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So, another week, another Perl 6 summary. Let's see if I can get through this one without calling Tim Bunce 'Tim Bunch' shall we? Or maybe I should leave a couple of deliberate errors in as a less than cunning ploy to get more feedback. Hmmm.
So, kicking off with the internals list as always:
Dan Sugalski, Graham Barr and Leopold Toetsch (who, incidentally,
turned 44 on the 16th, so not only does he contribute really useful
code, he makes Dan and I feel younger. Can this man do no wrong?) all
thought hard about Ken Fox's Hard Question from last week. The Hard
Question was: `If %h{"a"}[0][1] is a PASM P2["a";0;1], then what
is %h{"a"}{0}[1]?'. Leo thought that things would work because an
integer isn't a valid key type for a hash, so the second case would throw
a `Not a string' error. Dan thought that this might not be enough, so
we probably need an extra flag to designate whether a key element
should be taken as an array or hash lookup. Graham Barr agreed, citing
the `hash with objects as keys' example that seems to crop up
everywhere, and suggesting the rather lovely looking my @array is
indexed('a'..'b'); as another possibility. Graham also wondered how
the flag should be used, suggesting that it should get passed into a
vtable's lookup method, thus allowing the writing of PMCs that don't
care how they're looked up, or other PMCs that did cunning things
depending on how they were accessed. Dan agreed.
Sean O'Rourke supplied a patch that arranged for @ary[-1000], say,
to give undef when @ary has fewer than 1000 elements. Also
included was a patch which changed array's get_string() method to
return the array's get_integer() value converted to a string. Leo
Toetsch wasn't keen on this idea, wondering if it shouldn't return
something like "PerlArray(0xaddr)" by analogy with the behaviour of
PerlHash PMCs. Sean disagreed, pointing out that in Perl5 one could
say print "You scored $score out of" . @questions . "questions.",
and the array would stringify to the number of elements it
contained. Brent Dax pointed out that in Perl 6 one would have to
write print '\@foo has ' _ [email protected] _ ' elements'; because Perl 6
arrays stringify to their elements, separated by
.prop{sep} //= ' '. Sean didn't like this, but appeared to take the
point. Uri Guttman quibbled about style, and proposed print "\@foo
has $(@foo.length) elements";, which certainly does a good job of
making its intention explicit.
Sean O'Rourke was unhappy with the current lexical implementation, as
it doesn't seem to support different levels of static
nesting. Apparently this makes nested scopes hard to implement,
especially in the presence of Perl 6's %MY magic. So he sent a
patch for people to play with.
Jonathan Sillito liked the patch, and pointed to a different approach that would make taking closures easier, but which would possibly make lookup slightly less efficient. Sean wondered how Jon's scheme would handle recursion. Jon thought about that, and answered by outlining how you would implement closures using Sean's scheme, and proposing that Sean make a 'real' patch.
Jürgen oumlmmels had a pile of questions too, related to using Sean's patch to implement proper Scheme functions, and he proposed a set of ops for manipulating pads. Sean agreed that this looked useful.
Leopold Toetsch patched default.pmc to make almost all methods
throw meaningful exceptions. Sean O'Rourke reckoned that the patch
went a bit far, proposing a few places where having a slightly richer
default behaviour would be the Right Thing to do, and some others
where doing nothing was the right default behaviour -- the example given
was init. Leo countered that one should really have a
default_scalar.pmc for the first types, and that, for the second
type, the PMC should have an explicitly empty method. The thread
resembled the Monty Python Argument skit for a few messages (`Look,
this isn't a proper argument!', `Yes it is!', `No it isn't it's just
contradiction!'). After a couple of rounds of this, Sean showed his
(substantial) list of default behaviours that he thinks should be in
default.pmc, and Leo showed us his planned PMC hierarchy.
Dan came down on Leo's side.
groups.google.com -- Sean's list
groups.google.com -- Leo's hierarchy
Has there been a week since I started doing these summaries that hasn't seen a discussion of keys, keyed ops or key structures? This week's second keys thread was kicked off by Leopold Toetsch wondering about the legality of, for example:
add P0[P1], P2, P3[P4]
If it is legal, what PASM ops should be generated. The problem is that the naive approach of using an op based on the argument list would lead to a horrible explosion of specific opcodes to deal with the possible combinations of keyed and unkeyed arguments. Leo wondered if the instruction should get turned into:
add P0[P1], P2[<The Null Key>], P3[P4]
Tom Hughes and Leo batted this back and forth for a bit. Tom noted that it wouldn't be hard to create a null key: just create a key with 0 elements for every PMC that didn't otherwise have a key structure, but he still worried that we were looking at 64 different op codes for each 3 argument op.
Sean O'Rourke pointed out that if scratchpads do become `proper'
PMCs, then the various 3 argument keyed ops would become remarkably
useful. For instance @a[0] = %b{1} + $c could become
add P0["@a0";0], P0["%b";1], P0["$c"]
But Tom wasn't sure that this quite fit in with Leo's plan. Leo meanwhile produced an RFC with his proposals for how keyed opcodes should look.
