Playing with dot Perl.

Well, today's the day we play that silly game with the clocks. So, what to do with that extra hour? How about play around with a dot Perl?

That thread happened last week and it also showed up on $reddit, but somehow I missed it. Of course, as soon as I saw it, I had to try it!

mkdir perlgit
cd perlgit
git clone git://perl5.git.perl.org/perl.git
cd perl
git checkout -b leonbrocard/dot origin/leonbrocard/dot
sh Configure -de -Dusedevel -Dprefix=$PERLBREW_ROOT/perls/perl-5.15-dot
make
make test
make install

Wait, how come all the executables have the api_version on the end?

cd $PERLBREW_ROOT/perls/perl-5.15-dot/bin/
for file in *5.15.4; do 
  ln $file $(echo $file | sed 's/5.15.4$//')
done

Alrighty then, let's try it!

$ perlbrew switch perl-5.15-dot
$[ used in numeric lt (<) (did you mean $] ?) 
 at /loader/0x17f9100/App/perlbrew.pm line 1047.

Huh. I guess perlbrew doesn't like a name that doesn't end in a version number? No matter. Pressing on.

$ perl -E 'say "con" ~ "cat"'
syntax error at -e line 1, near ""con" ~"
Execution of -e aborted due to compilation errors.

Rats! The -E flag didn't enable the new dot feature.

$ perl -Mfeature=dot -E 'say "con" ~ "cat"'
concat

Hooray! Okay, how about that dot? Let's try using an OO module. Here's a little script that uses HTTP::Tiny to grab the Futurama quote from the Slashdot header (essentially, it's doing curl -s -I slashdot.org | grep 'X\-\(Fry\|Bender\)').

#!/usr/bin/env perl

use v5.15.4;
use warnings;
use feature qw(dot);
use HTTP::Tiny;

my $url = shift // 'http://slashdot.org/';

my $response = HTTP::Tiny.new.request('HEAD', $url);

# Oops! Dot doesn't interpolate.
# 
# die "Error $response.{status}: $response.{reason}"
#     unless $response.{success};

die 'Error ' ~ $response.{status} ~ ': ' ~ $response.{reason}
    unless $response.{success};

my %headers = %{$response.{headers}};

foreach (qw(fry bender)) {
    my $key = "x-$_";
    say "\u$_: $headers{$key}" if exists $headers{$key};
}

Aw, the dot didn't interpolate. I wanted to write that commented out bit, but instead I had to concatenate strings...yuck! It works, though

$ ./usedotperl.pl
Bender: Curse you, merciful Poseidon!

$ ./usedotperl.pl foo
Error 599: Internal Exception at ./usedotperl.pl line 17.

I don't think it really looks any nicer, but it is easier to type. The thing I hate about -> is having to type an unshifted character followed by a shifted character. I had the same complaint about comments in C in the old days (I switched to // just as soon as I could).

Anyway, it's fun to play with! If this feature ever makes it into Perl (unlikely, given the responses on p5p), I think interpolation has to be made to work. Also, I would want both -E and 'use v5.15;' (or whatever) to enable dot automatically.