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Re: [Haskell] ANNOUNCE: first Grapefruit release
by Jamie 16 Feb '09

16 Feb '09

On Mon, 16 Feb 2009, Wolfgang Jeltsch wrote: > [redirecting to haskell-cafe] > > Am Samstag, 14. Februar 2009 23:13 schrieben Sie: >> Great, does it run well on Windows and Mac platforms in addition to Linux >> platform which should run fine? > > Actually, I have no idea. ;-) > > Well, Grapefruit is a pure Haskell library without any own binding to C > libraries or whatever. For GUI stuff, Grapefruit relies completely on > Gtk2Hs. So if Gtk2Hs works, Grapefruit should work too. I just haven’t > tested it so far. Earlier Grapefruit code was successfully executed on > the Windows box of my co-developer. > > On the other hand, Grapefruit is designed to be implemented on top of > different toolkits, although currently there is only the Gtk2Hs backend. > So if you want to write a backend based on the Win32 API or Cocoa, this > would be very welcome. :-) Great. Well thought out design :) Other possible backends would be FLTK, GLUI, XBMC/Boxee (for set-top box apps) as well Qt and wxWidgets. I guess backends using Win32 API/Cocoa and FLTK would be the least bloated ones. >> I am planning to create video phone software and I was looking for good >> GUI toolkit that supports FRP so it looks like it is right time to use >> Grapefruit :) > > This would be really great. Writing applications with Grapefruit gives > me useful feedback and pressure for improvement. Note that currently the > set of supported widgets is very low but this is likely to change during > the next weeks and it should often be very easy to port Gtk2Hs widgets > to Grapefruit. Awesome! I'll be looking forward start using Grapefruit soon! :) >> Thanks >> >> Jamie > > Best wishes, > Wolfgang Jamie Clark

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createProcess shutting file handles
by Neil Mitchell 16 Feb '09

16 Feb '09

Hi, I want to run multiple programs and dump the stdout/stderr to a file, I've tried doing: h <- openFile file WriteMode let c = CreateProcess (RawCommand file []) Nothing Nothing Inherit (UseHandle h) (UseHandle h) False (_,_,_,pid) <- createProcess c waitForProcess pid hPutStrLn h "Test" But by the time I get to the hPutStrLn line it says: Main: test.log: hPutStr: illegal operation (handle is closed) What have I done wrong? Did createProcess close the handle, and is there a way round this? This is using GHC 6.10 on Windows with the new process-1.0.1.1 Thanks Neil

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Re: [Haskell-cafe] ANNOUNCE: first Grapefruit release
by Wolfgang Jeltsch 16 Feb '09

16 Feb '09

Am Sonntag, 15. Februar 2009 16:27 schrieben Sie: > Hi Wolfgang, > > Thank you for the excellent introduction Oh, I thought that you didn’t send you original question to the list and therefore answered you only privately. So the others don’t know yet the introduction you refer to (but see below). > (this would be good material to put on your Wiki). Done. :-) <http://haskell.org/haskellwiki/Grapefruit/Comparison_to_other_FRP_libraries> Conal, are you listening? If yes, could you please look over this page to make sure that I described your work correctly? Best wishes, Wolfgang

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Ann: Yogurt-0.3
by Martijn van Steenbergen 16 Feb '09

16 Feb '09

Dear Haskellers, I'm pleased to announce the release of Yogurt-0.3! This version improves over 0.2 in several ways: * It compiles and runs with GHC 6.10. * The Mud monad is now built on top of IO. * Vars are expressed as IORefs. No more unsafeCoerce needed. * Forking of threads is supported, with callback into the Mud monad: > type RunMud = forall a. Mud a -> IO a > forkWithCallback :: (RunMud -> IO ()) -> Mud ThreadId * Timers are no longer a primitive: they can be expressed as function of forkWithCallback. * Refactorings in the architecture: the features are a strict superset of the previous version while the number of lines of code has decreased by 10%. All feedback is appreciated! Thanks to Saizan on #haskell for helping me work around the predicative types. :-) The code is available at Google: http://code.google.com/p/yogurt-mud/ Kind regards, Martijn.

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Amazing
by Peter Verswyvelen 16 Feb '09

16 Feb '09

One of the things I liked a lot when working with C# was that as soon as my code compiled, it usually worked after an iteration of two.At least if we forget about the nasty imperative debugging that is needed after a while because of unanticipated and unchecked runtime side effects. After heaving read about Haskell and having written some small programs for the last year or so, I'm now finally writing a bigger program with it. It is not so easy yet since learning a language and trying to reach a deadline at the same time is hard :) However, it is just amazing that whenever my Haskell program compiles (which to be fair can take a while for an average Haskeller like me ;-), it just... works! I have heard rumors that this was the case, but I can really confirm it. A bit hurray for strong typing! (and if you don't like it, you can still use Dynamic and Typeable ;-)

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Re: permuting a list
by Jon Fairbairn 16 Feb '09

