literal thoughts

perl6.vim gets more love

Sun, 01 Mar 2015 20:30:00 +0000

tl;dr: Some tuits came my way, so Vim’s syntax highlighting of Perl 6 is much better and faster now. Try it!

<timotimo> hoelzro: i just skimmed the perl6 vim syntax and … oh crap

<timotimo> there’s just no way i could even make a dent in that thing

* psch usually turns off highlighting in vim because it’s so slow :/

<sorear> perl 6 is not really syntax-highlightable

So…yeah, perl6.vim is a bit of a beast.

Recent history of perl6.vim

Sometime in 2008 or so, I got interested in Perl 6, and I really wanted it to be nicely higlighted in my editor (Vim) as I learned. As it turned out, there was already a Vim syntax file for it, in the Pugs SVN repository. This was mostly the work of lpalmer++ and moritz++. It worked decently, but as I learned about more nooks and crannies of Perl 6 (there sure are enough of them) I started finding the limitations of the highlighting to be frustrating.

I wanted to make it better, so I started learning all about Vim’s regexes and syntax highlighting support. I began hacking on perl6.vim, and soon enough it grew to be the largest Vim syntax file in existence. Perl 6 is hard enough to parse already. Having to do so with Vim patterns, doubly so. I made some progress but eventually the performance of the highlighting suffered as it grew to support ever more complicated syntax.

In 2009, alester++ created the vim-perl repository on Github to consolidat Perl support for Vim. perl6.vim gained a new home shortly thereafter when he imported it from the Pugs repo. Around the same I discovered Text::VimColor and used it to create a test harness for the syntax highlighting of perl.vim and perl6.vim. I fixed a few Perl 5 highlighting bugs and added some tests for them, but I never got around to doing the same for Perl 6.

Since then, a few contributors (hoelzro++ et al) have continued to fix bugs in perl6.vim. In the meantime, Perl 6 has also evolved, and some of the assumptions perl6.vim has made are no longer valid.

A few weeks ago I went to FOSDEM 2015, where Larry announced that this Christmas would be The One™. That rekindled my interest in perl6.vim, and I’d like to share with you some of the progress I’ve made with it.

Performance

Vim 7.4 ships with a profiler for its syntax highlighting. I used it to identify a lot of inefficient patterns in the syntax file. I tried to reduce the use of zero-width assertions (lookarounds) and to make more use of nextgroup instead when possible. I also optimized many patterns to reject matches as soon as possible. As a result, Vim now needs to attempt much fewer matches, and the ones it does attempt are taking less time to do their work. Editing most Perl 6 files feels pretty snappy now, even STD.pm6.

Identifiers

In ftplugin/perl6.vim, I added the apostrophe and high-bit alphabetical characters (æóð...) to the list of characters vim recognizes in keywords (iskeyword) This allows all valid Perl 6 identifiers to be used in Vim commands that depend on matching keywords.

I also cleaned up the highlighting of Perl 6 idenfifiers, in particular adding support for the high-bit characters and better support for dashes, so these are now highlighted correctly in sub/package/variable/etc names.

Multiline comments

These have been updated to recognize the new #` prefix, and to be allowed at the beginning of a line. Previously, multiline comments with stacked delimiters (««, <<, <<<, etc) were not highlighted by default. Some profiling showed that doing so does not have a noticable performance impact, so I changed it to always highlight them.

Heredocs

I added highlighting of heredocs with qto, qqto, q:to, qq:to, q:heredoc, and qq:heredoc, for most commonly used delimiters.

Setting functions and methods

* TimToady wishes all these highlighters wouldn’t treat setting functions and methods as reserved words; they’re just functions and methods`

<moritz> TimToady: agreed

* flussence wishes perl6.vim didn’t highlight Test.pm functions as reserved words either…

By popular request, I removed highlighting of builtin functions and methods. This makes sense since there’s no way to avoid highlighting user-defined methods that happen to share the name of a builtin one.

Metaoperators

Highlighting these is one of the trickiest jobs of the syntax file. Yet it’s one of the most crucial because if you let e.g. a stray R< or [/ go unhighlighted, they will screw up the highlighting of the rest of the file by starting a string where there isn’t one.

I managed to make great improvements to the highlighting of reduce ([+]), hyper (»+«), post-hyper (@foo».bar), reverse/cross/sequence/zip (Rdiv, R<, etc), and set operators ((<), (>=)). All the spec tests for metaoperators I have looked at are now highlighted without issues.

Strings and patterns

Another part of the language that presents a challenge is /foo/, <bar>, <<baz>>, and «quux». Determining when these are not actually numeric division, less-than, or a hyperoperators is tricky. These things are now matched much more accurately. I also added support for the qqx and qqw operators.

