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deriving Show for GADT?
by nr＠cs.tufts.edu 14 Apr '09

14 Apr '09

I've got a fairly large GADT for which I wished to use deriving (Show) but I got a mysterious error message: Exp.hs:13:11: Can't make a derived instance of `Show (Exp a)' (`Exp' has non-Haskell-98 constructor(s)) In the data type declaration for `Exp' This is from GHC. Does anybody know a compiler option or other trick that will coax the compiler into producing a Show instance. (I know I can write one by hand, but I'd rather not bother.) Norman

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CFP Trends in Functional Programming
by Horváth Zoltán 14 Apr '09

14 Apr '09

Third call for papers 10th SYMPOSIUM ON TRENDS IN FUNCTIONAL PROGRAMMING TFP 2009 SELYE JANOS UNIVERSITY, KOMARNO, SLOVAKIA June 2-4, 2009 http://www.inf.elte.hu/tfp_cefp_2009 *** Submission deadline extended until 10th of May! *** The symposium on Trends in Functional Programming (TFP) is an international forum for researchers with interests in all aspects of functional programming languages, focusing on providing a broad view of current and future trends in Functional Programming. It aspires to be a lively environment for presenting the latest research results. Acceptance for the conference is based on full papers or extended abstracts, and a formal post-symposium refereeing process selects the best articles presented at the symposium for publication in a high-profile volume. TFP 2009 is hosted by the Selye Janos University, Komarno, Slovakia, and it is co-located with the 3rd Central-European Functional Programming School (CEFP 2009), which is held immediately before TFP 2009 (May 25-30). IMPORTANT DATES (ALL 2009) * Paper Submission: May 10 (extended) * Notification of Acceptance: May 12 * Camera Ready Symposium Proceedings Paper: May 14 * TFP Symposium: June 2-4, 2009 * Post Symposium Paper Submission: June 30 * Notification of Acceptance: September 7 * Camera Ready Revised Paper: September 21 SCOPE OF THE SYMPOSIUM As part of the Symposium's focus on trends we therefore identify the following five article categories. High-quality articles are solicited in any of these categories: * Research: leading-edge, previously unpublished research. * Position: on what new trends should or should not be. * Project: descriptions of recently started new projects. * Evaluation: what lessons can be drawn from a finished project. * Overview: summarizing work with respect to a trendy subject. Articles must be original and not submitted for simultaneous publication to any other forum. They may consider any aspect of functional programming: theoretical, implementation-oriented, or more experience- oriented. Applications of functional programming techniques to other languages are also within the scope of the symposium. Contributions on the following subject areas are particularly welcomed: * Dependently Typed Functional Programming * Validation and Verification of Functional Programs * Debugging for Functional Languages * Functional Programming and Security * Functional Programming and Mobility * Functional Programming to Animate/Prototype/Implement Systems from Formal or Semi-Formal Specifications * Functional Languages for Telecommunications Applications * Functional Languages for Embedded Systems * Functional Programming Applied to Global Computing * Functional GRIDs * Functional Programming Ideas in Imperative or Object-Oriented Settings (and the converse) * Interoperability with Imperative Programming Languages * Novel Memory Management Techniques * Parallel/Concurrent Functional Languages * Program Transformation Techniques * Empirical Performance Studies * Abstract/Virtual Machines and Compilers for Functional Languages * New Implementation Strategies * Any new emerging trend in the functional programming area If you are in doubt on whether your article is within the scope of TFP, please contact the TFP 2009 program chairs, Zoltan Horvath and Viktoria Zsok at tfp2009(a)inf.elte.hu<mailto:tfp2009@inf.elte.hu> SUBMISSION AND DRAFT PROCEEDINGS Acceptance of articles for presentation at the symposium is based on the screening process of full papers (15 pages) and extended abstracts (at least 3 pages). TFP encourages PhD students to submit papers. PhD students may request the program committee to provide extensive feedback on their full papers at the time of submission. Full papers describing work accepted for presentation must be completed before the symposium for publication in the draft proceedings. Further details can be found at the TFP 2009 website. POST-SYMPOSIUM REFEREEING AND PUBLICATION In addition to the draft symposium proceedings, we continue the TFP tradition of publishing a high-quality subset of contributions in the Intellect series on Trends in Functional Programming. PROGRAM COMMITTEE * Peter Achten (symp-chair), Radboud University Nijmegen, NL * John Clements, California Polytechnic State University, USA * Cormac Flanagan, University of California at Santa Cruz, USA * Jurriaan Hage, Utrecht University, NL * Kevin Hammond, University of St. Andrews, UK * Michael Hanus, Christian-Albrechts University zu Kiel, DE * Ralf Hinze, University of Oxford, UK * Zoltan Horvath (PC co-chair), Eotvos Lorand University, HU * Graham Hutton, University of Nottingham, UK * Johan Jeuring, Utrecht University, NL * Pieter Koopman (symp-chair), Radboud University Nijmegen, NL * Hans-Wolfgang Loidl, Ludwig-Maximilians University Munchen, DE * Rita Loogen, Philipps-University Marburg, DE * Greg Michaelson, Heriot-Watt University, UK * Marco T. Morazan, Seton Hall University, USA * Rex L Page, University of Oklahoma, USA * Sven-Bodo Scholz, University of Hertfordshire, UK * Clara Segura, University Complutense de Madrid, ES * Mary Sheeran, Chalmers University of Technology, SE * Phil Trinder, Heriot-Watt University, UK * Marko van Eekelen, Radboud University Nijmegen, NL * Varmo Vene, University of Tartu, EE * Viktoria Zsok (PC co-chair), Eotvos Lorand University, HU LOCATION The Conference Centre of Selye University, Komarno, Slovakia (http://www.selyeuni.sk/) is a new and excellent conference centre with modern equipment, lecture rooms and computer labs. Komarno is on the north bank of river Danube, the northern part of the city Komarom / Komarno. It is a charming old city with about 30 000 inhabitants, 90 km away from Budapest (the capital of Hungary), with good highway and railway connections and 90 km away from Bratislava (the capital of Slovakia), about 100 km from Vienna International Airport.

