grammar a.Dsl with org.eclipse.xtext.common.Terminals
...
Model:
	greetings+=Greeting*;
	
Greeting:
	Definition|Application;
	
Definition:
	'Def' name=ID '.';
Application:
	'App' def = [Definition] '.';

	
public static void main(String[] args) {
  String str =  "Def var."//
                    + "App var.";
  Injector injector =
  new DslStandaloneSetup().createInjectorAndDoEMFRegistration();
  XtextResourceSet resourceSet = injector.getInstance(XtextResourceSet.class);
  resourceSet.addLoadOption(XtextResource.OPTION_RESOLVE_ALL, Boolean.TRUE);
  DslParser tp = injector.getInstance(DslParser.class);
  Reader r = new StringReader(str);
  IParseResult pr = tp.doParse(r);
  Model m = (Model) pr.getRootASTElement();
  Application a = (Application) m.getGreetings().get(1);
  Definition def = a.getDef();
  //def is null
  System.out.println(def);
}

String modelString = "Hello Xtext! Hello World from Xtext!";
		Injector injector = new MyDslStandaloneSetup().createInjectorAndDoEMFRegistration();
		ResourceSet rs = injector.getInstance(ResourceSet.class);
		Resource r = rs.createResource(URI.createURI("dummy.mydsl"));
		r.load(new StringInputStream(modelString), null);
		Model m = (Model) r.getContents().get(0);