The Perl 6 Summary for the Week Ending 20020822
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:
The Compound Key discussions continue
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.
http://makeashorterlink.com/?P66B337E1
Return undef for negative indices
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 ' _ +@foo _ '
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.
http://makeashorterlink.com/?M17B627E1
A Lexicals pre-patch
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.
http://makeashorterlink.com/?U48B217E1
http://makeashorterlink.com/?K19B257E1
http://makeashorterlink.com/?K19B257E1
default.pmc patches
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.
http://makeashorterlink.com/?C1AB227E1
http://makeashorterlink.com/?K1BB157E1 -- Sean's list
http://makeashorterlink.com/?L2CB537E1 -- Leo's hierarchy
Keyed ops
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.
http://makeashorterlink.com/?L5DB157E1
http://makeashorterlink.com/?T2EB327E1
Meanwhile, in perl6-language...
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.
http://makeashorterlink.com/?X1FB217E1
http://makeashorterlink.com/?K20C257E1
http://makeashorterlink.com/?H51C617E1
http://makeashorterlink.com/?D32C127E1
Hotplug regexes, other misc regex questions
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 { $x _= "!" } .* !/;
Damian reckoned that if the above were allowed at all, then the match
should succeed, and offered answers (opinions) on the rest of Steve's
menagerie. One of his suggestions involved a superposition, but I think
he might have been joking. Larry also gave his somewhat more
authoritative answers.
http://makeashorterlink.com/?X23C127E1
http://makeashorterlink.com/?V24C367E1
http://makeashorterlink.com/?C25C317E1
Hyperoperators and dimensional extension
Brent Dax wondered about how hyperoperators would work with multiple
dimensions. Dan's answer can be summarized as `properly', which wasn't
quite specific enough for Brent, but Dan stuck to his guns. Dan also
demonstrated that whilst he may be an American, he knows how to spell
`behaviour'.
http://makeashorterlink.com/?U36C217E1
Regex query
Simon Cozens had a few questions about grammars and rules. He's trying
to write a grammar to parse a Linux /etc/raidtab file, and has a few
questions about `drilling down' into the match object. The thread is
tricky to summarize. However, in one post Larry said that `any list
forced into scalar context will make a ref in Perl 6' and gave
"$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.
http://makeashorterlink.com/?Y27C117E1
http://makeashorterlink.com/?H28C257E1 -- Pigeons, meet a cat.
Backtracking syntax
'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.
http://makeashorterlink.com/?P39C127E1
In Brief
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:
http://makeashorterlink.com/?Q1AC357E1
Who's Who in Perl 6
Who are you?
Leon Brocard, [EMAIL PROTECTED]
What do you do for/with Perl 6?
I'm currently more interested in the Parrot side of Perl 6. I mostly
tinker with Parrot assembly (PASM), and try to keep the
http://parrotcode.org/examples/ 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"
(http://conferences.oreillynet.com/cs/os2002/view/e_sess/2515),
which is something that we should make terribly easy to actually do.
Where are you coming from?
680x0 programming, mostly. Programming Parrot is like how you
remember programming assembly was, only higher level and more fun.
When do you think Perl 6 will be released?
Sooner than most people think.
Why are you doing this?
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...
You have 5 words. Describe yourself.
Orange Perl/Parrot Euro-hacker
Do you have anything to declare?
I enjoy optimising computer-generated SQL statements.
Acknowledgements
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 http://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.
--
Piers
"It is a truth universally acknowledged that a language in
possession of a rich syntax must be in need of a rewrite."
-- Jane Austen?
