package Animal;

sub new {
   return bless {}, shift;
}

sub to_string {
   die "pure virtual\n";
}

1;

package Animal::Dog;

use base qw/Animal/;

sub to_string {
   return "Hund";
}

1;

package Animal::Cat;

use base qw/Animal/;

sub to_string {
   return "Katze";
}

1;

package Animal::Mouse;

use base qw/Animal/;

sub to_string {
   return "Maus";
}

1;

package Animal::Farm;

sub new {
   return bless {}, shift;
}

sub add {
   my $self = shift;
   if(@_ > 1) {
      $self->add($_) foreach @_;
   } else {
      my $animal = shift;
      die "Is not an animal!" unless $animal->isa('Animal');
      $self->{animals} ||= [];
      push @{ $self->{animals} }, $animal;
   }
}

sub to_string {
   my $self = shift;
   $self->{animals} ||= [];
   return join ' ', map { $_->to_string } @{ $self->{animals} };
}

1;

# hier beginnt das script

#!/usr/bin/perl

use strict;

my $farm = Animal::Farm->new;
$farm->add(Animal::Dog->new);
$farm->add(Animal::Cat->new, Animal::Mouse->new);

my $template = HTML::Template::Compiled->new (
   filename => $tmpl_file,
   path => $mein_pfad,
   use_query => 1
);

$template->param( farm => $farm );

<%= farm.to_string %>