May 2009 - Haskell-Cafe

Problem with text and text-icu packages
by David Carter 12 May '09

12 May '09

Hi, I'm struggling with text-0.1 and text-icu-0.1, as announced at http://www.serpentine.com/blog/2009/02/27/finally-fast-unicode-support-for-… The code in http://pastebin.com/m7d8d9f91 is intended to read in a UTF-8 file a1.txt, reverse it twice, and write it out to another UTF-8 file a2.txt, which I would have thought should make a2.txt identical to a1.txt. Mostly it is, but sometimes it isn't, e.g.: % echo a > a1.txt % tryicu # <- my code % cat a2.txt ࠋ퐤 Specifically, a1.txt contains bytes 97 and 10, while a2.txt contains bytes 224 160 139 237 144 164. Have I misconstrued things, or is this a bug? I am running ghc 6.10.2 and ICU 4.0.1 on SuSE. Thanks for any help David

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Data.Map lookup signature
by Nico Rolle 12 May '09

12 May '09

Hi everyone. The docs in the web on http://www.haskell.org/ghc/docs define Data.Map.lookup as follows: http://www.haskell.org/ghc/docs lookup :: Ord k => k -> Map k a -> Maybe a but my version of ghci does i like that: Data.Map.lookup :: (Ord k, Monad m) => k -> Data.Map.Map k a -> m a but i need the 1. one. my version of ghci is 6.8.2 regards

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Re: [Haskell-cafe] Inferred typing?
by michael rice 12 May '09

12 May '09

I was looking at some code and couldn't figure out how it was returning a list since there were no list constructors present. Thanks! Michael --- On Tue, 5/12/09, Brent Yorgey <byorgey(a)seas.upenn.edu> wrote: From: Brent Yorgey <byorgey(a)seas.upenn.edu> Subject: Re: [Haskell-cafe] Inferred typing? To: haskell-cafe(a)haskell.org Date: Tuesday, May 12, 2009, 7:50 AM On Mon, May 11, 2009 at 10:59:01PM -0700, michael rice wrote: > In the code below, is the type returned by the return functions inferred from > the result type in the function type signature, i.e., just change the result > type to Maybe Int and the code will return a Maybe monad, (Just 4), instead of > a List monad? Indeed, it is. Try it! =) -Brent _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

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OT: Is conference dead?
by Dušan Kolář 12 May '09

12 May '09

Hello all, I'm sorry for the OT post, is the conference dead? I've got no mail since yeasterday afternoon. And that is quite unusual. Best regards, Dusan

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Inferred typing?
by michael rice 12 May '09

12 May '09

In the code below, is the type returned by the return functions inferred from the result type in the function type signature, i.e., just change the result type to Maybe Int and the code will return a Maybe monad, (Just 4), instead of a List monad? Michael ========= import Monad fn :: [Int] -> [Int] fn l = mzero `mplus` (return (head l)) `mplus` (return (last l)) ================ *Main> :l test5 [1 of 1] Compiling Main ( test5.hs, interpreted ) Ok, modules loaded: Main. *Main> fn [4,5,6,7,8] [4,8] *Main>

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Haskell Weekly News: Issue 117 - May 12, 2009
by Brent Yorgey 12 May '09

