- Haskell-Cafe - Haskell.org

Haskell in image processing
by Ralf Laemmel 23 Dec '09

23 Dec '09

Disclaimer: this is an Xmas gift as opposed to serious stuff. http://professor-fish.blogspot.com/2009/12/major-breakthrough-in-image-proc… Greetings, Ralf

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Missing symbol when trying to use OpenCLRaw
by Dan Piponi 23 Dec '09

23 Dec '09

Can anyone tell me what command line options I need to build a simple example using OpenCLRaw on MacOSX (ghc 6.10.4)? Using "-framework OpenCL" reduces the missing symbols down to just _clGetProgramInfo but I can't see how to eliminate that last one. Has anyone else played with OpenCLRaw? -- Dan

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ANN: hnn-0.1, a haskell neural network library
by Alp Mestan 23 Dec '09

23 Dec '09

Hi, I just released the first version of my Haskell Neural Network library. It provides the very minimal features anyone would need in a neural network library. It has yet to be completed (regarding the features) and there are some ways for opitmizations. Though, I'd be very glad to hear from Haskellers about this library, get feedback, etc. Some links to get started with HNN : http://www.haskell.org/haskellwiki/HNN http://hackage.haskell.org/package/hnn -- hackage page http://mestan.fr/haskell/hnn/ -- online documentation http://alpmestan.wordpress.com/2009/12/23/hnn-0-1-has-been-released/ Please don't hesitate to try it and play with it and give as much feedback as you want ! Haskelly yours. -- Alp Mestan http://alpmestan.wordpress.com/ http://alp.developpez.com/

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Control.Parallel and the Reader monad
by Paul Brauner 23 Dec '09

23 Dec '09

Hi, I'm facing the following problem. I've got come computation c :: a -> Reader e b that i'm running on several as: mapM c xs A natural optimisation of this program would to be to take advantage of Control.Parallel to run these computation in parallel, which seems sound since the Reader monad is commutative. Unfortunately, I didn't manage to do so. Has this situation been tackled with before ? Is there some library or function I've missed involving commutative monads and Control.Parallel ? Regards, Paul

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Children elements with HXT
by Tony Morris 23 Dec '09

23 Dec '09

I am trying to parse XML using HXT following http://www.haskell.org/haskellwiki/HXT/Conversion_of_Haskell_data_from/to_X… Here is my XML file (way.xml): <way id="27776903" visible="true" timestamp="2009-05-31T13:39:15Z" version="3" changeset="1368552" user="Matt" uid="70"> <tag k="access" v="private"/> <tag k="highway" v="service"/> </way> The problem is when parsing, by reading the <tag> entries into the list held by the Way data structure, I cannot get anything but an empty list. Here is my parsing code: import Text.XML.HXT.Arrow newtype Way = Way { tags :: [Tag] } deriving (Eq, Show) xpWay :: PU Way xpWay = xpElem "way" (xpWrap (Way, tags) (xpList xpTag)) data Tag = Tag { k :: String, v :: String } deriving (Eq, Show) xpTag :: PU Tag xpTag = xpElem "tag" (xpWrap (uncurry Tag, k &&& v) (xpPair (xpAttr "k" xpText) (xpAttr "v" xpText))) When I run, I get the following result: Main> run = runX (xunpickleDocument xpWay [] "way.xml") [Way {tags = []}] Why is the tags list empty instead of holding two entries? -- Tony Morris http://tmorris.net/

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profiling problem
by Ketil Malde 23 Dec '09

23 Dec '09

Hi, I guess I should report this? Previously, this program got a signal 11, and that happened somewhat later in the process, so I'm not sure how reproducible it is. Source and data is available, if it is of any interest. (This is using the GHC currently shipped with Ubuntu 9.10.) xml2x3prof: internal error: traverseWeakPtrList: not WEAK (GHC version 6.10.4 for x86_64_unknown_linux) Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug Command terminated by signal 6 3577.55user 48.81system 1:00:27elapsed 99%CPU (0avgtext+0avgdata 0maxresident)k 0inputs+0outputs (0major+1306970minor)pagefaults 0swaps -k -- If I haven't seen further, it is by standing in the footprints of giants

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Are functional dependencies around to stay?
by Günther Schmidt 22 Dec '09

22 Dec '09

Hi everyone, I'm wondering if there is any chance that functional dependencies will not be around in the future. I do not actually understand the subject yet as such, but I'd like to make sure before I get deeper into it that it's something that will be around in the time to come. What I understand of Haskell is that it's not so much "engineered" like other languages but more "derived" from Math, well the very foundations anyway. But some things I can not determine whether or not they are derived from math and thus will stay, or are engineered and might go away, functional dependencies for instance. Günther

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what happend with the docs of base-libs in 6.10.4
by Günther Schmidt 22 Dec '09

22 Dec '09

Hi, I was just trying to consult my html-documentation of ghc-6.10.4 libraries on Windows. Almost all of the Standard Monads are missing, State, Writer etc. What happened, how do I get them back? Günther

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Visible space with lhs2tex
by Felipe Lessa 22 Dec '09

22 Dec '09

Hello! Does anyone know if it is possible to turn spaces inside strings to visible spaces. That is, format " test" as "\textvisiblespace{}test" With the 'listings' package there's the option 'showspaces'. However, unfortunately this and obvious variations don't work: %format " " = "\textvisiblespace" Thanks in advance! :) -- Felipe.

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Re: [Haskell-cafe] sizeOf on a type
by Patai Gergely 22 Dec '09

22 Dec '09

Hi, > I would like to write a routine like > > nextPtr :: Storable a => Ptr a -> Ptr a > nextPtr = (`plusPtr` sizeOf (undefined :: a)) > > which increments a pointer by the correct amount, but > GHC complains that the type variable "a" is ambiguous. Maybe Foreign.Marshal.Array.advancePtr is what you really need in this case. Gergely -- http://www.fastmail.fm - The professional email service

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