3898031 · typeable/aeson

git.iko.soy/typeable/aeson

Change toJSON and fromJSON instances for Either.

Previously, fromJSON . toJSON == id was violated by the Either instances. In addition, if both types are parsable from the same JSON, then the Left is always given favor - which is probably not desirable. Instead, differentiate the instances using an array. This allows for "Either a a" to actually work instead of always chosing Left in FromJSON.

commit389803154c92676ae22c084ef23174170fe253d2 authorJared Hance <jaredhance@gmail.com> dateMon 25 Jul 2011, 09:46 (15 years ago) parent00a185a

1 file changed+10−3

compare with master

unifiedsplit

Data/Aeson/Types.hs+10−3

Data/Aeson/Types.hs+10−3

@@ -325,12 +325,19 @@ instance (FromJSON a) => FromJSON (Maybe a) where

325325 {-# INLINE parseJSON #-}

326326

327327instance (ToJSON a, ToJSON b) => ToJSON (Either a b) where

328− toJSON (Left a) = toJSON a

329− toJSON (Right b) = toJSON b

328+ toJSON (Left a) = Array (V.fromList [String "Left", toJSON a])

329+ toJSON (Right b) = Array (V.fromList [String "Right", toJSON b])

330330 {-# INLINE toJSON #-}

331331

332332instance (FromJSON a, FromJSON b) => FromJSON (Either a b) where

333− parseJSON a = Left <$> parseJSON a <|> Right <$> parseJSON a

333+ parseJSON v@(Array vec) =

334+ if V.length vec /= 2

335+ then typeMismatch "Either a b" v

336+ else case vec V.! 0 of

337+ "Left" -> Left <$> parseJSON (vec V.! 1)

338+ "Right" -> Right <$> parseJSON (vec V.! 1)

339+ _ -> typeMismatch "Either a b" v

340+ parseJSON v = typeMismatch "Either a b" v

334341 {-# INLINE parseJSON #-}

335342

336343instance ToJSON Bool where