my $channel = Channel.new();
sub a {
    b();
    gather {
    loop {
        take $channel.poll() // do {
            b();
            $channel.receive();
        }
    }
    }
}

sub b() {
    $channel.send(3);
    $channel.send(4);
}

for a() -> $a {
    say $a;
}
~