use strict;
use warnings;

my $ob1 = foo->new('alpha');
my $ob2 = foo->new('beta');

$ob1->write;
$ob2->write;

package foo;
    sub new{
        my $class = shift;
        my $subclass = shift;
        return bless {}, $subclass;
    }

package alpha;
    sub read{
        return "Alpha\n";
    }
    sub write{
        my $self = shift;
        print $self->read;
    }

package beta;
    sub read{
        return "Beta\n";
    }
    sub write{
        my $self = shift;
        print $self->read;
    }