### an element in the bag
sub new {
    my $class = shift;
    $self = { nextelement => undef, data => undef };
     
    bless $self, $class;
}
sub setNext {
    my ($self, $el) = @_;
    $self->{nextelement} = $el;
}
sub setData {
    my ($self, $d) = @_;
    $self->{data} = $d;
}