- Haskell-Cafe - Haskell.org

SDL program under MinGW
by sam lee 07 Dec '08

07 Dec '08

Hi. I am using Windows Vista. I installed the following: - ghc 6.8.3 (using official Windows binary installer) - MinGW (from http://nuwen.net/mingw.html) - SDL binding (from http://hackage.haskell.org/cgi-bin/hackage-scripts/package/SDL) I am trying to compile the following program: module Main where import qualified Graphics.UI.SDL as SDL main = do SDL.init [SDL.InitEverything] SDL.quit I get the following error: C:\Users\client\code\sandbox>ghc --make Example.hs Linking Example.exe ... C:\MinGW\lib/libSDLmain.a(SDL_win32_main.o)(.text+0x409):SDL_win32_main.c: undefined reference to `SDL_main' According to SDL faq (http://www.libsdl.org/faq.php?action=listentries&category=4#48) I should use "int main(int argc, char *argv[])", not "int main()" nor "WinMain()". Can anyone compile the above snippet on windows machine? I am using SDL library that is shipped with MinGW distribution that I'm using. I also recompiled SDL haskell binding with official SDL windows binary (http://www.libsdl.org/release/SDL-devel-1.2.13-mingw32.tar.gz) But I get the same undefined reference to SDL_main linker error. Do I need to have specific main IO action so that SDL would work in Haskell? Thank you. Sam.

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pbkdf2 on hackage Re: Re[2]: [Haskell-cafe] Password hashing
by Thomas Hartman 07 Dec '08

07 Dec '08

http://hackage.haskell.org/cgi-bin/hackage-scripts/package/PBKDF2 Since no one took up my code review request I just did the best I could and uploaded to hackage. There were indeed some mistakes in my initial post, fixed now. (Code review is still wished, though!) Alas, documentation doesn't build with hackage, altough it does for me locally. (Seems like almost everything I do these days -- what am I doing wrong?!) Also I'm open to folding this into a more established crypto package if there are any takers... psst, dominic. Also, dominic, shouldn't your crypto package be added to category Cryptography (a cabal file change) so it lists aside the other crypto packages? thanks, thomas. 2008/11/26 Thomas Hartman <tphyahoo(a)gmail.com>: > Sorry about the hideous formatting above. Reattached as a text file. > > t. > > 2008/11/26 Thomas Hartman <tphyahoo(a)gmail.com>: >> OK, I went ahead and implemented pbkdf2, following the algorithm >> linked to by bulat and Michael. >> >> If there are any crypto gurus who can code-review this I would be much >> obliged, and when I'm confident enough that this does the right thing >> I'll put it up on hackage. >> >> I don't do much crypto so this *definitely* needs a review before it >> becomes a library? >> >> How's this looks, cafe? >> >> Thanks! >> >> Thomas. >> >> >> {-# LANGUAGE ScopedTypeVariables #-} >> module Crypto.PBKDF2 (pbkdf2, pbkdf2') where >> >> import qualified Data.ByteString.Char8 as B >> import qualified Data.ByteString.Lazy as L >> import GHC.Word >> import Control.Monad (foldM) >> import Random >> import Data.Digest.SHA512 (hash) >> import Data.Word >> import Data.Bits >> import Data.Binary >> >> newtype Password = Password [Word8] >> newtype Salt = Salt [Word8] >> newtype HashedPass = HashedPass [Word8] >> deriving Show >> {- | A reasonable default for rsa pbkdf2? Actually I'm not really >> sure, ask folk with more experience. >> >>> pbkdf2 = pbkdf2' prfSHA512 512 512 512 >> -} >> t = pbkdf2 ( Password . toWord8s $ "meh" ) ( Salt . toWord8s $ "moo" ) >> pbkdf2 :: Password -> Salt -> HashedPass >> pbkdf2 = pbkdf2' prfSHA512 512 512 512 >> >> {- | Password Based Key Derivation Function, from RSA labs. >> >>> pbkdf2' prf hlen cIters dklen (Password pass) (Salt salt) >> -} >> pbkdf2' :: ([Word8] -> [Word8] -> [Word8]) -> Integer -> Integer -> >> Integer -> Password -> Salt -> HashedPass >> pbkdf2' prf hlen cIters dklen (Password pass) (Salt salt) >> | dklen > ( (2^32-1) * hlen) = error $ "pbkdf2, (dklen,hlen) : " ++ >> (show (dklen,hlen)) >> | otherwise = >> let --l,r :: Int >> l = ceiling $ (fromIntegral dklen) / (fromIntegral hlen ) >> r = dklen - ( (l-1) * hlen) >> ustream :: [Word8] -> [Word8] -> [[Word8]] >> ustream p s = let x = prf p s >> in x : ustream p x >> --us :: Integer -> [[Word8]] >> us i = take (fromIntegral cIters) $ ustream pass ( salt `myor` >> ((intToFourWord8s i) )) >> --f :: [Word8] -> [Word8] -> Integer -> Integer -> [Word8] >> f pass salt cIters i = foldr1 myxor $ us i >> ts :: [[Word8]] >> ts = map (f pass salt cIters) ( [1..l] ) >> in HashedPass . take (fromIntegral dklen) . concat $ ts >> >> -- The spec says >> -- Here, INT (i) is a four-octet encoding of the integer i, most >> significant octet first. >> -- I'm reading from the right... is this the right thing? >> toWord8s x = L.unpack . encode $ x >> >> --intToFourWord8s :: Integer -> [Word8] >> intToFourWord8s i = let w8s = toWord8s $ i >> in drop (length w8s -4) w8s >> >> myxor :: [Word8] -> [Word8] -> [Word8] >> myxor = zipWith xor >> >> myor :: [Word8] -> [Word8] -> [Word8] >> myor = zipWith (.|.) >> >> prfSHA512 :: [Word8] -> [Word8] -> [Word8] >> prfSHA512 x y = hash $ x ++ y >> >> >> 2008/11/26 John Meacham <john(a)repetae.net>: >>> What you are using there is not a salt, but rather a secret key. The >>> important thing about a salt is that it is different for _every user_. >>> and you actually store the salt unhashed along with the hash. (it is not >>> secret information). A salt protects against a dictionary attack, for >>> instance, you might have a dictionary of hash's and the common passwords >>> they go to but if you add a 32 bit salt, you would need 2^32 entries for >>> each dictionary word, making such an attack unworkable. You can also >>> trivially tell if two users have the _same_ password just by comparing >>> the hashes without a salt. >>> >>> John >>> >>> -- >>> John Meacham - ⑆repetae.net⑆john⑈ >>> _______________________________________________ >>> Haskell-Cafe mailing list >>> Haskell-Cafe(a)haskell.org >>> http://www.haskell.org/mailman/listinfo/haskell-cafe >>> >> >

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Trouble installing ghc-6.10.1 on linux
by Bit Connor 07 Dec '08

07 Dec '08

I'm trying to install ghc 6.10.1 on a machine with the crux distro. libc version 2.3.6 gcc 4.0.3 linux version 2.6.15.6 First I tried the binary version ghc-6.10.1-i386-unknown-linux.tar.bz2 and I very quickly get this error: $ ./configure checking build system type... i686-pc-linux-gnu checking host system type... i686-pc-linux-gnu checking target system type... i686-pc-linux-gnu Which we'll further canonicalise into: i386-unknown-linux checking for path to top of build tree... configure: error: cannot determine current directory $ Next I tried building the source version ghc-6.10.1-src.tar.bz2 using ghc 6.6 that is already installed. configure works but make eventually dies with: ... Configuring ghc-6.10.1... cabal-bin: At least the following dependencies are missing: Cabal -any, base <3, filepath >=1 && <1.2, haskell98 -any, hpc -any, template-haskell -any, unix -any make[2]: *** [boot.stage.2] Error 1 Any ideas? Thanks, Bit

