- Haskell-Cafe - Haskell.org

OS X 10.10
by Hans Aberg 18 Nov '14

18 Nov '14

The URL [1] says the platform “Works even on 10.10 beta!”, however, OS X 10.10.1 has just been released. Is there anyone out there who does not run the beta? :-) 1. https://www.haskell.org/platform/mac.html

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[ANN] elevator: getting to a top of a monad transformer stack
by Fumiaki Kinoshita 17 Nov '14

17 Nov '14

Hello everybody, I created an elevator to navigate a monad transformer stack, liberating us from creating a Monad* class and instances. The key function, elevate, can be whatever you need: elevate :: IO a -> IO a elevate :: IO a -> StateT s IO a elevate :: State s a -> StateT s IO a elevate :: IO a -> MaybeT (StateT s IO) a If you want to elevate actions above your monad, just write instance Tower YourMonad to declare that YourMonad is one-storied. Hackage: http://hackage.haskell.org/package/elevator-0.1/docs/Control-Elevator.html Cheers Fumiaki Kinoshita

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[Haskell] ANNOUNCE: Haskell Communities and Activities Report (27th ed., November 2014)
by Mihai Maruseac 17 Nov '14

17 Nov '14

On behalf of all the contributors, we are pleased to announce that the Haskell Communities and Activities Report (27th edition, November 2014) is now available, in PDF and HTML formats: http://haskell.org/communities/11-2014/report.pdf http://haskell.org/communities/11-2014/html/report.html Many thanks go to all the people that contributed to this report, both directly, by sending in descriptions, and indirectly, by doing all the interesting things that are reported. We hope you will find it as interesting a read as we did. If you have not encountered the Haskell Communities and Activities Reports before, you may like to know that the first of these reports was published in November 2001. Their goal is to improve the communication between the increasingly diverse groups, projects, and individuals working on, with, or inspired by Haskell. The idea behind these reports is simple: Every six months, a call goes out to all of you enjoying Haskell to contribute brief summaries of your own area of work. Many of you respond (eagerly, unprompted, and sometimes in time for the actual deadline) to the call. The editors collect all the contributions into a single report and feed that back to the community. When we try for the next update, six months from now, you might want to report on your own work, project, research area or group as well. So, please put the following into your diaries now: ======================================== End of April 2015: target deadline for contributions to the May 2015 edition of the HC&A Report ======================================== Unfortunately, many Haskellers working on interesting projects are so busy with their work that they seem to have lost the time to follow the Haskell related mailing lists and newsgroups, and have trouble even finding time to report on their work. If you are a member, user or friend of a project so burdened, please find someone willing to make time to report and ask them to "register" with the editors for a simple e-mail reminder in October (you could point us to them as well, and we can then politely ask if they want to contribute, but it might work better if you do the initial asking). Of course, they will still have to find the ten to fifteen minutes to draw up their report, but maybe we can increase our coverage of all that is going on in the community. Feel free to circulate this announcement further in order to reach people who might otherwise not see it. Enjoy! Mihai Maruseac and Alejandro Serrano Mena <hcar at haskell.org> -- Mihai Maruseac (MM) "If you don't know, the thing to do is not to get scared, but to learn." -- Atlas Shrugged.

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Using wreq Session handling in a monad transformer stack
by Cody Goodman 17 Nov '14