16 Feb '09

Heinrich Apfelmus <apfelmus(a)quantentunnel.de> writes: > The answer is a resounding "yes" and the main idea is that shuffling a > list is *essentially the same* as sorting a list; the minor difference > being that the former chooses a permutation at random while the latter > chooses a very particular permutation, namely the one that sorts the input. > > For the full exposition, see > > http://apfelmus.nfshost.com/random-permutations.html I haven't been following the thread, but my initial reaction would have been something like use System.Random.randoms to get a list rs and then do (roughly) randomPerm = map snd . sortBy (compare `on` fst) . zip rs How bad is that? I mean, how unfair does it get? -- Jón Fairbairn Jon.Fairbairn(a)cl.cam.ac.uk http://www.chaos.org.uk/~jf/Stuff-I-dont-want.html (updated 2009-01-31)

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ANNOUNCE: hslibsvm-2.88.0.1 - A FFI binding to LibSVM
by S. Günther 16 Feb '09

16 Feb '09

The result of the fact that I needed to use a support vector machine and didn't want to leave haskell land. LibSVM is a support vector machine library written in C++ with an exposed C interface. More information about LibSVM can be found at: http://www.csie.ntu.edu.tw/~cjlin/libsvm/ This is my first haskell package so any suggestions for improvement are welcome. kind regards Stephan Günther ----------------------------------------------------------------------------

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Re: [Haskell-beginners] Re: [Haskell-cafe] Re: permuting a list
by Alberto Ruiz 16 Feb '09

16 Feb '09

Heinrich Apfelmus wrote: > Alberto Ruiz wrote: >> How about using random doubles? >> >> randomPerm xs = fmap (map snd . sort . flip zip xs) rs >> where rs = fmap (randoms . mkStdGen) randomIO :: IO [Double] > > Interesting idea. The chance of duplicates should be negligible now, but > that's because we're using a large amount of random bits, far more than > n! would require. Another possibility is using infinite lists of random bits as keys. Then we only extract from the random number generator the number of bits required to avoid duplicates. -Alberto

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Confused by SYB example with zipping
by Henry Laxen 16 Feb '09

16 Feb '09

Dear Group, When trying to run the example at: http://www.cs.vu.nl/boilerplate/testsuite/gzip/Main.hs ghc 6.10.1 says A pattern type signature cannot bind scoped type variables `a' unless the pattern has a rigid type context In the pattern: f :: a -> a -> a In the definition of `mkTT': mkTT (f :: a -> a -> a) x y = case (cast x, cast y) of { (Just (x' :: a), Just (y' :: a)) -> cast (f x' y') _ -> Nothing } In the definition of `main': main = print $ gzip (mkTT maxS) genCom1 genCom2 where genCom1 = everywhere (mkT (double "Joost")) genCom genCom2 = everywhere (mkT (double "Marlow")) genCom double x (E (p@(P y _)) (S s)) | x == y = E p (S (2 * s)) double _ e = e maxS (S x) (S y) = S (max x y) .... Failed, modules loaded: CompanyDatatypes. --------------------------------------------------------------------- I must admit I don't really know what to make of this. Any insights would be appreciated. Thanks. Henry Laxen

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Parameterized monad transformers
by Miran Lipovača 16 Feb '09

16 Feb '09

Howdy y'all! I was reading sigfpe's Beyond Monads post (http://blog.sigfpe.com/2009/02/beyond-monads.html) about parameterized monads. Great post, makes you go: this is so elegant and simple, why didn't I think of that? Anyway, I was wondering whether those monads have corresponding transformers, and if so, what they look like and what they are good for? Is there any weight to the idea at all? I don't know much about monad transformer theory, but I do imagine that for transformers to be useful, they have to be stackable, so the underlying monad of a parameterized monad also has to be a parameterized monad. I asked around in #haskell and ski_ and I had a couple of ideas exploring the concept (although he did most of the exploring, I just carried his luggage). Seeing how parameterized monads are gotten by just loosening some restrictions on normal ones and drawing then parallels between them, I think the same methodology could be applied to transformers. So there should be a transformer version t of a parameterized monad m and a lifting operation plift that lifts m to t. At first I did what sigfpe did with non-transformer monads, which was to just implement the appropriate functions for the more general monads and see what GHCI tells us about the type. I first thought about having a parameterized StateT, PStateT: newtype PStateT m s1 s2 a = PStateT { runPStateT :: s1 -> m (a, s2) } along with a lifting operation plift :: (PMonad m) => m s1 s2 a -> t (m s1 s2) s3 s3 a but I don't think that's cool because of the different kind of the underlying monad. So then ski_ suggested newtype PStateT m (s1,s1') (s2,s2') a = PStateT { runPStateT :: s1 -> m s1' s2' (Pair a s2) } where (s1,s1') and (s2,s2') stand for the pair of types and not a (,) type constructor with two types applied as type parameters. That's why the pair in the result is represented as Pair a s2. Anyway, s1' and s2' represent the category tail and head of the underlying parameterized monad. With that, the lifting operation would have a type of plift :: (PMonad pm) => pm s1 s2 a -> t pm (s, s1) (s, s2) a basically I'm just wondering how you guys think the transformer versions of parameterized monads work and what their types should be. And if you think they're feasible at all. So basically just talk about parameterized monad transformers here :] Cheerio!

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