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latest Hood ?
by Simon Michael 07 Dec '08

07 Dec '08

Hugo Pacheco wrote: > The library also features the visualization of the intermediate data > structure of hylomorphisms with GHood. I hadn't come across GHood and Hood before, and they look quite a useful addition to the toolbox. http://www.haskell.org/hood says "The current released version of HOOD is the July 2000 release, but there is also a patch to all HOOD to work with GHC 5.00.". The Observe.lhs there doesn't immediately work with current GHC. Has anyone got an updated version, or is this available in some more recent library or package ? Or, I may have misunderstood, and Debug.Trace may do everything that Hood did. Still, a working Hood would be useful to get the nice visualisations of GHood. Thanks - Simon

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Can't cabal install readline
by Martijn van Steenbergen 07 Dec '08

07 Dec '08

Hello, This week I upgraded to GHC 6.10 using the .pkg installer. It installed without a single hiccup -- thanks! I've noticed two odd things: the standard library haddock that comes with the installer doesn't have links to the hs-coloured sources anymore (and neither does the online documentation); I miss that a lot. I also can't Ctrl+R anymore in GHCi to search my command history. But I can learn to live without those. Another minor inconvenience is that the packages I had installed (using cabal) are no longer available to GHC -- I think I will have to reinstall them. But I cannot continue working on my Yogurt project anymore, because it depends on readline, which fails to build: <snip> checking for rl_readline_version... yes checking for rl_begin_undo_group... no configure: error: readline not found, so this package cannot be built See `config.log' for more details. cabal: Error: some packages failed to install: Yogurt-0.2 depends on readline-1.0.1.0 which failed to install. readline-1.0.1.0 failed during the configure step. The exception was: exit: ExitFailure 1 The build failure mentions config.log which I cannot find anywhere on my system. I have readline installed using MacPorts without problems, and the cabal package worked fine too on the previous version of GHC. I'm on Intel Leopard. How can I get cabal install readline to succeed on the new GHC? Thanks much, Martijn.

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Haskell Weekly News: Issue 96 - December 6, 2008
by Brent Yorgey 07 Dec '08

07 Dec '08

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20081206 Issue 96 - December 06, 2008 --------------------------------------------------------------------------- Welcome to issue 96 of HWN, a newsletter covering developments in the [1]Haskell community. Announcements Haskell haikus. Gwern Branwen [2]announced that he has collected all known haikus about Haskell and put them on a [3]wiki page. Add more! Platforms that GHC supports. Simon Peyton-Jones [4]linked to a [5]new page clearly articulating what platforms GHC supports, and what platforms its maintainers would like it to support. If you're interested and willing to help sponsor a "Tier 2" platform, let them know! Using Data Parallel Haskell. Manuel Chakravarty [6]announced a new [7]wiki page with documentation for Data Parallel Haskell. DrHylo 0.0.1. Hugo Pacheco [8]announced the [9]release of [10]DrHylo, a tool for deriving hylomorphisms from a restricted Haskell syntax. It is based on the algorithm first presented in the paper Deriving Structural Hylomorphisms From Recursive Definitions at ICFP'96 by Hu, Iwasaki, and Takeichi. The generated code can be run with [11]Pointless Haskell, allowing the visualization of the recursion trees of Haskell functions. pointless-haskell 0.0.1. Hugo Pacheco [12]announced the [13]release of [14]Pointless Haskell, a library for point-free programming with recursion patterns defined as hylomorphisms, inspired in ideas from the PolyP library. The re-implementation of the library using type functions (in opposition to classes with functional dependencies) enables a type-level view of data types as the fixed points of functors and provides a better experience to the users in terms of code sanity. The library also features the visualization of the intermediate data structure of hylomorphisms with GHood. Projects that depend on the vty package?. Corey O'Connor [15]asked whether there are any other projects that depend on the [16]vty package. If so, let him know! The package also has a new [17]trac and wiki. haskell-src-exts 0.4.4. Niklas Broberg [18]announced the release of [19]haskell-src-exts 0.4.4, which adds support for pragmas. ChristmasTree 0.1. S. Doaitse Swierstra [20]announced the release of the [21]ChristmasTree package, which stands for "Changing Haskell's Read Implementation Such That by Manipulating Abstract Syntax Trees it Reads Expressions Efficiently". TTTAS. S. Doaitse Swierstra [22]announced the release of [23]TTTAS, a library for typed transformations of typed abstract syntax. GHood. Hugo Pacheco [24]announced that GHood, a graphical backend for the lightweight Hood Haskell debugger, has now been [25]released as a Cabal package. Discussion Animated line art. Andrew Coppin [26]asked for ideas on writing Haskell to generate some animations. Jobs Scala job in Boston writing quantitative finance software. Paul Chiusano [27]announced that [28]ClariFI is looking to hire developers with a strong background in functional programming to do a mixture of Scala and Java programming. ClariFI is a small company (about 15 developers) that specializes in software for quantitative investment management. This position is for the Boston office. If you're interested, send him an email. Blog noise [29]Haskell news from the [30]blogosphere. * Bryan O'Sullivan: [31]Functional programmers on Twitter. * Conal Elliott: [32]Sequences, segments, and signals. * >>> Gianfranco Alongi: [33]QuickCheck(ing) the code i C. * Edward Kmett: [34]The Pointed-Set Comonad. * Twan van Laarhoven: [35]Knight in n, part 3: rings. * "The GHC Team": [36]Explicit Stack Traces. * Real-World Haskell: [37]The Real World Haskell Book Club. * Real-World Haskell: [38]Real World Haskell: Now in Brazil. * >>> Matt Hellige: [39]Pointless fun. * Chung-chieh Shan: [40]The pointed-set monad. * Holumbus: [41]Status Update. * Paul R Brown: [42].editrc Tidbit for ghci. * Roman Cheplyaka: [43]DPH docs and project status. * David Sankel: [44]Introducing Reactive: Behaviors. * Manuel M T Chakravarty: [45]How to use Data Parallel Haskell.. * Conal Elliott: [46]Prettier functions for wrapping and wrapping. * Twan van Laarhoven: [47]Knight in n, part 2: combinatorics. * Yi: [48]Prototypes: Encoding OO-style inheritance in Haskell. * "Osfameron": [49]Functional Pe(a)rls v2 (now with Monads!) at the London Perl Workshop 2008. * Conal Elliott: [50]Sequences, streams, and segments. * Conal Elliott: [51]Early inspirations and new directions in functional reactive programming. * Clemens Fruhwirth: [52]XMonad GridSelect. About the Haskell Weekly News New editions are posted to [53]the Haskell mailing list as well as to [54]the Haskell Sequence and [55]Planet Haskell. [56]RSS is also available, and headlines appear on [57]haskell.org. To help create new editions of this newsletter, please see the information on [58]how to contribute. Send stories to byorgey at cis dot upenn dot edu. The darcs repository is available at darcs get [59]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://www.haskell.org//pipermail/haskell-cafe/2008-December/051529.html 3. http://haskell.org/haskellwiki/Haiku 4. http://article.gmane.org/gmane.comp.lang.haskell.glasgow.user/15958 5. http://hackage.haskell.org/trac/ghc/wiki/Platforms 6. http://www.haskell.org//pipermail/glasgow-haskell-users/2008-December/01627… 7. http://haskell.org/haskellwiki/GHC/Data_Parallel_Haskell 8. http://article.gmane.org/gmane.comp.lang.haskell.general/16668 9. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/DrHylo 10. http://haskell.di.uminho.pt/wiki/DrHylo 11. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/pointless-haskell 12. http://article.gmane.org/gmane.comp.lang.haskell.cafe/48598 13. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/pointless-haskell 14. http://haskell.di.uminho.pt/wiki/Pointless+Haskell 15. http://article.gmane.org/gmane.comp.lang.haskell.cafe/48471 16. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/vty 17. http://trac.haskell.org/vty/ 18. http://www.haskell.org//pipermail/haskell-cafe/2008-December/051444.html 19. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/haskell-src-exts… 20. http://www.haskell.org//pipermail/haskell/2008-December/020847.html 21. http://en.wikipedia.org/wiki/Sinterklaas 22. http://www.haskell.org//pipermail/haskell/2008-December/020848.html 23. http://www.cs.uu.nl/wiki/bin/view/Center/TTTAS 24. http://www.haskell.org//pipermail/haskell/2008-December/020849.html 25. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/GHood-0.0.2 26. http://www.haskell.org//pipermail/haskell-cafe/2008-December/051451.html 27. http://www.haskell.org//pipermail/haskell-cafe/2008-December/051295.html 28. http://clarifi.com/ 29. http://planet.haskell.org/ 30. http://haskell.org/haskellwiki/Blog_articles 31. http://www.serpentine.com/blog/2008/12/05/functional-programmers-on-twitter/ 32. http://conal.net/blog/posts/sequences-segments-and-signals/ 33. http://writert.blogspot.com/2008/12/quickchecking-code-i-c.html 34. http://comonad.com/reader/2008/the-pointed-set-comonad/ 35. http://twan.home.fmf.nl/blog/haskell/Knight3.details 36. http://ghcmutterings.wordpress.com/2008/12/04/explicit-stack-traces/ 37. http://www.realworldhaskell.org/blog/2008/12/03/the-real-world-haskell-book… 38. http://www.realworldhaskell.org/blog/2008/12/03/real-world-haskell-now-in-b… 39. http://matt.immute.net/content/pointless-fun 40. http://conway.rutgers.edu/~ccshan/wiki/blog/posts/Pointed_set/ 41. http://holumbus.fh-wedel.de/blog/?p=16 42. http://mult.ifario.us/p/editrc-tidbit-for-ghci 43. http://physics-dph.blogspot.com/2008/12/dph-docs-and-project-status.html 44. http://netsuperbrain.com/blog/posts/introducing-reactive-behaviors/ 45. http://justtesting.org/post/62610924 46. http://conal.net/blog/posts/prettier-functions-for-wrapping-and-wrapping/ 47. http://twan.home.fmf.nl/blog/haskell/Knight2.details 48. http://yi-editor.blogspot.com/2008/12/prototypes-encoding-oo-style.html 49. http://greenokapi.net/blog/2008/12/01/functional-pearls-v2-now-with-monads-… 50. http://conal.net/blog/posts/sequences-streams-and-segments/ 51. http://conal.net/blog/posts/early-inspirations-and-new-directions-in-functi… 52. http://blog.clemens.endorphin.org/2008/11/xmonad-gridselect.html 53. http://www.haskell.org/mailman/listinfo/haskell 54. http://sequence.complete.org/ 55. http://planet.haskell.org/ 56. http://sequence.complete.org/node/feed 57. http://haskell.org/ 58. http://haskell.org/haskellwiki/HWN 59. http://code.haskell.org/~byorgey/code/hwn/

