public Parser alphabetIs() {
        if (alphabetIsParser == null) {
           FutureParser future = scoped("alphabetIs");
           alphabetIsParser = future;
           future.setParser(
               sequence(
                   token("ALPHABET"),
                   identifier(),
                   optional(
                       token("IS")
                   ),
                   alphabetType()
               )
           );
        }

        return alphabetIsParser;
    }