If the problem is happening in HEAD, it's a legitimate bug. Please file a report and I'll take a look at it, as I'm in that area of the codebase right now. Thanks! Richard From: glasgow-haskell-users-bounces@haskell.org [mailto:glasgow-haskell-users-bounces@haskell.org] On Behalf Of Jeroen Weijers Sent: 21 June 2013 09:01 To: glasgow-haskell-users@haskell.org Subject: Type families causing the compiler to hang on recompilation Hello, 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. 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. Does anybody recognise the problem? Should I create a ticket? Cheers, Jeroen Weijers