static LS paragraphsTok(S s) {
  new ArrayList<S> tok;
  int l = s == null ? 0 : s.length();
  int i = 0;
  
  while true {
    IntRange r = tok_findNextEmptyLineWhitespace(s, i);
    if (r == null) break;
    
    tok.add(substring(s, i, r.start));
    tok.add(substring(s, r));
    i = r.end;
  }
  
  if (evenLength(tok)) tok.add("");
  ret tok;
}