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What's wrong with these foreign calls?
by Андрей Янкин 12 Jul '12

12 Jul '12

Hi all! I want to use GLFW-b ( http://hackage.haskell.org/packages/archive/GLFW-b/0.1.0.2/doc/html/Graphic…) and I wrote this: initWindow = do True <- GLFW.initialize print =<< GLFW.openGLProfile print =<< GLFW.getGlfwVersion print =<< *GLFW.getGlVersion* print "Trying to open the window" result <- GLFW.openWindow GLFW.defaultDisplayOptions print result And got this: DefaultProfile Version {versionBranch = [2,7,2], versionTags = []} Version {versionBranch = [*-1867951663,39789305,39789305*], versionTags = []} "Trying to open the window" False Why do I always get random numbers as GLVersion? How can I detect incompatibility preventing me from opening a window? Thanks in advance

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Hackage is down?
by Edward Amsden 12 Jul '12

12 Jul '12

http://www.downforeveryoneorjustme.com/hackage.haskell.org -- Edward Amsden Student Computer Science Rochester Institute of Technology www.edwardamsden.com

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Monad with limited backtracking
by Darryn Reid 12 Jul '12

12 Jul '12

Kind Sirs/Madams, Thanks in advance for your patience; the solution will no doubt be obvious to those with greater experience than me. I have formulated a monad to provide limited backtracking for implementing a rewrite system. The success case works fine, but my intention is that on failure the result should contain the list of input symbols consumed up to the failure, and it is this part that I would like some advice about. Code follows: ------------------------------------------------------------------------------- import Control.Monad import Debug.Trace newtype Rewrite a b = Rewrite { run :: Input a -> Result a b } data Input a = Input [a] data Result a b = Fail [a] | Ok b [a] deriving (Eq, Show) instance (Show a) => Monad (Rewrite a) where return y = Rewrite $ \(Input xs) -> Ok y xs p >>= f = Rewrite $ \inp -> case run p inp of Fail xs -> trace ("1.xs=" ++ show xs) $ Fail xs Ok y xs -> case run (f y) (Input xs) of Fail xs' -> trace ("2.xs=" ++ show xs) $ Fail xs okay -> okay instance (Show a) => MonadPlus (Rewrite a) where mzero = Rewrite $ \inp -> Fail [] p `mplus` q = Rewrite $ \inp -> case run p inp of Fail _ -> run q inp okay -> okay (>>=?) ::(Show a) => Rewrite a b -> (b -> Bool) -> Rewrite a b p >>=? f = p >>= \y -> guard (f y) >> return y next :: Rewrite a a next = Rewrite $ \(Input xs) -> case xs of [] -> Fail [] (x:xs') -> Ok x xs' exactly :: (Show a, Eq a) => [a] -> Rewrite a [a] exactly = mapM $ \i -> next >>=? (==i) ------------------------------------------------------------------------------- For example, using ghci: *Main> run (exactly [1,2]) (Input [1,2,3,4]) Ok [1,2] [3,4] which is what I intend. However, while the thing correctly reports failure, I cannot get it to return the list of symbols up to the point of failure: *Main> run (exactly [1,2,3]) (Input [1,2,7,4]) 1.xs=[] 2.xs=[4] 1.xs=[4] 1.xs=[4] 2.xs=[7,4] 1.xs=[7,4] 2.xs=[2,7,4] Fail [2,7,4] *I would like Fail [1,2] here instead* I thank you in advance for any guidance you might offer. Dr Darryn J Reid.

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Solutions for multi-platform compilation?
by Ivan Perez 12 Jul '12

12 Jul '12

Hi, I work developing multi-platform applications in Haskell. This poses the following problem: I cannot compile binaries for windows from linux (AFAIK). I "solved" this problem with the following sledgehammer: I installed windows in a VM, I installed GHC, I installed all the C/C++ headers & binaries of the libraries that I use (Gtk, OpenGL, SDL, OpenCV, etc.) their Haskell counterparts, and I created several scripts that connect to the VM using SSH, push the changes to the repo, cabal clean & cabal install all my packages in sequence without me having to even login into the windows machine. I did this because I was unable to get GHC to run properly in Wine at that time (over 2 years ago). This solution is still unsatisfactory because: 1) It's slow, even though Windows itself works fine (well, as well as windows can work, but it runs at a decent spped, I can play games and all). 2) When I update a library with lots of dependencies, or GHC itself, I have to rebuild almost everything. This is particularly painful with big packages like Gtk, for instance. Because I have to tell cabal where headers and libraries are located, updating a package is almost never an automatic process. I haven't always been able to make GHC "just pick them up" properly with pkg-config. 3) When I make a change in a library with lots of dependencies, recompiling all the packages can take several hours. I don't think it's a problem with my machine: I'm giving a fair amount of resources to windows, and I use a 3Ghz quadcore with 8GB of RAM. Another relevant fact is: I use this for commercial purposes. I have customers, each requiring a completely different program, they do not have infinite budgets and, if there's a problem in the compilation process and something requires my attention and manual intervention too often, my salary per hour can easily drop to a ridiculous amount. If I'm going to redo this, I'd rather just redo it once. Any suggestions? How do you solve this kind of problem in your work environment? Cheers, Ivan

