[GHC] #12772: (type f1 ~> f2 = forall a. f1 a -> f2 a) to core libraries

[GHC]

#12772: (type f1 ~> f2 = forall a. f1 a -> f2 a) to core libraries
-------------------------------------+-------------------------------------
           Reporter:  Iceland_jack   |             Owner:
               Type:  feature        |            Status:  new
  request                            |
           Priority:  normal         |         Milestone:
          Component:  Build System   |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 Is this something that belongs to core libraries (it has other names in
 the wild, `:~>`, `Natural`..)

 {{{#!hs
 type f1 ~> f2 = forall a. f1 a -> f2 a
 }}}

 I use it all the time and end up redefining it (it is such a short type
 that maybe it's not worth it)

 {{{#!hs
 unLift   :: Applicative f
          => Lift f a -> f a
 mapLift  :: (f a -> g a)
          -> (Lift f a -> Lift g a)
 mapFreeT :: (Functor f, Functor m)
          => (forall a. m a -> m' a)
          -> (FreeT f m a -> FreeT f m' a)
 mapFreeT :: (Functor f, Functor m)
          => (forall a. m a -> m' a)
          -> (FreeT f m a -> FreeT f m' a)
 vmap     :: (a -> a')
          -> (Vec a n -> Vec a' n)
 liftIO   :: MonadIO m
          => IO a -> m a
 hoist    :: Monad m
          => (forall a. m a -> n a)
          -> (t m b -> t n b)
 }}}

 becomes

 {{{#!hs
 unLift   :: Applicative f
          => Lift f ~> f
 mapLift  :: (f ~> g)
          -> (Lift f ~> Lift g)
 mapFreeT :: (Functor f, Functor m)
          => (m ~> m')
          -> (FreeT f m ~> FreeT f m')
 vmap     :: (a -> a')
          -> (Vec a ~> Vec a')
 liftIO   :: MonadIO m
          => IO ~> m
 hoist    :: Monad m
          => (m ~> n)
          -> (t m ~> t n)
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12772>
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