This Week on p5p 2000/04/23
- Notes
- Meta-Information
- Brief Update
- p5p to become Refereed?
- perlretut and perlrequick
- Threading Hilarity
- Line Disciplines
- Older Discussion of Disciplines
- Big Line Numbers
- Pseudohash Field Names, Hash Performance, and map Performance
- C with Embedded Perl
- `Unreachable’ code.
- sprintf Precision
- SDF Replacement
- Various
Notes
Meta-Information
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Brief Update
Since last time, Perl 5.6.0 has been released. As you can see, the version-numbering scheme has been changed. If it had not been changed, this would have been 5.006, or maybe 5.006_00.
Announcement for version 5.6.0
In the wake of this, list traffic was very high with various small bug reports and configuration problems. It has since quieted down.
Another major contributor to the high volume in late March and early April was a huge amount of whining and recrimination about whether or not 5.6.0 wasn’t any good. Gosh, p5p at its worst. Sarathy works like a dog to get 5.6.0 ready, and then after the release everyone started whining.
On the one hand were people complaining about bugs and how it was unstable and saying that nobody was going to switch, and there were some accusations that Sarathy was part of a Microsoft conspiracy to sabotage Perl. Blah blah blah. Then on the other hand were a lot of people saying that the changes were not significant enough to warrant a new version number.
(To this last point, I think Tom’s reply answers the point most effectively. The tone is characteristic of most of the entire discussion.)
You would think that at most one set of these assertions could be plausible; either Microsoft is trying to sabotage Perl by forcing a premature, unstable release, or the changes are too small to be worth releasing. You might think this, but you would be mistaken.
Now let’s close the book on this particularly disgraceful chapter.
p5p to become Refereed?
Partly as a result of the long, tedious, and irrelevant flamefest that took up so much time and energy in March and April, Sarathy proposed that the list be `refereed’. This is a little different from moderation: Most people’s messages go through normally, but if the referees agree, then messages in a certain thread or from a certain subscriber have to pass a moderator before they are sent to the list. Read the actual proposal before you make up your mind.
The following discussion was gratifyingly free of manifestoes, ultimatums, accusations, soapboxing, etc.
Sarathy: Many good people are not here anymore. Chip left, but has been brave enough to run a new list in an attempt to rediscover the old perl5-porters as we knew it. Jarkko disappeared, disgusted by all the name-calling and lurid behavior. Andy is gone too, thanks to useless arguments, personality clashes, and FUD-mongering. We simply cannot afford this.
A sideline here was that Jarkko expressed a desire that someone else pick up the Configure pumpkin. If you want to pick up the Configure pumpkin, contact Jarkko.
Jarkko: We need to educate more pumpkin holders.
perlretut and perlrequick
While I wasn’t doing reports, Mark Kvale submitted a draft of a perlretut man page which would be a tutorial for regular expression beginners. (Maybe you haven’t noticed that the existing perlre man page is incomprehensible unless you’ve been using sed for three years already.) I complained that perlretut was much too long, and Mark obligingly produced a cut-down version, perlrequick.
Threading Hilarity
Dan Sugalski discovered that the lock() function is not thread safe. I nominate this for Funniest Unintentional Perl Source Joke of 2000.
This started off another debate between Dan and Sarathy about the best appraoch for Perl threads. Dan’s patch added a mutex to every SV; Sarathy objected to this.
Dan Sugalski: Whenever there’s any sharing you have to deal with this. Sarathy: Sorry, I don’t have a VISA to enter the Land of Conclusions just now. :-) Dan: And apparently nobody’s granted a visa to enter the Land Of Even Partially Working Alternatives in the past two years either.
Discussion continued later in a second thread.
The discussion was really interesting, and I didn’t understand all of it. If someone wants to contribute a more detailed discussion of the issues for my next report, I’d be grateful to get it.
Line Disciplines
Simon Cozens did some work on the promised ‘line disciplines’ feature that didn’t quite materialize in 5.6.0. It’s a proof-of-concept, and it’s not quite finished. The idea is that you could associate a Perl (or XS) function with a filehandle, and then any time you read from the filehandle, the function is called to transform the input somehow. Typical transformations: Turn CRLF into LF for Windows machines; turn some national character set like ISO-2022 into Unicode or vice versa.
The rudiments of this are in Perl 5.6.0; see for example the documentation for binmode() in 5.6.0.
Older Discussion of Disciplines
Previous discussion part I Previous discussion part II
Big Line Numbers
James Jurach reported that when your program is more than 65,535 lines long, Perl reports the wrong line numbers for errors. It turns out that the line numbers are stored in the op node, and are only 16 bits long, to save space. (In a 64Kline program, 32-bit line numbers would consume and extra 128Kb space.) James submitted a patch that makes 32-bit line numbers a compile-time option.
Pseudohash Field Names, Hash Performance, and map Performance
Benjamin Tilly brought up a number of interesting points. First, the error message that says No such array field for a pseudohash does not say what the problem field name is. And second, that hash performance could degrade more gracefully than it does at present if, when the linked list in a bucket got too long, it was replaced with a binary search tree.
However, he did not provide patches for either of these things.
Later, Benjamin reported that map is quite slow in some cases, even slower than an all-Perl function to do the same thing. It appears that the grep function, which map is based on, is optimized to be fast in cases where the result list is no longer than the argmuent list. For grep, this is all cases. But is it not always true for map, the typical example being
%hash = map {($_ => 1)} @array;
Benjamin suggested how this might be fixed, but unfortunately did not provide a patch.
Benjamin also reported a bug in Math::BigInt; it crashes with Out of memory! when it shouldn’t. Hugo van der Sanden confirmed, and found a smaller test case:
perl -we 'use Math::BigInt ":constant"; for ($n = 1; $n < 10; $n++) { 1 }'
C with Embedded Perl
Vadim Konovalov came up with a very simple and convenient way to embed Perl code into a C program. It’s a simple preprocessor that works alongside the regular C preprocessor. Read about it.
`Unreachable’ code.
Someone named Zefram took issue with the part of the manual that says
[goto] also can't be used to go into a construct that is
optimized away.
His example:
if(0) {
FOO:
print"foo\n";
exit
}
print "1\n";
goto FOO;
Here the if block is optimized away, so the program prints 1 and then aborts with Can't find label FOO. Zefram rightly points out that he is not supposed to know what might or might not be optimized away, and that there should at least be a compile-time warning in this case. He also says:
Unreachable code elimination is a good thing. But if code has a label in front of it then there’s a fair chance that it’s not unreachable.
Hard to argue with that. However, there were no followups.
sprintf Precision
Someone wrote in (again) asking why sprintf("%.0f", 0.5) yielded 0 and not 1. I wouldn’t mention this, except that it attracted a followup from John Peacock, who said he was writing a Math::FixedPrecision module that might help with this sort of problem. It sounds interesting, and might be worth a look. Read about it.
SDF Replacement
Some time ago, Ian Clatworthy developed a document format called SDF, the Simple Document Format. It’s a markup language that’s easy to read, like POD, but more powerful, but also convertible to many other formats. (In some cases it uses POD as an intermediate format.)
Ian announced to p5p that he was working on a successor to SDF, called ANEML. He did this because he thought we’d be interested (I’m certainly interested) and because he thought someone might volunteer to help him. Many details are here.
Various
A large collection of bug reports, bug fixes, non-bug reports, questions, and answers. No spam this time.
Until next time I remain, your humble and obedient servant,
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