April 2010 - Glasgow-haskell-users

ANNOUNCE: GHC 6.12.2 Release Candidate 1
by Ian Lynagh 16 Apr '10

16 Apr '10

Hi all, We are pleased to announce the first release candidate for GHC 6.12.2: http://www.haskell.org/ghc/dist/6.12.2-rc1/ As well as the source tarball: ghc-6.12.1.20100330-src.tar.bz2 there are installers for Windows (i386) and OS X (i386), and binary distributions for x86_64/Linux and i386/Linux. Please test as much as possible; bugs are much cheaper if we find them before the release! Thanks Ian, on behalf of the GHC team

4 5

interaction of GADTs and data families: a bug?
by Sebastian Fischer 16 Apr '10

16 Apr '10

Dear GHC experts, Certain behaviour when using {-# LANGUAGE GADTs, TypeFamilies #-} surprises me. The following is accepted by GHC 6.12.1: data GADT a where BoolGADT :: GADT Bool foo :: GADT a -> a -> Int foo BoolGADT True = 42 But the following is not: data family DataFam a data instance DataFam Bool where BoolDataFam :: DataFam Bool fffuuuu :: DataFam a -> a -> Int fffuuuu BoolDataFam True = 42 GHC 6.12.1 throws the following error (GHC 6.10.4 panics): Couldn't match expected type `a' against inferred type `Bool' `a' is a rigid type variable bound by the type signature for `fffuuuu' at gadtDataFam.hs:13:19 In the pattern: BoolDataFam In the definition of `fffuuuu': fffuuuu BoolDataFam True = 42 I expect that `fffuuuu` should be accepted just like `foo`. Do I expect too much? Cheers, Sebastian -- Underestimating the novelty of the future is a time-honored tradition. (D.G.)

5 10

Advice on Multiple GHC installations
by Bradford Larsen 16 Apr '10

16 Apr '10

I would like to have several versions of ghc installed simultaneously, on the handful of Ubuntu systems I work on. In the past, I have had just a single version of ghc installed on each system, usually the most recent stable generic Linux binary installation. Three questions: 1. Does there exist an `experimental' apt repository for Ubuntu anywhere which packages versions of ghc more recent than 6.8? 2. If I cannot install multiple ghc versions from a different apt repository, does anyone have advice for how to work with multiple simultaneous installations? A how-to guide or anything like that? 3. Does having multiple installations break cabal at all? I'd like to be able to use ghc 6.12.* by default, but be able to selectively choose an older toolchain for compatibility purposes, bug hunting, etc. Thanks! Sincerely, Brad

5 7

testing 6.12.2-pre
by Serge D. Mechveliani 15 Apr '10

15 Apr '10

Dear GHC developers, I have tested ghc-6.12.1.20100330 on Debian Linux, i386-family, on the DoCon test, without profilig. It looks all right. ----------------- Serge Mechveliani mechvel(a)botik.ru