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Fwd: problems with hs-plugins load-eval
by Alberto G. Corona 07 Dec '08

07 Dec '08

I have a web server which load server extensions. these extensions eval-uate configuration files that contains code (user-editable workflow descriptions). The problem is that I need common definitions for the extensions and for the configurration files. This is not permitted by ha-plugins. The minimal code example are the files below. main loads eval.hs , that evaluate a expression. The common definitions are in Include.hs. The error is: *GHCi runtime linker: fatal error: I found a duplicate definition for symbol Include_sum1_srt whilst processing object file /home/magocoal/haskell/devel/votesWorkflow/src/unused/tests/Include.o This could be caused by: * Loading two different object files which export the same symbol * Specifying the same object file twice on the GHCi command line * An incorrect `package.conf' entry, causing some object to be loaded twice. GHCi cannot safely continue in this situation. Exiting now. Sorry. * ** Do you kno how to solve the problem while maintaining the functionality? -------Include.hs------- module Include where sum [x,y]= x+y ------Main.hs----- module Main where import Include import System.Plugins main= do s <-loadExec "eval.o" "mainc" print s loadExec:: String-> String->IO String loadExec file method = do mv <- load file ["."] [] method case mv of LoadSuccess mod v -> v :: IO String LoadFailure msg -> return $ concat msg ------------Eval.hs-------- module Eval(mainc) where import System.IO.Unsafe import System.Eval.Haskell mainc= do i <- unsafeEval_ "sum1 [1,2]" ["Include"] [] []["."] :: IO (Either [String] Int) return $ show i

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ANNOUNCE: pointless-haskell 0.0.1
by Hugo Pacheco 07 Dec '08

07 Dec '08

Dear Haskelleers, Alcino Cunha and me are pleased to announce the release of the Pointless Haskell library in Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/pointless-haskell Pointless Haskell is library for point-free programming with recursion patterns defined as hylomorphisms, inspired in ideas from the PolyP library. The re-implementation of the library using type functions (in opposition to classes with functional dependencies) enables a type-level view of data types as the fixed points of functors and provides a better experience to the users in terms of code sanity. The library also features the visualization of the intermediate data structure of hylomorphisms with GHood. I am giving birth to a website with some examples: http://haskell.di.uminho.pt/wiki/Pointless+Haskell Any feedback is welcome. Cheers, hugo -- www.di.uminho.pt/~hpacheco

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Functional version of this OO snippet
by Andrew Wagner 06 Dec '08

06 Dec '08

Hi all, public interface IEngine { void foo(); void bar(string bah); ... } public class Program { public void Run(IEngine engine){ while(true){ string command = GetLine(); if (command.startsWith("foo")){ engine.foo(); } else if (command.startsWith("bar")){ engine.bar(command); ... else break; } In other words, I want to provide the same UI across multiple implementations of the engine that actually processes the commands. Thanks in advance.

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Fun with type functions
by Simon Peyton-Jones 06 Dec '08

06 Dec '08

Friends GHC has embodied data type families since 6.8, and now type synonym families (aka type functions) in 6.10. However, apart from our initial papers there isn't much published material about how to *use* type families. But that hasn't stopped you: quite a few people are using them already, and of course there is a rich seam of work on using functional dependencies to express type-level computation. Ken Shan and Oleg Kiselyov and I are collaborating to write a paper for an upcoming workshop, under the general rubric of "Fun with type functions" (in homage to Thomas Hallgren's paper "Fun with functional dependencies" and Ralf Hinze's paper "Fun with phantom types"). So this message is to ask you: can you tell us about the most persuasive, fun application you've encountered, for type families or functional dependencies? Simple is good. It doesn't have to be elaborate: just something that does something useful you could not have done otherwise. Pointers to email threads are fine. Don't assume we already know about them (even if we participated in the thread :-) Part of what we're interested in is that *you* found the example compelling. Many thanks Simon, Ken, Oleg PS: I'm broadcasting this message to GHC-users and Haskell-cafe, but to avoid deluging ghc-users, please reply just to us and Haskell cafe. (Interested ghc-users can follow the threads there from the archives if they want.)

