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There is no Text.Regex module
by zaxis 17 Oct '09

17 Oct '09

In Archlinux i can use Text.Regex as below: import Text.Regex let [y,m,d] = map (\x -> read x::Int) $ splitRegex (mkRegex "-") dateStr However, in Ubuntu 9.10 it doesnot work reporting no Text.Regex module. So i download and install regex-base and regex-posix from Hackage. But it still doesnot work ! $dpkg -l ghc6 名称版本简介 ================================================================================== ghc6 6.10.4-1ubuntu2 GHC - the Glasgow Haskell Compilation system SIncerely! -- View this message in context: http://www.nabble.com/There-is-no-Text.Regex-module-tp25935308p25935308.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Haskell Weekly News: Issue 136 - October 17, 2009
by jfredett＠gmail.com 17 Oct '09

17 Oct '09

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20091017 Issue 136 - October 17, 2009 --------------------------------------------------------------------------- Welcome to issue 136 of HWN, a newsletter covering developments in the [1]Haskell community. Over the last week, fpisfun from reddit announced a [2]new subreddit for simple, direct applications of Haskell to common problems which normally might be solved by a perl script or bit of bash. There are a number of examples already there, and the numbers keep growing. It's not just command-line utilities either, there is also [3]this post on calculating the bend needed for a bay window curtainrod. There is plenty of great material if you're new to Haskell and looking for some basic examples of different simple projects, examples of using monads and functors appropriately, or just want to see some 'real' programs in Haskell, it's worth a look! Also, a small correction, due to some issues with the tools, unicode characters get replaced with their ASCII 'equivalents' so that an 'e' with an umlaut becomes an 'e' character. Thanks to Wolfram Kahl for pointing out that this change is not as innocent as I thought, apologies thusly to Guenther Schmidt (I'm told thats a better approximation of the correct spelling) for the error, I apologize in advance for any other similar errors. I'm working on improving the unicode support in the tools, but it's a nasty bug to catch. This was a long editorial, so I won't take any more of your time, Haskellers, the Haskell Weekly News! Announcements Call for Contributions - Haskell Communities and Activities Report, November 2009 edition. voigt [4]called for contributions to the November 2009 issue of the Haskell Communities and Activities Report. See post for details. Call for Participation: VSTTE 2009. Jean-Christophe Filliatre [5]announced a call for participation for the VSTTE Workshop. WFLP 2010 Call for papers. Pablo Nogueira [6]announced a call for papers for the 2010 WFLP. BAHUG Next meeting: October 21st at MIT (32G-882). Ravi Nanavati [7]announced the next meeting of the Boston Area Haskell User's Group. Which will be in the CSAIL Reading Room at MIT. This editor hopes to actually make it to this one, so maybe I'll see you there! fp-southwales, the South Wales Functional Programming User Group. Andy Gimblett [8]announced the formation of fp-southwales, a user group for anybody interested in functional programming in the area of south Wales, UK. The Monad.Reader (14) - Call for copy. Brent Yorgey [9]announced the call for copy for the next issue of `The Monad.Reader`, Issue #14 Extensions to Vec uploaded (useful for GPipe programs). Tobias Bexelius [10]announced two extensions to the Vec package: Vec-Transform and Vec-Boolean. Vec-Transform provides some 4x4 transform matrices such as perspective projection and rotation. Vec-Boolean provides Data.Boolan instances for the Vec data types. Bindings to FFMpeg library. Vasyl Pasternak [11]announced the next release of the hs-ffmpeg library. Downloadable from Hackage along with the ffmpeg-tutorials, which show capabilities of this library. The installation process is a bit tricky so Vasyl put up a [12]blog post which describes the installation process. Haskell Hackathon in Zurich, Switzerland. Johan Tibell [13]announced a Hackathon in Zurich, to be held in March in the Google office. No concrete date has been decided, but if your interested, make sure to add your name [14]here. Reverse Dependencies in Hackage (demo). Roel van Dijk [15]announced his patch to add reverse-dependencies to Hackage, see the linked post for information on where to see an example version of hackage. Discussion Relational Algebra. Guenther Schmidt [16]asked about whether or not a EDSL for relational algebra in Haskell. GHC devs. Andrew Coppin [17]asked about how many GHC Developers there are, and was somewhat surprised with the answer. Fuzzy Logic / Linguistic Variables. Neal Alexander [18]demonstrated an implementation of fuzzy logic taken from the book: 'Programming Game AI by Example' by Mat Buckland. In the book, the code was in C++, rewriting it in Haskell made for much more succint, readable code. Graph Library Using Associated Types. Lajos Nagy [19]asked about using Associated types in a Graph library. Is proof by testing possible? Muad'Dib [20]asked us Haskell Mentat's about whether it was possible to prove a function correct