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Control defaulting in ghci
by Roman Cheplyaka 12 Jul '12

12 Jul '12

Is there a way to control defaulting in ghci? (Like the "default" declaration in source files does.) ghci 7.4.1 doesn't accept "default" declarations. I tried loading a module with a "default" declaration, but that also didn't affect the ghci session. It would be ironic if this is possible in source files but not in ghci, since defaulting is much more useful in an interactive session than in modules. -- Roman I. Cheplyaka :: http://ro-che.info/

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GHC users on PowerPC and *BSD/Darwin?
by Erik de Castro Lopo 12 Jul '12

12 Jul '12

Hi all, Users of GHC on PowerPC would probably be aware of this bug: http://hackage.haskell.org/trac/ghc/ticket/2972 which causes GHCi to segfault as soon as it was started. Ben M. Collins has come up with a fix for this I am preparing it for submission to the GHC git tree. I have have tested it on linux-powerpc, but would also like to test it on *BSD/Darwin. Anybody out there interested? You will need: * A PowerPC machine running *BSD or Darwin. * A working GHC compiler. If you're interested email me at erikd AT mega-nerd dot com. Cheers, Erik -- ---------------------------------------------------------------------- Erik de Castro Lopo http://www.mega-nerd.com/

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Haskell Weekly News: Issue 235
by Daniel Santa Cruz 12 Jul '12