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efficient combination of foldl' and foldr -> foldl'r
by Henning Thielemann 06 Dec '08

06 Dec '08

I want to do a foldl' and a foldr in parallel on a list. I assumed it would be no good idea to run foldl' and foldr separately, because then the input list must be stored completely between the calls of foldl' and foldr. I wanted to be clever and implemented a routine which does foldl' and foldr in one go. But surprisingly, at least in GHCi, my clever routine is less efficient than the naive one. Is foldl'rNaive better than I expect, or is foldl'r worse than I hope? module FoldLR where import Data.List (foldl', ) import Control.Arrow (first, second, (***), ) foldl'r, foldl'rNaive :: (b -> a -> b) -> b -> (c -> d -> d) -> d -> [(a,c)] -> (b,d) foldl'r f b0 g d0 = first ($b0) . foldr (\(a,c) ~(k,d) -> (\b -> k $! f b a, g c d)) (id,d0) foldl'rNaive f b g d xs = (foldl' f b *** foldr g d) $ unzip xs test, testNaive :: (Integer, Char) test = second last $ foldl'r (+) 0 (:) "" $ replicate 1000000 (1,'a') {- *FoldLR> test (1000000,'a') (2.65 secs, 237509960 bytes) -} testNaive = second last $ foldl'rNaive (+) 0 (:) "" $ replicate 1000000 (1,'a') {- *FoldLR> testNaive (1000000,'a') (0.50 secs, 141034352 bytes) -}

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Gluing pipes
by Matt Hellige 06 Dec '08

06 Dec '08

>From time to time, I've wanted to have a more pleasant way of writing point-free compositions of curried functions. One might want to transform both the first and second arguments, for instance, or only the third argument, of a curried function. I've never known a (non-cryptic) way to do this. For example, given: f :: a -> b -> c g :: a1 -> a h :: b2 -> b I'd like to be able to write something like: \ x y -> f (g x) (h y) in a way that is both point-free and applicative. In other words, I'd like to apply a function to "pipes" or transformers rather than to values. Recent posts by Conal Elliott [1,2] got me thinking about this again, and I've found a simple solution. I use two of Conal's combinators: argument = flip (.) result = (.) And now we define: infixr 2 ~> f ~> g = argument f . result g infixl 1 $. ($.) = flip ($) Which lets us write: -- transform both arguments f $. g ~> h ~> id -- transform just the second argument f $. id ~> h ~> id The name ($.) is chosen to indicate that this is (roughly) a composition disguised as an application. The transformer spec to the right of ($.) looks like the type of the function to the left, and consists of a transformer for each argument and one for the result type. Of course, (~>) is right associative, and id can match the entire tail "in bulk", so we can also write something like: f $. g ~> id And of course, each transformer can be a pipeline, so assuming proper types, we can do things like: f $. id ~> (length.snd.unWrap) ~> wrap More details here: http://matt.immute.net/content/pointless-fun Questions: 1. Is there already another well-known way to do this? It seems a common enough problem... 2. Do these particular combinators already exist somewhere with other names? 3. Are there better names for these functions? Thanks! Matt [1] http://conal.net/blog/posts/semantic-editor-combinators/ [2] http://conal.net/blog/posts/prettier-functions-for-wrapping-and-wrapping/

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sending email via gmail Re: [Haskell-cafe] Sending email from a Haskell program
by Thomas Hartman 06 Dec '08

06 Dec '08

I ran into this problem when I wanted to send email from a HAppS web app, routing it through gmail. There actually used to be an SMTP client in HAppS but it was dropped a while ago. The most common workaround appears to be, just use sendmail. But I couldn't figure out a way to get sendmail to interface with gmail. (I think there is a way, there are blogs on it, I just wasn't patient enough to follow the directions.) What I finally did is, I have successfully followed the instructions in http://www.ericstockwell.com/?p=3 to send myself email from the command line. So I will probably use HSH to run shell commands in my haskell web apps, to send email. This process only took a few minutes, and seemed easier than the postfix/sendmail solutions I came across. Of course, this only works in unixy environments. thomas. 2007/9/27 brad clawsie <clawsie(a)fastmail.fm>: >> jmuk's HaskellNet project from last year? >> >> http://darcs.haskell.org/SoC/haskellnet/HaskellNet/IMAP.hs > > sweet! was there any documentation created for this? examples? > anything? have people tried to make this work with ssl/tls libs? > > by the way there looks like some other gems in the haskellnet > dir. what exactly was haskellnet - a project to code to the major > network protocols? are these libs stable? how does the HTTP lib stack > up against Network.HTTP? any info on this project would be > appreciated. > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

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deleting spam on the wiki
by Duncan Coutts 06 Dec '08

06 Dec '08

Who is able to delete wiki spam? http://haskell.org/haskellwiki/?title=Special:Contributions&target=Tomso123 All the pages created by this user appear to be spam (check the google translation) so the account should probably be deleted too. As I understand it, any registered user can revert changes to a page: http://www.haskell.org/haskellwiki/Help:Editing However if a registered user creates new spam pages then other ordinary registered users cannot revert that change. Is there some way of reporting spam pages to the appropriate people that I missed? Duncan

3 2

instance Applicative f => Applicative (StateT s f)
by Martijn van Steenbergen 06 Dec '08

06 Dec '08

Hello all, How do I implement the following? instance Applicative f => Applicative (StateT s f) The implementation of pure is trivial, but I can't figure out an implementation for <*>. Is it possible at all, or do I need to require f to be a monad? Thanks in advance, Martijn.

4 8

Quickcheck in industry - own experience.
by Gianfranco Alongi 05 Dec '08

05 Dec '08

http://writert.blogspot.com/2008/12/quickchecking-code-i-c.html /Gf

1 0

propogation of Error
by brad clawsie 05 Dec '08

05 Dec '08

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 hi. i have a partial library for parsing ogg files here: http://hpaste.org/12705 i have a question about an aspect of the code. in the function checkHeader there are a sequence of functions to check various elements in the header of a ogg file. if i test this function against a file that *isn't* an ogg file, i.e. badFile = "/home/user/.bashrc" :: String main = parseOgg badFile >>= (\x -> print x) i would expect to get back the Error from the *first* function in the sequence of functions in checkHeader (oggHeaderError from the oggHeader function). but instead i always see the Error from the *last* function in the sequence, OggPacketFlagError from the OggPacketFlag function. why is this? is there any way i can get the desired behavior...i.e. see the Error from the first function in the sequence that fails? thanks brad -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux) iEYEARECAAYFAkk4tQYACgkQxRg3RkRK91PD9gCePloWFIvE9WjcfApxR2RmnHQ0 pUgAn0WAzRQR/y2yE8yeYP1s7eKHyKDh =EcOM -----END PGP SIGNATURE-----

2 1

FunDeps vs. Associated Types
by Sebastian Fischer 05 Dec '08

05 Dec '08

Dear Haskellers, I have a question regarding the correspondence between functional dependencies and associated types. > {-# LANGUAGE TypeFamilies, > FlexibleInstances, > MultiParamTypeClasses, > FunctionalDependencies > #-} With associated types, we can define a (useless[^1]) type class > class Useless a > where > type T a > useless :: a -> T a and instances > instance Useless () > where > type T () = () > useless = id > > instance Useless a => Useless (() -> a) > where > type T (() -> a) = T a > useless f = useless (f ()) Now we can compute `()` in many different ways: useless () useless (\()->()) ... I thought I could express the same with a multi-parameter type class and a functional dependency: > class UselessFD a b | a -> b > where > uselessFD :: a -> b But the corresponding instances > instance UselessFD () () > where > uselessFD = id > > instance UselessFD a b => UselessFD (() -> a) b > where > uselessFD f = uselessFD (f ()) are not accepted (at least by ghc-6.10.1) without allowing undecidable instances: useless.lhs:50:2: Illegal instance declaration for `UselessFD (() -> a) b' (the Coverage Condition fails for one of the functional dependencies; Use -XUndecidableInstances to permit this) In the instance declaration for `UselessFD (() -> a) b' Is there a simple explanation for this? Cheers, Sebastian [^1]: Originally, I was implementing hidden generation of unique identifiers. So instead of `useless :: (() -> () -> ... -> ()) -> ()` I got something like `withUnique :: (ID -> ... -> ID -> a) -> a`.

