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ANNOUNCE: Parsec 3.1.1
by Antoine Latter 29 Jan '11

29 Jan '11

Parsec is a monadic combinator library that is well-documented, simple to use, and produces good error messages. Parsec is not inherently lazy/incremental and is not well-suited to handling large quantities of simply formatted data. Parsec 3 added to Parsec the ability to use Parsec as a monad transformer and generalizes the input Parsec accepts. This is a minor point release over Parsec 3.1.0. The changes in this release are: - A bug introduced in 3.1.0 which reduced the quality of error messages when failing to parse has been fixed - Typos in some of the Haddock documentation have been fixed - The package 'syb` is no longer a dependency Please note that there are a few changes which have not yet made it to the up-stream source repository, as code.haskell.org is experiencing a temporary outage. Link on Hackage: http://hackage.haskell.org/package/parsec-3.1.1 I'd like to thank Derek Elkins for prior his maintainer-ship of the package and for getting the Summer-Of-Code work released as parsec-3.0.

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3GB allocation, 75% CPU usage from a callback function
by Edward Amsden 29 Jan '11

29 Jan '11

I recently got the jack package from hackage working again. For those unfamiliar, jack is a callback-based audio server. Writing a client entails importing the C library or its bindings (the Sound.JACK module in my case), creating a client and some ports (using provided library functions), and then registering callbacks for audio processing. I've written a simple program that outputs a sine wave through JACK. The server's sample rate is 44100, which means that this function must be called 44100 times/second (it is buffered, so generally that would be in chunks of 64, 128, or 256). It is an IO function, which gives the only opportunity to keep track of time: (Note that the function produced by newSinWave is the one actually registered as a callback: newSinWave :: Int -> Float -> IO (CFloat -> IO CFloat) newSinWave sampleRate freq = do ioref <- newIORef (0::Integer) let multiplier = 2 * pi * freq / (fromIntegral sampleRate) return (\_ -> {-# SCC "sinWave" #-} do t <- readIORef ioref modifyIORef ioref (+1) return $ fromRational $ toRational $ sin (fromIntegral t * multiplier)) I profiled this since when my program registered with the jack server and started taking callbacks, it was using about 75% cpu (in contrast, the echo program included with the jack package uses less than 2%). The following two lines are of concern to me: "total alloc = 3,040,397,164 bytes (excludes profiling overheads)" My program uses 3GB of virtual memory over a 15 second run? " sinWave Main 341 1173295 100.0 100.0 0.0 0.0" and ~100% of that 75% cpu time is being spent in my callback. Is there something I'm doing wrong? At the very least, it shouldn't be using 3GB of memory. The only thing that needs to be saved between callbacks is the IORef, which is storing an Int. I assume that evaluating that whole construct in haskell may be too much timewise to put in a sound callback (or perhaps not), but 3GB of memory is ridiculous. Thoughts/hints/"you're doing it wrong" anyone? -- Edward Amsden Undergraduate Computer Science Rochester Institute of Technology www.edwardamsden.com

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GPL License of H-Matrix and prelude numeric
by gutti 29 Jan '11

29 Jan '11

Hi all, I realised that haskell in the base libraries tries to consistently stick to the permissive BSD license to also give the language traction in the commercial world. The H-Matrix and the prelude numeric packages however, which in my mind cover really important ground work, are issued under the resprictive GPL. Is that only because they link into other external GNU - libaries with GPL license ? -- If yes would be repackaging the haskell-native bits in an extra BSD package an option ? Cheers Phil -- View this message in context: http://haskell.1045720.n5.nabble.com/GPL-License-of-H-Matrix-and-prelude-nu… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Merry monad mixup?
by michael rice 28 Jan '11

28 Jan '11

The first and third work, but not the second. Why? Michael ============== f :: String -> IO () f s = do putStrLn s {- g :: [String] -> IO () g l = do s <- l putStrLn s -} {- h :: [Int] -> [Int] h l = do i <- l return (i+1) -} ============== serialize2.hs:29:9: Couldn't match expected type `[String]' against inferred type `IO String' In a stmt of a 'do' expression: s <- l In the expression: do { s <- l; putStrLn s } In the definition of `g': g l = do { s <- l; putStrLn s }

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source line annotations
by Evan Laforge 28 Jan '11

28 Jan '11

One of the first things I did when starting a larger haskell project was to write a preprocessor that would replace certain tokens with (token_srcpos (filename, func_name, lineno)) and then write x and x_srcpos versions of the various 'throw' and logging functions. This is extremely handy to have, and since logs are part of my app's UI, it's part of the app itself. I found out later that jhc has a pragma that basically does the same thing, only built in. My preprocessor works but has some problems. Namely, replacing non-qualified tokens requires parsing the source because you want to replace only function calls, not declarations, import / export lists, etc. I get around this because I always import qualified, but still I need to do some hacking to get qualified tokens ('lex' mysteriously doesn't understand them... aren't they in haskell 2010 now?) and not screw up on odd corners like backslash string continuations. Then I start wanting to e.g. replace 'throw' in the same module it's defined in, which really lets the dragons out because now I'm trying to replace unqualified names. Another problem is that the names to replace are hardcoded in the preprocessor. Not a problem for me, but would be for a general tool. My preprocessor works well, but occasionally I do have to go in and fix yet another odd corner that came up. Initially I thought I would only simplistically replace tokens and avoid using a full syntax parser, but to really do it correctly a full parser is needed. And of course this is specific to my style (qualified imports) and project. To do this in full generality really requires the compiler's help. But as I use it now, it's been extremely useful, especially for exceptions which may not carry a unique or easily greppable msg. Or any msg at all. Are there any more sophisticated tools out there that do this? Interest in extending ghc to support SRCLOC_ANNOTATE? Reasons why I don't actually want this after all?