in a finite number of tests. The discussion brought forth not only answers but some /very cool/ results about the application of compactness (in the topological sense) to testing. Blog noise [21]Haskell news from the [22]blogosphere. Blog posts from people new to the Haskell community are marked with >>>, be sure to welcome them! * Don Stewart (dons): [23]LACSS 2009: Domain Specific Languages and Haskell. * FP Lunch: [24]Factorising folds for faster functions. * Mikael Vejdemo Johansson (Syzygy-): [25][MATH 198] Lecture 4 and a question for the community. More of Syzygy's lectures on category theory, Syzygy also asks about what it means to 'integrate' a datatype. * Neil Brown: [26]Emulating Shared Mutable Variables with Message-Passing Processes. * Galois, Inc: [27]Tech Talk: Writing Linux Kernel Modules with Haskell. * Galois, Inc: [28]Domain Specific Languages for Domain Specific Problems. * FP-Syd: [29]Sydney FP Group: FP-Syd #18.. * Neil Brown: [30]The octopus, the boids and GHC 6.12.1rc1. * Brent Yorgey: [31]Call for submissions: Monad.Reader issue 15. * Brent Yorgey: [32]diagrams 0.2.1, and future plans. * Don Stewart (dons): [33]Self-optimizing data structures: using types to make lists faster. * Martijn van Steenbergen: [34]Context Synonyms. * Joachim Breitner: [35]arbtt: Now with Documentation. * Dan Piponi (sigfpe): [36]Vectors, Invariance, and Math APIs. * Creighton Hogg: [37]How to teach Category Theory?. Quotes of the Week * sproingie: How do you beta-reduce a problem like Maria * Baughn: There's also the language, Quine, whose interpreter is implemented as a symlink to /bin/cat * benmachine: [on the best editor] opinions vary. from correct opinions i.e. mine to other ones. [editor's comment: Obviously, this question is settled, the best editor is *garbled*] * pozic: statistics. a wonderful tool to control people. * FunctorSalad: I think the 'asks', 'gets' etc family of names is sort of cute, like the program is talking about itself in the third person * mmorrow:: Right, that's just beggin for a State monad. About the Haskell Weekly News New editions are posted to [38]the Haskell mailing list as well as to [39]the Haskell Sequence and [40]Planet Haskell. [41]RSS is also available, and headlines appear on [42]haskell.org. To help create new editions of this newsletter, please see the information on [43]how to contribute. Send stories to jfredett . at . gmail . dot . com. The darcs repository is available at darcs get [44]http://patch-tag.com/r/jfredett/HWN2/pullrepo HWN2 . References 1. http://haskell.org/ 2. http://www.reddit.com/r/EnHaskell 3. http://www.reddit.com/r/EnHaskell/comments/9syi3/calculating_the_bend_for_a… 4. http://article.gmane.org/gmane.comp.lang.haskell.general/17572 5. http://article.gmane.org/gmane.comp.lang.haskell.general/17570 6. http://article.gmane.org/gmane.comp.lang.haskell.cafe/64933 7. http://article.gmane.org/gmane.comp.lang.haskell.cafe/64928 8. http://article.gmane.org/gmane.comp.lang.haskell.cafe/64858 9. http://article.gmane.org/gmane.comp.lang.haskell.cafe/64717 10. http://article.gmane.org/gmane.comp.lang.haskell.cafe/64673 11. http://article.gmane.org/gmane.comp.lang.haskell.cafe/64901 12. http://progandprog.blogspot.com/2009/10/video-processing-on-haskell-easy.ht… 13. http://article.gmane.org/gmane.comp.lang.haskell.cafe/64947 14. http://haskell.org/haskellwiki/ZuriHac#Possible_Attendees 15. http://article.gmane.org/gmane.comp.lang.haskell.cafe/64915 16. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/64899 17. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/64867 18. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/64860 19. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/64812 20. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/64757 21. http://planet.haskell.org/ 22. http://haskell.org/haskellwiki/Blog_articles 23. http://donsbot.wordpress.com/2009/10/16/lacss-2009-domain-specific-language… 24. http://sneezy.cs.nott.ac.uk/fplunch/weblog/?p=267 25. http://blog.mikael.johanssons.org/archive/2009/10/math-198-lecture-4-and-a-… 26. http://chplib.wordpress.com/2009/10/14/emulating-shared-mutable-variables-w… 27. http://www.galois.com/blog/2009/10/13/haskellkernelmodules/ 28. http://www.galois.com/blog/2009/10/13/domain-specific-languages-for-domain-… 29. http://www.mega-nerd.com/erikd/Blog/FP-Syd/fp-syd-18.html 30. http://chplib.wordpress.com/2009/10/12/the-octopus-the-boids-and-ghc-6-12-1… 31. http://byorgey.wordpress.com/2009/10/12/call-for-submissions-monad-reader-i… 32. http://byorgey.wordpress.com/2009/09/24/diagrams-0-2-1-and-future-plans/ 33. http://donsbot.wordpress.com/2009/10/11/self-optimizing-data-structures-usi… 34. http://martijn.van.steenbergen.nl/journal/2009/10/11/context-synonyms/ 35. https://www.joachim-breitner.de/blog/archives/342-arbtt-Now-with-Documentat… 36. http://blog.sigfpe.com/2009/10/vectors-invariance-and-math-apis.html 37. http://abstractabsurd.blogspot.com/2009/10/how-to-teach-category-theory.html 38. http://www.haskell.org/mailman/listinfo/haskell 39. http://sequence.complete.org/ 40. http://planet.haskell.org/ 41. http://sequence.complete.org/node/feed 42. http://haskell.org/ 43. http://haskell.org/haskellwiki/HWN 44. http://patch-tag.com/r/jfredett/HWN2/pullrepo%20HWN2

