FromField and ToField instances for Either

Database/SQLite/Simple/FromField.hs

@@ -34,7 +34,7 @@ module Database.SQLite.Simple.FromField
     , returnError
     ) where
 
-import           Control.Applicative (Applicative, (<$>), pure)
+import           Control.Applicative (Applicative, (<$>), (<|>), pure)
 import           Control.Exception (SomeException(..), Exception)
 import           Data.ByteString (ByteString)
 import qualified Data.ByteString.Char8 as B
@@ -102,6 +102,9 @@ instance (FromField a) => FromField (Maybe a) where
     fromField (Field SQLNull _) = pure Nothing
     fromField f                 = Just <$> fromField f
 
+instance (FromField a, FromField b) => FromField (Either a b) where
+  fromField f = (Left <$> fromField f) <|> (Right <$> fromField f)
+
 instance FromField Null where
     fromField (Field SQLNull _) = pure Null
     fromField f                 = returnError ConversionFailed f "data is not null"

Database/SQLite/Simple/ToField.hs

@@ -47,6 +47,11 @@ instance (ToField a) => ToField (Maybe a) where
     toField (Just a) = toField a
     {-# INLINE toField #-}
 
+instance (ToField a, ToField b) => ToField (Either a b) where
+    toField (Left a) = toField a
+    toField (Right b) = toField b
+    {-# INLINE toField #-}
+
 instance ToField Null where
     toField _ = Base.SQLNull
     {-# INLINE toField #-}