static long stupidFib_collab(ICollab collab, int n) {
  new Var<Long> var;
  stupidFib_collab(collab, n, result -> {
    var.set(result);
    collab.done();
  });
  collab.run();
  ret var!;
}

svoid stupidFib_collab(ICollab collab, int n, LongConsumer continuation) {
  if (n < 3) ret with continuation.accept(1L);
  
  LongPairCollector collector = new {
    void complete(long a, long b) {
      continuation.accept(a+b);
    }
  };
  
  collab.addWork(-> stupidFib_collab(collab, n-1, collector.setterForA()));
  collab.addWork(-> stupidFib_collab(collab, n-2, collector.setterForB()));
}

Began life as a copy of #1035559