static L<IntRange> splitIntoRandomRangesOfApproximateLength(double avgLength, IntRange base) {
  int i = base.start;
  new L<IntRange> out;
  int safety = 0;
  while (i < base.end && safety++ < l(base)) {
    double randVal = random(avgLength*2);
    int j = min(base.end, i+max(1, iround(randVal)));
    out.add(intRange(i, j));
    i = j;
  }
  ret out;
}