public Parser whileKeyModifier() {
        if (whileKeyModifierParser == null) {
           FutureParser future = scoped("whileKeyModifier");
           whileKeyModifierParser = future;
           future.setParser(
               sequence(
                   token("WHILE"),
                   optional(
                       sequence(
                           token("KEY"),
                           optional(
                               token("IS")
                           )
                       )
                   ),
                   optional(
                       negationOp()
                   ),
                   token("LIKE"),
                   star(
                       likeMods()
                   ),
                   choice(
                       identifier(),
                       literal()
                   )
               )
           );
        }

        return whileKeyModifierParser;
    }