2 1

two type-level programming questions
by Nicolas Frisby 05 Dec '08

05 Dec '08

1) Type families, associated types, synonyms... can anything replace the use of TypeCast for explicit instance selection? Section 2, bullet 4 of http://www.haskell.org/haskellwiki/GHC/AdvancedOverlap indicates a negative response. Any other ideas? 2) Any progress/options for kind polymorphism in instances? Thanks for your time.

3 3

manipulating predicate formulae
by Ganesh Sittampalam 05 Dec '08

05 Dec '08

Hi, Are there any Haskell libraries around for manipulating predicate formulae? I had a look on hackage but couldn't spot anything. I am generating complex expressions that I'd like some programmatic help in simplifying. Cheers, Ganesh

4 7

Hat cannot use with ghc 6.10?
by Magicloud 05 Dec '08

05 Dec '08

Hi, I want to do some tracing, and I thought hat could help. Well hmake and hat both could not been made with ghc 6.10....

1 0

Finall Call For Papers (DSL WC)
by Emir Pasalic 05 Dec '08

05 Dec '08

*** IFIP Working Conference on Domain Specific Languages (DSL WC) *** July 15-17, 2009, Oxford http://www.hope.cs.rice.edu/twiki/bin/view/WG211/DSLWC * Call for Papers Domain-specific languages are emerging as a fundamental component of software engineering practice. DSLs are often introduced when new domains such as web-scripting or markup come into existence, but it is also common to see DSLs being introduced and adopted for traditional domains such as parsing and data description. Developing software using DSLs has many benefits. DSLs are often designed based on existing notations that are already in use by experts in a given domain. As such, successful DSLs often reduce or eliminate the effort needed to transform the concept or innovation produced by the domain expert into an executable artifact or even a deliverable software product. DSL implementations can capture and mechanize a significant portion of the repetitive and mechanical tasks that a domain expert traditionally needed to perform in order to produce an executable. DSLs can in many cases capture and make widely available special expertise that only top specialists in a given domain might have. By capturing expert knowledge and reducing repetitive tasks, DSLs often also lead to software that is significantly more portable, more reliable and more understandable than it would otherwise be. DSLs can be viewed as having a dual role to general-purpose languages: whereas general purpose languages try to do everything as well as possible, DSLs are designed to find a domain where they can solve some class of problems -- no matter how small -- in the best possible way. Widely known examples of DSLs include Matlab, Verilog, SQL, LINQ, JavaScript, PERL, HTML, Open GL, Tcl/Tk, Macromedia Director, Mathematica/Maple, AutoLisp/AutoCAD, XSLT, RPM, Make, lex/yacc, LaTeX, PostScript, Excel, among many others. But while these tools have been widely successful, they still fall short of realizing the full idea behind them. The goal of this conference is to explore the extent to which incorporating modern principles of language design and software engineering can benefit existing and future domain-specific languages. The ultimate goal of using DSLs is to improve programmer productivity and software quality. Often, this is achieved by reducing the cost of initial software development as well as maintenance costs. These improvements - programs being easier to write and maintain - materialize as a result of domain-specific guarantees, analyses, testing techniques, verification techniques, and optimizations. * Paper Criteria Papers are sought addressing the research problems, fundamental principles, and practical techniques of DSLs, including but not limited to: - Foundations, including semantics, formal methods, type theory, and complexity theory - Language design, ranging from concrete syntax to semantic and typing issues - Software engineering, including domain analysis, software design, and round-trip engineering - Software processes, including metrics for software and language evaluation - Implementation techniques, including parsing, compiling, and program generation - Program analysis and automated transformation - Reverse engineering, re-engineering, design discovery, automated refactoring - Hardware/software codesign - Programming environments, including visual languages, debuggers, and testing infrastructure - Teaching DSLs and the use of DSLs in teaching Case studies, including engineering, bioinformatics, hardware specification languages, parallel computing languages, real-time and embedded systems, and networked and distributed domains Papers will be judged on the depth of their insight and the extent to which they translate specific experience into general lessons for domain-specific language designers and implementers, and software engineers. Papers can range from the practical to the theoretical; where appropriate, they should refer to actual languages, tools, and techniques, provide pointers to full definitions and implementations, and include empirical data on results. * Important Dates - July 23rd, 2008: First Call for Papers - November 12th, 2008: Final Call for Papers - December 14th, 2008: Abstract submission due. - December 21st, 2008: Paper submission deadline. - February 23rd, 2009: Author notification of decisions - March 22nd, 2009: Camera ready manuscripts due * Instructions for Authors Proceedings will be published in the Springer LNCS series. Submissions and final manuscripts are to follow the LNCS stylesheet formatting guidelines, and are not to exceed 25 pages. Please submit your manuscripts online using the EasyChair conference management system. * Program Committee Jon Bentley, Avayalabs Martin Erwig, Oregon State University Jeff Gray, University of Alabama at Birmingham Robert Grimm, New York University Jim Grundy, Intel Strategic CAD Labs Tom Henzinger, EPFL Sam Kamin, UIUC Dick Kieburtz, Portland State University Ralf Lämmel, University of Koblenz Julia Lawall, University of Copenhagen Benjamin Pierce, University of Pennsylvania Vivek Sarkar, Rice University Jeremy Siek, University of Colorado at Boulder José Nuno Oliveira, University of Minho Doaitse Swierstra, Utrecht University Walid Taha (Chair), Rice University Eelco Visser, Delft University William Waite, University of Colorado at Boulder Stephanie Weirich, University of Pennsylvania * Organizers General Chair: Jeremy Gibbons, Oxford University Publicity Chair: Emir Pasalic, LogicBlox

1 0

class method name scope
by Jason Dusek 05 Dec '08

05 Dec '08

What proposals are out there to address the issue of scoping class methods? I always feel I must be careful, when exposing a class definition that I want clients to be able to extend, that I mustn't step on the namespace with semantically appropriate but overly general names (e.g. 'run'). It'd be nice if class method names were module scoped and could be qualified. -- _jsn

2 4

Re: [Haskell-cafe] detecting socket closure in haskell
by Donn Cave 05 Dec '08

05 Dec '08

Quoth "Tim Docker" <timd(a)macquarie.com.au>: | Hence I seem to need a means of detecting that a socket has been closed | remotely, without actually reading from it. . Does anyone know how to do | this? One reference I've found is this: | | http://stefan.buettcher.org/cs/conn_closed.html | | Apparently recv() with appropriate flags can detect this - though I'm | not convinced that the code as shown on that page doesn't busy wait when | there is unread data from the client. Right - poll() will still find data there, after the "peek", so you'll be running that loop as fast as you can make the 2 system calls, and what I think might be worse, it should keep reading the same 32 bytes at the head of the buffer ... and never notice the connection close. Well, I haven't tried it, but this solution doesn't make sense to me. | Any tips or pointers? Perhaps what I'm trying to do is not currently | possible in haskell, without using the FFI (which would be ok). Or | perhaps it's not possible in linux at all. I don't know of a way to do it in C. I think it's very likely that the kernel finds out only after all the data has been delivered through the network interface, so by the time you can even in principle know that the connection closed, all the data will either have been processed by the client or reside in memory somewhere on the computer. I guess you might try your buffering thread, and if you're really worried about undue amounts of buffered data, set some maximum size, where you either stop trying to notice end-of-file, or switch to another storage medium (e.g., disk file.) Donn

