Parse error with type instances

```
{-# 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'

Start with the supplied TypeLevelDefunctionalization reproducer and inspect how the Haskell parser handles the data declaration followed by the type instance. Done means this input no longer produces the reported parse error; no specific source file or test is named in the issue.

Written by the indexing model from the issue text.