[GHC] #1968: data family + GADT: not implemented yet

[GHC]

#1968: data family + GADT: not implemented yet
------------------------------------------------+---------------------------
 Reporter:  Remi                                |          Owner:  chak            
     Type:  bug                                 |         Status:  new             
 Priority:  normal                              |      Milestone:  6.10 branch     
Component:  Compiler (Type checker)             |        Version:  6.9             
 Severity:  normal                              |     Resolution:                  
 Keywords:  data type family GADT choose_univs  |     Difficulty:  Moderate (1 day)
 Testcase:                                      |   Architecture:  Multiple        
       Os:  Multiple                            |  
------------------------------------------------+---------------------------
Changes (by guest):

 * cc: tora at zonetora.co.uk (added)

Comment:

 Also interested in this. Will the implementation allow varying non-
 instance types?

 {{{
 {-# LANGUAGE TypeFamilies, KindSignatures, GADTs #-}
 module Foo2 where

 data family Blah x :: * -> *

 data instance Blah Bool where
   Bool1 :: Blah Bool Int
   Bool2 :: Blah Bool Char

 data instance Blah Char where
   Char1 :: Blah Char Int
   Char2 :: Blah Char Char
 }}}

 {{{
 >ghc-6.9.20080401 -c Foo2.hs
 ghc-6.9.20080401: panic! (the 'impossible' happened)
   (GHC version 6.9.20080401 for x86_64-unknown-linux):
         typecheck/TcTyClsDecls.lhs:(883,4)-(889,42): Non-exhaustive
 patterns in function choose_univs
 }}}

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1968#comment:3>
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