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REMINDER: Haskell Communities and Activities Report, May 2011 edition
by Janis Voigtländer 27 Apr '11

27 Apr '11

Dear all, It is not yet too late to contribute to the 20th edition of the ================================================================ Haskell Communities & Activities Report http://tinyurl.com/haskcar Submission deadline: this weekend (please send your contributions to hcar at haskell.org, in plain text or LaTeX format) ================================================================ If you haven't already, please write an entry for your new project or update your old entry. More information can be found in the original Call for Contributions at http://www.haskell.org/pipermail/haskell/2011-April/022720.html I look forward to your contributions, Janis (current editor) -- Jun.-Prof. Dr. Janis Voigtländer http://www.iai.uni-bonn.de/~jv/ mailto:jv@iai.uni-bonn.de

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[GSoC] Text/UTF-8: Call for Benchmarks
by Jasper Van der Jeugt 27 Apr '11

27 Apr '11

Hello all, I'm very glad that I have been accepted again this year for the Google Summer of Code [1] program for haskell.org. My project aims to improve the text [2] library by converting it to internally use UTF-8 instead of UTF-16. UTF-8 and UTF-16 both have advantages and disadvantages, which actually makes it a pretty complicated choice. I've written about this a little in my [3] (especially see Tom Harper's master dissertation if you're interested in the subject). To support a decision here on UTF-8 vs. UTF-16, lots of benchmarks will be needed. Hence, this is the first focus of the GSoC project: collecting a large benchmark suite which models real-world usage of the text library. This is why I'd like to ask everyone who has written/knows libraries or applications that use the text library extensively to inform me of these efforts. The reverse dependencies list on Hackage is a good starting point for me but it doesn't point out how popular these packages are and how intensively they use the text library. I will then convert a subset of this code to a benchmark suite using criterion. Open source code means more reliable benchmarks, because I can publish the code I used for them. However, I'm also willing to sign non-disclosure agreements if this means I can try out what effects the changes have on large systems. There's several ways to contact me: you can reply to this thread, or you can mail me privately using `jaspervdj+text@gmail.com`. Thanks in advance for any help! [1]: http://code.google.com/soc/ [2]: http://hackage.haskell.org/package/text [3]: http://jaspervdj.be/files/2011-gsoc-text-utf8-proposal.html Cheers, Jasper

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ANNOUNCE: New version Feldspar
by Emil Axelsson 27 Apr '11

27 Apr '11

On behalf of the Feldspar team, I'm happy to announce version 0.4.0.2 of feldspar-language and feldspar-compiler: http://hackage.haskell.org/package/feldspar-language http://hackage.haskell.org/package/feldspar-compiler Feldspar is an embedded domain-specific language for generating code for embedded applications, in particular for digital signal processing. For more information, see our web pages: http://feldspar.inf.elte.hu/feldspar/ http://feldspar.inf.elte.hu/ A brief list of changes since the last version: * Support for GHC 7. * Including a fresh tutorial for new users. * Improved C code generation (efficiency and readability). - Efficient vector append. - More unified representation of arrays in the C code. - Etc. * A new sequential construct for unfolding vectors using an accumulating parameter. * Support for structs. * New optimization: common sub-expression elimination. * Lots of restructuring under the hood. * Bugfixes. / Emil

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How to update the RNG per call (State monad) when generating QuickCheck arbitraries?
by Daniel Kahlenberg 27 Apr '11

27 Apr '11

Maybe this is a beginners question... But here my problems description: > import Random > import Control.Monad > import qualified Control.Monad.State as S > import Test.QuickCheck.Gen > import Test.QuickCheck.Arbitrary Each thing can have one of three types: > data Ontology = Thing1 Bool > | ThingK Bool > deriving (Show, Eq) > instance Arbitrary Ontology where > arbitrary = > oneof [ return $ Thing1 True > , return $ ThingK True > , return $ Thing1 False > , return $ ThingK False ] Liked to have a state monad runner for my arbitrary things as in "Real World Haskell", "Chapter 14. Monads" ("Random values in the state monad"). [RWH]: > -- file: ch14/Random.hs > type RandomState a = S.State StdGen a [RWH]: < -- file: ch14/Random.hs < getRandom :: Random a => RandomState a < getRandom = < S.get >>= \gen -> < let (val, gen') = random gen in < S.put gen' >> < return val [RWH]: < -- file: ch14/Random.hs < getTwoRandoms :: Random a => RandomState (a, a) < getTwoRandoms = liftM2 (,) getRandom getRandom [RWH]: < -- file: ch14/Random.hs < runTwoRandoms :: IO (Int, Int) < runTwoRandoms = do < oldState <- getStdGen < let (result, newState) = S.runState getTwoRandoms oldState < setStdGen newState < return result Thought getRandom function would be the best place to inject my unGen function call, but cannot get it to type-check: > getRandom :: Random a => RandomState [a] > getRandom = > S.get >>= \gen -> > let (val, gen') = liftM2 (,) (unGen arbitrary gen 12) (random gen) in > S.put gen' >> > return val A function not almost fulfilling my needs but the Random Number Generator isn't updated... I liked to have different [Ontology] occasions per call: > genArray :: [Ontology] > genArray = unGen arbitrary (mkStdGen 42) 12 :: [Ontology] Does anyone have the patience to help me out at least one step further? Cheers Daniel

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plugins and cabal build
by Michael Snoyman 27 Apr '11

27 Apr '11

Hi all, I'm experimenting with using the plugins package for yesod devel server. The basic approach is to use cabal for building the object files, and then load them with plugins. I can get everything to work when I compile with "ghc --make", but I believe name mangling is getting in the way with the "cabal build" route. Can someone give some guidance on how to properly mangle the function names so that plugins can load them? Thanks, Michael

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Creating polygons in qtHaskell
by Øystein Kolsrud 26 Apr '11

26 Apr '11

Hi! I'm using qtHaskell and I'm trying to create a QGraphicsPolygonItem object. From what I see I need to create a QPolygonF item that I can supply to the constructor, but to populate the QPolygonF I need to use methods of the QVector class that QPolygonF inherits and I can't figure out how to do that. It seems that QVector is not part of the qtHaskell library. What I would like to do is something like this (where mypoints is a list of QPointF): makePolygon = do polygon <- qPolygonF () mapM (pushBack polygon) mypoints qGraphicsPolygonItem_nf polygon However, pushBack doesn't seem to be available. Does anyone know a way to do this? -- Mvh Øystein Kolsrud

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ANNOUNCE: iteratee-compress 0.2.0.0
by Maciej Piechotka 26 Apr '11

26 Apr '11

Iteratee-compress provides compressing and decompressing enumerators including flushing (using John Lato's implementation). Currently only gzip and bzip is provided but LZMA is planned. Changes from previous version: - Add BZip support Next goals: - LZMA support - Generic interface for flushing To think about: - Should inner iteratee be able to request flushing Regards

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Re: [Haskell-cafe] Question about the Monad instance for Iteratee (from the enumerator package)
by John Lato 26 Apr '11

26 Apr '11

Joining slightly late... > From: John Millikin <jmillikin(a)gmail.com> > > John Lato's "iteratee" package is based on IterateeMCPS.hs[1]. I used > IterateeM.hs for "enumerator", because when I benchmarked them the non-CPS > version was something like 10% faster on most operations. > Based on tests I did before iteratee-0.4, the fastest implementation was Oleg's alternate design which is in the comments of IterateeM.hs. I don't think any current packages use that however, with good reason. I'd be interested to see the results of a shootout between iteratee and enumerator. I would expect them to be basically equivalent most of the time, with maybe two or three operations with a small (but consistent) difference one way or the other. John L.

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Haskell User Group starter kit
by Eric Y. Kow 26 Apr '11

26 Apr '11

Hi all, We may be coming to a time where we start to see Haskell User Groups or Functional Programming clubs popping up all the over the place. Maybe it's a good time to put our heads together and figure out what we can do to nurture these groups, to keep them going strong rather than fizzling out. One idea might be create some sort of Haskell User Group starter kit so that individual groups can hit the ground running with some concrete ideas. http://www.haskell.org/haskellwiki/Haskell_User_Group My hope is that it would provide just enough material for a group to reach critical mass. So just enough stuff to account for the different kinds of activities a HUG may want to do (eg. Coding Dojos vs Talks vs Reading Group), but not so much that HUGs feel intimidated or stifled. Have you started a HUG recently? Or are you thinking of starting one? Maybe you could contribute just one idea to the kit? More welcome, of course :-) -- Eric Kow <http://www.nltg.brighton.ac.uk/home/Eric.Kow> For a faster response, try +44 (0)1273 64 2905 or xmpp:kowey@jabber.fr (Jabber or Google Talk only)

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Re: [Haskell-cafe] How to update the RNG per call (State monad) when generating QuickCheck arbitraries?
by Bryan O'Sullivan 26 Apr '11

26 Apr '11

On Tue, Apr 26, 2011 at 9:16 AM, Daniel Kahlenberg <d.kahlenberg(a)gmail.com>wrote: > > hold on I'd like to have the genArray call generating distinctive > results in one IO execution The problem you're seeing is due to the fact that you're not taking the final RNG state from the first execution of your code and passing it as the initial state to the second. Since you're initialising each one with the same RNG state, you're getting the same results in each case.

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