Grammars

Grammars are a whole other language in their own right, and this is where there is still the most room for improvement (of both performance and accuracy) in the syntax file. I still don’t know grammars well enough, but I’ve fixed all the highlighting issues I’ve found. STD.pm6 in its entirety is now highlighted properly, although Vim can still get confused occasionally until you scroll a bit or tell it to redraw the screen.

Pod

The biggest change here is that I added highlighting of indented Pod blocks. As part of the indentifier improvements mentioned above, Pod block names containing hyphens or high-bit alphabetical chars are now correctly highlighted.

Folding

I added rudimentary support for syntax-based folding (disabled by default).

Miscellaneous

I improved highlighting of numbers and version literals
Fixed a few issues where interpolated things weren’t highlighted as such
Made big improvements to highlighting of transliteration (tr///, tr{}{}, etc) operators
Added highlighting of bare/anonymous sigils in more places
Highlighted the Unicode set operators (∈, ≽, et al)
Certain keywords (like die, state, etc) are no longer highlighted where they shouldn’t be, e.g. as method calls ($foo.state)

Testing

Of course, I added tests for every improvement and bugfix listed above, so at least the highlighting should not be getting worse from now on.

END

All open vim-perl Github issues relating to Perl 6 highlighting bugs have been resolved. If you discover any more problems, please open new issues.

I tried patching perl6/doc to add an option to use Text::VimColor to highlight code blocks in the documentation. While it does result in richer and more accurate highlighting than the default pygments-based highlighter, it is painfully slow to generate. This is because Text::VimColor (and 2html.vim, on which it is based) extracts Vim’s highlighting by calling the synID() function at every character position in the file, which is very slow. So while it may only take Vim a few dozen milliseconds to highlight an entire file, extracting the highlighting state into something usable by an external tool takes several seconds. I wonder how difficult it would be to patch Vim (or NeoVim) to export an entire file’s highlighting in a more efficient manner…

To close, here is a sample of some meaningless code that used to get perl6.vim confused but just looks nice now:

class Johnny's::Super-Cool::Module;

my $cööl-páttérn #`[why hello there] = /foo+/;
sub infix:«foo» { }

sub foo-bar (Int $a where * > 3, @bar, Str $b = 'foo') {
    my $document = qto/END/;
        you there
    END

    my $document = qq:heredoc/END/;
        and $b
    END

    my $result = qqx/ls -l bla/;
    my @bla = [+] @bar;
    my @list = @bla Z, @bar;
    say "yes" if $set1 (<) $set2;

    =for Pro-tip
    Pay careful attention to the following code

    if $a !< 4 {
        @bar».bla: "this &nice-func() thing";
    }
    my $bin = -0b01010;

    (1,2)[*/2];
    say $@foo.perl;
    m:s/foo/$bar/;
}

sub foo (Int:D $bla) is cached { }

Testing vim syntax files

Tue, 01 Sep 2009 13:13:00 +0000

Yesterday, Andy Lester opened an issue for vim-perl on github about adding an automated test suite. I’ve thought about doing something like this before, so last night got busy with prototyping a test harness.

What I’ve got so far (in my fork) is a test file that uses Text::VimColor to generate HTML and compare it against a reference HTML document to determine if the syntax file is doing its job. If a reference file can’t be found, it will create it and skip that test. Here’s what it looks like:

$ make test
prove -rv t
t/01_highlighting.t .. 
ok 1 - Correct output for t_source/perl/basic.t
ok 2 # skip Created t_source/perl/advanced.t.html
ok 3 - Correct output for t_source/perl6/basic.t
1..3
ok
All tests successful.

In case of failure, it will use Test::Differences to show you what’s wrong, and write the incorrect output to disk for you to inspect:

$ vim syntax/perl6.vim # make a bad change
$ make test
prove -rv t
t/01_highlighting.t .. 
ok 1 - Correct output for t_source/perl/basic.t
ok 2 - Correct output for t_source/perl/advanced.t
not ok 3 - Correct output for t_source/perl6/basic.t

#   Failed test 'Correct output for t_source/perl6/basic.t'
#   at t/01_highlighting.t line 77.
#
«output from Test::Differences showing the offending lines»
# You can inspect the incorrect output at t_source/perl6/basic.t_fail.html
1..3
# Looks like you failed 1 test of 3.
Dubious, test returned 1 (wstat 256, 0x100)
Failed 1/3 subtests

The only big downside to this is that 01_highlighting.t tests all the source files in one go. You currently can’t tell it to only test one specific file.