1 0

detecting socket closure in haskell
by Tim Docker 05 Dec '08

05 Dec '08

This is a haskell + networking question... I have a multi threaded haskell server, which accepts client connections, processes their requests, and returns results. It currently works as desired, except where a client drops a connection whilst the server is processing a request. In this circumstance, the server currently doesn't notice that the client has gone until it finishes the processing and attempt to read the next request. I'd like to change it so that the request is aborted as soon as the client disconnects. One way of doing this would would be to maintain a separate thread that is always reading from the client, and buffers until the main thread needs the information. Whilst this would detect the remote close, it also would potentially consume large amounts of memory to maintain this buffer. Hence I seem to need a means of detecting that a socket has been closed remotely, without actually reading from it. . Does anyone know how to do this? One reference I've found is this: http://stefan.buettcher.org/cs/conn_closed.html Apparently recv() with appropriate flags can detect this - though I'm not convinced that the code as shown on that page doesn't busy wait when there is unread data from the client. Any tips or pointers? Perhaps what I'm trying to do is not currently possible in haskell, without using the FFI (which would be ok). Or perhaps it's not possible in linux at all. Thanks, Tim

2 1

ANN: "Real World Haskell", now shipping
by Bryan O'Sullivan 04 Dec '08

04 Dec '08

Good evening - John Goerzen, Don Stewart and I are delighted to announce the availability of our book, "Real World Haskell". It is 710 pages long, and published by O'Reilly Media. This is the first book to comprehensively cover modern Haskell programming. From an introduction to functional programming, it focuses on teaching through many worked examples. We discuss the "awkward squad" of I/O, concurrency, and exceptions. We cover network programming, databases, and system hacking. We motivate and work with monoids, applicative functors, monads, and monad transformers. We show you how to debug code, and how to ship well-tested software. Better yet, the book is available under a Creative Commons license, so you can read as much of it as you please before you buy: http://book.realworldhaskell.org/ We developed this book with the enthusiastic and voluble support of the Haskell community, and we are proud to share our work in a fashion that will help newcomers to our field. And best of all, if you order now (at least in North America), you can have a copy of the book in your hands in a matter of days. Thank you from all of us to our friends in the Haskell world who have been so generous with their feedback and kind words!

17 34

gmp license == no commercial/closed source haskell software ??
by Lionel Barret De Nazaris 04 Dec '08

04 Dec '08

I've just discovered the GMP license problem. (see http://hackage.haskell.org/trac/ghc/wiki/ReplacingGMPNotes) From my understanding, the gmp is GPL, GHC statically links it on windows. As a consequence, any program compiled using GHC must be distributed under a GPL compatible license. In the threads I've read, some workarounds are proposed on linux and OsX, but I didn't see anything on windows. Is the situation still the same ? Does anybody know a work-around to make a closed-source programm in haskell without violating the GPL ? ( Note this could block Haskell in our company. ) -- Best Regards, lionel Barret de Nazaris, ========================= Gamr7 : Cities for Games http://www.gamr7.com

6 5

GHC on Fedora 10 - getMBlock: mmap: Permission denied
by Fraser Wilson 04 Dec '08

04 Dec '08

Hi all, Has anybody seen this? I thought it might be an SELinux thing, but then I wouldn't expect GHC or darcs to run. Audley is a fairly simple program in operating system feature terms, but I get the same error with anything I build myself. [fraser@astroboy audley]$ ./dist/build/audley/audley audley: internal error: getMBlock: mmap: Permission denied (GHC version 6.8.3 for i386_unknown_linux) Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug Aborted [fraser@astroboy audley]$ ghc --version The Glorious Glasgow Haskell Compilation System, version 6.8.3 [fraser@astroboy audley]$ cat /proc/version Linux version 2.6.27-0.352.rc7.git1.fc10.i686 ( mockbuild(a)x86-5.fedora.phx.redhat.com) (gcc version 4.3.2 20080917 (Red Hat 4.3.2-4) (GCC) ) #1 SMP Tue Sep 23 21:26:04 EDT 2008 [fraser@astroboy audley]$ cheers, Fraser. -- http://thewhitelion.org/mysister

4 5

is there something special about the Num instance?
by Anatoly Yakovenko 04 Dec '08

04 Dec '08

module Test where --why does this work: data Test = Test class Foo t where foo :: Num v => t -> v -> IO () instance Foo Test where foo _ 1 = print $ "one" foo _ _ = print $ "not one" --but this doesn't? class Bar t where bar :: Foo v => t -> v -> IO () instance Bar Test where bar _ Test = print $ "test" bar _ _ = print $ "not test"

3 3

Re: [Haskell-cafe] is there something special about the Num instance?
by Yuriy 04 Dec '08

04 Dec '08

Numeric literals are special. Their type is (Num t) => t, so it can belong to any type that is instance of Num. Whereas Test belongs to Test type only so you cannot call bar on any instance of Foo. So your pattern constrains type signature of bar more then it is constrained by class declaration. On Wed, Dec 03, 2008 at 03:05:37PM -0800, Anatoly Yakovenko wrote: > module Test where > --why does this work: > data Test = Test > > class Foo t where > foo :: Num v => t -> v -> IO () > > instance Foo Test where > foo _ 1 = print $ "one" > foo _ _ = print $ "not one" > > --but this doesn't? > > class Bar t where > bar :: Foo v => t -> v -> IO () > > instance Bar Test where > bar _ Test = print $ "test" > bar _ _ = print $ "not test" > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe

1 0

Re: [Haskell-cafe] library to process zip files
by Yuriy 04 Dec '08

04 Dec '08

Almost as fast as typing "proper" google query :) Thanks. On Wed, Dec 03, 2008 at 06:01:59PM -0500, Jeff Heard wrote: > http://hackage.haskell.org/cgi-bin/hackage-scripts/package/zip-archive > > On Wed, Dec 3, 2008 at 5:59 PM, Yuriy <yuriy.halytskyy(a)gmail.com> wrote: > > On Thu, Dec 04, 2008 at 11:56:10AM +1300, Yuriy wrote: > > Hi, > > > > Is there any haskell library to work with ZIP file format? > > > > Thanks, > > Yuriy > > _______________________________________________ > > Haskell-Cafe mailing list > > Haskell-Cafe(a)haskell.org > > http://www.haskell.org/mailman/listinfo/haskell-cafe > >

1 0

library to process zip files
by Yuriy 04 Dec '08

04 Dec '08

On Thu, Dec 04, 2008 at 11:56:10AM +1300, Yuriy wrote: Hi, Is there any haskell library to work with ZIP file format? Thanks, Yuriy

