Notes
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There were just under 300 messages this week.
5.6.1-TRIAL3 is out there
Just before going to press, Sarathy pushed trial 3 out of the door; get it from $CPAN/authors/id/G/GS/GSAR/perl-5.6.1-TRIAL3.tar.gz.
Please test it as widely as possible, run your favourite bugs through
it, and so on. If you're not one of the smoke testers, now would be a
good time to start; subscribe to
daily-build@perl.org and get yourself a copy of
SmokingJacket - that would be a great help for us.
Robin Houston vs. goto
Why anyone wants to maintain
goto is quite beyond me, but Robin Houston's been doing it rather well this
week. The first bug he fixed was to do with lexical variables losing
their values when a
goto happens in their scope:
for ($i=1; $i<=1; $i++) {
my $var='val';
print "before \$var='$var'\n";
goto jump;
jump:
print "after \$var='$var'\n";
}
Here's his analysis:
Wow! This is a venerable bug, dating at least back to 5.00404.When a for(;;) is compiled, there's no nextstate immediately before the enterloop, and so when pp_goto does this:
case CXt_LOOP: gotoprobe = cx->blk_oldcop->op_sibling; break;gotoprobe ends up pointing into a dead end.
That means that the label doesn't get found until the next context up is searched; and so the loop context is left and re-entered when the goto is executed.
Next, he fixed a bug which meant that
eval { goto foo; }; die "OK\n"; foreach $i(1,2,3) { foo: die "Inconclusive\n"; }
would not get caught by the
eval. This was because
goto failed to pop the stack frames as it left an
eval.
For his hat-trick, he made
goto work in nested
eval structures.
my $foo if 0
One of the (many) perl5-porters dirty secrets is that if you say
sub marine {
my $scope = "up" if 0;
return $scope++;
}
print marine(),"\n" for 0..10;
you get the lexical variable
$scope increasing from 0 to 10, instead of being reinitialised every time. In
effect, you get a static variable. Very nice.
Of course, this is completely undocumented and you'd be foolish to rely
on it, but it generates no warnings and passes
use strict happily. It's come about completely by accident, since the optimiser
optimises away the initialisation. David Madison claimed it was a bug,
but most people seem to think of it as an unexploded feature.
Jarkko will be adding lexical warnings to mark it as deprecated.
Johan also pointed out that
open with more than 3 arguments doesn't currently pass the later arguments
onto the program being called: his spectacular example was
open (FH, "-|", "deleteallfiles", "-tempfilesonly")
which deletes all files, not just the temp files. Nick said it was on his list of things to do, and called for patches.
More POD Nits
Michael Stevens produced some more POD patches this week, and the
discussion about how strict
podchecker can be continued from last week, spurred on by Jarkko sending Michael's
patched to the maintainers of core modules.
Ilya, Sarathy and others
grumbled about
podchecker's insistence on
=over 4
instead of just `plain'
=over
Michael patched
podchecker to remove that warning, although Jarkko was impressed that
perl5-porters had managed to degenerate to squabbling over 2 bytes of
documentation. A new low.
Not content, Ilya managed to get it down to 1 byte, by grouching about
L<foo
bar>
being an error where
L<foo bar>
was not. Michael patched
podchecker to remove that warning too, which has the nice result that you can
reformat paragraphs in your POD (with Alt-Q or gqap, depending on
religion) without worrying about it breaking the semantics.
More on the reset bug
Jarkko reported that Sarathy's patch to fix the
reset bug of a couple of weeks ago still produced erratic results on various
platforms.
Alan found the heap corruption in Purify, and reported that "this bug is
unchanged since the last discussion of it on the list a couple of weeks
back." (But noted that the anon sub leak is finally fixed!) Jarkko
pointed out that this was because Sarathy's patch wasn't applied to the
repository, and that the problem was that the linked list of pattern
match operators was getting corrupted. That's to say, when you have a
regular expression like
/.a\d/ it contains a list of nodes: any character, a literal
a, any digit. For some reason, when the regular expression was being
freed from memory, one of the nodes, let's say the literal
a, was pointing not to an "any digit" node, but to West hyperspace.
Radu Greab zeroed in on the problem: the regular expression was being cleared twice. He provided the beginnings of a patch; Sarathy suggested it was on the right lines, but wanted to reference count regular expression nodes. His version of the patch caused all sorts of problems, and Radu came up with something else to change the regular expression node list into a doubly-linked list. That was still imperfect, and Sarathy wanted to know why his patch caused all sorts of problems. Jarkko unfortunately ran out of time to do some debugging on this.
So it's still out there, and a very, very weird bug it is too. Something
is going very wrong with the freeing of PMOPs. We've only seen it on
Linux and Tru64 when the
-DDEBUGGING and
-g flags are on, so far. Stranger and stranger.
Distributive arrow operator
David Lloyd suggested that the arrow operator should be distributive, so that:
($foo, $bar)->baz();
does
$foo->baz(); $bar->baz();
Not a bad idea, although various people pulled out the old "would break old code" mainstay.
He developed his idea, suggesting that
([1,2], [3,4])->[0]
should return
1,3, and also that
($arrayref)->[0..15]
should return
map { $arrayref->[$_] } 0..15
I thought this was beautiful, and tossed it over to the perl6-language list, together with the natural extension of
@a = ($foo, $bar) . $baz # @a = map { $_.$baz } ($foo, $baz)
which reminded MJD of APL.
Various
I made a misattribution last week, saying that Philip Newton provided a
documentation patch for
use integer. Although Philip does some storming work, that wasn't one of his - it
belonged to Robert Spier. Sorry, Robert. John Allen produced another one
this week.
Ilya made
perldoc work on OS/2. John Allen suggested that we should use the subroutine
attribute syntax to extend builtins:
time :milli() for hi-res time, for instance. Nothing happened.
Charles Lane (he of the weird email address) produced a fix to tidy up
the test suite a little; tests should use
$^X instead of
./perl to keep VMS and other dinosaurs happy.
Kurt Starsinic has been patching up some of the standard utilities to be
warnings and strict clean; so far we've seen his patch to
h2ph.
Merijn found loads and loads of bugs in the 5.6.1 trials on AIX and HP/UX, which Sarathy ran around cleaning up. Good work, both.
Brian Ingerson has, sadly, decided that his excellent Inline module is not going to be mature enough for 5.8.0. Still, I heartily hope something like it ships with Perl 6. Have you played with Inline yet? No? Go and play with Inline immediately, and until next week I remain, your humble and obedient servant,
Simon Cozens