More docs added

Mon, 17 Aug 2009 23:52:00 +0000

I’ve added Jonathan Scott Duff’s introduction to Perl 6 regexes to Perl6-Doc as perlreintro. In addition I put in a first draft of a perlobjintro. Neither of these correspond to names from the set of Perl 5 man pages, which is fitting since they are not directly based on them. So, Perl6-Doc now has 4 man pages, the aforementioned two as well as perlintro and perlsyn. I’ll be carefully adding to and polishing these in the near future. I’m hesitant to start on man pages relating to modules, IO, laziness/iterators, and other very important features, as the specs (and implementation) for those are still shifting heavily from month to month.

I’ve been thinking about using the Perl Table Index as initial source material for the magical syntax recognition feature, the implementation of which has remained elusive for a while. The current implementation is just a proof-of- concept with only a few terms as of yet. However, Damian Conway just published a significant update to Synopsis 26 on Perl documentation, focused on tying docs to code, so it might be time to figure out some Pod-ish source format for the terms to be stored in. Writing Pod is a breeze, so it should be easy to contribute new terms.

grok also needs more love. I’m not as happy as I’d like to be with some of its implementation details, most notably how it picks out functions from Synopses 29 and 32, using simple regexes (to be fair, this is exactly what good ol’ perldoc -f does). It should parse the Pod and pick out parts of the document tree instead, I think. There are also still a few visual differences between textual output of Pod 5 and Pod 6 that I have to address. Pod 5 textual output is pleasingly indented (gradually depending on the current heading level), which makes it very easy to follow, while Pod 6 is not.

As a sidenote, I believe I’ve found what was causing intermittent FAIL reports from CPAN testers. Some machines had a pretty old version of Pod::Simple which didn’t take well to subclassing. Another failure was caused by an old Pod::Parser (deprecated, but relied on by Pod::Xhtml) version which didn’t recognize =encoding directives. The relevant distributions now depend on newer versions of those troublesome modules.

Tagging, FAIL, regexes

Wed, 29 Jul 2009 19:03:00 +0000

I’m currently working on making grok index all X<> (and maybe C<>) tags in Pod documents. The user will then be able to look them up and see which docs contain the search term in question.

Gábor Szabó has already done something like this for the Perl 6 Synopses. His implementation only looked for formatting codes using the standard <> format, but I just patched it to look for << >>, <<< >>>, and «» tags as well. Ideally I would like to use a Pod parser to get the tags, but it’s just using regexes for now. Gábor also asked me to have grok look up the predefined subrules from Synopsis 5, which I think would be a good addition.

For a while, I’ve been getting some rare FAIL reports about grok from CPAN testers. It seems to be two problems that always manifest themselves at the same time. One of them is obviously because the tester has an old version of Pod::Parser which doesn’t understand the =encoding directive, but the other one is more mysterious. I’ll have to do some more digging, as I haven’t been able to reproduce it on my machines.

Jonathan Scott Duff pointed me to his unpublished introduction to Perl 6 regexes which I could use as a starting point for a perlretut man page. I haven’t got it into a releasable state yet, but it will soon.

Grok refactor

Fri, 24 Jul 2009 13:30:00 +0000

As the title suggests, I reorganized the grok a bit, in addition to adding a few new features.

The code is now more modular, and much easier to maintain. I added support for looking up individual functions/methods from all the chapters of Synopsis 32. In other news, Perl6::Doc 0.42 is just out, which includes first drafts of perlintro and perlsyn documents, which grok will now find.

This brings the total number of things known to grok up by almost a hundred:

$ grok -i|wc -l
613

On to the man pages

Wed, 22 Jul 2009 18:31:00 +0000

This week I’ve been working on the perlintro document found in the pugs repository, as well as porting Perl 5’s perlsyn. These are the most “basic” man pages about the language, and should be ported first (especially since many of the more specific bits in Perl 6 are still in flux).

As for perlintro, I can see a few more-than-trivial things that need changing. For one thing, the introduction to regular expressions is very casual, but Perl 6’s regex/grammar support has seen a major overhaul. Simply translating the examples to the Perl 6 equivalent seems to just make them longer, which gives the wrong impression. Focusing less on quick-and-dirty examples and more on the big picture might help the newcomer here, as grammars are integral to Perl 6, not just some special strings with weird syntax as they were in ol’ Perl 5.

A lot of special cases and “warts” have been replaced with new, exciting concepts that show up again and again in Perl (laziness, autothreading, all blocks are closures, everything is an object) that need to be touched upon. You could say that in Perl 6, the harmony / idiosyncrasy ratio has been lowered, and that’s a very good thing. Some of these can be saved for perlsyn, but nonetheless, they need to be introduced well.

