public Parser typedefClause() {
        if (typedefClauseParser == null) {
           FutureParser future = scoped("typedefClause");
           typedefClauseParser = future;
           future.setParser(
               sequence(
                   optional(
                       token("IS")
                   ),
                   token("TYPEDEF")
               )
           );
        }

        return typedefClauseParser;
    }