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Same code, system, but different arch using Win32 for reading registry.
by Akos Marton 07 Apr '17

07 Apr '17

Dear Haskellers, The setup: Having a binary compiled on either x86 or x64 system (same installation, utilizing stack) in order to preserve compatibility against x64 systems. Actually, not to have 2 separate executable for each, that would be the overall goal. However it surprises me when running the x86 .exe utilizing Win32-2.5.4.1 package with ghc-8.0.2, reading out a registry key fails on x64 system with the following:/ / /me.exe: RegOpenKey: invalid argument (The system cannot find the file specified.)/ That would be fine, however the key does exists. When same code, same system, but the .exe built to be x64 it runs like a charm. A couple of question, which some of them eventually will not make sense, but still: - Can it be ghc code optimization issue? - but this is a runtime check in IO, if so, how? - Yes, I could use a built-in windows system command and parse the input of that; unless absolutely necessary I would not introduce another dependency (system package). Would love to solve it with the currently utilized weapons. - the issue just puzzles me... I would know the answer if possible. - Is it more library (Win32), ghc, binary I generate, issue? What library can I use to detect a system's architecture which works in this scenario? Another thing which convoluted in the issue... The function, /getSystemInfo :: IO SYSTEM_INFO, /can read out the underlying architecture. When compiled on x86 and run on x64 it would tell me: "I am running on x86". That's failure. Most importantly: what is the obvious I am missing? Thank you for your insights! Best, Akos Ps.: Would you/we need sample code to puzzle about I can quickly weld one. - not sure if necessary.

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State monad to help pass around game settings
by Dave Martin 07 Apr '17

07 Apr '17

I'm trying to write a game with a "settings menu" where the user can adjust gameplay options. Right now I pass all the settings around as parameters. I'm trying to figure out how to use the State monad to simplify this task, but I can't figure out how to start. Or maybe my whole design approach is wrongheaded, and not in keeping with best practices. Haskell is my first language. This is the kind of thing I have now: mainM color shape = putStrLn "\n\nMain Menu" >> (putStrLn . unlines) [ "(1) Set", "(2) Display", "(3) Quit"] >> putStr "? " >> getChar >>= \c -> case c of '1' -> set color shape '2' -> display color shape '3' -> return () _ -> mainM color shape set color shape = putStrLn "\n\nSettings" >> (putStrLn . unlines) [ "(1) Color", "(2) Shape", "(3) Main Menu"] >> putStr "? " >> getChar >>= \c -> case c of '1' -> setColor color shape '2' -> setShape color shape '3' -> mainM color shape _ -> set color shape setColor color shape = putStr ("\n\nColor is " ++ color ++ ". New color? ") >> getLine >>= \cs -> set cs shape setShape color shape = putStr ("\n\nShape is " ++ shape ++ ". New shape? ") >> getLine >>= \cs -> set color cs display color shape = putStrLn ("\n\nColor is " ++ color ++ ". Shape is " ++ shape ++ ".") >> mainM color shape

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[Call for Contributions] Haskell Communities and Activities Report, May 2017 edition (32nd edition)
by Mihai Maruseac 02 Apr '17

02 Apr '17

Dear all, We would like to collect contributions for the 32nd edition (10000th edition) of the ============================================================ Haskell Communities & Activities Report http://www.haskell.org/haskellwiki/Haskell_Communities_and_Activities_Report Submission deadline: 30 April 2017 (please send your contributions to hcar at haskell.org, in plain text or LaTeX format, both are equally accepted) ============================================================ This is the short story: * If you are working on any project that is in some way related to Haskell, please write a short entry and submit it. Even if the project is very small or unfinished or you think it is not important enough --- please reconsider and submit an entry anyway! * If you are interested in an existing project related to Haskell that has not previously been mentioned in the HCAR, please tell us, so that we can contact the project leaders and ask them to submit an entry. * If you are working on a project that is looking for contributors, please write a short entry and submit it, mentioning that your are looking for contributors. * Feel free to pass on this call for contributions to others that might be interested. More detailed information: The Haskell Communities & Activities Report is a bi-annual overview of the state of Haskell as well as Haskell-related projects over the last, and possibly the upcoming six months. If you have only recently been exposed to Haskell, it might be a good idea to browse the previous edition --- you will find interesting projects described as well as several starting points and links that may provide answers to many questions. Contributions will be collected until the submission deadline. They will then be compiled into a coherent report that is published online as soon as it is ready. As always, this is a great opportunity to update your webpages, make new releases, announce or even start new projects, or to talk about developments you want every Haskeller to know about! Looking forward to your contributions, Mihai Maruseac FAQ: Q: What format should I write in? A: The usual format is a LaTeX source file, adhering to the template that is available at: http://haskell.org/communities/05-2017/template.tex There is also a LaTeX style file at http://haskell.org/communities/05-2017/hcar.sty that you can use to preview your entry. If you do not know LaTeX or don't want to use it or don't have time to translate your entry into it, then please use plain text, it is better to have an entry in plain-text which we will translate than not have it at all. If you modify an old entry that you have written for an earlier edition of the report, you should soon receive your old entry as a template (provided we have your valid email address). Please modify that template, rather than using your own version of the old entry as a template. Q: Can I include Haskell code? A: Yes. Please use lhs2tex syntax (http://www.andres-loeh.de/lhs2tex/) The report is compiled in mode polycode.fmt. Q: Can I include images? A: Yes, you are even encouraged to do so. Please use .jpg or .png format, then. PNG is preferred for simplicity. Q: Should I send files in .zip archives or similar? A: No, plain file attachments are the way. Q: How much should I write? A: Authors are asked to limit entries to about one column of text. A general introduction is helpful. Apart from that, you should focus on recent or upcoming developments. Pointers to online content can be given for more comprehensive or "historic" overviews of a project. Images do not count towards the length limit, so you may want to use this opportunity to pep up entries. There is no minimum length of an entry! The report aims for being as complete as possible, so please consider writing an entry, even if it is only a few lines long. Q: Which topics are relevant? A: All topics which are related to Haskell in some way are relevant. We usually had reports from users of Haskell (private, academic, or commercial), from authors or contributors to projects related to Haskell, from people working on the Haskell language, libraries, on language extensions or variants. We also like reports about distributions of Haskell software, Haskell infrastructure, books and tutorials on Haskell. Reports on past and upcoming events related to Haskell are also relevant. Finally, there might be new topics we do not even think about. As a rule of thumb: if in doubt, then it probably is relevant and has a place in the HCAR. You can also simply ask us. Q: Is unfinished work relevant? Are ideas for projects relevant? A: Yes! You can use the HCAR to talk about projects you are currently working on. You can use it to look for other developers that might help you. You can use HCAR to ask for more contributors to your project, it is a good way to gain visibility and traction. Q: If I do not update my entry, but want to keep it in the report, what should I do? A: Tell us that there are no changes. The old entry will typically be reused in this case, but it might be dropped if it is older than a year, to give more room and more attention to projects that change a lot. Do not resend complete entries if you have not changed them. Q: Will I get confirmation if I send an entry? How do I know whether my email has even reached its destination, and not ended up in a spam folder? A: Prior to publication of the final report, we will send a draft to all contributors, for possible corrections. So if you do not hear from us within two weeks after the deadline, it is safer to send another mail and check whether your first one was received. -- Mihai Maruseac (MM) "If you can't solve a problem, then there's an easier problem you can solve: find it." -- George Polya

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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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