Last week's discussion of argument passing continued on its merry way. As well as a certain amount of debate as to the meaning of `topicalize', Larry clarified a few points. For instance, current thinking seems to be that if you want to capture the caller's topic in a named variable you'd do:
sub (...) is given ($x) { ... }
which would set the sub's $x variable to the same value as its caller's
$_. He also offered some comments on good style when using $_ and
made Angel Faus's day when he told us that it's looking like parameter
defaults will be specified by = rather than //=. Sean O'Rourke
wasn't entirely sure about the is given syntax, but Larry pointed
out that Sean's proposed syntax wouldn't allow for prototyping
`CORE::print, among other things.' It also looks like we're going
to be using exists to see whether a parameter got passed or not.
Steve Fink asked a few questions, mostly relating to pattern closures having side effects, supplying a few pathological (psychotic?) patterns as examples. My particular `favourite' was
my $x = "the letter x";
print "yes" if $x =~ /the { $x _= "!" } .* !/;
Damian reckoned that if the above were allowed at all, then the match should succeed, and offered answers (opinions) on the rest of Steve's menagerie. One of his suggestions involved a superposition, but I think he might have been joking. Larry also gave his somewhat more authoritative answers.
Brent Dax wondered about how hyperoperators would work with multiple dimensions. Dan's answer can be summarized as `properly', which wasn't quite specific enough for Brent, but Dan stuck to his guns. Dan also demonstrated that whilst he may be an American, he knows how to spell `behaviour'.
Simon Cozens had a few questions about grammars and rules. He's trying
to write a grammar to parse a Linux /etc/raidtab file, and has a
few questions about `drilling down' into the match object. The thread
is tricky to summarize. However, in one post Larry said that `any
list forced into scalar context will make a ref in Perl 6' and gave
$arrayref = (1,2,3) as an example. This caused a thread explosion,
which has boiled over into the current week as people followed the
implications of that through (some even going so far as to wonder if
that meant we wouldn't need [...] any more). Frankly, things got
ugly (at least syntactically). I'm tempted to draw a veil over some of
the ugliness; if you want to, read the thread. I'm waiting for Larry
to get back home and make everything better with another of his
shockingly wise postings. No pressure Larry.
groups.google.com -- Pigeons, meet a cat.
'Ralph' doesn't like the backtracking syntax, and proposed replacing
:, ::, :::, <commit> and <cut> with :,
:], :>, :/ and :// respectively. Simon Cozens and
Markus Laire spoke up against the proposal.
Leopold Toetsch has sent Dan a patch to implement a proposed hierarchy of PMC classes. Leo was this week's official patchmonster, submitting patches to make core_ops*.c more readable, improve predereferencing in interpreter.c, add a test case for restarting the interpreter and squeezing out a 10% increase in life performance. (This last one brought some questions from Mike Lambert.)
Simon `Unix Guru' Cozens popped in with some bug spots. First, he
pointed out that the magic number in a .pbc file wasn't being taken
into account in time. Then he found that queens.pasm was solving
the somewhat trivial `one queen problem', rather than the more
impressive `8 queens' problem. Finally, he pointed out that the hanoi
program seemed to be slightly broken too. And then the week ran out.
Garret Goebbel pointed us all at a survey of native interfaces for several languages, which can be found at: xarch.tu-graz.ac.at
Leon Brocard, [email protected]
I'm currently more interested in the Parrot side of Perl 6. I mostly tinker with Parrot assembly (PASM), and try to keep the parrotcode.org page up to date with current Parrot thinking. Sometimes I convert C code to PASM by hand. Sometimes I think evil things about converting other bytecode formats (say, Java's ..class files) to Parrot. I presented a talk at the O'Reilly Open Source Conference called "Targeting Parrot" (conferences.oreillynet.com which is something that we should make terribly easy to actually do.
680x0 programming, mostly. Programming Parrot is like how you remember programming assembly was, only higher level and more fun.
Sooner than most people think.
For fun, of course. And because it's interesting to see the development process behind a fast, portable virtual machine. Actually implementing Perl 6 on top of Parrot is just a simple matter of programming...
Orange Perl/Parrot Euro-hacker
I enjoy optimising computer-generated SQL statements.
It looks like Wednesday is becoming summary mail out day now. Surprisingly time consuming so it is...
Thanks to Leon Brocard for answering the questionnaire, making it embarrassingly easy for me to mention his name this week. I'm now running really low on sets of answers. Come on people, mail your answers to mailto:[email protected] and fame and... well fame anyway will be yours.
Once more, thanks to the crack proof readers on rhizomatic.net and elsewhere. This week's primary proof readers were: Kate Pugh, Paul Makepeace and Simon Bisson. Thanks people.
If you think this summary has value, then please send your money to the Perl Foundation donate.perl-foundation.org and help support the ongoing development of Perl 6. As usual, the fee paid by the O'Reilly Network for their publication of this summary has been donated directly to the Perl Foundation.