[GHC] #8968: Pattern synonyms and GADTs

[GHC]

#8968: Pattern synonyms and GADTs
----------------------------------------------+----------------------------
        Reporter:  kosmikus                   |            Owner:
            Type:  bug                        |           Status:  new
        Priority:  normal                     |        Milestone:
       Component:  Compiler (Type checker)    |          Version:
      Resolution:                             |  7.8.1-rc2
Operating System:  Unknown/Multiple           |         Keywords:
 Type of failure:  GHC rejects valid program  |     Architecture:
       Test Case:                             |  Unknown/Multiple
        Blocking:                             |       Difficulty:  Unknown
                                              |       Blocked By:
                                              |  Related Tickets:
----------------------------------------------+----------------------------

Comment (by cactus):

 We don't have frontend support for pattern synonym signatures (see #8584).
 However, this can be worked around using the technique described in #8584,
 so I was able to get your code to typecheck by modifying it as:


 {{{
 {-# LANGUAGE GADTs, KindSignatures, PatternSynonyms, ScopedTypeVariables
 #-}

 data X :: (* -> *) -> * -> * where
   Y :: f Int -> X f Int

 pattern C x = (Y (Just x) :: X Maybe Int)

 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8968#comment:3>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler