Perl6 Summary for the week ending 2002-09-01
Well, it's been a week. Damian came to London and made our heads spin;
perl6-language erupted in a flurry of interesting, high signal/noise
threads; Parrot reached its 0.0.8 release; Larry made many of his
wonderfully unexpected but obviously *right* interjections and the world
kept on turning.
So, we'll kick of with perl6-internals as usual.
DOD etc
The 'elimination of garbage collection handwaving' thread continued as
Nicholas Clark asked a hard question about garbage collection and dead
object detection (DOD). As far as Nick could tell, it seems that `if we
have unrefcounted "deterministic destruction" objects somewhere freely
in the GC system, then we'll be needing a DOD run after every statement'
and he noted that `All ways of doing deterministic destruction seem to
have considerable overhead'. Sean O'Rourke wondered if we could use a
hybrid `full GC + refcounts where needed' scheme, but Juergen Boemmels
pointed out that refcounting would be contagious. Anything which
contained a reference to a refcounted object would need to be refcounted
in its turn...
Meanwhile, Mike Lambert wondered why we needed to promise deterministic
destruction in the first place and proposed a couple of schemes to deal
with the canonical `filehandle' case. Sean O'Rourke and Steve Fink both
came forward with cases where deterministic destruction proved useful,
and where Mike's scheme didn't really work. And that's where the thread
came to rest. I have the feeling that it, or a thread like it, will be
back.
http://makeashorterlink.com/?K11642DA1
Dynamic Keys
Tom Hughes, who has been doing good work on keyed access wondered about
dealing with dynamic keys, and proposed a way forward. Dan asked whether
Tom had looked at the proposed ops in PDD06, and pointed out that
dynamic keys didn't necessarily need to go the whole PMC hog. `They're
our internal structures--we can screw with them as we need :)'. Tom
pointed out a few issues with the PDD06 op set, and proposed a few more
ops with a (hopefully) consistent naming scheme. So far he's had no
answer to the questions he raised in that post.
http://makeashorterlink.com/?P12621DA1
Perl6 Test Failures
Steve Fink wondered about all the test failures he keeps seeing for Perl
6; he doesn't want to go trying to make a language neutral regex engine
play nicely with the Perl6 engine when that engine is in such a state of
flux. Sean O'Rourke suggested nailing down some calling conventions and
then both teams could code to those conventions. Steve pointed out that,
so far, he knows of at least 5 attempts at a regex engine in parrot.
Leopold Toetsch suggested Steve try the tests again, forcing a grammar
rebuild, and the test failures got all better.
http://makeashorterlink.com/?R23631DA1
Regex status
On Wednesday, Dan wondered where we were with Apocalypse/Exegesis 5
compatible patterns/rules/regexes. Sean O'Rourke told him. (Answer:
Still some way to go, but making good speed.)
http://makeashorterlink.com/?U14651DA1
Counting down to 0.0.8
On Thursday, Jeff Goff posted his timetable for 0.0.8, `Octarine'
release of Parrot, complete with a 25 hour code freeze. Markus wondered
if using a GMT timetable might be more friendly for every one who wasn't
on the East Coast of the United States. Parrot actually saw release on
Monday September the second, which is slightly outside the scope of this
summary, but I'll let it sneak in anyway.
http://makeashorterlink.com/?Z55612DA1
http://makeashorterlink.com/?A16623DA1
An `Oops' moment.
Leopold Toetsch found an interesting bug with the GC system interacting
with initialization. examples/life.ar.p6 is a Perl6 implementation of
Conway's Life, which has a rather lengthy initialization phase, after
which it checks the @ARGS array, which is conventionally placed in "P0"
at startup. But there's a catch. By the time it comes to make the check,
@ARGS has been garbage collected. Peter Gibbs posted a quick fix patch,
and Mike Lambert stuck his hand up to being a `lazy bum', but reckoned
that Steve Fink's fixes should solve the problem.
http://makeashorterlink.com/?U27631DA1
Various changes to IMCC
Whilst `idly toying' with IMCC, Steve Fink made a bunch of speculative
changes, bundled 'em up in a patch and offered them to the list. I'm not
sure what people thought of the changes, but the thread morphed into a
discussion of generating conditional makefiles and making sure that IMCC
and the other tools needed to get the Perl6 compiler working were as
portable as possible. Mike Lambert pointed out that it may make sense to
have the files generated by bison/flex checked directly into the
repository, since then those tools wouldn't be needed except by people
who go messing with the grammar.
