February 2009 - Haskell-Cafe

Sparse vector operations
by Grzegorz Chrupala 27 Feb '09

27 Feb '09

Hi all, In a couple of my projects I have needed to perform operations on (very) sparse vectors. I came up with the attached simple module which defines a typeclass and implements instances for simple and nested (Int)Maps. Is this the right way to go about it? Am I reinventing some wheels? Comments welcome. Best, -- Grzegorz http://www.nabble.com/file/p22247686/SparseVector.hs SparseVector.hs -- View this message in context: http://www.nabble.com/Sparse-vector-operations-tp22247686p22247686.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Trouble building ArrayRef 0.1.3
by Mads Lindstrøm 27 Feb '09

27 Feb '09

Hi When I try to build ArrayRef 0.1.3 I get: Control/Concurrent/LockingBZ.hs:159:54: Ambiguous type variable `e' in the constraint: `Exception e' arising from a use of `throw' at Control/Concurrent/LockingBZ.hs:159:54-60 Probable fix: add a type signature that fixes these type variable(s) I am compiling with: > runhaskell Setup.hs build I run Debian Linux with GHC 6.10.1. Anybody has a solution for my problem? Greetings, Mads Lindstrøm

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Making the pointfree package work with cabal
by Niemeijer, R.A. 27 Feb '09

27 Feb '09

Today I was very happy to discover the pointfree package, since lambdabot unfortunately doesn't work on Windows. The package works just fine, but the installation process is less than ideal. "cabal install pointfree" doesn't work and to install it manually you have to add containers and array to the build-depends list in the cabal file. To get rid of the warning about the build type you have to add build-type: Simple. I asked in the IRC channel what the best course of action was to fix this and they referred me here. The author of the package is Thomas Jäger, who should go by the IRC name TheHunter. I would hereby like to ask him to make these small changes and upload a new version, or to give me or someone else permission to do so. Regards, Remco Niemeijer

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Data.Binary, strict reading
by Neil Mitchell 27 Feb '09

27 Feb '09

Hi, I want to read a file using Data.Binary, and I want to read the file strictly - i.e. when I leave the read file I want to guarantee the handle is closed. The reason is that (possibly immediately after) I need to write to the file. The following is the magic I need to use - is it all necessary, is it guaranteed correct, should I use something else? src <- decodeFile "_make/_make" Map.size mp `seq` performGC Thanks for all the helpful replies to the last post, I think I've nearly come up with a minimal test case I can give you, or at least characterise where the issue might lie. But I'll post to that thread when I've got the details. Thanks Neil

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Strict version of Data.Map.map
by Edsko de Vries 27 Feb '09

27 Feb '09

Hi, Is it possible to write a strict version of Data.Map.map (so that the Map becomes strict in the elements as well as the keys)? Thanks, Edsko

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darcs and Google Summer of Code
by Eric Kow 27 Feb '09

27 Feb '09

Dear Haskellers, Recently, there has been a suggestion that darcs apply to be a mentoring organisation for Google Summer of Code in its own right. Thanks! I think we will definitely try this out! Ideas: GUI and hashed-storage ----------------------------- So far, we have two active projects, active in the sense that there are interested students and mentors. The first is to work towards a sort of graphical interface for darcs (as has been suggested on this list). I suspect that we what we will likely do with this idea is to refine it into something that may either be part of a GUI (like a patch dependency viewer), or which will make it much easier for third parties to write a GUI in the future. I'll note that last year, we had a few interested students for this year and a potential mentor (Shelarcy from wxHaskell). Hopefully we can call on them again this year? There is also some work by Wolgang Jeltsch and students that we could talk about extending into a GSoC project. The second idea is to continue our performance work. Petr Ročkai has done some very interesting work in optimising the way that darcs stores files for its hashed and darcs-2 format repositories. In one of his tests, he reports having a possible tenfold speed-up in darcs whatsnew times, and a halving of the number of filesystem calls in one his tests. <http://bugs.darcs.net/issue1202>. It would be very interesting to see Petr continue this sort of work and perhaps tie it into of some of the other optimisations the darcs community have in mind. Anyway, you may be interested to know that we have a parallel discussion going on about this on the darcs-users list: http://lists.osuosl.org/pipermail/darcs-users/2009-February/017766.html We are also keeping a summary of this discussion here with our active ideas: http://wiki.darcs.net/index.html/GoogleSummerOfCode Hackathon --------- Finally, darcs will be holding its second hacking sprint within the Haskell Hackathon, April 17-19, Utrecht. There's already at least 5 of us from darcs/camp, and we would love to see more of you. Or if you're already planning on joining Hac5, come hack a little darcs while you're there! http://wiki.darcs.net/index.html/Sprints/2009-04 Hope to see you soon, -- Eric Kow <http://www.nltg.brighton.ac.uk/home/Eric.Kow> PGP Key ID: 08AC04F9

