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list comprehension doesn't work
by John 16 May '13

16 May '13

Hi, I have to write a function which returns a list of all pairs (x,y) where x, y ∈ N AND: – x is the product of two natural numbers (x = a · b, where a, b ∈ N) AND – x is really bigger than 5 but really smaller than 500, AND – y is a squer number (y = c² where c ∈ N) NOT greater than 1000, AND – x is a divisor of y. My attempt is as follows: listPairs :: [(Int, Int)] listPairs = [(x,y) | x<-[0..], y<-[0..], x<-[0..]*[0..], x > 5, x < 500, (y*y) < 1001, mod y x == 0] However it doesn't work unfortunatly Could anyone tell me where my mistake is? Thanks. -- View this message in context: http://haskell.1045720.n5.nabble.com/list-comprehension-doesn-t-work-tp5730… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Haskell Weekly News: Issue 267
by Daniel Santa Cruz 16 May '13

16 May '13

Welcome to issue 267 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers the week of April 28 to May 11, 2013. Quotes of the Week * ciaranm: a category is just a category in the category of categories * cmccann: the Either monad is like the Maybe monad, except with something instead of Nothing. * sclv: Q: Why are the adjunctions of Galois connections backwards? A: He never got the hang of duals. * acowley: blackdog's experience with IDEs is apparently both more sensual and more culinary than mine * cmccann: shachaf jokes are what the quotes section of HWN is for. cmccann: though lately there have been not as many :[ shachaf: cmccann: Hey, there wasn't a single shachaf quote in the last HWN! shachaf: Leave me alone. shachaf: There were two cmccann quotes. * edwardk: cmccann: i'm NDA'd out of that space for a while ;) elliott: edwardk just collects NDAs so that he can focus. * trapdInIO: in java everything happens elsewhere * edwardk: i never bothered to release the c preprocessor because it was entangled with an old compiler of mind * acowley: I get nervous when I haven't triggered the impossible for more than a month or so :/ * hpc: be careful, excessive consumption of lenses will go straight to your type signature * acowley: The longer I leave this function named "jumanji" the less I want to find a better name * ion: The next step is unsafeCoerce. At that point youâre halfway into implementing lens. * bos: i'm not sure edwardk is a good model to follow. (a) because you won't be able to, and (b) because you won't be able to. Top Reddit Stories * John Carmack interested in doing a moderate-sized project in Haskell Domain: twitter.com, Score: 136, Comments: 30 On Reddit: [1] http://goo.gl/7rJpH Original: [2] http://goo.gl/yL9kV * John Carmack starting port of Wolf 3D in Haskell Domain: twitter.com, Score: 108, Comments: 19 On Reddit: [3] http://goo.gl/MKkiI Original: [4] http://goo.gl/SN7Mp * Haskell for all: Program imperatively using Haskell lenses Domain: haskellforall.com, Score: 103, Comments: 80 On Reddit: [5] http://goo.gl/FIfUd Original: [6] http://goo.gl/zkEHI * unm-hip a Haskell Image Processing Library Domain: self.haskell, Score: 71, Comments: 18 On Reddit: [7] http://goo.gl/erMhx Original: [8] http://goo.gl/erMhx * Crit-bit trees in Haskell: fast, and open to contributors! Domain: github.com, Score: 56, Comments: 16 On Reddit: [9] http://goo.gl/1vQMS Original: [10] http://goo.gl/08byj * Tutorial on HLearn's Markov networks, monoids, and "type level lenses" explained with Futurama Domain: izbicki.me, Score: 53, Comments: 10 On Reddit: [11] http://goo.gl/3mYuD Original: [12] http://goo.gl/4WjnU * Cool mailing list archive I stumbled on: Haskell controlling garbage trucks Domain: haskell.org, Score: 49, Comments: 2 On Reddit: [13] http://goo.gl/h8p4y Original: [14] http://goo.gl/kSGkx * Haskell intuition Domain: self.haskell, Score: 49, Comments: 23 On Reddit: [15] http://goo.gl/F04IM Original: [16] http://goo.gl/F04IM * The Difference between Recursion & Induction Domain: blog.ezyang.com, Score: 47, Comments: 3 On Reddit: [17] http://goo.gl/mZN3T Original: [18] http://goo.gl/z2jZx * Yesod 1.2 released Domain: yesodweb.com, Score: 45, Comments: 8 On Reddit: [19] http://goo.gl/el7dt Original: [20] http://goo.gl/lqBM9 * Haskell 2014 committee has now been formed Domain: thread.gmane.org, Score: 42, Comments: 27 On Reddit: [21] http://goo.gl/okojc Original: [22] http://goo.gl/1g6FG * Web Frameworks Benchmark 4 (includes WAI) Domain: techempower.com, Score: 41, Comments: 60 On Reddit: [23] http://goo.gl/FLGJu Original: [24] http://goo.gl/AJbhV * Haskell for all: pipes-3.3.0: Folds and uniting ListT with Proxy Domain: haskellforall.com, Score: 41, Comments: 14 On Reddit: [25] http://goo.gl/sO1EK Original: [26] http://goo.gl/5rZ0u * First working program using the Repa plugin Domain: disciple-devel.blogspot.com, Score: 39, Comments: 5 On Reddit: [27] http://goo.gl/bQgfV Original: [28] http://goo.gl/9K5Qk * How to use Hoogle from GHCi Domain: youtube.com, Score: 36, Comments: 2 On Reddit: [29] http://goo.gl/9V9o7 Original: [30] http://goo.gl/LU7Zk * 4th Episode of "The Pragmatic Haskeller": HTTP and more Domain: cakesolutions.net, Score: 35, Comments: 3 On Reddit: [31] http://goo.gl/rMLyC Original: [32] http://goo.gl/npjKm * A monadic joke Domain: self.haskell, Score: 34, Comments: 28 On Reddit: [33] http://goo.gl/OmwSp Original: [34] http://goo.gl/OmwSp * A "Natural" Theorem Prover in Haskell — By Tim Gowers! Domain: gowers.wordpress.com, Score: 34, Comments: 5 On Reddit: [35] http://goo.gl/OomyR Original: [36] http://goo.gl/LWNHW * Towards a Haskell Logic Library Domain: spin.atomicobject.com, Score: 30, Comments: 1 On Reddit: [37] http://goo.gl/puVS7 Original: [38] http://goo.gl/7dXA0 * Barabra Liskov - Keynote: The Power of Abstraction Domain: infoq.com, Score: 29, Comments: 25 On Reddit: [39] http://goo.gl/B7AZJ Original: [40] http://goo.gl/SSYSm Top StackOverflow Questions * What constitutes a fold for types other than list? votes: 34, answers: 4 Read on SO: [41] http://goo.gl/AkbgP * Lazy vs Strict implementations of data structures votes: 19, answers: 2 Read on SO: [42] http://goo.gl/De1VO * Compiling very large constants with GHC votes: 17, answers: 1 Read on SO: [43] http://goo.gl/mWOMz * Haskell Tree splitting: Can someone please explain this line? votes: 16, answers: 1 Read on SO: [44] http://goo.gl/ZVaQE * Could cabal notice about unused package in dependencies? votes: 15, answers: 1 Read on SO: [45] http://goo.gl/IUOx2 * How can eta-reduction of a well typed function result in a type error? votes: 14, answers: 2 Read on SO: [46] http://goo.gl/3A4hu * What is so special about Monads? votes: 14, answers: 4 Read on SO: [47] http://goo.gl/CF7BC * Why does ghci desugar type lists and type families? Can this be selectively disabled? votes: 13, answers: 0 Read on SO: [48] http://goo.gl/QBmM7 * How are functors in Haskell and OCaml similar? votes: 13, answers: 1 Read on SO: [49] http://goo.gl/rIYKy * Monitoring GHC activity votes: 10, answers: 1 Read on SO: [50] http://goo.gl/q7WuU * Why isn't the Prelude's words function written more simply? votes: 10, answers: 1 Read on SO: [51] http://goo.gl/W1TqA * How to design a monadic stack? votes: 10, answers: 2 Read on SO: [52] http://goo.gl/LAeJI * How to generate arbitrary instances of a simple type for quickcheck votes: 9, answers: 2 Read on SO: [53] http://goo.gl/oCesk Until next time, +Daniel Santa Cruz References 1. https://twitter.com/ID_AA_Carmack/status/331557216488390656 2. http://www.reddit.com/r/haskell/comments/1dv4ij/john_carmack_interested_in_… 3. https://twitter.com/id_aa_carmack/status/331918309916295168 4. http://www.reddit.com/r/haskell/comments/1dwjup/john_carmack_starting_port_… 5. http://www.haskellforall.com/2013/05/program-imperatively-using-haskell.html 6. http://www.reddit.com/r/haskell/comments/1dpk2b/haskell_for_all_program_imp… 7. http://www.reddit.com/r/haskell/comments/1dzk73/unmhip_a_haskell_image_proc… 8. http://www.reddit.com/r/haskell/comments/1dzk73/unmhip_a_haskell_image_proc… 9. https://github.com/bos/critbit 10. http://www.reddit.com/r/haskell/comments/1e1ywq/critbit_trees_in_haskell_fa… 11. http://izbicki.me/blog/markov-networks-monoids-and-futurama 12. http://www.reddit.com/r/haskell/comments/1e0759/tutorial_on_hlearns_markov_… 13. http://www.haskell.org/pipermail/haskell-cafe/2010-April/075647.html 14. http://www.reddit.com/r/haskell/comments/1df8fy/cool_mailing_list_archive_i… 15. http://www.reddit.com/r/haskell/comments/1e3cl0/haskell_intuition/ 16. http://www.reddit.com/r/haskell/comments/1e3cl0/haskell_intuition/ 17. http://blog.ezyang.com/2013/04/the-difference-between-recursion-induction/ 18. http://www.reddit.com/r/haskell/comments/1dbwp4/the_difference_between_recu… 19. http://www.yesodweb.com/blog/2013/05/yesod-1-2-released 20. http://www.reddit.com/r/haskell/comments/1dko1d/yesod_12_released/ 21. http://thread.gmane.org/gmane.comp.lang.haskell.general/19796 22. http://www.reddit.com/r/haskell/comments/1dhbjr/haskell_2014_committee_has_… 23. http://www.techempower.com/blog/2013/05/02/frameworks-round-4/ 24. http://www.reddit.com/r/haskell/comments/1dk73s/web_frameworks_benchmark_4_… 25. http://www.haskellforall.com/2013/05/pipes-330-folds-and-uniting-listt-with… 26. http://www.reddit.com/r/haskell/comments/1dsuto/haskell_for_all_pipes330_fo… 27. http://disciple-devel.blogspot.com/2013/05/first-working-program-using-repa… 28. http://www.reddit.com/r/haskell/comments/1dm7a6/first_working_program_using… 29. http://www.youtube.com/watch?v=QpDQhGYPqkU 30. http://www.reddit.com/r/haskell/comments/1dxx4m/how_to_use_hoogle_from_ghci/ 31. http://www.cakesolutions.net/teamblogs/2013/04/28/tph-episode-4-http-and-mo… 32. http://www.reddit.com/r/haskell/comments/1d9zou/4th_episode_of_the_pragmati… 33. http://www.reddit.com/r/haskell/comments/1dcfso/a_monadic_joke/ 34. http://www.reddit.com/r/haskell/comments/1dcfso/a_monadic_joke/ 35. http://gowers.wordpress.com/2013/04/14/answers-results-of-polls-and-a-brief… 36. http://www.reddit.com/r/haskell/comments/1dtw7v/a_natural_theorem_prover_in… 37. http://spin.atomicobject.com/2013/05/10/haskell-logic-library/?utm_source=t… 38. http://www.reddit.com/r/haskell/comments/1e2okw/towards_a_haskell_logic_lib… 39. http://www.infoq.com/presentations/programming-abstraction-liskov 40. http://www.reddit.com/r/haskell/comments/1dodfb/barabra_liskov_keynote_the_… 41. http://stackoverflow.com/questions/16426463/what-constitutes-a-fold-for-typ… 42. http://stackoverflow.com/questions/16296571/lazy-vs-strict-implementations-… 43. http://stackoverflow.com/questions/16348340/compiling-very-large-constants-… 44. http://stackoverflow.com/questions/16267497/haskell-tree-splitting-can-some… 45. http://stackoverflow.com/questions/16390273/could-cabal-notice-about-unused… 46. http://stackoverflow.com/questions/16402942/how-can-eta-reduction-of-a-well… 47. http://stackoverflow.com/questions/16439025/what-is-so-special-about-monads 48. http://stackoverflow.com/questions/16346293/why-does-ghci-desugar-type-list… 49. http://stackoverflow.com/questions/16353066/how-are-functors-in-haskell-and… 50. http://stackoverflow.com/questions/16348118/monitoring-ghc-activity 51. http://stackoverflow.com/questions/16446274/why-isnt-the-preludes-words-fun… 52. http://stackoverflow.com/questions/16457111/how-to-design-a-monadic-stack 53. http://stackoverflow.com/questions/16440208/how-to-generate-arbitrary-insta… 54. https://plus.google.com/105107667630152149014/about

