# Impure
sub walk_and_do
{
    my $self = shift;

    foreach my $child (@{$self->children})
    {
        return 0 unless $child->walk_and_do;
    }

    return 0 unless $self->do_my_stuff;

    return 1;
}

#####

# Pure
sub walk_and_do
{
    my $self = shift;

    my $rc = 1;
    foreach my $child (@{$self->children})
    {
        $rc = $child->walk_and_do;
        last unless $rc;
    }

    unless ($rc)
    {
        $rc = $self->do_my_stuff;
    }

    return $rc;
}