- Haskell-Cafe - Haskell.org

Hughes' parallel annotations for fixing a space leak
by Heinrich Apfelmus 22 Apr '10

22 Apr '10

Dear haskell-cafe, I've been thinking about space leaks lately. In particular, I've been studying the tricky example with pairs break [] = ([],[]) break (x:xs) = if x == '\n' then ([],xs) else (x:ys,zs) where (ys,zs) = break xs which was discussed in the papers Jan Sparud. Fixing some space leaks without a garbage collector. http://bit.ly/cOxcVJ Philip Wadler. Fixing some space leaks with a garbage collector. http://homepages.inf.ed.ac.uk/wadler/topics/garbage-collection.html As I understand it, GHC implements the technique from Sparud's paper, so this is a solved problem. (It will only kick in when compiled with optimization, though, so -O0 will make the above leak in GHC 6.10.4 if I checked that correctly.) Now, I'm wondering about alternative solutions. Wadler mentions some sort of parallel combinators break xs = (PAR before '\n' ys, PAR after '\n' zs) where (ys,zs) = SYNCLIST xs which were introduced by John Hughes in his Phd thesis from 1983. They are intriguing! Unfortunately, I haven't been able to procure a copy of Hughes' thesis, either electronic or in paper. :( Can anyone help? Are there any other resources about this parallel approach? Regards, Heinrich Apfelmus -- http://apfelmus.nfshost.com

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Adopting MissingPy?
by John Goerzen 22 Apr '10

22 Apr '10

Hi folks, MissingPy is a library I wrote a little while back that allows you to call Python code from Haskell. It's on Hackage and, as far as I know, still works. Trouble is, the need I used to have for it is gone. So I no longer use it myself for anything, and thus it is starting to bitrot. Would anyone like to take over maintenance of this project? Thanks, -- John

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Philadelphia Haskell hackathon -- reduced hotel rate ends Friday April 23!
by Brent Yorgey 21 Apr '10

21 Apr '10

There is still plenty of space to register [1] for Hac phi 2010, but time is running out to get a hotel room at a reduced rate --- if you want the special rate for the block of rooms we have reserved at the Club Quarters, you must contact the hotel by this Friday, April 23. Instructions are on the wiki [2]. If you have been thinking of coming but are not sure, let me emphasize that last year's Hac phi was great fun---it will be an excellent time to make new friends, expand your brain, eat good food, and of course write some Haskell. You are welcome and encouraged to attend whether you just want to learn Haskell or have been using it for 10 years! You also do not have to come for the whole time; feel free to come just for a day or even an afternoon. The original announcement is below. -Brent ---------- Hac phi 2010 is a Haskell hackathon/get-together to be held May 21-23 at the University of Pennsylvania in Philadelphia. The hackathon will officially kick off at 2:30 Friday afternoon, and go until 5pm on Sunday (with breaks for sleep, of course). Last year's Hac phi was a lot of fun, and many people have already expressed interest in coming back this year. I want to stress that everyone is welcome---you do not have to be a Haskell guru to attend! Helping hack on someone else's project could be a great way to increase your Haskell-fu. If you plan on coming, please officially register [1]. Registration, travel, lodging and many other details can be found on the Hac phi wiki [2]. Note that we're in a different space this year and may have to cap attendance, so register early. We're also looking for a few people interested in giving short (15-20 min.) talks, probably on Saturday afternoon. Anything of interest to the Haskell community is fair game---a project you've been working on, a paper, a quick tutorial. If you'd like to give a talk, add it on the wiki [3]. Hope to see you in Philadelphia! -The Hac φ team [1] http://haskell.org/haskellwiki/Hac_φ/Register [2] http://haskell.org/haskellwiki/Hac_φ [3] http://haskell.org/haskellwiki/Hac_φ/Talks

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Re: [Haskell-cafe] ANN: forkable-monad 0.1
by Limestraël 21 Apr '10

21 Apr '10

Nice initiative! By the way, since this is a monad, I think a better place than Control.Concurrent.Forkable would be Control.Monad.Forkable. It's just a suggestion. > 2010/4/21 David Anderson <dave(a)natulte.net> > > Dear Haskellers, >> >> I'm happy, and only slightly intimidated, to announce the initial >> release of forkable-monad. >> >> The short version is that forkable-monad exports a replacement forkIO >> that lets you do this: >> >> type MyMonad = ReaderT Config (StateT Ctx IO) >> >> startThread :: MyMonad ThreadId >> startThread = forkIO threadMain >> >> threadMain :: MyMonad () >> threadMain = forever $ liftIO $ putStrLn "Painless monad stack forking!" >> >> Note the lack of monad stack deconstruction and reconstruction to >> transport it over to the new thread. You'll find the details in the >> Haddock documentation for the module. >> >> forkable-monad is available: >> >> * On hackage: http://hackage.haskell.org/package/forkable-monad >> * Via cabal: cabal install forkable-monad >> * Source and issue tracker: http://code.google.com/p/forkable-monad/ >> >> Feedback is of course welcome. As this is my first published Haskell >> code and Hackage upload, I expect there will be quite a bit! >> >> - Dave >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> > >

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ANN: GPipe-Collada - Collada for Haskell!
by Tobias Bexelius 21 Apr '10

