See if this still fails on GHC 8.2

checkiffails.hs

type Cat k = k -> k -> Type

data T = D | I

type family
  Interp (a :: T) :: Type where
  Interp I = Int
  Interp D = Double

data Fn :: (T, T) -> Type where
 Exp   :: Fn '(D, D)
 Sqrt  :: Fn '(D, D)
 Mod   :: Int -> Fn '(I, I)
 Round :: Fn '(D, I)
 (:.:) :: Fn '(b, c) -> Fn '(a, b) -> Fn '(a, c)

eval :: Fn '(a, b) -> Arr Interp0 (->) a b
eval Exp     = Arr exp
eval Sqrt    = Arr sqrt
eval Round   = Arr round
eval (Mod m) = Arr (`mod` m)
eval (f:.:g) = eval f . eval g

newtype Arr :: (a ~> Type) -> Cat Type -> Cat a where
  Arr :: (cat (ty_fam ^ a) (ty_fam ^ b)) -> Arr ty_fam cat a b

newtype Arr' (cat :: Cat k) a b where
  Arr' :: (cat a b) -> Arr' cat a b
  deriving Category

-- instance forall k_ab1l k_ab1m (cat_ab1n :: Cat k_ab1m).
--               Category cat_ab1n =>
--               Category (Arr' cat_ab1n) where
--        id
--          = coerce
--              (Control.Category.id :: cat_aaWR a_a6y3 a_a6y3) ::
--              forall (a_a6y3 :: k_Xb0s). Main.Arr' cat_aaWR a_a6y3 a_a6y3
--        (.)
--          = coerce
--              ((.) ::
--                 cat_aaWR b_a6y4 c_a6y5
--                 -> cat_aaWR a_a6y6 b_a6y4 -> cat_aaWR a_a6y6 c_a6y5) ::
--              forall (b_a6y4 :: k_Xb0s) (c_a6y5 :: k_Xb0s) (a_a6y6 :: k_Xb0s).
--              Arr' cat_aaWR b_a6y4 c_a6y5
--              -> Arr' cat_aaWR a_a6y6 b_a6y4
--                 -> Arr' cat_aaWR a_a6y6 c_a6y5


instance Category cat => Category (Arr ty_fun cat) where
  id = Arr id

  Arr f . Arr g = Arr (f . g)

data TyFun :: Type -> Type -> Type

type a ~> b = TyFun a b -> Type

data Interp0 :: T ~> Type

type family
  (f :: a ~> b) ^ (x :: a) :: b where
  Interp0 ^ a = Interp a