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Incremental array updates
by Daniel Kraft 27 Feb '09

27 Feb '09

Hi, I seem to be a little stuck with incremental array updates... I've got an array of "few" (some thousand) integers, but have to do a calculation where I incrementally build up the array. For sake of simplicity, for now I don't use a State-Monad but simply pass the array as state down the recursive calls. Unfortunatelly, I seem to experience problems with lazyness; when I run my program, memory usage goes up to horrific values! The simple program below reproduces this; when run on my machine, it uses up about 300 MB of real and 300 MB of virtual memory, and the system starts swapping like mad! I compiled with ghc --make -O3, ghc version 6.8.3 if that matters. BTW, I tried to make the array update strict using the `seq` as below, but with no effect... What am I doing wrong here? Many thanks, Daniel import Data.Array; arraySize = 1000 limit = 100000 type MyArray = Array Int Int emptyArray :: MyArray emptyArray = array (0, arraySize - 1) [ (i, 0) | i <- [0 .. arraySize - 1] ] procOne :: Int -> MyArray -> MyArray procOne a cnt | a > limit = cnt | otherwise = let ind = a `mod` arraySize oldcnt = cnt ! ind newarr = cnt // [(ind, oldcnt + 1)] in procOne (a + 1) (newarr `seq` newarr) main :: IO () main = do arr <- return $ procOne 0 emptyArray print $ arr ! 42

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ByteString questions
by Galchin, Vasili 27 Feb '09

27 Feb '09

Hello, 1) I noticed there is no "open" function in Data.ByteString. So when I call writeFile or readFile is there an implicit open? 2) For both readFile and writeFile, the first parameter is of type FilePath (which is of course alliased to just String). In any case, for Windows and POSIX OS's like Linux can read and write to a serial device like RS232 by specfiying the device path, e.g. /dev/tty01? Thanks, Vasili

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Missing documentation for Haddock
by Colin Paul Adams 27 Feb '09

27 Feb '09

On http://haskell.org/haddock/doc/html/module-attributes.html the not-home attribute is missing (it's documentation is present, but the attribute itself is not named). -- Colin Adams Preston Lancashire

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base-4 + gtk2hs-0.10.0 licensing
by Victor Nazarov 27 Feb '09

27 Feb '09

I wonder what software licence I can use to release my application. I've developed some education tool with the following dependencies: % ghci Main.hs GHCi, version 6.10.1: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer ... linking ... done. Loading package base ... linking ... done. Ok, modules loaded: Main, UI, Lambda, Lambda.Eval, Lambda.Zipper, Lambda.Show, Lambda.Parser, Lambda.Common. Prelude Main> main Loading package syb ... linking ... done. Loading package array-0.2.0.0 ... linking ... done. Loading package containers-0.2.0.0 ... linking ... done. Loading package bytestring-0.9.1.4 ... linking ... done. Loading package Win32-2.2.0.0 ... linking ... done. Loading package parsec-2.1.0.1 ... linking ... done. Loading package mtl-1.1.0.2 ... linking ... done. Loading package old-locale-1.0.0.1 ... linking ... done. Loading package time-1.1.2.2 ... linking ... done. Loading package glib-0.10.0 ... linking ... done. Loading package cairo-0.10.0 ... linking ... done. Loading package gtk-0.10.0 ... linking ... done. Loading package glade-0.10.0 ... linking ... done. I just don't know the options and I think licensing is subtle enough to ask for suggestions. Thanks in advance. -- Victor

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