- Haskell-Cafe - Haskell.org

Stable pointers: use of cast to/from Ptr
by Yves Parès 13 Feb '12

13 Feb '12

Hello, According to the documentation ( http://hackage.haskell.org/packages/archive/base/4.5.0.0/doc/html/Foreign-S…) StablePtrs aims at being opaque on C-side. But they provide functions to be casted to/from regular *void**'s. Does that mean if for instance you have a StablePtr CInt you can cast it to Ptr () and alter it on C-side? void alter(void* data) { int* x = (int*)data; *x = 42; } -------------------------------------------------- -- using 'unsafe' doesn't change anything. foreign import ccall safe "alter" alter :: Ptr () -> IO () main = do sptr <- newStablePtr (0 :: CInt) deRefStablePtr sptr >>= print alter (castStablePtrToPtr sptr) -- SEGFAULTS! deRefStablePtr sptr >>= print freeStablePtr sptr But I tried it, and it doesn't work: I got a segfault when 'alter' is called. Is it normal? Does this mean I can only use my pointer as opaque? (Which I know to be working, as I already got a C function call back into Haskell and pass it the StablePtr via a 'foreign export') But in that case, what is the use of castStablePtrToPtr/castPtrToStablePtr, as you can already pass StablePtrs to and from C code? Thanks!

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hmatrix under ghci on x86_64
by Tom Doris 13 Feb '12

13 Feb '12

I'm using ghci + hmatrix and a few other packages as a Haskell based replacement for Matlab, everything works well so far in terms of available functionality. However, I have encountered an issue when running in ghci on x86_64 systems - calls into functions that in turn call gsl functions will result in a bus error, e.g: Prelude> :m +Numeric.Container Prelude Numeric.Container> randomVector 10 Gaussian 10 fromList Bus error (core dumped) I attached gdb and found the bus error was happening in gsl_rng_alloc() but some investigation indicate that the problem is probably due to this bug in ghci: http://hackage.haskell.org/trac/ghc/ticket/2912 which has been marked as a duplicate of http://hackage.haskell.org/trac/ghc/ticket/781 and a recent update to 781 indicates that it won't be addressed until at least v 7.6.1 (781 also references http://hackage.haskell.org/trac/ghc/ticket/3658 and it seems that this is a pretty large piece of work - moving to fully dynamically linked ghci which has been around for a while and pushed back a few times). Does anyone know of a workaround that would allow ghci to use wrapped gsl functionality on x86_64 systems in the meantime? Most linux boxes used by quants are x86_64 now, so this issue will impact many people who would like to use Haskell instead of Matlab. Thanks

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[ANNOUNCE] fb package, bindings to Facebook's API
by Felipe Almeida Lessa 13 Feb '12

13 Feb '12

Hello, everyone! I'm pleased to finally announce the fb package, a Haskell-only package that provides bindings to Facebook's API. This package is sponsored by my employer, which will soon enough be able to become the copyright holder of all of our open source contributions. http://hackage.haskell.org/package/fb It's by no means complete, but we thrive to be as correct as possible and to turn API errors into type errors caught at compile time. Right now the current version is fb 0.7.2. While this is the first announcement, this package is already being actively used by Facebook authentication code on Yesod (yesod-auth-fb package) and internally at my day job's projects. Hope you find it useful! =) Cheers, -- Felipe.

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Re: [Haskell-cafe] ANN: stm-conduit-0.2.1
by John Lato 13 Feb '12

13 Feb '12

> Message: 6 > Date: Sun, 12 Feb 2012 01:47:40 -0500 > From: wren ng thornton <wren(a)freegeek.org> > Subject: Re: [Haskell-cafe] ANN: stm-conduit-0.2.1 > To: Haskell Cafe <haskell-cafe(a)haskell.org> > Message-ID: <4F37608C.3090808(a)freegeek.org> > Content-Type: text/plain; charset=ISO-8859-1; format=flowed > > On 2/9/12 2:29 PM, Felipe Almeida Lessa wrote: >> Your package uses TMChans which AFAIK are unbounded. That means that >> if the writer is faster than the reader, then everything will be kept >> into memory. This means that using TMChans you may no longer say that >> your program uses a constant amount of memory. Actually, you lose a >> lot of your space reasoning since, being concurrent processes, you >> can't guarantee almost anything wrt. progress of the reader. > > Of course, you're free to use TBMChans instead, which are bounded :) This is what I did in iteratee-stm. The stm-chans package is very nice. (and the results with iteratee-stm were very good as well) John L.

