October 2008 - Glasgow-haskell-users

RE: Type classes in GADTs
by C Rodrigues 30 Oct '08

30 Oct '08

Thanks for the explanation. I see how this wouldn't behave nicely with automatic class constraint inference. I didn't test the example on any other GHC versions. I will probably end up passing in the Eq dictionary from outside like Daniil suggested. I would prefer to do the following, but GHC doesn't accept the type signature. evidenceOfEq :: CAOp a -> (Eq a => b) -> b Neither does it accept data EqConstraint a b = EqConstraint (Eq a => b). Foiled again. _________________________________________________________________ Want to read Hotmail messages in Outlook? The Wordsmiths show you how. http://windowslive.com/connect/post/wedowindowslive.spaces.live.com-Blog-cn…

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Type classes in GADTs
by C Rodrigues 30 Oct '08

30 Oct '08

I discovered that closed type classes can be implicitly defined using GADTs. The GADT value itself acts like a class dictionary. However, GHC (6.8.3) doesn't know anything about these type classes, and it won't infer any class memberships. In the example below, an instance of Eq is not recognized. So is this within the domain of GHC's type inference, not something it shoud infer, or a bug? {-# OPTIONS_GHC -XTypeFamilies -XGADTs -XEmptyDataDecls #-} module CaseAnalysisOnGADTs where -- Commutative and associative operators. data CAOp a where Sum :: CAOp Int Disj :: CAOp Bool Concat :: CAOp String {- For any non-bottom value of type 'CAOp a', the value will have type -- CAOp Int, CAOp Bool, or CAOp String. Int, Bool, and String are all -- members of Eq. Therefore, if we have a non-bottom value of type -- 'CAOp a' then 'a' is a member of Eq. -} data D a = D !(CAOp a) (a, a) -- However, GHC won't figure this out. noEvidenceOfEq :: D a -> Bool noEvidenceOfEq (D op (e1, e2)) = e1 == e2 -- Error, no instance (Eq a) -- Unless you force it to do case analysis on constructors. evidenceOfEq :: CAOp a -> a -> a -> Bool evidenceOfEq Sum = (==) evidenceOfEq Disj = (==) evidenceOfEq Concat = (==) -- Then you can use the result from that, but GHC still won't -- recognize it as an Eq instance. useEvidenceOfEq :: D a -> Bool useEvidenceOfEq (D op (e1, e2)) = evidenceOfEq op e1 e2 _________________________________________________________________ You live life beyond your PC. So now Windows goes beyond your PC. http://clk.atdmt.com/MRT/go/115298556/direct/01/

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Re: [Haskell-cafe] Re: ghc-6.11 + OpenGL/GLUT crashes on WinXP
by Conal Elliott 28 Oct '08

28 Oct '08

No display lists. The crash happens during the GLUT call "initialize". I can trigger it from ghci with the following simple incantation: Prelude> import Graphics.UI.GLUT Prelude Graphics.UI.GLUT> initialize "foo" [] And no trouble under ghc 6.9.20080622. Stumped. :( - Conal On Tue, Oct 28, 2008 at 3:14 PM, Jefferson Heard < jefferson.r.heard(a)gmail.com> wrote: > Conal, are you using display lists at all? I've had problems with > allocating lists, but you seem to be able to leave off the allocation > step in Windows on nVidia cards so long as you're careful not to > conflict names yourself. > > On Tue, Oct 28, 2008 at 4:03 PM, Matti Niemenmaa > <matti.niemenmaa+news(a)iki.fi <matti.niemenmaa%2Bnews(a)iki.fi>> wrote: > > Conal Elliott wrote: > >> I am using glut32 rather than freeglut (and no need for patching the > darcs > >> GLUT). I wonder if glut32-vs-freeglut could account for > crash-vs-nocrash on > >> 6.10 and 6.11 but not 6.9. I'd love to hear from someone on Windows and > >> glut32. > > > > Windows XP with SP3 > > ghc-6.10.20081007 > > glut32 > > > > Works fine for me. > > > > Taking a look at my GL headers, I did have to mess with at least glut.h > to get > > something to work---whether it was to build HOpenGL, to make programs > linkable, > > or to make them runnable, I'm not sure. In any case, what I did was force > > GLUTAPIENTRY to be #defined as __stdcall. > > > > _______________________________________________ > > Haskell-Cafe mailing list > > Haskell-Cafe(a)haskell.org > > http://www.haskell.org/mailman/listinfo/haskell-cafe > > > > > > -- > I try to take things like a crow; war and chaos don't always ruin a > picnic, they just mean you have to be careful what you swallow. > > -- Jessica Edwards > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