http://makeashorterlink.com/?F28652DA1
Concatenation failing
Leon Brocard (phew, I was worried I was going to have to run his
questionnaire this week) found a bug where concatenation fails
occasionally leaving no clues as to why. He attached some sample code
which illustrates the problem. Peter Sinnott noted that Parrot seems to
be getting confused about the length of the strings involved. Peter
Gibbs meanwhile offered a patch and Mike Lambert reckoned it fixed a bug
in his code, but couldn't for the life of him work out why. Peter
reckons it has to do with "unmake_COW" resizing the allocation and
causing confusion elsewhere. I get the feeling that what we have now is
a `symptomatic' fix in search of a fix for an underlying issue. But I'm
just a summarizer.
Markus Laire found what he thinks might be another bug, but I've no idea
if it's fixed by Peter Gibbs' patch.
http://makeashorterlink.com/?N69623DA1
http://makeashorterlink.com/?V3A623DA1
IRIX64 alignment problem
Steven McDougall chased down a bug causing t/pmc/perlhash.t to throw a
bus error, but wasn't at all sure how to go about fixing it, and asked
for advice. Bryan C. Warnock offered a few pointers, as did Peter Gibbs,
but we don't have a fix yet.
http://makeashorterlink.com/?M3B615DA1
Meanwhile, in perl6-language
Prototypes, grammars and subs, oh my!
Thom Boyer wondered what "while"'s signature would be. He'd considered
"sub while (bool $test, &body);" and "sub (&test, &body);" but neither
really fit. Larry agreed and offered
sub while (&test is expr, &body);
and then, reaching deeper into his bag of tricks, he pulled out the
wonderful/scary
sub while (&test is rx/<expr>/, &body);
(Think about that for a moment. What is proposed that you'll be able to
specify a grammar for your functions argument list, which is definitely
something that made *me* sit up and take notice.) Damian sat up and took
notice too, offering some refinements and did some thinking aloud.
Damian suggested that maybe the prototype should look like "sub while (
&test is specified(/<Perl.expr>/), &body);". Damian also suggested
blurring the line still further between statements and expressions by
having the likes of "for" return a value, and had some thoughts on
multimethods. Trey Harris also offered some more comments on
multimethods.
All of which leaves me looking forward with bated breath for Apocalypse
6.
Quote of the thread: "The whole point of making Perl 6 parse itself with
regexes is to make this sort of stuff easy." -- Larry
http://makeashorterlink.com/?H1C632DA1
http://makeashorterlink.com/?E1D623DA1
Rule, rx and sub
Deborah Ariel Pickett summarized the state of her understanding of the
difference between "rule" and "rx" and wondered if there was any case
where
... rule ...
and ... rx ...
(given the same "..."s in both cases), lead to valid, but different
semantics. Uri Guttman thinks not. Damian thinks so, and provided an
example. (It was joked, on the London.pm mailing list (by Damian
himself) that Damian is currently our only real, live Perl6
interpreter.). Luke Palmer raised a red flag about Damian's example;
Damian thinks it wasn't a red flag, but left it to Larry to adjudicate.
This also provoke a certain amount of discussion about the philosophy
behind some of the design decisions so far.
Glenn Linderman wondered if "rx" shouldn't be respelled, as the term
`regex' is being deprecated. Damian suggested that "rx" actually stood
for `Rule eXpedient', but I'm not sure he convinced anyone (himself
included). Ever the linguist, Larry observed that `we can tweak what
people mean by "regular expression", but there's no way on earth we can
stop them from using the term.' and that, no matter how many editions it
goes through, Friedl's book is always going to be called *Mastering
Regular Expressions*. So, Larry is `encouraging use of the technical
term "regex" as a way to not precisely mean "regular expression".'
Piers Cawley raised a question about when "}" terminates a statement and
got it wrong. This subthread led to a short discussion on good Perl 6
style. Damian told us that `Any subroutine/function like "if" that has a
signature that ends in a &sub argument can be parsed without the
trailing semicolon', which I don't remember seeing in any Apocalypse.