17 Nov '14

Could I somehow add a Wreq.Session.Session to my monad transformer stack? Should I use something other than Wreq? How would I create a default Session, Wreq doesn't seem to export the constructor. Basically I want to achieve Sessions/cookie handling. lpaste of my code: http://lpaste.net/114405 my full code (for those who want to view in email): {-# LANGUAGE OverloadedStrings #-} module Network.Scraper.State where import Control.Lens ((^.)) import Control.Monad import Control.Monad.IO.Class (liftIO) import qualified Control.Monad.Trans.State.Strict as ST import qualified Data.ByteString.Lazy as LBS import Data.Maybe (fromJust, fromMaybe) import Data.Monoid import qualified Data.Text as T import qualified Data.Text.IO as TIO import Network.Wreq (FormParam (..)) import qualified Network.Wreq as Wreq import Network.Wreq.Session (Session (..), withSession) import qualified Network.Wreq.Session as Sesh import Network.Wreq.Types import Safe import Text.HTML.DOM (parseLBS) import Text.XML.Cursor import qualified Text.XML.Cursor.Generic as CG data ScraperState = PS { currentOptions :: Wreq.Options , currentHtml :: LBS.ByteString , currentCursor :: Maybe Cursor , currentSession :: Session } deriving (Show) type Scraper = ST.StateT ScraperState IO toCursor = fromDocument . parseLBS initialSt = PS { currentOptions = Wreq.defaults , currentHtml = ("" :: LBS.ByteString) , currentCursor = Nothing -- , currentSession = ... how do I get a Session? Wreq doesn't seem to export this type } setCurrentOptions :: Wreq.Options -> Scraper () setCurrentOptions o = do scraper <- ST.get ST.put $ scraper { currentOptions = o } -- getCurrentPage :: Shpider Page getCurrentCursor :: Scraper (Maybe Cursor) getCurrentCursor = do scraper <- ST.get return $ currentCursor scraper getCurrentSession :: Scraper (Session) getCurrentSession = do scraper <- ST.get return $ currentSession scraper setCurrentSession :: Session -> Scraper () setCurrentSession s = do scraper <- ST.get ST.put $ scraper { currentSession = s} setCurrentCursor :: Cursor -> Scraper ( ) setCurrentCursor c = do scraper <- ST.get ST.put $ scraper { currentCursor = Just c } setCurrentHtml :: LBS.ByteString -> Scraper () setCurrentHtml html = do scraper <- ST.get ST.put $ scraper { currentHtml = html } runScraper :: Scraper a -> IO a runScraper k = evalScraperWith k initialSt evalScraperWith :: Scraper a -> ScraperState -> IO a evalScraperWith k s = withSession $ \sesh -> do -- set the current session to the mutable session variable return $ setCurrentSession sesh ST.evalStateT k s formShortInfo' f = formInfo' where go Nothing = "N/A" go (Just x) = x formInfo = (headMay . attribute "name" $ f, headMay . attribute "action" $ f) formInfo' = (\(x,y) -> (go x, go y)) formInfo ppTuple :: (T.Text, T.Text) -> T.Text ppTuple = \(x,y) -> "[" <> x <> "]" <> ": " <> y -- move to ../Spider.hs printFormNames :: Scraper () printFormNames = do c <- getCurrentCursor let c' = fromMaybe (error "No cursor set") c forms = c' $// element "form" formInfo = map (ppTuple . formShortInfo') forms liftIO $ mapM_ (TIO.putStrLn) formInfo getFormByName :: T.Text -> Scraper [Cursor] getFormByName name = do c <- getCurrentCursor let c' = fromMaybe (error "No cursor set") c return $ c' $// element "form" >=> attributeIs "name" name get :: String -> Scraper (LBS.ByteString) get url = do r <- liftIO $ Wreq.get url let html = r ^. Wreq.responseBody setCurrentHtml html setCurrentCursor (toCursor html) return html post :: Postable a => String -> a -> Scraper (LBS.ByteString) post url params = do r <- liftIO $ Wreq.post url params let html = r ^. Wreq.responseBody setCurrentHtml html setCurrentCursor (toCursor html) return html test :: Scraper () test = do get "https://www.google.com" >> printFormNames

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Re: [Haskell-cafe] data analysis question
by Dominic Steinitz 17 Nov '14

17 Nov '14

I’d much prefer that. I really dislike the google group experience. I’ll drop Austin a note. Dominic Steinitz dominic(a)steinitz.org http://idontgetoutmuch.wordpress.com On 15 Nov 2014, at 15:42, Ben Gamari <ben(a)smart-cactus.org> wrote: > On November 15, 2014 1:54:38 AM EST, Dominic Steinitz <dominic(a)steinitz.org> wrote: >> Mark Fredrickson <mark.m.fredrickson <at> gmail.com> writes: >> >>> >>> Is there a mailing list for statistics/analytics/simulation/numerical >>> analysis/etc. using Haskell? If not, I purpose we start one. (Not to >>> take away from general discussion, but to provide a forum to hash out >>> these issues among the primary user base). >> >> Sadly not but I think there are sufficient numbers of people >> interested in this subject that it is probably worth setting one up. I >> really don't like the google group experience but maybe that is the >> best place to start? >> > I agree that this would be a worthwhile forum to have. Why not just stay with Haskell.org infrastructure? I'm sure Austin would set up a mailing list for the cause. > > Cheers, > > - Ben > > >

