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Archive for the ‘Programming’ Category

Relative Popularity

Posted in Perl on March 14, 2011| 2 Comments »

It’s hard to objectively measure Perl’s popularity compared to Python or Ruby. Even before nerds-central used job availability as a measurement, the ease of finding a job was a key requirement for me.

Who cares if I love Ruby if I can’t use it for the 10 hours a day I’m working?

Anecdotal evidence

In the last twelve years I’ve had no difficulty finding plenty of Perl work. In the past couple of years, I’ve had a few calls about Python jobs, but probably ten times fewer than the number of Perl calls I get. Hold the front page – Perl is ten times more popular than Python.

Well, no. Of course I get a lot more Perl calls. I’m a Perl programmer, and my résumé mentions Perl all over the place. Anyone calling about Python must really be desperate!

But I notice that a lot of Python programmers working at Python-centric firms apply similar logic. All the folks they work with do Python, clearly no-one does Perl anymore. Thank goodness – Python is finally the winner it always deserved to be.

Why do people care?

Network effects are important. All other things being equal, a language with more users will get more libraries, will have more companies using it, will get more users, will get more libraries, etc. vs a language with fewer users. And, popularity aside, none of the big three scripting languages has a huge advantage over the others.

Except of course that Perl was the first mover.

So, what can you do if you don’t have a real advantage you can point to? That’s right – you trash-talk the leader, hope you can convince enough people there is a real problem and when they jump ship hopefully you’ll be the one left with the positive feedback loop.

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“I don’t know Perl but…”

Posted in Perl on March 7, 2011| 11 Comments »

Michael Murdock doesn’t believe in anti-Perlism. Of course he has to indulge in some of his own.

“Every developer with whom I have discussed this issue says roughly the same thing: It’s very difficult to pick up a piece of Perl code, even when it’s your own, and be able to quickly understand the gist of it.”

I find it hard to understand French but I don’t go round saying it is a speak-only language.

You couldn’t make it up. Or was the irony intentional?

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Replacing sed

Posted in Perl, tagged , on February 28, 2011| 6 Comments »

I’ve spoken about processing logfiles with perl previously. Occasionally though, I still reach for sed.

Say I have a logfile that looks like this:

[ <timestamp> ] : somefunc()
[ <timestamp> ] : interesting line 1
[ <timestamp> ] : interesting line 2
... 1000s of lines
[ <timestamp> ] : somefunc()
[ <timestamp> ] : interesting line 1
[ <timestamp> ] : interesting line 2
... 1000s of lines

Picking out lines following a pattern is easy with sed – p prints the current match and n takes the next line.

$ < log.txt sed -n '/somefunc()/ {p;n;p;n;p}'
[ <timestamp> ] : somefunc()
[ <timestamp> ] : interesting line 1
[ <timestamp> ] : interesting line 2
[ <timestamp> ] : somefunc()
[ <timestamp> ] : interesting line 1
[ <timestamp> ] : interesting line 2

My first attempt to replace that with perl looks a bit ugly

< log.txt \
perl -ne 'if (/somefunc\(\)/) {print; print scalar(<>) for (1..2)}'

I’m not that happy with the module I came up with to hide the messiness either.

package Logfiles;

require Exporter;
our @ISA = qw(Exporter);
our @EXPORT_OK = qw(process);

use Carp;

sub process (&$;$)
{
    my ($sub, $regex, $lines) = @_;
    $lines ||= 0;
    return unless /$regex/;
    if (! $lines) {
        $sub->($_);
    } else {
        croak "process() arg 3 not ref ARRAY" unless ref($lines) eq 'ARRAY';
        my $line = 0;
        my @lines = @$lines;
        while (1) {
            if ($lines[0] == $line) {
                $sub->($_);
                shift @lines;
            }
            ++$line;
            last if ($line > $lines[0] or (not @lines));
            $_ = <>;
        }
    }
}

1;

But at least my typical spelunking looks a little cleaner now.

< log.txt perl -MLogfiles=process -ne \
    'process { print } qr/somefunc\(\)/, [0..2]'

Any suggestions on how to improve this (without reverting to sed)?

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Moose Types

Posted in Perl, tagged , on February 21, 2011| 1 Comment »

Rants about generalisations notwithstanding, I’m a fan of typeful programming (I’m sure I’d love Ada). For a script that will be moderately complex, I like to sit down and think about the types I’m going to use before I start.

