{
    my %position;
    sub elements(\@;$) {
        my $arr = shift;
        my $amt = shift || 1;        
        if(not exists $position{$arr} or $position{$arr} < $#$arr) {
            my ($start, $next) = ($position{$arr}, $position{$arr} += $amt);
            return @$arr[$start .. $next - 1];
        }
        else {
            delete $position{$arr};
            return;
        }
    }
}