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Munich Haskell Meeting
by Heinrich Hördegen 24 Jan '12

24 Jan '12

Dear all, I hope, all of you had a good start into this year. For Munich's Haskellers, it's time for our next get-together. With a number of participants between 12 and 14, our last meetings have been a real success. Let's continue this joyful events. Even if you don't live at Munich, if you can make it one day, we will be happy to receive you there. Check out the dates! So, this year's first get-together will take place next week, Monday, 30. January at Cafe Puck, our usual venue. If you plan to join, please go to the site and click the button: http://www.haskell-munich.de/dates This will help us to reserve tables. With hope of a large attendance, have a nice time, Heinrich -- -- hoerdegen(a)funktional.info www.funktional.info --

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Happy holidays Haskell
by R J 24 Jan '12

24 Jan '12

hello Haskell ever since I started this my life has been better than ever http://www.news13open.com

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[C][enums][newbie] What is natural Haskell representation of such enum?
by Данило Глинський 24 Jan '12

24 Jan '12

What is natural Haskell representation of such enum? enum TypeMask { UNIT, GAMEOBJECT, CREATURE_OR_GAMEOBJECT = UNIT | GAMEOBJECT }; More sophisticated question is: and what data structures must be used when converting this naturally one to Haskell? // 1-byte flaged enum enum TypeMask { // ... UNIT = 0x0004, GAMEOBJECT = 0x0008, // ... CREATURE_OR_GAMEOBJECT = UNIT | GAMEOBJECT WORLDOBJECT = UNIT | PLAYER | GAMEOBJECT | DYNAMICOBJECT | CORPSE // ... even more enum combos ... };

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Finding longest common prefixes in a list
by Gwern Branwen 24 Jan '12

