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How to use roots package?
by Artyom Kazak 24 Mar '11

24 Mar '11

Hi Café! roots (http://hackage.haskell.org/package/roots) is a package to solve equations like "f(x)==0". In RootFinder class there is an 'defaultNSteps' value, which is used as maximal count of iterations functions like findRoot and traceRoot can make. By default it is 250, but sometimes it's not enough. How can I use another value instead of 250? Should I write my own RootFinder instance, or findRoot function? Thanks in advance. — Artyom.

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a finite free category
by Vasili I. Galchin 23 Mar '11

23 Mar '11

Hello, Does there exist Haskell to generate a finite free category from a finite multipath graph with loops? Thank you, Vasilki

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Installation of Haskell Platform on CentOS 5.5
by frode k 23 Mar '11

23 Mar '11

Hi. I've spent some time trying to setup the Haskell Platform on CentOS 5.5: # cat /proc/version Linux version 2.6.18-028stab070.14 (root@rhel5-build-x64) (gcc version 4.1.2 20080704 (Red Hat 4.1.2-46)) #1 SMP Thu Nov 18 16:04:02 MSK 2010 I've compiled from source, similar to what is done here: http://www.haskell.org/pipermail/haskell-cafe/2010-April/076489.html Installation of GHC 7.0.2 failed: # ./configure --prefix=/usr/haskell-platform-2011.2.0.0/ checking for path to top of build tree... utils/ghc-pwd/dist/build/tmp/ghc-pwd: /lib64/libc.so.6: version `GLIBC_2.9' not found (required by utils/ghc-pwd/dist/build/tmp/ghc-pwd) utils/ghc-pwd/dist/build/tmp/ghc-pwd: /lib64/libc.so.6: version `GLIBC_2.7' not found (required by utils/ghc-pwd/dist/build/tmp/ghc-pwd) configure: error: cannot determine current directory I had to use GHS 6.12.3 which compiled without errors. However when I tried installing the Haskell Platform I ran into problems. Briefly, this is what I did and what happened trying to "make" it: wget http://hackage.haskell.org/platform/2010.2.0.0/haskell-platform-2010.2.0.0.… unpack... ./configure --prefix=/usr/haskell-platform-2010.2.0.0/ make # make scripts/build.sh ************************************************** Scanning system for any installed Haskell Platform components... Found:None. New packages to install: None! All done. ************************************************** Building "/usr/haskell-platform-2010.2.0.0/bin/ghc" "--make" "Setup" "-o" "Setup" "-package" "Cabal-1.8.0.6" Linking Setup ... collect2: ld terminated with signal 15 [Terminated] Error: Compiling the Setup script failed make: *** [build.stamp] Error 2 I first thought it was related to the fact that Cabal was using the /tmp directory for executables, but the alias trick (alias cabal="TMPDIR=/foo cabal") did not help. Anyone have got any ideas on what might be causing this? Can it me any missing dependencies? I've gone through the list described at http://www.vex.net/~trebla/haskell/haskell-platform.xhtml and used "yum install" to get the software mentioned. Regards, Frode

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Haskell internship in the south of France
by David Waern 23 Mar '11

23 Mar '11

To all undergrads on this list: Are you a student looking for an internship? Do you want to work with Haskell in the south of France? My company, Amadeus, is able to offer an internship on the subject of property-based testing of XML schema based web service APIs. The project goal is to write an XML test case generation tool in Haskell. The exact length of the intership can be discussed. It may be six months or a full year. XML based web services may not be the most fashionable technology, but this is a chance to apply Haskell to real world problems! Also, you get to work in Sophia-Antipolis, a beautiful technology park close to Nice on the French riviera. Contact me if you're interested! David

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Looking for feedback on my attempt at a tree construction edsl
by C K Kashyap 23 Mar '11

23 Mar '11

Hi, With my "edsl", one can describe a tree like this - import TreeEdsl import Data.Tree createTree :: TreeContext String () createTree = do insertSubTree "Fruits" $ do insertLeaf "Apple" insertLeaf "Mango" insertSubTree "Arbitrary" $ do insertSubTree "Numbers" $ do insertLeaf "1" insertLeaf "2" insertLeaf "3" insertSubTree "Letters" $ do insertLeaf "A" insertLeaf "B" insertLeaf "C" return () main = do tree <- process "root" createTree putStrLn (drawTree (fmap show tree)) return () and get a tree like this - "root" | +- "Arbitrary" | | | +- "Letters" | | | | | +- "C" | | | | | +- "B" | | | | | `- "A" | | | `- "Numbers" | | | +- "3" | | | +- "2" | | | `- "1" | `- "Fruits" | +- "Mango" | `- "Apple" My code is here https://github.com/ckkashyap/LearningPrograms/blob/master/Haskell/edsl/Tree… I'd appreciate your feedback on this. Does this qualify to be a edsl? Regards, Kashyap

