public Parser usage() {
        if (usageParser == null) {
           FutureParser future = scoped("usage");
           usageParser = future;
           future.setParser(
               sequence(
                   optional(
                       sequence(
                           token("USAGE"),
                           optional(
                               token("IS")
                           )
                       )
                   ),
                   usageClause()
               )
           );
        }

        return usageParser;
    }