May 2011 - Haskell-Cafe

ANN: stm-chans 1.2.0
by wren ng thornton 07 May '11

07 May '11

-------------------------------------------- -- stm-chans 1.2.0 -------------------------------------------- The stm-chans package offers a collection of channel types, similar to Control.Concurrent.STM.TChan but with additional features. -------------------------------------------- -- Changes (since 1.0.0) -------------------------------------------- * (Version 1.1.0) Added tryWriteTBChan. * (Version 1.1.0) Added tryWriteTBMChan. * Some major performance improvements in TBChan and TBMChan, thanks to Thomas DuBuisson. In particular, these improvements reduce contention between readers and writers, improving throughput by up to 2--3 times when producers and consumers are running in separate OS threads. The cost for non-parallel programs is trivial (<1% worst-case running time, per Criterion). * Added estimateFreeSlotsTBChan, freeSlotsTBChan, estimateFreeSlotsTBMChan, and freeSlotsTBMChan. These functions return either the exact number or a lower-bound on the number of free slots available before the channels will block/retry. * Some other minor optimizations and code improvements. -------------------------------------------- -- Long description -------------------------------------------- In particular stm-chans offers these types: * Control.Concurrent.STM.TBChan: Bounded FIFO channels. When the channel is full, writers will block/retry. This ensures that the writers do not get too far ahead of the readers, which helps to make sure that memory and cpu resources are used responsibly. * Control.Concurrent.STM.TMChan: Closeable FIFO channels. This is like TChan (Maybe a) but with a monotonicity guarantee that once Nothing is returned all future reads will be Nothing as well. * Control.Concurrent.STM.TBMChan: Bounded Closeable FIFO channels. This combines the capabilities of TBChan and TMChan. In addition, the stm-chans package offers a (partial) compatibility layer for some recent API improvements to the stm package (see ticket #5104 [1]). These new functions include: * tryReadTChan :: TChan a -> STM (Maybe a) A version of readTChan which does not retry. Instead it returns Nothing if no value is available. * peekTChan :: TChan a -> STM a Get the next value from the TChan without removing it, retrying if the channel is empty. * tryPeekTChan :: TChan a -> STM (Maybe a) A version of peekTChan which does not retry. Instead it returns Nothing if no value is available. [1] http://hackage.haskell.org/trac/ghc/ticket/5104 -------------------------------------------- -- Links -------------------------------------------- Homepage: http://code.haskell.org/~wren/ Hackage: http://hackage.haskell.org/package/stm-chans Darcs: http://community.haskell.org/~wren/stm-chans Haddock (Darcs version): http://community.haskell.org/~wren/stm-chans/dist/doc/html/stm-chans -- Live well, ~wren

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Do exist globally available hosting project services?
by Facundo Domínguez 07 May '11

07 May '11

Dear haskellers, I was reading the terms of service of the Haskell Community Server and found this statement: "Users residing in countries on the United States Office of Foreign Assets Control sanction list, including Cuba, Iran, Libya, North Korea, Sudan and Syria, may not post or access CONTENT available through OUR services." I wonder whether there is a solution for hosting projects which does not discriminate people by their place of residence. http://code.haskell.org http://www.patch-tag.com https://github.com all seem to be ruled under USA laws. Would anybody recommend an alternative? Best, Facundo

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ANN: timeplot-0.3.0 - the analyst's swiss army knife for visualizing ad-hoc log files
by Eugene Kirpichov 06 May '11

06 May '11

Hello fellow haskellers, I announce the release of timeplot-0.3.0, the "analyst's swiss army knife for visualizing ad-hoc log files". Links: * http://jkff.info/presentation/two-visualization-tools - a presentation saying what the tools are all about and giving plenty of graphical examples on cluster computing use cases. At the end of the presentation there's also a couple of slides about installation. It is a little bit outdated, it corresponds to versions just before 0.3.0. * http://hackage.haskell.org/package/timeplot * http://github.com/jkff/timeplot * The sibling tool, splot - for visualizing the activity of many concurrent processes - http://hackage.haskell.org/package/splot and http://github.com/jkff/splot . It has also gotten a couple of new features since my last announcement. The major new feature of tplot is the introduction of subplots, the <<'within' plots>>. It allows one to plot data from several sub-tracks on one track of the graph: - several line- or dot-plots - several plots of sums or cumulative sums, perhaps stacked (to see how the sub-tracks contribute to the total sum - e.g. if your log speaks about different types of overhead and you wish to see how they contribute to the total) - stacked "activity count" plot - a generalization of the previous "activity count" plot, which allows you to, given a log saying like "Machine started servicing job JOB1 ... Machine finished servicing job JOB1" etc, plot how many machines are servicing each job at any moment, in a stacked fashion - so, how loads by different jobs contribute to the whole cluster's load. The "activity frequency" plot plots the same on a relative scale. The syntax is, for example: "within[.] dots" or "within[.] acount" or even "within[.] duration cumsum stacked" etc. Note that these are of course just example use cases and the tool is universal, it is not in any sense specialized to clusters, jobs, overheads or actually even to logs. I'd like to encourage you to give it a try and look around for a use case :) If you do give the tool a try, please tell me if something goes wrong, be it an installation problem or a bug (the version is fresh released, so this is quite possible). -- Eugene Kirpichov Principal Engineer, Mirantis Inc. http://www.mirantis.com/ Editor, http://fprog.ru/

