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