[GHC] #13067: Abstract closed type families don't work with Backpack

4 Jan 2017


      #13067: Abstract closed type families don't work with Backpack
-------------------------------------+-------------------------------------
           Reporter:  ezyang         |             Owner:  ezyang
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:  8.2.1
          Component:  Compiler       |           Version:  8.1
  (Type checker)                     |
           Keywords:  backpack       |  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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 This should typecheck:

 {{{
 {-# LANGUAGE TypeFamilies #-}
 unit p where
     module A where
         type family ClosedFam a where
             ClosedFam a = Int

 unit sig where
     signature A where
         type family ClosedFam a where ..

 unit main where
     dependency sig[A=p:A]
 }}}

 but instead we confusingly report:

 {{{
 foo.bkp:9:9: error:
     Type constructor ‘ClosedFam’ has conflicting definitions in the module
     and its hsig file
     Main module: type family ClosedFam a :: *
     Hsig file:  type family ClosedFam a :: *
 }}}

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13067
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