the patch hadn't been applied because it broke a test
or two, and Will Coleda, Andy Dougherty, Patrick and Leo set about
helping to track it down. It looks like the issues have been found, and
work continues to fix them.
<http://xrl.us/gzb2>
'make languages' should continue after building a language failed
Have you ever looked through the Parrot Makefiles and wondered what the
deal is with '.dummy'? If so, all is explained in this thread.
<http://xrl.us/gzb3>
PMC syntax
Klaas-Jan Stol asked if there's any documentation about the complete
syntax for .pmc files when writing PMCs. Apparently there isn't, apart
from the source of pmc2c.pl, but Will Coleda and Leo helped Klaas-Jan
out.
<http://xrl.us/gzb4>
Embedding ParTcl
Thilo Planz had some problems embedding ParTcl into a PIR application.
It mostly worked, but he had a few questions. Will Coleda helped out
again.
<http://xrl.us/gzb5>
Compiling Dynamic PMCs
Klaas-Jan had more questions about compiling PMCs. Dynamic ones this
time. It appears that the docs he was following didn't quite reflect
reality. Leo solved the problem and Klaas-Jan sent in a doc patch.
Hurrah!
<http://xrl.us/gzb6>
Parrot cannot start up if STDERR or STDOUT is closed
Michael Schwern pointed out that parrot won't start if you close either
STDOUT or STDERR. Eschewing the standard joke response ("Doctor, it
hurts when I do this." "Well don't do that then.") Jerry Gay wrote a
test and Leo fixed it.
<http://xrl.us/gzb7>
Accessing Hash with strings/keys
Apparently Klaas-Jan is working on writing a lua compiler to target
Parrot. He's obviously working on it a good deal at the moment :)
He wanted to know how he could extend the standard Hash PMC to return
'None' if no key is found. As is traditional in these cases, Leo helped
him out. It turns out that part of the problem is that pmc2c.pl isn't
that strict in its syntax checking. If anyone reading this has the
tuits...
<http://xrl.us/gzb8>
Does it cost anything to use a big PMC everywhere
In a move guaranteed to gladden at least Dan Sugalski's heart, Amir
Karger popped up to say that he's working getting the Z-machine
interpreter working. He wondered if there was any way of dedicating a
register to a particular constant in order to avoid copying a global
every time he called a sub. Leo helped out.
<http://xrl.us/gzb9>
Super!
Leo announced that he'd added a new Super PMC which will make it easier
to call superclass methods.
<http://xrl.us/gzca>
Lua Project
Klaas-Jan unveiled his project to get the Lua compiler targetting
Parrot. It's apparently 'far from complete', but hey, it's good to
welcome yet another language to the parrot cage.
<http://xrl.us/gzcb>
<http://xrl.us/gzcc>
Announcing mod_parrot 0.3
Jeff Horwitz announced the release of mod_parrot 0.3, complete with
support for all Apache hooks, autogeneration of request_rec methods and
a mod_pugs proof of concept. Crumbs. And there's more. Check out the
announcement, download the code and start making Apache do weird things.
Go on, you know you want to.
<http://www.smashing.org/mod_parrot>
<http://xrl.us/gzcd>
Meanwhile, in perl6-language
The Use and Abuse of Liskov
Damian and Luke's discussion of the right way to do MMD looks to be
finally winding down. It seems Luke's convinced Damian of the
righteousness of his cause (or at least, if he's wrong, he's wrong in a
subtler way than Damian realised.) I don't think there's been a final
decision as yet, but we're definitely moving forward.
<http://xrl.us/gzce>
Slurpy parameters and auto flattening
Ingo Blechschmidt asked for some clarification of the behaviour of
slurpy parameters. It's not often I hope that Luke is wrong, but I
really hope the answer he gave Ingo isn't the true state of things.