12 May '09

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20090512 Issue 117 - May 12, 2009 --------------------------------------------------------------------------- Welcome to issue 117 of HWN, a newsletter covering developments in the [1]Haskell community. The Haskell Platform is here! Announcements The Haskell Platform. Don Stewart [2]announced the first release of the [3]Haskell Platform: a single, standard Haskell distribution for every system. The Haskell Platform is a blessed library and tool suite for Haskell culled from Hackage, along with installers for a wide variety of systems. It saves developers work picking and choosing the best Haskell libraries and tools to use for a task. GHC version 6.10.3. Ian Lynagh [4]announced the release of [5]GHC 6.10.3. This release contains a handful of bugfixes relative to 6.10.2 and better line editing support in GHCi, so updating is recommend. See the [6]release notes for more details. Bindings for libguestfs. Richard W.M. Jones [7]announced some [8]partial bindings for [9]libguestfs. Heads up: Conflicting versions of network-2.2.1. Johan Tibell [10]announced a heads-up that the version of network-2.2.1 that shipped with GHC 6.10 differs from the one on Hackage. If you want the API additions that are present in network-2.2.1 on Hackage, be sure to use network-2.2.1.1 instead. hpc-strobe-0.1: Hpc-generated strobes for a running Haskell program. Thorkil Naur [11]announced the initial release of [12]hpc-strobe, a rudimentary library that demonstrates the possibility of using Hpc (Haskell Program Coverage) to inspect the state of a running Haskell program. hpc-strobe uses the basic machinery provided by Hpc to produce multiple tix files, also called strobes, representing the coverage at different times while the program is running. By subtracting such two tix files, again using Hpc machinery, a tix file representing the expressions used between the times of recording the subtracted tix files is produced. This may be used, for example, to get a better idea of what a long-running program is doing. It could also be used as a profiling tool, getting information about how many times individual expressions are used. BUG FIX release of regex-tdfa-1.1.2. ChrisK [13]announced version 1.1.2 of [14]regex-tdfa, a bug-fix release. Silkworm game. Duane Johnson [15]announced the release of [16]Silkworm, a game written in Haskell using [17]Hipmunk and GLFW. Discussion Platform policy question: API compatibility in minor releases. Duncan Coutts began a [18]discussion on versioning policies for major and minor releases, for packages included in the Haskell Platform. See also the [19]newly started discussion on the purpose of Haskell Platform releases. Blog noise [20]Haskell news from the [21]blogosphere. Blog posts from people new to the Haskell community are marked with >>>, be sure to welcome them! * Magnus Therning: [22]Vim haskellmode packaged for Arch. * Manuel M T Chakravarty: [23]Instant Generics: Fast and Easy.. * Bjorn Buckwalter: [24]May 2009 HCAR Submissions. * Gtk2HS: [25]Gtk2HS 0.10.1 Released. * Magnus Therning: [26]Arch and Haskell, on little snag. * Mikael Vejdemo Johansson (DrSyzygy): [27]Gröbner bases for operads - Or "What I did in my vacation". * Mads Lindstrøm: [28]WxGeneric 0.6.0. * Osfameron: [29]Is currying monadic?. * James Iry: [30]A Brief, Incomplete, and Mostly Wrong History of Programming Languages. * Duane Johnson: [31]Visualizing Typed Functions. * Well-Typed.Com: [32]Next steps for the Haskell Platform. * Don Stewart (dons): [33]The Haskell Platform. * Luke Palmer: [34]Lazy Partial Evaluation. * Christopher Lane Hinson: [35]Vec is Good. * LHC Team: [36]Constructor specialization and laziness.. * Lee Pike: [37]An Atomic Fibonacci Server: Exploring the Atom (Haskell) DSL. * John Van Enk: [38]Atom & Arduino :: First Program (pt. 2). * >>> Chris Forno: [39]Is Haskell a Good Choice for Web Applications?. * >>> Sparky: [40]Haskell and Eclipse [Part 2]. * >>> Brit Butler: [41]Playing with Haskell. * Duane Johnson: [42]Silkworm Game written in Haskell. * Matthew Podwysocki: [43]Functional Composition and Partial Application . * >>> Takashi: [44]A Prolog In Haskell. * >>> mokehehe: [45]Using DirectX from Haskell. * >>> mokehehe: [46]AO bench in Haskell. Quotes of the Week * jfredett: My haskell-spider senses were tingling, I just overshot RT and went for the Halting Problem. * NeilBrown: I heard that if