gistfile1.pl

package Objects::Document;

use 5.010_001;
use strict;
use warnings;

our $VERSION = 1;

use Moose;
use Moose::Util::TypeConstraints;

subtype 'SpokenLanguage'
    => as 'Str'
    => where { $_ eq 'fr' || $_ eq 'en' }
    => message { 'known spoken languages: en, fr' };

has 'name' => (
    is => 'ro',
    isa => 'Str',
    required => 1,
);

has 'written_in' => (
    is => 'ro',
    isa => 'SpokenLanguage',
);

no Moose;
__PACKAGE__->meta->make_immutable;
1;