This led to a discussion about what was legal in a prototype specifier,
ending when Larry told us that it'd be possible to specify a grammar as
a function's prototype.
http://makeashorterlink.com/?G3F656DA1
http://makeashorterlink.com/?C10753DA1
http://makeashorterlink.com/?V21742DA1
http://makeashorterlink.com/?C22751DA1
Auto deserialization
At the root of what turned into a large thread, Steve Canfield asked a
deceptively simple question: `[Will] code like this Do What I Mean: "my
Date $bday = 'June 24, 2002'"'? We weren't entirely sure what he meant
by that...
The thread was long, and pretty much unsummarizable, but we ended up
with the rather pleasant looking "my Date $date .= new('Jun 24,
20002')", the idea being that, because $date is known to be a "Date",
even if it's undefined, then it's possible to make a static method call
on it. The response to this suggestion spilt over into the next week,
but `favourable' would be a good description of it.
http://makeashorterlink.com/?P23712DA1
http://makeashorterlink.com/?M14721DA1
Hypothetical synonyms
Aaron Sherman wondered if he would be able to write
$stuff = $field if m{^\s*[
"(.*?)" {let $field = $1} |
(\S+) {let $field = $2}]};
Larry thought
my $stuff;
m{^\s*[
"$stuff:=(.*?)" |
$stuff:=(\S+)
]};
was a better way of doing it, saying that he saw no `particular reason
why a top-level regex can't refer to variables in the surrounding scope,
either by default, or via a :modifier of some sort.'
Uri Guttman, in possibly the first ever Perl 6 golf post (he denies it's
really golf), suggested a way of shortening the pattern further, and
Larry trumped him by shortening it to "my $field = /<shellword>/", which
led Nicholas Clark to wonder about oneliners along the lines of "my
$data = /<xml>/" and wondered if the Perl regex engine would be faster
than using "expat". Nick also wondered if Perl 6 would give shorter golf
solutions than Perl 5.
There was quite a bit more in this thread, but my summarizing skills are
failing.
http://makeashorterlink.com/?X15721DA1 -- Thread starts here, it's
jolly good.
Does ::: constrain the pattern engine implementation
Deven T. Corzine wondered if the presence of ":::" and friends in the
pattern language meant we'd constrained the possible implementation of
the pattern engine before we'd started, and if we could implement
something that didn't do backtracking. General opinion seemed to be that
we couldn't avoid backtracking, but Deven wondered if it wouldn't be
possible to use a non backtracking implementation for some special
cases. The consensus appears to be `If you build it, and it's faster, we
will come'.
http://makeashorterlink.com/?N16733DA1
Backtracking into "{ code }"
Ken Fox wondered if
rule expr1 { <term> { /@operators/ or fail } <term> };
and
rule expr2 { <term> @operators <term> }
were equivalent. Damian thought not, and added that "expr1" should
probably be rewritten as "rule expr1 { <term> { m:cont/@operators/ or
fail } <term> }". Larry says that we *will* backtrack into subrules.
Again, the whole thread is worth reading if you're interested in the
rules/patterns/regex engine.
http://makeashorterlink.com/?D67741DA1
Prebinding questions
Philip Hellyer asked a bunch of questions sparked by Damian's talk about
Perl 6 to London.pm (at the Conway Hall no less, London.pm knows how to
find appropriate venues). Damian answered them.
http://makeashorterlink.com/?E38721DA1
"@array = %hash"
Nicholas Clark noted that "@array = %hash", for a hash of n elements
would return an array of n pairs. The Perl5 style, returning a list of
2n elements, keys and values interleaved would be "@array = %hash.kv".
All this led Nick to wonder what happened in the other direction.
Obviously "%hash = @list_of_pairs" was going to do the right thing, but
what about "%hash = @kv_array". And, more worryingly, what about
%hash = ("Something", "mixing", pairs => "and", "scalars");
It turns out that the @kv_array case will Just Work, and the last case
will cause discussion to break out. Damian thought that the example
above would throw an error because there are 5 elements in the list.
