Parse error with type instances

[PaNaVTEC]

{-# LANGUAGE DataKinds              #-}
{-# LANGUAGE KindSignatures         #-}
{-# LANGUAGE PolyKinds              #-}
{-# LANGUAGE TypeFamilies           #-}
{-# LANGUAGE TypeOperators          #-}
{-# LANGUAGE UndecidableInstances   #-}

module TypeLevelDefunctionalization where

import           Data.Kind       (Constraint, Type)
import qualified GHC.TypeLits as TL
...
data AddNat :: TL.Nat -> TL.Nat -> Exp TL.Nat
type instance Eval' (AddNat a a') = a TL.+ a'

Parse error Found: data AddNat :: TL.Nat -> TL.Nat -> Exp TL.Nat

type instance Eval' (AddNat a a') = a TL.+ a'