May 2014 - Haskell-Cafe

Typeclasses -- if does not satisfy
by Dmitry Bogatov 24 May '14

24 May '14

Hello! I am working on package to generalize common `runSomeThing` and `runSomethingT` functions. It is very easy to generalize runStateT and runReaderT like class Runnable a where type RunResult a run :: a -> RunResult a instance Runnable (StateT s m a) where --- Why ScopedTypeVariables do not work here? type RunResult (StateT s m a) = s -> m (a, s) run = runStateT --- ReaderT absolutely the same But problem is that `State s a` is in fact `StateT s Identity a` and I get type family conflicts. In fact, it boils down to following: type family TestIdentity (m :: * -> *) type instance TestIdentity Identity = Int type instance TestIdentity m = () -- Anything but Identity. In general, with all this TypeClass magic, I have a lot of ways that something belong to some class, and no (aside OverlappingInstances) to tell that it does NOT belong. I belive, there is reason to, but I do not see it. Also, seems even TH does not helps here. PS. Please, keep me in To: -- Best regards, Dmitry Bogatov <KAction(a)gnu.org>, Free Software supporter, esperantisto and netiquette guardian. git://kaction.name/rc-files.git GPG: 54B7F00D

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haskell on OpenBSD 5.5
by Michael S 23 May '14

23 May '14

Good day all, I installed OpenBSD 5.5 in order to learn haskell. There are a few glitches however. I installed the haskell-platform meta-package and the issues I noticed are: - hs-vector wouldn't install - ghci wouldn't start, the message: unable to load package `integer-gmp' Has anyone experienced the same issue? Is this happening on OpenBSD 5.4? Is this OpenBSD specific? Thanks in advance.

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hasktags and sublime?
by Edsko de Vries 23 May '14

23 May '14

Hey, has anyone has much luck with hasktags and sublime (3, OSX)? If I create the tags file with hasktags -c it complains that it cannot find any relevant tags file, and when I create it with hasktags -e that warning disappears but I can't jump to any definition (it always says that the tag is not found). -E

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OpenGL performance issue on OSX
by Michael Baker 23 May '14

23 May '14

I'm using OpenGLRaw and I'm getting 3 frames per second trying to draw 8000 triangles. When I profile the application, I see that almost all of the time is taken by a call to CGLFlushDrawable, which is apparently OSX's function for swapping the back buffer to the front buffer. Has anyone else run into a problem like this? I seem to recall a thread a while ago about a Haskell specific OpenGL performance issue, but I can't find it now.

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Haskell-cafe] Yesod can't build on 64 bit 7.8.2 Windows
by Stuart Mills 22 May '14

22 May '14

Apparently in going to Mingw 64 the packages "system-fileio" and "unix-compat" no longer compiled because some Windows routines were not available in their expected "names". I reported the issues and John Milikin quickly patched "system-fileio" (thanks John, if you're listening). The unix-compat issue is still outstanding (not sure if it's still being maintained), but I was able to patch it by adding underscores to elements like "snprintf". ( _snprintf works, _stat instead of stat, etc.) These were the same types of changes that worked for system-fileio. Note that this approach may break Win32. The next issue is when linking with yaml (ghc.exe: panic!). This was reported as a GHC bug 2 weeks ago (#9080) by maun, who was trying to build GHCJS. I get the exact same error in building Yesod. Because of Yesod, I think #9080 should be promoted to high priority, and it would be great if someone could bring unix-compat up to date. Thanks Stuart

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using withAnnotations from Graphics.Rendering.Plot.Figure
by Albert Cardona 22 May '14

22 May '14

Hi all, given two Vector and a list of strings, I generate a plot of one vector as a function of the other [1]. At each x,y point, I am trying to place the corresponding string. For the purpose, I zip3 all three sequences, define an annotation function, and invoke it with mapM_ in the context of withAnnotations [2]: withPlot (1, 1) $ do ... let annotation (x, y, label) = text (x + 2, y) (setText label) in withAnnotations $ do mapM_ annotation $ zip3 (toList vx) (toList vy) labels The code above compiles and runs, the plot shows, but no text annotations appear at all. I understand that I am not using the Annote monad correctly: the mapM_ drops every returned value, so the state is not altered. What is the correct way to invoke withAnnotations over a list of (x, y, String) ? Needless to say, I am a beginner in Haskell. Apologies if the above is too trivial. Thanks very much in advance. Albert [1] https://github.com/acardona/haskell-lib/blob/master/CATMAID/Analysis/Graph/… [2] http://hackage.haskell.org/package/plot-0.2.3/docs/Graphics-Rendering-Plot-… -- http://albert.rierol.net http://www.ini.uzh.ch/~acardona/

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instance Alternative (Either [a])
by Corentin Dupont 22 May '14

