// returns last value of predicate
sbool sleepWhile(IF0<Bool> pred, O... _) {
  optPar int interval = 50; // ms
  optPar double max = 10.0; // seconds
  long time = sysNow();
  do {
    if (!pred!) false;
    sleep(interval);
  } while (sysNow() <= time+toMS(max));
  true;
}