June 2013 - Haskell-Cafe

[haskell.org Google Summer of Code] The Summer of Code is officially under way.
by Edward Kmett 18 Jun '13

18 Jun '13

The "getting to know your mentor" period has passed and the Summer of Code has officially begun. Keep in mind that mid-term evaluations will begin July 29th, so students will need to hit the ground running. I'm looking forward to seeing what we can accomplish together this year! -Edward

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opengl type confusion
by briand＠aracnet.com 17 Jun '13

17 Jun '13

This, wireframe :: Double -> Double -> Double -> IO () wireframe wx wy wz = do -- yz plane renderPrimitive LineLoop $ do vertex $ Vertex3 0.0 0.0 0.0 vertex $ Vertex3 0.0 wy 0.0 vertex $ Vertex3 0.0 wy wz vertex $ Vertex3 0.0 0.0 wz produces this: No instance for (VertexComponent Double) arising from a use of `vertex' Possible fix: add an instance declaration for (VertexComponent Double) In the expression: vertex In a stmt of a 'do' block: vertex $ Vertex3 0.0 wy 0.0 In the second argument of `($)', namely `do { vertex $ Vertex3 0.0 0.0 0.0; vertex $ Vertex3 0.0 wy 0.0; vertex $ Vertex3 0.0 wy wz; vertex $ Vertex3 0.0 0.0 wz }' and thusly this :-( Changing the declaration to GLdouble -> GLdouble -> GLdouble -> IO() and using (0.0::GLdouble) fixes it, and I'm not clear on why it's not automagic. There are many times I see the compiler doing type conversion an numerican arguments although sometimes the occasional fracSomethingIntegralorOther is required. I was hoping for some enlightenment. Thank you. Brian

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ANN: custom-hackage
by Niklas Hambüchen 16 Jun '13

16 Jun '13

https://github.com/nh2/custom-hackage An (almost trivial) script to generate 00-index.tar.gz which is necessary to run your own `remote-repo`. If you are a company that has to rely on that not everybody with a Hackage account can run arbitrary code on your computer at your next cabal install, and you want to make available only select versions of packages (as opposed to a full hackage mirror), this is for you. Just drop your tars into the directory structure, run the script and serve it over HTTP.

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ANNOUNCE: som-4.0 (for data analysis and visualisation)
by Amy de Buitléir 16 Jun '13

16 Jun '13

Do you have some data that you'd like to understand better? I'm happy to announce a new release of a package called som that may help: http://hackage.haskell.org/package/som https://github.com/mhwombat/som/wiki (wiki) A Kohonen Self-organising Map (SOM) maps input patterns onto a regular grid (usually two-dimensional) where each node in the grid is a model of the input data, and does so using a method which ensures that any topological relationships within the input data are also represented in the grid. This implementation supports the use of non-numeric patterns. In layman's terms, a SOM can be useful when you want to discover the underlying structure of some data. I have a brief tutorial in the wiki, which I hope to expand over the next few weeks. WHAT'S NEW - It is now easier to for non-math types to create a SOM (see defaultSOM) - Added another example to the wiki

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Call for Papers IFL 2013
by publicityifl＠gmail.com 16 Jun '13