In other news, I noticed that perldoc.perl.org has seen a facelift. I wonder if the software behind it might be used to power a Perl 6 doc site sometime in the future.

Lucky 0.13

Thu, 16 Jul 2009 06:42:00 +0000

I just uploaded grok 0.13 to PAUSE. It has the things I mentioned in my last post, plus some bug fixes.

grok can look up quite a few things now (527 including documents such as Synopses), but many of the answers it provides lack thoroughness. According to my project schedule, it’s time to start writing new documentation. That means I can focus on making these answers better.

I should also write/update a tutorial pretty soon, though I’m not exactly sure where I’ll start. I could update the perlintro in the Pugs repository and add it to Perl6::Doc, or I could use the Perl 6 part of the book Perl 6 and Parrot Essentials which was donated to the Perl Foundation by O’Reilly. That one is a bit longer, so I might just use it for a more detailed introduction (something like Perl 5’s perlsyn).

P.S. Since I’ve got the Pod 5 ANSI-color renderer mostly working now, users of Perl 5’s perldoc who like colors might want to install Pod::Text::Ansi and put the following in their ~/.bashrc (or equivalent):

export PERLDOC="-MPod::Text::Ansi"

Half way there

Sat, 11 Jul 2009 01:54:00 +0000

With Summer of Code’s mid-term evaluations coming up, some interesting things are about to happen to grok. I was contacted by Herbert Breunung, author of Perl6::Doc (formerly Perl6::Bible), which is a project that shares some of grok’s goals.

He told me that he doesn’t have enough time to maintain his project anymore and would like some sort of merge to happen. I said I’d look into it. His project bundles all the Synopses, Apocalypses, Exegeses, and some other Perl 6 documentation, and ships with a perldoc wrapper for reading them. What I would like to do is to move all documentation out of the grok distribution and update/add more to Perl6::Doc while eliminating the perldoc wrapper (in favor of grok).

He also brought to my attention the Perl Table Index, a sort of Perl 6 glossary. Ahmad Zawawi has just patched his Padre::Plugin::Perl6 to feed this index to grok. I will probably port the Perl Table Index to the Perl6::Doc distribution and make grok look things up in it.

I’ve started writing a Pod::Text subclass as well as amending Perl6::Perldoc::To::Ansi to conform to a consistent color scheme when using the default ANSI-colored output.

Something which grok should eventually be able to do is recognize arbitrary Perl 6 syntax (at very fine level of granularity, that is) and tell you what it means. A first stab at this will be to simply include a table of some common ones and look those up. Stuff like my, +, and so on. Doing this reliably is the original inspiration for the u4x project (Userdocs for Christmas), of which grok is a part.

I hope to make a release of grok and Perl6::Doc shortly which will include all of the above.

grok 0.09 is out

Wed, 01 Jul 2009 19:33:00 +0000

The code is starting to take a more stable form. I’ve prepended an underscore to all private/internal subroutines and documented the rest. Perl authors wishing to use grok’s functionality will now have an easier time doing so.

I’ve also added various author tests to the distribution to help keep the code in shape (or at least remind me when it’s not), notably Test::Pod, Test::Pod::Coverage, and Test::Perl::Critic.

Since my last blog post, grok has gained a few features. It can print the name of the target file (like perldoc -l), print an index of known documentation files, output xhtml, and detect whether the target file has Pod 5 or Pod 6 in it. It’s also got some Win32 fixes and more informative error messages.

Pretty soon I will start bringing in some more docs to bundle with it. Tutorials and such. I will also most likely implement function documentation lookup (like perldoc -f) in grok.

grok update

Fri, 26 Jun 2009 05:54:00 +0000

Some things have kept me very busy lately and I’m a bit behind on my GSoC schedule. I’m starting to catch up now, though.

First of all, as of version 0.05, you can now easily install grok from the command line on most operating systems like so:

$ cpanp -i App::Grok

It can handle Pod 5 files now (via Pod::Text) as well (which most of the Perl 6 Synopses are written in). The ANSI-colored output looks a bit different than the Pod 6 output because Pod::Text is very conservative in its use of colors. I’ll probably make them more similar later to keep it consistent.

When called interactively, grok now uses your system’s pager to view the output by default.

It will now treat an argument as a Pod 6 file to read if said argument doesn’t match a known documentation target. As for the targets, the only known ones so far are the synopses (which are bundled with grok for now), so you can do things like:

$ grok s02
$ grok s32-rules

First GSoC post

Wed, 27 May 2009 17:25:00 +0000

I officially started on my Google Summer of Code project (project details here) last weekend.

