March 2009 - Haskell-Cafe

SQL Parsers in Haskell
by Mads Lindstrøm 17 Mar '09

17 Mar '09

Hi Haskelleers Has anybody written a SQL parser in Haskell (and is willing to share the code) ? Greetings, Mads Lindstrøm

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ANNOUNCE: libffi 0.1 released
by Remi Turk 17 Mar '09

17 Mar '09

I am happy to announce libffi 0.1, binding to the C library libffi, allowing C functions to be called whose types are not known before run-time. Why? Sometimes you can't use the haskell foreign function interface because you parse the type of the function from somewhere else, i.e. you're writing an interpreter for a language that has an FFI itself. What? The main function it exports is: callFFI :: FunPtr a -> RetType b -> [Arg] -> IO b And because code is worth a thousand words, here a small program that uses C to write a 1Gb buffer of random garbage to a file: > import System.Posix.DynamicLinker > import Foreign.LibFFI > > main = do > malloc <- dlsym Default "malloc" > creat <- dlsym Default "creat" > write <- dlsym Default "write" > let sz = 2 ^ 30 > buf <- callFFI malloc (retPtr retVoid) [argCSize sz] > fd <- callFFI creat retCInt [argString "/tmp/test", argCUInt 0o644] > n <- callFFI write retCSize [argCInt fd, argPtr buf, argCSize sz] > putStrLn $ show n ++ " bytes written" It should work on any 32/64bits machine on which libffi works, but has been primarily tested on linux x86_64. The current libffi is not exception-safe (exception = memory leak) and callFFI has quite some overhead that would be unnecessary with another api. It is, however, very easy to use :) More interesting examples are included in examples/ in the package. Where? Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/libffi Module docs: http://www.science.uva.nl/~rturk/doc/libffi-0.1 Cheers, Remi

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DLL Hell: OpenGL
by Mark Spezzano 17 Mar '09

17 Mar '09

Hi all, I’m trying to make the Teapot OpenGL example in Haskell on Windows. It keeps coming up with this: C:\Users\Mark\workspace2\OpenGLPractice\src>ghc --make Teapot Linking Teapot.exe ... C:\ghc\ghc-6.10.1\gcc-lib\ld.exe: cannot find -lSM collect2: ld returned 1 exit status As far as I know, -lSM is to do with XWindows (not windows Vista).How do I fix this ? What’s going on? I’ve been on this problem now for hours, and all I wanted to do was get a window up on the screen. Sigh Mark Spezzano No virus found in this outgoing message. Checked by AVG. Version: 7.5.557 / Virus Database: 270.11.15/2004 - Release Date: 16/03/2009 7:04 AM

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GHC Core - technical document
by Peter Verswyvelen 17 Mar '09

17 Mar '09

Does an up-to-date technical document exist describing GHC Core? Google found http://www.haskell.org/ghc/docs/papers/core.ps.gz I'm not sure this document reflects the current state of art.

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Haskell, OpenGL on Windows
by Mark Spezzano 17 Mar '09

17 Mar '09

Hi, Can someone PLEASE help me to understand exactly how to configure OpenGL on Window using Haskell. I'm using Eclipse IDE. When I try to run the file Test1.hs in GHCi then I get the following error: Loading package syb ... linking ... done. Loading package base-3.0.3.0 ... linking ... done. Loading package array-0.2.0.0 ... linking ... done. Loading package containers-0.2.0.0 ... linking ... done. Loading package OpenGL-2.2.1.1 ... can't load .so/.DLL for: GL (addDLL: could not load DLL) Prelude Main> I've copied the GLUT dll into Windows/System32. Is there some flag or option that I need to enable to tell Haskell where to go to link in the library. What do I do with the other .h and .lib files from GLUT? Thanks Mark

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Re: [Haskell-cafe] Polynomial and VectorSpace
by Henning Thielemann 16 Mar '09

16 Mar '09

On Mon, 16 Mar 2009, Matthew Donadio wrote: > Thy polynomial and matrix libraries weren't really developed to be stand > alone libraries. I was developing some DSP libraries that required > polynomial and matrix math, so I implemented what I needed so I could test > the DSP. Both libraries work for lower orders, but I suspect they are buggy > with big inputs. My long term goal was to interface with LAPACK and/or GSL > for the numeric heavy lifting, but that never happened. > > The same goes for the FFT library. That was written in support of the DSP > libraries, and also as a learning exercise for me (to better understand > how/why the FFT works). FFTW was the long term goal. In the meantime fftw and gsl-matrix interfaces exist on Hackage.

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using Typeable with STRefs
by Michael Vanier 16 Mar '09

16 Mar '09

Hi, I'm having a problem using Typeable with STRefs. Basically, I want to store STRefs (among other things) in a universal type. STRef is an instance of Typeable2, which means that STRef s a is Typeable if s and a are both Typeable. The problem is that the state type s is opaque and I can see no way to make it Typeable (other than making it RealWorld, and I don't want to use IO for this). If this is the case, then AFAICT there is no point in having STRefs be instances of Typeable2. Am I missing something? Here's the code I'd like to write: import Data.Typeable import Data.STRef import Control.Monad.ST data Value = forall a . Typeable a => V a deriving Typeable getValue :: Typeable a => Value -> Maybe a getValue (V v) = cast v -- I need the Typeable s constraint for the code to compile, but I'd rather leave it out. test :: Typeable s => ST s Integer test = do ref <- newSTRef (10 :: Integer) let refVal = V ref case getValue refVal of Nothing -> error "BAD" Just r -> readSTRef r -- This doesn't compile, because s is not Typeable. test2 :: Integer test2 = runST test Thanks in advance, Mike

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darcs fundraising drive - only $720 left to go!
by Eric Kow 16 Mar '09

16 Mar '09

Hi everybody, Just a quick update on the fundraising drive. We are trying to raise $1000 to help pay for travel to the upcoming Haskell hackathon (the second of our biannual darcs hacking sprints). So far we have raised $280, so we're almost a third of the way there. Think you can help? Details on this page http://www.darcs.net/donations.html Many thanks! Eric PS. Ultimately, what we are trying to buy is *time*. So if you have a few spare moments in your week, the most generous donation you can make is by offering us a little of your time. Come join us in Utrecht, 17-19 April or on #darcs! Otherwise, we accept Paypal :-) -- Eric Kow <http://www.nltg.brighton.ac.uk/home/Eric.Kow> PGP Key ID: 08AC04F9

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Re: [Haskell-cafe] Lambda-Cube 3D render engine
by Csaba Hruska 16 Mar '09

16 Mar '09

2009/3/16 Duane Johnson <duane.johnson(a)gmail.com> > Looks great! > By any chance, is the mesh loading functionality separate from the texture > loading? > Yes, it is completly separated from material, it only refers to material's name. You can define the material writing a nice human readable script: http://www.ogre3d.org/docs/manual/manual_14.html#SEC23 > > -- Duane Johnson > > On Mar 16, 2009, at 1:01 PM, Csaba Hruska wrote: > > Hi! > > I've created a wiki page for my project. > Currently only some text and screenshot are available. > Additional documentation and source code are coming soon.. :) > > http://www.haskell.org/haskellwiki/LambdaCubeEngine > > Cheers, > Csaba Hruska > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > > >

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Polynomial and VectorSpace
by Peter Verswyvelen 16 Mar '09

16 Mar '09

The DSP package on Hackage seems to contain complex polynomial functions. It seems these functions are completely independent of the other DSP functions, so this package could be split of? Also, polynomials form a vector space, so could be made an instance of VectorSpace class?

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