16 Jun '13

Hello, Please, find below the second call for papers for IFL 2013. Please forward these to anyone you think may be interested. Apologies for any duplicates you may receive. best regards, Jurriaan Hage Publicity Chair of IFL CALL FOR PAPERS 25th SYMPOSIUM ON IMPLEMENTATION AND APPLICATION OF FUNCTIONAL LANGUAGES - IFL 2013 RADBOUD UNIVERSITY NIJMEGEN, THE NETHERLANDS ACM In-Cooperation / ACM SIGPLAN AUGUST 28 - 30 2013 "Landgoed Holthurnsche Hof" http://ifl2013.cs.ru.nl We are proud to announce that the 25th edition of the IFL series returns to its roots at the Radboud University Nijmegen in the Netherlands. The symposium is held from 28th to 30th of August 2013. Scope ----- The goal of the IFL symposia is to bring together researchers actively engaged in the implementation and application of functional and function-based programming languages. IFL 2013 will be a venue for researchers to present and discuss new ideas and concepts, work in progress, and publication-ripe results related to the implementation and application of functional languages and function-based programming. Following the IFL tradition, IFL 2013 will use a post-symposium review process to produce the formal proceedings which will be published in the ACM Digital Library. All participants of IFL 2013 are invited to submit either a draft paper or an extended abstract describing work to be presented at the symposium. At no time may work submitted to IFL be simultaneously submitted to other venues; submissions must adhere to ACM SIGPLAN's republication policy: http://www.sigplan.org/Resources/Policies/Republication The submissions will be screened by the program committee chair to make sure they are within the scope of IFL, and will appear in the draft proceedings distributed at the symposium. Submissions appearing in the draft proceedings are not peer-reviewed publications. Hence, publications that appear only in the draft proceedings do not count as publication for the ACM SIGPLAN republication policy. After the symposium, authors will be given the opportunity to incorporate the feedback from discussions at the symposium and will be invited to submit a revised full article for the formal review process. From the revised submissions, the program committee will select papers for the formal proceedings considering their correctness, novelty, originality, relevance, significance, and clarity. Invited Speaker --------------- Lennart Augustsson, currently employed by the Standard Chartered Bank, well-known for his work on Haskell, parallel Haskell, Cayenne, and Bluespec, is the invited speaker of IFL 2013. He will be talking about practical applications of functional programming. Submission Details ------------------ Submission deadline draft papers: July 31 Notification of acceptance for presentation: August 2 Early registration deadline: August 7 Late registration deadline: August 14 Submission deadline for pre-symposium proceedings: August 21 25th IFL Symposium: August 28-30 Submission deadline for post-symposium proceedings: November 11 Notification of acceptance for post-symposium proceedings: December 18 Camera-ready version for post-symposium proceedings: February 3 2014 Prospective authors are encouraged to submit papers or extended abstracts to be published in the draft proceedings and to present them at the symposium. All contributions must be written in English. Papers must adhere to the standard ACM two columns conference format. For the pre-symposium proceedings we adopt a 'weak' page limit of 12 pages. For the post-symposium proceedings the page limit of 12 pages is firm. A suitable document template for LaTeX can be found at: http://www.acm.org/sigs/sigplan/authorInformation.htm Papers are to be submitted via the conference's EasyChair submission page: https://www.easychair.org/conferences/?conf=ifl2013 Topics ------ IFL welcomes submissions describing practical and theoretical work as well as submissions describing applications and tools in the context of functional programming. If you are not sure whether your work is appropriate for IFL 2013, please contact the PC chair at rinus(a)cs.ru.nl. Topics of interest include, but are not limited to: language concepts type systems, type checking, type inferencing compilation techniques staged compilation run-time function specialization run-time code generation partial evaluation (abstract) interpretation metaprogramming generic programming automatic program generation array processing concurrent/parallel programming concurrent/parallel program execution embedded systems web applications (embedded) domain specific languages security novel memory management techniques run-time profiling performance measurements debugging and tracing virtual/abstract machine architectures validation, verification of functional programs tools and programming techniques (industrial) applications Peter Landin Prize ------------------ The Peter Landin Prize is awarded to the best paper presented at the symposium every year. The honoured article is selected by the program committee based on the submissions received for the formal review process. The prize carries a cash award equivalent to 150 Euros. Programme committee ------------------- Thomas Arts, Quviq, Gothenburg, Sweden Andrew Butterfield, Trinity College, Dublin, Ireland Edwin Brady, University of St. Andrews, UK Clemens Grelck, University of Amsterdam, Netherlands Adam Granicz, IntelliFactory, Budapest, Hungary Jeremy Gibbons, University of Oxford, UK Fritz Henglein, University of Copenhagen, Denmark Stephan Herhut, Intel Labs, Santa Clara, US Ralf Hinze (co-chair), University of Oxford, UK Zoltán Horváth, Eötvös Loránd University, Budapest, Hungary Zhenjiang Hu, University of Tokyo, Japan Mauro Jaskelioff, Universidad Nacional de Rosario, Argentina Johan Jeuring, University of Utrecht, Netherlands Rita Loogen, University of Marburg, Germany Marco T. Morazán, Seton Hall University, New Jersey, US Dominic Orchard, University of Cambridge, UK Rinus Plasmeijer (chair), Radboud University Nijmegen, Netherlands Tim Sheard, Portland State University, US Sam Tobin-Hochstadt, Northeastern University / Indiana University, US Peter Thiemann, University of Freiburg, Germany Simon Thompson, University of Kent, UK Venue ----- The 25th IFL is organized by the Radboud University Nijmegen, Model Based Software Development Department at the Nijmegen Institute for Computing and Information Sciences. The event is held in the Landgoed Holthurnsche Hof, a rural estate in the woodlands surrounding Nijmegen. It can be reached quickly and easily by public transport.

