public Parser codeSet() {
        if (codeSetParser == null) {
           FutureParser future = scoped("codeSet");
           codeSetParser = future;
           future.setParser(
               sequence(
                   token("CODE-SET"),
                   optional(
                       token("IS")
                   ),
                   alphabetName(),
                   optional(
                       sequence(
                           token("FOR"),
                           plus(
                               identifier()
                           )
                       )
                   )
               )
           );
        }

        return codeSetParser;
    }