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</o:shapelayout></xml><![endif]--></head><body lang=EN-GB link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";mso-fareast-language:EN-US'>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.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";mso-fareast-language:EN-US'>Thanks!<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";mso-fareast-language:EN-US'>Richard<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><b><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri","sans-serif"'>From:</span></b><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri","sans-serif"'> glasgow-haskell-users-bounces@haskell.org [mailto:glasgow-haskell-users-bounces@haskell.org] <b>On Behalf Of </b>Jeroen Weijers<br><b>Sent:</b> 21 June 2013 09:01<br><b>To:</b> glasgow-haskell-users@haskell.org<br><b>Subject:</b> Type families causing the compiler to hang on recompilation<o:p></o:p></span></p><p class=MsoNormal><o:p> </o:p></p><div><p class=MsoNormal>Hello,<o:p></o:p></p><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>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.<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>I have tested the problem with GHC (x86_64) 7.6.2. 7.6.3 and HEAD.<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>It seems to be very similar to a problem I had earlier: <a href="http://hackage.haskell.org/trac/ghc/ticket/7321">http://hackage.haskell.org/trac/ghc/ticket/7321</a><o:p></o:p></p></div><div><p class=MsoNormal>but this time there are no GADTs involved.<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>The code of module A (clutter that doesn't contribute to the problem has been removed):<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><div><p class=MsoNormal>> {-# LANGUAGE FlexibleInstances, UndecidableInstances #-}<o:p></o:p></p></div><div><p class=MsoNormal>> {-# LANGUAGE GADTs #-}<o:p></o:p></p></div><div><p class=MsoNormal>> {-# LANGUAGE MultiParamTypeClasses #-}<o:p></o:p></p></div><div><p class=MsoNormal>> {-# LANGUAGE TypeFamilies, TypeOperators, ScopedTypeVariables #-}<o:p></o:p></p></div><div><p class=MsoNormal>> {-# LANGUAGE FlexibleContexts #-}<o:p></o:p></p></div><div><p class=MsoNormal>> {-# LANGUAGE DataKinds, PolyKinds #-}<o:p></o:p></p></div><div><p class=MsoNormal>> <o:p></o:p></p></div><div><p class=MsoNormal>> module A where<o:p></o:p></p></div><div><p class=MsoNormal>> <o:p></o:p></p></div><div><p class=MsoNormal>> import GHC.Generics<o:p></o:p></p></div><div><p class=MsoNormal>> <o:p></o:p></p></div><div><p class=MsoNormal>> class QA a where<o:p></o:p></p></div><div><p class=MsoNormal>> type QRep a<o:p></o:p></p></div><div><p class=MsoNormal>> type QRep a = QRep (GRep (Rep a))<o:p></o:p></p></div><div><p class=MsoNormal>> <o:p></o:p></p></div><div><p class=MsoNormal>> instance QA () where<o:p></o:p></p></div><div><p class=MsoNormal>> type QRep () = ()<o:p></o:p></p></div><div><p class=MsoNormal>> <o:p></o:p></p></div><div><p class=MsoNormal>> -- Kind-polymorphic proxies;<o:p></o:p></p></div><div><p class=MsoNormal>> data Pr (a :: k) = Pr<o:p></o:p></p></div><div><p class=MsoNormal>> <o:p></o:p></p></div><div><p class=MsoNormal>> class (QA (GRep f)) => CaseOf (f :: * -> *) where<o:p></o:p></p></div><div><p class=MsoNormal>> type Alg f r k :: *<o:p></o:p></p></div><div><p class=MsoNormal>> type GRep f :: *<o:p></o:p></p></div><div><p class=MsoNormal>> <o:p></o:p></p></div><div><p class=MsoNormal>> -- Only used for the product structure<o:p></o:p></p></div><div><p class=MsoNormal>> class QA (ProdRep f) => CaseOfProd (f :: * -> *) where<o:p></o:p></p></div><div><p class=MsoNormal>> type ProdAlg f r :: *<o:p></o:p></p></div><div><p class=MsoNormal>> type ProdRep f :: *<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>The code of module B:<o:p></o:p></p></div><div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>> module B where<o:p></o:p></p></div><div><p class=MsoNormal>> import qualified A<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>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. <o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>Does anybody recognise the problem? Should I create a ticket?<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>Cheers,<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>Jeroen Weijers<o:p></o:p></p></div></div></div></div></div></body></html>