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Can't build Gtk2hs on Windows
by Andrew Coppin 06 May '11

06 May '11

Today I tried to install Gtk2hs. Big mistake! Last time I tried it, it was quite easy. Now that it uses Cabal, even on Windows you can compile this stuff from source fairly easily. It's just that you have to fiddle with environment variables to make it find stuff. However... 1. Since the move of haskell.org, the gtk2hs homepage has vanished off the face of the Earth. Is there any danger we might get this back some day? 2. http://hackage.haskell.org/trac/gtk2hs/ticket/1203 (In other words, every time you try to cabal install a GTK-related package, it fails during the register step, and you need to hand-edit Gtk2HsSetup.hs to fix the issue.) 3. http://hackage.haskell.org/trac/gtk2hs/ticket/1209 (In other words, certain GTK-related packages just plain fail to build due to undefined names or missing header files or...) In summary, it's just utterly broken. Which is very frustrating, given that not so long ago it was working really well. (I never did get Glade to work though... although it looks like that might be fixed now, if I could just get past all the other issues.)

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ANN: syntactic-0.1
by Emil Axelsson 06 May '11

06 May '11

I'm happy to announce the first release of syntactic: http://hackage.haskell.org/package/syntactic providing generic abstract syntax and utilities for embedded languages. To get an idea of what it's about, check out the tiny(!) implementation of (simplified) Feldspar in the Examples directory: http://projects.haskell.org/syntactic/Examples/MuFeldspar The library is intended to provide a growing set of utilities for embedded languages. In particular, I hope to be able to provide safe interfaces to various unsafe techniques for speeding things up. Comments, patches and clients are welcome! / Emil

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CFP: APLAS 2011, Kenting, Taiwan
by Shin-Cheng Mu 06 May '11

