static S unparsePoem(L<E> poem) {
  new L<S> l;
  for (E e : poem) {
    S s;
    if (e.q != null)
      s = "Usr: " + trim(e.q);
    else if (e.a != null)
      s = "Bot: " + trim(e.a);
    else if (e.state != null)
      s = "[" + trim(e.state) + "]";
    else
      s = "?";
    if (e.comment != null)
      s += " // " + e.comment;
    l.add(s);
  }
  ret joinLines(l);
}