// expects a "good tree" now

abstract sclass DialogBot {

  sbool debug, repeat = true;

  OccTree<E> tree, node;

  *(OccTree<E> *tree) { node = tree; }

  void take(E e) {

    selectMatching(e);

  }

  E getSingleOutput() {

    E e = nextBotOutput();

    if (e != null)

      select(node, e);

    ret e;

  }

  void rewind() {

    node = node.parent;

  }

  E findMatch(OccTree<E> node, E in) {

    for (E e : keys(node.followUp))

      if (matchE(e, in))

        ret e;

    null;

  }

  bool selectMatching(E in) {

    E e = findMatch(node, in);

    bool rep = false;

    if (repeat && e == null && node != tree) {

      e = findMatch(tree, in);

      rep = true;

    }

    if (e != null) {

      if (debug) {

        if (rep)

          print("Repeat!");

        print("Selecting " + struct(e) + " matching " + struct(in));

      }

      select(rep ? tree : node, e);

      true;

    }

    if (debug)

      print("No match for " + structure(in) + " in " + structure(node.followUpKeys()));

    false;

  }

  abstract bool matchE(E a, E b);

  E nextBotOutput() {

    new L<E> l;

    Collection<E> follows = keys(node.followUp);

    for (E e : follows)

      if (e.a() || isCommand(e))

        l.add(e);

    if (empty(l)) null; // fail("no good bot output: " + struct(node.followUpKeys()));

    if (l(l) > 1) fail("unclear bot output: " + struct(follows));

    ret first(l);

  }

  void select(OccTree<E> n, E e) {

    node = n.followUp(e);

    if (node == null) fail("can't select " + structure(e));

  }

  bool isCommand(E e) {

    ret e.state() && matchStart("bot", e.state);

  }

}

sclass LooseBot extends DialogBot {

  *(OccTree<E> node) { super(node); }

  bool matchE(E a, E b) {

    // standard NL matching

    ret eq(a.type(), b.type()) && match(a.text(), b.text());

  }  

}