use strict;
use warnings;


{ 
    package Taxon;
    sub new { bless {nodes=>[]}, shift; };
	
    sub add_node {
	   my $self = shift;
	   my $node = shift;
	   return 1 if $self->has_node($node);
	   push @{$self->{nodes}}, $node;
	   $node->set_taxon($self);
    }

	sub has_node  { 
	    my $self = shift;
	    my $node = shift;
		return grep { $_ eq $node } $self->get_nodes();
	}
	
	sub get_nodes { @{shift->{nodes}} };
}

{ 
    package Node;
    
	sub new { bless {_taxon=>''}, shift; };
	
	sub taxon {
	   my $self = shift;
	   return $self->{'_taxon'};
	}
	
    sub set_taxon {
	   my $self  = shift;
	   my $taxon = shift;
	   return if $self->{'_taxon'} eq $taxon;
	   $self->{'_taxon'} = $taxon;
	   $self->{'_taxon'}->add_node($self);
    }
}

my $node  = new Node;
my $taxon = new Taxon;
print '$node->taxon() = ', $node->taxon(), "\n";
print '$taxon->get_nodes() = ', $taxon->get_nodes(), "\n";

$node->set_taxon($taxon);
print '$node->taxon() = ', $node->taxon(), "\n";
print '$taxon->get_nodes() = ', $taxon->get_nodes(), "\n";

$node  = new Node;
$taxon = new Taxon;
print '$node->taxon() = ', $node->taxon(), "\n";
print '$taxon->get_nodes() = ', $taxon->get_nodes(), "\n";

$taxon->add_node($node);
print '$node->taxon() = ', $node->taxon(), "\n";
print '$taxon->get_nodes() = ', $taxon->get_nodes(), "\n";


##</code><code>##

use strict;
use warnings;


{ 
    package Taxon;
    sub new { bless {nodes=>[]}, shift; };
	
    sub add_node {
	   my $self = shift;
	   my $node = shift;
	   $self->_add_node($node);
	   $node->_set_taxon($self);
    }
    
	sub _add_node {
	   my $self = shift;
	   my $node = shift;
	   return 1 if $self->has_node($node);
	   push @{$self->{nodes}}, $node;
    }

	

	sub has_node  { 
	    my $self = shift;
	    my $node = shift;
		return grep { $_ eq $node } $self->get_nodes();
	}
	
	sub get_nodes { @{shift->{nodes}} };
}

{ 
    package Node;
    
	sub new { bless {_taxon=>''}, shift; };
	
	sub taxon {
	   my $self = shift;
	   return $self->{'_taxon'};
	}
	
    sub set_taxon {
	   my $self  = shift;
	   my $taxon = shift;
	   $self->_set_taxon($taxon);
	   $taxon->_add_node($self);
    }

    sub _set_taxon {
	   my $self  = shift;
	   my $taxon = shift;
	   $self->{'_taxon'} = $taxon;
    }
	
}

my $node  = new Node;
my $taxon = new Taxon;
print '$node->taxon() = ', $node->taxon(), "\n";
print '$taxon->get_nodes() = ', $taxon->get_nodes(), "\n";

$node->set_taxon($taxon);
print '$node->taxon() = ', $node->taxon(), "\n";
print '$taxon->get_nodes() = ', $taxon->get_nodes(), "\n";

$node  = new Node;
$taxon = new Taxon;
print '$node->taxon() = ', $node->taxon(), "\n";
print '$taxon->get_nodes() = ', $taxon->get_nodes(), "\n";

$taxon->add_node($node);
print '$node->taxon() = ', $node->taxon(), "\n";
print '$taxon->get_nodes() = ', $taxon->get_nodes(), "\n";