Re: [Haskell-beginners] Problem with typeclass

Hello Sebastien Try

(fromJValue (JBool True)) :: Bool

Or

(fromJValue (JBool True)) :: JValue

The class function /fromJValue/ is polymorphic on its answer, so you need to tell GHC / GHCi what type the answer will be. GHC can't infer it because it could be more than one type. Best wishes Stephen