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Good to find you on LinkedIn
by Daniel Díaz Casanueva 16 May '13

16 May '13

LinkedIn ------------ Daniel Díaz Casanueva requested to add you as a connection on LinkedIn: ------------------------------------------ Minh Thu, I'd like to add you to my professional network on LinkedIn. - Daniel Accept invitation from Daniel Díaz Casanueva http://www.linkedin.com/e/uc6lxc-hgr1egm6-6q/XvIdBwmueHfd6vFMPXXdLaqreCbl5o… View profile of Daniel Díaz Casanueva http://www.linkedin.com/e/uc6lxc-hgr1egm6-6q/rso/255311896/LIky/name/227245… ------------------------------------------ You are receiving Invitation emails. This email was intended for Minh Thu Vo. Learn why this is included: http://www.linkedin.com/e/uc6lxc-hgr1egm6-6q/plh/http%3A%2F%2Fhelp%2Elinked… (c) 2012, LinkedIn Corporation. 2029 Stierlin Ct, Mountain View, CA 94043, USA.

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Trouble with Debug.Trace when using a library
by hanjoosten 15 May '13

15 May '13

My project is split in two packages, A and B, where B uses A. All together, there are about 100 haskell modules. Currently, there seems to be a loop somewere, that only seems to occur when working with rather large datastructures. I use trace (from Debug.Trace) to see what exactly is going on. As long as I trace functions from B, trace works as expected. However, at some point I need to trace into functions supplied by package A. In package A I have a function like this: (I have simplified the function) fA :: SomeInput -> SomeResult fA a = let x = f a in trace ("Entering fA") x (The function f is defined in package A) In package B, I have a function like this: fB :: SomeInput -> SomeResult fB a = let x = fA a in trace ( "Entering fB") x At runtime, I get the message Entering fB and then nothing more. a lot of cpu is used, but no more output. I have made some wrappers like the ones above. As long as they are in the same package, trace works fine. However, when entering a function from the other package, there is no more debug output. This is very anoying. Anyone some suggestions? Is this a bug? I use the haskell platform 12.4.0.0 on a windows 7 machine. -- View this message in context: http://haskell.1045720.n5.nabble.com/Trouble-with-Debug-Trace-when-using-a-… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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whats with cabal and libgmp.so.3
by Rustom Mody 14 May '13

14 May '13

Today cabal suddenly started giving me errors that libgmp.so.3 is not found Moving away my old .cabal makes it work again Any explanations? [I am on debian testing. I think the causing factor was that debian switched major versions recently. There were a lot of updates... Nothing that looked like it was related to ghc]

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ANN: Robot - Simulate keyboard and mouse events under X11
by Chris Wong 14 May '13

14 May '13

I'm pleased to announce the initial release of Robot! Robot lets you send fake keyboard and mouse events, just like its namesake in Java. Only X11 systems are supported right now (via XTest), but Windows and Mac can be added later if anyone cares. ## Features + Simple API (only 9 functions and 3 types) + Few dependencies + Exception safe -- unlike with other libraries, all keys and buttons are released automatically when the robot terminates. `bracket` and `finally` are used where appropriate. ## Links Hackage: http://hackage.haskell.org/package/robot-1.0 Examples: https://github.com/lfairy/robot/tree/master/examples Happy hacking! Chris -- Chris Wong, fixpoint conjurer e: lambda.fairy(a)gmail.com w: http://lfairy.github.io/

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fromIntegral not enough?
by Christopher Howard 14 May '13

14 May '13

This is probably a haskell-beginners sort of question, but I usually get about 4x as many responses from cafe, about 10x as fast. I have code like so: code: -------- data Xy a = Xy a a class Coord2 a where coords2 :: Fractional b => a b -> Xy b data CircAppr a b = CircAppr a b b -- number of points, rotation angle, radius deriving (Show) instance Integral a => Coord2 (CircAppr a) where coords2 (CircAppr divns ang rad) = let dAng = 2 * pi / (fromIntegral divns) in let angles = map (* dAng) [0..divns] in undefined -- To be coded... -------- In the instance definition divns is an integral trying to divide a fractional. I hoped wrapping it in fromIntegral would coerce, but apparently not: quote: -------- Could not deduce (Fractional a) arising from a use of `/' from the context (Integral a) bound by the instance declaration at /scratch/cmhoward/pulse-spin/pulse-spin.hs:34:10-42 or from (Fractional b) bound by the type signature for coords2 :: Fractional b => CircAppr a b -> Xy b at /scratch/cmhoward/pulse-spin/pulse-spin.hs:(36,3)-(39,15) Possible fix: add (Fractional a) to the context of the type signature for coords2 :: Fractional b => CircAppr a b -> Xy b or the instance declaration In the expression: 2 * pi / (fromIntegral divns) In an equation for `dAng': dAng = 2 * pi / (fromIntegral divns) In the expression: let dAng = 2 * pi / (fromIntegral divns) in let angles = map (* dAng) [0 .. divns] in undefined -------- So, I'm wondering how I can do what I'm trying to do here, while still keeping my types as generic as possible. -- frigidcode.com

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Problem with mailman at projects.haskell.org
by Tim Docker 13 May '13

13 May '13

Hi, Has anyone noticed problems with the mailman instance running at projects.haskell.org? As best I can see there are no new posts in any of the hosted list archives since mid April. I know that there have been posts made to chart(a)projects.haskell.org in May, and these have neither be distributed or archived. I've not had a response from mailman(a)projects.haskell.org. Tim

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Release Candidates for Haskell Platform 2013.2
by Mark Lentczner 13 May '13

13 May '13

*Some of the release candidates for Haskell Platform 2013.2 are up.* *These are what I expect to simply "re-brand" as the release, unless anyone uncovers some issues.* *If you decide to test these out, please let me know how it goes.* * * The Mac OS X RC2 installers: *32bit: *Haskell Platform 2013.2.0.0 32bit rc2.signed.pkg<http://www.ozonehouse.com/mark/platform/Haskell%20Platform%202013.2.0.0%203…> *64bit: *Haskell Platform 2013.2.0.0 64bit rc2.signed.pkg<http://www.ozonehouse.com/mark/platform/Haskell%20Platform%202013.2.0.0%206…> The source tarball (RC1): haskell-platform-2013.2.0.0-rc1.tar.gz<http://www.ozonehouse.com/mark/platform/haskell-platform-2013.2.0.0-rc1.tar…> *Notable new things in Haskell Platform 2013.2:* - GHC 7.6.3 - Major update to *OpenGL* & *GLUT* - New packages: - *attoparsec* - *case-insensitive* - *hashable* - *unordered-containers* — Mark "mad releaser" Lentczner