3 3

Can't install Criterion package on ghc ..
by Mozhgan kabiri 13 Apr '10

13 Apr '10

Hi, I am trying to install Criterion package, but I keep getting an error and I can't figure it out why it is like this !! mozhgan@Mozhgan-KCh:~$ cabal install Criterion Resolving dependencies... Configuring vector-algorithms-0.3... Preprocessing library vector-algorithms-0.3... Building vector-algorithms-0.3... [1 of 9] Compiling Data.Vector.Algorithms.Common ( Data/Vector/Algorithms/Common. hs, dist/build/Data/Vector/Algorithms/Common.o ) [2 of 9] Compiling Data.Vector.Algorithms.Search ( Data/Vector/Algorithms/Search.hs, dist/build/Data/Vector/Algorithms/Search.o ) [3 of 9] Compiling Data.Vector.Algorithms.Radix ( Data/Vector/Algorithms/Radix.hs, dist/build/Data/Vector/Algorithms/Radix.o ) [4 of 9] Compiling Data.Vector.Algorithms.Optimal ( Data/Vector/Algorithms/Optimal.hs, dist/build/Data/Vector/Algorithms/Optimal.o ) [5 of 9] Compiling Data.Vector.Algorithms.Insertion ( Data/Vector/Algorithms/Insertion.hs, dist/build/Data/Vector/Algorithms/Insertion.o ) [6 of 9] Compiling Data.Vector.Algorithms.Merge ( Data/Vector/Algorithms/Merge.hs, dist/build/Data/Vector/Algorithms/Merge.o ) [7 of 9] Compiling Data.Vector.Algorithms.TriHeap ( Data/Vector/Algorithms/TriHeap.hs, dist/build/Data/Vector/Algorithms/TriHeap.o ) [8 of 9] Compiling Data.Vector.Algorithms.Intro ( Data/Vector/Algorithms/Intro.hs, dist/build/Data/Vector/Algorithms/Intro.o ) ghc: panic! (the 'impossible' happened) (GHC version 6.10.4 for i386-unknown-linux): idInfo co{v a9WB} [tv] Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug cabal: Error: some packages failed to install: criterion-0.5.0.0 depends on vector-algorithms-0.3 which failed to install. statistics-0.5.1.0 depends on vector-algorithms-0.3 which failed to install. vector-algorithms-0.3 failed during the building phase. The exception was: exit: ExitFailure 1 I tried to install Statistics and vector-algorithms package separately before installing the Criterion package itself .. but it wasn't successful. Thanks, Mozhgan

1 0

Can't install Criterion package on ghc ..
by Mozhgan kabiri 13 Apr '10

13 Apr '10

Hi, I am trying to install Criterion package, but I keep getting an error and I can't figure it out why it is like this !! mozhgan@Mozhgan-KCh:~$ cabal install Criterion Resolving dependencies... Configuring vector-algorithms-0.3... Preprocessing library vector-algorithms-0.3... Building vector-algorithms-0.3... [1 of 9] Compiling Data.Vector.Algorithms.Common ( Data/Vector/Algorithms/Common.hs, dist/build/Data/Vector/Algorithms/Common.o ) [2 of 9] Compiling Data.Vector.Algorithms.Search ( Data/Vector/Algorithms/Search.hs, dist/build/Data/Vector/Algorithms/Search.o ) [3 of 9] Compiling Data.Vector.Algorithms.Radix ( Data/Vector/Algorithms/Radix.hs, dist/build/Data/Vector/Algorithms/Radix.o ) [4 of 9] Compiling Data.Vector.Algorithms.Optimal ( Data/Vector/Algorithms/Optimal.hs, dist/build/Data/Vector/Algorithms/Optimal.o ) [5 of 9] Compiling Data.Vector.Algorithms.Insertion ( Data/Vector/Algorithms/Insertion.hs, dist/build/Data/Vector/Algorithms/Insertion.o ) [6 of 9] Compiling Data.Vector.Algorithms.Merge ( Data/Vector/Algorithms/Merge.hs, dist/build/Data/Vector/Algorithms/Merge.o ) [7 of 9] Compiling Data.Vector.Algorithms.TriHeap ( Data/Vector/Algorithms/TriHeap.hs, dist/build/Data/Vector/Algorithms/TriHeap.o ) [8 of 9] Compiling Data.Vector.Algorithms.Intro ( Data/Vector/Algorithms/Intro.hs, dist/build/Data/Vector/Algorithms/Intro.o ) ghc: panic! (the 'impossible' happened) (GHC version 6.10.4 for i386-unknown-linux): idInfo co{v a9WB} [tv] Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug cabal: Error: some packages failed to install: criterion-0.5.0.0 depends on vector-algorithms-0.3 which failed to install. statistics-0.5.1.0 depends on vector-algorithms-0.3 which failed to install. vector-algorithms-0.3 failed during the building phase. The exception was: exit: ExitFailure 1 I tried to install Statistics and vector-algorithms package separately before installing the Criterion package itself .. but it wasn't successful. Thanks, Mozhgan

