[GHC] #11376: Inconsistent specified type variables among functions and datatypes/classes when using -XTypeApplications

[GHC]

#11376: Inconsistent specified type variables among functions and datatypes/classes
when using -XTypeApplications
-------------------------------------+-------------------------------------
        Reporter:  RyanGlScott       |                Owner:  goldfire
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.1
  checker)                           |             Keywords:
      Resolution:                    |  TypeApplications
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  Other             |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by RyanGlScott):

 Another troubling aspect of this that I discovered recently: GHC appears
 to quantify type variables in typeclass methods differently now. Compare
 this (GHC 7.10.3):

 {{{
 $ /opt/ghc/7.10.3/bin/ghci -fprint-explicit-foralls
 GHCi, version 7.10.3: http://www.haskell.org/ghc/  :? for help
 λ> import GHC.Generics
 λ> :t datatypeName
 datatypeName
   :: forall d (t :: * -> (* -> *) -> * -> *) (f :: * -> *) a.
      Datatype d =>
      t d f a -> [Char]
 }}}

 to this (GHC 8.0):

 {{{
 $ /opt/ghc/8.0.1/bin/ghci -fprint-explicit-foralls
 GHCi, version 8.0.0.20160323: http://www.haskell.org/ghc/  :? for help
 Loaded GHCi configuration from /home/ryanglscott/.ghci
 λ> import GHC.Generics
 λ> :t datatypeName
 datatypeName
   :: forall {k} (d :: k).
      Datatype d =>
      forall {k1} (t :: k -> (* -> *) -> k1 -> *) (f :: *
                                                        -> *) (a :: k1).
      t d f a -> [Char]
 }}}

 I'm not sure what's going on with the GHC 8.0-reported type signature at
 all.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11376#comment:13>
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