public Parser chainStatement() {
        if (chainStatementParser == null) {
           FutureParser future = scoped("chainStatement");
           chainStatementParser = future;
           future.setParser(
               sequence(
                   token("CHAIN"),
                   choice(
                       identifier(),
                       literal()
                   ),
                   optional(
                       chainUsing()
                   ),
                   optional(
                       token("END-CHAIN")
                   )
               )
           );
        }

        return chainStatementParser;
    }