[GHC] #14139: Kind signature not accepted (singletons)

[GHC]

#14139: Kind signature not accepted (singletons)
-------------------------------------+-------------------------------------
        Reporter:  Iceland_jack      |                Owner:  (none)
            Type:  bug               |               Status:  closed
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.1
      Resolution:  duplicate         |             Keywords:  TypeInType
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #13365            |  Differential Rev(s):
       Wiki Page:                    |
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Changes (by RyanGlScott):

 * status:  new => closed
 * resolution:   => duplicate
 * related:   => #13365


Comment:

 Yep, this is a CUSK issue.
 [http://git.haskell.org/ghc.git/blob/1cdceb9fa3bc3ad01b2d840caad8e735513e14ed:/docs/users_guide/glasgow_exts.rst#l8524
 Here] is the relevant section of the users' guide:

 {{{
 -  For a datatype with a top-level ``::`` when :ghc-flag:`-XTypeInType`
    is in effect: all kind variables introduced after the ``::`` must
    be explicitly quantified. ::

      -- -XTypeInType is on
      data T1 :: k -> *            -- No CUSK: `k` is not explicitly
 quantified
      data T2 :: forall k. k -> *  -- CUSK: `k` is bound explicitly
      data T3 :: forall (k :: *). k -> *   -- still a CUSK

    Note that the first example would indeed have a CUSK without
    :ghc-flag:`-XTypeInType`.
 }}}

 In your example, `v` is not explicitly quantified in the kind signature of
 `Some`, which explains why its kind defaults to `*` (and results in the
 error message you see).

 Since this asks to improve the error message to warn about CUSK behavior,
 I'll close this as a duplicate of #13365, which seeks the same goal.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14139#comment:2>
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