06 May '11

========================================================== APLAS 2011 Call For Papers Ninth Asian Symposium on Programming Languages and Systems Kenting, Taiwan, December 5--7, 2011 (co-located with CPP 2011) http://flolac.iis.sinica.edu.tw/aplas11/ ========================================================== BACKGROUND: APLAS aims at stimulating programming language research by providing a forum for the presentation of latest results and the exchange of ideas in topics concerned with programming languages and systems. APLAS is based in Asia, but is an international forum that serves the worldwide programming language community. APLAS is sponsored by the Asian Association for Foundation of Software (AAFS) founded by Asian researchers in cooperation with many researchers from Europe and the USA. The past APLAS symposiums were successfully held in Shanghai ('10), Seoul ('09), Bangalore ('08), Singapore ('07), Sydney ('06), Tsukuba ('05), Taipei ('04) and Beijing ('03) after three informal workshops. Proceedings of the past symposiums were published in Springer-Verlag's LNCS 6461, 5904, 5356, 4807, 4279, 3780, 3302, and 2895. The 2011 edition will be held at Kenting, a seaside resort in Southern Taiwan. TOPICS: The symposium is devoted to both foundational and practical issues in programming languages and systems. Papers are solicited on, but not limited to, the following topics: + semantics, logics, foundational theory; + design of languages and foundational calculi; + type systems; + compilers, interpreters, abstract machines; + program derivation and transformation; + program analysis, verification, model-checking, software security; + concurrency, constraints, domain-specific languages; + tools for programming, verification, implementation. APLAS 2011 is not limited to topics discussed in previous symposiums. Papers identifying future directions of programming and those addressing the rapid changes of the underlying computing platforms are especially welcome. Demonstration of systems and tools in the scope of APLAS are welcome to the System and Tool presentations category. Authors concerned about the appropriateness of a topic are welcome to consult with Program Chair prior to submission. IMPORTANT DATES: Abstract Deadline: June 13, 2011 Submission Deadline: June 17, 2011 (GMT) Notification: August 29, 2011 Camera-Ready: September 19, 2011 INVITED SPEAKERS: Nikolaj Bjorner, Microsoft Research Redmond Ranjit Jhala, UC San Diego Peter O'Hearn, Queen Mary U. London Sriram Rajamani, Microsoft Research India SUBMISSION INFORMATION: We solicit submissions in two categories: Regular research papers, describing original research results, including tool development and case studies, from a perspective of scientific research. Regular research papers should not exceed 16 pages in the Springer LNCS format, including bibliography and figures. They should clearly identify what has been accomplished and why it is significant. Submissions will be judged on the basis of significance, relevance, correctness, originality, and clarity. In case of lack of space, proofs, experimental results, or any information supporting the technical results of the paper could be provided as Appendix or a link to a web page. System and Tool presentations, describing systems or tools that support theory, program construction, reasoning, and/or program execution in the scope of APLAS. Unlike presentations of regular research papers, presentation of accepted papers in this category is expected to be centered around a demonstration. The paper and the demonstration should identify the novelties of the tools and use motivating examples. System and Tool papers should not exceed 8 pages in the Springer LNCS format, including bibliography and figures. Submissions will be judged based on both the papers and the systems or tools as described in the papers. It is highly desirable that the tools are available on the web. Papers should be submitted electronically via the submission web page at http://www.easychair.org/conferences/?conf=aplas2011. Acceptable formats are PostScript or PDF, viewable by Ghostview or Acrobat Reader. Submitted papers must be unpublished and not submitted for publication elsewhere. Papers must be written in English. The proceedings are planned to be published as a volume in Springer-Verlag's Lecture Notes in Computer Science series. Accepted papers must be presented at the conference. GENERAL CHAIR: Tyng-Ruey Chuang, Academia Sinica, Taiwan PROGRAM CHAIR: Hongseok Yang, Queen Mary U. London aplas2011(a)easychair.org PROGRAM COMMITTEE: Lars Birkedal (ITU, Denmark) James Brotherston (Imperial College, UK) Kung Chen (National Chengchi U., Taiwan) Wenguang Chen (Tsinghua U., China) Wei-Ngan Chin (NUS, Singapore) Javier Esparza (TUM, Germany) Xinyu Feng (USTC, China) Jerome Feret (INRIA, France) Matthew Fluet (RIT, USA) Rajiv Gupta (UC Riverside, USA) Masahito Hasegawa (Kyoto U., Japan) Radha Jagadeesan (Depaul U., USA) Naoki Kobayashi (Tohoku U., Japan) Daniel Kroning (U. Oxford, UK) Rupak Majumdar (MPI-SWS, Germany) Andrzej Murawski (U. Leicester, UK) Paulo Oliva (Queen Mary U. London, UK) Doron Peled (Bar Ilan U., Israel) Sukyoung Ryu (KAIST, Korea) Sriram Sankaranarayanan (U. Colorado, USA) Armando Solar-Lezama (MIT, USA) Sam Staton (U. Cambridge, UK) Viktor Vafeiadis (MPI-SWS, Germany) Kapil Vaswani (MSR, India) Martin Vechev (IBM, USA) Peng Wu (IBM, USA) Hongseok Yang (Queen Mary U. London, UK) Pen-Chung Yew (Academia Sinica, Taiwan) ORGANIZERS: Mike Dodds, U. Cambridge (Poster chair) Shin-Cheng Mu, Academia Sinica, Taiwan (Local arrangement chair) Noam Rinetzky, Queen Mary U. London (Publicity chair) Yih-Kuen Tsay, National Taiwan University (Finance chair)

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Usage of rewrite rule specialization in Hackage
by Scott Kilpatrick 05 May '11

05 May '11

I'm looking for "real" code that uses the kind of GHC rewrite rule that specializes a polymorphic function with another one, as described here <http://www.haskell.org/ghc/docs/latest/html/users_guide/rewrite- rules.html#rule-spec>. Can anyone point me to any popular packages in Hackage that make use of this? Thanks, Scott

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Haskell statistics for use of TypeFamilies and FunctionalDependencies
by Gwern Branwen 05 May '11

05 May '11

Continuing my investigation of my local copies of patch-tag+github+c.h.o+misc repositories (, I rewrote my haskell-src-exts script to examine LANGUAGE extensions in use (ignoring any .cabal flags): import Language.Haskell.Exts import qualified Data.Foldable as F (concat) import Control.Monad (when) main :: IO () main = do args <- fmap lines $ getContents mapM_ (\a -> checkAndPrint a `catch` (\_ -> return ())) args checkAndPrint :: FilePath -> IO () checkAndPrint fs = do x <- readFile fs let exts = F.concat $ readExtensions x let exts' = filter (\y -> y == FunctionalDependencies || y == TypeFamilies) exts when (not $ null exts') $ putStr (fs++":") >> (putStrLn $ unwords $ map show exts) return () The attachment is the gzipped* result of `find . -type f -name "*?hs" | sort | runhaskell ~/extensions.hs >> ~/exts.txt`. Notes: - 3597 files matched either LANUAGE - there were: 2685 users of TypeFamilies 1030 users of FunctionalDependencies 118 users of TypeFamilies+FunctionalDependencies 2.7k TypeFamilies may be surprisingly large; if so, it may be due to GHC and its duplicates; 947 lines match the string 'ghc' and 721 lines match both 'ghc' and 'TypeFamilies'. * 500k is a bit much for an attachment -- gwern http://www.gwern.net