you chant "I don't think this can be done in Haskell" three times in front of a text editor, Don Stewart appears and implements it in one line... * bos: The last couple of times I've wanted a book like that, I wrote the book myself. It's a very effective way to get the book you want, compared to wishing. * edwardk: {-# LANGUAGE time to pay the cutting edge typing features tax #-} * SPJ: Haha this is good news, I have slipped functional programming into your brain without you realising it is something very weird. * EvilTerran: writing machine code by hand on tape with a magnetised needle looks good compared to PHP :P * Athas: I like Lisp for its extreme expressivity, but I think it's easier to make Haskell more powerful, than to make Lisp more statically safe. * roconnor: I can't wait for the Density Comonad chapter of "learn you a haskell" About the Haskell Weekly News New editions are posted to [47]the Haskell mailing list as well as to [48]the Haskell Sequence and [49]Planet Haskell. [50]RSS is also available, and headlines appear on [51]haskell.org. To help create new editions of this newsletter, please see the information on [52]how to contribute. Send stories to byorgey at cis dot upenn dot edu. The darcs repository is available at darcs get [53]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://article.gmane.org/gmane.comp.lang.haskell.cafe/58095 3. http://hackage.haskell.org/platform/ 4. http://article.gmane.org/gmane.comp.lang.haskell.general/17178 5. http://www.haskell.org/ghc/ 6. http://haskell.org/ghc/docs/6.10.3/html/users_guide/release-6-10-3.html 7. http://article.gmane.org/gmane.comp.lang.haskell.cafe/58358 8. http://git.et.redhat.com/?p=libguestfs.git;a=blob;f=haskell/Guestfs.hs;hb=H… 9. http://et.redhat.com/~rjones/libguestfs/ 10. http://article.gmane.org/gmane.comp.lang.haskell.cafe/58349 11. http://article.gmane.org/gmane.comp.lang.haskell.cafe/58286 12. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hpc%2Dstrobe 13. http://article.gmane.org/gmane.comp.lang.haskell.cafe/58067 14. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/regex-tdfa 15. http://article.gmane.org/gmane.comp.lang.haskell.cafe/57886 16. http://blog.inquirylabs.com/2009/05/02/silkworm-game-written-in-haskell/ 17. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Hipmunk 18. http://thread.gmane.org/gmane.comp.lang.haskell.libraries/11001 19. http://thread.gmane.org/gmane.comp.lang.haskell.libraries/11035 20. http://planet.haskell.org/ 21. http://haskell.org/haskellwiki/Blog_articles 22. http://therning.org/magnus/archives/617 23. http://justtesting.org/post/106219682 24. http://flygdynamikern.blogspot.com/2009/05/may-2009-hcar-submissions.html 25. http://haskell.org/gtk2hs/archives/2009/05/10/gtk2hs-0101-released/ 26. http://therning.org/magnus/archives/599 27. http://blog.mikael.johanssons.org/archive/2009/05/grobner-bases-for-operads… 28. http://lindstroem.wordpress.com/2009/05/08/wxgeneric-0-6-0/ 29. http://greenokapi.net/blog/2009/05/07/is-currying-monadic/ 30. http://james-iry.blogspot.com/2009/05/brief-incomplete-and-mostly-wrong.html 31. http://blog.inquirylabs.com/2009/05/07/visualizing-typed-functions/ 32. http://blog.well-typed.com/2009/05/next-steps-for-the-haskell-platform/ 33. http://donsbot.wordpress.com/2009/05/06/the-haskell-platform/ 34. http://lukepalmer.wordpress.com/2009/05/04/lazy-partial-evaluation/ 35. http://blog.downstairspeople.org/2009/05/05/vec-is-good/ 36. http://lhc-compiler.blogspot.com/2009/05/constructor-specialization-and-laz… 37. http://leepike.wordpress.com/2009/05/05/an-atomic-fibonacci-server-explorin… 38. http://blog.sw17ch.com/wordpress/?p=111 39. http://jekor.com/article/is-haskell-a-good-choice-for-web-applications 40. http://sdasrath.blogspot.com/2009/05/20090402-haskell-and-eclipse-part-2.ht… 41. http://redlinernotes.com/blog/?p=937 42. http://blog.inquirylabs.com/2009/05/02/silkworm-game-written-in-haskell/ 43. http://weblogs.asp.net/podwysocki/archive/2009/05/01/functional-composition… 44. http://propella.blogspot.com/2009/04/prolog-in-haskell.html 45. http://mokehehe.blogspot.com/ 46. http://mokehehe.blogspot.com/2009/04/ao-bench-in-haskell.html 47. http://www.haskell.org/mailman/listinfo/haskell 48. http://sequence.complete.org/ 49. http://planet.haskell.org/ 50. http://sequence.complete.org/node/feed 51. http://haskell.org/ 52. http://haskell.org/haskellwiki/HWN 53. http://code.haskell.org/~byorgey/code/hwn/

