August 2009 - Haskell-Cafe

Snow Leopard Breaks GHC
by David Leimbach 27 Sep '09

27 Sep '09

Just thought I'd point out that my old GHC install is now broken by the update to Snow Leopard. Dave

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matching types in Haskell
by pat browne 17 Sep '09

17 Sep '09

Hi, I wish to align or match some Haskell types in order to represent a set of ontologies and their embedded concpts [1]. I am not sure wheather modules or classes could be used. I have done this task in a language called Maude[2]. The code is below. I appreciate that Maude is not very popular so there is a brief description below. This diagram below represents the semantics of what I am trying to achive. I want to construct MERGEDONTOLOGY from ONTOLOGY1 and ONTOLOGY2 both of which are based on COMMON. MERGEDONTOLOGY { Woman, RiverBank, FinancialBank, HumanBeing} /\ /\ / \ / \ / \ / \ / \ / \ ONTOLOGY1 ONTOLOGY2 {Woman, Bank, Person} {Woman, Bank, Human} /\ /\ \ / \ / \ / \ / \ / \ / \ / {Woman , Person} COMMMON Each Maude module represents (below) a distinct ontology, each sort (or type in Haskell) represents a concept. This example includes both synonyms and homonyms. I want to align ONTOLOGY1 and ONTOLOGY2 w.r.t COMMON to produce MERGEDONTOLOGY. The details of the concepts are as follows. The Woman concept should be the same in all ontologies, there is only one Woman concept and it is named as such in each ontology. Hence there should be only one Woman.MERGEDONTOLOGY There is only one concept HumanBeing.MERGEDONTOLOGY, but there are 3 synonyms Human.ONTOLOGY2, Person.ONTOLOGY1, and Person.COMMON It would seem that Person.COMMON should be mapped (or renamed?) to Human.ONTOLOGY2 which in turn is renamed (or mapped) to HumanBeing.MERGEDONTOLOGY. The homonyms are Bank.ONTOLOGY1 and Bank.ONTOLOGY2 which should become distinct entities in RiverBank.MERGEDONTOLOGY and FinancialBank.MERGEDONTOLOGY My question is how should this be done in Haskell. Is there a classes only solution? Is ther a module only solution? Or do I need both? Regards, Pat ============================================= Brief description of Maude code In the Maude Language the module is the basic conceptual unit. Sorts are declared in modules Every line ends with a space dot. In this case each module is bracketed by fth .. endfth There are various types of mappings between modules. In this case I used renamings where the syntax is *( name_in_source_module to name_in_target_module....) The keyword protecting is a type of inport. The + symbol between the modules forms a new module that includes all the information in each of its arguments ============================== fth COMMON is sorts Woman Person . endfth fth ONTOLOGY1 is protecting COMMON . sorts Bank . endfth fth ONTOLOGY2 is protecting COMMON *( sort Person to Human) . sorts Bank . endfth fth MERGEDONTOLOGY is including (ONTOLOGY1 * (sort Bank to RiverBank,sort Person to HumanBeing)) + (ONTOLOGY2 * (sort Human to HumanBeing, sort Bank to FinancialBank)) . endfth with the command show all MERGEDONTOLOGY the system will produce the following module fth MERGEDONTOLOGY0 is sorts Woman HumanBeing FinancialBank RiverBank . endfth ================================ Reference [1]Shapes of Alignments Construction, Combination, and Computation by Oliver Kutz, Till Mossakowsk, and Mihai Codescu http://www.informatik.uni-bremen.de/~okutz/shapes.pdf [2] Informa tiom on Maude at: http://maude.cs.uiuc.edu/

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Announce: EnumMap-0.0.1
by John Van Enk 15 Sep '09

15 Sep '09

Hi List, I've uploaded a first version of EnumMap to hackage. EnumMap is a generalization of IntMap that constrains the key to Enum rather than forcing it to be Int. I have no idea what impact this has on performance, but it still passes all the tests that ship with IntMap. (My guess is that performance will be similar/identical unless I've missed something.) If this package competes in speed (especially with an Int key) with IntMap, I'd expect this could be merged into the containers package as an IntMap replacement. The source comments/copyright/license hasn't been changed since this is a derivative work of the original IntMap package. http://hackage.haskell.org/package/EnumMap Comments/benchmarks/criticism is appreciated. Merging this in with containers eventually would be more appreciated. :) John Van Enk

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HDBC Oracle bindings(?/!)
by Thiago Arrais 15 Sep '09

15 Sep '09

Are there Oracle bindings for HDBC anywhere? The HDBC project page talks about Oracle backends but there isn't an Oracle-specific driver listed (I assume one can reach an Oracle backend through the ODBC interface?). I started writing Oracle bindings for HDBC based on the Takusen code. It was done mostly for playing than for anything else and certainly isn't production ready, but it is available in a darcs repo at http://thiagoarrais.com/repos/hdbc-oracle in case anyone is interested. This code isn't ready for prime time yet and I'm looking for some that *is*. Is there such a thing already? Cheers, Thiago Arrais -- Enjoy Chaos - http://blog.thiagoarrais.com Thoughts, ideas and useless ranting about software development and technology

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Can't install chp (confused by cabal yet again)
by Colin Paul Adams 14 Sep '09

14 Sep '09

I tried a cabal install chp: It complained that base was hidden. So I unpacked the archive, and tried installing using runhaskell Setup configure/build/install. Now I get (from install): Setup: You need to re-run the 'configure' command. The version of Cabal being used has changed (was Cabal-1.6.0.3, now Cabal-1.6.0.2). So I repeated the process and get the same message again. ghc version is 6.10.3 Also: cabal --version cabal-install version 0.6.2 using version 1.6.0.2 of the Cabal library Where does this 1-6.0.3 come from (Ghc HEAD perhaps?)? What can I do about it? -- Colin Adams Preston Lancashire