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How often is the planet updated?
by Magnus Therning 05 May '11

05 May '11

I see that Planet Haskell hasn't been updated since April 26. Is something wrong with it, or does it really not update more often than that? /M -- Magnus Therning OpenPGP: 0xAB4DFBA4 email: magnus(a)therning.org jabber: magnus(a)therning.org twitter: magthe http://therning.org/magnus

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2nd CFP: ACM SIGPLAN 7th Workshop on Generic Programming (WGP 2011)
by Shin-Cheng Mu 05 May '11

05 May '11

====================================================================== CALL FOR PAPERS WGP 2011 7th ACM SIGPLAN Workshop on Generic Programming Tokyo, Japan Sunday, September 18th, 2011 http://flolac.iis.sinica.edu.tw/wgp11/ Collocated with the International Conference on Functional Programming (ICFP 2011) ====================================================================== Goals of the workshop --------------------- Generic programming is about making programs more adaptable by making them more general. Generic programs often embody non-traditional kinds of polymorphism; ordinary programs are obtained from them by suitably instantiating their parameters. In contrast with normal programs, the parameters of a generic program are often quite rich in structure; for example they may be other programs, types or type constructors, class hierarchies, or even programming paradigms. Generic programming techniques have always been of interest, both to practitioners and to theoreticians, and, for at least 20 years, generic programming techniques have been a specific focus of research in the functional and object-oriented programming communities. Generic programming has gradually spread to more and more mainstream languages, and today is widely used in industry. This workshop brings together leading researchers and practitioners in generic programming from around the world, and features papers capturing the state of the art in this important area. We welcome contributions on all aspects, theoretical as well as practical, of * generic programming, * programming with (C++) concepts, * meta-programming, * programming with type classes, * programming with modules, * programming with dependent types, * polytypic programming, * adaptive object-oriented programming, * component-based programming, * strategic programming, * aspect-oriented programming, * family polymorphism, * object-oriented generic programming, * and so on. Organizers ---------- Co-Chair Jaakko Järvi, Texas A&M University, USA Co-Chair Shin-Cheng Mu, Academia Sinica, Taiwan Programme Committee ------------------- Dave Abrahams, BoostPro Computing, USA Magne Haveraaen, Universitetet i Bergen, Norway Akimasa Morihata, Tohoku University, Japan Pablo Nogueira, Universidad Politécnica de Madrid, Spain Ulf Norell, Chalmers University of Technology and University of Gothenberg, Sweden Ross Paterson, City University London, UK Rinus Plasmeijer, Radboud University Nijmegen, The Netherlands Sibylle Schupp, Technische Universität Hamburg-Harburg, Germany Andrew Sutton, Kent State University, USA Tarmo Uustalu, Institute of Cybernetics, Estonia Important Information --------------------- We plan to have formal proceedings, published by the ACM. Submission details Deadline for submission: Monday 2011-06-06 Notification of acceptance: Tuesday 2011-07-01 Final submission due: Monday 2011-07-25 Workshop: Sunday 2011-09-18 Authors should submit papers, in postscript or PDF format, formatted for A4 paper, to the WGP11 EasyChair instance by the above deadline. The length should be restricted to 12 pages in standard (two-column, 9pt) ACM format. Accepted papers are published by the ACM and will additionally appear in the ACM digital library. History of the Workshop on Generic Programming ---------------------------------------------- This year: * Tokyo, Japan 2011 (affiliated with ICFP11) Earlier Workshops on Generic Programming have been held in * Baltimore, Maryland, US 2010 (affiliated with ICFP10) * Edinburgh, UK 2009 (affiliated with ICFP09) * Victoria, BC, Canada 2008 (affiliated with ICFP), * Portland 2006 (affiliated with ICFP), * Ponte de Lima 2000 (affiliated with MPC), * Marstrand 1998 (affiliated with MPC). Furthermore, there were a few informal workshops * Utrecht 2005 (informal workshop), * Dagstuhl 2002 (IFIP WG2.1 Working Conference), * Nottingham 2001 (informal workshop), There were also (closely related) DGP workshops in Oxford (June 3-4 2004), and a Spring School on DGP in Nottingham (April 24-27 2006, which had a half-day workshop attached). Additional information: The WGP steering committee consists of J. Gibbons, R. Hinze, P. Jansson, J. Järvi, J. Jeuring, B. Oliveira, S. Schupp, and M. Zalewski

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