#!/usr/bin/pugs

use v6;

sub NL2 (++@loop) {
    coro {
        given (@loop.elems) {
            when 0  { yield [] }
            when 1  { @loop[0].map:{ yield [$^first] }; yield undef }
            default {
                for @loop[0] -> $first {
                    my &rest = NL2(loop => @loop[1..Inf]);
                    my @rest;
                    while @rest = rest() {
                       yield [$first, @rest];
                    }
                }
                yield undef;
            }
        }
    }
}


my &iter = NL2(loop => ([0..2], [3..5], [6..8]));
my ($cnt, $item);

say "ITER {++$cnt}: {$item.perl}" while $item = iter;