[GHC] #15236: GHCi pretty-prints (->)'s fixity poorly

[GHC]

#15236: GHCi pretty-prints (->)'s fixity poorly
-------------------------------------+-------------------------------------
        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.4.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D4799
       Wiki Page:                    |
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Comment (by Ben Gamari <ben@…>):

 In [changeset:"3397396a385ef9f493cf1e20894e88d21dfec48d/ghc" 3397396/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="3397396a385ef9f493cf1e20894e88d21dfec48d"
 Fix #15236 by removing parentheses from funTyConName

 Currently, `funTyConName` is defined as:

 ```lang=haskell
 funTyConName = mkPrimTyConName (fsLit "(->)") funTyConKey funTyCon
 ```

 What's strange about this definition is that there are extraneous
 parentheses around `->`, which is quite unlike every other infix
 `Name`. As a result, the `:info (->)` output is totally garbled (see
 Trac #15236).

 It's quite straightforward to fix that particular bug by removing the
 extraneous parentheses. However, it turns out that this makes some
 test output involving `Show` instances for `TypeRep` look less
 appealing, since `->` is no longer surrounded with parentheses when
 applied prefix. But neither were any /other/ infix type constructors!
 The right fix there was to change `showTypeable` to put parentheses
 around prefix applications of infix tycons.

 Test Plan: ./validate

 Reviewers: bgamari, hvr

 Reviewed By: bgamari

 Subscribers: rwbarton, thomie, carter

 GHC Trac Issues: #15236

 Differential Revision: https://phabricator.haskell.org/D4799
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15236#comment:2>
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