2 1

Problem building HXQ on Mac OS 10.5.5
by Tobias Kräntzer 04 Dec '08

04 Dec '08

Hi, I'm new to haskell and wonted to start tinkering a bit with this language, specifically with HXQ. I have installed ghc with macports. Now while building HXQ I get the following error: Main.hs:20:9: Not in scope: type constructor or class `C.SomeException' Unfortunately I'm also new to Mac OS X. Before I developed on Linux. It would be great, if someone could give me a hint. Thanks, Tobias PS: Below the details -- ~$ cabal install hxq Resolving dependencies... 'HXQ-0.11.0' is cached. Configuring HXQ-0.11.0... Preprocessing library HXQ-0.11.0... Preprocessing executables for HXQ-0.11.0... Building HXQ-0.11.0... . . . Loading package haskell98 ... linking ... done. [20 of 21] Compiling Text.XML.HXQ.XQuery ( src/Text/XML/HXQ/XQuery.hs, dist/build/xquery/xquery-tmp/Text/XML/HXQ/XQuery.o ) [21 of 21] Compiling Main ( Main.hs, dist/build/xquery/ xquery-tmp/Main.o ) Main.hs:20:9: Not in scope: type constructor or class `C.SomeException' cabal: Error: some packages failed to install: HXQ-0.11.0 failed during the building phase. The exception was: exit: ExitFailure 1 -- ~$ ghc-pkg list /opt/local/lib/ghc-6.10.1/./package.conf: Cabal-1.6.0.1, HUnit-1.2.0.3, QuickCheck-1.2.0.0, array-0.2.0.0, base-3.0.3.0, base-4.0.0.0, bytestring-0.9.1.4, containers-0.2.0.0, directory-1.0.0.2, (dph-base-0.3), (dph-par-0.3), (dph-prim-interface-0.3), (dph-prim-par-0.3), (dph-prim-seq-0.3), (dph-seq-0.3), editline-0.2.1.0, filepath-1.1.0.1, (ghc-6.10.1), ghc-prim-0.1.0.0, haddock-2.3.0, haskell-src-1.0.1.3, haskell98-1.0.1.0, hpc-0.5.0.2, html-1.0.1.2, integer-0.1.0.0, mtl-1.1.0.2, network-2.2.0.1, old-locale-1.0.0.1, old-time-1.0.0.1, packedstring-0.1.0.1, parallel-1.1.0.0, parsec-2.1.0.1, pretty-1.0.1.0, process-1.0.1.0, random-1.0.0.1, regex-base-0.72.0.2, regex-compat-0.71.0.1, regex-posix-0.72.0.3, rts-1.0, stm-2.1.1.2, syb-0.1.0.0, template-haskell-2.3.0.0, time-1.1.2.2, unix-2.3.1.0, xhtml-3000.2.0.1 /Users/tobias/.ghc/i386-darwin-6.10.1/package.conf: readline-1.0.1.0 -- Tobias Kräntzer info(a)tobias-kraentzer.de

2 1

handles and foreign C functions
by Andrea Rossato 04 Dec '08

04 Dec '08

Hello, suppose a simple C function like this: void printStuff(FILE *f) { fprintf (f, "Hello World\n"); } In order to use it I need to import fopen and pass to it a Ptr CFile: foreign import ccall unsafe "fopen" fopen :: CString -> CString -> IO (Ptr CFile) foreign import ccall unsafe "fclose" fclose :: Ptr CFile -> IO CInt foreign import ccall unsafe "printStuff" printStuff :: Ptr CFile -> IO () main = withCString "tmp.txt" $ \cpath -> withCString "w" $ \cmode -> do cfile <- throwErrnoIfNull "fopen: " (fopen cpath cmode) printStuff cfile fclose cfile How can I pass to printStuff a stdout FILE pointer? If, for instance, I do: foreign import ccall unsafe "stdout" c_stdout :: Ptr CFile main = withCString "tmp.txt" $ \cpath -> withCString "w" $ \cmode -> do printStuff c_stdout I get a segmentation fault. What am I missing? TIA Andrea

2 4

Re: [Haskell-cafe] Problem building HXQ on Mac OS 10.5.5
by Tobias Kräntzer 03 Dec '08

03 Dec '08

Hi, Am 03.12.2008 um 02:00 schrieb Gwern Branwen: > I haven't looked at the source, so take this as off-the-cuff: try > importing not Control.Exception but Control.OldException. changing "Control.Exception"to "Control.OldException" didn't work. But changing "SomeException" to "Exception" seems to solve the problem (see below). At least I can now built it and use xquery. I think these days I get more in to it and understand what I was doing. ;-) Could it be a problem with the version of GHC? I'm using 6.10.1. Is "SomeException" still supported? At the moment I don't know how to look these things up. Regard, . . . Tobias -- Original: #if __GLASGOW_HASKELL__ >= 609 type E = C.SomeException #else type E = C.Exception #endif -- Modified: type E = C.Exception -- Tobias Kräntzer | Scharnweberstraße 52a | 10247 Berlin Telefon: +49-30-75636668 | +49-178-1353136 XMPP: anagrom_ataf(a)jabber.ccc.de

1 0

Cabal and Hat?
by Magnus Therning 03 Dec '08

03 Dec '08

Is it possible to use cabal to build the files that hat would need to do tracing (i.e. .htx files)? /M -- Magnus Therning (OpenPGP: 0xAB4DFBA4) magnus＠therning．org Jabber: magnus＠therning．org http://therning.org/magnus identi.ca|twitter: magthe

2 1

ByteString web site papers
by Galchin, Vasili 03 Dec '08

03 Dec '08

Hello, http://www.cse.unsw.edu.au/~dons/fps.html Are the papers/slides still up-to-date for someone to get up-to-speed on ByteString motivation and implementation? Anything more recent? Regards, Vasili

2 1

Data.ByteString vs Data.ByteString.Lazy vs Data.ByteString.Char8
by Galchin, Vasili 03 Dec '08

03 Dec '08

Hello, Some mention is made in corresponding web pages about implementation difference of these three different DataString impl. Any advice? Regards, Vasili

3 9

Re: What causes <<loop>>?
by Martin Hofmann 03 Dec '08

03 Dec '08

I was not sure about it, so I just speculated. Anyway, thanks a lot. martin

1 0

What causes <<loop>>?
by Martin Hofmann 03 Dec '08

03 Dec '08

I've already posted this mail on haskell-cafe, but apparently the subject suggested a too simple question, so I try it here again. I am picking up a discussion with the same topic from haskell-users on 8th November. Thunks with reference on themselves was mentioned as main reason for <<loop>>. > A safe recursive definition would be > let x = Foo (x+1) > However, if you leave out the constructor, > let x = x + 1 > you get a <<loop>> (or a deadlock). > Are there any other reasons? I am trying to debug monadic code which stores state information in a record maintaining several Data.Maps, but in vain so far. A state is modified/changed in several steps by a compound function i.e. changeA $ changeB $ changeC state Could this also lead to a deadlock? If so, can I prevent this using CPS? If the state transformation is the main purpose/computation of the monad at all, is it better to use CPS? Is code using mtl, records or Data.Map more prone to <<loop>> or does this not matter at all. How can I identify self-referencing thunks more easily? Is there any rule of thumb to prevent <<loop>>? Are there any less obvious newbie mistakes causing <<loop> then the one above? Sorry, a lot of questions at once, but I am kind of helpless because I can't find any reason of my <<loop>>, so any comments, experience, and tips are highly appreciated. Thanks, Martin

3 3

Install Yi editor with GHC 6.10.1
by Andy Stewart 03 Dec '08

03 Dec '08

Hi all, I have install GHC 6.10.1 and Gtk2hs (darcs version) in Debian. So i want to ask, have anyone install Yi (darcs version) with GHC 6.10.1 successfully? And the best way to install darcs version Yi? Thank you very much! -- Andy

