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Haskell User Group Hamburg (Germany) - Meeting Thursday November 8th 2012
by Stefan Schmidt 31 Oct '12

31 Oct '12

Hello cafe, there's an upcomming meeting of the Haskell user group Hamburg next week on Thursday, November 8th. We'll start 19:00 at the fortytools GmbH in Hamburg (Georgsplatz 10, 20099 Hamburg). We don't have a program or talk yet. Maybe we'll discuss our experiences from the last ICFP and the Haskell Symposium. If you are interested to join us, have a look at our doodle (only in german) http://www.doodle.com/gvdsbsyfz7a7427g Be careful: the Google Maps link in the Doodle may direct you to the old address. Georgsplatz 10, 20099 Hamburg is the new one. Further announcements will be made via Twitter, so you may want to follow https://twitter.com/hug_hh.

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ANNOUNCE: btree-concurrent
by Johan Brinch 31 Oct '12

31 Oct '12

Greetings Haskellers, We are pleased to announce this new package, featuring a concurrent b-tree developed as part of our master's thesis on backup systems. The package features code related to STM, caching, QuickCheck and of course concurrency and parallelism. And it's also on Hackage: http://hackage.haskell.org/package/btree-concurrent In case the build fails on Hackage and the documentation doesn't work, it's also available here: http://hindsight.dk/doc/html/btree-concurrent Credits to Thomas Conway of Melbourne University, for discussions related to the implementation, and to our supervisor Ken Friis Larsen of University of Copenhagen. And now, the description of the package: ===== A backend agnostic, concurrent BTree with relaxed balance[1] written in Haskell using a mix of IO operations and pure STM. Although the code does work, it is neither production-ready nor complete. Features include: * Caching: While nodes are periodically saved on persistent storage (e.g. disk) they are cached in-memory during operations. * Live flushing: It is possible to save the current version of the tree to disk and run modifying operations at the same time. The nodes are updated buttom-up to ensure a valid tree in the case of a crash. * Backend agnosticism: A simple API is used as an abstraction for the persistent storage. * Verification: The test-suite uses QuickCheck to compare the trees behaviour to that of Data.Map. Deficients include: * Memory greedy. Nodes are not stored in a compact fashion and are constantly being serialised/deserialised. * findMin and findMax are incomplete and may fail (see the TODO for details). * The implementation does not parallelise well. [1] B-trees with relaxed balance, K. S. Larsen & R. Fagerberg, Parallel Processing Symposium, 1995. Proceedings., 9th International -- Johan Brinch & Morten Brøns-Pedersen

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ANNOUNCE: plat
by Miguel Mitrofanov 30 Oct '12

30 Oct '12

My current project at work has a web interface. Therefore I needed an HTML templating library. I've tried several and found them all unsatisfactory. Most of them generate Haskell code from templates (with Template Haskell or a separate utility), and I don't like metaprogramming; and recompiling the program every time you make a small change in the template kinda defeats the purpose. Other libraries make it PITA to implement basic things, like iterating over an array. So, I'm proud to announce the first release of another template library: plat-0.1.0.1 (http://hackage.haskell.org/package/plat) An example of what it does. If your data looks like do "name" =: "Mac's tools" "staff" =: [ do "index" =: "1" "name" =: "Alice" , do "name" =: "Bob" "index" =: "2" "bad" =: True , do "index" =: "3" "name" =: "Nicolás" ] and your template is List of employees at @name: @staff[person @person.index@.. @person.name@{@!person.bad (going to be fired)@|@}@ @]@# There won't be an empty line in the result Then the result you get would be this: List of employees at Mac's tools: 1. Alice 2. Bob (going to be fired) 3. Nicolás Keep in mind, that it's actually a string template library, and the resulting string doesn't have to be valid HTML, or any HTML at all. I haven't benchmarked this library - since I intended to use it for web interface in an program which won't be released outside, speed was not in my priorities; but I'll work on that in future versions. Also, templates are supposed to be in UTF-8, as I've successfully forgot all about other encodings. So, if you want binary templates, I'm afraid, this library is not for you.