24 Jan '12

Recently I wanted to sort through a large folder of varied files and figure out what is a 'natural' folder to split out, where natural means something like >4 files with the same prefix. (This might be author, genre, subject, whatever I felt was important when I was naming the file.) Now usually I name files with hyphens as the delimiters like the hypothetical '1998-wadler-monads.pdf', and it would be easy to write a stdin/stdout filter to break Strings on hyphens and sort by whatever is most common. But this is rather hardwired, can I solve the more general problem of finding the longest common prefixes, whatever they are? This turns out to be much more difficult than simply finding 'the' longest common prefix (which is usually ""). I found an algorithm of sorts at http://stackoverflow.com/a/6634624 but it was easier described than implemented. Eventually I wrote what I *think* is a correct program, but it's definitely of the write-only sort. Perhaps people have better implementations somewhere? I saw a lot of discussion of tries, but I didn't go that route. The code, followed by an example: #!/usr/bin/env runhaskell import Data.List (intercalate, isPrefixOf, nub, sort) main :: IO () main = interact (unlines . intercalate [""] . chunkFiles . lines ) -- basic algorithm from <http://stackoverflow.com/a/6634624> chunkFiles :: Ord a => [[a]] -> [[[a]]] chunkFiles f = map (\(_,b) -> filter (isPrefixOf b) f) $ sort $ map (\x -> (countPrefixes x f,x)) (e $ bar f) sharedPrefixes :: Ord a => [[a]] -> [a] sharedPrefixes [] = [] sharedPrefixes s = foldr1 sp2 s where sp2 l1 l2 = map fst . takeWhile (uncurry (==)) $ zip l1 l2 traverse :: Ord a => [[a]] -> [[a]] traverse [] = [] traverse x = sharedPrefixes (take 2 x) : traverse (drop 1 x) bar :: Ord a => [[a]] -> [[a]] bar = nub . sort . traverse . sort countPrefixes :: (Ord a) => [a] -> [[a]] -> Int countPrefixes x xs = length $ filter (x `isPrefixOf`) xs e :: Eq a => [[a]] -> [[a]] e y = map fst $ filter snd $ map (\x -> (x, (==) 1 $ length . filter id $ map (x `isPrefixOf`) y)) y {- Example input from `ls`: chorus-kiminoshiranaimonogatari.ogg chorus-mrmusic.ogg choucho-lastnightgoodnight.ogg dylanislame-aikotoba.ogg electriclove-エレクトリック・ラブ-korskremix.ogg gumi-bacon8-justhangingaround.ogg gumi-iapologizetoyou.ogg gumi-montblanc.ogg gumi-mozaikrole.ogg gumi-ハッピーシンセサイザ.ogg gumi-showasengirl.ogg gumi-sweetfloatflatsスイートフロートアパート.ogg gumi-timewarpedafterchoppingmystagbeetle.ogg gumi-オリジナル曲-付きホシメグリ.ogg gumi-ミクオリジナル親友.ogg kaito-byakkoyano.ogg kaito-flowertail.ogg kasaneteto-tam-ochamekinou重音テト吹っ切れたおちゃめ機能.ogg len-crime-timetosaygoodbye.ogg len-fire◎flower.ogg len-ponponpon.ogg lily-prototype.ogg luka-apolxcore-waitingforyou.ogg luka-dimトロイ.ogg luka-dion-myheartwillgoon.ogg luka-dirgefilozofio-dirgeasleepinjesus.ogg luka-アゴアニキ-doubelariatダブルラリアット.ogg luka-emon-heartbeats.ogg luka-emonloid3-ハローハロー.ogg luka-everybreathyoutake.ogg luka-オリジナル-garden.ogg luka-justbefriends.ogg lukameiko-gemini.ogg luka-milkyway.ogg luka-やみくろ-かいぎ.ogg luka-tic-tick.ogg luka-torinouta.ogg luka-zeijakukei-shounenshoujo.ogg luka-勝手にアニメ-nologic-作ってみた.ogg luka-駄目人間.ogg meiko-artemis-awake.ogg miku-9ronicleプラチナ.ogg miku-acolorlinkingworld-この世界の下で.ogg miku-acolorlinkingworld-青い花.ogg miku-a+jugos-lullabyforkindness.ogg miku-akayaka-beacon.ogg miku-akayakap-sunrise.ogg miku-aoihana.ogg miku-arabianresponse.ogg miku-avtechno-tear.ogg miku-こえをきかせてcicci.ogg miku-cleantears-remind2011natsu-greenhillzonecrystiararemix.ogg miku-cleantears-remind2011natsu-夏影summerwindremix.ogg miku-clocklockworks.ogg miku-dancedancevol2-runner.ogg miku-daniwellp-chaoticuniverse.ogg miku-dixieflatline-shinonomescrumble.ogg miku-electricloveエレクトリックラヴ.ogg miku-elegumitokyo-kissmebaby.ogg miku-galaxyodyssey-cryingirl.ogg miku-galaxyodyssey-galaxyspacelines.ogg miku-hakamairi.ogg miku-haruna.ogg miku-heartshooter.ogg miku-hoshikuzutokakera.ogg miku-innes.ogg miku-innocence初音ミク.ogg miku-jemappelle-motion-likeyou.ogg