June 2008 - Haskell-Cafe

Re: [Haskell-cafe] ANNOUNCE: hfann-01
by Olivier Boudry 09 Jun '08

09 Jun '08

On Mon, Jun 9, 2008 at 11:29 AM, Don Stewart <dons(a)galois.com> wrote: > Excellent. Would you like to upload it to hackage.haskell.org, so it can > be easily installed with the 'cabal install' tool? > > Hi all, As suggested by Don, I just uploaded the hfann package to hackage.haskell.org. It's available here: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hfann Best regards, Olivier.

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"sum" in hmatrix and blas?
by Xiao-Yong Jin 09 Jun '08

09 Jun '08

Hi, probably I am just being dumb, but what is the most efficient way to do a sum of every elements in a Vector of either hmatrix or blas? I know there is sum of absolute values from BLAS. So what about I want a plain "sum"? I can only think of the following two ways. 1. Using Data.List.foldl', so it is > sum' = foldl' (+) 0 . toList in hmatrix or > sum' = foldl' (+) 0 . elems in blas. 2. Using <.>, so it is > sum' v = constant 1 (dim v) <.> v in hmatrix or > sum' v = constant (dim v) 1 <.> v in blas. Which one is better? I guess it probably depends on the internal implementation of BLAS, but I am actually thinking in some thing similar to > t += *v++; Any delightful idea to convert my mind from a C shaped one to a Haskell shaped one? Best, Xiao-Yong -- c/* __o/* <\ * (__ */\ <

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ANNOUNCE: hfann-01
by Olivier Boudry 09 Jun '08

09 Jun '08

Hi all, I'm pleased to announce the first release of the hfann module ( http://code.haskell.org/~oboudry/hfann/) This module is an interface to the "Fast Artificial Neural Network (FANN)" library (see http://leenissen.dk/fann/) This is an early release. At the moment the hfann module does not cover all the functions found in the FANN library but it should be useable to train and use simple Neural Networks. At least is can be used to run an equivalent of the "Getting Started" example found in http://leenissen.dk/fann/html/files2/gettingstarted-txt.html. The module was developped on Windows XP with GHC-6.8.2. The README should provide you with all required information to install this module. The haddock documentation should give enough information to get started using it. == Installation == Download version 2.0 of the FANN library from: http://leenissen.dk/fann/download.php and build it according to the instruction found on: http://leenissen.dk/fann/html/files2/installation-txt.html Get the hfann module darcs get http://code.haskell.org/~oboudry/hfann/ Build it using Cabal runghc Setup.lhs configure runghc Setup.lhs build runghc Setup.lhs haddock runghc Setup.lhs install == Examples == Training an ANN to the xor function: > import HFANN > main = do > withStandardFann [2,3,1] $ \fann -> do > setActivationFunctionHidden fann fannSigmoidSymetric > setActivationFunctionOutput fann fannSigmoidSymetric > trainOnFile fann "xor.data" -- train data > 20000 -- max epochs > 100 -- epochs between reports > 0.001 -- desired error > saveFann fann "xor.ann" C:\Temp\Haskell\hfann\examples\xor>Train.exe Max epochs 20000. Desired error: 0.0010000000. Epochs 1. Current error: 0.2503675520. Bit fail 4. Epochs 100. Current error: 0.0181358512. Bit fail 0. Epochs 169. Current error: 0.0009599295. Bit fail 0. Using the trained ANN on the 4 possible input values to the xor function (-1 = False, 1 = True). > import HFANN > main = do > withSavedFann "xor.ann" $ \fann -> do > mapM_ (\x -> runFann fann x >>= print) [[-1,-1],[-1,1],[1,-1],[1,1]] C:\Temp\Haskell\hfann\examples\xor>Use.exe [-0.950566361876292] [0.9178714756661263] [0.9457588340834527] [-0.9482816646878051] The "xor.data" training data content: 4 2 1 -1 -1 -1 -1 1 1 1 -1 1 1 1 -1 The files for this example can be found in the "examples/xor" directory == Bug reports, suggestions and comments are welcome. You can send them directly to my e-mail address. Olivier.

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Moving "forall" over type constructors
by Klaus Ostermann 09 Jun '08

09 Jun '08

At first I'd like to thank Claus, Ryan, Edsko, Luke and Derek for their quite helpful replies to my previous thread. In the course of following their advice I encountered the problem of moving a "forall" quantifier over a wrapper type constructor. If I have > newtype Wrapper a = Wrapper a and I instantiate Wrapper with a polymorphic type, then it is possible to move the quantifier outside: > outside :: Wrapper (forall a. (t a)) -> (forall a. Wrapper (t a)) > outside(Wrapper x) = Wrapper x (surprisingly the code does not work with the implementation 'outside x = x'; I guess this is a ghc bug) However, the other way around does not work: > inside :: (forall a. Wrapper (t a))-> Wrapper (forall a. (t a)) > inside x= x results in the following error: Couldn't match expected type `forall a. t a' against inferred type `t a' Expected type: Wrapper (forall a1. t a1) Inferred type: Wrapper (t a) In the expression: x In the definition of `inside': inside x = x Any ideas on how to make this work? Klaus