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Call for Presentations: Compose Conference [New York, Jan 30-Feb 1]
by Gershom B 16 Nov '14

16 Nov '14

Compose is a new conference for typed functional programmers, focused specifically on Haskell, OCaml, F#, and related technologies. It will be held in New York from Jan 30-Feb 1, and registration is opening shortly. http://www.composeconference.org/ Below is our call for presentations. We recognize the deadline is tight, so feel free to submit proposals and ideas on the less-polished side. Call for Presentations and Speakers. http://www.composeconference.org/call/index.html --- The audience for Compose is Haskell, OCaml, or F# developers who are looking to increase their skills or learn new technologies and libraries. Presentations should be aimed at teaching or introducing new ideas or tools. We are also interested in presentations aiming at taking complex concepts, such as program derivation, and putting them into productive use. However proposals on anything that you suspect our audience may find interesting are welcome. The following are some of the types of talks we would welcome: Library/Tool Talks — Exploring the uses of a powerful toolkit or library, be it for parsing, testing, data access and analysis, or anything else. Production Systems — Experience reports on deploying functional techniques in real systems; insights revealed, mistakes made, lessons learned. Theory made Practical — Just because it’s locked away in papers doesn’t mean it’s hard! Accessible lectures on classic results and why they matter to us today. Such talks can include simply introducing the principles of a field of research so as to help the audience read up on it in the future; from abstract machines to program derivation to branch-and-bound algorithms, the sky’s the limit. We also welcome proposals for more formal tutorials for the Sunday unconference. Such tutorials should be aimed at a smaller audience of beginner-to-novice understanding, and ideally include hands-on exercises. The due date for submissions is November 30, 2014. We will send out notice of acceptance by 10 December. We prefer that submissions be via the EasyChair website (https://easychair.org/conferences/?conf=compose2015) Please suggest a title, and describe the topic you intend to speak on. Additional information may be included on both your expertise and the interesting elements of your topic, going on what might be included in a public abstract. Furthermore, if your abstract doesn't feel "final"—don't worry! We'll work with you to polish it up. If you want to discuss your proposal(s) before submitting, or to further nail down what you intend to speak on, please feel free to contact us at info(a)composeconference.org. We're happy to work with you, even if you are a new or inexperienced speaker, to help your talk be great. —Gershom

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How can I improve the pipes's performance with a huge file?
by zhangjun.julian 16 Nov '14

16 Nov '14

Dear cafe I have 2 file, I want zip the 2 file as couple, and then count each couple's repeat times? The file had more than 40M rows, I use pipe to write code as blow. When I test with 8768000 rows input, it take 30 secs When I test with 18768000 rows input, it take 74 secs But when I test with whole file (40M rows), it take more than 20 minutes and not finished yet. It take more than 9G memorys, and the disk is also busy all time. The result will less than 10k rows, so I had no idea why the memory is so huge. I had use the “http://hackage.haskell.org/package/visual-prof” to profile and improve the performance with the small file But I don’t know how to deal with the “hang” situation. Anyone can give me some help, Thanks. =================================== import System.IO import System.Environment import Pipes import qualified Pipes.Prelude as P import qualified Data.Map as DM import Data.List emptyMap = DM.empty::(DM.Map (String,String) Int) keyCount num = do readHandle1 <- openFile "dataByColumn/click" ReadMode readHandle2 <- openFile "dataByColumn/hour" ReadMode writeHadle <- openFile "output" AppendMode rCount num readHandle1 readHandle2 writeHadle hClose writeHadle hClose readHandle1 hClose readHandle2 mapToString::DM.Map (String,String) Int-> String mapToString m = unlines $ map eachItem itemList where itemList = DM.toList m eachItem ((x,y),i) = show x ++ "," ++ show y ++ "," ++ show i --rCount::Int -> [String] -> Handle->Handle -> IO() rCount num readHandle1 readHandle2 writeHadle = do rt <- P.fold (\x y -> DM.unionWith (+) x y) emptyMap id $ P.zipWith (\x y -> DM.singleton (x,y) 1) (P.fromHandle readHandle1) (P.fromHandle readHandle2) >-> P.take num hPutStr writeHadle $ mapToString rt main = do s<- getArgs let num = (read . head) s keyCount num