miku-jemappelle-motion-ohwell.ogg miku-jevannip-myfavoritesummer.ogg miku-kakokyuudance-過呼吸ダンス.ogg miku-kz-packaged.ogg miku-kz-tellyourworld.ogg miku-lastscene.ogg miku-lostmemories付き-初音ミク.ogg miku-lovelyday.ogg miku-いいわけlove_song.ogg mikulukagumi-prayfor.ogg miku-maple-初音ミク楓-オリジナル曲.ogg miku-more1.5.ogg miku-m(a)rk-eklosion.ogg miku-m(a)rk-kirch.ogg miku-nana-ボーナストラック-ハッピー般若コア.ogg miku-nekomimiswitch.ogg miku-nightrainbow.ogg miku-noyounome.ogg miku-むかしむかしのきょうのぼくオリジナル.ogg miku-pandolistp-neverendinghammertime.ogg miku-ジラートP-birthdayofeden-deepsleep.ogg miku-ジラートP-birthdayofeden-水中読書.ogg miku-plustellia-dear.ogg miku-plustellia-壁の彩度-crazygirl.ogg miku-plustellia-壁の彩度-discoradio.ogg miku-ぽわぽわP-ストロボライト.ogg miku-rabbitforgets.ogg miku-re:package-lastnightgoodnight.ogg miku-re:package-ourmusic.ogg miku-re:package-sutorobonaitsu.ogg miku-rollinggirl.ogg miku-ryo-メルト-melt.ogg miku-senseiniitteyaro.ogg miku-sevencolors-レモネード.ogg miku-shoukinosatadenia.ogg miku-stratosphere.ogg miku-supernova.ogg miku-tam-lastnightgoodnight.ogg miku-tanatofobia.ogg miku-thearmyforyourenvy-スーパー・ノヴァ.ogg miku-theendlesslove.ogg miku-tinyparadise-snowflake.ogg miku-tinyparadise-tinyparadise.ogg miku-unfragment.ogg miku-worldismine-ルドイズマイン.ogg miku-yakiimo.ogg miku-文学少年の憂鬱-オリジナル.ogg miku-カラフルポップビートオリジナル曲.ogg miku-杯本選life.ogg miku-杯本選初音ミクどういうことなのダンス.ogg miku-般若心経beautyfloor-buddhamix.ogg miku-般若心経ポップ.ogg niconicochorus-blackrockshooter.ogg niconicochorus-justbefriends.ogg rin-dixieflatline-gemini.ogg rin-elegumitokyo-二人、恋してgirlsside.ogg rin-helloworld.ogg rin-jutenija.ogg rin-lastnightgoodnight.ogg rin-ripples-evergreen.ogg rin-っ´ω｀c.ogg rollinggirl-piano.ogg seeu-gagain-따라리라ddadada.ogg utau-雪歌ユフbeyondオリジナル曲.ogg yuki-discochocolatheque.ogg yuki-shouwasenhosiga^ru.ogg yuki-shouwasenhosiga^ru.ogg Example output from `ls | ~/lcp.hs`: chorus-kiminoshiranaimonogatari.ogg chorus-mrmusic.ogg gumi-montblanc.ogg gumi-mozaikrole.ogg gumi-showasengirl.ogg gumi-sweetfloatflatsスイートフロートアパート.ogg kaito-byakkoyano.ogg kaito-flowertail.ogg luka-emon-heartbeats.ogg luka-emonloid3-ハローハロー.ogg luka-tic-tick.ogg luka-torinouta.ogg miku-acolorlinkingworld-この世界の下で.ogg miku-acolorlinkingworld-青い花.ogg miku-akayaka-beacon.ogg miku-akayakap-sunrise.ogg miku-cleantears-remind2011natsu-greenhillzonecrystiararemix.ogg miku-cleantears-remind2011natsu-夏影summerwindremix.ogg miku-dancedancevol2-runner.ogg miku-daniwellp-chaoticuniverse.ogg miku-electricloveエレクトリックラヴ.ogg miku-elegumitokyo-kissmebaby.ogg miku-galaxyodyssey-cryingirl.ogg miku-galaxyodyssey-galaxyspacelines.ogg miku-hakamairi.ogg miku-haruna.ogg miku-innes.ogg miku-innocence初音ミク.ogg miku-jemappelle-motion-likeyou.ogg miku-jemappelle-motion-ohwell.ogg miku-kz-packaged.ogg miku-kz-tellyourworld.ogg miku-lostmemories付き-初音ミク.ogg miku-lovelyday.ogg miku-m(a)rk-eklosion.ogg miku-m(a)rk-kirch.ogg miku-plustellia-壁の彩度-crazygirl.ogg miku-plustellia-壁の彩度-discoradio.ogg miku-senseiniitteyaro.ogg miku-sevencolors-レモネード.ogg miku-tam-lastnightgoodnight.ogg miku-tanatofobia.ogg miku-thearmyforyourenvy-スーパー・ノヴァ.ogg miku-theendlesslove.ogg miku-tinyparadise-snowflake.ogg miku-tinyparadise-tinyparadise.ogg miku-ジラートP-birthdayofeden-deepsleep.ogg miku-ジラートP-birthdayofeden-水中読書.ogg miku-杯本選life.ogg miku-杯本選初音ミクどういうことなのダンス.ogg miku-般若心経beautyfloor-buddhamix.ogg miku-般若心経ポップ.ogg niconicochorus-blackrockshooter.ogg niconicochorus-justbefriends.ogg len-crime-timetosaygoodbye.ogg len-fire◎flower.ogg len-ponponpon.ogg luka-dimトロイ.ogg luka-dion-myheartwillgoon.ogg luka-dirgefilozofio-dirgeasleepinjesus.ogg miku-re:package-lastnightgoodnight.ogg miku-re:package-ourmusic.ogg miku-re:package-sutorobonaitsu.ogg miku-nana-ボーナストラック-ハッピー般若コア.ogg miku-nekomimiswitch.ogg miku-nightrainbow.ogg miku-noyounome.ogg rin-dixieflatline-gemini.ogg rin-elegumitokyo-二人、恋してgirlsside.ogg rin-helloworld.ogg rin-jutenija.ogg rin-lastnightgoodnight.ogg rin-ripples-evergreen.ogg rin-っ´ω｀c.ogg -} -- gwern http://www.gwern.net

