abstract sclass CTNode {

  new LinkedHashSet<CTNode> children;

  toString { ret shortClassName(this) + ": " + toString2(); }

  abstract S toString2();

  bool add(CTNode n) { ret children.add(n); }

}

sclass TextNode > CTNode {

  S text;

  *() {}

  *(S *text) {}

  S toString2() { ret quote(text); }

}

sclass TokNode > CTNode {

  L<S> tok;

  *() {}

  *(LS *tok) {}

  S toString2() { ret sfu(tok); }

  public bool equals(O o) { ret stdEq(this, o, 'tok); }

  public int hashCode() { ret stdHash(this, 'tok); }

}

sclass ObjectNode > CTNode {

  O obj;

  *() {}

  *(O *obj) {}

  S toString2() { ret sfu(obj); }

  public bool equals(O o) { ret stdEq(this, o, 'obj); }

  public int hashCode() { ret stdHash(this, 'obj); }

}

sclass OpNode > CTNode {

  S op;

  bool haveResult;

  O result; // this is the result coming back up from the operation

  *() {}

  *(S *op) {}

  S toString2() { ret haveResult ? result + " <- " + op : op; }

  public bool equals(O o) { ret stdEq(this, o, 'op); }

  public int hashCode() { ret stdHash(this, 'op); }

  void setResult(O o) {

    result = o;

    haveResult = true;

  }

}