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ANNOUNCE IDynamic-0.1
by Alberto G. Corona 16 Oct '09

16 Oct '09

IDynamic is variant of Data.Dynamic that can be indexed, serialized., stored, transmitted trough communications etc. So it can be used in abstract data containers, persistence, communications etc. http://hackage.haskell.org/package/IDynamic I Just uploaded it, so the documentation has not been created by Hackage. However I uincluded an example in the pachage. {-# OPTIONS -XTypeSynonymInstances #-} module Main where import Data.IResource import Data.IDynamic import Data.Typeable instance IResource Int where keyResource x= "I" serialize = show deserialize = read defPath _= "saved/" instance IResource String where keyResource x= take 5 x serialize = show deserialize = read defPath _= "saved/" main= do putStrLn "see the code to know the meaning of he results" registerType :: IO Int -- register both datatypes (Int, and String) registerType :: IO String let x= 1 :: Int let list= [IDynamic x, IDynamic "hello, how are you"] --typical Dynamic usage let assoc= zip (map keyResource list) list print $ lookup (keyResource (5 ::Int)) assoc -- lookup a IDynamic object from a container and show it mapM writeResource list mds ← readResource $ IDynamic "hello" -- save both objects case mds of Nothing → error "must have been Just!" --why? Just ds → do putStrLn $ serialize ds -- serialize the dynamic object and print it let str= fromIDyn ds :: String -- casting putStrLn str -- print the string read let y= fromIDyn ds :: Int -- casting error print y

