March 2017 - Beginners

Multiline code in GHCi
by Shishir Srivastava 29 Aug '17

29 Aug '17

Hi, I am trying to run this basic multiline code in GHCi. I am not sure if this is even possible without writing it in a file and compiling it in a traditional way. ------- Prelude> :set +m Prelude> let main1 = do Prelude| a <- readLn Prelude| return a Prelude| Prelude> Prelude> main1 <interactive>:75:1: No instance for (Show (IO b0)) arising from a use of `print' In the first argument of `print', namely `it' In a stmt of an interactive GHCi command: print it ------- Could someone please confirm if the function can be defined and called like this in GHCi or point to where am going wrong. Thanks, Shishir Srivastava

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how does hgearman-client work?
by info＠maximka.de 18 Apr '17

18 Apr '17

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Suggestions for way to improve / clean up this code?
by Erik Tillett 28 Mar '17

28 Mar '17

I'm looking for sugestions on how to better structure this code. I stuck it in a pastbin: https://pastebin.com/gQFmvq6W/ Would a State monad help? Thanks!

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Parallel processing...
by mike h 27 Mar '17

27 Mar '17

Hi, I have a list of lists - a grid [[ ]] of complex numbers and I map a function over each number in the grid. Each computation on a value at (r, c) is independent of any and all other calculations. This strikes me as being something that can be done in parallel by creating , say 4 quadrants and mapping over each and combining when done, or doing each row in parallel etc. etc. So I'm really just asking for advice or pointers on the Haskell libraries etc that I should start with but I'm not really looking to import an uber-package that will do most of it for me. I want to learn a little more Haskell by working from a few concurrency primitives. Thanks Mike

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Call for participation: Utrecht Summer School
by Wouter Swierstra 27 Mar '17

27 Mar '17

Call for Participation SUMMER SCHOOL ON APPLIED FUNCTIONAL PROGRAMMING Utrecht, the Netherlands, 21-25 August 2017 http://www.afp.school ## ABOUT The Applied Functional Programming summer school has been running for almost ten years. We aim to educate aspiring Haskell programmers beyond the basic material covered by many textbooks. The lectures will cover several more advanced topics regarding the theory and practice of Haskell programming, including topics such as: * lambda calculus; * monads and monad transformers; * lazy evaluation; * generalized algebraic data types; * type families and type-level programming; * concurrency and parallelism. The summer school consists of a mix of lectures, labs, and a busy social program. ## LECTURERS Utrecht staff: * Johan Jeuring * Doaitse Swierstra * Wouter Swierstra Guest lectures: * Simon Marlow (Concurrency and parallelism) * Luite Stegeman (GHCJS) ## PREREQUISITES We expect students to have a basic familiarity with Haskell already. You should be able to write recursive functions over algebraic data types, such as lists and trees. There is a great deal of material readily available that covers this material. If you’ve already started learning Haskell and are looking to take your functional programming skills to the next level, this is the course for you. ## DATES Registration deadline: 1 August, 2017 School: 21-25 August ## COSTS €1700 - Housing and registration €1500 - Registration only We offer a €1000 discount for students and staff members affiliated with a university. ## FURTHER INFORMATION Further information, including instructions on how to register, is available on our website: http://www.afp.school

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LYAH example
by sasa bogicevic 22 Mar '17

22 Mar '17

Hi All, Can someone clarify the example I got from LYAH book. This let statement is kinda confusing to me : applyLog :: (a, String) -> (a -> (b, String)) -> (b, String) applyLog (x, log) f = let (y, newLog) = f x in (y, log ++ newLog) I know that f applied to x should produce y and we append log with newLog but when reading ... f x in (y, ... I just don't see how f x becomes y in the let statement. Seems more readable if we could write ... = (f x, log ++ newLog) Thanks, Sasa { name: Bogicevic Sasa phone: +381606006200 }

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State, StateT, or ST for game settings?
by Dave Martin 18 Mar '17

18 Mar '17

I would like to create a game with a "main menu" offering the user a choice of "playing the game" or accessing a "settings menu," in which he can change defaults that would affect the game play (e.g. board size, etc.). I know (barely) enough about the "IO monad" to write the menus and the basic gameplay, but what device do I need in order to manage the settings? A State monad? A StateT monad transformer? An ST monad? None of the above? I have some basic familiarity with the first two, but not enough to really grasp how they are actually used.

