sclass HuffmanTree is BitIO {
  settable Node root;
  
  /*
  algebraic Node {
    constructor Branch {
      settable Node zero;
      settable Node one;
    }
    constructor Leaf {
      settable byte literal;
    }
  }
  */
  
  abstract static class Node is BitIO {}
  
  static class Branch > Node {
    settable Node zero;
    settable Node one;
    
    public void readWrite(BitHead head) {  
      head.writeBit(1);
      head.exchange(zero);
      head.exchange(one);
    }
  }
  
  static class Leaf > Node {
    settable byte literal;
    
    *() {}
    *(int literal) { literal((byte) literal); }
    
    public void readWrite(BitHead head) {  
      head.writeBit(0);
      head.writeByte(literal);
    }
  }
  
  public void readWrite(BitHead head) {
    node.readWrite(head);
  }
}