This Week on p5p 1999/12/19

Dec 19, 1999 by Mark-Jason Dominus

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More 5.005_63 Results

Sarathy’s Announcement includes a list of changes and a substantial TODO list for 5.005_64.

There was the usual collection of bug reports that follows a new release, mostly concerning compilation and configuration issues.

$^H and %^H

Stéphane Payrard complained that even though %^H is mentioned in perldiag, it is not described in perlvar. Ilya protested that you cannot get that diagnostic unless you actually use %^H, in which case he assumes that you understand the diagnostic. Nevertheless, he provided doc patches that discuss $^H and %^H in perlvar. I deem this patch Important Reading for Perl Expert Wanna-Bes.

Perl RPMs

Johann Vromans supplied an RPM for Perl 5.005_63.

Elaine Ashton suggested sending it to Red Hat, and this sparked a discussion about whether it was a good idea to widely advertise the existence of an RPM for an experimental development release of Perl—the fear was that beginners would come along and grab the RPM and install a development version of Perl on their systems, and then be puzzled and upset when it didn’t work.

Sarathy said that he would distribute the RPM with future development releases, so that the people who test the Perl development releases could test the RPM also.

In the course of this, someone named Pixel said that he or she make a `hackperl package for Linux-Mandrake’. I don’t know what this is, but People using Mandrake might be interested to read the message.

Another interesting sideline: Randy J. Ray mentioned that he had tried to make the RPM C library into a Perl module, but had not been successful, because h2xs cannot parse rpm.h. Perhaps someone else would like to take a look at this.

Bennett Todd worked on an automatic RPM packager for Perl modules. Details are here. Andy Dougherty advised caution:

Andy: It would indeed be far nicer to have helpful feedback and discussions from various “vendors” before everything is set in stone to make sure we do something reasonable and don’t have folks feel they are continually fighting a system. I’d be happy to discuss such issues with anyone interested.

There was a rather long discussion, most of thish I did not follow, since I am not very familiar with RPMs. People who use Red Hat systems might find it illuminating.

The discussion included a sidetrack about support for version number literals in Perl 5.6. You will be able to write v5.3.40 and it will be compiled as if you had written "\x{5}\x{3}\x{28}" instead; this means that (for example) v5.3.40 lt v5.29.12 is true. The root of this part of the discussion is here.

Development Continues on Ilya’s Patches

This is getting to be my favorite part of the report, because even if the rest of the week is a bunch of boring flamage or irrelevant nattering, there is always something interesting going on in the Ilya department. Many thanks to Ilya and Sarathy for tirelessly supplying me with an endless stream of interesting technical content.

Change to xsubpp

Last week, Sarathy declined to put in Ilya’s improvement to xsubpp unless he also provided a way to turn it off. Ilya did this. There is now an environment variable that will turn it off.

Closed Filhandle in Signal Handler

Thomas Stromberg reported an interesting bug. He has a filehandle through which he is writing to a pipe. A close on this filehandle waits for the command on the other end of the pipe to terminate. While his program is doing this, it gets an alarm signal. Tom wants to terminate the program and clean up. If he simply returns from the signal handler, the close call is restarted and the program hangs again. So he tries closing the filehandle in the signal handler; this make Perl dump core.

He supplied a sample test program, but there was no discussion, perhaps because the sample program uses /bin/pax on the other end of the pipe, or perhaps because everyone knows that Perl signal handlers are hopeless. In any case, I was able to demonstrate the problem by changing /bin/pax to sleep 10.

pad_findlex Needs to be Recursive

Mr. or Ms. Pixel reported a bug in lexical closures. Here it is a demonstration:

    for (1..5) {
      my $t = $_;
      push @subs, sub { sub { $t }};
    }

    for (@subs) {
      print "-- ", &{&$_};
    }

This should print out --1--2--3--4--5but unfortunately the wrong $t has been captured by the closures. If you are still not sure that this is a bug, note that changing sub { sub { $t }} to sub { $t; sub { $t }} produces the correct behavior. (Thanks to Randy J. Ray and Jeff Pinyan for pointing this out.)

Larry predicts that Sarathy will fix this in the course of rewriting the pad code for 5.005_64. Sarathy remained mute.

Conversion Specifier Bug

Nicholas Clark reported a test failure for 5.005_63: Warning test #247 was yielding

/[a\b]/: Unrecognized escape \ in character class passed through at - line 3.

when it should have said

/[a\zb]/: Unrecognized escape \ in character class passed through at - line 3.

instead. That does not sound like a big problem, does it? I initially filed this in the `not interesting’ folder. Robin Barker tracked down the problem. The variable that held the missing z character was actually a UV, which is an unsigned long. But it was being printf‘ed with a %c conversion specifier. On a little-endian machine, this would probably have worked properly.

And now you know why we have regression tests.

Robin submitted a very interesting patch which enables printf format checking throughout the Perl code. he turned up a number of potential problems.

The Trivial Test

Mike McFaden submitted a perlbug report with no report; all we have is his Perl configuration.

François Désarménien: Whoa ! This is really the simplest perl program I’ve ever seen !

But then it turned out to be interesting after all: Hans Mulder pointed out that if you run the Perl test harness and tell it to execute no tests, it dies with a divide-by-zero error. Hans submitted a patch for this.

eof() at the Beginning of the Input

Background

Ralph Corderoy submitted a patch for this. I belatedly award Ralph Corderoy the `New Perl Person to Watch’ for December 1999. Thank you, Ralph.

Missing $VERSIONs

Michael Schwern posted a list of eighty standard modules that do not set $VERSION. He proposed modifying all of them to say that their version was 1.00. Sarathy objected:

Sarathy: What we really need is a mechanism to attach meta-information about a module (in the form of structured pod/XML, for instance). If done correctly, this would allow modules to “publish” their interfaces for run time type-discovery and other COM/CORBA-like functionality.

Simon Cozens reported that CTAN is doing something like this.

In the course of this, Ask Bjørn Hansen mentioned something I thought was very valuable and should be better known: The CPAN.pm module has a wh command. Try it.

Overly magical range operator

Tom Phoenix discovered that the magical range generation operator .. is magical even when its second argument is a number:

    @items = "0" .. -1;
    print scalar(@items);

This prints 100, because the string "0" is autoincremented until its length is greater than the length of "-1". He supplied a patch.

Array::Virtual

Tim Bunce forwarded a message from Andrew Ford, who is working on an Array::Virtual module that will let him tie a Perl array to a very sparse memory-mapped array of numbers. Most of the discussion apparently went on in the modules mailing list. This module as been on the module list in the `idea’ stage for a long time. There was some discussion about the appropriate calling interface for it. Read about it.

Reloading Modules that use fields

Apparently this doesn’t work— fields.pm tries to insert the field names into the %FIELDS array twice. John Tobey provided a patch.

However, there was no discussion.

New Improved File::Find

Johan Vromans reports that the new, improved File::Find does not work on /, because it normalizes the directory name to the empty string. Whoops.

Various

A large collection of bug reports, bug fixes, non-bug reports, questions, and answers. And spam.

Also, we got a perlbug report from someone named ################################################################################@cso.fmr.com.

Until next time, I remain, your humble and obedient servant,

Mark-Jason Dominus

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