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Subtle difference between standard instances
by David Sankel 28 Oct '08

28 Oct '08

We, at Anygma, noticed that a and b below have different behavior: a, b :: (Int->Int) -> (Int,Int) -> (Int,Int) a = fmap b = second See the blog post at http://netsuperbrain.com/blog/?p=74. The standard instances for Functor, Monad, and Applicative for tuples is strict. The Arrow on (->) when applied to tuples with first and second, however is non-strict. It is a subtle discrepancy, but it does make a difference for FRP when deriving these standard instances. Any objections to making the Functor, Monad, and Applicative instances for tuples non-strict like Arrows? David

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Re: [Haskell-cafe] ghc-6.11 + OpenGL/GLUT crashes on WinXP
by Conal Elliott 28 Oct '08

28 Oct '08

Thanks, David. Helpful data point. I am using glut32 rather than freeglut (and no need for patching the darcs GLUT). I wonder if glut32-vs-freeglut could account for crash-vs-nocrash on 6.10 and 6.11 but not 6.9. I'd love to hear from someone on Windows and glut32. Please do post a wiki page on freeglut + ghc on windows and let us know here. Could you integrate your glutWin32 patch into the darcs GLUT? - Conal On Tue, Oct 28, 2008 at 8:48 AM, David Sankel <camior(a)gmail.com> wrote: > My setup worked: > > - Windows XP. > - ghc-6.11.20081024 > - freeglut 2.4.0 > - darcs version of GLUT (with patched glutGetProcAddress [attached]) > - darcs version of OpenGL > > Getting freeglut going with ghc on windows is a bit involved. I could write > a walkthrough if there's enough interest. > > David > > 2008/10/25 Conal Elliott <conal(a)conal.net> > >> I'm getting crashes from ghc-6.10.0.20081007 and ghc-6.11.20081024 when >> doing a very simple GLUT program (below) with OpenGL-2.2.1.1 and >> GLUT-2.1.1.2 (the latest from Hackage), running on WinXP. It works fine on >> ghc-6.9.20080622 . >> >> I'd appreciate hearing about other attempts with these versions on Windows >> systems. >> >> Thanks, - Conal >> >> >> import Graphics.UI.GLUT >> >> main :: IO () >> main = do putStrLn "Initializing" >> getArgsAndInitialize >> return () >> >> >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> >>

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Instrumenting overlapping instances
by J. Garrett Morris 27 Oct '08

27 Oct '08

Hello, I'm currently studying the use of overlapping instances, and I was hoping to instrument GHC to produce some variety of list of instances that overlapped. I haven't done any GHC hacking so far, so I'm not entirely familiar with the code base. Does anyone have any guidance on which modules I should likely need to modify? Thanks, /g

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ghc-6.11 + OpenGL/GLUT crashes on WinXP
by Conal Elliott 25 Oct '08

25 Oct '08

I'm getting crashes from ghc-6.10.0.20081007 and ghc-6.11.20081024 when doing a very simple GLUT program (below) with OpenGL-2.2.1.1 and GLUT-2.1.1.2 (the latest from Hackage), running on WinXP. It works fine on ghc-6.9.20080622 . I'd appreciate hearing about other attempts with these versions on Windows systems. Thanks, - Conal import Graphics.UI.GLUT main :: IO () main = do putStrLn "Initializing" getArgsAndInitialize return ()

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Re: SVN binding with Haskell
by Christian Maeder 24 Oct '08

