Type operators aren't printed infix

[nibro]

Reported by stepcut:

If you have something like:

instance Foo Int where
   type Dependencies Int = (Account AccountData) :+: Int

It gets transformed to:

instance Foo Int where
       type Dependencies Int = ((:+:) Account AccountData Int)

However, with out the parens around (Account AccountData) GHC thinks you are passing three arguments to (:+:). And, in fact, the parens in the input source are normally not required either.

[nibro]

A simple matter of changing the pretty printing routine for the TyInfix? constructor.