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Classes: functional dependency (type -> value)
by Belka 12 May '09

12 May '09

Hello, communion people! I seek for your advice in a matter, where it's really hard for me to determine a good programming style. Here's the problem. I'm generalizing multiple authorization procedures to one, using class definition. (if of any interest, the code is in the end.) The problem essense is folowing: ---------------- data SomeRole = Role1 | Role2 | Role3 class SomeClass a b c | a -> b, c where f1 :: ... f2 :: ... ... fn :: ... role :: SomeRole -- <-- here is the problem I want to have a fuctional dependency from a type "a" on a value of *role*, so that I could easily "inspect" the *role* from within any other class members. Is it possible? Or do I rougly violate some style traditions? Some real code using wished feature: --------------------------------------- data AuthentificationPurpose = JustValidateInput | JustGenerateForOutput | ValidateInputAndGenerateForOutput type AuthSucceded = Bool class AuthentificationStructure t_env t_realInput t_assumption t_keySet | t_realInput -> t_assumptionInput, t_keySet where authentificationPurpose :: AuthentificationPurpose makeAssumption :: t_env -> t_realInput -> IO (Either ErrorMessage t_assumption) makeFinalKeySet :: (t_realInput, t_assumption) -> t_keySet validateRealKeySet_with_Assumed :: t_realInput -> t_keySet -> Maybe ErrorMessage tryLogTheValidKey :: t_env -> (t_realInput, t_assumption) -> IO (Maybe ErrorMessage) tryLogTheAuthTry :: t_env -> (t_realInput, t_assumption, AuthSucceded) -> IO (Maybe ErrorMessage) authentificate :: AuthentificationStructure t_env t_realInput t_assumptionInput t_keySet => t_env -> t_businessInput -> IO (Either ErrorMessage (t_assumption, t_keySet)) authentificate env realInput = do err_or_assumption <- makeAssumption env realInput case err_or_assumption of Left err_msg -> return $ Left "Error! Assumption maker failed. Lower level error message: " ++ err_msg Just assumption -> do key_set <- makeFinalKeySet (realInput, assumption) err_or_keyset1 <- case authentificationPurpose of JustGenerateForOutput -> return $ Right key_set JustValidateInput -> do mb_failure <- validateRealKeySet_with_Assumed t_realInput key_set case mb_failure of Just err_msg -> return $ Left "Error! Invalid set of auth keys. Lower level error message: " ++ err_msg Nothing -> return $ Right key_set ValidateInputAndGenerateForOutput err_or_keyset2 <- case err_or_keyset1 of Left err_msg -> return err_or_keyset1 Right key_set -> do mb_failure <- tryLogTheValidKey env (realInput, assumption) case mb_failure of Just err_msg -> return $ Left "Error! Could not log valid key. Lower level error message: " ++ err_msg Nothing -> return err_or_keyset1 mb_failure <- tryLogTheAuthTry env (realInput, assumption, isRight err_or_keyset2) case mb_failure of Just err_msg1 -> case err_or_keyset2 of Left err_msg2 -> return $ Left ("1. " ++ err_msg2 ++ "\n2. " ++ err_msg1) Right _ -> return $ Left err_msg1 Nothing -> case err_or_keyset2 of Left err_msg -> return $ Left err_msg Right key_set -> return $ Right (assumption, key_set) --------------------------------- Best regards, Belka -- View this message in context: http://www.nabble.com/Classes%3A-functional-dependency-%28type--%3E-value%2… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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OT: Languages (was: Is Haskell a Good Choice for Web Applications? (ANN: Vocabulink))
by Kalman Noel 12 May '09

