úÎ u iNoneSince  is a GADT, our  function needs a / type class in order to be implemented. Which  @ gets used is chosen in compile-time. As a bonus, we implement   in the same way. From  fb-persistent'. Since 0.1.3. Note that your fields  should either be of type  or  , not a polymorphic  kind.  Expiration time of s is saved with  precision of one second. From  fb-persistent. Since 0.1.2. We use  ByteString% for historical purposes in order to  maintain compatibility with fb < 0.13. From  fb-persistent. Since 0.1.            fb-persistent-0.2.1Facebook.PersistentAccessTokenKind fb-0.13.4.2Facebook.Types AccessTokencereal-0.3.5.2Data.SerializegetaccessTokenGetput$fPersistFieldAccessTokenUserAccessTokenAppAccessToken$fPersistFieldId$fPersistFieldActionaccessTokenPutgetTextputTextgetIdputId putUTCTime getUTCTimeaccessTokenUnknownVersion$fAccessTokenKindAppKind$fAccessTokenKindUserKind