error.hs

data T a = T {element :: a, element2 :: a, element3 :: String} deriving (Show)

class F a where
  mes :: a -> String

instance F Int where mes _ = "Int"
instance F Double where mes _ = "Double"

mkDefaultT :: (F a, Num a) => a -> T a
mkDefaultT x = T x x (mes x)

defaultT :: (F a, Num a) => T a
defaultT = mkDefaultT 0

-- error!
modifiedT :: T Double
modifiedT = defaultT {
  element = 1.0 :: Double
  , element2 = 0.0 :: Double
}