249          * This can occur if the language evolves and new kinds of directive are added.

   249          * This can occur if the language evolves and new kinds of directive are added.

   250          * @param d  the directive to visit

   250          * @param d  the directive to visit

   251          * @param p  a visitor-specified parameter

   251          * @param p  a visitor-specified parameter

   252          * @return a visitor-specified result

   252          * @return a visitor-specified result

   253          * @throws UnknownDirectiveException a visitor implementation may optionally throw this exception

   253          * @throws UnknownDirectiveException a visitor implementation may optionally throw this exception

   255          */

   255          */

   256         default R visitUnknown(Directive d, P p) {

   256         default R visitUnknown(Directive d, P p) {

   257             throw new UnknownDirectiveException(d, p);

   257             throw new UnknownDirectiveException(d, p);

   258         }

   258         }

   259     }

   259     }