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Quick question for a slow program
by Slavomir Kaslev 09 Jun '08

09 Jun '08

Hello, I was just brushing my haskell-fu skills writing a solution for Google Treasure Hunt Problem 4. Hers is what it looks like: > primes = sieve [2..] > where > sieve (p:xs) = p : sieve [x | x <- xs, x `mod` p /= 0] > > sumOf n l = sum (take n l) : sumOf n (tail l) > > find l = foldl1 aux l > where > aux (x:xs) (y:ys) | x == y = x : aux xs ys > | x < y = aux xs (y:ys) > | x > y = aux (x:xs) ys > > puzzle = find (reverse [primes, p7, p17, p41, p541]) > where > p7 = sumOf 7 primes > p17 = sumOf 17 primes > p41 = sumOf 41 primes > p541 = sumOf 541 primes > > main = do mapM (\x -> putStrLn $ show x) puzzle While the code is quite readable and straight forward it is as slow as tortoise with four legs broken. What optimizations would you suggest, while still keeping the code clear and highlevel? Thank you in advance. Cheers. -- Slavomir Kaslev

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Package updates on haskell.org
by Don Stewart 09 Jun '08

09 Jun '08

The HWN, which I'm sadly too busy to maintain now, had a useful function of generating recent package releases and getting them on the wiki, and to people's inboxes. This facility has been replaced by two processes: 1) Users can subscribe to recent package updates via RSS: http://hackage.haskell.org/packages/archive/recent.rss 2) The 'hackage2hwn' script now runs to keep the http://haskell.org 'Recent Package Updates' section fresh, listing the latest updates. So you can always find the newest 20 packages by looking at haskell.org Cheers, Don

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Fwd: [Haskell-cafe] FunPtr error?
by Galchin, Vasili 08 Jun '08

08 Jun '08

So Luke .. how do I go from (Sigval -> ()), i..e notifyFunc, to FunPtr using the suggested data constructors? On Sun, Jun 8, 2008 at 10:01 PM, Luke Palmer <lrpalmer(a)gmail.com> wrote: > 2008/6/8 Galchin, Vasili <vigalchin(a)gmail.com>: > > Hello, > > > > I am getting what is to me a mysterious error in a test case that I > am > > writing: > > vigalchin@ubuntu:~/FTP/Haskell/unix-2.2.0.0/tests/timer$ runhaskell > > Setup.lhs build > > Preprocessing executables for Test-1.0... > > Building Test-1.0... > > [1 of 1] Compiling Main ( ./timer.hs, > > dist/build/timer/timer-tmp/Main.o ) > > > > ./timer.hs:11:45: Not in scope: data constructor `FunPtr' > > There is a *type* called FunPtr in scope, but not a data constructor > as you are using it. That is, you could say: > > foo :: FunPtr (Int -> IO ()) > > That is, use the type called FunPtr, but you may not use a *function* > called FunPtr, because it doesn't exist. You need to use functions > like nullFunPtr, castPtrToFunPtr, etc. to construct FunPtrs. > > Luke >

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Vancouver Haskell users meeting
by Jon Strait 08 Jun '08

08 Jun '08

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Printing a random list
by Bryan Catanzaro 08 Jun '08

08 Jun '08

I'm just starting out with Haskell, and I could use some help. I'm trying to create a random list and print it out, which seems simple enough, but has been giving me problems. Here's what I have: module Main where import IO import Random randomList :: Random a => a -> a-> [IO a] randomList lbound ubound = randomRIO(lbound, ubound) : randomList lbound ubound main = do myRandomList <- sequence(randomList(0::Int 255)) putStrLn(show(take(10 myRandomList))) ----- So, I have tried to make a randomList action which defines an infinite random list, bounded by lbound and ubound. It seems that to print this, I need to convert between randomList, which is of type [IO a] to something like IO [a], which is what sequence should do for me. Then I just want to print out the first 10 elements. I'm currently getting the error "Only unit numeric type pattern is valid", pointing to 0::Int 255 in the code. I'm not sure what this means. I'm sure I'm looking at this the wrong way, since I'm new to Haskell and haven't quite wrapped my head around it yet. Maybe you can fix the problem by showing me a more Haskell approach to creating a random list and printing it... =) Thanks! - bryan catanzaro

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Patrick Perry's BLAS package
by Alberto Ruiz 08 Jun '08

08 Jun '08

Hello all, I have just noticed that yesterday this fantastic package has been uploaded to hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/blas-0.4 We finally have a high quality library for numeric linear algebra. This is very good news for the Haskell community. Patrick, many thanks for your excellent work. Do you have similar plans for LAPACK? Alberto

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