February 2009 - Haskell-Cafe

CFP: 5th Haskell Hackathon, April 17-19, Utrecht
by Sean Leather 12 Feb '09

12 Feb '09

Call for participation: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The 5th Haskell Hackathon April 17 - 19, 2009 Utrecht, The Netherlands ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The Haskell Hackathon is a collaborative coding festival with a simple focus: build and improve Haskell libraries, tools, and infrastructure. Of course, we have fun doing it, too! All hackers are welcome to visit and work on various Haskell-related projects. You decide what you want to work on! Lists of projects and concerted efforts are collected on the Hac5 website. == General Information == Information about the projects as well as practicalities such as traveling, accommodation, etc. is available from the Hac5 website: http://haskell.org/haskellwiki/Hac5 == Registration == Please register by following the instructions on the registration page: http://haskell.org/haskellwiki/Hac5/Register Once you've registered, please add your info to the attendees self-organizing page: http://haskell.org/haskellwiki/Hac5/Attendees If you are looking to share costs or want to meet up prior to the Hackathon with other attendees, feel free to organize via the Attendees wiki page or join the Hackathon IRC channel on freenode: #haskell-hac5 == Organizers == Andres Löh, Utrecht University (UU) José Pedro Magalhães, UU Sean Leather, UU Eelco Lempsink, UU + Tupil Chris Eidhof, UU + Tupil ... and more ...

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TASE 2009 - CALL FOR PAPERS
by CRACIUN F. 12 Feb '09

12 Feb '09

TASE 2009 - Final CALL FOR PAPERS ****************************************** * 3rd IEEE International Symposium on * Theoretical Aspects of Software Engineering * (TASE 2009) * 29-31 July 2009, Tianjin, China * http://www.dur.ac.uk/ieee.tase2009 * * For more information email: IEEE.TASE2009(a)durham.ac.uk ********************************************************** Large scale software systems and the Internet are of growing concern to academia and industry. This poses new challenges to the various aspects of software engineering, for instance, the reliability of software development, web-oriented software architecture and aspect and object-orientation techniques. As a result, new concepts and methodologies are required to enhance the development of software engineering from theoretical aspects. TASE 2009 is a forum for researchers from academia, industry and government to present ideas, results, and ongoing research on theoretical advances in software engineering. TASE 2009 is the third in a series of conference, sponsored by IEEE CS and IFIP. The first TASE conference was held in Shanghai, China, in June 2007. The second TASE conference was held in Nanjing, China, in June 2008. Topics of Interest: Authors are invited to submit high quality technical papers describing original and unpublished work in all theoretical aspects of software engineering. Topics of interest include, but are not limited to: * Requirements Engineering * Specification and Verification * Program Analysis * Software Testing * Model-Driven Engineering * Software Architectures and Design * Aspect and Object Orientation * Embedded and Real-Time Systems * Software Processes and Workflows * Component-Based Software Engineering * Software Safety, Security and Reliability * Reverse Engineering and Software Maintenance * Service-Oriented Computing * Semantic Web and Web Services * Type System and Theory * Program Logics and Calculus * Dependable Concurrency * Software Model Checking Program Co-Chairs ----------------- Wei-Ngan Chin (National Univ. of Singapore, Singapore) Shengchao Qin (Durham University, UK) Program Committee ----------------- Bernhard Aichernig (Graz University of Technology, Austria) Stefan Andrei (Lamar University, USA) Keijiro Araki (Kyushu University, Japan) Farhad Arbab (CWI and Leiden University, Netherlands) Jonathan Bowen (King's College London, UK) Michael Butler (University of Southampton, UK) Juan Chen (Microsoft Research, USA) Tyng-Ruey Chuang (Academica Sinica, Taiwan) Jim Davies (University of Oxford, UK) Zhenhua Duan (Xidian University, China) Xinyu Feng (Toyota Technological Inst. at Chicago, USA) Dieter Gollmann (Hamburg University of Technology, Germany) Tetsuo Ida (University of Tsukuba, Japan) Radu Iosif (Verimag, CNRS, France) Xuandong Li (Nanjing University, China) Kung-Kiu Lau (University of Manchester, UK) Shaoying Liu (Hosei University, Japan) Dorel Lucanu (University of Iasi, Romania) Tom Maibaum (McMaster University, Canada) Darko Marinov (Univ. of Illinois at Urbana-Champaign, USA) Hong Mei (Peking University, China) Huaikou Miao (Shanghai University, China) Peter Mueller (ETH Zurich, Switzerland) Viet Ha Nguyen (Vietnam National University, Vietnam) Sungwoo Park (Pohang Univ. of Science and Technology, Korea) Corneliu Popeea (MPI-SWS, Germany) Geguang Pu (East China Normal University, China) Zongyan Qiu (Peking University, China) Volker Stolz (UNU/IIST, Macau) Jing Sun (University of Auckland, New Zealand) Jun Sun (National Univ. of Singapore, Singapore) Kenji Taguchi (National Institute of Informatics, Japan) Yih-Kuen Tsay (National Taiwan University, Taiwan) Elizabeth Vidal (San Agustin National University, Peru) Ji Wang (National University of Defense Technology, China) Linzhang Wang (Nanjing University, China) Xianbing Wang (Wuhan University, China) Wang Yi (Uppsala University, Sweden) Jim Woodcock (University of York, UK) Hongyu Zhang (Tsinghua University, China) Jian Zhang (Chinese Academy of Sciences, China) Jianjun Zhao (Shanghai Jiao Tong University, China) Hong Zhu (Oxford Brookes University, UK) Huibiao Zhu (East China Normal University, China) Important Dates: February 20, 2009: Title and abstract submission deadline February 27, 2009: Paper submission deadline April 20, 2009: Acceptance/rejection notification May 11, 2009: Camera-ready version due July 29 - 31, 2009: TASE 2009