21 Apr '10

Hi, I've uploaded GPipe-Collada-0.1.0 to hackage (http://hackage.haskell.org/package/GPipe-Collada-0.1.0) that enables you to load Collada files to be used with GPipe. Check out Graphics.GPipe.Collada.Utils.viewScene for an example on how to use loaded Collada scenes (http://hackage.haskell.org/packages/archive/GPipe-Collada/0.1.0/doc/html/Gr…) For more information regarding Collada, including free sample files, visit http://www.collada.org. Cheers! Tobias _________________________________________________________________ Surfa tryggt med Internet Explorer 8 http://www.microsoft.com/sverige/windows/internet-explorer/default.aspx

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ANNOUNCE: Agata-0.2.0
by Jonas Almström Duregård 21 Apr '10

21 Apr '10

I'm pleased to announce Agata (Agata Generates Algebraic Types Automatically)! Avoiding excessive details, usage is best described by a small example: {-#LANGUAGE TemplateHaskell #-} import Test.QuickCheck import Test.AgataTH data X a b = X [Either a b] deriving Show data Y = Y deriving Show data Z = Z deriving Show $(agatath $ deriveall [''X,''Y,''Z]) main = sample (arbitrary :: Gen (X Y Z)) This code derives instances of Test.QuickCheck.Arbitrary for the data types X, Y and Z. http://hackage.haskell.org/package/Agata Regards Jonas

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Re: [Haskell-cafe] Bulk Synchronous Parallel
by Jason Dusek 21 Apr '10

21 Apr '10

2010/4/21 Aaron D. Ball <aarondball(a)gmail.com>: > I don't need a tool that automatically figures out how to distribute > any workload in an intelligent way and handles all the communication > for me. You are right in general. Only if you want to rely on purity and a few source code annotations to get you parallelism relatively cheaply do you care about these compiler approaches. This is something that Haskell can do that Ruby, C and friends really can not do -- thus I mention it. > If I have the basic building block, which is the ability to > serialize a Haskell expression with its dependencies and read them > into another Haskell instance where I can evaluate them, I can handle > the other pieces, which are > > - passing strings back and forth in whatever way is convenient > - deciding how to divide up my workload. Do add also, configuring servers and their connections. > In the Ruby universe, DRb combines the serialization and "passing > strings around" job and lets me figure out how to divide up the work, > and it would be delightful if there were something similarly simple in > the Haskell world. I think Holumbus has got some promising stuff for user-managed distributed workers: http://holumbus.fh-wedel.de/trac/browser/distribution What do you think? -- Jason Dusek

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instance Eq (a -> b)
by Ashley Yakeley 21 Apr '10

21 Apr '10

Why isn't there an instance Eq (a -> b) ? allValues :: (Bounded a,Enum a) => [a] allValues = enumFrom minBound instance (Bounded a,Enum a,Eq b) => Eq (a -> b) where p == q = fmap p allValues == fmap q allValues Of course, it's not perfect, since empty types are finite but not Bounded. One can nevertheless make them instances of Bounded with undefined bounds, and have enumFrom and friends always return the empty list. It seems one should also be able to write instance (Bounded a,Enum a) => Traversable (a -> b) where ??? But this turns out to be curiously hard. -- Ashley Yakeley

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hamming distance allocation
by Arnoldo Muller 21 Apr '10

21 Apr '10

Hello all: I want to generate some hamming distance statistics about a set of strings. As explained in another e-mail in this list, I used the following code to call the functions: (exampl holds the list of strings of size w) filter (\x -> x /= 0) $ map (uncurry hammingX) [(xs, ys) | xs <- exampl, ys <- exampl] I have two hamming functions: -- hamming distance for variable length strings hamming :: String -> String -> Int hamming x y = hamming' x y 0 where hamming' [] _ !c = c hamming' _ [] !c = c hamming' (x:xs) (y:ys) !c | x == y = hamming' xs ys c | otherwise = hamming' xs ys (c + 1) -- function posted in this mailing list hamming2 :: String -> String -> Int hamming2 xs ys = length (filter not (zipWith (==) xs ys)) I am executing these functions millions of times and the bottleneck of my program is in them as explained by running in profiling mode with +RTS -K400M -p -RTS The costlier function is the hamming distance COST CENTRE MODULE %time %alloc hamming Distances 66.6 41.9 It says that it is performing 41% of the allocations. In the case of hamming2 the allocations go as far as 52%. I could understand that there are allocations in "hamming2" because we are creating pairs, but in the case of "hamming" there should be no allocation. How can I execute my hamming functions without allocating memory? Best regards, Arnoldo Muller

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Re: [Haskell-cafe] Re: Move MonadIO to base
by Anders Kaseorg 21 Apr '10

21 Apr '10

On Tue, 20 Apr 2010, wren ng thornton wrote: > -- | The isomorphic Haskell98 version > class Monad m => MonadJoinIO m where > -- | Embed the IO into the monad m > joinIO :: IO (m a) -> m a > > -- | Extract the IO computation to the top level, > -- rendering the m pure from IO. > partIO :: m a -> IO (m a) > > -- | The isomorphisms > joinIO' m = morphIO (m >>=) > morphIO' f = joinIO (f partIO) To establish an isomorphism, you also need to define partIO from morphIO. For example, I don’t see how I could define partIO :: IO a -> IO (ReaderT r IO a) that extracts effects into the outer IO, because the effects depend on some unknown state of type r. By the way: > This bounced because I have different emails registered for cafe@ and > libraries@, so forwarding it along to the cafe. You can sign up both addresses for the list, then log in to the Mailman web interface ( http://www.haskell.org/mailman/listinfo/haskell-cafe → Unsubscribe or edit options) and disable mail delivery on one of them. Then you get one copy of each message but you can post from either address. Anders

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