svoid withCancelPoint(VF1<CancelPoint> r) {
  temp CancelPoint cp = newCancelPoint();
  try {
    callF(r, cp);
  } catch e {
    e = innerException(e);
    if (!(e instanceof CancelToCancelPoint && e/CancelToCancelPoint.cp == cp))
      rethrow(e);
  }
}

svoid withCancelPoint(IVF1<CancelPoint> r) {
  temp CancelPoint cp = newCancelPoint();
  try {
    r.get(cp);
  } catch e {
    e = innerException(e);
    if (!(e instanceof CancelToCancelPoint && e/CancelToCancelPoint.cp == cp))
      rethrow(e);
  }
}