12 Jul '12

Welcome to issue 235 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers the week of July 1 to 7, 2012. Quotes of the Week * Kukkua: They say there are two things, once mastered, you will harness boundless strength from the cosmos itself, continuations and monads. * startling: saying "monad" within earshot of a muggle is pretty funny * maybefbi: Haskell is forcing me to think a lot * Wadler says: So, the essence of XML is this: the problem it solves is not hard, and it does not solve the problem well. Top Reddit Stories * This is what my first attempt at writing code in Haskell went like Domain: self.haskell, Score: 82, Comments: 32 On Reddit: [1] http://goo.gl/uq3Tt Original: [2] http://goo.gl/uq3Tt * The Architecture of Open Source Applications: The Glasgow Haskell Compiler Domain: aosabook.org, Score: 59, Comments: 5 On Reddit: [3] http://goo.gl/5v906 Original: [4] http://goo.gl/yYqUJ * Slides for 7 lectures on Parallel and Concurrent Haskell (including GPU programming with Accelerate) Domain: community.haskell.org, Score: 51, Comments: 10 On Reddit: [5] http://goo.gl/pmGsr Original: [6] http://goo.gl/wumiT * How pythoners view Haskell compared with Python Domain: wiki.python.org, Score: 40, Comments: 70 On Reddit: [7] http://goo.gl/Xe3AF Original: [8] http://goo.gl/ydpyj * How I made the switch to functional programming. Domain: self.haskell, Score: 38, Comments: 14 On Reddit: [9] http://goo.gl/m6IXs Original: [10] http://goo.gl/m6IXs * Why Functional Matters: Your white board will never be the same Domain: blog.jessitron.com, Score: 35, Comments: 5 On Reddit: [11] http://goo.gl/b71zi Original: [12] http://goo.gl/SkJaA * Building a better AES package Domain: tab.snarc.org, Score: 33, Comments: 19 On Reddit: [13] http://goo.gl/A0hwE Original: [14] http://goo.gl/0p9PE * FP Complete is hiring Haskell programmers Domain: haskellers.com, Score: 32, Comments: 4 On Reddit: [15] http://goo.gl/L8Xuh Original: [16] http://goo.gl/6AxT7 * Parallel and Concurrent Programming in Haskell (Lab exercises by Simon Marlow) Domain: community.haskell.org, Score: 31, Comments: On Reddit: [17] http://goo.gl/cjBJ0 Original: [18] http://goo.gl/olFva * pipes 2.1 released with prettier Frame, using indexed and restricted monads Domain: haskellforall.com, Score: 30, Comments: 31 On Reddit: [19] http://goo.gl/Trajz Original: [20] http://goo.gl/vqluc * conduit 0.5.0 released, now with extensive tutorial Domain: hackage.haskell.org, Score: 27, Comments: 2 On Reddit: [21] http://goo.gl/s5Wmh Original: [22] http://goo.gl/RUrpw * A (experimental) treat for Emacs interactive-mode users Domain: youtube.com, Score: 26, Comments: 2 On Reddit: [23] http://goo.gl/13wD9 Original: [24] http://goo.gl/C54V5 * Exploring CPU design using Haskell - Introduction to the architecture Domain: random.axman6.com, Score: 25, Comments: 17 On Reddit: [25] http://goo.gl/f1v2M Original: [26] http://goo.gl/xvSUF * Haskell is dead! (pun intended, not a flame :D) Domain: i.imgur.com, Score: 22, Comments: 37 On Reddit: [27] http://goo.gl/jPRu9 Original: [28] http://goo.gl/2DclX * Announcing lens-family-core, lens-family, and lens-family-th Domain: self.haskell, Score: 22, Comments: 8 On Reddit: [29] http://goo.gl/Axyxs Original: [30] http://goo.gl/Axyxs * Happstack Irregular News Issue #2 Domain: happstack.com, Score: 21, Comments: 3 On Reddit: [31] http://goo.gl/n7a0Z Original: [32] http://goo.gl/kU7OV * "Tying the Knot" using the RWS Monad Domain: mergeconflict.com, Score: 21, Comments: 16 On Reddit: [33] http://goo.gl/FavKj Original: [34] http://goo.gl/TESiO * LiveScript: a more functional JavaScript Domain: gkz.github.com, Score: 18, Comments: 9 On Reddit: [35] http://goo.gl/NQecG Original: [36] http://goo.gl/1hsTo Top StackOverflow Questions * Functional design patterns votes: 36, answers: 5 Read on SO: [37] http://goo.gl/hjzwm * Using return vs. not using return in the list monad votes: 22, answers: 6 Read on SO: [38] http://goo.gl/zkQH1 * Compute as much of a list as possible in a fixed time votes: 19, answers: 3 Read on SO: [39] http://goo.gl/BpBFe * Why is `logBase 10 x` slower than `log x / log 10`, even when specialized? votes: 16, answers: 2 Read on SO: [40] http://goo.gl/4rkTi * How has Haskell changed? votes: 16, answers: 2 Read on SO: [41] http://goo.gl/Rkz41 * What are the similarities and differences among Haskell indentation modes for Emacs? votes: 16, answers: 0 Read on SO: [42] http://goo.gl/xHn7L * Arrow equivalent of mapM? votes: 9, answers: 1 Read on SO: [43] http://goo.gl/XlQWR * Can I pass a pattern into a function? votes: 9, answers: 2 Read on SO: [44] http://goo.gl/J6N3w * Referential transparency and mmap in Haskell votes: 8, answers: 1 Read on SO: [45] http://goo.gl/iJGp5 * Is EC2 Ubuntu 12.04 different, if compiling Haskell locally? votes: 7, answers: 1 Read on SO: [46] http://goo.gl/Qivdq Until next time, Daniel Santa Cruz References 1. http://www.reddit.com/r/haskell/comments/w3k4v/this_is_what_my_first_attemp… 2. http://www.reddit.com/r/haskell/comments/w3k4v/this_is_what_my_first_attemp… 3. http://www.aosabook.org/en/ghc.html 4. http://www.reddit.com/r/haskell/comments/w2skx/the_architecture_of_open_sou… 5. http://community.haskell.org/~simonmar/slides/cadarache2012/ 6. http://www.reddit.com/r/haskell/comments/vyzj8/slides_for_7_lectures_on_par… 7. http://wiki.python.org/moin/PythonVsHaskell 8. http://www.reddit.com/r/haskell/comments/w2jiv/how_pythoners_view_haskell_c… 9. http://www.reddit.com/r/haskell/comments/w77xy/how_i_made_the_switch_to_fun… 10. http://www.reddit.com/r/haskell/comments/w77xy/how_i_made_the_switch_to_fun… 11. http://blog.jessitron.com/2012/06/why-functional-matters-your-white-board.h… 12. http://www.reddit.com/r/haskell/comments/w1453/why_functional_matters_your_… 13. http://tab.snarc.org/posts/haskell/2012-07-07-building-a-better-haskell-aes… 14. http://www.reddit.com/r/haskell/comments/w6btf/building_a_better_aes_packag… 15. http://www.haskellers.com/jobs/14 16. http://www.reddit.com/r/haskell/comments/w4xyc/fp_complete_is_hiring_haskel… 17. http://community.haskell.org/~simonmar/lab-exercises-cadarache.pdf 18. http://www.reddit.com/r/haskell/comments/vzpfy/parallel_and_concurrent_prog… 19. http://www.haskellforall.com/2012/07/pipes-21-and-index-core-10-indexed.html 20. http://www.reddit.com/r/haskell/comments/vx1dt/pipes_21_released_with_prett… 21. http://hackage.haskell.org/packages/archive/conduit/0.5.0/doc/html/Data-Con… 22. http://www.reddit.com/r/haskell/comments/vwge4/conduit_050_released_now_wit… 23. http://www.youtube.com/watch?v=pu9AGSOySlE 24. http://www.reddit.com/r/haskell/comments/w1k7s/a_experimental_treat_for_ema… 25. http://random.axman6.com/blog/?p=327 26. http://www.reddit.com/r/haskell/comments/w4aan/exploring_cpu_design_using_h… 27. http://i.imgur.com/zzQrx.png 28. http://www.reddit.com/r/haskell/comments/vvkkm/haskell_is_dead_pun_intended… 29. http://www.reddit.com/r/haskell/comments/w5ine/announcing_lensfamilycore_le… 30. http://www.reddit.com/r/haskell/comments/w5ine/announcing_lensfamilycore_le… 31. http://www.happstack.com/C/ViewPage/12 32. http://www.reddit.com/r/haskell/comments/vxi3c/happstack_irregular_news_iss… 33. http://mergeconflict.com/archives/57 34. http://www.reddit.com/r/haskell/comments/w0haf/tying_the_knot_using_the_rws… 35. http://gkz.github.com/LiveScript/ 36. http://www.reddit.com/r/haskell/comments/w39a3/livescript_a_more_functional… 37. http://stackoverflow.com/questions/11339637/functional-design-patterns 38. http://stackoverflow.com/questions/11323300/using-return-vs-not-using-retur… 39. http://stackoverflow.com/questions/11320180/compute-as-much-of-a-list-as-po… 40. http://stackoverflow.com/questions/11290929/why-is-logbase-10-x-slower-than… 41. http://stackoverflow.com/questions/11296157/how-has-haskell-changed 42. http://stackoverflow.com/questions/11365815/what-are-the-similarities-and-d… 43. http://stackoverflow.com/questions/11303642/arrow-equivalent-of-mapm 44. http://stackoverflow.com/questions/11336687/can-i-pass-a-pattern-into-a-fun… 45. http://stackoverflow.com/questions/11283975/referential-transparency-and-mm… 46. http://stackoverflow.com/questions/11278733/is-ec2-ubuntu-12-04-different-i…