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parse block comments
by mike h 18 Mar '17

18 Mar '17

Hi, Below is code I’m building up for simple monadic and applicative parsers from first principles. I’ve just added code for single line Haskell style comments. -- comment being '--' comment :: Parser () comment = do string "--" many (sat ( /='\n') ) return () — or as applicative comment' = string "--" *> many (sat (/='\n') ) I’d really appreciate help on writing a function for multi line comments! “{-“ and end with “-}” I know I need some sort of look ahead but can’t quite get the feel of how! Thanks Mike ====================================== import Control.Applicative import Data.Char newtype Parser a = P (String -> [(a,String)]) parse :: Parser a -> String -> [(a,String)] parse (P p) = p item :: Parser Char item = P (\s -> case s of [] -> [] (x:xs) -> [(x, xs)]) instance Functor Parser where -- fmap :: (a -> b) -> f a -> f b fmap g p = P (\inp -> case parse p inp of [] -> [] [(x, xs)] -> [(g x, xs)]) instance Applicative Parser where -- pure :: a -> Parser a -- (<*>) :: Parser (a -> b) -> Parser a -> Parser b pure x = P (\inp -> [(x, inp)]) pab <*> pa = P (\inp -> case parse pab inp of [] -> [] [(aTob, out)] -> parse (fmap aTob pa) out) three :: Parser (Char, Char) three = pure g <*> item <*> item <*> item where g x y z = (x, z) instance Monad Parser where -- return :: a -> Parser a return x = P (\inp -> [(x, inp)]) -- (>>=) :: Parser a -> (a -> Parser b) -> Parser b pa >>= f = P (\inp -> case parse pa inp of [] -> [] [(a, out)] -> parse (f a) out) instance Alternative Parser where -- empty :: Parser a empty = P (\inp -> []) -- (<|>) :: Parser a-> Parser a -> Parser a -- if p1 works the that one otherwise p2 p1 <|> p2 = P (\inp -> case parse p1 inp of [] -> parse p2 inp out -> out) sat :: (Char -> Bool) -> Parser Char sat p = do x <- item if p x then return x else empty digit :: Parser Char digit = sat isDigit lower :: Parser Char lower = sat isLower upper :: Parser Char upper = sat isUpper letter :: Parser Char letter = sat isAlpha alphanum :: Parser Char alphanum = sat isAlphaNum char :: Char -> Parser Char char x = sat (==x) string :: String -> Parser String string [] = return [] string s@(x:xs) = do char x *> string xs *> return s ident :: Parser String ident = do x <- lower xs <- many alphanum return (x:xs) ident' :: Parser String ident' = pure (:) <*> lower <*> many alphanum nat :: Parser Int nat = do xs <- some digit return (read xs) nat' :: Parser Int nat' = pure read <*> some digit space :: Parser () space = do many (sat isSpace ) return () space' :: Parser () space' = many (sat isSpace ) *> return () int :: Parser Int int = do char '-' n <- nat return (-n) <|> nat int' :: Parser Int int' = char '-' *> pure ((-1)*) <*> nat <|> nat token :: Parser a -> Parser a token p = do space v <- p space return v token' :: Parser a -> Parser a token' p = space *> p <* space identifier :: Parser String identifier = token ident natural :: Parser Int natural = token nat integer :: Parser Int integer = token int symbol :: String -> Parser String symbol xs = token (string xs) nats :: Parser [Int] nats = do symbol "[" n <- natural ns <- many ( do symbol "," natural ) symbol "]" return (n:ns) -- comment being '--' comment :: Parser () comment = do string "--" many (sat ( /='\n') ) return () comment' = string "--" *> many (sat (/='\n') ) nats' :: Parser [Int] -- sequence and ignore "[" and the rest -- the rest is fmap list cons into result of natural and the apply that to many others and -- finally ignore the closing "]" nats' = symbol "[" >> (:) <$> natural <*> many (symbol "," >> natural) <* symbol "]"