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Monads, do and strictness
by Victor S. Miller 24 Jan '12

24 Jan '12

The "do" notation translates do {x <- a;f} into a>>=(\x -> f) However when we're working in the IO monad the semantics we want requires that the lambda expression be strict in its argument. So is this a special case for IO? If I wanted this behavior in other monads is there a way to specify that? Victor Sent from my iPhone

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ANN: OpenCL 1.0.3.0 package
by Luis Cabellos 23 Jan '12

23 Jan '12

Hello, I update the OpenCL package with the last changes. The most important thing, currently it fully implements OpenCL 1.0. IMPORTANT, some functions change signature (e,g: clSetKernelArg, and clCreateContext* ) Thanks all comments in the previous version, issues and pulls in github. # Where to get it * Hackage page (http://hackage.haskell.org/package/OpenCL) * Repository (https://github.com/zhensydow/opencl) * Bugs (https://github.com/zhensydow/opencl/issues) # Changes * Move to Control.Parallel.OpenCL (thanks Jason Dagit) * Added Image functions * Added clExecuteNativeKernel * Fixes on Windows, Macos and Linux versions (thanks Anthony Cowley, ehird, axman6) * Fix bug with preprocessor code in OpenCL source code * Fix clSetKernelArg to allow cannot specify size of local memory arrays Thanks, Luis Cabellos

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Can't install hspec
by Erik de Castro Lopo 23 Jan '12

23 Jan '12

Hi all, I'm trying to cabal install hspec and I get the following: Resolving dependencies... /tmp/hspec-0.9.04062/hspec-0.9.0/Setup.lhs:2:10: Could not find module `System' It is a member of the hidden package `haskell98-2.0.0.0'. Use -v to see a list of the files searched for. cabal: Error: some packages failed to install: hspec-0.9.0 failed during the configure step. The exception was: ExitFailure 1 This is with ghc-7.2.2. Any clues how I can get around this? Cheers, Erik -- ---------------------------------------------------------------------- Erik de Castro Lopo http://www.mega-nerd.com/

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Idris
by Ryan Ingram 23 Jan '12