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data analysis question
by Tobias Pflug 15 Nov '14

15 Nov '14

Hi, just the other day I talked to a friend of mine who works for an online radio service who told me he was currently looking into how best work with assorted usage data: currently 250 million entries as a 12GB in a csv comprising of information such as which channel was tuned in for how long with which user agent and what not. He accidentally ran into K and Q programming language (*1) which apparently work nicely for this as unfamiliar as it might seem. This certainly is not my area of expertise at all. I was just wondering how some of you would suggest to approach this with Haskell. How would you most efficiently parse such data evaluating custom queries ? Thanks for your time, Tobi [1] (http://en.wikipedia.org/wiki/K_(programming_language) [2] http://en.wikipedia.org/wiki/Q_(programming_language_from_Kx_Systems)

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Re: [Haskell-cafe] Programming videogames in haskell
by sean.seefried＠gmail.com 15 Nov '14

15 Nov '14

Hi Quentin, I am currently building a game in Haskell that I plan to deploy to iOS and Android. It’s built using a combination of SDL2 and Cairo (for vector graphics) and Hipmunk (for physics via the Chipmunk C library). As in Ivan Perez's case I’m not using the Hackage versions of the SDL2 bindings. Instead I’m using the versions found on Github at [1] and [2]. I have recently managed to deploy my game to Android but this has not been a straightforward process. Building a GHC cross compiler for ARM was a time consuming process but greatly aided by the using the script found in the stable-ghc-snapshot branch of joehy’s repo on Github [3]. Building all the libraries I needed was even less straightforward. (I’ve written more about this in a post script) Deploying to iOS should be a much more straightforward process since there is official GHC support for iOS and you can download a binary distribution of the cross compiler at [4]. (Scroll down to find Luke Iannini’s distribution. Luke Iannini, Steven Blackheath put in a lot of hard work over many months to provide iOS support for GHC.) I’ve also had a play around with Helm which uses the Elerea FRP library, SDL2 and Cairo. I think it’s a pretty good little library for prototyping, although you will need to learn FRP (Functional Reactive Programming) in the process. Cheers, Sean p.s. Here is a little more detail on targeting ARM. Many of the libraries, notably the SDL2 binding, did not work out of the box with a cross compiler since they did not use Cabal’s Distribution.Simple and required that Setup.hs was compiled and run. Unfortunately this just does not work with a cross-compiler since you can’t run the code on your host machine. The work around is to build it using GHC targeting the host machine and to run that. This works okay, but a straight “cabal install” will not. A more serious problem I ran into was that the SDL2 binding requires the use of hsc2c. hsc2c has a --cross-compile flag but it does not support all of the hsc2c directives, specifically the “let” directive which is used by SDL2. [1] https://github.com/Lemmih/hsSDL2 [2] https://github.com/jdeseno/hs-sdl2-mixer [3] https://github.com/joeyh/ghc-android [4] https://www.haskell.org/ghc/download_ghc_7_8_3

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Programming videogames in haskell
by Quentin Le Guennec 14 Nov '14

14 Nov '14

Hello, We're building a indie game studio with some friends. I am the lead developper and i am planning to write the game logic and graphics in haskell. I would like to know if some of you have some experience in game developpement in haskell, functionnal reactive programming in particular. Furthermore, knowing which tools/DSL's/libraries i could use and where to get good documentation could really help me. Elise Huard recently wrote an ebook about game programming in haskell, did some of you read it ? Is it worth buying it ? Thanks for your feedback. -- Quentin Le Guennec

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