static class LCombineTwoFunctions extends LearnerImpl {
  static boolean debug;
  Function f, g;

  public void processInOut(Object in, Object out) {
    if (f != null) return;
    List<Function> functions = allFunctions();
    
    // simple version without really checking multiple candidates
    for (Function f : functions) {
      Object o = tryProcess(f, in);
      if (o != null) {
        if (debug)
          debug("in=" + structure(in) + ", f=" + structure(f) + ", o=" + structure(o));
        for (Function g : functions) {
          Object x = tryProcess(g, o);
          if (out.equals(x)) {
            if (debug)
              debug("bingo! " + structure(g));
            this.f = f;
            this.g = g;
            return;
          }
        }
      }
    }
  }
  
  public Object processIn(Object in) {
    return g.process(f.process(in));
  }
  
  static Object tryProcess(Function f, Object in) {
    try {
      return f.process(in);
    } catch (Throwable e) {
      return null;
    }
  }
}