The spin() method is the most complex as it does all the real work of simulating the slot machine (the object itself just stores the current state of the machine and ancillary data). The first thing we will need to do is figure out how much is being bet on this spin:

    sub spin {
        my $self = shift;
        my $bet  = $self->bet(shift);
        $bet = < $bet < 3? $bet : 3;
        $bet = $bet < $self->credits()? $bet : $self->credits();

We obtain the $bet value by calling the bet() method with the second argument (if any). We then check that the bet doesn’t exceed 3, and finally check that it doesn’t exceed our remaining credits. Next we get the spin result itself:

        my $spin = join('', map{$symbols[rand @symbols]}1..3);
        $self->{spin} = $spin;

Here we have used map() to create a list of three random elements from the @symbols array and joined them into a single string, and we set the ‘spin’ attribute of the object. Next we need to calculate the payoff for this spin:

        my $payoff = 0;
        if($spin =~ /^(\d)\1\1$/){
            $payoff = $payoff{$spin}->($bet);
        } elsif ($spin =~ /^[123][123][123]$/) {
            $payoff = $payoff{any}->($bet);
        }

Here we first check if the spin contains three matching digits (using a regex), and if so we call the subroutine from the %payoff hash to obtain the payoff for that spin. The special case of ‘any’ is taken care of by the elsif clause. Lastly, we need to adjust the attributes:

        $self->{credits} -= $bet;
        $self->{credits} += $payoff;
        $self->{paid}     = $payoff;
        $self->{win}      = $payoff;
    }

We first subtract the $bet amount from the credits, then add any payoff (we could have done this in one step). Then we set the ‘paid’ attribute to equal the current payoff, and finally, we set the ‘win’ attribute to the payoff as well. Why? if the payoff is zero, then the win will be false, if there is a payoff, then the value will be true. So, rather than setting it to 0 or 1, we simply set it to the payoff itself.

Now we have a complete object oriented slot module. The complete module is:

    package Slot;
    use strict;
    my %payoff = (
        "777"  => sub {$_[0] * 500},
        "333"  => sub {$_[0] * 80},
        "222"  => sub {$_[0] * 20},
        "111"  => sub {$_[0] * 5},
        "any"  => sub {$_[0] * 2},
        "000"  => sub {$_[0] * 1},
        );

    my @symbols = (0,7,0,3,0,2,0,1);

    sub new {
        my $class   = shift;
        my $credits = shift || 100;
        my $self  = {credits => $credits,
                     bet     => 1,
                     win     => 0,
                     paid    => 0,
                     spin    => undef,
                    };
        bless $self, $class;
    }

    sub credits {
        my $self = shift;
        $self->{credits};
    }
    sub bet {
        my $self = shift;
        $self->{bet} = shift||$self->{bet};
    }

    sub spin {
        my $self = shift;
        my $bet  = $self->bet(shift);
        $bet = $bet < 3? $bet : 3;
        $bet = $bet < $self->credits()? $bet : $self->credits();
        my $spin = join('', map{$symbols[rand @symbols]}1..3);
        $self->{spin} = $spin;
        my $payoff = 0;
        if($spin =~ /^(\d)\1\1$/){
            $payoff = $payoff{$spin}->($bet);
        } elsif ($spin =~ /^[123][123][123]$/) {
            $payoff = $payoff{any}->($bet);
        }
        $self->{credits} -= $bet;
        $self->{credits} += $payoff;
        $self->{paid}     = $payoff;
        $self->{win}      = $payoff;
    }

    sub display_results {
        my $self = shift;
        print join(" ", split //, $self->{spin}),"\n";
        if ($self->{win}){
            print "Winner paid: $self->{paid} credits!!\n\n";
        } else {
            print "Better luck next time\n\n";
        }

    }
    1;
    __END__

And the interactive test script is:

    #!/usr/bin/perl -w
    use strict;
    use Slot;
    my $slot = Slot->new(100);
    while(1){
        my $credits  = $slot->credits();
        my $curr_bet = $slot->bet();
        last if $credits < 1;

        print "You have $credits remaining: max bet is 3\n";
        print "Enter your bet [$curr_bet]: ";

        chomp(my $bet = <STDIN>);
        last if $bet eq 'q';
        $bet ||= $curr_bet;

        $slot->spin($bet);
        $slot->display_results();
    }

    print "Game Over\n";
    print "You have ", $slot->credits(), " remaining\n";
    print "Thank you for playing\n";
    __END__

I have played a few times and always seem to lose my credits in a short time — so I guess it’s just like the real thing :-)