24 Oct '08

Hi, I've install HsSVN (version 0.3.3) using ghc-6.8.3 and Cabal-1.4.0.1, but it was a real pain (under i686 Linux 2.6.22.18-0.2-default #1 SMP) 1. I had to install subversion-devel-1.4.4-30 (of course) 2. configure went through after setting: export CPATH=/usr/include/apr-1:/usr/include/subversion-1 3. building failed with: Program error: <handle>: IO.getContents: protocol error (input contains non-character data - use binary I/O for binary data) because some comments in the sources (i.e. Subversion/FileSystem.hsc) contain funny (japanese?) characters that hsc2hs does not like. (Under Solaris and Mac this was no problem, though.) I used iconv to convert the sources and finally the included HelloWorld example went through. 4. Under Solaris, only apr-1-config and apu-1-config found the proper include path (so I needed to adjust the configure.ac file) 5. The file HsSVN.buildinfo.in has no final newline, so that the last line (containing the ld-options:) is missing in HsSVN.buildinfo after configure! 6. Running the examples under Solaris failed with: -bash-3.1$ ./HelloWorld Creating a repository "repos"... The youngest revision of the repository is 0 Storing a file "/hello" in it... HelloWorld: user error (withSubversion: caught an SvnError: UnknownError 22: Can't set position pointer in file 'repos/db/revs/0': Invalid argument) Cheers Christian Shahzad wrote: > Dear Sir/Madam, > > I am doctoral student and researcher in Technical University Vienna. I > need to manage Subversion client and run SVN commands through > Haskell6.8 , and I need to make that application for ubuntu and Windows, > Can you guide me how to make any API for Haskell to use Subversion. > > I was thinking to use c2hs to make an interface from C++ to haskell but > I could not find that a solution. There is a Package HsSVN but is also > not working. > > Can you please guide me to the solution.. > > Best Regards > > Syed

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More detail on breakage with ghc-6.10
by Duncan Coutts 23 Oct '08

23 Oct '08

All, We've been using the cabal-install build reporting stuff to get more detailed info on build failures with ghc-6.10 vs 6.8. cabal-install generates these build-reports.log files and individual log files for each build. Below is a list of packages that worked with 6.8 and fail with 6.10. If your package is on this list then you might like to take a look at the actual failure. I've posted the logs here: http://haskell.org/~duncan/ghc/hackage-failures-ghc-6.10/ There's one set for ghc-6.8 and one for 6.10. We can get quite a bit of info from these build-reports.log files just using grep, sort, uniq etc. However we also have a parser for it so we can write more interesting queries. For example, we're interested in regressions: reports68 <- fmap parseList (readFile "ghc-6.8/build-reports.log") reports610 <- fmap parseList (readFile "ghc-6.10/build-reports.log") let merged = mergeBy (comparing package) (sortBy (comparing package) reports68) (sortBy (comparing package) reports610) worked InstallOk = True worked _ = False failed InstallOk = False failed (DependencyFailed _) = False failed _ = True regressions = [ new | InBoth old new <- merged , worked (installOutcome old) && failed (installOutcome new) ] print (length regressions) mapM_ (putStrLn . display . package) regressions There are 58 in this list. Though some have been since fixed and it doesn't count packages that fail due to dependencies failing. Here's our current list. I've pruned a couple that I know have been fixed. ArrayRef-0.1.2 CLASE-2008.9.23.2 EdisonCore-1.2.1.2 HPDF-1.4 HTF-0.1 HaLeX-1.1 Hashell-0.15 Hipmunk-0.2 MemoTrie-0.0 NewBinary-0.1.1 OpenAFP-1.1 PArrows-0.1 TypeCompose-0.5 Vec-0.9.2 WebBits-0.9.2 YamlReference-0.9.2 Yampa-0.9.2.2 arrows-0.4 bytestring-show-0.2 cabal-setup-1.2.1 chp-1.1.0 cmath-0.3 fixpoint-0.1 frag-1.1.1 harpy-0.4 hasim-0.1 hask-home-2007.12.6 heap-0.4.0 hetris-0.2 hexpat-0.2 hinstaller-2008.2.16 hint-0.2.4.1 hslackbuilder-0.0.1 hsx-0.4.4 hxt-8.1.0 iException-0.0.1 libGenI-0.16.1 list-extras-0.2.2 logfloat-0.9.1 mage-1.1.0 numeric-prelude-0.0.4 parameterized-data-0.1.3 plugins-1.3 quantum-arrow-0.0.4 regex-tdfa-0.94 stream-fusion-0.1.1 streamproc-1.1 stringtable-atom-0.0.4 time-1.1.2.1 typalyze-0.1.1 unicode-prelude-0.1 utf8-light-0.3 xmonad-contrib-0.8 xmonad-utils-0.1 yhccore-0.9 Duncan

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Getting the location of data files from ghc-pkg?
by Robin Green 23 Oct '08

23 Oct '08

Is there any way of finding out where the Data-files specified in a .cabal file have been installed to? I want to script finding some TeX support files that are installed as part of the Functional MetaPost library. -- Robin

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