I’ve been tasked with writing a perldoc equivalent for Perl 6. I’ve decided to write it in Perl 5 for now, since it’s already got Perl6::Perldoc, which is a fast and feature-complete parser for the Perl 6 version of Pod (see specification), as well as lots of other useful CPAN modules which I won’t have to rewrite in Perl 6 (yet).

The program will be called grok (repository). So far it’s just a barebones command-line reader for Pod 6, but I did create an ANSI-colored terminal renderer for Perl6::Perldoc. It might be too colorful for some people’s taste currently, so maybe I’ll tone it down a little. I think Ruby’s ri documentation reader is the only such tool which colors the output, and I thought it was a nice enough feature (one of many!) to copy. I’ve also been looking at pydoc and javadoc in search of interesting features to implement.

The plan is to make it more modern and extensive than perldoc. One interesting thing I might end up doing is making use of STD (the standard Perl 6 grammar) to parse arbitrary syntax, so you could do stuff like grok '[*]' and the program would tease the expression apart and show you documentation for both the [] and the * operators.

Some portion of the project also includes writing new documentation for Perl 6. I haven’t written any yet, but I bet it will be fun. Before doing so, we first have to figure out how to organize the the docs. Since Perl 6 is a specification, it’s not as obvious as with Perl 5, where the docs are included (sometimes inline) with the implementation.

POE::Component::IRC 6.00 is here

Thu, 05 Mar 2009 03:03:00 +0000

POE::Component::IRC version 6.00 has just been released on CPAN. I’ve neglected to blog about PoCo::IRC since I started contributing to it, but since a new major release has been rolled out[1], now would be a good time. Also, as it turns out, next May will be the tenth anniversary of the project’s first release.

For the uninitiated, POE::Component::IRC is an event-driven IRC client library built on top of POE. People mostly use it to write bots. Some have made that even easier by creating a simpler interface suited to that task (see Bot::BasicBot).

I became involved in the project about 14 months ago, fixing bugs and adding features. There’ve been about 50 releases during that time, so there’s something for everybody. Following is a list of the most prominent ones.

Important squashed bugs

Quite a few DCC-related bugs have been fixed, error handling and diagnostics have been improved.
A bug causing the NickReclaim plugin to only try to reclaim the nick once has been fixed.
POE::Component::IRC::State was reacting incorrectly to some WHO replies sent by IRC servers that veered from the RFCs, causing it to hold inconsistent information. This has been fixed.
When raw messages were enabled, the raw line was not provided with CTCP-related events. Fixed.
POE::Component::IRC::State would issue more WHO commands than necessary when another user would join more than one of the component’s channels. No more.

New major features

POE::Component::IRC::Common, which provides many helper functions, now has functions for identifying and stripping color/formatting from IRC messages. It also defines IRC color constants for use in messages.
We now handle FreeNode’s IDENTIFY-MSG capability, which means that can you always know whether a user had identified with NickServ when s/he wrote a particular message.
Sending and receiving files with spaces in them over DCC is now supported.
All DCC-related events now provide the IP address of the peer.
DCC resume support has been implemented.
The BotTraffic plugin now send an event for every CTCP ACTION issued by the client.
We now guard against sending IRC protocol messages that are too long and might get us booted off the server.
The Connector plugin (takes care of maintaining the connection to the IRC server) now supports cycling through a list of servers when reconnecting.
The CTCP plugin can now respond to CTCP SOURCE requests for you.
POE::Component::IRC::State and can now track the away status of users for you.
POE::Component::IRC::State now keeps track of a channel’s creation time.
Added NICKSERV, SERVLIST, and SQUERY commands.
Plugins can now respond to custom events which have not been explicitly defined by POE::Component::IRC.

New plugins

I wrote 5 additional core plugins:

First of all, the Logger plugin. It logs channel/private/dcc chat activity to files on disk like normal IRC clients do.
Then there’s AutoJoin, which takes care of keeping you on your favorite channels, whatever happens.
NickServID deals with identifying your user to NickServ.
A CycleEmpty plugin which reclaims ops on channels that become empty.
BotCommand, which allows you to register commands that your bot handles, and get back an appropriate event when one is issued.

Testing

The test suite has been reorganized, many tests improved and more added. The test coverage (as reported by Devel::Cover) has increased from 40% (version 5.48) to 61% (version 6.00).

Refactoring

Much refactoring was done. The coding and indenting style has also been made consistent across the project, and many spotty coding practices have been eliminated (thanks, Perl::Critic).

