!7

abstract sclass InFlight {
  L actions() { null; }
  abstract L<InFlight> consumeToken(S token);
}

InFlight > JustAction {
  O action;
  
  *() {}
  *(O *action) {}
  
  L actions() { ret ll(action); }
  L<InFlight> consumeToken(S token) { null; }
}

InFlight > AcceptWord {
  S word;
  InFlight next;
  
  *() {}
  *(S *word, InFlight *next) {}
  
  L<InFlight> consumeToken(S token) {
    if (!eqic(token, word)) null;
    ret ll(next);
  }
}

sclass Parsing {
  Iterator<S> it;
  new L<InFlight> inFlight;
  
  *(S text, InFlight... l) {
    addAll(inFlight, l);
    it = javaTokC(text).iterator();
  }
  
  void run {
    actions();
    while (it.hasNext()) step();
  }
  
  void step {
    S token = it.next();
    new L<InFlight> l2;
    for (InFlight f : inFlight)
      addAll(l2, f.consumeToken(token));
    print("New number: " + l(l2));
    inFlight = l2;
    actions();
  }
  
  void actions {
    for (InFlight f : inFlight)
      for (O action : unnull(f.actions()))
        runAction(action);
  }
  
  void runAction(O o) {
    print("Action! " + struct(o));
  }
}

p {
  Parsing pp = new Parsing("I am here",
    JustAction("start"),
    AcceptWord("yes", JustAction("yes")),
    AcceptWord("i", AcceptWord("am", AcceptWord("here",
      JustAction("I am here!"));
  pp.run();
}

Began life as a copy of #1008783