[GHC] #6152: Type synonym for Type family + DataKinds won't recompile due to internal error

[GHC]

#6152: Type synonym for Type family + DataKinds won't recompile due to internal
error
---------------------------------------+------------------------------------
 Reporter:  konn                       |          Owner:                
     Type:  bug                        |         Status:  new           
 Priority:  normal                     |      Component:  Compiler      
  Version:  7.4.1                      |       Keywords:                
       Os:  MacOS X                    |   Architecture:  x86_64 (amd64)
  Failure:  GHC rejects valid program  |       Testcase:                
Blockedby:                             |       Blocking:                
  Related:                             |  
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 I have following program:
 {{{
 {-# LANGUAGE DataKinds, TypeFamilies, GADTs #-}
 module Main where

 data U = Unit

 data SU (a :: U) where
   SInt :: SU Unit

 type family I (a :: U) :: U
 type instance I Unit = Unit

 type SUI a = SU (I a)

 main :: IO ()
 main = return ()
 }}}

 This program compiles successfully, but won't recompile due to an internal
 error.

 {{{
 $ ghc WontCompile.hs
 [1 of 1] Compiling Main             ( WontCompile.hs, WontCompile.o )
 Linking WontCompile ...

 $ ghc WontCompile.hs -fforce-recomp
 [1 of 1] Compiling Main             ( WontCompile.hs, WontCompile.o )

 WontCompile.hs:12:18:
     GHC internal error: `I' is not in scope during type checking, but it
 passed the renamer
     tcl_env of environment: [(a9O, AThing k_a9X)]
     In the type `SU (I a)'
     In the type synonym declaration for `SUI'
 }}}

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6152>
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