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The Monad.Reader (14) - Call for copy
by Wouter Swierstra 14 Apr '09

14 Apr '09

Call for Copy The Monad.Reader - Issue 14 Please consider writing something for the next issue of The Monad.Reader. The deadline for Issue 14 is: ** May 15, 2009 ** The Monad.Reader is a electronic magazine about all things Haskell. Check out the website and browse the previous editions to learn more: http://www.haskell.org/haskellwiki/The_Monad.Reader * Submission Details * Get in touch if you intend to submit something -- the sooner you let me know what you're up to, the better. Please submit articles for the next issue to me by e-mail (wouter at chalmers.se). Articles should be written according to the guidelines available from: http://www.haskell.org/haskellwiki/The_Monad.Reader Please submit your article in PDF, together with any source files you used. The sources will be released together with the magazine under a BSD license. Looking forward to your submission, Wouter

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Haskell Weekly News: Issue 113 - April 13, 2009
by Brent Yorgey 13 Apr '09

13 Apr '09

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20090413 Issue 113 - April 13, 2009 --------------------------------------------------------------------------- Welcome to issue 113 of HWN, a newsletter covering developments in the [1]Haskell community. Announcements xmobar-0.9.2. Andrea Rossato [2]announced the release of [3]xmobar-0.9.2, which features a fix for a longstanding resource leakage bug, new nested color definitions, and more. CFP Haskell Symposium 2009. Stephanie Weirich [4]reminded everyone that there are only 4 weeks until the submission deadline for the [5]2009 Haskell Symposium! hmatrix-static: statically-sized linear algebra. Reiner Pope [6]announced the release of [7]hmatrix-static, a thin wrapper over Alberto Ruiz's excellent [8]hmatrix library for linear algebra. The main additions of hmatrix-static over hmatrix are that vectors and matrices have their length encoded in their types, and vectors and matrices may be constructed and destructed using view patterns, affording a clean, safe syntax. haskellmode for Vim now at projects.haskell.org. Claus Reinke [9]announced that the Haskell mode plugins for Vim have just completed their move to their [10]new home, and took the opportunity to reiterate what they can do (quite a lot, it seems), and mention that some screencasts are available. MSem replacement for QSem. ChrisK [11]announced [12]MSem, a proposed replacement module for Control.Concurrent.QSem. Hac5 is almost upon us!. Sean Leather [13]reminded everyone that in six days, tens of crazy/obsessed, type-safe, functional programmers will be converging on Utrecht to commence execution of the [14]5th Haskell Hackathon, from April 17-19, 2009 in Utrecht, The Netherlands! The local organizing team welcomes you all and looks forward to all of the new developments that come out of everyone's undying quest to write more and better code. Yogurt-0.4. Martijn van Steenbergen [15]announced version 0.4 of [16]Yogurt, a functional MUD client. Version 0.4 makes Yogurt available as a standalone executable that is able to dynamically load and reload Yogurt scripts. Elerea, another FRP library. Patai Gergely [17]announced the release of [18]Elerea, aka "Eventless reactivity", a minimalistic FRP implementation that comes with a convenient applicative interface, supports recursive definition of signals and signals fed from outside by IO actions, plays nice with resources, and is the result of some furious hacking. There are working examples to show off the current capabilities of the library, found in the separate [19]elerea-examples package. tree-monad 0.2. Sebastian Fischer [20]announced version 0.2 of the [21]tree-monad package, which provides instances of MonadPlus that represent the search space of non- deterministic computations as a tree. Version 0.2 implements an optimized CPS version of the tree. HCard -- A library for implementing card-like structures.. Joe Fredette [22]announced the release of [23]HCard, a library which supports a card-like data structures and uses associated types to provide shuffling, dealing, and