// assigns probability pStart for first element, pEnd for last element
//   (rest linearly interpolated)
//
// f may return an instance of IProbabilistic (or a normal Runnable)

static <A> void probabilisticForEach(IProbabilisticScheduler scheduler, double pStart, double pEnd, Cl<A> l, IVF1<A> f) {
  if (scheduler == null || f == null) ret;
  probabilisticForEach(scheduler, pStart, pEnd, iterator(l), 0, l(l), 1.0, f);
}
  
static <A> void probabilisticForEach(IProbabilisticScheduler scheduler, double pStart, double pEnd, Iterator<A> it, int i, int n, double myProb, IVF1<A> f) {
  assertTrue(pEnd <= pStart);
  if (scheduler == null || f == null || !it.hasNext()) ret;
  
  // get element
  A a = it.next();
  
  // calculate probability for element
  double p = blend(pStart, pEnd, doubleRatio(i, n-1));
  
  // run client function
  scheduler.at(new Runnable {
    run { f.get(a); }
    toString { ret formatFunctionCall(f, a); }
  });
  
  // schedule next element at lower probability
  scheduler.atRelative(doubleRatio(p, myProb), ->
    probabilisticForEach(scheduler, pStart, pEnd, it, i+1, n, p, f));
}