[GHC] #10653: PatternSynonyms should be imported/exported as part of the wildcard notation

[GHC]

#10653: PatternSynonyms should be imported/exported as part of the wildcard
notation
-------------------------------------+-------------------------------------
        Reporter:  gridaphobe        |                   Owner:  mpickering
            Type:  feature request   |                  Status:  new
        Priority:  high              |               Milestone:  8.0.1
       Component:  Compiler          |                 Version:  7.11
      Resolution:                    |                Keywords:
                                     |  PatternSynonyms, pattern synonyms
Operating System:  Unknown/Multiple  |            Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
-------------------------------------+-------------------------------------

Comment (by simonpj):

 I just want to check that you really intend this to work
 {{{
 module M( Maybe(P) ) where
   pattern P x y = (x, True, y)

 module N( T(P, X, Y) ) where
   import M( Maybe(..) )
   data T = X | Y
 }}}
 Pattern synonym `P` has ''absolutely nothing'' to do with the `Maybe`, but
 as I understand it module `M` is legal under this proposal, and anyone
 going `import M( Maybe(..) )` will get `P` in scope.

 Then module `N` gets the `P` from the import, and attaches it to the also-
 unrelated data type `T`.

 I think it's all well-defined, but perhaps rather surprising.  Is there a
 consensus that this is the behaviour we all want; or has it perhaps simply
 not been discussed?

 A possible restriction might be that you can only add `P` to an export of
 a data type `T` if `P`'s type has form `... -> T t1 ..tn`.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10653#comment:30>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler