Monthly Archives: February 2013

Texinfo 5.0 in Perl

There was a story on Slashdot on Sunday saying that the new version of Texinfo had replaced the old, C, implementation of makeinfo with one written in Perl.

I thought it would be interesting to look at the Perl they’ve written. This is, after all, a reasonably large example of Perl code that will be getting a bit of attention in the open source[1] world. If you want to look too, you can download the tarball or browse the CVS repository. In both cases, the Perl code is in the directory called ‘tp’.

This first thing to note is that this is obviously code which has been written by programmers who know their craft. This has not been written by script kiddies. There are, however, some rather bizarre touches which imply that the authors don’t know Perl as well as they might hope.

  • The code is nicely partitioned into modules. And many of the modules are really classes. But some of the modules (the ones in the init directory) have no package statement. So they are more like Perl4-style libraries than what we’d recognise as modules.
  • Many (in fact it might be all) of the subroutines in the modules have prototypes. In many cases, that doesn’t do any harm (although Perl prototypes don’t really address the issues that most people assume they address). But many of these subroutines are called as methods. And prototypes have no effect on method calls at all.
  • There is rather more use of package variables (instead of lexical variables) than I’d be comfortable using in my code.
  • I can see no use of CPAN modules. Perhaps there are no CPAN modules that help with this code. But I’d find that surprising in a project of this size.

Then I started to wonder which version of Perl they were targetting. So I searched for “use 5.xxx” statements. And found quite a range. Many of the files insist on 5.006 and most of the rest want 5.00405 – which I consider a scarily old version of Perl to try and support. There was one file that wanted 5.007_003. Then in one file (Texinfo::Parser) I found this:

# We need the unicode stuff.
use 5.006;

Reading the original Slashdot story, it claimed that one of the improvements in this new version was its Unicode support. And suggesting that you need Perl 5.006 for decent Unicode shows some major misunderstanding. Perl 5.006 was probably the point at which the Perl 5 Porters started to take Unicode seriously. It took until 5.12 or 5.14 before they got it right. Trying to support Unicode properly on anything earlier is almost certainly doomed to failure.

It’s great that another heavily-used project has started to use Perl. But it’s a shame that people might mistake this 5.6-era code for state of the art Perl. I can’t help wondering if this is a symptom of the “Perl 5 can’t have a new version number” problem that I’ve been reading about recently

I’ll get in touch with the Texinfo team and make some suggestions to them, of course.

Update: I emailed the Texinfo mailing list with a link to this blog post. I got a reply from Patrick Dumas who wrote most of this Perl code. His reply is available on the mailing list archives.

[1] Sorry, it’s a GNU project so obviously I mean “free”, not “open source”.

Training Debrief

I’ve spent a lot of the last seven days running training courses. It might be interesting to share some thoughts about how they went.

Last Saturday was Perl School 4. A week before the course I was a little worried about ticket sales, but I did a bit of marketing early last week and managed to more than double sales in a few days. In the end I had 27 people signed up.

Perl School is always enjoyable. I think that people often turn up with quite low expectations as it’s so cheap. So it’s fun to overturn those expectations and give them a day of high quality training. People obviously recognise that as I’m getting a lot of repeat business – at least one person has come along to three of the four courses so far.

Many of the courses I give are overviews of Perl at various levels. This one was just about DBIx::Class so it was great to be able to go into a lot more depth on a single topic. Of course, DBIx::Class is a great subject to cover and it was fun explaining its more powerful corners to a room of people who don’t know much about it.

I thought it went well. But don’t just take my word for it. I’ve been asking attendees to fill in feedback forms about all the Perl School courses and I’ve published a page summarising that feedback.

Then this week has been two two-day courses for flossUK. Two day courses give us time to include practical sessions so that people go home having actually tried out the techniques that I’ve taught – which nicely reinforces the lessons. I really enjoy those sessions as you really see lightbulb moments as people see how easy it is to use these tools. This afternoon, for example, it was great to see people getting a simple Catalyst application up and running in less than an hour. An hour later people were really impressed as I introduced them to Plack::Middleware::Debug and showed them how I could get detailed DBIC_TRACE output on the web page by making tiny changes to the application code. At least one person went away determined to reimplement a number of key applications in Catalyst as soon as possible.

And that, to me, is the joy of running training courses. It’s great to open people’s eyes to the possibilities that these new tools give them. I love to see them leave filled with renewed enthusiasm for the language.

Perl Books

The Perl community on LinkedIn is fascinating. It’s a great way to see how Perl is perceived and used outside of the echo chamber. And that’s a real eye-opener.

Here’s an example. Every few weeks (it seems) someone asks for advice on Perl books.At that point a few people will jump in with sensible suggestions. But for every reasonable suggestion, you’ll get three or four people suggesting something from this list:

  • Something horribly out of date. A lot of publishers stopped updating their Perl books about ten years ago. The most recent version of Perl Black Book that I can find is from 2001. Teach Yourself Perl in 21 Days was last updated in 2002. Perl By Example dates from 2007. I haven’t read any of these books, so I can’t comment on their quality, but I’d be really wary of suggesting that someone learns Perl from a book that is so out of date. Before the days of Amazon, these books would quietly disappear from bookshops, but now they always seem to be available.
  • Something out of date, but that used to be great. There are plenty of books that I would have recommended when they were current, but that I wouldn’t really want to recommend now. A lot of these are O’Reilly books that haven’t been updated recently – Advanced Perl Programming and The Perl Cookbook, for example. I’m sure there’s lots of good stuff in those books. But I really wouldn’t want anyone to read them if they didn’t already have enough experience to update the Perl to current best practices. I sometimes recommend these books myself, but only in specific circumstances. Whenever I run a course on OO Perl I mention Damian’s book. But I also point out that there have been a lot of advances in the area since the book was published. And, I have to confess, my own Data Munging with Perl fits firmly in this category.
  • Something of dubious provenance.  Most of these discussions will, at some point, attract a link to some dubious web site in Eastern Europe that contains the full text of O’Reilly’s various CD bookshelves. I know that these sites exist and I know that there’s nothing that O’Reilly can do about them, But I’d rather not see them mentioned on a professional site like LinkedIn. And quite apart from the copyright issues, there’s the fact that most of the books on these sites fall firmly into the first category above. They’re all over ten years old.
  • Some great tutorial on the internet. I’ve talked about the problems of old and dodgy tutorials before. And things definitely seem to be looking up. We are getting more good tutorials out there. But people still insist on sharing links to the tutorial that they learned from. Even if it’s appalling.

In a recent discussion someone said (and I’m paraphrasing) “just go to Amazon and look for the highest rated books”. I think there are two problems with that:

  1. The people who are rating beginner’s programming books on Amazon are usually the least qualified people to do that. Sure, they can tell how easy the book was to read and how well they picked up what the author taught them. But they have noway of knowing whether what they learned was accurate or useful.
  2. Amazon ratings last forever. But, as noted above, the quality of a technical book in fast-moving subject like programming falls over time. Perhaps Amazon ratings on programming books should have a half-life.

Here are some examples of things that you’re going to miss out on by using outdated Perl references.

  • say – We all love say, don’t we?
  • Lexical filehandles – Storing filehandles in lexical variables is great. I no longer have to worry about bareword filehandles being reused elsewhere in the code.
  • Defined or operator – There’s now no excuse for the $val ||= $default bug.
  • given/when – Perl has a switch statement. And it’s better than anyone else’s :)
  • Unicode support – Perl’s Unicode support is second to none. Except, if you’re using an old version of Perl in which case it’s a bit rubbish. And if you’re reading about Perl in an old book, then you won’t know about it.
  • State variables – Ok, I don’t use those every day. But when I need them, they make my code cleaner.

And then there are all the great CPAN modules that aren’t covered in books that were written before they were released. Would you really want to introduce someone to OO Perl without mentioning Moose?

My rules for recommending books are pretty simple. They should be books that I’ve found useful and they should have been published in the last few years. And given the falling numbers of Perl books that are published each year, that’s now a rather small number of books. Perhaps a dozen or so.

Am I being too harsh? Can beginners get something useful out of older Perl books? How do you decide whether to recommend a book to a colleague?