public Parser requiredPhrase() {
        if (requiredPhraseParser == null) {
           FutureParser future = scoped("requiredPhrase");
           requiredPhraseParser = future;
           future.setParser(
               choice(
                   token("REQUIRED"),
                   token("EMPTY-CHECK")
               )
           );
        }

        return requiredPhraseParser;
    }