#!/usr/bin/perl

use strict;
use warnings;

use Language::AttributeGrammar;

package Leaf;

sub new{
  return bless { value => $_[1] }, 'Leaf';
}

package Branch;

sub new{
  return bless { value => $_[1], _list => undef }, 'Branch';
}

sub add_child{
  my $self = shift;
  push @{ $self->{_list} }, @_;
  return $self;
}

sub list {
  if (@_) {
    bless { head => $_[0], tail => list(@_[1..$#_]) }, 'Cons';
  }
  else {
    bless {}, 'Nil';
  }
}

sub children{
  return list( @{ $_[0]->{_list} });
}