Template Haskell pretty-printer doesn't parenthesize infix datatype names in data declarations

If you run this program:

{-# LANGUAGE ExistentialQuantification #-}
{-# LANGUAGE PolyKinds #-}
{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE TypeOperators #-}
module Foo where

import Language.Haskell.TH

main :: IO ()
main = do
  putStrLn $([d| data a :~: b where Refl1 :: a :~: a |] >>= stringE . pprint)
  putStrLn $([d| data a :~~: b  = a ~ b => Refl2     |] >>= stringE . pprint)

$ /opt/ghc/8.2.1/bin/runghc Foo.hs
data :~:_0 a_1 b_2 where Refl1_3 :: :~:_0 a_4 a_4
data :~~:_0 a_1 b_2 = a_1 ~ b_2 => Refl2_3

It'll print the output incorrectly. Those infix names :~: and :~~: ought to be surrounded by parentheses, since they're used in prefix position.

Trac metadata

Trac field	Value
Version	8.0.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Template Haskell
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