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Re: [Haskell-beginners] Beginners Digest, Vol 104, Issue 16
by tscosj tscosj 15 Mar '17

15 Mar '17

[image: Inline image 1] "Problem Opening Wizard" I've Eclipse "Version: Neon.2 Release (4.6.2) Build id: 20161208-0600" installed on macOS El Capitan 10.11.6. "The selected wizard could not be started. Plug-in net.sf.eclipsefp.haskell.ui was unable to load class net.sf.eclipsefp.haskell.ui.wizards.NewHaskellProjectWizard. An error occurred while automatically activating bundle net.sf.eclipsefp.haskell.ui (482)." Albert. Anyone has the same problem and solved it? Thanks. On Thu, Feb 23, 2017 at 1:10 AM, <beginners-request(a)haskell.org> wrote: > Send Beginners mailing list submissions to > beginners(a)haskell.org > > To subscribe or unsubscribe via the World Wide Web, visit > http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners > or, via email, send a message with subject or body 'help' to > beginners-request(a)haskell.org > > You can reach the person managing the list at > beginners-owner(a)haskell.org > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Beginners digest..." > > > Today's Topics: > > 1. Re: Type error when using splitOn function. (Francesco Ariis) > 2. Re: Type error when using splitOn function. (S. H. Aegis) > 3. How to link two Types (PICCA Frederic-Emmanuel) > 4. Re: How to link two Types (David McBride) > 5. Re: How to link two Types (PICCA Frederic-Emmanuel) > 6. Re: How to link two Types (David McBride) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Wed, 22 Feb 2017 14:31:16 +0100 > From: Francesco Ariis <fa-ml(a)ariis.it> > To: beginners(a)haskell.org > Subject: Re: [Haskell-beginners] Type error when using splitOn > function. > Message-ID: <20170222133116.GA14860(a)casa.casa> > Content-Type: text/plain; charset=us-ascii > > On Wed, Feb 22, 2017 at 09:02:22PM +0900, S. H. Aegis wrote: > > Thank you so much. > > > > --makeRxDxList :: Functor f => f Text -> f [Text] > > Above signature comes from ghci using command :t > > My intention is > > makeRxDxList :: Text -> [[Text]] > > but, I got error, and try several times and below codes pass a complier. > > makeRxDxList rowRxDx = fmap (\x -> splitOn (pack ",") x) rowRxDx -- This > > code pass a compile. > > and then, I run ghci, type :t, and got below signature. > > makeRxDxList :: Functor f => f Text -> f [Text] > > > > Your kind answer says, I cannot help using fmap. right? ^^; > > Thanks again. > > Then this: > > makeRxDxList :: Text -> [[Text]] > makeRxDxList rowRxDx = fmap f (lines rowRxDx) > -- you imported Prelude hiding map, so we will use fmap > where > f :: Text -> [Text] > f x = splitOn (pack ",") x > > should do (at least it typechecks). > > GHC errors may not have the prettiest formatting ever, but they are > very useful, the most important bits being line & column of the offending > expression plus the "expected this but got that" part; get acquainted > with them! > > > > ------------------------------ > > Message: 2 > Date: Wed, 22 Feb 2017 22:41:10 +0900 > From: "S. H. Aegis" <shaegis(a)gmail.com> > To: The Haskell-Beginners Mailing List - Discussion of primarily > beginner-level topics related to Haskell <beginners(a)haskell.org> > Subject: Re: [Haskell-beginners] Type error when using splitOn > function. > Message-ID: > <CAJp-NqxZ5gAqQT8-Swd+PE-ys_PVSAJo1c74+B-UuFabJr_F4w@mail. > gmail.com> > Content-Type: text/plain; charset="utf-8" > > It works !!! (^O^) > Thank you so much. > > Have a nice day~! > > 2017-02-22 22:31 GMT+09:00 Francesco Ariis <fa-ml(a)ariis.it>: > > > On Wed, Feb 22, 2017 at 09:02:22PM +0900, S. H. Aegis wrote: > > > Thank you so much. > > > > > > --makeRxDxList :: Functor f => f Text -> f [Text] > > > Above signature comes from ghci using command :t > > > My intention is > > > makeRxDxList :: Text -> [[Text]] > > > but, I got error, and try several times and below codes pass a > complier. > > > makeRxDxList rowRxDx = fmap (\x -> splitOn (pack ",") x) rowRxDx -- > This > > > code pass a compile. > > > and then, I run ghci, type :t, and got below signature. > > > makeRxDxList :: Functor f => f Text -> f [Text] > > > > > > Your kind answer says, I cannot help using fmap. right? ^^; > > > Thanks again. > > > > Then this: > > > > makeRxDxList :: Text -> [[Text]] > > makeRxDxList rowRxDx = fmap f (lines rowRxDx) > > -- you imported Prelude hiding map, so we will use fmap > > where > > f :: Text -> [Text] > > f x = splitOn (pack ",") x > > > > should do (at least it typechecks). > > > > GHC errors may not have the prettiest formatting ever, but they are > > very useful, the most important bits being line & column of the offending > > expression plus the "expected this but got that" part; get acquainted > > with them! > > > > _______________________________________________ > > Beginners mailing list > > Beginners(a)haskell.org > > http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners > > > > > > -- > Sok Ha, CHANG > Dr. Chang's Clinic. #203. 503-23. AmSa-Dong, GangDong-Gu, Seoul. > Tel: +82-2-442-7585 >