Any library that will enable me to specify my types more precisely and concisely is obviously a win.

And speaking of Moose…

Moose has a bunch of methods to specify your types and a built-in type hierarchy available that you can build off.

Abusing an example I’ve used before:

use Moose;
use Moose::Util::TypeConstraints;
use MooseX::Params::Validate;

subtype 'LegalDrinkingAge'
    => as 'Int'
    => where { $_ >= 18 }
;

coerce 'LegalDrinkingAge'
    => from 'Int'
    => via { 1 }
;

sub can_legally_drink
{
    my $age = pos_validated_list(
        \@_,
        { isa => 'LegalDrinkingAge' },
    );

    return 1;
}

print can_legally_drink(18), "\n";
print can_legally_drink(17), "\n";

Checking for a LegalDrinkingAge type here is obviously the wrong thing to do, but for the purposes of the example it will do.

The resulting error is fine, if a little ugly.

$ perl5.10.1 moose-types.pl
1
Parameter #1 ("17") to main::can_legally_drink did not pass the 'checking type constraint for LegalDrinkingAge' callback
 at /u/packages/lib/perl5/site_perl/5.10.1/MooseX/Params/Validate.pm line 168
        MooseX::Params::Validate::pos_validated_list('ARRAY(0x976ce40)', 'HASH(0x911b6f8)') called at moose-types.pl line 24
        main::can_legally_drink(17) called at moose-types.pl line 33

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Recommendation: Learn Regular Expressions

Posted in Programming, tagged , on February 14, 2011| 4 Comments »

Zawinski not withstanding, regular expressions are a hugely useful addition to a programmer’s toolbox. I learnt about them from Jeffrey Friedl’s excellent Mastering Regular Expressions1.

Why am I thinking about this now?

So, I was asked to review a perl script and it was pretty good, apart from the fact that the main regex2 didn’t quite match all the expected patterns.

The line to match was:

<some_tag>quickbrownfox</some_tag>

Other valid values within the tags included quick,brown,fox or quick brown fox.

And the regex in the script was:

m{\<some_tag\>(\w+)\<\/some_tag\>}

As you can see, there were also a few unnecessary backslashes.

I suggested [^<]+ instead of \w+ with my reasons.

The developer changed the regex to:

m{\<some_tag\>\s*(\w+)\s*\<\/some_tag\>}

Okay slightly better, but it still didn’t match all the possibilities.

I pointed out a valid pattern it didn’t match and asked again for [^<]+.

This was the result:

m{\<some_tag\>(\s*[^<]+\s*)\<\/some_tag\>}

Okay, fine. The \s space matchers are redundant, but at least it covers everything.

So basically, if you find yourself writing a bunch of regex regularly, and you don’t really understand it, you could do worse than read Friedl’s book.

1. Not an affiliate link

2. I know… "parsing" xml with regex will unleash cuthulu or something. It’s not my script.

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Why did Google choose Python?

Posted in Perl, tagged , , , on January 31, 2011| 36 Comments »

I wouldn’t get into google (their interviews don’t select for my brand of genius). But that’s fine as I wouldn’t be able to write perl there anyway.

I was trying to think of a few reasons why Google would have chosen Python over Perl as their primary scripting language. A number of the ones I came up with are less relevant than they used to be.

Python integrates better with C++

Boost.Python promises seamless interoperability between the two languages. It has been a while since I’ve been tempted to embed a scripting language in my C++ apps so I’m not sure what the counterpart is in Perl if any.

Python "threads"

Back in the day, these were better than the Perl offering. More recently, on Unix at least; with Coro, AnyEvent, Twisted, etc. it’s a wash.

Windows Implementation

A few years ago, the various Perl Windows implementations were not very high quality. Strawberry Perl has changed all that though. It’s awesome.

Jython et el.

Was Jython around when Google was choosing Python? I guess it was.

Perl (5) hasn’t escaped its VM as well as Python and Ruby. Having said that, the Jythons and JRubys of the world are always second class citizens compared to the original C VM as no-one can be bothered to rewrite all the C extensions.

Easier to avoid making a mess as a secondary language?

Experts in either language can write clean, efficient code. But what about folks who are expert in C++ and Java and use either Perl or Python on the side and only occasionally?