22 May '14

Hi guys! I'd like to implement the instance in the subject: instance Alternative (Either [a]) However the instance in Control.Monad.Trans.Error.Error gets in the way... I cannot use this one, it works only with Strings. My use case is that the Either handle in the Right a final value, or else in the Left a list of things "left to do" to compute the value. How can I do? Thanks! Corentin

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extending Do notation
by silvio 22 May '14

22 May '14

#The problem > grep -r ">>=" base | head -3 getExecutablePath = _NSGetExecutablePath >>= realpath then peek p_argv >>= peek >>= peekFilePath ... = getFileSystemEncoding >>= \enc -> GHC.withCString enc fp f > grep -r "flip" base | head -3 ... (o,n,[] ) -> return (foldl (flip id) defaultOptions o, n) peekCString s = getForeignEncoding >>= flip GHC.peekCString s peekCStringLen s = getForeignEncoding >>= flip GHC.peekCStringLen s I don't know how often i've seen this one ... >>= flip ... when really we it should have been ... {...} Only because we can't just execute an IO action and fill in the result. And this list doesn't even include examples where the programmer had to resort to making a pointless temp variable just to avoid using too many complicated functions. #The solution > grep -r ">>=" base | head -3 getExecutablePath = _do realpath { _NSGetExecutablePath } then peekFilePath { peek {peek p_argv} } ... = do GHC.withCString {getFileSystemEncoding} fp f > grep -r "flip" base | head -3 ... (o,n,[] ) -> return (foldl (flip id) defaultOptions o, n) -- leave peekCString s = GHC.peekCString {getForeignEncoding} s peekCStringLen s = GHC.peekCStringLen {getForeignEncoding} s I think there is no use of {} in haskell that does not come after a key word but has an expression inside. But it could be some other syntax too. silvio

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Announce: ghc-imported-from-0.2.0.4
by Carlo Hamalainen 22 May '14

22 May '14

Hi, I have released v0.2.0.4 of my utility ghc-imported-from. It lets you quickly jump to the Haddock documentation for a symbol in a Haskell source file. This version has a few bug fixes, is significantly faster, and has better support for cabal sandboxes. Short screencast showing the vim plugin: https://www.youtube.com/watch?v=7yO_VGCWMu8 (make sure it plays in 720p HD) Hackage page: http://hackage.haskell.org/package/ghc-imported-from-0.2.0.4 Vim plugin: https://github.com/carlohamalainen/ghcimportedfrom-vim Cheers, -- Carlo Hamalainen http://carlo-hamalainen.net

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[Haskell] ANNOUNCE: Haskell Communities and Activities Report (26th ed., May 2014)
by Mihai Maruseac 22 May '14

22 May '14

On behalf of all the contributors, we are pleased to announce that the Haskell Communities and Activities Report (26th edition, May 2014) is now available, in PDF and HTML formats: http://www.haskell.org/communities/05-2014/report.pdf http://www.haskell.org/communities/05-2014/html/report.html Many thanks go to all the people that contributed to this report, both directly, by sending in descriptions, and indirectly, by doing all the interesting things that are reported. We hope you will find it as interesting a read as we did. If you have not encountered the Haskell Communities and Activities Reports before, you may like to know that the first of these reports was published in November 2001. Their goal is to improve the communication between the increasingly diverse groups, projects, and individuals working on, with, or inspired by Haskell. The idea behind these reports is simple: Every six months, a call goes out to all of you enjoying Haskell to contribute brief summaries of your own area of work. Many of you respond (eagerly, unprompted, and sometimes in time for the actual deadline) to the call. The editors collect all the contributions into a single report and feed that back to the community. When we try for the next update, six months from now, you might want to report on your own work, project, research area or group as well. So, please put the following into your diaries now: ======================================== End of October 2014: target deadline for contributions to the November 2014 edition of the HC&A Report ======================================== Unfortunately, many Haskellers working on interesting projects are so busy with their work that they seem to have lost the time to follow the Haskell related mailing lists and newsgroups, and have trouble even finding time to report on their work. If you are a member, user or friend of a project so burdened, please find someone willing to make time to report and ask them to "register" with the editors for a simple e-mail reminder in October (you could point us to them as well, and we can then politely ask if they want to contribute, but it might work better if you do the initial asking). Of course, they will still have to find the ten to fifteen minutes to draw up their report, but maybe we can increase our coverage of all that is going on in the community. Feel free to circulate this announcement further in order to reach people who might otherwise not see it. Enjoy! Mihai Maruseac and Alejandro Serrano Mena <hcar at haskell.org> -- Mihai Maruseac (MM) "If you don't know, the thing to do is not to get scared, but to learn." -- Atlas Shrugged.

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