- Haskell-Cafe - Haskell.org

ANN: funsat 0.5, a SAT solver written in Haskell
by Denis Bueno 10 Jun '08

10 Jun '08

Hi all, It is my pleasure to announce the first reasonable release of funsat, a modern, DPLL-style SAT solver written in Haskell. Funsat solves formulas in conjunctive normal form and produces a total variable assignment for satisfiable problems. It is available from Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/funsat http://churn.ath.cx/funsat.html As well as in a Git repo, which contains many benchmark files funsat can solve. git clone http://churn.ath.cx/funsat Funsat is intended to be reasonably efficient for practical problems and convenient to use as a constraint-solving backend in other software. The former is achieved by using several well-known techniques from the literature including two-watched literals, conflict-directed learning, non-chronological backtracking, a VSIDS-like dynamic variable ordering, and restarts. The latter is supported currently by efficient unsatisfiable core generation, which generates a minimal unsatisfiable problem for a given unsatisfiable problem. In the future, I plan to add support for converting boolean circuits into CNF, as well as support for other types of constraints. Please try it out and report bugs! (This email is the one listed on the website.) -- Denis

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File locking wishlist
by Joachim Breitner 09 Jun '08

09 Jun '08

Hi, for a program of mine (darcswatch[1]), a rather long running process is run at certain events (by cron, and by new emails). I want to achieve that: * Only one instance of the program runs at a time. * If new events come in while the program runs, it should re-run itself * There is information attached to the events (only one Bool ATM) So I’d like to implement something with this, or a similar, interface: ======================================================================= module MyLocking where -- | tries to get the lock. If it fails, notifies the running process -- to re-start itself afterwards, with the given information -- returns True if the lock was aquired lockOrMark :: Show a => FilePath -> a -> IO Bool -- | release the lock. If new events have come in, they are returned -- in the list, and the lock is still kept. If the list is empty, -- the lock was successfully released. releaseLock :: Read a => FilePath -> IO [a] ======================================================================= I would use this module in this way: realWork args = do someStuff args newArgs <- releaseLock "someDir/" unless (null newArgs) $ do -- we missed some events, so re-run and then try again. let newArg = combineInSomeWay newArgs realWork newArg main = do args <- getArgs l <- lockOrMark "someDir/" args when l $ do -- we got the lock, so lets work realWork args I hope this makes the idea clear. How could a possible implementation look like, when all operations should be atomic? I was considering this, would it work fine? lockOrMark would try to create a directory in the path. Whoever creates the directory has the lock. If it works, create. If it fails, because the directory already exists, then write the given args to a temporary file with a unique name, and move it into that directory. If that fails (because the directory has disappeared, i.e. the lock released), start over with trying to create the directory. If it works, then you are done. releaseLock would try to rmdir the directory. If that succeeds, no files have been in there, so no events were missed. If it does not succeed, then there were files. Read and delete them and return the list of arguments contained in them. Greetings, Joachim [1] http://darcswatch.nomeata.de/ -- Joachim Breitner e-Mail: mail(a)joachim-breitner.de Homepage: http://www.joachim-breitner.de ICQ#: 74513189 Jabber-ID: nomeata(a)joachim-breitner.de

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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 09 Jun '08

09 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 09 Jun '08

09 Jun '08

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