#!/usr/bin/perl
use strict;
{   
    package person;
    #basic person
    sub new {
    	my ($class, $name) = @_;
    	my $self  = { 'name' => $name };
    	bless $self, $class;
    	return $self;
    }

    sub tellName  {
            my ($self) = $_[0];
            return $self->{'name'};
    }

    sub introduce {
            my ($self) = $_[0];
            print "Hello, I'm ", $self->tellName(), "\n";
    }
}

{
    package child;
    #person + ability to know parents
    our @ISA = qw(person);    # inherits from person

    sub new {
        my ($class, $name, $mom, $dad) = @_;
    	my $self = $class->SUPER::new($name);
        $self->{mom} = $mom;
        $self->{dad} = $dad;
    	bless $self, $class;
    	return $self;
    }

    sub introduce {
            my($self)=$_[0];
            $self->SUPER::introduce();
            for (qw/mom dad/) {
                if ($self->{$_}) {
                    print "Here's my $_: ",   $self->{$_}->tellName();
                }
            }
    }
}    

package main;

my $mom = new person("Alice");
$mom->introduce();      # that time it works.

print "\n";

my $son = new child("Fred", $mom);
$son->introduce();