static int loadTextFilePart_iterator_chunkSize = 65536;

// TODO: close on failure
static Iterator<S> loadTextFilePart_iterator(File file, long start, long end) {
  if (end-start <= loadTextFilePart_iterator_chunkSize)
    ret ll(loadTextFilePart(file, start, end));
  final FileInputStream in = newFileInputStream(file);
  in.skip(start);
  final byte[] buf = new byte[loadTextFilePart_iterator_chunkSize];
  final new UTF8Processor p;
  ret iteratorFF(func -> S {
    S s = readChunkThroughUTF8Processor(p, in, buf);
    ret empty(s) ? endMarker() : s;
  });
}