POE::Filter::CTCP was merged with POE::Filter::IRC:Compat, and the former was removed. DCC support has been moved into its own plugin, and the plugin system itself has been ripped out in favor of POE::Component::Pluggable (which is based on the aforementioned plugin system).

Using the project’s current Perl::Critic parameters, version 6.00 has zero policy violations in 11,791 lines of code, compared to version 5.48’s 242 violations in 10,634 lines of code. The average McCabe score of subroutines also dropped from 4.21 to 3.45.

Documentation

Last but not least, the Pod docs have been improved. Errors have been fixed, much more formatting and linking has been added for easier reading and browsing, consistency has been improved, and many sections have been expanded.

I also added a cookbook with a few recipes showing off some of the things one can do with POE::Component::IRC.

Credits

Thanks to all the users who provided feedback, bug reports and patches. You helped make this happen. I also couldn’t have done many of these things without the help of Chris ‘BinGOs’ Williams, the senior maintainer of POE::Component::IRC.

Now go write some IRC bots (or clients)!

Notes:

It’s actually quite an insignificant release. Historically, POE::Component::IRC versions have always passed the whole-number boundaries naturally as part of a regular “bump the version number up by 0.02 for the next release” process.

Spicing up IRC with MegaHAL

Fri, 29 Aug 2008 04:45:00 +0000

I released POE::Component::IRC::Plugin::MegaHAL the other day, a POE::Component::IRC plugin for the esteemed and humorous conversation simulator known as MegaHAL. This makes it very easy to add a MegaHAL brain to an IRC bot. I wrote one and fed him IRC logs of a channel that I frequent, then let him loose online (he’s a “he” because the IRC logs primarily include ramblings from male users). Some examples of his brilliance follow.

<failo> Or maybe it's about sexual liberation and not perl & python.
<failo> Yes, printing passport photos at home is surely a sign of a flock of aids infected prisoners with big sloppy dicks.
<failo> I heard failo is a fact of evolution that cannot be shown because it looks like he knows what electricity is
<failo> Fucking get your cock out and jerk each other off in proportion to how much dexter's wedding dinner is going your way
<failo> Sir you had me at "balls."
<failo> Every porn dvd has a "grill setting"
<failo> So only 2% of americans also believe that the government is composed of thong-wearing oiled-up muscle boys.
<failo> Increased struggling from the bees made honey in the darkened cubicle, waiting for another musky man-pole to probe its way through the light to go mushroom hunting with me
<failo> I bet all drug users keep a human skull on their myspace page.
<failo> Earle: everybody's gay for a prison system in which millions of our descendants murder each other in prison.
<failo> Either you're gay or associated with all drugs.
<failo> The war on polarbears is going to cum buckets into my gaping /dev/null.

I’m afraid these results say more about the quality of conversation in this channel than they do about anything else…

Perl book (mini) reviews

Sun, 04 May 2008 21:33:00 +0000

I much prefer reading things in well typeset paperback books than on computer screens. The subject of Perl is no exception. I’ve got quite a few Perl books. Some reviews are in order. I haven’t actually written a book review in many years, so they won’t be very “in-depth”, though.

Oh, and by the way, this, too, is a Perl blog.

Programming Perl

By Larry Wall, Tom Christiansen, and Jon Orwant

Ah, the Camel book. The latest edition is about 7 years old now, but it has stood the test of time. If you only read one Perl book, make it this one. Aside from being a comprehensive and detailed reference on the language, it’s also funny. One of my favorite passages is the start of chapter 10, Packages:

In this chapter, we get to start having fun, because we get to start talking about software design. If we’re going to talk about good software design, we have to talk about Laziness, Impatience, and Hubris, the basis of good software design.

We’ve all fallen into the trap of using cut-and-paste when we should have defined a higher-level abstraction, if only just a loop or a subroutine.*

To be sure, some folks have gone to the opposite extreme of defining ever-growing mounds of higher-level abstractions when they should have used cut-and-paste.† Generally, though, most of us need to think about using more abstraction rather than less.

Caught somewhere in the middle are the people who have a balanced view of how much abstraction is good, but who jump the gun on writing their own abstractions when they should be reusing existing code.‡

――――――――――

* This is a form of False Laziness.

† This is a form of False Hubris.

‡ You guessed it — this is False Impatience. But if you’re determined to reinvent the wheel, at least try to invent a better one.

The book is written for programmers, so if you’ve haven’t programmed before, you should probably start with an easier book. I’ve heard “Learning Perl” is pretty good.