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Set monad
by oleg＠okmij.org 13 May '13

13 May '13

The question of Set monad comes up quite regularly, most recently at http://www.ittc.ku.edu/csdlblog/?p=134 Indeed, we cannot make Data.Set.Set to be the instance of Monad type class -- not immediately, that it. That does not mean that there is no Set Monad, a non-determinism monad that returns the set of answers, rather than a list. I mean genuine *monad*, rather than a restricted, generalized, etc. monad. It is surprising that the question of the Set monad still comes up given how simple it is to implement it. Footnote 4 in the ICFP 2009 paper on ``Purely Functional Lazy Non-deterministic Programming'' described the idea, which is probably folklore. Just in case, here is the elaboration, a Set monad transformer. {-# LANGUAGE TypeSynonymInstances, FlexibleInstances #-} module SetMonad where import qualified Data.Set as S import Control.Monad.Cont -- Since ContT is a bona fide monad transformer, so is SetMonadT r. type SetMonadT r = ContT (S.Set r) -- These are the only two places the Ord constraint shows up instance (Ord r, Monad m) => MonadPlus (SetMonadT r m) where mzero = ContT $ \k -> return S.empty mplus m1 m2 = ContT $ \k -> liftM2 S.union (runContT m1 k) (runContT m2 k) runSet :: (Monad m, Ord r) => SetMonadT r m r -> m (S.Set r) runSet m = runContT m (return . S.singleton) choose :: MonadPlus m => [a] -> m a choose = msum . map return test1 = print =<< runSet (do n1 <- choose [1..5] n2 <- choose [1..5] let n = n1 + n2 guard $ n < 7 return n) -- fromList [2,3,4,5,6] -- Values to choose from might be higher-order or actions test1' = print =<< runSet (do n1 <- choose . map return $ [1..5] n2 <- choose . map return $ [1..5] n <- liftM2 (+) n1 n2 guard $ n < 7 return n) -- fromList [2,3,4,5,6] test2 = print =<< runSet (do i <- choose [1..10] j <- choose [1..10] k <- choose [1..10] guard $ i*i + j*j == k * k return (i,j,k)) -- fromList [(3,4,5),(4,3,5),(6,8,10),(8,6,10)] test3 = print =<< runSet (do i <- choose [1..10] j <- choose [1..10] k <- choose [1..10] guard $ i*i + j*j == k * k return k) -- fromList [5,10]

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ANN haskdogs-0.3.2
by Sergey Mironov 13 May '13

13 May '13

Hi. I'm pleased to announce haskdogs-0.3.2, a source navigation helper. Haskdogs is a small HSH-based tool which calls hasktags to create tag file for entire haskell project. It takes into account first-level dependencies by recursively scanning imports and adding matching packages to the final tag list. As a result, programmer can use her text editor supporting tags (vim, for example) to jump directly to definition of any function she uses. Note that haskdogs call Unix shell commands like 'test' or 'mkdir' so this tool will likely fail to work on pure Windows platforms. In return, haskdogs is pretty small - only 125 lines long. Changes: * Generate extended tag file by default (hasktags -c -x) * Add -d command line option which allows user to specify additional source directories * Fix no-sources bug Github: https://github.com/ierton/haskdogs See also Vim-hint at https://github.com/ierton/haskdogs#vim-hint Install: cabal install hasktags haskdogs Usage: haskdogs [-d (FILE|'-')] [FLAGS] FLAGS will be passed to hasktags as-is followed by a list of files. Defaults to -c -x. Basically, just run haskdogs in your Haskell project directory Thanks to yihuang for the contributions! Sergey

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Haskell Platform's libstdc++-6.dll may be interfering with other applications
by Andrew Pennebaker 13 May '13

13 May '13

I use a number of different programming languages, so I have Haskell Platform, Strawberry Perl, Node.js, RVM, and Git Bash installed at the same time. I've noticed that compiling packages with C dependencies (e.g. using node-gyp during "npm install node-mhash", or doing "cpan install PAR::Packer") often crashes during the build process with a popup: The procedure entry point __gxx_personality_sj0 could not be located in the dynamic link library libstdc++-6.dll. As Roderich Schupp points out<https://rt.cpan.org/Public/Bug/Display.html?id=84949>, it appears that the different libstdc++-6.dll's are interfering with one another. Haskell Platform comes with one, Vagrant comes with one, GIMP comes with one, MinGW comes with one, and Strawberry Perl comes with two! Objdump seems to indicate that Haskell Platform's DLL is the one to blame. $ find /c/ -name libstdc++-6.dll 2>/dev/null /c/DevKit/mingw/bin/libstdc++-6.dll /c/Program Files/GIMP 2/bin/libstdc++-6.dll /c/Program Files/Haskell Platform/2012.4.0.0/mingw/bin/libstdc++-6.dll /c/strawberry/c/bin/libstdc++-6.dll /c/strawberry/perl/bin/libstdc++-6.dll /c/vagrant/vagrant/embedded/mingw/bin/libstdc++-6.dll $ objdump -ax /c/DevKit/mingw/bin/libstdc++-6.dll | ack gxx_personality [3896] __gxx_personality_sj0 $ objdump -ax /c/Program\ Files/GIMP\ 2/bin/libstdc++-6.dll | ack gxx_personality [3499] __gxx_personality_sj0 $ objdump -ax /c/Program\ Files/Haskell\ Platform/2012.4.0.0/mingw/bin/libstdc++-6.dll | ack gxx_personality [3401] __gxx_personality_v0 $ objdump -ax /c/strawberry/c/bin/libstdc++-6.dll | ack gxx_personality [3510] __gxx_personality_sj0 $ objdump -ax /c/strawberry/perl/bin/libstdc++-6.dll | ack gxx_personality [3510] __gxx_personality_sj0 $ objdump -ax /c/vagrant/vagrant/embedded/mingw/bin/libstdc++-6.dll | ack gxx_personality [3896] __gxx_personality_sj0 Would updating Haskell Platform's libstdc++-6.dll fix this issue? Is there some way to cordon Haskell Platform off from the rest of the system, while still making ghc.exe and friends available on PATH? Here are my system specs, I figure they're highly relevant. $ specs haskell perl node ruby git os Specs: specs 0.4 https://github.com/mcandre/specs#readme cabal --version cabal-install version 0.14.0 using version 1.14.0 of the Cabal library ghc --version The Glorious Glasgow Haskell Compilation System, version 7.4.2 ghc-pkg field haskell-platform version version: 2012.4.0.0 cpan --version c:\strawberry\perl\bin/cpan version 1.5902 calling Getopt::Std::getopts (version 1.07 [paranoid]), running under Perl version 5.16.2. [Now continuing due to backward compatibility and excessive paranoia. See 'perldoc Getopt::Std' about $Getopt::Std::STANDARD_HELP_VERSION.] Nothing to install! perl --version This is perl 5, version 16, subversion 2 (v5.16.2) built for MSWin32-x86-multi-thread Copyright 1987-2012, Larry Wall Perl may be copied only under the terms of either the Artistic License or the GNU General Public License, which may be found in the Perl 5 source kit. Complete documentation for Perl, including FAQ lists, should be found on this system using "man perl" or "perldoc perl". If you have access to the Internet, point your browser at http://www.perl.org/, the Perl Home Page. npm --version 1.2.17 node --version v0.10.3 bundle --version Bundler version 1.3.2 gem --version 2.0.3 ruby --version ruby 1.9.3p374 (2013-01-15) [i386-mingw32] git --version git version 1.8.0.msysgit.0 systeminfo | findstr /B /C:"OS Name" /C:"OS Version" OS Name: Microsoft Windows XP Professional OS Version: 5.1.2600 Service Pack 3 Build 2600 -- Cheers, Andrew Pennebaker www.yellosoft.us

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ANN: stm-chans 2.0.0
by wren ng thornton 13 May '13

13 May '13

-------------------------------------------- -- stm-chans 2.0.0 -------------------------------------------- The stm-chans package offers a collection of channel types, similar to Control.Concurrent.STM.{TChan,TQueue} but with additional features. -------------------------------------------- -- Changes (since 1.3.1) -------------------------------------------- * (by kudah) Added TMQueue and TBMQueue, which are like the corresponding T*Chans except using the new T*Queue data types in stm >= 2.4. We use CPP to provide compatibility shims for older versions of stm. -------------------------------------------- -- Long description -------------------------------------------- In particular stm-chans offers the following data types: * Control.Concurrent.STM.TBChan: Bounded FIFO channels. When the channel is full, writers will block/retry. This ensures that the writers do not get too far ahead of the readers, which helps to make sure that memory and cpu resources are used responsibly. * Control.Concurrent.STM.TMChan: Closeable FIFO channels. * Control.Concurrent.STM.TMQueue: Closeable FIFO queues. Like TChan (Maybe a) but with a monotonicity guarantee that once Nothing is returned all future reads will be Nothing as well. * Control.Concurrent.STM.TBMChan: Bounded Closeable FIFO channels. * Control.Concurrent.STM.TBMQueue: Bounded Closeable FIFO queues. Combines the capabilities of TBChan and TMChan. In addition, the stm-chans package offers a (partial) compatibility layer for various changes to the stm package. These include backwards compatibility for the T*Queue types, as well as various API improvements (see ticket #5104 [1]). [1] http://hackage.haskell.org/trac/ghc/ticket/5104 -------------------------------------------- -- Links -------------------------------------------- Homepage: http://code.haskell.org/~wren/ Hackage: http://hackage.haskell.org/package/stm-chans Darcs: http://community.haskell.org/~wren/stm-chans Haddock (Darcs version): http://community.haskell.org/~wren/stm-chans/dist/doc/html/stm-chans -- Live well, ~wren