I think such usage for a large system will result in unwieldy code in either language, unless the large system is curated by experts, but for small to medium systems in the absence of experts, python may have the edge.

Rabid anti-Perlism

Even smart folks I know seem to think Perl is lacking in some way in comparison to Python. I haven’t managed to get them to enumerate any reasons though so I figure they are speaking from a position of ignorance. This could have been the case for the folks making the decisions for google too or, more likely, they may have considered some of the other reasons on my list.

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Ironman Perl and Google Reader

Posted in Perl, tagged , on January 24, 2011| 4 Comments »

I’m subscribed to Ironman Perl’s full Atom feed in google reader. Most posts display nicely, especially if they use embedded css like mine (boo – bad practice Jared) 😉

However, it seems as though there is some strange interaction between certain feeds, Ironman and Google Reader. Take a look at this post from Mark Fowler:

Ironman Perl in Google Reader

Everything has been stripped, even the paragraphs and line feeds.

At first I thought it was only feeds burned with feedburner, but it isn’t as simple as that.

Another minor nit: detection of the word perl isn’t done at the beginning and end of the words. Hence, properly would cause a post to show up in the feed, even if it has nothing to do with perl.

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More on REPLs

Posted in Perl, tagged on January 21, 2011| Leave a Comment »

Most people who think they want a REPL don’t actually want a REPL. It is what a REPL can give them – a Perl (or a Python or a Ruby) machine to which you can add functionality a bit at a time.

For an emacser like me, a sufficiently flexible command-line REPL can give me that incrementally adaptable machine. For most people, a graphical interface to that machine would probably be better.

And thanks, folks, for the suggestions of REPLs to take a look at. No doubt I’ll get around to evaluating a few of them at some point.

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The Problem with Scripting Language REPLs

Posted in Perl, tagged , on January 13, 2011| 12 Comments »

I figured out what the problem is with Devel::REPL and the command line REPLs provided by Python and Ruby – evaluation is not a separate step. When I press enter, I’m forced to evaluate the current line.

Yes, you say, that is what REPL means – Read, Evalute, Print, Loop. Evaluate comes after Read.

In reality, usable REPLs, such as Emacs1, let you control when the read evaluate print sequence happens. I can craft the most beautiful function I can think of. Better still, if I change my mind, I can easily modify the function and redefine it with a keystroke. Well, a key chord at least.

In contrast, with Devel::REPL, once I have pressed enter, changing my mind is painful. Integrating it with Emacs comint will probably alleviate a lot of that pain.

Or better yet, as Anonymous recommends, I should take a look at Sepia or PDE which already have emacs integration. Having said that, basic integration is, what, 20 lines of emacs-lisp?

1. Yes, Emacs is a REPL. Kinda.

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Devel::REPL – a Perl Read Eval Print Loop

Posted in Perl, tagged , on January 4, 2011| 4 Comments »

I’m somewhat amused at one of the more recent comments here – Nathan L. Walls defends his "choice" of Ruby with some very woolly justifications (emphasis mine):

"Ruby’s community feels more vibrant. No, not something you can measure. It is a feeling."

"Yes, there are equivalents in Perl, but they are far rougher. Again, not really measurable, but a feeling."

Of course, his day job is still writing Perl. Moving swiftly on…

Devel::Repl

The main thing I got out of the comment apart from a chuckle, was it motivated me to look at Devel::REPL.

One of the other main tools in my toolbox is emacs and when writing emacs lisp, I make full use of the REPL. But I’ve never even wanted an equivalent in Perl.

One cpanm invocation later and I’m ready.

Wait, no I’m not. I copied Caleb’s repl.rc config to make it more usable. I added MultiLine::PPI which resulted in a bunch of errors at start-up. It turns out I need to add File::Next and B::Keywords separately.

$ cpanm File::Next
$ cpanm B::Keywords

Okay, now I’m good to go.

First REPL session

$ jared@localhost $ re.pl
$ sub f
$ {
> say 'h';
> say 'hello';
> }
h
hello
1 $ f();
Runtime error: Undefined subroutine &Devel::REPL::Plugin::Packages::DefaultScratchpad::f called at (eval 290) line 5.
$ sub f {
> say 'h';
> say 'hello';
> }
$ f();
h
hello
1 $

It still isn’t quite perfect. But to be honest, I find it (and the Python and irb REPLs) pretty useless. I probably need to look into integrating it with emacs comint.

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