The Perl Cookbook

By Tom Christiansen and Nathan Torkington

Here is another highly useful book. If you read the Camel book and thought “What next?”, then this book is the answer. It’s got 900 pages of recipes for how to do everything from sorting hashes to writing pre-forking TCP servers. Each one of the 22 chapters begins with a few pages of very informative discussion of the problem domain at hand. This book has been extremely useful to me. It saves you a lot of Googling and looking through various Perl man pages. I highly recommend it.

Mastering Regular Expressions

By Jeffrey Friedl

While not strictly a Perl book, it is about regular expressions, which were to a large extent popularized by Perl. Or the other way around. Or both. I’m not sure. But hey, at least the chapter on Perl is the longest one in the book.

Anyway, the book truly lives up to its title. It describes in detail how regular expression engines work, how to write effecient expressions, how programming languages support regexes, and more. Until I read this book, I did not know that there are two main approaches to writing a regular expression engine, a DFA (deterministic finite automaton) and an NFA (nondeterministic finite automaton), or that the fastest way to strip leading and trailing whitespace is (usually) like so:

s/^\s+//;
s/s+$//;

I hadn’t actually learned Perl before getting this book. Perl is used in most of the examples in the book, which is what got me interested in the language.

Mastering Algorithms with Perl

By Jon Orwant, Jarkko Hietaniemi, and John Macdonald

I’m not a computer scientist. Perhaps that’s why I found this book so interesting. It has working Perl code accompanying all the algorithms that are explained in the book, as well as discussions of pertinent CPAN modules. Though I suspect that last part might be a bit outdated, as the book was written almost a decade ago. If you know Perl and would like a hands-on introduction to algorithms, this book is great.

Perl Best Practices

By Damian Conway

I liked this book. I like my code especially clean and readable, and this book has very good guidelines that can help achieve that. The book is a joy to read (it has humour!), and it’s got very useful appendices at the end with quick summaries of all the guidelines. Then, if you want to audit your source code according to some of these (and other) guidelines, you can use the excellent Perl::Critic module.

Perl Hacks

By chromatic, Damian Conway, and Curtis “Ovid” Poe

This one is sort of like The Perl Cookbook, except it focuses more on the process of working with Perl rather than specific solutions to various programmatic problems. As such, it’s not really aimed at beginners. It has many very useful tricks regarding things like customizing your editor for Perl, working with modules, (ab)using the guts of Perl, and debugging. There’s something in it for everyone.

Higher-Order Perl

By Mark Jason Dominus

Now it’s getting interesting. In this book, the author tries to familiarize the reader with ways of programming most common in purely functional languages like Lisp and Haskell. That makes it very different from most Perl books (in a good way). The book is all about “being clever” as the author has said, so you’re bound to learn something from it. I certainly have. The topics covered include recursion, dispatch tables, currying, and parsing, to name a few. There are plans to turn the book into wiki, but I I’m not sure when that’ll happen.

Perl 6 and Parrot Essentials

By Allison Randal, Dan Sugalski, and Leopold Toetsch

This book is an excellent introduction to Perl 6 and Parrot (the virtual machine which will run Perl 6), though I’ve been told that the Parrot bits are a little dated now. I read it in one sitting, it was that exciting. I realize that his book is about programming, and that this statement makes me a total geek. Oh well, there’s no looking back, Perl 6 will be awesome! The first half of the book covers the Perl 6 language, while the second covers the design of Parrot. I didn’t absorb as much as I could have from the second half as I don’t know much about parsing or compilers, but the first half more than made up for it. I really wish I could use all those nifty featues in my code right now. In the meantime, Pugs will have to quence the thirst of those like me who are excited about Perl 6.

Perl 6 Now

By Scott Walters

I didn’t get much out of this book. For one, many things are explained which most Perl users already know, so I flipped over many pages while reading it. Secondly, many of the Perl 6 ideas are illustrated with modules that use source filters, which are known to be unreliable, so you definitely wouldn’t use them in production code.

Catalyst

By Jonathan Rockway

The chapters in this book follow a very practical approach, diving right in and showing you various common ways of using Catalyst. I haven’t written much using this fine web framework, so there isn’t really much more I can say about the content of the book. I can say something about the lack of content though. This book is missing an overview of Catalyst, and a better explanation of how all the parts fits together. Some discussion on the MVC architecture and how Catalyst implements it would have been nice as well. Seeing as the book is quite short, there would be plenty of room for these things.

Perl Medic

By Peter J. Scott

I was not disappointed by this book. It delivers what is promised. Having recently started working on an old codebase, I found the book very useful. Testing, refactoring, benchmarking, debugging; all these things are well laid out by the author. It also has a useful chapter on upgrading code written for older versions on Perl, and discusses how to make use of newer features.

