static class FStringAsChars extends ReversibleFunctionImpl {
  public O process(Object _in) {
    String in = cast _in;
    new L<S> list;
    for (int i = 0; i < in.length(); i++)
      list.add(in.substring(i, i+1));
    ret list;
  }
  
  public O unprocess(Object _in) {
    List<String> l = cast _in;
    return join("", l);
  }
}

Began life as a copy of #1000510