static L<IntRange> joinIntRangesWithDistanceLessThan(L<IntRange> l, int threshold) {
  new L<IntRange> out;
  
  for i over l: {
    IntRange r = l.get(i);
    if (i == 0 || r.start-last(out).end >= threshold)
      out.add(r);
    else
      setLast(out, intRange(last(out).start, r.end));
  }
  
  ret out;
}