IRC and character encoding

Thu, 01 May 2008 01:44:00 +0000

A while ago, I wrote an IRC logger for POE::Component::IRC, which is an IRC client module for Perl. The main challenge I faced was the issue of character encodings. Since IRC is ripe with clients that use different encodings, messages must be reliably decoded before they are written to a file.

You see, RFC 1459, the standards document describing the IRC protocol, does not regulate the use of character encodings:

2.2 Character codes

No specific character set is specified. The protocol is based on a
set of codes which are composed of eight (8) bits, making up an
octet. Each message may be composed of any number of these octets;
however, some octet values are used for control codes which act as
message delimiters.

Regardless of being an 8-bit protocol, the delimiters and keywords
are such that protocol is mostly usable from USASCII terminal and a
telnet connection.

ASCII uses the first 7 bits. So, from the looks of it, you should only be able to rely on the first seven bits representing an ASCII character, the interpretation of the last bit being anyone’s guess. That’s bad.

For most of IRC’s history, the most popular IRC client has been mIRC. Until recently, mIRC decoded incoming messages using the ANSI code page that was currently being used on the user’s Windows system. This meant that whenever mIRC users wanted to communicate using anything other than ASCII characters, they’d better be using the same code page. In later versions, mIRC decodes incoming messages as UTF-8 if they look UTF-8 encoded, or code page 1252 (used by most Westerners). As for how it does this, I cannot know since mIRC is closed-source.

The open-source client irssi handles the situation similarly. It uses GLib’s g_utf8_validate() function to check if the incoming message is UTF-8 encoded, otherwise it falls back to CP1252 by default. As for XChat, it uses the same GLib function, but if it determines that the message is not UTF-8, XChat decodes the message in a rather novel way. Here is an excerpt from its src/common/text.c:

/* converts a CP1252/ISO-8859-1(5) hybrid to UTF-8                           */
/* Features: 1. It never fails, all 00-FF chars are converted to valid UTF-8 */
/*           2. Uses CP1252 in the range 80-9f because ISO doesn't have any- */
/*              thing useful in this range and it helps us receive from mIRC */
/*           3. The five undefined chars in CP1252 80-9f are replaced with   */
/*              ISO-8859-15 control codes.                                   */
/*           4. Handles 0xa4 as a Euro symbol ala ISO-8859-15.               */
/*           5. Uses ISO-8859-1 (which matches CP1252) for everything else.  */
/*           6. This routine measured 3x faster than g_convert :)            */

How would I handle this in Perl? I don’t want to depend on GLib, and I don’t want to write any C code (requiring the user to have a C compiler). At first I tried using Encode::Detect, but there are two problems with it. It’s an extra dependency, and more importantly, it works heuristically, deciding which character set is being used based on the number of occurences of each character code. As such, it’s only reliable when large amounts of data are involved. Like a whole web page, for example, which is what the code was written for. Then I learned of Encode::Guess, which is included with Perl as of version 5.6.0. The following decodes $line as UTF-8 if Encode::Guess is sure that it’s UTF-8. Otherwise it decodes it as CP1252.

use Encode qw(decode);
use Encode::Guess;

my $utf8 = guess_encoding($line, 'utf8');
$line = ref $utf8 ? decode('utf8', $line) : decode('cp1252', $line);

So far this method has worked flawlessly for me on channels with mixed encodings. However, I don’t know exactly how Encode::Guess works, so I’m not as confident in this method as I could be. Any feedback on this issue would be quite welcome.

literal thoughts

perl6.vim gets more love

Recent history of perl6.vim

Performance

Identifiers

Multiline comments

Heredocs

Setting functions and methods

Metaoperators

Strings and patterns

Grammars

Pod

Folding

Miscellaneous

Testing

__END__

Testing vim syntax files

More docs added

Tagging, FAIL, regexes

Grok refactor

On to the man pages

Lucky 0.13

Half way there

grok 0.09 is out

grok update

First GSoC post

POE::Component::IRC 6.00 is here

Important squashed bugs

New major features

New plugins

Testing

Refactoring

Documentation

Credits

Spicing up IRC with MegaHAL

Perl book (mini) reviews

Programming Perl

The Perl Cookbook

Mastering Regular Expressions

Mastering Algorithms with Perl

Perl Best Practices

Perl Hacks

Higher-Order Perl

Perl 6 and Parrot Essentials

Perl 6 Now

Catalyst

Perl Medic

IRC and character encoding

END