while( defined( my $item = $iter1->() ) {
    print "1: $item\n";
}

while( defined( my $item = $iter2->() ) {
    print "2: $item\n";
}
while( defined( my $item = $iter2->() ) {
    print "3: $item\n";
}

#outputs:
1: 1
1: 2
1: 3
2: y
2: n
3: 7
3: 14
3: 21
3: 28

##</code><code>##

$nl_iter = NestedLoops( \@Loops ); # some fancy magic for \@Loops

while( my @items = $nl_iter->() ) {
    print join ", " @items;
    print "\n";
}

#outputs:
1, y, 7
1, y, 14
1, y, 21
1, y, 28
1, n, 7
1, n, 14
...
3, n, 21
3, n, 28