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wondering about a MonadIO instance for a heap data type
by Qi Qi 12 Jul '12

12 Jul '12

Hi, I was wondering about creating an instance of MonadIO for a heap data. Any hints? data Heap a = E | T Int a (Heap a) (Heap a) deriving (Eq, Ord, Read, Show) The reason is that I want to use liftIO during a heapsort to print out intermediate results. Thanks. Qi Qi

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There is some article mentioning that FP is mainly good for mathematical and list programming.
by KC 11 Jul '12

11 Jul '12

There is some article mentioning that functional programming is mainly good for mathematical programming and list programming because otherwise it is to cryptic for business and database applications. Being semi-intelligent, I thought I could reduce what others think of as cryptic but maybe instead of 18 wheels I have only 17 wheels. :D -- -- Regards, KC

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DPH matrix product
by mblanco 11 Jul '12

11 Jul '12

Hi, I'm trying to implement a matrix product example using DPH. This is the code: ------------------------------------------------------------------------------------------------------------------- type MMultType = Double type Matrix = [:[:MMultType:]:] type MVector = [:MMultType:] type Matrix_wrapper = PArray (PArray MMultType) {-# NOINLINE matMult_wrapper #-} matMult_wrapper :: Matrix_wrapper -> Matrix_wrapper -> Matrix_wrapper matMult_wrapper mA mB = toPArrayP (mapP toPArrayP (matMult (fromNestedPArrayP mA) (fromNestedPArrayP mB))) matMult :: Matrix -> Matrix -> Matrix matMult mA mB = mapP (\row -> mapP (\col -> dotp row col) (transposeP mB)) mA dotp :: MVector -> MVector -> MMultType dotp row col = D.sumP (zipWithP (D.*) row col) transposeP :: Matrix -> Matrix transposeP m = let h = lengthP m w = lengthP (m !: 0) rh = I.enumFromToP 0 (h I.- 1) rw = I.enumFromToP 0 (w I.- 1) in if h I.== 0 then [: :] else mapP (\y -> mapP (\x -> m !: x !: y) rh) rw ------------------------------------------------------------------------------------------------------------------- My problem is at execution time, on matrices of size 300*300 the program does finish (although it is very slow), but on 700*700 it consumes GBs of RAM until the process is aborted. In the paper "Work Efficient Higher-Order Vectorisation" it is explained that a work complexity problem (wich involved unnecesary array replication) was recently treated. So at first I thought the code implementation related to the paper had not been uploaded to hackage. But as I understand it must have been, as that seems to be the motive of the "dph-lifted-vseg" package. Does anybody notice the problem with the example or if the problem is related to the subject treated in the paper? Thanks in advance!

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