public Parser equalToOp() {
        if (equalToOpParser == null) {
           FutureParser future = scoped("equalToOp");
           equalToOpParser = future;
           future.setParser(
               choice(
                   sequence(
                       token("EQUAL"),
                       optional(
                           token("TO")
                       )
                   ),
                   token("=")
               )
           );
        }

        return equalToOpParser;
    }