A use-case I've had for a quick right-biased Java Either I threw together is handling a migration from java.util.Date to java.time.LocalDate: List<LocalDat

A use-case I've had for a quick right-biased Java Either I threw together is handling a migration from java.util.Date to java.time.LocalDate: List<LocalDate> dobs = users.stream() .map(person -> Either.either(person::getDeprecatedDob, person::getDobLocalDate)) .map(oldOrNewFormat -> oldOrNewFormat.fold( (Date oldFormat) -> convertOldFormatToNew(oldFormat), (LocalDate newFormat) -> newFormat, )) .collect(Collectors.toList()); I use the right-biased-ness of the Either to prefer the new format, if available, but failing that, use the old format and then convert as needed.