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Problems with GHC API and error handling
by Daniel F 16 Jun '13

16 Jun '13

Hello, everyone. I am in need of setting up custom exception handlers when using GHC API to compile modules. Right now I have the following piece of code: * Main.hs: -------------------------------------------------------------------------------------------------- import GHC import GHC.Paths import MonadUtils import Exception import Panic import Unsafe.Coerce import System.IO.Unsafe handleException :: (ExceptionMonad m, MonadIO m) => m a -> m (Either String a) handleException m = ghandle (\(ex :: SomeException) -> return (Left (show ex))) $ handleGhcException (\ge -> return (Left (showGhcException ge ""))) $ flip gfinally (liftIO restoreHandlers) $ m >>= return . Right initGhc :: Ghc () initGhc = do dfs <- getSessionDynFlags setSessionDynFlags $ dfs { hscTarget = HscInterpreted , ghcLink = LinkInMemory } return () test :: IO (Either String Int) test = handleException $ runGhc (Just libdir) $ do initGhc setTargets =<< sequence [ guessTarget "./test/file1.hs" Nothing ] graph <- depanal [] False loaded <- load LoadAllTargets -- when (failed loaded) $ throw LoadingException setContext (map (IIModule . moduleName . ms_mod) graph) let expr = "main" ty <- exprType expr -- throws exception if doesn't typecheck output ty res <- unsafePerformIO . unsafeCoerce <$> compileExpr expr return res -------------------------------------------------------------------------------------------------- * file1.hs: ---------------------------- module Main where main = do return x ---------------------------- The problem is when I run the 'test' function above I receive the following output: h> test test/file1.hs:4:10: Not in scope: `x' Left "Cannot add module Main to context: not a home module" it :: Either String Int So, if I understand this correctly, my exception handler does indeed catch an exception correctly, however, I still receive some output which I want to be captured. Is there a way to do this? -- Sincerely yours, -- Daniil Frumin

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Efficiency/Evaluation Question
by Christopher Howard 15 Jun '13

15 Jun '13

I'm working through some beginner-level "keyboard problems" I found at users.csc.calpoly.edu. One problem is the Saddle Points problem: quote: -------- Write a program to search for the "saddle points" in a 5 by 5 array of integers. A saddle point is a cell whose value is greater than or equal to any in its row, and less than or equal to any in its column. There may be more than one saddle point in the array. Print out the coordinates of any saddle points your program finds. Print out "No saddle points" if there are none. -------- Let's say I use a simple list grid like so: code: -------- array = Grid 5 [ [1,5,3,6,4] , [8,2,6,3,8] , [3,8,7,2,9] , [0,3,7,1,2] , [7,2,7,4,5] ] data Grid = Grid Int [[Int]] -------- And let's say I take a brute force approach, moving through each cell, checking to see if it is the greatest in its row and the least in its column. And say I have functions like so for getting rows and columns: code: -------- row (Grid s l) n = if (n >= s) then [] else l !! n col g@(Grid s l) n = if (n >= s) then [] else col_ g n 0 where col_ (Grid s l) n i = if (i >= s) then [] else (head l !! n) : col_ (Grid s (tail l)) n (i + 1) -------- My question: With the way Haskell works (thunks, lazy evaluation, and all that mystery), is it actually worth the trouble of /precalculating/ the maximum row values and minimum column values, to compare cell values against? Or will, for example, something like (smallest_list_value (col array 1)) definitely only evaluate once? -- frigidcode.com

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Improved ghc-pkg cache warnings
by Andrew Pennebaker 15 Jun '13

