static L<Map> downloadOrGetYouTubeComments(S youTubeURL) {
  S youTubeID = extractYoutubeID(youTubeURL);
  File f = youTubeCommentsCacheFile(youTubeID);
  if (fileExists(f))
    ret (L) unstructureLines(loadTextFile(f));
  ret downloadYouTubeComments(youTubeURL);
}