1 0

Stream processing
by oleg＠okmij.org 13 May '13

13 May '13

I'm a bit curious > * be reliable in the presence of async exceptions (solved by conduit, > pipes-safe), > > * hold on to resources only as long as necessary (solved by conduit > and to some degree by pipes-safe), Are you aware of http://okmij.org/ftp/Streams.html#regions which describes both resource deallocation and async signals. Could you tell what you think is deficient in that code? > * ideally also allow upstream communication (solved by pipes and to > some degree by conduit). Are you aware (of, admittedly) old message whose title was specifically ``Sending messages up-and-down the iteratee-enumerator chain'' http://www.haskell.org/pipermail/haskell-cafe/2011-May/091870.html (there were several messages in that thread). Here is the code for those messages http://okmij.org/ftp/Haskell/Iteratee/UpDown.hs

3 2

Google Summer of Code Proposal - Communicating with mobile devices
by Marcos Pividori 13 May '13

13 May '13

Greetings, I am a Computer Science student from Argentina. I am interested in working this summer in a project related to Haskell for the Google Summer of Code. I have been discussing my idea with Michael Snoyman in order to have a clearer idea. Now, I would like to know the community interest in this project. I want to develop a server-side library in Haskell for sending push notifications to devices running different OS, such as Android, iOS, Windows Phone, BlackBerry, and so on. To pass a subject, I have recently worked with Yesod (a Web Framework based in Haskell) developing a server to comunicate with Android-powered devices through Google Cloud Messaging. (It is available: https://github.com/MarcosPividori/Yesod-server-for-GCM – It is a Spanish commented version because it was a project for my University, I will replace it for an English version in the next weeks) To develop this project, I have read a lot about this service and Yesod libraries, and I developed two programs, a server written in Haskell and an Android application for mobile phones. Also, I developed an EDSL to write programs which exchange information with the devices. I would be really grateful if you could give me your opinion about this project and the proposal. I want some feedback in order to know if this would be a useful tool and what you would like to get out of it. *Communicating with mobile devices* * * *Abstract* The aim of this project is to develop a server-side library in Haskell for sending push notifications to devices running different OS, such as Android, iOS, Windows Phone, BlackBerry, and so on. The fact is that every company is developing Push Notification services, and these are very similar. Then, I want to find the fundamental concepts to construct a library which enable to configure the options for the different services and send messages easily. When I say they are very similar, I refer to the fact that they all are asynchronous, best-effort services that offers third-party developers a channel to send data to apps from a cloud service in a power-efficient manner. The most popular are: - Google Cloud Messaging (Android) - Apple Push Notification Service (iPhone / iPad) - Microsoft Push Notification Service (Windows Phone) - BlackBerry Push Service (BlackBerry) - Windows Push Notification Services (Windows 8) - etc. Once we have this libraries, I will investigate the possibility of mainting a "back and forth" communication between a server and mobile devices and I will develop a library to handle this. * * *Motivation and expected benefits* I think this idea would be very useful because it will allow all Haskell developers to open to a new world of mobile devices and to build useful programs/services that interact with them. Pushing data to smartphones provides users with instant access to desired updates as they happen, such as news and weather, sports scores, stock prices and other time-sensitive content. The push services provide an efficient way to quickly push timely information updates to many smartphones at once, in a centrally managed and controlled manner. Generally, you can also be very selective in who you send information to, including individual customers or many customers (multicast). This services minimizes the impact on the smartphones battery life. Instead of actively checking for new data, the applications can remain closed. Once the data is delivered, the application can be launched in the background to process it as needed. This processes offer an alternative to other less efficient methods, such as polling, where a device regularly polls an application server to see if new content is available. The main differences between the services, refer to details as: the maxim payload length, the quality of service, queueing the messages or not, and the time limit for this, the way the messages are handled in the devices, etc. As all the libraries to access to these services are developed in Java, I thought that it would be a good idea to offer an option to Haskell programmers. Taking advantage of the similarity of these services, I could develop a very adaptable library which fits the necessities for each one and at the same time offer an abstraction to the user. *Deliverables.* * * * An API library to build and send messages including: - GCM and a demo Android app. - APN and a demo iOS app. - Microsoft Push Notification Service (Windows Phone) and a demo app. - Documentation for all the code developed. Including the explantation on how to use the server library and how to try the demo apps. * A library to handle a "back and forth" comunication between a server and mobile devices. Tools to mantain a state of the connection and manage with a lot of devices at the same time. A Yesod app example of the use of this library and a demo app for each OS (Android, iOS, Windows Phone, etc) to manage this communication. * Optionally: - an API for communication through BlackBerry Push Service (BlackBerry). - an API for communication through Windows Push Notification Services (Windows 8). *Technical Considerations* In the developing of the APIs for the communication through Push Notifications, I will aim to develop a good abstraction and find the properties in common between the differents services in order to develope an customizable tool but at the same time with a common structure. I want to let the user build messages and send these in a simple way following each protocol. Also, I will abstract the process of registering the devices in the server and let the user manage the different registrations behind a similar abstraccion. To develop a “back and forth” comunication between a server and mobile devices, I will investigate the different possibilities of maintaining a state of the connection. It could be through the use of cookies stored by the clients or maintaining some extra information in the server which would enable it to identify the different connections and provide the appropiate services.

3 3

GPGPU
by Christopher Howard 12 May '13

12 May '13

Has anybody on the list been playing around with OpenCL at all? I'm just starting to look into it - need to get a newer Radeon card, I think - but I'm strongly interested in GPGPU programming. -- frigidcode.com

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Re: [Haskell-cafe] Categories (cont.)
by wren ng thornton 12 May '13

12 May '13

On 5/8/13 12:14 PM, Conal Elliott wrote: > Hi Wren, > > Have you taken this "constrained categories" experiment further, > particularly for adding products? As I mentioned in a haskell-cafe note > yesterday, I tried and got a frightening proliferation of constraints when > defining method defaults and utility functions (e.g., left- or > right-associating). I haven't investigated further since my previous emails on the idea. When working with them, though, I did notice that things work out a lot better with separate unary constraints on domains and codomains, as opposed to having a binary constraint that relates domains to codomains. (The latter is, of course, strictly more powerful; which may be the problem.) As another part of that project, however, I've been working on type-level arithmetic, and that also leads to a frightening proliferation of constraints. The problem is that even though we can implement the definitions of addition, comparison, etc, there's no good way to teach the constraint solver facts like: m < S m m <= m+n -- For natural numbers, not integers. m <= n -> exists o. n == m+o m <= n -> n <= o -> m <= o etc The introduction of these facts would introduce nondeterminism into the resolution of constraints--- since the solver would need to decide between using the inductive definitions vs these auxilliary facts. My impression is that the difficulties here are the same for both cases... -- Live well, ~wren

1 0

Stream processing
by Ertugrul Söylemez 12 May '13

12 May '13

Hello everybody, I'm trying to formulate the stream processing problem, which doesn't seem to be solved fully by the currently existing patterns. I'm experimenting with a new idea, but I want to make sure that I don't miss any defining features of the problem, so here is my list. A stream processing abstraction should: * have a categorically proven design (solved by iteratees, pipes), * be composable (solved by all of them), * be reasonably easy to understand and work with (solved by conduit, pipes), * support leftovers (solved by conduit and to some degree by iteratees), * be reliable in the presence of async exceptions (solved by conduit, pipes-safe), * hold on to resources only as long as necessary (solved by conduit and to some degree by pipes-safe), * ideally also allow upstream communication (solved by pipes and to some degree by conduit). * be fast (solved by all of them). Anything else you would put in that list? Greets, Ertugrul -- Not to be or to be and (not to be or to be and (not to be or to be and (not to be or to be and ... that is the list monad.

3 3

I wish cabal-dev to travel back in time
by Alberto G. Corona 11 May '13

11 May '13

Hi Café: I created just now an issue in cabal-dev: https://github.com/creswick/cabal-dev/issues/101 When compiling old developments, I wish cabal-dev to install and build dependencies that were available at a that time I don't know if there are alternatives to solving this issue. I think that this is very useful and necessary, specially now when library updates are increasingly frequent. Maybe this problem is already solved and I just don´t know (as is often the case, for example when, in a sudden aha moment, I reinvented cabal-install months after the release). That is the reason why I tell you about it here in order to discuss it. motivation: I´m installing now an old soft development. Since many of my dependencies were labeled with -any or with > , neither I neither cabal know which library versions are the right ones. By taking into account a date parameter, cabal-dev can figure out which libraries were the latest and the right ones at that time. -- Alberto.

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Re: [Haskell-cafe] Reinventing a solution to configuration problem
by oleg＠okmij.org 11 May '13

11 May '13

I guess you might like then http://okmij.org/ftp/Haskell/types.html#Prepose which discusses implicit parameters and their drawbacks (see Sec 6.2).

1 0

Typeclass with an `or' restriction.
by oleg＠okmij.org 11 May '13

11 May '13

Mateusz Kowalczyk wrote: > Is there a way however to do something along the lines of: > > class Eq a => Foo a where bar :: a -> a -> Bool bar = (==) > > > > class Num a => Foo a where bar :: a -> a -> Bool bar _ _ = False > This would allow us to make an instance of Num be an instance of Foo > or an instance of Eq to be an instance of Foo. GADTs are a particular good way to constraint disjunction, if you can live with the closed universe. (In the following example I took a liberty to replace Int with Ord, to make the example crispier.) > {-# LANGUAGE GADTs #-} > > data OrdEq a where > Ord :: Ord a => OrdEq a -- representation of Ord dict > Eq :: Eq a => OrdEq a -- representation of Eq dict > > bar :: OrdEq a -> a -> a -> Bool > bar Ord x y = x > y > bar Eq x y = x == y The function bar has almost the desired signature, only (OrdEq a ->) has the ordinary arrow rather than the double arrow. We can fix that: > class Dict a where > repr :: OrdEq a > > -- We state that for Int, we prefer Ord > instance Dict Int where > repr = Ord > > bar' :: Dict a => a -> a -> Bool > bar' = bar repr > > test = bar' (1::Int) 2 I can see the utility of this: something like C++ STL iterators and algorithms? An algorithm could test if a bidirectional iterator is available, or it has to do, less efficiently, with unidirectional. Of course we can use ordinary type classes, at the cost of the significant repetition. In the OrdEq example above, there are only two choices of the algorithm for Bar: either the type supports Ord, or the type supports Eq. So the choice depends on wide sets of types rather than on types themselves.

