class Hello(Print,Stop) extends Chain {
  Print p;
  method continue(Passive accumulator) {
    p = new Print(Passive,Chain);
    p.next = new Stop(Passive);
    goto p.continue(new "Hello, world!"(Passive));
  }
}

class PrintTwice(Print) extends Print {
  Print p1;
  Print p2;
  method continue(Passive accumulator) {
    p2 = new Print(Passive,Chain);
    p2.next = next;
    p1 = new Print(Passive,Chain);
    p1.next = p2;
    goto p1.continue(accumulator);
  }
}

class HelloProgram(Hello,PrintTwice,Chain,Stop) extends Program {
  Hello h;
  method continue(Passive accumulator) {
    h = new Hello(Passive,Chain,PrintTwice,Stop);
    goto h.continue(new 0(Passive));
  }
}