Type family causing GHC to hang on recompilation

I am having a problem with (re)compiling some code I have. I have two modules A and B. In A I have some classes and instances and B uses this. When I try to compile B (with cabal or ghc --make) the first time everything works. When I now modify B (add a space) B is recompiled but the compiler hangs and doesn't seems to be doing anything.

I have tested the problem with GHC (x86_64) 7.6.2. 7.6.3 and HEAD (build on 20/06/2013).

It seems to be very similar to a problem I had earlier: http://hackage.haskell.org/trac/ghc/ticket/7321 but this time there are no GADTs involved.

The code of module A (clutter that doesn't contribute to the problem has been removed):

> {-# LANGUAGE FlexibleInstances, UndecidableInstances     #-}
> {-# LANGUAGE GADTs                 #-}
> {-# LANGUAGE MultiParamTypeClasses #-}
> {-# LANGUAGE TypeFamilies, TypeOperators, ScopedTypeVariables #-}
> {-# LANGUAGE FlexibleContexts #-}
> {-# LANGUAGE DataKinds, PolyKinds #-}
> 
> module A where
> 
> import GHC.Generics
> 
> class QA a where
>   type QRep a
>   type QRep a = QRep (GRep (Rep a))
> 
> instance QA () where
>   type QRep () = ()
> 
> -- Kind-polymorphic proxies;
> data Pr (a :: k) = Pr
> 
> class (QA (GRep f)) => CaseOf (f :: * -> *) where
>     type Alg f r k :: *
>     type GRep f :: *
> 
> -- Only used for the product structure
> class QA (ProdRep f) => CaseOfProd (f :: * -> *) where
>   type ProdAlg f r :: *
>   type ProdRep f :: *

The code of module B:

> module B where
> import qualified A

Given that the code type checks (and if I do not recompile and make an executable directly it actually works) I think this is a bug that might be similar to the bug mentioned in ticket 7321.

Trac metadata

Trac field	Value
Version	7.6.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	jeroen.weijers@uni-tuebingen.de
Operating system
Architecture