fixed name of this script itself and added "feature" pragma

twitter_displayer.pl

#!/usr/bin/perl
# TWITTER_USERNAME=xxx TWITTER_PASSWORD=xxx plackup -s Twiggy twitter_displayer.pl
use AnyEvent::Twitter::Stream;
use Markapl;
use autobox::Core;
use autobox::Encode;
use feature qw(state);

my $buf = [];

# NOTE: $stream should live outside this PSGI file scope
# Change state to our if you're using perl 5.8
state $stream = AnyEvent::Twitter::Stream->new(
    username => $ENV{TWITTER_USERNAME},
    password => $ENV{TWITTER_PASSWORD},
    method => 'sample',
    on_tweet => sub {
        my $tweet = shift;
        return unless $tweet->{user};
        $buf->unshift($tweet);
        $buf = $buf->slice(0..9) if $buf->size >= 10;
    },
);

sub {
    my $mp = html {
      body {
        ul { $buf->map(sub {
          li {
            b{ $_->{user}->{screen_name} };
            ': ' . $_->{text};
          }
        })}
      }
    };
    return [
        200, 
        [ 'Content-Type', 'text/html; charset=utf-8' ], 
        [ $mp->()->encode('utf8') ],
    ];
};