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Fwd: [Haskell-cafe] Re: Best Editor In Windows
by Alberto G. Corona 16 Oct '09

16 Oct '09

I use Leksah. It´s an IDE . It works fine in Windows. http://leksah.org/ http://leksah.org/Leksah-0.6.1.0.exe By the way, keep the good work Leksah people !. 2009/10/16 Stefan Monnier <monnier(a)iro.umontreal.ca> > The only thing I haven't figured out is how to do tab-completion of > > words in the ghci buffer. Do I need to use a different key > > combination? I couldn't find that in the documentation. > > I think it's just a missing feature. > > > Stefan > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

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Generating random enums
by michael rice 16 Oct '09

16 Oct '09

What is the minimum I need to do to get this function to generate a three direction tuple? Michael ===================== import System.Random import Data.Ord data Dir = North | South | East | West deriving (Show, Read, Eq, Enum, Ord, Bounded) threeDirs :: StdGen -> (Dir,Dir,Dir) threeDirs gen = let (firstDir, newGen) = random gen (secondDir, newGen') = random newGen (thirdDir, newGen'') = random newGen' in (firstDir, secondDir, thirdDir) ===================== GHCi, version 6.10.3: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer ... linking ... done. Loading package base ... linking ... done. Prelude> :l dir.hs [1 of 1] Compiling Main ( dir.hs, interpreted ) dir.hs:15:29: No instance for (Random Dir) arising from a use of `random' at dir.hs:15:29-42 Possible fix: add an instance declaration for (Random Dir) In the expression: random newGen' In a pattern binding: (thirdDir, newGen'') = random newGen' In the expression: let (firstDir, newGen) = random gen (secondDir, newGen') = random newGen (thirdDir, newGen'') = random newGen' in (firstDir, secondDir, thirdDir) Failed, modules loaded: none. Prelude>

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Fwd: [Haskell-cafe] x -> String
by Alberto G. Corona 16 Oct '09

16 Oct '09

yep add Show to your abstrac container. , for example: data SDynamic= forall a.Show a => SDynamic a instance Show SDynamic where show (SDynamic a)= show a 2009/10/16 David Virebayre <dav.vire%2Bhaskell(a)gmail.com<dav.vire%252Bhaskell(a)gmail.com> > On Fri, Oct 16, 2009 at 8:19 PM, Andrew Coppin > <andrewcoppin(a)btinternet.com> wrote: > > Is there any way that you can turn an arbitrary Haskell value into a > string? > > > I rephrase: There *is* a way to turn arbitrary values into strings. I > know > > there is, because the GHCi debugger *does* it. The question is, does > anybody > > know of an /easy/ way to do this? > > Ghci only displays values with a Show instance. > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

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package name in TypeRep?
by Johannes Waldmann 16 Oct '09

16 Oct '09

Dear all, I want a function that produces the URL of the haddocumentation of a given type, generically. My solution is that the argument (type) is an instance of Data.Typeable and I am parsing the output of show of the TypeRep, cf. http://dfa.imn.htwk-leipzig.de/cgi-bin/cvsweb/common/Gateway/Help.hs?rev=1.… That stops working when I split my project into several packages. Is there a way to obtain the package name from the TypeRep? Because I seem to need it to procuce the correct URL. Or else, is there a way to merge all the per-package haddock outputs? Perhaps a pseudo-package that imports all and re-exports everything? Best - Johannes.

