gistfile1.txt

    method start-processes {
        my $p = Promise.new;
        $p.keep(1);

        for @!processes -> $level {
            my @not-started := $level.list.grep({ !$_.started });
            $p = $p.then: {
                my @promises := @not-started.map: { $_.start }
                await Promise.allof(@promises) if @promises;
            }
        }

        $p;
    }