sS recursiveJoin(Iterable l) {
  new StringBuilder buf;
  recursiveJoin_impl(buf, l);
  ret str(buf);
}

svoid recursiveJoin_impl(StringBuilder buf, Iterable l) {
  if (l != null) for (O o : l)
    if (o cast Iterable)
      recursiveJoin_impl(buf, o);
    else
      buf.append(o);
}