normalize.hs

class Normalize f where
  normalize :: f -> f
  default normalize :: (Generic f, GenericNormalize (Rep f)) => f -> f
  normalize = to . genericNormalize . from

instance {-# OVERLAPPABLE #-} Normalize a where
  normalize = id

instance Normalize (Maybe T.Text) where
  normalize (Just "") = Nothing
  normalize x = x

instance Normalize (Maybe [a]) where
  normalize (Just []) = Nothing
  normalize x = x

class GenericNormalize f where
  genericNormalize :: f p -> f p

instance (GenericNormalize f, GenericNormalize g) => GenericNormalize (f :*: g) where
  genericNormalize (a :*: b) =
    genericNormalize a :*: genericNormalize b

instance (GenericNormalize f, GenericNormalize g) => GenericNormalize (f :+: g) where
  genericNormalize (L1 a) = L1 (genericNormalize a)
  genericNormalize (R1 a) = R1 (genericNormalize a)

instance GenericNormalize f => GenericNormalize (M1 i c f) where
  genericNormalize (M1 a) = M1 (genericNormalize a)

instance (Normalize a) => GenericNormalize (Rec0 (Maybe a)) where
  genericNormalize (K1 a) = K1 (normalize a)