public Parser selectClause() {
        if (selectClauseParser == null) {
           FutureParser future = scoped("selectClause");
           selectClauseParser = future;
           future.setParser(
               sequence(
                   token("SELECT"),
                   optional(
                       choice(
                           token("OPTIONAL"),
                           sequence(
                               token("NOT"),
                               token("OPTIONAL")
                           )
                       )
                   ),
                   fileName()
               )
           );
        }

        return selectClauseParser;
    }