sclass AdaptiveIdentifierCompression {
  new SS shortenings;
  new SS expansions;
  S escapeWord = "xx";
  S newCodeMaker = lowerCaseAlphabet();
  ItIt<S> it;
  
  void init {
    codeIterator if null = allWordsOfAlphabet(codeAlphabet);
  }
  
  S encode(S token) {
    if (!isIdentifier(token)) ret token;
    
    init();
    S code = shortenings.get(token);
    if (code != null)
      ret code;
      
    /*new LS out;
    S expanded = expansion.get(code);
    if (expanded != null) {
      out.add(escapeWord);
      S originalCode = shortenings.get(expanded);
      shortenings.put(...);
    }*/
    
    code = newCode();
    shortenings.put(token, code);
    expansions.put(code, token);
    ret token;
  }
  
  S newCode() {
    S code;
    do {
      code = newCodeMaker!;
    } while (shortenings.containsKey(code));
  }
}