$ perl -d:Trace dalek
>> dalek:4: $| = 1;
>> dalek:48: my $phaser = Phaser->new('Exterminator');
>> dalek:11:     my ($class, $name) = @_;
>> dalek:12:     my  $self = {};
>> dalek:13:     $self->{name} = $name;
>> dalek:14:     return bless $self, $class;
>> dalek:49: my $enemy  = Dalek ->new($phaser);
>> dalek:22:     my ($class, $phaser_ref) = @_;
>> dalek:23:     my  $self = {};
>> dalek:24:     $self->{phaser} = $phaser_ref;
>> dalek:25:     return bless $self, $class;
>> dalek:51: print 'My enemy is a ',        ref $enemy,
My enemy is a Dalek with a phaser named Exterminator
>> dalek:53: print $enemy->exterminate();
>> dalek:30:     return 'Firing phaser ' . $_[0]->{phaser}->{name} . "\n";
Firing phaser Exterminator
>> dalek:55: print 'My enemy must ', $enemy->obey(),
>> dalek:35:     return 'obey';
>> (eval 1)[dalek:55]:1: $enemy->exterminate()
Use of uninitialized value in print at dalek line 55.
My enemy must obey. His phaser is named Exterminator. Bye!
>> dalek:40:     my ($self) = @_;
>> dalek:41:     print 'DESTROYing a Dalek (phaser is ', $self->{phaser}->{name}, ")\n";
DESTROYing a Dalek (phaser is Exterminator)
>> dalek:42:     $self->{phaser}->{name} = 'Obliterator';
>> dalek:60: print $@ if $@;
Can't call method "exterminate" on an undefined value at (eval 1)[dalek:55] line 1.
>> dalek:62: print 'The phaser is named ', $phaser->{name}, "\n";
The phaser is named Obliterator