<http://xrl.us/gzcf>
Exposing the Garbage Collector
Bah! I propose a simple, slow, yet powerful feature which can be used to
implement a whole bunch of other possible APIs for getting at stuff and
people go and suggest making any one of various heavier APIs the One
True API. It's enough to make a person despair.
Ah... apologies, I'm letting personal concerns get in the way of the
summary, but what the hell, I'm leaving it.
<http://xrl.us/gzcg>
Messing with the type hierarchy
Luke had a few things to say about what happens when you monkey with the
type hierarchy. So he said them. The usual suspects joined in, most of
them addressing the particular instance that Luke had chosen to
illustrate his point, rather than discussing the broader point, but hey,
this is perl6-language, that's what happens.
Luke's broader question was "Should it be possible to write a class that
isn't a leaf in the existing hierarchy?" The example that everyone
addressed was the idea of writing a 'Complex' class that wedged in
between 'Real' and 'Num' in the hierarchy (which, as several people
pointed out, isn't necessarily the right way to think about it anyway,
hence the discussion).
My gut feeling was that the answer to the general question should be
"Yes, but be very, very careful and don't be surprise if it bites you
later".
<http://xrl.us/gzch>
Elimination of Item|Pair and Any|Junction
The discussion of appropriate default prototypes the like continued.
Autrijus proposed a way of rejigging the type hierarchy to make default
argument types a little clearer. I found things getting a little weird
to be honest -- there's even talk of eliminating 'Object' as a type
name, which seems a little strange.
<http://xrl.us/gzci>
Execution platform object? Gestalt?
Randal proposed that, as the number of possible platforms that Perl 6
can run on proliferates, it'd be really handy if there was some useful
global that held knowledge about the platform and its capabilities. He
proposed $*OS as a decent place to put it. Larry thought we probably
would have something like that, but thought that there might end up
being two globals, $*OS and $*VM. The usual "Why don't we call it..."
thread sprang up, but it seems that the most important upshot is that
this particular bike shed will definitely be painted.
<http://xrl.us/gzcj>
The meaning of "returns"
The continuing invasion by the rampaging hordes from p6c continued
apace. This time Autrijus had a discussion on the implications of
"returns" and its implications for type inferencing.
<http://xrl.us/gzck>
Lazy list syntax
Flavio S. Glock wondered how to go about creating a lazy list from an
object. Apparently the magic he was missing was "prefix:=", which is
syntactic sugar for calling the ".next" method on anything that supports
iteration. Which is nice.
<http://xrl.us/gzcm>
An idea for doing pack
David Formosa had an idea about a possible "pack" API, he outlined it on
the list. Yuval Kogman seemed to like it, but there's been nothing from
anyone else on the list.
<http://xrl.us/gzcn>
Inferring (Foo of Int).does(Foo of Any)
Autrijus again, this time thinking about the kind of type inferences
that can be done with Perl aggregate types. Once I'd got my head in the
right space, it made a great deal of sense, even if
(Array of Item).does(Array of Int); # false
(Array of Int).does(Array of Item); # also false!
made my head hurt the first time I read it.
<http://xrl.us/gzco>
Garbage Collector API
Various additions to the proposed Garbage Collector API were proposed.
<http://xrl.us/gzcp>
"$value.confess()"
Brent Royal-Gordon had a cunning idea for debugging of having Perl 6
capture the call stack at their point of creation and stashing that in a
property called confess, which could be examined in a debugging context
to find out where a value came from. As he pointed out, this would be
expensive, but useful. He's currently Warnocked, but I get the feeling
it should be possible to write an extension to do what he wants without
adding anything extra to Perl 6 itself. It might be a little tricky if
he wants the call stack to change on mutation though.
<http://xrl.us/gzcq>
Slurpy "is rw" arrays
Having got clarification of the behaviour of normal slurpy arrays, Ingo
Blechschmidt asked for clarification of the behaviour of Slurp "is rw"
arrays. Adriano Ferreira and Thomas Sandlaß seemed to talk sense in
reply.