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Safe lens?
by Greg Fitzgerald 30 Oct '12

30 Oct '12

Why are getters from the 'lens' package unsafe? Is there a subset like Data.Label.Pure from 'fclabels' that can be imported safely? $ cat a.hs {-# LANGUAGE Safe #-} import Control.Lens.Getter main = print 123 $ runghc a.hs a.hs:3:1: Control.Lens.Getter: Can't be safely imported! The module itself isn't safe. Thanks, Greg

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ANNOUNCE: network-house
by Niklas Hambüchen 30 Oct '12

30 Oct '12

In absence of a library that easily parses network packages from recorded raw data (not sockets), I have taken the network stack from the House project and put it into a separate package, network-house. http://hackage.haskell.org/package/network-house This library allows you to parse Ethernet, TCP, UDP, IPv4, IPv6, ICMP, DHCP and TFTP packages from raw data (e.g. recorded traffic). I have left the source code almost unmodified (apart from the relocation of one module and a few necessary LANGUAGE pragmas). As House development itself seems dormant, I invite you to collaborate on the network stack on https://github.com/nh2/network-house. If you would like to contribute, these are the things it definitely needs: * A ByteString interface (it currently works on UArrays). If you know what the most performant way is to convert a UArray to a ByteString, please let me know. * Some examples how to use it * Haddock documentation and code cleanup * Somebody should ask the original authors if they would like to relax the license from GPL to BSD. Cheers Niklas

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Optimal line length for haskell
by Rustom Mody 30 Oct '12

30 Oct '12

There was a recent discussion on the python list regarding maximum line length. It occured to me that beautiful haskell programs tend to be plump (ie have long lines) compared to other languages whose programs are 'skinnier'. My thoughts on this are at http://blog.languager.org/2012/10/layout-imperative-in-functional.html. Are there more striking examples than the lexer from the standard prelude? [Or any other thoughts/opinions :-) ] Thanks, Rusi

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GHC maintenance on Arch
by timothyhobbs＠seznam.cz 30 Oct '12

30 Oct '12

Hello, Who is in charge of the ghc and haskell packages on Arch linux? The current system isn't working. Arch linux tends to update packages very quickly. For ghc, always having the latest ghc isn't a good thing. At least if you actually want to get some work done. A majority of the time the latest GHC is unusable. This is because the packages in hackage simply don't keep up. With the current ghc version(7.6.1) even some basic packages in hackage are not upgraded yet. Right now, a large number of other haskell related packages are in the arch repos. Other than gtk2hs, I think these packages are pointless duplications. In the other cases, it has been my experience that it is simpler to maintain these packages through cabal rather than through pacman. Support for these packages in Arch should probably be dropped. If you want to get work done in Arch with haskell, you should only install ghc and cabal-install(right now, you'll have to search the Internet for the old binaries, because the arch repos usually don't keep the old versions around). Then you should add these packages to "IgnorePkg =" in pacman.conf this way things won't break every couple of months. You can then choose to upgrade when you wish. I hope that someone who is involved with the haskell Arch stuff reads this. The current model needs to be rethought. Linux should be sane by default, but I've lost many many hours learning that arch's relationship with haskell is not so :( Probably the best solution would be to make Arch automatically keep two versions of ghc around at any given time. Thank you for your time, Timothy Hobbs

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TAP 2013: 1st Call for Papers
by Achim D. Brucker 29 Oct '12