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Execution error in using text-icu on windows
by S. H. Aegis 04 Mar '17

04 Mar '17

Hi. I worte some code. and fixed some errors with the help of good persons. Now, this utility works properly in Stack environment. How can I install this utility in other computer? This utility use text-icu and I coded this utility on windows. Of course, I want to work this utility on other windows OS. I copied %stackPath%\.stack-work\install\~\bin\samCheceker-exe.exe to some other folder, and execution through CMD. But I got error message that says "libicuuc57.dll dose not exist. so program can't start. please re-install the program." I copied libicuuc57.dll, and so... as like programming newbees, but failed. "stack install" command was the same result. How can I install the Executable File to other windows system? Thank you. Sincerely, S. Chang. ------------------ samChecker.cabal ------------------ name: samChecker3 version: 0.1.0.0 -- synopsis: -- description: homepage: https://github.com/githubuser/samChecker3#readme license: BSD3 license-file: LICENSE author: Author name here maintainer: example(a)example.com copyright: 2017 Author name here category: Web build-type: Simple extra-source-files: README.md cabal-version: >=1.10 library hs-source-dirs: src exposed-modules: Lib build-depends: base >= 4.7 && < 5 , text , text-icu , bytestring , regex-tdfa default-language: Haskell2010 executable samChecker3-exe hs-source-dirs: app main-is: Main.hs ghc-options: -threaded -rtsopts -with-rtsopts=-N build-depends: base , samChecker3 , text , text-icu , bytestring , regex-tdfa default-language: Haskell2010 test-suite samChecker3-test type: exitcode-stdio-1.0 hs-source-dirs: test main-is: Spec.hs build-depends: base , samChecker3 ghc-options: -threaded -rtsopts -with-rtsopts=-N default-language: Haskell2010 source-repository head type: git location: https://github.com/githubuser/samChecker3 ----------- Main.hs ----------- module Main where import Lib import System.Environment --import System.FilePath.Windows import Data.Text.ICU.Convert -- There is Codec.Text.IConv, too. import qualified Data.Text as T import qualified Data.Text.IO as TIO import qualified Data.ByteString as BS main :: IO () main = do args <- getArgs -- 1st=SAM 2nd=csv conv <- open "MS949" Nothing -- byteSAM :: ByteString --byteSAM <- BS.readFile "C:\\Users\\shaeg\\Documents\\Haskell\\samChecker3\\BoHom.dat" byteSAM <- BS.readFile (args !! 0) -- byteRxDxData :: ByteString --byteRxDxData <- BS.readFile "C:\\Users\\shaeg\\Documents\\Haskell\\samChecker3\\RxDxData.csv" byteRxDxData <- BS.readFile (args !! 