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IsString instances for attoparsec-text
by Yitzchak Gale 28 Jan '11

28 Jan '11

Hi Felipe, Thanks so much for implementing the attoparsec-text package. Could you please add an IsString instance for Parser Text, parallel to the one in attoparsec? You may have missed this because of it being an orphan instance in attoparsec. It should be something like: instance IsString (Parser T.Text) where fromString = string . T.pack Thanks, Yitz

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Re: [Haskell-cafe] Haskell for children? Any experience?
by John Peterson 28 Jan '11

28 Jan '11

Hi all, I've had good luck with Haskore as a way to bring kids into functional programming. It's nice in that you can get a lot done in just 2 or 3 hours. Lately I've switched over to a 3D game engine using FRP to make the programming simple. I've been running a summer camp (https://www.western.edu/academics/computerscience/computer-camp.html) using this software with a lot of success. Unfortunately I had to abandon Haskell to get to our game engine, so I've rebuilt FRP on top of Python. The programming style is functional but it would be nice to have a real type system. We're in the process of getting a public release together this term. I really need to get all my web content moved off Yale - I'll be happy to share the software / papers with anyone that's interested. My slides and papers should re John Peterson jpeterson(a)western.edu

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Cabal proxy configuration
by Azeem -ul-Hasan 28 Jan '11

28 Jan '11

My university requires the students to use internet through an authenticated http proxy. How do I configure cabal for that? I am using Ubuntu. Please be detailed about it. Thanks Azeem

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Re: [Haskell-cafe] tricky recursive type instance method
by Antoine Latter 28 Jan '11

28 Jan '11

On Thu, Jan 27, 2011 at 10:09 PM, Frank Kuehnel <kuehnelf(a)gmail.com> wrote: > Hi Antoine, > > I've turned on the OverlappingInstances option > > this is what I get, when I execute > >> conj ((C 1 2) :: (Complex Int)) > > Overlapping instances for DAlgebra (Complex Float) (Complex Float) > arising from a use of `conj' > Matching instances: > instance [overlap ok] Real a => DAlgebra a a > -- Defined at Clifford.hs:21:10-31 > instance [overlap ok] (Real r, Num a, DAlgebra a r) => > DAlgebra (Complex a) r > I'm guessing GHC can't pick which instance to use, because neither one follows the rules for being more specific than the other. I tried to read the manual on it, but I don't have a clear answer for you: http://www.haskell.org/ghc/docs/7.0.1/html/users_guide/type-class-extension… If I change the `DAlgebra a a` instance to `DAlgebra Integer Integer` I can get examples to work fine. Antoine > > On Jan 27, 2011, at 8:00 PM, Antoine Latter wrote: > >> On Thu, Jan 27, 2011 at 9:35 PM, Frank Kuehnel <vincef13(a)mac.com> wrote: >>> Hi folks, >>> >>> how do I make this work: I want a division algebra over a field k, and I want to define >>> the conjugation of complex numbers, i.e. conj (C 1 2) but also the conjugation of tensors of complex numbers >>> conj (C (C 1 2) (C 1 4)) >>> >>> ghci load that stuff butt barfs on a simple >>>> conj (C 1 2) >>> >>> with >>> instance Real a => DAlgebra a a -- Defined at Clifford.hs:20:10-31 >>> instance (Real r, Num a, DAlgebra a r) => DAlgebra (Complex a) r >>> >>> >>> here's the code: >>> >>> -- for a normed division algebra we need a norm and conjugation! >>> class DAlgebra a k | a -> k where -- need functional dependence because conj doesn't refer to k >>> conj :: a -> a >>> abs2 :: a -> k >>> >>> -- real numbers are a division algebra >>> instance Real a => DAlgebra a a where >>> conj = id >>> abs2 x = x*x >>> >>> -- Complex numbers form a normed commutative division algebra >>> data Complex a = C a a deriving (Eq,Show) >>> >>> instance Num a => Num (Complex a) where >>> fromInteger a = C (fromInteger a) 0 >>> (C a b)+(C a' b') = C (a+a') (b+b') >>> (C a b)-(C a' b') = C (a-a') (b-b') >>> (C a b)*(C a' b') = C (a*a'-b*b') (a*b'+b*a') >>> >>> instance (Real r, Num a, DAlgebra a r) => DAlgebra (Complex a) r where >>> conj (C a b) = C a (conj (-b)) >>> abs2 (C a b) = (abs2 a) + (abs2 b) >>> >> >> >> What error are you getting in GHCi? It wasn't immediately clear from >> your email, but maybe I missed it. >> >> It looks like you have overlapping instances between `DAlgebra a a` >> and `DAlgebra (Complex a) r`, so if that's what you want you'll need >> to making sure you have the OverlappingInstances extension turned on. >> >> You might run in to other issues further on. >> >> Antoine >> >>> >>> Thanks for you help! >>> >>> _______________________________________________ >>> Haskell-Cafe mailing list >>> Haskell-Cafe(a)haskell.org >>> http://www.haskell.org/mailman/listinfo/haskell-cafe >>> > >

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bizzaro Network.Curl problems
by Michael Litchard 28 Jan '11

28 Jan '11

Has anyone ever experienced a situation similar to this? Wrote toy code to learn how to make a cookie jar. Toy code succeeds, add functionality and better organization. new improved program works correcty, as far as forming correct headers and GET requests. no cookie jar.. Checked old toy code, still works. Reduces new program to bare essentials until it looks like old toy program. Still, no cookie jar. Upshot is we are starting to suspect libcurl itself here and not the Network.Curl wrapper. Anyway, please respond if this bizzaro problem sounds familiar.

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