[GHC] #15872: Odd pretty printing of equality constraint in kind ('GHC.Types.Eq# <>)

[GHC]

#15872: Odd pretty printing of equality constraint in kind ('GHC.Types.Eq# <>)
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        Reporter:  Iceland_jack      |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.6.2
      Resolution:                    |             Keywords:  TypeInType
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Poor/confusing    |  Unknown/Multiple
  error message                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #13933            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by RyanGlScott):

 In GHC HEAD (as of commit 2257a86daa72db382eb927df12a718669d5491f8), you
 get the following error when compiling the original program:

 {{{
 GHCi, version 8.7.20181129: http://www.haskell.org/ghc/  :? for help
 Loaded GHCi configuration from /home/rgscott/.ghci
 [1 of 1] Compiling Main             ( ../Bug.hs, interpreted )

 ../Bug.hs:10:1: error:
     • Illegal constraint in a kind: forall (a :: WHICH).
                                     (a ~ 'OP) =>
                                     * -> * -> *
     • In the data type declaration for ‘Fun’
    |
 10 | data Fun :: forall (a :: WHICH). a ~ OP => Type -> Type -> Type where
    |
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^...
 }}}

 Which would suggest that this issue is now moot.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15872#comment:4>
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