23 Jan '12

Has anyone played with Idris (http://idris-lang.org/) at all? It looks interesting, and I'd love to play with it, but unfortunately I only have windows machines up and running at the moment and the documentation seems to imply it only builds on unixy systems. I'm curious how difficult it would be to get a win32 implementation up and running. -- ryan

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Compiling dph package with ghc-7.4.0.20111219
by mukesh tiwari 23 Jan '12

23 Jan '12

Hello all I have installed ghc-7.4.0.20111219 and this announcement<http://www.haskell.org/pipermail/glasgow-haskell-users/2011-December/021310…>says that "The release candidate accidentally includes the random, primitive, vector and dph libraries. The final release will not include them". I tried to compile a program [ntro@localhost src]$ ghc-7.4.0.20111219 -c -Odph -fdph-par ParallelMat.hs ghc: unrecognised flags: -fdph-par Usage: For basic information, try the `--help' option. [ntro@localhost src]$ ghc-7.2.1 -c -Odph -fdph-par ParallelMat.hs Also in ghc-7.4.0.20111219 --help , i don't see any option related data parallel haskell. I search the ghc manual <http://www.haskell.org/ghc/dist/stable/docs/html/users_guide/> and got one reference for data parallel haskell<http://www.haskell.org/ghc/dist/stable/docs/html/users_guide/lang-parallel.…>. This link again redirects to data parallel haskell <http://www.haskell.org/haskellwiki/GHC/Data_Parallel_Haskell> wiki page using ghc-7.2.1. Could some one please tell me how to compile haskell program using dph with ghc-7.4.0.20111219. Regards Mukesh Tiwari

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Right tree structure for complicated problem
by Pierre Penninckx 22 Jan '12

22 Jan '12

Hello everyone, So here is what I want to achieve: I'd like a program that calculates the time needed for water to flow out of a circuit made out of tube. The rules are : - There are multiple sources of water and only one exit. - The water can only take one path from a source to the exit. - Of course, a source of water contains a certain amount of water at the beginning. ### Algorithm Here's the concept of how it should be working: #1 The tubes are connected together : 1 parent with n childs. This looks really like a tree: data Tree = Leaf { getVolume::Int } | Path { getMaxFlow::Int , getFlow::Int , getOpen::Bool , getChilds::[Tree} } But this structure doesn't work well :( (see later why) When I determine the time taken by the water to flow down to the exit, I need to take water jams (haha) into account. To do this, the algorithm begins by the exit node and "distribute" it's maximum flow through the childs, but only to open tubes. And the childs distribute their flow to their own child. Repeat until you reach a Leaf. example : Path 5 0 True [Path 4 0 True [], Path 3 0 True [], Path 3 0 False []] after distribution: Path 5 5 True [Path 4 4 True [], Path 3 2 True [], Path 3 0 False []] #2 After the distribution, you must get the water out. Easy, the time taken by the water to flow down is, in pseudo code: max( for all leafs : getVolume * getFlow ) ### Problem My problem, is this : I must be able to change the "distribution" the flow of the parent to its childs: in my example, I said "take the biggest child, give it all you can and give the rest to the other childs, repeat" but I could have said "give first to the lowest child" or "give a certain percentage depending of the sum of the childs max capacity" So I can't map simply over the childs: distribute :: (Int -> Int -> Int) -> Tree -> Tree distribute _ (Leaf a) = Leaf a distribute f path@(Path _ _ False _) = path distribute f (Path max cur open childs) = Path max (f cur) open (map f childs) I must indeed let the distribution function choose to which childs it wants to give: distribute :: (Int -> [Tree] -> [Tree]) -> Tree -> Tree distribute f (Path max use open child) = Path max use open $ map (distribute (f use)) newChilds where newChilds = f use childs And I find this quite awful... I know Hakell is everything about data structure, so I suppose my data structure is awful too. Do you have any suggestions/remarks to help me? Sorry I made it so long, but you needed to know what I wanted to acheive to help me (I hope I made it crystal clear ^^). Thanks, Ibiz

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