[GHC] #13637: Printing type operators adds extraneous parenthesis

[GHC]

#13637: Printing type operators adds extraneous parenthesis
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        Reporter:  darchon           |                Owner:  alanz
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.1-rc2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by alanz):

 I am investigating this, and suspect I may not be the culprit, it deals
 directly with `Type`, and the printing process goes through
 `pprTypeForUser ty` which is

 {{{#!haskell
 pprTypeForUser :: Type -> SDoc
 -- The type is tidied
 pprTypeForUser ty
   = pprSigmaType tidy_ty
   where
     (_, tidy_ty)     = tidyOpenType emptyTidyEnv ty
      -- Often the types/kinds we print in ghci are fully generalised
      -- and have no free variables, but it turns out that we sometimes
      -- print un-generalised kinds (eg when doing :k T), so it's
      -- better to use tidyOpenType here
 }}

 And in turn `tidyOpenType` ends up in `tidyOpenTypes`, which changed as a
 result of https://github.com/ghc/ghc/commit/e9bf7bb5cc9

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13637#comment:2>
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