Re: [Haskell-cafe] Typeclasses question in "Real World Haskell" book

26 Jul 2010


      How about:

*Main> fromJValue (JBool True) :: Either JSONError Bool
Right True
*Main> 

Doaitse


On 26 jul 2010, at 15:16, Angel de Vicente wrote:
...
data JValue = JString String
           | JNumber Double
           | JBool Bool
           | JNull
           | JObject [(String, JValue)]
           | JArray [JValue]
             deriving (Eq, Ord, Show)
type JSONError = String
class JSON a where
   toJValue :: a -> JValue
   fromJValue :: JValue -> Either JSONError a
instance JSON JValue where
   toJValue = id
   fromJValue = Right
instance JSON Bool where
   toJValue = JBool
   fromJValue (JBool b) = Right b
   fromJValue _ = Left "not a JSON boolean"

Re: [Haskell-cafe] Typeclasses question in "Real World Haskell" book

S. Doaitse Swierstra