public Parser callGivingOrReturning() {
        if (callGivingOrReturningParser == null) {
           FutureParser future = scoped("callGivingOrReturning");
           callGivingOrReturningParser = future;
           future.setParser(
               sequence(
                   choice(
                       token("GIVING"),
                       token("RETURNING")
                   ),
                   optional(
                       choice(
                           token("INTO"),
                           sequence(
                               token("ADDRESS"),
                               token("OF")
                           )
                       )
                   ),
                   identifier()
               )
           );
        }

        return callGivingOrReturningParser;
    }