15 Jun '13

When ghc-pkg observes your cache is out of date, it displays a helpful warning, recommending "ghc-pkg recache". However, sometimes running this command does not fix the problem, because it targets the wrong cache. For out of date global caches, "ghc-pkg --global recache" successfully clears the warning. For out of date user caches, "ghc-pkg --user recache" clears the warning. In the future, could ghc-pkg display the command more specific to the problem? -- Cheers, Andrew Pennebaker www.yellosoft.us

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Haskell Platform 2013.2.0.0 64bit.pkg
by Richard A. O'Keefe 15 Jun '13

15 Jun '13

Today I cleared out everything, using uninstall-hs and rm -rf ~/.cabal ~/Library/Haskell I downloaded Haskell Platform 2013.2.0.0 64bit.pkg and installed it. I was unsuccessful in installing the packages I wanted using cabal install, which suggested running ghc-pkg check. So I cleared out everything again and reinstalled the HP. In the admin account, ghc-pkg check says Warning: haddock-interfaces: /Library/Haskell/ghc-7.6.3/lib/haskell-platform-2013.2.0.0/ doc/html/haskell-platform.haddock doesn't exist or isn't a file Warning: haddock-html: /Library/Haskell/ghc-7.6.3/lib/haskell-platform-2013.2.0.0/ doc/html doesn't exist or isn't a directory

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Testing invasive proposals with Hackager
by Niklas Hambüchen 14 Jun '13

14 Jun '13

In many discussions we make guesses about how much code proposals like Functor => Monad would break. You can use https://github.com/dterei/Hackager to build all of Hackage (preferably in a VM). Of course many packages have external dependencies, so I'd like to share the following list of packages to save you some time. (These are the names of packages suited for a Ubuntu 13.04 VM, and with these installed, 2800 packages are successfully built and 1700 failing, so it's quite good coverage. If you find more packages that improve on this, please add them.) acl-dev attr-dev binutils-dev cfitsio-dev expect-dev freeglut3-dev libadns1-dev libalure-dev libasound-dev libaspell-dev libatlas-dev libaugeas-dev libavcodec-dev libavfilter-dev libavformat-dev libavutil-dev libbibutils-dev libbluetooth-dev libbz2-dev libcal3d12-dev libcmph-dev libcrack2-dev libcrypto++-dev libcsound64-dev libctemplate-dev libcurl-dev libcv-dev libcwiid-dev libdb-dev libdevil-dev libdpkg-dev libev-dev libevent-dev libexif-dev libfam-dev libfcgi-dev libfftw3-dev libfltk1.3-dev libfreenect-dev libftgl-dev libfuse-dev libgd2-xpm-dev libgeoip-dev libglfw-dev libglpk-dev libgmime-2.6-dev libgnome-keyring-dev libgnutls-dev libgnutls-dev libgpcl-dev libhighgui-dev libimlib2-dev libinsighttoolkit4-dev libjasper-dev libjudy-dev libkyotocabinet-dev liblapack-dev libldap2-dev libldap2-dev libleveldb-dev libmagic-dev libmarkdown2-dev libmecab-dev libmpfr-dev libmtp-dev libmx-dev libmysqlclient-dev libncurses-dev libncurses-dev libnotmuch-dev libobjc-4.7-dev libodbc1 libode-dev libogg-dev libois-dev libopenal-dev libpam0g-dev libpcap-dev libpoker-eval-dev libportaudio-dev libpulse-dev libqd-dev libqrencode-dev libraw1394-dev libreadline-dev libscsynth1 libselinux-dev libsnappy-dev libsndfile1-dev libsqlite3-dev libssl-dev libssl-dev libst-dev libsvm-dev libtalloc-dev libtbb-dev libtheora-dev libtiff-dev libtokyocabinet-dev libtokyotyrant-dev libtre-dev libuuid-dev libv4l-dev libvxl1-dev libxapian-dev libxen-dev libxerces-c-dev libxine-dev libxmmsclient-dev libxosd-dev libxqilla-dev libxss-dev libxtst-dev libyaml-dev libz-dev libzephyr-dev libzmq-dev linux-libc-dev tcl-dev wx2.8-headers xmms2-dev

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