package Turtle;

sub new
{
my $class=shift;
my $self={};
@{$self}{qw(x y theta mirror)}=@_;
bless $self, $class;
}

sub forward
{
my $self=shift;
my ($r, $what)=@_;
my ($newx, $newy)=($self->{x}+$r* sin($self->{theta}),
                   $self->{y}+$r*-cos($self->{theta}));
if ($what)
	{
	&$what($self->{x}, $self->{y}, $newx, $newy);	# Do something related to motion
	}												# According to the coderef passed in
($self->{x}, $self->{y})=($newx, $newy);			# And change the old coords
}

sub turn
{
my $self=shift;
my $dtheta=shift;
$self->{theta}+=$dtheta*$self->{mirror};
}

sub state
{
my $self=shift;
@{$self}{qw(x y theta mirror)};
}

sub setstate
{
my $self=shift;
@{$self}{qw(x y theta mirror)}=@_;
}

sub mirror
{
my $self=shift;
$self->{mirror}*=-1;
}

"Turtle.pm";