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Help optimising a Haskell program
by David MacIver 23 Mar '11

23 Mar '11

Hi, I have a Haskell program I'm trying to optimise, and could use some assistance. It's for rank aggregation - taking a bunch of partial rankings of some items from users and turning them into an overall ranking (aka "That thing that Hammer Principle does"). The code is here: https://github.com/DRMacIver/hs-rank-aggregation. The interesting code lives in the Algorithms.RankAggregation module. The sample data I'm running it on is samples/electornot (voting data from http://electornot.org.uk/) Here's a profile: https://gist.github.com/1ee9356f45330e9f8caa Here's a recent profile: https://gist.github.com/1ee9356f45330e9f8caa It's doing pretty well on this data, in that it's taking 8 seconds for 180k records (down from about 80 seconds earlier today) on my computer, but I'd like it to be faster - ideally under a second. Admittedly this is an arbitrary figure and I will just move the goal posts if I achieve it, but it would still be nice. :-) I suspect that it may be hitting the limits of what can be improved without actually changing the algorithm (which I'm open to doing, but not if it makes the results significantly worse), but the last 3 or 4 times I've thought that it was shortly followed by an optimisation which halved the runtime or better. In particular the most likely culprit for improvement is to deal with the fact that it allocates nearly 5GB of data (that appears to be mostly transient - watching the process as it runs the memory usage never seems to raise above 150MB, which is large but unproblematic). The biggest culprit for this is divideAndConquer which is probably generating a silly number of intermediate lists, but it's not obvious how to fix that - maybe by making the tree structure in the recursion more explicit? Don't know. Suggestions very welcome. Regards, David

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Computing the multiplication table of a group using the GHC inliner ; )
by Daniel Schüssler 23 Mar '11

23 Mar '11

Hello, turns out that you can define the group operation of the symmetric group on 3 elements in this abstract way (via the isomorphism to the group of bijective functions from a three-element type to itself): s3mult g2 g1 = fromFun (toFun g2 . toFun g1) and convince GHC to compile it down to a nested case statement. It even somehow made the left multiplication with the identity non-strict. Just thought it's neat ;) $ ghc-core S3.hs -funfolding-use-threshold=64 ... -- identifiers manually un-qualified for readability s3mult = \ (g2_ahA :: S3) (g1_ahB :: S3) -> case g2_ahA of _ { S3abc -> g1_ahB; S3bca -> case g1_ahB of _ { S3abc -> S3bca; S3bca -> S3cab; S3cab -> S3abc; S3acb -> S3bac; S3bac -> S3cba; S3cba -> S3acb }; S3cab -> case g1_ahB of _ { S3abc -> S3cab; S3bca -> S3abc; S3cab -> S3bca; S3acb -> S3cba; S3bac -> S3acb; S3cba -> S3bac }; S3acb -> case g1_ahB of _ { S3abc -> S3acb; S3bca -> S3cba; S3cab -> S3bac; S3acb -> S3abc; S3bac -> S3cab; S3cba -> S3bca }; S3bac -> case g1_ahB of _ { S3abc -> S3bac; S3bca -> S3acb; S3cab -> S3cba; S3acb -> S3bca; S3bac -> S3abc; S3cba -> S3cab }; S3cba -> case g1_ahB of _ { S3abc -> S3cba; S3bca -> S3bac; S3cab -> S3acb; S3acb -> S3cab; S3bac -> S3bca; S3cba -> S3abc } } -- inverse s3inv = \ (g_ahC :: S3) -> case g_ahC of _ { S3abc -> S3abc; S3bca -> S3cab; S3cab -> S3bca; S3acb -> S3acb; S3bac -> S3bac; S3cba -> S3cba } --- end core --- --- source --- module S3 where -- | Symmetric group / permutation group on 3 elements data S3 = S3abc | S3bca | S3cab | S3acb | S3bac | S3cba deriving(Eq) -- | Returns an element of S3 satisfying the given predicate s3the :: (S3 -> Bool) -> S3 s3the p | p S3abc = S3abc | p S3acb = S3acb | p S3bac = S3bac | p S3bca = S3bca | p S3cba = S3cba | p S3cab = S3cab | otherwise = error "s3the: no element satisfies the predicate" data ABC = A | B | C deriving(Eq) toFun :: S3 -> ABC -> ABC toFun g = case g of S3abc -> mkFun A B C S3bca -> mkFun B C A S3cab -> mkFun C A B S3acb -> mkFun A C B S3bac -> mkFun B A C S3cba -> mkFun C B A where mkFun imA _ _ A = imA mkFun _ imB _ B = imB mkFun _ _ imC _ = imC fromFun :: (ABC -> ABC) -> S3 fromFun f = s3the (\g -> toFun g A == f A && toFun g B == f B) s3mult :: S3 -> S3 -> S3 s3mult g2 g1 = fromFun (toFun g2 . toFun g1) s3inv g = s3the (\g' -> s3mult g' g == S3abc)

