This Week in Perl 6, through August 2, 2005
In case you were wondering, Darwin ports didn't work its 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
There were 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 it happens in perl6-language as Autrijus and others seek clarification.
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 he seems to have directed towards being able to do useful things and optimizations with Type information) in this thread.
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.
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 behavior (lexical scopes really are lexical) makes a compiler writer's head hurt. Autrijus outlined a plan for making it work.
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 someone could apply it any time soon, because he had another patch that depended on it.
It turned out that the patch broke a test or two, and Will Coleda, Andy Dougherty, Patrick, and Leo set about helping to track it down. It looks like they have found the issues, and work continues to fix them.
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, this thread explains
everything.
Klaas-Jan Stol asked if there's any documentation on 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.
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.
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!
STDERR or STDOUT is ClosedMichael 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.
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 there is no key 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 ...
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.
Leo announced that he'd added a new Super PMC which will make
it easier to call superclass methods.
Klaas-Jan unveiled his project to get the Lua compiler targeting Parrot. It's apparently "far from complete," but hey, it's good to welcome yet another language to the Parrot cage.
mod_parrot 0.3Jeff 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.
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by Piers Cawley
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 realized.) I don't think there's been a final decision as yet, but we're definitely moving forward.
Ingo Blechschmidt asked for some clarification of the behavior 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.
Bah! I propose a simple, slow, yet powerful feature that is useful 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.
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."
Item|Pair and Any|JunctionThe discussion of appropriate default prototypes and 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.
Randal proposed that, as the number of possible platforms that Perl 6 can
run on proliferates, it'd be really handy if there were 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.
returnsThe 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.
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.
packDavid 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.
(Foo of Int).does(Foo of Any)Autrijus again, this time thinking about the kind of type inferences that Perl aggregate types allow. Once I had 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.
Various people proposed additions to the proposed Garbage Collector API.
$value.confess()Brent Royal-Gordon had a cunning idea for debugging: having Perl 6 capture
the call stack at its point of creation and stashing that in a property
called confess, which he could examine in a debugging context to
find out where a value came from. As he pointed out, this would be expensive,
but useful. He's currently Warnocked, but I get the feeling it should be
possible to write an extension to do what he wants without adding anything
extra to Perl 6 itself. It might be a little tricky if he wants the call stack
to change on mutation, though.
is rw ArraysHaving received clarification of the behavior of normal slurpy arrays, Ingo
Blechschmidt asked for clarification of the behavior of Slurp is
rw arrays. Adriano Ferreira and Thomas Sandlaß seemed to talk
sense in reply.
.assuming in S06Autrijus wondered if code like:
&textfrom := &substr.assuming(:str($text) :len(Inf))found in Synopsis 6 was a mistake, or if the syntax should 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.
In a currently Warnocked post, David Formosa outlined a potential problem with lazy IO.
sub
foo ($x) returns ref($x)In his continuing discussion of the Perl 6 type system and the inferences that you can draw 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.
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by Piers Cawley
&say's
Return ValueGaal Yahas thought that &print and &say
should fail on errors and return the printed string on success
(but true). Larry thought not. It looks like they'll end up returning a
Boolean or throwing an exception.
$arrayref.refIngo continues his ongoing task of getting clarification of the semantics of a whole host of things. This time he wanted to know about the behavior of references. Larry clarified.
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.
Ingo asks, "Is it legal to bind a hash to an array, or vice versa?"
Larry answers, "Not at the moment."
Gaal Yahas wondered what function in a module to call when you
use or no it.
Warnock applies.
&{} and *{}Autrijus wondered if we really need the & sigil. Warnock
applies.
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 Warnock claimed it, but the
References: header in Andrew Shitov's posed discussed below was a
little broken.
zip
with ()Some strange behavior of zip caught out Andrew Shitov. Ingo
explained the problem. 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.
map and grepIngo 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-5-ish,
behavior back. Thomas Sandlaß wondered if simply explicitly declaring
the given block's argument as rw wouldn't do the job. There is no
word from @Larry yet.
Damn. Couldn't think of a word beginning with "a" that means "conference." [Editor's note: attendance?] 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.
geeksunite.org: tell all your friends; this cannot stand.
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