Error with data instance and type operators

[ndmitchell]

From ndmitchell/hlint#450 by @LeanderK:

{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE GADTs                  #-}
{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE TypeInType #-}
module Test where

import           Data.Singletons.Prelude
import           Data.Singletons.TypeLits
import           Data.Type.Equality            ((:~:) (..), (:~~:) (..))

data instance Sing (z :: (a :~: b)) where
    SRefl :: Sing Refl

Gives a parse error on the :~:.

[elaforge]

This is probably the same thing, also a parse error with haskell-src-exts but not ghc:

{-# LANGUAGE DataKinds, TypeOperators #-}
import Data.Proxy (Proxy(..))
import qualified GHC.TypeLits as TypeLits

f :: Proxy n -> Proxy (n TypeLits.+ 1)
f Proxy = Proxy

[LeanderK]

I think here is another example

import           Data.Type.Equality            ((:~:) (..), (:~~:) (..))

[mpickering]

At least one problem is that kinds and types are still parsed differently in HSE but in GHC, they are parsed as the same thing. I'm not going to work on this any more for now.

[AshleyYakeley]

#414 may fix this.