static <A> A withDeepReturn(IVF1<DeepReturnSite<A>> r) {
  temp new DeepReturnSite<A> site;
  try {
    r.get(site);
  } catch e {
    e = innerException(e);
    if (e instanceof DeepReturn && e/DeepReturn.site == site)
      ret site!;
    else
      rethrow(e);
  }
  null;
}