Another school thought that, because PAIRs are first class objects in
Perl 6, the code should work, with one of the keys of the hash being the
pair "(pairs =" 'and')>. Damian thought not, and discussion ensued. I'm
afraid I'm not entirely well qualified to summarize this thread as I'm
one of those who thinks Damian is wrong, or at least, not yet
sufficiently correct. However, for now, the state of the design is such
that pairs are `special' and it takes an effort of compile time will to
use them as keys (or values come to that) in a hash.
http://makeashorterlink.com/?G19752DA1
Regex stuff
Choosing a deliberately vague subject line in an effort to give the
summarizer a headache, Piers Cawley asked a question about binding to
numeric hypotheticals. It turns out that binding to a numeric
hypothetical variable in a regular expression is special cased
(resetting the numeric `counter') and even mentioned in the appropriate
apocalypse, and the problem that Piers thought he saw doesn't actually
exist.
http://makeashorterlink.com/?G6A752DA1
Atomicness and \n
Aaron Sherman wondered what "\n" would be translated to in a Perl 6
pattern. Aaron proposed "<[\x0a\x0d...]+>". Damian thought it was
"<[\x0a\x0d]>", and Ken Fox thought it would be something like "\0xd
\0xa | \x0d | \x0a". Personally I think it'll be "[ \0xd \0xa |
<[\x0a\x0d...]> ]". (I also believe that whoever came up with the idea
of a two character end of line marker should be taken out and shot, but
that's another story entirely).
The news from London
On Thursday Damian managed to deliver his Perl 6 prospectus talk in
about 3.5 hours. Okay, it *sounds* like a long time, but Damian told us
that, on average, the talk runs to 5 hours. The 'one question' rule
introduced by London.pm seems to have worked well. As predicted a whole
load of lights went on over peoples heads as they started to 'get' how
the whole thing hung together.
Anyway, the one question rule led to a bunch of questions about Perl 6
cropping up on the London.pm mailing list that haven't (yet) been cross
posted to perl6-language. One interesting question concerned what
happens when bare/if/while/do/when/etc blocks have "return" in them.
Damian answered that they throw a 'return' control exception, which the
control structure catches and re-throws. Piers wondered how you'd go
about writing your own looping construct and made a couple of proposals
about the treatment of control exceptions.
Quote of the London.pm threads: `yImoj Perl javDIch!' which, as everyone
knows, is the Klingon for `Be Perl6. Now!'.
http://makeashorterlink.com/?Y3B721DA1
http://makeashorterlink.com/?E2C752DA1
Call for assistance
Next week is the Zurich Perl 6 mini conference, and I won't be there.
Soon after that is YAPC::Europe 2002, and I won't be there either. This
week, Damian is in Belfast and will be talking to Belfast.pm about
stuff, guess what, I'm not there either. If anyone would like to send me
some Perl 6 related reports for the summary from any of these events I
would be *enormously* grateful. Thanks in advance.
Squashing a myth
You may have come across the `Damian Conway is looking for graduate
students' meme. I know I have, and I repeated it at one of Damian's
talks in London. Guess what, it's not true (as I should have realised).
Damian is no longer associated with any institute of higher learning and
is not looking for graduate students. Kindly readjust your memeplexes.
In Brief
Pete Sergeant pointed us all at some work he'd done toward building an
'operations dictionary' for Parrot. Available at
http://grou.ch/parrot/index.cgi.
Over the course of a surprisingly long thread, Steve Lambert, Markus
Laire and Leopold Toetsch and a few of the usual suspects got IMCC and
Perl6 compiling properly with Windows.
Bryan C. Warnock offered a large patch to parrot's glossary.pod; a
document worth reading. Bryan also PODified byteorder.dev so it would
show up correctly on http://www.parrotcode.org/docs/. Bryan also added
POD title blocks to a pile of PODs. Kudos to the docmonster.
Daniel Grunblatt added conditional breakpoints and watchpoints to the
Parrot Debugger. Steve Fink also waved a magic wand over the debugger
and fixed up a bunch of problems. Well done chaps.
Andy Dougherty wondered about how up to date MANIFEST is. There were 497
files listed in MANIFEST, but a fresh CVS checkout runs to 2215 files.
Daniel Grunblatt thinks he's added all the important files to MANIFEST.
Sean O'Rourke made some big changes to IMCC; newlines within statements
are no longer allowed, and there's been some `significant changes to
register allocation and spilling.'
