interface I {
  in void e();
  behaviour {
    on e: {}
  }
}

interface II {
  in void e();
  in void f();
  out void cb();
  behaviour {
    bool busy = false;
    [!busy]
       on e: busy = true;
    [busy] {
       on e: illegal;
       on inevitable: { cb; busy = false; }
    }
    on f: {}
  }
}

component DirectAndDeferredReply {
  provides I p;
  requires II r;
  behaviour {
    bool busy = false;
    bool direct = false;
    [!busy] {
      on p.e():
	blocking if (direct) {
          r.f();
 	  p.reply();
          direct = !direct;
        }
	else {
          r.e();
          busy = true;
          direct = !direct;
        }
      on r.cb: illegal;
    }
    [busy] {
      on p.e(): illegal;
      on r.cb():
         { p.reply(); busy = false; }
    }
  }
}