The following code

{-# LANGUAGE AutoDeriveTypeable #-}
{-# LANGUAGE TypeOperators #-}
import Data.Typeable

data a :*: b = Pair a b

main = print (typeOf (Pair 'a' 'b'))

prints

:*: Char Char

which is not valid Haskell. I belive it should print

(:*:) Char Char

In my particular case I am using Hint to interpret a type involving type operators. Hint uses showed TypeRep as a type annotation:

let type_str = show $ Data.Typeable.typeOf wit
...
let expr_typesig = concat [parens e, " :: ", type_str]

What results in a parse error.

I can write a patch if someone confirms that's the desired behavior and doesn't break anything.