1 0

Re: [Haskell-cafe] Stream Processing
by Gabriel Gonzalez 11 May '13

11 May '13

As far as I can tell, the only thing on that list not solved currently by `pipes` is leftovers, but I will be releasing that very soon. > Hello everybody, > > I'm trying to formulate the stream processing problem, which doesn't > seem to be solved fully by the currently existing patterns. I'm > experimenting with a new idea, but I want to make sure that I don't miss > any defining features of the problem, so here is my list. A stream > processing abstraction should: > > * have a categorically proven design (solved by iteratees, pipes), > > * be composable (solved by all of them), > > * be reasonably easy to understand and work with (solved by conduit, > pipes), > > * support leftovers (solved by conduit and to some degree by > iteratees), > > * be reliable in the presence of async exceptions (solved by conduit, > pipes-safe), > > * hold on to resources only as long as necessary (solved by conduit > and to some degree by pipes-safe), > > * ideally also allow upstream communication (solved by pipes and to > some degree by conduit). > > * be fast (solved by all of them). > > Anything else you would put in that list? > > > Greets, > Ertugrul >

1 0

A use case for *real* existential types
by Leon Smith 11 May '13

11 May '13

I've been working on a new Haskell interface to the linux kernel's inotify system, which allows applications to subscribe to and be notified of filesystem events. An application first issues a system call that returns a file descriptor that notification events can be read from, and then issues further system calls to watch particular paths for events. These return a watch descriptor (which is just an integer) that can be used to unsubscribe from those events. Now, of course an application can open multiple inotify descriptors, and when removing watch descriptors, you want to remove it from the same inotify descriptor that contains it; otherwise you run the risk of deleting a completely different watch descriptor. So the natural question here is if we can employ the type system to enforce this correspondence. Phantom types immediately come to mind, as this problem is almost the same as ensuring that STRefs are only ever used in a single ST computation. The twist is that the inotify interface has nothing analogous to runST, which does the "heavy lifting" of the type magic behind the ST monad. This twist is very simple to deal with if you have real existential types, with the relevant part of the interface looking approximately like init :: exists a. IO (Inotify a) addWatch :: Inotify a -> FilePath -> IO (Watch a) rmWatch :: Inotify a -> Watch a -> IO () UHC supports this just fine, as demonstrated by a mockup attached to this email. However a solution for GHC is not obvious to me.

4 8

Where is haskell-platform?
by Clark Gaebel 11 May '13

11 May '13

I'm looking for the version of haskell platform that was "supposed" to be released May 6. It seems like it isn't out yet. What's preventing this from happening, and is there anything I can do to help? Regards, - Clark

1 0

Constrained Category, Arrow, ArrowChoice, etc?
by Conal Elliott 10 May '13

10 May '13

I'm using a collection of classes similar to Category, Arrow, ArrowChoice, etc (though without arr and with methods like fst, snd, dup, etc). I think I need some associated constraints (via ConstraintKinds), so I've tried adding them. However, I'm getting terribly complex multiplication of these constraints in the signatures of method defaults and utility functions, and I don't know how to tame them. Has anyone tried adding associated constraints to Category etc? Thanks, -- Conal

2 4

Typeclass with an ‘or’ restriction.
by Mateusz Kowalczyk 10 May '13

10 May '13

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Greetings, We can currently do something like > class (Num a, Eq a) => Foo a where bar :: a -> a -> Bool bar = > (==) This means that our `a' has to be an instance of Num and Eq. Apologies for a bit of an artificial example. Is there a way however to do something along the lines of: > class Eq a => Foo a where bar :: a -> a -> Bool bar = (==) > > class Num a => Foo a where bar :: a -> a -> Bool bar _ _ = False This would allow us to make an instance of Num be an instance of Foo or an instance of Eq to be an instance of Foo. The compiler currently complains about multiple declarations. Is there currently a way to achieve this? The main issue I can see with this is that given an instance of both, Num and Eq, it wouldn't be possible to pick the correct default implementation. Purely a theoretical question. - -- Mateusz K. -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.19 (GNU/Linux) iQIcBAEBAgAGBQJRjP0hAAoJEM1mucMq2pqX30wP/0d0TQHs4S3G5TBw+T1baI6n g/5k/YlPmSgS3FaO8JMQsb2uqL8dGPZGUN7d2ohwcigtXS88KWH4u4rTjrs1+p8o ktS+vIE4kEEedTAX6wmP2Zn+rvK2zFGboCafaX/a/IxT5CbwYZ97RrWCjzz1jlPs S/VlhNHcTQ7Cf/0pa0xJ1kbao+vBHiWtWjxcdzCT/6zS86+jm9vz8qrYT3TWUd3y AJXPBjRuXeyz+RDv18yrth7hMlAvaeoWzmC4gbGFHC68/Oq2l8kz+4dt6ApN+mIy l73wNjrU185YoZ2dkuKTIph8/BadgkD+9ktkgZZ/NlqxElc596BdbOcMfVk4rz4A 0nWqaLa4QctIthghJ1UNfKS8lQzkVVRT6e03LYdgPkqJm1HQxkjHL/WieV2NEoRf 1K9S4SVW8Aq/ML/Gmx782Z3jMECfnYWntf9gSOwFASB64tVej1iUxb7UsfxJAL1t ysf9MjcbZsHe3M/JAq4f8HtHoZoiIG/TTjD0yo74owssJDfOTDqmYMriyelcnUf6 hDCPZyUqLPMTNVx07T+gwfXJoE1HK20hzVe2o1dPBZ8Kb2KJbNg0+sUSB3/v6O8e EJ6w7aQ3OnZUACd1i2uLZiphMF8d8va4T8eTFUyROODHvaPv6netzr8gPcIXhpVO 5OwyMfO54cinZYen7+HR =iAYY -----END PGP SIGNATURE-----

2 1

Reinventing a solution to configuration problem
by Krzysztof Skrzętnicki 10 May '13

10 May '13

Hello Cafe, I came up with (actually reinvented [1]) a solution to configuration problem. For example configuration: data Config = Config { port :: Int, verbosity :: Int, logfile :: FilePath } deriving Show the basic idea is to use implicit parameters: runServer :: (?config :: Config) => IO () The problem is that it is tiresome to decorate all functions in this way. It is also non composable. For example if we switch to using two separate configuration entities like this: data LogConfig = LogConfig { verbosity :: Int, logfile :: FilePath } data NetConfig = NetConfig { port :: Int } we suddenly have to fix types all over the place. Yuck. The extended idea here (compared to [2]) is to use type synonym with all required parameters. This is simple (but requires at least Rank2Types): type ConfIO a = (?config :: Config) => IO a All the functions requiring config will now be simply in ConfIO monad which is really IO with a bonus. A great feature of this solution is that we don't need to use liftIO anywhere. The core *problem* with this approach is that at least current version of GHC fails to propagate implicit parameters the way it propagate typeclass requirements. For example I would like the following function to have (inferred) type -- printConfig :: (?config :: Config) => IO () printConfig = print (?config :: Config) Instead GHC will complain about unbound implicit parameter. Similar problem from GHCi session: Prelude> let f = print (?conf :: Int) <interactive>:11:16: Unbound implicit parameter (?conf::Int) arising from a use of implicit parameter `?conf' In the first argument of `print', namely `(?conf :: Int)' In the expression: print (?conf :: Int) In an equation for `f': f = print (?conf :: Int) For reason I don't fully understand this is fixed by disabling monomorphic restriction. The documentation mentions the problem but in a different context: http://www.haskell.org/ghc/docs/latest/html/users_guide/other-type-extensio… *TL;DR*: A nice solution to configuration problem is to use implicit parameters and type synonym for IO monad extended with implicit configuration parameters. It requires Rank2Types for defining the synonym and NoMonomorphismRestriction for lightweight use. Best regards, Krzysztof Skrzętnicki [1] I only realised this after starting the writing of this email. The implicit parameters solution is given at least in [2]. Somehow I didn't came across it before. [2] "Global Variables in Haskell (2004)"<http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.23.145&rep=rep1&ty…> by John Hughes

1 0

Flip around type parameters?
by Christopher Howard 10 May '13

10 May '13

Hi. Does Haskell allow you to flip around type parameters somehow? I was playing around with toy code (still learning the fundamentals) and I came up with a class like this: code: -------- class Rotatable2D a where rotate :: (Num b) => (a b) -> b -> (a b) -------- It was easy to make an instance of a generic single-parameter type: code: -------- data Angle a = Angle a deriving (Show) instance Rotatable2D Angle where rotate (Angle a) b = Angle (a + b) -------- But let's say I have something a little more complicated: code: -------- data CircAppr a b = CircAppr a a b -- radius, rotation angle, number of points -------- I think I need something like so: -------- instance Rotatable2D (\x -> CircAppr x a) where rotate (CircAppr a b c) d = CircAppr a (b + d) c -------- But I tried that and it isn't valid syntax. -- frigidcode.com

2 1

Fwd: Error compiling transformers-base-0.4.1 (debian 64 bits, ghc-7.4.2)
by jean-christophe mincke 09 May '13