1) TIO.putStrLn $ T.concat $ checkRxDxSAM (toUnicode conv byteRxDxData) (toUnicode conv byteSAM) ----------- Lib.hs ----------- module Lib -- ( readSAM -- , readCSV -- , checkRxDxSAM -- ) where where import Data.Text as T import Data.Text.IO as TIO import Data.Text.ICU.Convert import qualified Data.ByteString as BS import Text.Regex.TDFA import Data.Text.ICU as I import Prelude hiding (take, drop, map, lines) type RowSAM = Text type SAM = [Text] type Case = Text type RowRxDx = Text type RxDx = [Text] type RxDxList = [[Text]] type Rx = Text type Dx = Text type MediName = Text type Message = Text type ErrorMessage = Text type Date = Text type PtName = Text checkRxDxSAM :: RowRxDx -> RowSAM -> [ErrorMessage] checkRxDxSAM rxDx sam = [pickupError r s | r <- (makeTuple rxDx), s <- makeSamData sam] makeSamData :: RowSAM -> SAM makeSamData sam = splitIntoCase sam makeTuple :: RowRxDx -> [(Rx, Dx, MediName)] makeTuple rxDx = zip3 (makeRxList rxDx) (makeDxList rxDx) (makeMediNameList rxDx) makeMediNameList :: RowRxDx -> [MediName] makeMediNameList rxDx = fmap pickupMediName $ makeRxDxList rxDx makeDxList :: RowRxDx -> [Dx] makeDxList rxDx = fmap pickupDx $ makeRxDxList rxDx makeRxList :: RowRxDx -> [Rx] makeRxList rxDx = fmap pickupRx $ makeRxDxList rxDx makeRxDxList :: RowRxDx -> RxDxList makeRxDxList rowRxDx = fmap f (lines rowRxDx) where f :: Text -> [Text] f x = splitOn (pack ",") x pickupError :: (Rx, Dx, Message) -> Case -> ErrorMessage pickupError (rxCode, dxCode, errMsg) ptCase = case isErrorRxDx rxCode dxCode ptCase of --True -> append (pickupCaseDate ptCase) $ append (pack " ") $ append (pickupPtName ptCase) $ append (pack " Omit ") $ append dxCode $ append (pack " for ") errMsg True -> append (pickupCaseDate ptCase) $ append (pack " ") $ append (pickupPtName ptCase) $ append (pack " Omit ") $ append dxCode $ append (pack " for ") $ append errMsg (pack "\n") False -> T.empty pickupMediName :: RxDx -> MediName pickupMediName rxDx = rxDx !! 0 pickupDx :: RxDx -> Dx pickupDx rxDx = rxDx !! 2 pickupRx :: RxDx -> Rx pickupRx rxDx = rxDx !! 1 pickupPtName :: Case -> PtName pickupPtName ptCase = take 3 $ drop 45 ptCase pickupCaseDate :: Case -> Date pickupCaseDate ptCase = take 8 $ drop (348 + 2) ptCase isErrorRxDx :: Rx -> Dx -> Case -> Bool isErrorRxDx rxCode dxCode ptCase = case isExistRx rxCode ptCase of True -> if (isExistDx dxCode ptCase) then False else True False -> False isExistDx :: Dx -> Case -> Bool --isExistDx dxCode ptCase = (unpack ptCase) =~ (unpack dxCode) isExistDx dxCode ptCase = case (I.find (regex [] dxCode) ptCase) of Just x -> True Nothing -> False isExistRx :: Rx -> Case -> Bool isExistRx rxCode ptCase = rxCode `isInfixOf` ptCase splitIntoCase :: RowSAM -> SAM splitIntoCase = splitOn $ pack "AH021" --readCSV :: IO Text --readCSV = pack <$> readFile "/Users/shaegis/Documents/Haskell/samChecker3/RxDxData.csv" --readSAM:: IO Text --readSAM = pack <$> readFile "/Users/shaegis/Documents/Haskell/samChecker3/BoHomUTF8.dat"

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