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Install GTK on Windows
by Daniel Díaz 23 Mar '11

23 Mar '11

Hi, cafe, I know this has been treated many times, but I've tried install GTK so hard without any success that I decided to ask for help. Firstly, I followed the instructions listed in HaskellWiki [1]. No results. Then, I followed the instruction from the Mark Shroyer blog [2]. No results. I did some mixing of the two guides, too, but my error was always the same: Configuring cairo-0.12.0... [...] setup.exe: Missing dependencies on foreign libraries: * Missing C libraries: z, cairo Configuring glib-0.12.0... [...] setup.exe: Missing dependencies on foreign libraries: * Missing C libraries: gobject-2.0, gthread-2.0, glib-2.0, intl I've searched for these libraries, and, with --extra-include-dirs=, I've included them. But the same error was thrown. I'm sure I'm doing something wrong or, perhaps, I'm missing something. Any help is welcomed! Thanks in advance, Daniel Díaz References: [1] http://www.haskell.org/haskellwiki/Gtk2Hs [2] http://markshroyer.com/2010/10/gtk2hs-on-windows/

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Haskell and friends in Spanish
by Manuel Hernandez 22 Mar '11

22 Mar '11

Dear Haskellers, I have tried to compile from my own work and from several sources a university-level course in functional and logic programming, and the result is a prospect of a book (*right now only in Spanish*), which I have entitled "Programación declarativa". Perhaps someone could be interested in giving it a look. The book is big (more than 400pp and 2Mb) and eclectic wrt declarative topics (ranging from Scheme to Prolog), but Haskell has an ample treatment. Some parts of the book are even unfinished, but I think the book may be valuable for some Spanish-speaking people wishing to learn declarative programming through functional programming and Prolog. The book can be downloaded from: http://sites.google.com/site/writingsmhg/haskell/SpanishDeclarativeProgramm… Corrections and suggestions are welcome. Bests, -- Dr Manuel Hernández Gutiérrez Profesor-Investigador, Oficina num. 14 Coordinador del Doctorado en Tecnologías de Cómputo Aplicado. Área de Estudios de Posgrado. Instituto de Computación Universidad Tecnológica de la Mixteca Km 2.5 de la Carretera a Acatlima Huajuapan de León, Oaxaca, México 69000 Tel. +52 (953) 53 2 03 99 extensión 200 Fax +52 (953) 53 2 02 14 www.utm.mx

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Bamse package virus false positive
by Isaac Potoczny-Jones 22 Mar '11

22 Mar '11

We have realized that a file in the Bamse distribution in Hackage is being flagged by some virus scanners as malicious, including Symantec and McAfee. We have worked with Microsoft, Symantec, and McAfee to analyze the data. All parties have concluded that this file is not malicious, but we wanted to let the community know in case you run across a similar issue. We have notified the maintainer. Symantec and McAfee have updated their rules accordingly and will no longer flag this file, but other virus scanners might continue to flag it. Note that if you use Bamse to build MSI packages, inclusion of this file could cause some scanners to flag the package. The details of this file are as follows: File name: Folder.exe File Size: 83249 byte MD5: 9f939a06344af9b242a7b43849defb40 SHA1: a9faf0915d1ea142b161bec57792ef2ca379ce5b URL: http://hackage.haskell.org/package/bamse From the package description: "Bamse is a framework for building Windows Installers for your Windows applications, giving you a comprehensive set of features to put together MSIs using Haskell." peace, isaac

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