12 May '09

wren ng thornton schrieb: > Chris Forno (jekor) wrote: >> That being said, Esperanto, and even Japanese sentence structure perhaps >> is not as different as an agglutinative language like German. I'll need >> to study it more to find out. > > Actually, Japanese is agglutinative too (moreso than German is). I take it the above calling German agglutinative was sort of a typo, because well, it isn't, except having many compound words. Esperanto, on the other hand, is usually described as agglutinative. Kalman

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ANN: AAIP Workshop on ICFP Deadline Extension
by Martin Hofmann 12 May '09

12 May '09

AAIP Workshop on ICFP Deadline Extension Please note that the submission deadline for the 3rd Workshop on Approaches and Applications of Inductive Programming has been extended to May 25. The workshop takes place for the first time at the 14th ACM SIGPLAN International Conference on Functional Programming (ICFP 2009) in Edinburgh, Scotland. If a sufficient number of high quality papers is submitted, there will be a Post-Workshop Proceedings Volume published at Springer LNCS. The workshop will present three invited speakers from the research area of functional programming who have done excellent work to make use of inductive programming techniques. The full Call for Papers and further information are available at http://www.cogsys.wiai.uni-bamberg.de/aaip09/ Submit to the workshop and help to tighten the link between the functional programming and the inductive programming community! Best regards, Ute Schmid, Rinus Plasmeijer and Emanuel Kitzelmann

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Re: [Haskell-cafe] Hoogle: converting binary .hoo into text?
by Peter Verswyvelen 11 May '09

11 May '09

On Mon, May 11, 2009 at 10:25 AM, Neil Mitchell <ndmitchell(a)gmail.com>wrote: > Hi Peter, > > > I would like to use the Hoogle text format in C#. > > Out of curiosity, why? I'm just interested to know what work you're doing. Sure. We're building with a graphical representation of a Haskellish language (a tiny subset of Haskell actually). The target audience is graphical artists and designers. For testing, I would like to populate the library with primitives taken from the Haskell base libraries. I tried using the GHC API for it, but got stuck. I got the advice in #haskell to parse the Hoogle format, which indeed looks simple enough for the task. > Hoogle on Hackage comes with a bunch of binary *.hoo files. Can these be > > converted to text/xml? If not, is the binary format documented? > > The binary format is documented in the code, and there is a show command. > Try: > > hoogle +base --dump > > However the binary format is not an encoding of the text format, it > throws away lots of data, and precomputes interesting tables etc. If > you want the original, the binary is probably not that useful. > > I do have a complete set of text files though. I can upload them to > the Hoogle website, or I can distribute them with the hackage package. > I could just email them to you privately. What seems the best option > for everyone? I'm not everyone but I guess it would be useful in general. From within Haskell, ideally one would just use the GHC API (or Cabal API) to extract all information I guess, but for usage in other languages, an easy to parse format is better no? (maybe even XML, but that is bulky :-) > I know I can build hoo files using "cabal haddock --hoogle". But doing > this > > on the BASE package (which I need) from Hackage fails (I'm on Windows, > using > > MSYS): > > configure: creating ./config.status > > config.status: error: cannot find input file: include/HsBaseConfig.h.in > > Does anyone have an easy solution? Maybe I just need to switch to Linux > to > > get this working? :-) > > I have a small pile of hacks to get the base library building with > Hoogle. You are welcome to look at them (data/generate in the Hoogle > repo). Caution: these hacks may make your eyes bleed, and certainly > won't work for anything but the GHC/base version pair that I last did > it on. > > Thanks > > Neil >

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