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A universal data store interface
by Sergiu Ivanov 13 Feb '12

13 Feb '12

Hello, I am interested in applying for GSoC-2012 with the Haskell community. (I think I've told that to quite a number of people already, sorry for the duplicate.) I'm currently digging my way towards http://hackage.haskell.org/trac/ghc/ticket/4213 . However, instead of focusing on a single project right now, I'd like to diversify a bit and consider at least one more project. I've come over this: http://hackage.haskell.org/trac/summer-of-code/ticket/1605 . It looks quite interesting and also promising in the sense that it is going to be useful to many people. However, this page http://hackage.haskell.org/trac/summer-of-code/report/1 states the priority is undefined for this project, which makes me wonder whether the Haskell community would be interested in having a GSoC student work on the task. If the community is interested in having a student assigned to this task, I'd be glad to submit proposal for this project as well. Sergiu

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ghc-mod v1.10.3
by Kazu Yamamoto 13 Feb '12

13 Feb '12

Hello, I have just released ghc-mod v1.10.3. C-cC-t of this version was powered by Hideyuki Tanaka. The old implementation just show the type of the current expression on Emacs. Howver, the new implementation first show the type of the current expression and the expression is highlighted. If you type C-cC-t again, the region is enlarged to its upper expression, and its type is displayed. # I don't know well but this is called "annot" in the OCaml community Enjoy! --Kazu

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ANN: stm-conduit-0.2.1
by Clark Gaebel 13 Feb '12

13 Feb '12

Hi all, I've just released stm-conduit [1] on Hackage. This package introduces conduits to the wonderful world of concurrency. My package solves the common problem of constant bottleneck switching loaders have. This is when, for example, we stream XML from the disk and then parse the XML in one conduit pipeline. While it streams a file from the disk, the process is clearly IO bound, and while it parses the XML, the process is CPU bound. By putting each task on its own thread, the disk IO doesn't need to wait for the CPU to parse a document before loading the next file. By using stm-based conduits, we have full resource utilization. The way it does this is by creating a source and sink for TChans, letting us stream data between conduits and channels. There are more examples in the docs. Check it out! Regards, - clark [1] http://hackage.haskell.org/package/stm-conduit

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question regarding Data.Array.Accelerate
by Philipp 12 Feb '12

12 Feb '12

Hi, I have read the papers about the accelerate package that provides a high-level interface to nvidia's cuda library and am very intrigued. However, I have some start-up problems. Is this the right place for such questions? In particular, I'm having trouble with lifting and unlifting. From what I understood, I should be able to use unlift to get an Int from an Exp (Plain Int), but when I try, for example, (unlift . lift) (1::Int) :: Int ghci complains with "No instance for (Unlift Int)". I have the latest versions of accelerate (accelerate-0.9.0.1) and ghc (version 7.4.1). I think I'm missing something obvious, so if any of you could point it out to me I would be glad. Thanks, Philipp -- View this message in context: http://haskell.1045720.n5.nabble.com/question-regarding-Data-Array-Accelera… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Calling OpenGL functions from multiple threads
by Clark Gaebel 12 Feb '12

12 Feb '12

Do the OpenGL bindings on Hackage expose anything like glXMakeCurrent [1]? I need to use OpenGL functions from multiple threads (note: not at once, I protect it with an MVar), but that's forbidden in extension-less OpenGL. Thanks, - clark [1] http://www.talisman.org/opengl-1.1/Reference/glXMakeCurrent.html

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Any advices on optimizing an array processing in a pitch tuner
by Dmitry Vyal 12 Feb '12

12 Feb '12

Hello Haskellers, Recently I've revived my old toy project. It's a sound spectrum analyzer with Gtk2hs interface. I decided to rewrite it into a pitch tuner. Basically I'm done, but I've ran into performance difficulties while trying to rise a resolution in a frequency space. The original code used Storable arrays to get data out of fftw, for some processing I convert it to lists, which obviously hinders performance. I've heard there are some modern efficient array processing libraries available. So I hope I can avoid writing all those low-level for loops. Any hints on how to optimize and prettify the code are welcome. Repository is located at https://github.com/akamaus/HTuner Best regards, Dmitry

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