2 2

Deriving
by Daryoush Mehrtash 03 Dec '08

03 Dec '08

What happens when a type adds driving such as: newtype SupplyT s m a = SupplyT (StateT [s] m a) deriving (Functor <http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#t:Funct…>, Monad <http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#t:Monad>, MonadTrans, MonadIO) Two questions: How does the deriving implement the instance? Is there a way for me to add my own classes in the deriving? for example newtype ..... deriving( xyz) Thanks

4 3

Compatible problem with GHC 6.10.1
by Andy Stewart 03 Dec '08

03 Dec '08

Hi all, I use Debian and GHC 6.8.2-7 Have install cabal, xmonad, gtk2hs with GHC 6.8.2-7 But when upgrade to GHC 6.10.1, i failed to install XMonad 0.8 and gtk2hs 0.9.13 I heard someone install success with develop version. So anyone success install XMonad and gtk2hs with GHC 6.10.1? BTW, i want to know the details compatible problem between 6.8 with 6.10? Is most libraries have compatible with GHC 6.10.1? Any suggestions? Thanks. -- Andy

5 14

The Knight's Tour: solutions please
by Don Stewart 03 Dec '08

03 Dec '08

Lee Pike forwarded the following: "Solving the Knight's Tour Puzzle In 60 Lines of Python" http://developers.slashdot.org/article.pl?sid=08/11/30/1722203 Seems that perhaps (someone expert in) Haskell could do even better? Maybe even parallelize the problem? :) So, team, anyone want to implement a Knight's Tour solver in a list monad/list comprehension one liner? These little puzzles are made for fast languages with backtracking monads.... Post solutions to the wiki.. -- Don

5 9

Moving the messages for compiler to another file?
by nml 03 Dec '08

03 Dec '08

How about moving the messages for compiler to an additional file? My motivation is that we often face a trade-off between aesthetical(elegant code) and practical(efficient code). Like pragmas and strictness annotations, I often feel they make the source code ugly. They don't affect the semantics of our programs, do they? Some people would say this beautifying should be accomplished by an editor, like hiding/showing option for those information. But such separation has additional benefits. For instance, making the source code more compiler-independent. (yeah, this is not the case with language-extensions) And we avoid dispersing those information among our lines. (or even files) In some cases, it would be convenient. I'm not sure if this idea is reasonable, reachable or just naive. Suggestions? Best regards -nml

2 1

GHC 6.10 and OpenGL
by Paul L 03 Dec '08

03 Dec '08

Hi everyone, It's sad to see the OpenGL binding being dropped from GHC binary installers starting from 6.10. Though this issue has been brought up and discussed before, I'm sure a lot of people who based their work on OpenGL would share the same sympathy. I'm not here to argue whether this decision by GHC dev team is right or wrong, but what's really causing the pain is that the OpenGL binding doesn't have its own binary installer for Windows, and compilation from source on this platform is non-trivial. I wouldn't recommend doing it for ordinary users. So my question is, are we going to see a binary installer for OpenGL binding provided separately from either HOpenGL site, or Hackage? Or even the GHC installation page? -- Regards, Paul Liu Yale Haskell Group http://www.haskell.org/yale

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global variables for foreign C functions
by Andrea Rossato 03 Dec '08

03 Dec '08

Hello, I'm writing the bindings to a C library which uses, in some functions, global variables. To make it clearer, those functions need a global variable to be defined. A C program using my_function, one of the library functions, would look like: char progname[] = "a_program_name"; int main( int argc, char *argv[] ) { param p; my_function ( &p ) etc. I've been searching the ML, the wiki, the net, etc. without finding some examples on how such things are dealt with in Haskell - is it possible, BTW? If I import those functions without defining the global variable I get a linker error: /usr/lib/mylib.a(cfile.o): In function `my_function': cfile.c:(.text+0x510): undefined reference to `progname' I hope the issue is clear. Any help would be greatly appreciated. Andrea

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The Knight's Tour: solutions please
by oleg＠okmij.org 03 Dec '08

03 Dec '08

Yes, there is a solution for n=99 and for n=100 for that matter -- which can be found under one second. I only had to make a trivial modification to the previously posted code > tour n k s b | k > n*n = return b > | otherwise = do next <- (foldr mplus mzero).map return $ successors n b s > tour n (k+1) next $ insrt next k b I replaced foldl1 mplus with foldr mplus zero. Here are the results: for n=99, the first line of the board is 1 4 2885 214 309 6 311 216 307 8 315 218 305 10 319 220 303 12 2021 222 301 14 1727 224 299 16 1699 226 297 18 1561 228 295 20 1247 230 293 22 1227 232 291 24 1165 234 289 26 1007 236 287 28 965 238 285 30 775 240 283 32 759 242 281 34 625 244 279 36 559 246 277 38 543 248 275 40 455 250 273 42 435 252 271 44 407 254 269 46 377 256 267 48 365 258 65 50 63 60 67 52 55 time is 0m0.730s n=100 1 4 205 9996 209 6 207 9940 211 8 9897 9900 213 10 9895 9906 215 12 9809 9880 217 14 9807 9740 219 16 9799 9072 221 18 8445 8864 223 20 8443 8378 225 22 8347 8352 227 24 8331 7860 229 26 7863 7844 231 28 7749 7754 233 30 7735 7742 235 32 7733 7320 237 34 677 640 239 36 597 568 241 38 535 540 243 40 517 500 245 42 473 452 247 44 371 358 249 46 305 310 251 48 293 286 253 50 291 270 255 52 259 262 time is 0m0.373s For n=101, time is 0m0.388s wren ng thornton wrote: > FWIW, fair choice (interleave) is much slower than unfair choice (mplus) > in logict. Unfortunately this means you need to know a lot about the > problem domain to correctly choose between them when maximal performance > is at stake; just using fair choice everywhere costs too much for many > problems. I believe that FBackTrack relieves one from making the above choice: the ordinary mplus is FBackTrack is both fair and speedy. There is no longer any need for interleave; btw, interleave does not ensure completeness, whereas FBackTrack, I conjecture, implements a complete search procedure: if there is a solution, FBackTrack will eventually find one. The only `drawback' of using FBackTrack is that the order of the answers (if there are several) is essentially unpredictable. Informally, the answers are delivered in the order of the difficulty of finding them. This drawback is relative however: if we insist that the sequence of answers of (m1 `mplus` m2) is the concatenation of the sequences of answers of m1 and then m2, our search procedure is incomplete.

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Sugestion for a basic Utf8 type.
by Mauricio 03 Dec '08

03 Dec '08

Hi, I would like to sugest a new basic type in Haskell. What if we had something like this (with any other quoting character): «Je ne parle pas français. Meu nome é Maurício. ¿Hablas español?» This would be of type Utf8. I think now it is not a bad idea, since Haskell source code is supposed to be utf-8. The internal representation of this datatype would be a null terminated utf-8 byte vector. No standard operations would be defined on that type, i.e., it would be a “communication standard” between everybody, but module writers could develop different basic usage based on operations on them using Foreign. (I think it would be dificult to set default operations, since there are so many things you can do with utf-8.) Pros: * There would be no doubt you can use utf-8 when using this, since there's no conversion involved. * Cleaner code on utf8 operations, maybe. There are many utf8 modules today with different goals in mind, I thing it would be nice if they could share this common basic type and a common underline implementation. Cons: * Probably, many. I have no deep understanding of Haskell. Thanks for your attention, Maurício

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import
by Galchin, Vasili 02 Dec '08

02 Dec '08

Hello, I am a little uncertain about "import" semantics in a hierarchical package ... i.e. if I import the root of a package root do I get everything under the "root's" namespace, i.e. the namespace tree? thanks, vasili

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