29 Oct '12

(Apologies if you receive this announcement multiple times. We also apologize for resending the first call for papers, the original announcement contained an incorrect URL to easychair.) **************************************************** *** *** *** TAP 2013 *** *** *** *** Abstract submission: January 25, 2013 *** *** Paper submission: February 1, 2013 *** **************************************************** *** TAP 2013 solicits both full papers and *** *** (industrial) experience/tool papers *** *** in combining proofs and (security) testing *** **************************************************** CALL FOR PAPERS 7th INTERNATIONAL CONFERENCE ON TESTS AND PROOFS (TAP 2013) http://www.spacios.eu/TAP2013 Budapest, Hungary, June 17-21, 2013 The TAP conference is devoted to the synergy of proofs and tests, to the application of techniques from both sides and their combination for the advancement of software quality. Testing and proving seem to be contradictory techniques: once you have proved your program to be correct then additional testing seems pointless; on the other hand, when such a proof in not feasible, then testing the program seems to be the only option. This view has dominated the research community since the dawn of computer science, and has resulted in distinct communities pursuing the seemingly orthogonal research areas. However, the development of both approaches has lead to the discovery of common issues and to the realization of potential synergy. Perhaps, use of model checking in testing was one of the first signs that a counterexample to a proof may be interpreted as a test case. Recent breakthroughs in deductive techniques such as satisfiability modulo theories, abstract interpretation, and interactive theorem proving, have paved the way for new and practically effective methods of powering testing techniques. Moreover, since formal, proof-based verification is costly, testing invariants and background theories can be helpful to detect errors early and to improve cost effectiveness. Summing up, in the past few years an increasing number of research efforts have encountered the need for combining proofs and tests, dropping earlier dogmatic views of incompatibility and taking instead the best of what each of these software engineering domains has to offer. The TAP conference aims to bring together researchers and practitioners working in the converging fields of testing and proving, and will offer a generous allocation of papers, panels and informal discussions. Topics of interest cover theory definitions, tool constructions and experimentations, and include (other topics related to TAP are welcome): - Bridging the gap between concrete and symbolic techniques, e.g. using proof search in satisfiability modulo theories solvers to enhance various testing techniques - Transfer of concepts from testing to proving (e.g., coverage criteria) and from proving to testing - Program proving with the aid of testing techniques - New problematics in automated reasoning emerging from specificities of test generation - Verification and testing techniques combining proofs and tests - Generation of test data, oracles, or preambles by deductive techniques such as: theorem proving, model checking, symbolic execution, constraint logic programming - Model-based testing and verification - Generation of specifications by deduction - Automatic bug finding - Debugging of programs combining static and dynamic analysis - Formal frameworks - Tool descriptions and experience reports - Case studies combining tests and proofs - Domain specific applications of testing and proving to new application domains such as validating security protocols, vulnerability detection of programs, security Important Dates: ================ Abstract submission: January 25, 2013 Paper submission: February 1, 2013 Notification: March 3, 2013 Camera ready version: April 5, 2013 TAP conference: June 17-21, 2013 Program Chairs: =============== Margus Veanes (Microsoft Research, USA) Luca Vigano` (University of Verona, Italy) Program Committee: ================== TBA Submission: =========== Please submit your papers via easychair https://www.easychair.org/conferences/?conf=tap2013 (submission page to be opened in due time) TAP 2013 will accept two types of papers: - Research papers: full papers with at most 16 pages in LNCS format (pdf), which have to be original, unpublished and not submitted elsewhere. - Short contributions: work in progress, (industrial) experience reports or tool demonstrations, position statements; an extended abstract with at most 6 pages in LNCS format (pdf) is expected. Subject to final approval by Springer, accepted papers will be published in the Springer LNCS series and will be available at the conference. The contents of previous TAP proceedings is available at: http://www.informatik.uni-trier.de/~ley/db/conf/tap/ -- Dr. Achim D. Brucker, SAP AG, SAP Research Vincenz-Priessnitz-Str. 1, D-76131 Karlsruhe, Phone: +49 6227 7-52595 http://www.brucker.ch

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[Off-topic] How unimportant it is whether submarines can swim (EWD1056)
by Henk-Jan van Tuyl 29 Oct '12

29 Oct '12

L.S., I thought you might be interested to know, that I have translated one of prof. Edsger W. Dijkstra's writings to English[0]. I will submit this translation to the E. W. Dijkstra Archive of the University of Texas[1]. Some of the highlights: - can submarines swim? - redefining mathematics - something unimaginably unimaginable - a baby faster than fighter jets Regards, Henk-Jan van Tuyl [0] http://members.chello.nl/hjgtuyl/computing/EWD1056.html [1] http://www.cs.utexas.edu/users/EWD/welcome.html -- http://Van.Tuyl.eu/ http://members.chello.nl/hjgtuyl/tourdemonad.html Haskell programming --

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Teaching Haskell @ MOOCs like Coursera or Udacity
by niket 29 Oct '12

29 Oct '12

I am a novice in Haskell but I would love to see the gurus out here teaching Haskell on MOOCs like Coursera or Udacity. Dr Martin Odersky is doing it for Scala here: https://www.coursera.org/course/progfun I would love to see Haskell growing on such new platforms! Regards, Niket

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