static int loadTextFilePart_iterator_chunkSize = 65536;

// TODO: close on failure
static Iterable<S> loadTextFilePart_iterator(File file, long start, long end) ctex {
  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 -> O {
    S s = readChunkThroughUTF8Processor(p, in, buf);
    //print("Chunk read: " + l(s));
    if (nempty(s)) ret s;
    in.close();
    ret endMarker();
  });
}

Began life as a copy of #1006741