svoid assertDoublesVeryClose(S msg default "", double x, double y, double threshold) {
  if (abs(x-y) > threshold)
    fail(msg, x, y);
}

svoid assertDoublesVeryClose(IF0<S> msg, double x, double y, double threshold) {
  if (abs(x-y) > threshold)
    fail(callF(msg), x, y);
}