-- WO-E222: an actor's state or message must not be (or contain) a traced
-- class — aliased graphs cannot cross shard heaps. Node is traced by
-- inference (self-referential); Box contains it.

class Node {
  next: ?Node
  v: Int
}

class Box {
  head: ?Node
}

class Keeper {
  fn receive(msg: Box) {
    if msg.head == nil { print("empty"); } else { print("full"); }
  }
}

fn main() -> Int {
  let a = spawn Keeper {};
  return 0;
}