public Parser suppressClause() {
        if (suppressClauseParser == null) {
           FutureParser future = scoped("suppressClause");
           suppressClauseParser = future;
           future.setParser(
               sequence(
                   token("SUPPRESS"),
                   optional(
                       token("WHEN")
                   ),
                   choice(
                       zero(),
                       space(),
                       sequence(
                           optional(
                               token("ALL")
                           ),
                           literal()
                       )
                   )
               )
           );
        }

        return suppressClauseParser;
    }