Bryan C. Warnock wondered about the file permissioning inconsistency in
the parrot source tree. Andy Dougherty pointed out that it wasn't
(quite) as inconsistent as it looked; build scripts should be left
without execute bits so that makefile authors would use the more
portable "$(PERL) script.pl", which makes no assumptions about the
whereabouts of perl.
Peter Gibbs offered a *huge* patch, merging his `African Grey' parrot
tweaks with the CVS parrot. It's not been applied in CVS, but
http://makeashorterlink.com/?O1D741DA1 has the details.
Jason Gloudon wondered about temporary PMCs used in opcodes like "ADD
Px, Py, Pz", and wondered what "set_pmc" should do in the simple case.
Sean O'Rourke pointed out that often one wouldn't need to create
transient PMCs because one could use the specialist string and number
registers to hold the temporaries. Sean voted for `morph' in the simple
"set_pmc" case.
Jonathan Sillito contributed a patch allowing for hierarchical lookup of
lexical variables in scratchpads, and which makes subroutines into real
closures (by virtue of the hierarchical lookup up of lexical
variables...). Warnock's Dilemma applies...
Andy Dougherty did some cleaning up of the build process, removing lint
and cruft from the Makefiles and Configure.pl. Hmmm... I wonder how far
we are from our goal of 'compile a miniparrot, use that to execute the
more advanced config script, and then compile the full parrot', and
removing the dependency on Perl to build parrot...
Now that we have ICU in the repository Angel Faus wondered how we should
deal with differently encoded strings. No answers yet.
Andy Dougherty wondered if the time had come to make IMCC build with
plain old yacc and lex instead of depending on bison and flex. Leopold
Toetsch reckoned that that would be a good idea and asked Andy for his
patches.
Leopold found a bug in "mul", "div", "mod", "sub", "concat" when
operating on PMCs. So he fixed it. I'm not sure if the patch has been
applied.
Jürgen Bömmels got fed up with MANIFEST not being accurate. So he wrote
an automated test which compares the MANIFEST with CVS/Entries and
complains if they don't match. I don't know if it's been checked in yet,
but when it does, let's hope the committer remembers to update the
manifest.
Steve Fink has a patch which stops Configure.pl touching files unless
they've actually changed, and wondered if it would be of any use to
people not actually working on Configure. Nicholas Clark took the
opportunity to point us at http://ccache.samba.org/.
Steve Fink also submitted a flurry of clean up patches, many of which
look like they'll get applied once 0.0.8 has been released.
Dan noted that Hashes are an order of magnitude slower to GC than, say
PerlStrings, and two orders of magnitude slower than PerlInts. Which
isn't good. Dan wondered if there might be a way to get less GC
overhead. Steve Fink offered a few suggestions.
`:/::/:::/<commit> makes backtrack fail current atom/group/rule/match.'
-- Markus Laire summarizes the various backtracking assertions.
Who's who in Perl 6
Who are you?
Miko (pronounced "Mike-Oh") O'Sullivan, Father of Melody, Husband of
Starflower, Follower of Jesus, Author of The Idocs Guide to HTML
What do you do for/with Perl 6?
Participate in perl6-language, generally by suggesting small
features that I think would make life a lot easier for programmers.
Where are you coming from?
I come from the perspective that a) I want things to just work
without a lot of startup effort on my part b) I believe that things
can in fact actually do that c) Perl does d) Perl can do so even
more e) I'm pretty normal in these feelings. Oh, also Blacksburg,
VA, USA.
When do you think Perl 6 will be released?
Put me down for June 6, 2003, 1:37:03 am EST.
Why are you doing this?
I'm sort of like a Lab (i.e. the dog) that instinctively jumps into
a lake: I just must do it.
You have 5 words. Describe yourself.
Impatient.
Do you have anything to declare?
I declare a lot of public static constants.
Acknowledgements
Thanks to Gill for putting up with me last night while I sat and pretty
much ignored everything as I worked on this summary. For some reason,
perl6-language threads are much harder to summarize well; I *always*
take longer to write a summary when that list is busy.
As usual, if you liked this summary, please send money to the Perl
Foundation at http://donate.perl-foundation.org/ to support the
ongoing development of Perl.
This week's summary was funded by the O'Reilly Network, who now pay the
publication fee for the summaries directly to the Perl Foundation. So, a
big thank you to them.
--
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?