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Re: cabal: : openFile: does not exist (No such file or directory)
by Thomas Hartman 03 Sep '09

03 Sep '09

cabal -v3 update will give you a more verbose version of what is going wrong. cabal --help regrettably, cabal --help doesn't tell you this but there is always the man page I suppose. 2009/7/16 Tony Hannan <tonyhannan2(a)gmail.com>: > Hello, > > I'm on Ubuntu 8.10. > I installed ghc 6.10.4 (from binary package: > ghc-6.10.4-i386-unknown-linux-n.tar.bz2). > I installed haskell-platform-2009.2.0.1 (from source package: > haskell-platform-2009.2.0.1.tar.gz). It contains cabal-install-0.6.2. > > Then when I run "cabal update", I get the following error: > cabal: : openFile: does not exist (No such file or directory) > > Any ideas? > > Thanks, > Tony > > _______________________________________________ > Libraries mailing list > Libraries(a)haskell.org > http://www.haskell.org/mailman/listinfo/libraries > >

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Cleaning up stable names?
by Peter Verswyvelen 02 Sep '09

02 Sep '09

>From the documentation, I don't think I grasp how stable names work. >From the docs: "There is no deRefStableName operation. You can't get back from a stable name to the original Haskell object. The reason for this is that the existence of a stable name for an object does not guarantee the existence of the object itself; it can still be garbage collected." >From this I can conclude that stable names behave a bit like weak pointers. However, suppose I have a hash table of these stable names. How can I remove the redundant stable names from the table? I mean removing stable names that refer to an object that is garbage collected? I don't see any function for checking that (e.g. isStableNameTargetAlive or something) Thanks, Peter

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Slow IO?
by Steve 02 Sep '09

02 Sep '09

Hi, I'm tackling a Sphere Online Judge tutorial question where it tests how fast you can process input data. You need to achieve at least 2.5MB of input data per second at runtime (on an old machine running ghc 6.6.1). This is probably close to the limit of Haskell's ability. https://www.spoj.pl/problems/INTEST/ I can see that 24 haskell programmers have solved it, but most are very close to the 8 secs limit (and 6/24 are even over the limit!). Here's my code. It fails with a "time limit exceeded" error. (I think it would calculate the correct result, eventually). module Main where import qualified Data.List as DLi import qualified System.IO as SIO main :: IO () main = do line1 <- SIO.hGetLine SIO.stdin let k = read $ words line1 !! 1 s <- SIO.hGetContents SIO.stdin print $ count s k count :: String -> Int -> Int count s k = DLi.foldl' foldFunc 0 (map read $ words s) where foldFunc :: Int -> Int -> Int foldFunc a b | mod b k == 0 = a+1 | otherwise = a I tried using Data.ByteString but then found that 'read' needs a String, not a ByteString. I tried using buffered IO, but it did not make any difference. Any suggestions on how to speed it up? Regards, Steve

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GUI library
by Michael Mossey 01 Sep '09

01 Sep '09

I want to choose a GUI library for my project. Some background: I'm a beginner to functional programming and have been working through Haskell books for a few months now. I'm not just learning Haskell for s**ts and giggles; my purpose is to write music-composition-related code; in particular, I want to write a graphical musical score editor. (Why write my own editor, you may ask? Because I want to fully integrate it with computer-assisted-composition algorithms that I plan to write, also in Haskell.) I decided to use Haskell for its great features as a functional programming language. Regarding a choice of GUI library, I want these factors: - it needs to provide at a minimum a drawing surface, a place I can draw lines and insert characters, in addition to all the standard widgets and layout capabilities we have to come to expect from a GUI library. - This is a Windows application. - it needs to be non-confusing for an intermediate-beginner Haskeller. Hopefully good documentation and examples will exist on the web. - It might be nice to have advanced graphics capability such as Qt provides, things like antialiasied shapes, and a canvas with efficient refresh (refereshes only the area that was exposed, and if your canvas items are only primitives, it can do refreshes from within C++ (no need to touch your Haskell code at all). However I'm wondering if qtHaskell fits my criteria "well-documented" and "lots of examples aimed at beginners". Thanks, Mike

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Re: [Haskell-cafe] Takusen - is anyone currently using it on Win32 - ODBC?
by Günther Schmidt 01 Sep '09

01 Sep '09

Hi Anton, well the problem isn't really accessing the data as such, it's quite easy to use HDBC.ODBC for instance to read in the data in a very comfortable way. I was explicitly asking for Takusen because it make certain guarantees regarding resources, memory consumption and such. One of the files for instance has 298 k lines. A glance over sushi revealed that parsec is involved so I can only presume it is read into memory all at once. That would certainly be a problem. Thanks, Günther Am 31.08.2009, 19:47 Uhr, schrieb Anton van Straaten <anton(a)appsolutions.com>: > Günther Schmidt wrote: >> My app then needs to read in dynamic data, a set of 4 CSV files, and I >> had been using Microsofts ODBC driver with HDBC.ODBC and that worked >> too. >> When I try to swap it for Takusen though I get an >> *** Exception: DBError ("HY","C00") 106 "[Microsoft][ODBC Text >> Driver] >> Optional Feature was not implemented >> Which is a bit of a shame, because using the ODBC text driver was much >> simpler than parsing the CSV files. > > A simple but powerful way to access CSV files is via TxtSushi, which > gives SQL access to CSV files, without needing ODBC: > > Home page: http://keithsheppard.name/txt-sushi/ > Hackage: http://hackage.haskell.org/package/txt-sushi > > You'd have to use it directly, since afaik it won't work with Takusen, > although a Takusen back end for it ought to be possible. > > Anton >

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