[GHC] #14175: Panic repSplitTyConApp_maybe

[GHC]

#14175: Panic repSplitTyConApp_maybe
-------------------------------------+-------------------------------------
        Reporter:  dfeuer            |                Owner:  (none)
            Type:  bug               |               Status:  closed
        Priority:  normal            |            Milestone:  8.2.2
       Component:  Compiler (Type    |              Version:  8.2.1
  checker)                           |
      Resolution:  fixed             |             Keywords:  TypeInType
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  Compile-time      |            Test Case:  indexed-
  crash or panic                     |  types/should_fail/T14175
      Blocked By:                    |             Blocking:
 Related Tickets:  #13910            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by RyanGlScott):

 After this patch, GHC HEAD gives this error for the program in comment:2:

 {{{
 Bug.hs:11:3: error:
     • Expected kind ‘(k -> *) -> (k -> *) -> *’,
         but ‘CD :: (k -> *) -> (k -> *) -> *’ has kind ‘Maybe a
                                                         -> Maybe a -> *’
     • In the data instance declaration for ‘CD’
       In the instance declaration for ‘C (Maybe a)’
    |
 11 |   data CD :: (k -> *) -> (k -> *) -> *
    |   ^^^^^^^
 }}}

 And this error for the program in comment:4:

 {{{
 Bug.hs:13:3: error:
     • Expected kind ‘(k -> *) -> *’,
         but ‘CD k (a :: k -> *) :: (k -> *) -> *’ has kind ‘k -> *’
     • In the data instance declaration for ‘CD’
       In the instance declaration for ‘C (Maybe a)’
    |
 13 |   data CD k (a :: k -> *) :: (k -> *) -> *
    |   ^^^^^^^^^^^^^^^^^^^^^^^
 }}}

 As you observed, these error messages aren't great and could likely be
 improved. Should I open a separate ticket for this?

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14175#comment:9>
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