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Merging classes
by pat browne 16 Oct '09

16 Oct '09

Hi, Following on from my earlier *Merging modules* email, where I tried to simulate ontology merging with Haskell modules; http://article.gmane.org/gmane.comp.lang.haskell.cafe/64943 I *think* that the type of merging that I am attempting is difficult with modules so I gave classes a try. I did not get very far (see below). Perhaps I need a combination of type classes and modules. In fairness this is more of a specification task than a programming task and perhaps I am barking up the wrong tree. Any help appreciated. Regards, Pat ============================================== attempting an ontology merge with type classes For specification of requirement see http://article.gmane.org/gmane.comp.lang.haskell.cafe/64943 ============================================== -- Data types for COMMON data Woman = WomanC data Person = PersonC -- Additional data type for ONTOLOGY1 data Bank = BankC -- Additional data type for ONTOLOGY2 -- but how do I let type Bank have the same name in both classes and -- still be distinct (homonyms) in the merged class -- data Bank = BankC class COMMON a b where class (COMMON a b) => ONTOLOGY1 a b where class (COMMON a b) => ONTOLOGY2 a b where class (ONTOLOGY1 a b, ONTOLOGY2 a b) => MERGEDONTOLOGY a b where -- not really sure how to proceed from here instance COMMON Woman Person where

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How to reliably open and close resources in MonadIO in the presence of exceptions?
by Bas van Dijk 16 Oct '09

16 Oct '09

> import Control.Monad.Trans ( MonadIO, liftIO ) > import Control.Exception ( throwIO, ArithException(DivideByZero), onException ) > import Foreign.Marshal.Alloc ( malloc, free ) > import Foreign.Storable ( poke, peek ) Suppose we define a function which receives a computation in an arbitrary monad that is capable of lifting IO actions and returns a computation in the same monad: > foo :: MonadIO m => m () -> m () In 'foo', I would like to open some resource (in this case: allocate memory) and after performing some lifted IO actions and some arbitrary computations in 'm' I want to close the resource (in this case: freeing the allocated memory). Of course the resource should also be closed when an exception is thrown in some lifted IO computation. If I was performing a computation directly in IO I could use: alloca :: Storable a => (Ptr a -> IO b) -> IO b which allocates the memory, performs some action on it and frees the memory after the action terminates (either normally or via an exception). Unfortunately the type of 'alloca' does not allow it to be used in our arbitrary monad 'm'. So it looks like I'm forced to manually allocate the memory using 'malloc' and finally free it using 'free'. To handle exceptions in lifted IO computations I have to put a (`onException` free ptr) around every lifted IO computation: For example: > foo action = do ptr <- liftIO malloc > liftIO $ putStrLn "aaa" `onException` free ptr > liftIO $ poke ptr (3 :: Int) `onException` free ptr > liftIO $ putStrLn "bbb" `onException` free ptr > action > x <- liftIO $ peek ptr `onException` free ptr > liftIO $ print x `onException` free ptr > liftIO $ putStrLn "ccc" `onException` free ptr > liftIO $ free ptr I find this rather ugly. What's worse is that exceptions, thrown in lifted IO computations in 'action' can't be handled! For example, the following won't free the memory: > bar :: MonadIO m => m () > bar = foo action > where > action = liftIO $ throwIO DivideByZero So my question is: How can I reliably open and close resources in MonadIO? And as a supplementary question: Is it possible to define a generalized alloca: genAlloca :: (MonadIO m, Storable a) => (Ptr a -> m b) -> m b Thanks, Bas

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ANN: Haskell Hackathon in Zurich, Switzerland
by Johan Tibell 16 Oct '09

16 Oct '09

Hi all! We are in the early stages of planning a Haskell hackathon/get together, ZuriHac, to be held this March at the Google office, in Zurich, Switzerland. Right now we're looking at four possible dates (Friday-Sunday): March 5-7, March 12-14, March 19-21, or March 26-28. If you might be interested in attending, please add your name on the wiki page: http://haskell.org/haskellwiki/ZuriHac#Possible_Attendees If you don't have an account on the wiki feel free to just respond to this email. If there are any dates that absolutely don't work for you then please note them on the wiki. I'll come back with a finalized date and more details soon. Hope to see you in Zurich! Johan Tibell (tibbe)

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