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HXT + Segmentation Fault
by rodrigo.bonifacio 12 Feb '09

12 Feb '09

Hi all, I'm trying to parse some XML files using HXT. However, even the examples available on the twiki fail. I guess that the problem is related to some library version, but I'm not sure. The error reported is: "Segmentation fault". Thanks in advance. Compiling with GHC-6.8.3 running on MAC/OS Tiger Packages: Cabal-1.2.4.0, HUnit-1.2.0.0, QuickCheck-1.1.0.0, array-0.1.0.0, base-3.0.2.0, bitset-0.6, bytestring-0.9.0.1.1, cgi-3001.1.6.0, containers-0.1.0.2, curl-1.3.3, directory-1.0.0.1, fgl-5.4.2.0, filepath-1.1.0.0, funsat-0.5.1, ghc-6.8.3, haskell-src-1.0.1.2, haskell98-1.0.1.0, hpc-0.5.0.1, html-1.0.1.1, hxt-8.1.0, (mtl-1.1.0.1), mtl-1.1.0.2, (network-2.2.0.0), network-2.2.0.1, old-locale-1.0.0.0, old-time-1.0.0.0, packedstring-0.1.0.0, parallel-1.0.0.1, parse-dimacs-1.2, parsec-2.1.0.1, parsec-3.0.0, pcre-light-0.3.1, pretty-1.0.0.0, process-1.0.0.1, random-1.0.0.0, readline-1.0.1.0, regex-base-0.72.0.1, regex-compat-0.71.0.1, regex-posix-0.72.0.2, rts-1.0, stm-2.1.1.1, tagsoup-0.6, template-haskell-2.2.0.0, time-1.1.2.1, unix-2.3.0.1, xhtml-3000.2.0.0

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Re: [Haskell] Google Summer of Code
by John Lato 12 Feb '09

12 Feb '09

Hi Bulat, I know you've talked about performance in the past, and I don't want to start a huge argument, but do you have recent data to back this up? IIRC you're using ghc 6.6, yes? I haven't looked at H.264 (and I realize it's compressed, so the situation is different from my work), however ghc can generate very fast code for binary I/O. Check out (shameless self-promotion) http://johnlato.blogspot.com for my recent writeup on creating a high-performance, pure-Haskell, Iteratee-based WAVE file reader. Sincerely, John Lato > > anyway it's impossible due to slow code generated by ghc > > > -- > Best regards, > Bulat mailto:Bulat.Ziganshin@gmail.com >