09 May '13

Thank you Sjoerd, Unfortunately this does not work. I think the problem is linked to the evaluation of the condition (in Base.hs) #if !MIN_VERSION_base(4,4,0) && HS_TRANSFORMERS_BASE__ORPHANS Just as a test, I modified the file and added the following lines A. negation of min_version #if *!*MIN_VERSION_base(4,4,0) rgfyfgruyfgreuy -- making sure the compilation fails #endif B #if MIN_VERSION_base(4,4,0) rgfyfgruyfgreuy -- making sure the compilation fails #endif In both case the compilations failed (cabal clean, configure, build). That is, it seems that the #if always evaluate to true... I am surely missing something here... Regards J-C On Thu, May 9, 2013 at 4:13 PM, Sjoerd Visscher <sjoerd(a)w3future.com> wrote: > There's a flag to turn it off, does that work? Try cabal install > transformers-base -f-OrphanInstances > > Sjoerd > > On May 9, 2013, at 2:47 PM, jean-christophe mincke < > jeanchristophe.mincke(a)gmail.com> wrote: > > Hello Café > > I am running into problems when installing transformers-base-0.4.1. > > Has anyone an idea about what is going on? > > REM : this is a "brand new" debian install, I have just install ghc, cabal > install cabal-install etc. > > Thank you > > very much > > J-C > > cabal install transformers-base > Resolving dependencies... > Downloading transformers-base-0.4.1... > Configuring transformers-base-0.4.1... > Preprocessing library transformers-base-0.4.1... > Building transformers-base-0.4.1... > [1 of 1] Compiling Control.Monad.Base ( src/Control/Monad/Base.hs, > dist/build/Control/Monad/Base.o ) > > src/Control/Monad/Base.hs:63:10: > Duplicate instance declarations: > instance Applicative (L.ST <http://l.st/> s) > -- Defined at src/Control/Monad/Base.hs:63:10 > instance Applicative (L.ST <http://l.st/> s) -- Defined in > `Control.Applicative' > > src/Control/Monad/Base.hs:67:10: > Duplicate instance declarations: > instance Applicative (S.ST <http://s.st/> s) > -- Defined at src/Control/Monad/Base.hs:67:10 > instance Applicative (S.ST <http://s.st/> s) -- Defined in > `Control.Applicative' > cabal: Error: some packages failed to install: > transformers-base-0.4.1 failed during the building phase. The exception > was: > ExitFailure 1 > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > > >

1 1

Accessing resource files in tests
by Graham Berks 09 May '13

09 May '13

Hi, whats the recommended way to access a resource file for a test within cabal. I have a text file containing data that I use in a test and want to be able to access it in a root path independent manner. Thanks

2 1

Re: [Haskell-cafe] Interfacing Java/Haskell
by Hans Georg Schaathun 09 May '13

09 May '13

On Thu, May 09, 2013 at 11:29:19AM -0400, Dan Mead wrote: > if you're on the jvm already why not consider clojure? This is why (from the clojure site you referenced): «Clojure is impure, in that it doesn't force your program to be referentially transparent, and doesn't strive for 'provable' programs.» I won't say anything about the general suitability of clojure, but I will not learn a new language at this stage unless it gives me purity, strictness, and transparency. But thanks anyway. It is useful to be aware of. > otherwise you'll have to do some fancy JNI calls and worry about calling > haskell from C, like this > http://www.haskell.org/haskellwiki/Calling_Haskell_from_C I was afraid so, and JNI appears to have a rumour for awkwardness, although there might be some simplifying overlays. -- :-- Hans Georg

1 0

What symbol / atom/ interned-string package is currently preferred?
by Ryan Newton 09 May '13

09 May '13

Hi cafe, I use symbols all the time when manipulating code. I vacillate between using stringtable-atom, symbol, and simple-atom. Unfortunately: - Stringtable-atom is has a broken build right now (GHC 7.6). (Also I've had some crashes with it in the past.) - simple-atom has dependency upper bounds that restrict it to GHC <= 7.0 - "symbol" has a design flaw, which is that it exposes the constructor for Symbol, which reveals the (nondeterministic) unique Int IDs. I.e. it is not "SafeHaskell". I submitted a pull request to relax simple-atom, but perhaps there are other packages people use with which I am not aware? Thanks, -Ryan

5 5

ghci: Difference in garbage collection etc. between REPL and function
by Niklas Hambüchen 09 May '13

09 May '13

I have an annoying bug in a C binding that can be triggered like this: handle <- open ... prep <- makePreparedStatement handle "INSERT ..." performGC runStatement prep close handle If I run these steps one by one in ghci, garbage ends up in my handle as expected. However, if I "let main = do ..." this whole block in order to pack it in a test case, it does not happen, neither in ghci nor ghc. What might be the special magic in ghci's REPL that allows me to trigger my bug so easily there? Thanks Niklas

3 5

Error compiling transformers-base-0.4.1 (debian 64 bits, ghc-7.4.2)
by jean-christophe mincke 09 May '13

09 May '13

Hello Café I am running into problems when installing transformers-base-0.4.1. Has anyone an idea about what is going on? REM : this is a "brand new" debian install, I have just install ghc, cabal install cabal-install etc. Thank you very much J-C cabal install transformers-base Resolving dependencies... Downloading transformers-base-0.4.1... Configuring transformers-base-0.4.1... Preprocessing library transformers-base-0.4.1... Building transformers-base-0.4.1... [1 of 1] Compiling Control.Monad.Base ( src/Control/Monad/Base.hs, dist/build/Control/Monad/Base.o ) src/Control/Monad/Base.hs:63:10: Duplicate instance declarations: instance Applicative (L.ST s) -- Defined at src/Control/Monad/Base.hs:63:10 instance Applicative (L.ST s) -- Defined in `Control.Applicative' src/Control/Monad/Base.hs:67:10: Duplicate instance declarations: instance Applicative (S.ST s) -- Defined at src/Control/Monad/Base.hs:67:10 instance Applicative (S.ST s) -- Defined in `Control.Applicative' cabal: Error: some packages failed to install: transformers-base-0.4.1 failed during the building phase. The exception was: ExitFailure 1

2 1

Test access resources files in cabal-dev
by Graham Berks 09 May '13

09 May '13

Hi, whats the recommended way to access a resource file for a test within cabal. I have a text file containing data that I use in a test and want to be able to access it in a root path independent manner. Thanks

1 0

Algebra in Haskell
by Robert Goss 09 May '13

09 May '13

Dear all, There are several libraries in haskell for abstract algebra but they don't seem to cover my use case I was wondering if other people have had similar issues and if there are any packages I am missing. What I am prinicpaly interested in is operation on algebraic stuctures (homomorphisms, kernels, quotients, colimits, etc) whereas most algebra packages seem to just give operations on the elements of an algebraic structure. So I would like to be able to write something like... g = freeGroup(["x","y"]) h = freeGroup(["z"]) phi = grpMorphismOnGens([("x","z"^6) , ("y","z")]) k = grpKernel phi (gens,rels) = grpPresentation (grpQuotient g k) Thank you, Robert Goss

1 0

Formal Methods/Functional programming job position at Intel
by Levent Erkok 09 May '13

09 May '13

Our formal methods team at Intel has a full-time position available that I think would be a good fit for functional programming and formal methods enthusiasts. I'm including the description below. Do not hesitate to contact me if you've any questions, or just want to talk about it in general. To apply for the position, please visit: http://www.intel.com/jobs/jobsearch/index.htm, and in the "advanced search" area enter the job number: 709631. Thanks, -Levent. Job Description *Formal Methods & Validation Architect* *-* *709631* Description If you're interested in products going into future super computer markets then the Intel® Many Integrated Core (Intel® MIC) Hardware Engineering Group is the place for you! We design and validate silicon chips with many Intel cores integrated inside being used in high performance computing architectures. In this position you will work as part of the pre-silicon formal methods, tools, and verification team to support a continued high quality of the future Intel many core processor products. You will work together with Intel's formal verification and validation community, the Formal Verification Center of Expertise (FV CoE) in a team of experts in formal methods and AV Validation. Your specific responsibilities will include defining formal verification (FV) test plans as well as Cluster Test Environment (CTE) based test plans for dynamic simulation validation (DV). The goal is to help optimize a combined use of FV and CTE based validation techniques (DV) and contribute to an increasing use of formal methods at Intel. Based on the test plans you will write properties in formal language, and prove the properties using our model checkers and theorem proving tools. You will also write CTE based test cases and coverage plans. Your area of strength may currently lie within either FV or DV with strong skills rooted in software development. But through your skills and work, you will become an expert in both formal methods and validation technologies. You will interact very closely with design teams, and other validation teams, as well as with Intel's internal R&D groups that continue to improve and develop formal method and verification tools. You must be able to communicate effectively with various technical groups and coordinate activities amongst those groups.

