interface ihello {
  in void hello();
  in void cruel();
  behaviour {
    on hello: {}
    on cruel: {}
  }
}

interface iworld {
  out void world();
  behaviour {
    on inevitable: world;
  }
}

component hello_block {
  provides ihello h;
  requires iworld w;
  behaviour {
    bool blocked=false;
    [!blocked] {
      on h.hello(): blocking blocked=true;
      on w.world(): {}
    }
    [blocked] {
      on w.world(): {h.reply (); blocked=false;}
      on h.hello (): {}
    }
    on h.cruel(): {}
  }
}