public Parser onException() {
        if (onExceptionParser == null) {
           FutureParser future = scoped("onException");
           onExceptionParser = future;
           future.setParser(
               sequence(
                   optional(
                       token("ON")
                   ),
                   token("EXCEPTION"),
                   nestedStatements()
               )
           );
        }

        return onExceptionParser;
    }