1 0

Deriving regression or bad code?
by Ron Alford 12 Apr '10

12 Apr '10

I've attached the simplest example of my code that used to compile in GHC 6.10 now gives the error in GHC 6.12.1: baddata.hs:33:14: No instances for (Data Const, Data Var) arising from the 'deriving' clause of a data type declaration at baddata.hs:33:14-17 Possible fix: add an instance declaration for (Data Const, Data Var) or use a standalone 'deriving instance' declaration instead, so you can specify the instance context yourself When deriving the instance for (Data (Domain e g)) If I replace: > data Domain e g = Domain > (Expr (Const :+: Var)) > deriving (Data, Typeable) with: > data Domain e g = Domain > (Expr (Const)) > deriving (Data, Typeable) then everything compiles. If nothing else, the error message is misleading. -Ron

2 5

GHC internal error
by Philip Weaver 06 Apr '10

06 Apr '10

Hi all, A program that I built with GHC is crashing at runtime with the following error: internal error: eval_thunk_selector: strange selectee 12 I have not found much via Google, just an old post regarding ghc 6.0 that recommends cleaning and rebuilding. I have cleaned the build directory and re-built the executable, and I still get the error. The program is a compiler, and this error began showing up after I added support for memoization of results using the ST Monad and STRefs. For example, the following function creates a reference to a thunk: newMutableRef m = do ref <- newSTRef $ error "access ref too soon!" let m' = do r <- m writeSTRef ref (return r) return r writeSTRef ref m' return $ ref Here's some information about my system: - GHC 6.12.1 - Mac OS X 10.6.3 (Snow Leopard) So, what could cause this error? Any suggestions that can help me narrow down the problem would be greatly appreciated. If this is in fact a GHC bug, I'd like to find a workaround for now and also reproduce it in a small example so I can file a bug report. - Philip

3 3

ClockTime closure linking issue
by Gracjan Polak 05 Apr '10

05 Apr '10

Hi all, Probable bug in GHC, I want to inquire before I report it proper. Did anybody see something like this: c:\Sources\happstack\happstack\templates\project>cabal build [1 of 1] Compiling Main ( Setup.hs, dist\setup\Main.o ) Linking .\dist\setup\setup.exe ... Preprocessing executables for guestbook-1.0... Building guestbook-1.0... [11 of 11] Compiling Main ( src\Main.hs, dist\build\guestbook-server \guestbook-server-tmp\Main.o ) Linking dist\build\guestbook-server\guestbook-server.exe ... dist\build\guestbook-server\guestbook-server-tmp\GuestBook\State2.o:fake:(.text+ 0x6d89): undefined reference to `happstackzm0zi4zi3_HappstackziStateziClockTime_ constrZMabmKZN_closure' dist\build\guestbook-server\guestbook-server-tmp\GuestBook\State2.o:fake:(.text+ 0x6dd1): undefined reference to `happstackzm0zi4zi3_HappstackziStateziClockTime_ dataTypeZMabmJZN_closure' [...lots of same messages skipped...] collect2: ld returned 1 exit status Application is from http://patch-tag.com/r/mae/happstack/snapshot/current/content/pretty/happst… The Glorious Glasgow Haskell Compilation System, version 6.12.1 System Windows Vista 32bit. Help! -- Gracjan

2 2

Different behavior of GHC 6.10.1 and Hugs (Sep 2006)
by Vladimir Reshetnikov 03 Apr '10

03 Apr '10

Hi list, GHC 6.10.1: Prelude> :t let f x y = return x == return y in f let f x y = return x == return y in f :: (Eq (m a), Monad m) => a -> a -> Bool Hugs (Sep 2006): Hugs> :t let f x y = return x == return y in f ERROR - Ambiguous type signature in inferred type *** ambiguous type : (Eq (a b), Monad a) => b -> b -> Bool *** assigned to : f Who is right? -- Thanks Vladimir

2 1