<http://xrl.us/gzcr>
Curious use of ".assuming" in S06
Autrijus wondered if code like:
&textfrom := &substr.assuming(:str($text) :len(Inf))
found in Synopsis 6 was a mistake, or if the syntax was supposed to be
like that. It turns out that the syntax is supposed to be like that.
Apparently being able to do without the commas was one of the reasons
for making colon pair syntax look like that.
<http://xrl.us/gzcs>
Laziness and IO
In a currently Warnocked post, David Formosa outlined a potential
problem with lazy IO.
<http://xrl.us/gzct>
"sub foo ($x) returns ref($x)"
In his continuing discussion of the Perl 6 type system and the
inferences that can be drawn about it, Autrijus posted a discussion of
how to declare that a function that returns a value with the same type
as its argument. He suggested that the best way forward would be to
declare something like:
sub identity ($x) returns ref($x) { ... }
and asked for better suggestions. Thomas Sandlaß had suggestions.
<http://xrl.us/gzcu>
&say's return value
Gaal Yahas thought that &print, &say should "fail" on errors and return
the printed string on success (but true). Larry thought not. So it looks
like they'll end up returning a Boolean or throwing an exception.
<http://xrl.us/gzcv>
"$arrayref.ref"
Ingo continues his ongoing task of getting clarification of the
semantics of a whole host of things. This time he wanted to know about
the behaviour of references. Larry clarified.
<http://xrl.us/gzcw>
Binding scalars to aggregates
Next up in Ingo's clarification project was binding scalars to
aggregates (or did he mean binding aggregates to scalars?). Again, Larry
came through with answers. It turns out that there's more to this than
meets the eye at first glance. Autrijus's post on Containers over in
perl6-compiler addresses some of these issues as well.
<http://xrl.us/gzcx>
Binding hashes to arrays?
Ingo asks "Is it legal to bind a hash to an array or vice versa?"
Larry answers "Not at the moment."
<http://xrl.us/gzcy>
Module init hooks and pragmas
Gaal Yahas wondered what function in a module gets called when you 'use'
or 'no' it.
Warnock applies.
<http://xrl.us/gzcz>
Eliminating "&{}" and "*{}"
Autrijus wondered if we really need the "&" sigil. Warnock applies.
<http://xrl.us/gzc2>
Stringification of Pairs
For some reason Ingo's shortest question ("How do pairs stringify?")
attracted the largest response. Well, at first blush it looks like it
did. What actually happened was that it got Warnocked but the
References: header in Andrew Shitov's posed discussed below was a little
broken...
<http://xrl.us/gzc3>
"zip" with ()
Andrew Shitov got caught out by some strange behaviour of "zip". Ingo
explained what the problem was. There was quite a bit of discussion of
the various subtleties exposed.
Sometimes I pity the poor swine who's going to have to write Programming
Perl 6. It's going to make the current camel look like a slim volume if
we're not careful.
<http://xrl.us/gzc4>
Mutating "map" and "grep"
Ingo Blechschmidt wondered if it was true that Perl 6's grep, map, etc,
wouldn't allow mutating values in their source array. He wondered if it
would be possible to use a pragma to get the old, Perl 5ish, behaviour
back. Thomas Sandlaß wondered if simply explicitly declaring the given
block's argument as "rw" wouldn't do the job. No word from @Larry yet.
<http://xrl.us/gzc5>
Acknowledgements, adverts, apologies, alliteration and Conference envy
Damn... couldn't think of a word beginning with 'a' that means
'conference'. To all you lucky people in Portland at OSCON, I wish I was
there and am a seething mass of envy. Well, not that seething: I'm
consoling myself by going to the WorldCon in Glasgow instead.
Help Chip
<http://geeksunite.org/>, tell all your friends, this cannot stand.
The usual Coda
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<http://www.bofh.org.uk/>
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<http://xrl.us/gzc6>