1 0

Categories (cont.)
by Christopher Howard 08 May '13

08 May '13

I've perhaps been trying everyones patiences with my noobish CT questions, but if you'll bear with me a little longer: I happened to notice that there is in fact a Category class in Haskell base, in Control.Category: quote: -------- class Category cat where A class for categories. id and (.) must form a monoid. Methods id :: cat a a the identity morphism (.) :: cat b c -> cat a b -> cat a c morphism composition -------- However, the documentation lists only two instances of Category, functions (->) and Kleisli Monad. For instruction purposes, could someone show me an example or two of how to make instances of this class, perhaps for a few of the common types? My initial thoughts were something like so: code: -------- instance Category Integer where id = 1 (.) = (*) -- and instance Category [a] where id = [] (.) = (++) ------- But these lead to kind mis-matches. -- frigidcode.com

9 14

Mutually recursive modules
by Roman Cheplyaka 08 May '13

08 May '13

I wonder whether it's always possible to break cycles using GHC's .hs-boot files. Consider the following schematic example: module A where import B data A f :: B -> A f = undefined B.g module B where import A data B g :: A -> B g = undefined A.f A.hs-boot must give a type signature for f, and since the signature contains 'B', it must import 'B'. Ditto for B.hs-boot — it must import 'A'. Even if we treat all imports as {-# SOURCE #-}, there is still a cycle between the hs-boot files. So, am I right in understanding that these recursive modules cannot be compiled by GHC at all? Roman

2 2

Incrementation fails
by John 08 May '13

08 May '13

Hello All, I'm in a big trouble with incrementation of a counter in this code. It doesn't increment. Could you please tell me where the problem ist and how can I solve it? replaceBasedIdx :: String -> [String] -> String -> String replaceBasedIdx findStr replaceStrList myText = replaceBasedIdxSub findStr replaceStrList myText 0 replaceBasedIdxSub :: String -> [String] -> String -> Int -> String replaceBasedIdxSub findStr replaceStrList myText counter = loop myText where loop [] = [] loop myText = let (prefix, rest) = splitAt n myText in if findStr == prefix -- found an occurrence? then (replaceStrList !! (counter+1)) ++ loop rest -- yes: replace it else head myText : loop (tail myText) -- no: keep looking n = length findStr Thank you very mutch! Greetings! -- View this message in context: http://haskell.1045720.n5.nabble.com/Incrementation-fails-tp5729905.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

2 3

Munich 13.5., live sequencer
by Heinrich Hördegen 08 May '13

08 May '13

Dear all, Henning Thielemann will give a demonstration of his live sequencer in Munich on the 13th of May (next Monday): http://www.youtube.com/watch?v=88jK162l6mE We begin at 19h00 at Oetingenstr. 67, 80538 Munich, room 157 (first floor, central). As everything is live, please bring your laptops along, if you want to participate interactivly. Heinrich

1 0

Stream fusion and span/break/group/init/tails
by Edward Z. Yang 07 May '13

07 May '13

Hello all, (cc'd stream fusion paper authors) I noticed that the current implementation of stream fusion does not support "multiple-return" stream combinators, e.g. break :: (a -> Bool) -> [a] -> ([a], [a]). I thought a little bit about how might one go about implement this, but the problem seems nontrivial. (One possibility is to extend the definition of Step to support multiple return, but the details are a mess!) Nor, as far as I can tell, does the paper give any treatment of the subject. Has anyone thought about this subject in some detail? Thanks, Edward

8 23

PPDP 2013: 2nd Call for Papers
by Tom Schrijvers 07 May '13

07 May '13

===================================================================== 2nd Call for papers 15th International Symposium on Principles and Practice of Declarative Programming PPDP 2013 Special Issue of Science of Computer Programming (SCP) Madrid, Spain, September 16-18, 2013 (co-located with LOPSTR 2013) http://users.ugent.be/~tschrijv/PPDP2013/ ====================================================================== EXTENDED SUBMISSION DEADLINE: JUNE 13, 2013 PPDP 2013 is a forum that brings together researchers from the declarative programming communities, including those working in the logic, constraint and functional programming paradigms, but also embracing a variety of other paradigms such as visual programming, executable specification languages, database languages, and knowledge representation languages. The goal is to stimulate research in the use of logical formalisms and methods for specifying, performing, and analysing computations, including mechanisms for mobility, modularity, concurrency, object-orientation, security, verification and static analysis. Papers related to the use of declarative paradigms and tools in industry and education are especially solicited. Topics of interest include, but are not limited to: * Functional programming * Logic programming * Answer-set programming * Functional-logic programming * Declarative visual languages * Constraint Handling Rules * Parallel implementation and concurrency * Monads, type classes and dependent type systems * Declarative domain-specific languages * Termination, resource analysis and the verification of declarative programs * Transformation and partial evaluation of declarative languages * Language extensions for security and tabulation * Probabilistic modelling in a declarative language and modelling reactivity * Memory management and the implementation of declarative systems * Practical experiences and industrial application This year the conference will be co-located with the 23nd International Symposium on Logic-Based Program Synthesis and Transformation (LOPSTR 2013) and held in cooperation with ACM SIGPLAN. The conference will be held in Madrid, Spain. Previous symposia were held at Leuven (Belgium), Odense (Denmark), Hagenberg (Austria), Coimbra (Portugal), Valencia (Spain), Wroclaw (Poland), Venice (Italy), Lisboa (Portugal), Verona (Italy), Uppsala (Sweden), Pittsburgh (USA), Florence (Italy), Montreal (Canada), and Paris (France). Papers must describe original work, be written and presented in English, and must not substantially overlap with papers that have been published or that are simultaneously submitted to a journal, conference, or workshop with refereed proceedings. Work that already appeared in unpublished or informally published workshop proceedings may be submitted (please contact the PC chair in case of questions). Proceedings will be published in the ACM International Conference Proceedings Series. After the symposium, a selection of the best papers will be invited to extend their submissions in the light of the feedback solicited at the symposium. The papers are expected to include at least 30% extra material over and above the PPDP version. Then, after another round of reviewing, these revised papers will be published in a special issue of SCP with a target publication date by Elsevier of 2014. Important Dates Abstract Submission: June 10, 2013 Paper submission: June 13, 2013 Notification: July 18, 2013 Camera-ready: August 4, 2013 Symposium: September 16-18, 2013 Invites for SCP: October 2, 2013 Submission of SCP: December 11, 2013 Notification from SCP: February 22, 2014 Camera-ready for SCP: March 14, 2014 Authors should submit an electronic copy of the paper (written in English) in PDF. Each submission must include on its first page the paper title; authors and their affiliations; abstract; and three to four keywords. The keywords will be used to assist us in selecting appropriate reviewers for the paper. Papers should consist of no more than 12 pages, formatted following the ACM SIG proceedings template (option 1). The 12 page limit must include references but excludes well-marked appendices not intended for publication. Referees are not required to read the appendices, and thus papers should be intelligible without them. Program Committee Sergio Antoy Portland State University, USA Manuel Carro IMDEA Software Institute, Spain Iliano Cervesato Carnegie Mellon University, Qatar Agostino Dovier Universita degli Studi di Udine, Italy Maria Garcia de la Banda Monash University, Australia Ralf Hinze University of Oxford, UK Yukiyoshi Kameyama University of Tsukuba, Japan Oleg Kiselyov USA Yanhong Annie Liu State University of New York at Stony Brook, USA Stefan Monnier Universite de Montreal, Canada Alan Mycroft University of Cambrige, UK Bruno C. d. S. Oliveira National University of Singapore, Singapore Alberto Pettorossi Universita di Roma Tor Vergata, Italy Enrico Pontelli New Mexico State University, USA Kristoffer Rose IBM Research, USA Sukyoung Ryu KAIST, South Korea Vitor Santos Costa University of Porto, Portugal Torsten Schaub University Potsdam, Germany Tom Schrijvers Ghent University, Belgium Martin Sulzmann Hochschule Karlsruhe, Germany Wouter Swierstra Universiteit Utrecht, The Netherlands Tarmo Uustalu Institute of Cybernetics, Estonia Janis Voigtlaender University of Bonn, Germany Meng Wang Chalmers University of Technology, Sweden Jan Wielemaker Universiteit van Amsterdam, The Netherlands Program Chair Tom Schrijvers Department of Applied Mathematics and Computer Science Ghent University 9000 Gent, Belgium General Chair Ricardo Pena Facultad de Informatica Universidad Complutense de Madrid 28040 Madrid, Spain

1 0

Request for input on "Programming in Haskell"
by Graham Hutton 07 May '13

07 May '13

Have you taught a course using Hutton's textbook on Programming in Haskell? If so, please read on! As part of the national assessment of universities in the UK that takes place every 5-6 years, I'm producing a case study on the impact of the book on student and professional training. The case study will include a number of quotes from academic and industrial users who have used the book for teaching purposes. If you have taught a course using the book any time from January 2008 onwards, and would be willing to provide a short quote (2-3 sentences) for the case study, that would be very much appreciated. It doesn't matter if you are no longer teaching the course or are not currently using the book. If you are interested, drop me an email and I'll explain what's involved. Many thanks, Graham Hutton -- Prof Graham Hutton Functional Programming Lab School of Computer Science University of Nottingham, UK http://www.cs.nott.ac.uk/~gmh This message and any attachment are intended solely for the addressee and may contain confidential information. If you have received this message in error, please send it back to me, and immediately delete it. Please do not use, copy or disclose the information contained in this message or in any attachment. Any views or opinions expressed by the author of this email do not necessarily reflect the views of the University of Nottingham. This message has been checked for viruses but the contents of an attachment may still contain software viruses which could damage your computer system: you are advised to perform your own checks. Email communications with the University of Nottingham may be monitored as permitted by UK legislation.

1 0

Re: [Haskell-cafe] Hackage checking maintainership of packages
by Clark Gaebel 07 May '13

