// Example of livelock due to endless iteration.
// (List Iterator is not guaranteed to reach list end.)

interface Iterator
{
  extern element $int$;
  enum end {yes, no};
  in end next(element elmt);

  behaviour
  {
    end done = end.no;
    on next: [done.no] {reply(done); done = end.yes;}
    on next: {reply(done);}
  }
}

interface IList
{
  in void step();

  behaviour
  {
    on step:{}
  }
}

component List
{
  provides IList pp;
  requires Iterator list;

  behaviour
  {
    Iterator.end head()
    {
      Iterator.element elmt;
      Iterator.end it = list.next(elmt);
      return it;
    }

    void tail(Iterator.end done)
    {
      if (done == Iterator.end.no)
      {
        Iterator.element elmt;
        done = list.next(elmt);
        tail(done);
      }
    }

    on pp.step():
    {
      Iterator.end it = head();
      tail(it);
    }
  }
}