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Writing a generic event handler
by John Ky 12 Feb '09

12 Feb '09

Hi Haskell Cafe, I'm interested in writing some events and event handlers in Haskell. I already have a Loop data structure, and I intend to use it for this purpose: -- Create event tEvent <- newLoop (return ()) -- Register event handlers tHandler1 <- newLoop (putStrLn "Handler1") tHandler2 <- newLoop (putStrLn "Handler2") splice tEvent tHandler1 splice tEvent tHandler2 -- Fire event action <- doLoop tEvent action doLoop :: Monad m => TVar (Loop (m ())) -> STM (m ()) doLoop tLoop = do aLoop <- readAsList tLoop return $ sequence_ aLoop My question is: Is it possible to write a generic doLoop that works over arbitrary functions? For instance the following code wouldn't work because the event provides one argument and the handler takes one argument: -- Create event tEvent <- newLoop (\x -> return ()) -- Register event handlers tHandler1 <- newLoop (\x -> putStrLn ("Handler1" ++ show x)) tHandler2 <- newLoop (\x -> putStrLn ("Handler2" ++ show x)) splice tEvent tHandler1 splice tEvent tHandler2 -- Fire event action <- doLoop tEvent action 123 Thanks, -John Full source code for Loop type: module Fx.STM.Loop where import Control.Monad import Fx.STM.Util import GHC.Conc import System.IO.Unsafe -- Transactional loop. A loop is a circular link list. data Loop a = ItemLink { item :: a , prev :: TVar (Loop a) , next :: TVar (Loop a) } -- Create a new empty transactional loop. newLoop :: a -> STM (TVar (Loop a)) newLoop item = do tLoop <- newTVar undefined writeTVar tLoop (ItemLink item tLoop tLoop) return tLoop -- Splice two transactional loops. This will join two loops if they were -- originally separate, or split a single loop if the links were originally -- part of the same loop. No change occurs if the two links are identical. splice :: TVar (Loop a) -> TVar (Loop a) -> STM () splice tLink0 tLink1 = do aLink0 <- readTVar tLink0 aLink1 <- readTVar tLink1 let tLink0Prev = prev aLink0 let tLink1Prev = prev aLink1 writeTVar tLink0 aLink0 { prev = tLink1Prev } writeTVar tLink1 aLink1 { prev = tLink0Prev } aLink0Prev <- readTVar tLink0Prev aLink1Prev <- readTVar tLink1Prev writeTVar tLink0Prev aLink0Prev { next = tLink1 } writeTVar tLink1Prev aLink1Prev { next = tLink0 } return () -- Unlink a single link from a transactional loop. unlink :: TVar (Loop a) -> STM () unlink tLink = do (ItemLink item tLinkPrev tLinkNext) <- readTVar tLink aLinkPrev <- readTVar tLinkPrev writeTVar tLinkPrev aLinkPrev { next = tLinkNext } aLinkNext <- readTVar tLinkNext writeTVar tLinkNext aLinkNext { prev = tLinkPrev } writeTVar tLink (ItemLink item tLink tLink) return () -- Read the length of the loop. readLength :: TVar (Loop a) -> STM Int readLength tLink = do list <- readAsList tLink return $ length list readLinks :: TVar (Loop a) -> STM [TVar (Loop a)] readLinks tLink = readLinksUntil tLink tLink readLinksUntil :: TVar (Loop a) -> TVar (Loop a) -> STM [TVar (Loop a)] readLinksUntil tLink tLinkEnd = do (ItemLink _ tLinkPrev tLinkNext) <- readTVar tLink return [] if tLinkNext == tLinkEnd then return [tLink] else do tail <- readLinksUntil tLinkNext tLinkEnd return $ tLink:tail -- Read the elements of the loop as a list starting from tLink. readAsList :: TVar (Loop a) -> STM [a] readAsList tLink = readAsListUntil tLink tLink -- Read the elements of the loop as a list starting from tLink -- and terminating non-inclusively at tLinkEnd. readAsListUntil :: TVar (Loop a) -> TVar (Loop a) -> STM [a] readAsListUntil tLink tLinkEnd = do (ItemLink item tLinkPrev tLinkNext) <- readTVar tLink if tLinkNext == tLinkEnd then return [item] else do tail <- readAsListUntil tLinkNext tLinkEnd return $ item:tail -- Create a new loop from a list. newFromList :: [a] -> STM (TVar (Loop a)) newFromList [item] = newLoop item newFromList (item:items) = do tLink <- newLoop item tLinkRest <- newFromList items splice tLink tLinkRest return tLink doLoop :: Monad m => TVar (Loop (m ())) -> STM (m ()) doLoop tLoop = do aLoop <- readAsList tLoop return $ sequence_ aLoop

