anchor.diff:    List files = new List();
   
     // parse arguments
  +  var options = new Options();
     for (var option in options.arguments) {
       if (option.startsWith('-') && files.isEmpty()) {
         if (option == '-n') {
  
positive.code: #import('../../lib/petitparser.dart');
  #import('lisplib.dart');
  
  void mainWithOptions(Options options) {
  
    // default options
    bool standardLibrary = true;
  
negative.code:   if (interactiveMode || files.isEmpty()) {
      evalInteractive(parser, environment, stdin, stdout);
    }
  }
  