07 May '13

If there's a github link in the package url, it could check the last update to the default branch. If it's more than 6 months ago, an email to the maintainer of "is this package maintained?" can be sent. If there's no reply in 3 months, the package is marked as unmaintained. If the email is ever responded to or a new version is uploaded, the package can be un-marked. - Clark On Sunday, May 5, 2013, Lyndon Maydwell wrote: > I've got it! > > The answer was staring us in the face all along... We can just introduce > backwards-compatibility breaking changes into GHC-head and see if the > project fails to compile for x-time! That way we're SURE it's unmaintained. > > I'll stop sending emails now. > > > On Mon, May 6, 2013 at 10:44 AM, Clark Gaebel <cgaebel(a)uwaterloo.ca>wrote: > > If there's a github link in the package url, it could check the last > update to the default branch. If it's more than 6 months ago, an email to > the maintainer of "is this package maintained?" can be sent. If there's no > reply in 3 months, the package is marked as unmaintained. If the email is > ever responded to or a new version is uploaded, the package can be > un-marked. > > - Clark > > > On Sunday, May 5, 2013, Lyndon Maydwell wrote: > > But what if the package is already perfect? > > Jokes aside, I think that activity alone wouldn't be a good indicator. > > > On Mon, May 6, 2013 at 9:59 AM, Conrad Parker <conrad(a)metadecks.org>wrote: > > On 6 May 2013 09:42, Felipe Almeida Lessa <felipe.lessa(a)gmail.com> wrote: > > Just checking the repo wouldn't work. It may still have some activity > > but not be maintained and vice-versa. > > ok, how about this: if the maintainer feels that their repo and > maintenance activities are non-injective they can additionally provide > an http-accessible URL for the maintenance activity. Hackage can then > do an HTTP HEAD request on that URL and use the Last-Modified response > header as an indication of the last time of maintenance activity. I'm > being a bit tongue-in-cheek, but actually this would allow you to > point hackage to a blog as evidence of maintenance activity. > > I like the idea of just pinging the code repo. > > Conrad. > > > On Sun, May 5, 2013 at 2:19 PM, Doug Burke <dburke.gw(a)gmail.com> wrote: > >> > >> On May 5, 2013 7:25 AM, "Petr Pudlák" <petr.mvd(a)gmail.com> wrote: > >>> > >>> Hi, > >>> > >>> on another thread there was a suggestion which perhaps went unnoticed > by > >>> most: > >>> > >>>> ---------- Forwarded message ---------- > >>>> From: Niklas Hambüchen <mail(a)nh2.me> > >>>> Date: 2013/5/4 > >>>> ... > >>>> I would even be happy with newhackage sending every package > maintainer a > >>>> quarterly question "Would you still call your project X 'maintained'?" > >>>> for each package they maintain; Hackage could really give us better > >>>> indications concerning this. > >>> > >>> > >>> This sounds to me like a very good idea. It could be as simple as "If > you > >>> consider yourself to be the maintainer of package X please just hit > reply > >>> and send." If Hackage doesn't get an answer, it'd just would display > some > >>> red text like "This package seems to be unmaintained since D.M.Y." > >>> > >>> Best regards, > >>> Petr > >>> > >> > >> For those packages that give a repository, a query could be done > >> automatically to see when it was last updated. It's not the same thing > as > >> 'being maintained', but is less annoying for those people with many > packages > >> on hackage. > >> > >> Doug > >> > >> > >> _______________________________________________ > >> Haskell-Cafe mailing list > >> Haskell-Cafe(a)haskell.org > >> http://www.haskell.org/mailman/listinfo/haskell-cafe > >> > > > > > > > > -- > > Felipe. > > > > _______________________________________________ > > Haskell-Cafe mailing list > > Haskell-Cafe(a)haskell.org > > http://www.haskell.org/mailman/listinfo/haskell-cafe > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > >

6 6

Hackage checking maintainership of packages
by Petr Pudlák 07 May '13

07 May '13

Hi, on another thread there was a suggestion which perhaps went unnoticed by most: ---------- Forwarded message ---------- > From: Niklas Hambüchen <mail(a)nh2.me> > Date: 2013/5/4 > ... > I would even be happy with newhackage sending every package maintainer a > quarterly question "Would you still call your project X 'maintained'?" > for each package they maintain; Hackage could really give us better > indications concerning this. This sounds to me like a very good idea. It could be as simple as "If you consider yourself to be the maintainer of package X please just hit reply and send." If Hackage doesn't get an answer, it'd just would display some red text like "This package seems to be unmaintained since D.M.Y." Best regards, Petr

14 20

Fwd: Backward compatibility
by Adrian May 06 May '13

06 May '13

Oops, forgot hit hit reply-all the first time, well spotted by Niklas... ---------- Forwarded message ---------- From: Adrian May <adrian.alexander.may(a)gmail.com> Date: 5 May 2013 14:22 Subject: Re: [Haskell-cafe] Backward compatibility To: Niklas Hambüchen <mail(a)nh2.me> > The fact that it doesn't build and that the last change is from 2007 the > *is* the warning that it is completely unmaintained and not the way to > do things today. > > (One could even say that by making it build on 7.6, I have removed this > warning and given the illusion that everything is fine.) > That only makes sense if you assume everybody is familiar with Haskell and its culture. But that neglects trying to make it attractive to people who aren't. Of course I agree that it would be better if there were warnings on > their web sites that said "sorry guys, this project is dead now". > > I would even be happy with newhackage sending every package maintainer a > quarterly question "Would you still call your project X 'maintained'?" > for each package they maintain; Hackage could really give us better > indications concerning this. > > Something like that would make a lot of sense to me. > Still I'd say that in this case, the fact that it did not build, hasn't > had a single change in the last half decade, and that you cannot find > any recent discussion about it anywhere on the Internet, make it pretty > clear what is going on here, even for non-technical people. Half a decade is nothing to most programming cultures. A newbie looks for sample code and blames himself if he can't get it working. > > Please don't say that it's my culture's fault. > > From your story it sounds like you have a problem with developer > simplemindedness and management wars idiocy. Nobody is forcing you to be part of that. There are a lot of places ... Perhaps I'd rather help those who need it than preach to the converted. You summed it up nicely as two problems: (1) bitchy managers and (2) untrained programmers. I'd like to use Haskell to help with (2) but I still have to work around (1). My plan is to start by winning the hearts and minds of the developers before sticking my neck out far enough to get it severed. There's another plan where I'm pitching VCs about a start up, in which case I'd have a lot more control, but I'd still have to prove that my elite imperative squad were willing and able to learn a new trick before committing myself. I've actually learned quite a lot from this discussion and that largely enables me to preempt any Rails-day problems. But that's only me. Lots of people might be flirting with Haskell just out of curiosity and bouncing off it for these reasons. There have been a lot of good ideas suggested about how to minimise that, and I'd also throw in that it would be cool if people could tell the compiler to behave as it did half a decade ago when the code was written so people could prove to themselves that the code works in principle, then they could clock the compiler forward little by little, reading its release notes along the way. That's a lot friendlier than being confronted with an apparently endless series of error messages when you've barely learned to read them, and not even knowing if you're making things better or worse. If the desired compiler/modules version was in the makefile, that, I think, would be a general solution. The FPComplete thing also looks helpful. I could use that to sell the language to newbies. The mercenaries would come later though. Thanks to everybody for helping out with this. Adrian.

8 8

help understanding zlib space leak
by diego souza 06 May '13

06 May '13

Dear haskellers, I'd like assistance figuring out a strange space leak using zlib package. To make it easier to reproduce I've come up with the following snippet that pretty much resumes up the problem I'm trying to solve: > -- omitting imports and function signatures > encode = compress . L.fromChunks > > main = do { hSetBinaryMode stdout True > ; hSetBinaryMode stdin True > ; hSetBuffering stdin NoBuffering > ; hSetBuffering stdout NoBuffering > ; loop [] > } > where loop buff > | length buff == 64 = L.hPut stdout (encode buff) >> loop [] > | otherwise = do { eof <- hIsEOF stdin > ; when (not eof) (fmap (: buff) (B.hGetSome stdin 512) >>= loop) > } N.B.: Removing the `compress' function from the above code also removes the space leak. Now, feeding the above program with ~8GB worth of binary data: > $ uname -a Linux mephisto.localhost.localdomain 3.8.7-1-ARCH #1 SMP PREEMPT Sat Apr 13 09:01:47 CEST 2013 x86_64 GNU/Linux > $ ghc --version The Glorious Glasgow Haskell Compilation System, version 7.6.3 > $ ghc -W -Wall -rtsopts --make -O2 test.hs > $ sudo dd if=/dev/sda bs=4K count=2048K | ./test +RTS -M1M -s >/dev/null ... 8589934592 bytes (8.6 GB) copied, 277.263 s, 31.0 MB/s ... 2 MB total memory in use (0 MB lost due to fragmentation) ... Which is fine. However, monitoring the RSS size is a different story: > $ while pidof test; do ps -o rss= -p $(pidof test); done | tail 16967 25620 16967 25628 16967 25628 16967 25628 16967 # ~16M 0 I know the RSS usually overestimates the memory consumption but the problem is that it is forever growing. The following I found very intriguing: * `+RTS -hc` gives me no hint about whats wrong [at least I couldn't see one]; * `+RTS -M1M` doesn't produce an error; * removing the `compress' functions makes the problem disappear; I couldn't figure these out and I don't think this is matter of strictness, though. Has anyone seen this before? Thanks in advance, ~dsouza

1 1

Follow up on type error diagnosis for DSLs in Haskell
by Jurriaan Hage 06 May '13

06 May '13

Dear all (and in particular Alberto G. Corona and Stephen Tetley), First of all, thanks Stephen for pointing out our work to Alberto. Second, you may be interested to know that I just (as in two weeks ago) obtained a grant to hire a PhD student to scale the work of the ICFP '03 paper (as mentioned by Stephen) up to Haskell 2011 (or whatever variant will be appropriate). The plan is to first prototype this work in the UHC compiler, and, if succesful, build it into the GHC. I shall surely send out a job vancancy on some of the Haskell mailing lists. best, Jurriaan Hage

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[ANN] xmobar 0.17 released
by Jose A. Ortega Ruiz 05 May '13

05 May '13

I've just released version 0.17 of xmobar, a lightweight system monitor written in Haskell. Homepage: http://xmobar.org Release notes: http://xmobar.org/releases.html _New features_ - Icons support: it's now possible to insert bitmaps in the template (Edward O'Callaghan, Alexander Polakov and Tomáš Janoušek). - Initial support for reacting to mouse clicks (Alexander Polakov). - New `TopP` and `BottomP` alignments, taking left and right paddings (thanks to Dmitry Malikov). - New `<freeratio>` field for memory monitor (Peter Simons). - New `allDesktops` and `overrideRedirect` configuration options, providing dock behaviour in tiling WMs (when set to True and False respectively). Cf. discussion at [github #105]. - Experimental `-d` (start as a dock) option, may address [github #67] in some window managers. _Bug fixes_ - Partial (as reports go) fix for [github #77]. - Safer volume plugin (Dmitry Malikov). - Battery percentage capped at 100% (RJ Regenold). Enjoy! -- I always pass on good advice. It's the only thing to do with it. It is never any use to oneself. -Oscar Wilde

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