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The Haskell re-branding exercise
by Paul Johnson 12 Feb '09

12 Feb '09

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(Off-topic) CUDA
by Andrew Coppin 11 Feb '09

11 Feb '09

And so, inspired by the marketing litrature, I just spent £££ on a very expensive new GPU that supports CUDA. The only problem is... I can't seem to get any software to use it. Does anybody know how to make this stuff actually work? (Also... Haskell on the GPU. It's been talked about for years, but will it ever actually happen?)

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Re: [Haskell] Google Summer of Code 2009
by Benja Fallenstein 11 Feb '09

11 Feb '09

Hi all, On Tue, Feb 10, 2009 at 3:26 PM, Malcolm Wallace <Malcolm.Wallace(a)cs.york.ac.uk> wrote: > If you have ideas for student projects that you think would benefit the > Haskell community, now is the time to start discussing them on mailing > lists of your choice. We especially encourage students to communicate > with the wider community (...) I have a project that I've tinkered with doing for a while, but have never actually gotten around to, and I'm wondering whether there would be interest from the community in using it. Actually, two related projects: (1) A library for working with hashable data structures, including a hashable finger tree with sequence, map and set types based on it. Surprisingly, there does not seem to be much library support for working with hashes in Haskell beyond the bare-bones, imperative Data.HashTable, even though pure functional programming and hashes Go Well Together. I'm pulling these bounds out of my intuition, but hashable collections should give amortized O(1) comparison for equality and amortized O(log n) comparison for order, and you could use them as set values and map keys without efficiency blowing up in your face. The library should probably also include support for hashtables based on the various kinds of pure and monad-encapsulated arrays we have in Haskell, and maybe include support for interning values; unsafePerformIO, weak references and friends were originally introduced with the intention to support interned values in a way that programmers can tailor to their own needs, but it would be nice to have some default library support. (2) Based on this, a serialization library that would recognize if it has already written a particular value from memory to the same file, and write a pointer to the first occurrence of that value instead of serializing the actual value again, making it efficient to serialize versioned data structures. The idea is to make something similar to HAppS' MACID, but where MACID serializes the different kinds of updates that you can do for your data, this library would simply do the update in memory, then serialize the whole updated value to disk, but actually *writing* only the *new* parts of the data structure. (I think this could be simpler to use, and would be in a sense more elegant and 'haskelly' than the MACID approach. On the other hand, we already *have* MACID.) So, anybody out there who looks at these things and thinks "this could be useful"? :-) Thanks, - Benja

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ANN : happs-tutorial 0.7
by Creighton Hogg 11 Feb '09

11 Feb '09

Hello, I'm pleased to announce the release of happs-tutorial 0.7 on Hackage. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/happs-tutorial This is the first release of happs-tutorial built against the new Happstack project. Not much has changed in content since the last release except a few minor cleanups & a little bit of reorganization. The 0.8 release will consist of more extensive additions, with the primary focus being a walk through of multimaster. I've taken over the development of the tutorial from Thomas Hartman, who has already put a rather massive effort into making HAppS/Happstack more accessible. Please feel free to e-mail me with any comments, errata, or threats of bodily harm. Cheers, Creighton Hogg

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GMP on Mac OS X linked statically by default
by David Leimbach 11 Feb '09

11 Feb '09

Was there a reason for this? If so, it'd be nice if the package that was build explained why... otherwise it feels kind of arbitrary, and would be nice if there was documentation available to make it link dynamically in case someone didn't want to LGPL their program. Anyone know the steps to make it link dynamically? Dave

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