void->void feedbackloop FibFeed {
  join roundrobin(0, 1);
  body PeekAdd();
  loop IntPrinter();
  split roundrobin (0, 1);
  enqueue 0;
  enqueue 1;
}

int->int filter PeekAdd {
  work push 1 pop 1 peek 2 {
    push(peek(1) + pop());
  }
}

int->int filter IntPrinter {
  work pop 1 push 1 {
    println(peek((0)));
    push(pop());
  }
}