[GHC] #1769: Deriving Typeable for data families

[GHC]

#1769: Deriving Typeable for data families
-------------------------------------------------+--------------------------
  Reporter:  chak                                |          Owner:  chak            
      Type:  task                                |         Status:  closed          
  Priority:  low                                 |      Milestone:  7.0.1           
 Component:  Compiler (Type checker)             |        Version:  6.9             
Resolution:  fixed                               |       Keywords:                  
  Testcase:  indexed-types/should_compile/T1769  |      Blockedby:                  
Difficulty:  Unknown                             |             Os:  Unknown/Multiple
  Blocking:                                      |   Architecture:  Unknown/Multiple
   Failure:  None/Unknown                        |  
-------------------------------------------------+--------------------------

Comment(by heatsink):

 Replying to [comment:10 mitar]:

 As a workaround, you can derive from Typeable without this feature by
 writing your own instance.

 {{{
 data family T a

 instance Typeable a => Typeable (T a) where
   typeOf x = mkTyConApp (mkTyCon "T") [typeOf (unT x)]
     where
       unT :: T a -> a
       unT = undefined
 }}}

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1769#comment:11>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler