// finds a fixed element, e.g. a Java token

static class LCertainElement extends LearnerImpl {

  static boolean debug;

  ReversibleFunction f; // e.g. JavaTok

  String element;

  *(ReversibleFunction *f) {}

  public void processInOut(Object _in, Object _out) {

    String in = (String) _in, out = (String) _out;

    Set<String> set = new HashSet<String>(getMarked(out));

    if (debug)

      System.out.println("LCertainElement: set=" + set);

    if (set.size() == 1)

      element = set.iterator().next();

    if (debug)

      System.out.println("LCertainElement: element=" + element);

  }

  public Object processIn(Object _in) {

    List<String> l = (List<String>) f.process(_in);

    new List<String> l2;

    for (String x : l)

      l2.add(x.equals(element) ? "[[" + x + "]]" : x);

    return f.unprocess(l2);

  }

  // returns positions in marked string (from/to/from/to...)

  static List<Integer> getFindMarkers2(String s) {

    List<Integer> l = new ArrayList<Integer>();

    int i = 0;

    while (i < s.length()) {

      int j = s.indexOf("[[", i);

      if (j < 0) break;

      int k = s.indexOf("]]", j+2);

      if (k < 0) break;

      l.add(j);

      l.add(k+2);

      i = k+2;

    }

    return l;

  }

  static List<String> getMarked(String s) {

    List<Integer> l = getFindMarkers2(s);

    new List<String> result;

    for (int i = 0; i < l.size(); i += 2)

      result.add(s.substring(l.get(i)+2, l.get(i+1)-2));

    return result;

  }

}