use v6;

sub NestedLoop (++@loop, +%opt, +$code) returns Ref{
    my @pos = 0 xx (@loop.elems - 1), -1;
    return sub {
        if ++@pos[-1] > @loop[-1].end {
            for reverse 0 .. @pos.end - 1 -> $i {
                next if @pos[$i] == @loop[$i].end;
                ++@pos[$i];
                @pos = (@pos[0..$i], 0 xx (@pos.end - $i)) and last;
            }
        }
        return () if @pos[-1] > @loop[-1].end;
        return map -> $i { @loop[$i][@pos[$i]] } 0 .. @pos.end;
    };
};

my $next = NestedLoop(loop => ([0..2], [0..2], [0..2]));
my @group;
while @group = $next() { say ~@group; }