abstract sclass Adapter {
  void learn(S in, S out) {}
  S get(S in) { ret in; }
  O remember() { null; }
  void rewind(O o) {}
}

abstract sclass DialogBot {
  sbool debug, repeat = true;
  OccTree2 tree;
  new L<OccTree2> nodes;
  new L<L> rewindStack;
  new L adapterRewind;
  Adapter adapter;
  
  *(OccTree2 *tree) { nodes.add(tree); }
  *(OccTree2 tree, Adapter adapter) {
    this(tree);
    this.adapter = adapter;
  }
  
  void take(E in) {
    remember();
    if (repeat) setAdd(nodes, tree);
    new L<OccTree2> l;
    for (OccTree2 node : nodes)
      for (OccTree2 n : node.next)
        if (matchE(adapt(n.e), in))
          l.add(n);
          
    if (adapter != null)
      for (OccTree2 n : l)
        adapter.learn(adapt(n.e).text(), in.text());
        
    nodes = l;
  }
  
  E adapt(E e) {
    if (adapter != null)
      ret new E(adapter.get(e.text()), e.type()); // TODO: security when rewriting states
    ret e;
  }
  
  void remember() {
    if (rewindStack != null) {
      rewindStack.add(cloneList(nodes));
      if (adapter != null)
        adapterRewind.add(adapter.remember());
    }
  }
  
  E getSingleOutput() {
    remember();
    new L<OccTree2> l;
    for (OccTree2 node : nodes)
      for (OccTree2 n : node.next)
        if (n.e.a() || isCommand(n.e))
          l.add(n);
    nodes = l;
    ret nempty(nodes) ? adapt(first(nodes).e) : null;
  }
  
  void rewind() {
    nodes = popLast(rewindStack);
    if (adapter != null)
      adapter.rewind(popLast(adapterRewind));
  }
  
  abstract bool matchE(E a, E b);
  
  bool isCommand(E e) {
    ret e.state() && matchStart("bot", e.state);
  }
  
  void noRewind() {
    rewindStack = null;
  }
}

sclass LooseBot extends DialogBot {
  *(OccTree2 node) { super(node); }
  *(OccTree2 tree, Adapter adapter) { super(tree, adapter); }
  
  bool matchE(E a, E b) {
    // standard NL matching
    ret eq(a.type(), b.type()) && match(a.text(), b.text());
  }  
}

sclass WordAdapter extends Adapter {
  new Map<S, S> wordMap;
  
  void learn(S in, S out) {
    L<S> t1 = nlTok2(dropPunctuation2(in));
    L<S> t2 = nlTok2(dropPunctuation2(out));
    if (l(t1) != l(t2)) ret;
    
    for (int i = 1; i < l(t1); i += 2) {
      S w1 = t1.get(i), w2 = t2.get(i);
      if (!eqic(w1, w2))
        // just overwrite - be flexible!
        wordMap.put(w1.toLowerCase(), w2.toLowerCase());
    }
  }
  
  S get(S s) {
    L<S> tok = nlTok2(s);
    for (int i = 1; i < l(tok); i += 2) {
      S w = wordMap.get(tok.get(i).toLowerCase());
      if (nempty(w))
        tok.set(i, w);
    }
    ret join(tok);
  }
  
  O remember() { ret cloneMap(wordMap); }
  void rewind(O o) { wordMap = (Map) o; }
  
}

Began life as a copy of #1003410