[Haskell-beginners] Couldn't match expected type with actual type

Hello, I have function with following signature: get :: a -> Value b I don't know concrete type of b. It can be Value Int or Value String or something else. How can i to write function only for testing? I need something like this: get :: a -> Value b get k = (Value "some_data"') but i got error: Couldn't match expected type `b' with actual type `[Char]' `b' is a rigid type variable bound by the type signature for get :: a -> Value b at Test.hs:39:8 In the first argument of `Value', namely `"some_data"' In the expression: (Value "some_data") In an equation for `get': get k = (Value "some_data") Failed, modules loaded: none. Value data declaration: data Value b = Value b deriving (Show) Thank you.