other facilities. It's general enough to support many different types of playing cards; it currently comes with the common "French Deck" (4-suit, 13 card deck that is very common in the US) implemented and an example cribbage scoring application. SVGFonts 0.1. Tillmann Vogt [24]announced his first Haskell library, [25]SVGFonts 0.1, which parses the relatively unknown SVG Font format to produce outlines of characters. The big advantage of this format is that it is XML, which means easy parsing and manipulating. network-bytestring 0.1.2. Johan Tibell [26]announced a new release of [27]network-bytestring, a Haskell library for fast socket I/O using ByteStrings. New in this release is support for scatter/gather I/O (also known as vectored I/O). Scatter/gather I/O provides more efficient I/O by using one system call to send several separate pieces of data and by avoiding unnecessary copying. Jobs Lecturer in Computer Science, University of Leicester. Roy L. Crole [28]announced an opening for a lectureship at the University of Leicester. The successful candidate will have a strong or promising research record in computer science, with a background in formal foundations (either algorithms and complexity, or semantics of programming or modelling languages), and will be able to contribute to undergraduate and postgraduate teaching and supervision in software engineering. Blog noise [29]Haskell news from the [30]blogosphere. * Mark Wassell: [31]Edge Detection in Haskell. * Sean Leather: [32]Latest on the incremental fold and attributes. * Sean Leather: [33]Haskell mode for Vim on a Mac. * Sean Leather: [34]Incremental attributes. * >>> Human Constraints: [35]Haskell Type Hackery. * LHC Team: [36]A new beginning.. * London Haskell Users Group: [37]Don Stewart: Engineering Large Projects in Haskell: A Decade of Haskell at Galois. * Ulisses Costa: [38]More Hylomorphisms in Haskell. * Ulisses Costa: [39]Anamorphisms in Haskell. * London Haskell Users Group: [40]Next Meeting: Don Stewart from Galois. * LHC Team: [41]Hello world!. * mightybyte: [42]Adding Authentication to the Blog App. * Leon Smith: [43]Polynomial multiplication. * Joe Fredette: [44]Card games, scorekeeping, and ... Associated Datatypes?. * mightybyte: [45]Basic Happstack Blog App. * mightybyte: [46]A Standalone Auth Framework for Happstack. * Mads Lindstrøm: [47]Introducing WxGeneric. * happstack.com: [48]2 new projects that use Happstack. * >>> Brant Carlson: [49]Lightning Modeling in Haskell. * Leon Smith: [50]Lloyd Allison's Corecursive Queues. About the Haskell Weekly News New editions are posted to [51]the Haskell mailing list as well as to [52]the Haskell Sequence and [53]Planet Haskell. [54]RSS is also available, and headlines appear on [55]haskell.org. To help create new editions of this newsletter, please see the information on [56]how to contribute. Send stories to byorgey at cis dot upenn dot edu. The darcs repository is available at darcs get [57]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://article.gmane.org/gmane.comp.lang.haskell.general/17080 3. http://code.haskell.org/~arossato/xmobar/ 4. http://article.gmane.org/gmane.comp.lang.haskell.general/17072 5. http://haskell.org/haskell-symposium/2009/ 6. http://article.gmane.org/gmane.comp.lang.haskell.cafe/56772 7. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hmatrix-static 8. http://www.hmatrix.googlepages.com/ 9. http://article.gmane.org/gmane.comp.lang.haskell.cafe/56495 10. http://projects.haskell.org/haskellmode-vim/ 11. http://article.gmane.org/gmane.comp.lang.haskell.cafe/56761 12. http://haskell.org/haskellwiki/SafeConcurrent 13. http://article.gmane.org/gmane.comp.lang.haskell.cafe/56758 14. http://haskell.org/haskellwiki/Hac5 15. http://article.gmane.org/gmane.comp.lang.haskell.cafe/56747 16. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Yogurt 17. http://article.gmane.org/gmane.comp.lang.haskell.cafe/56731 18. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/elerea 19. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/elerea-examples 20. http://article.gmane.org/gmane.comp.lang.haskell.cafe/56639 21. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/tree%2Dmonad 22. http://article.gmane.org/gmane.comp.lang.haskell.cafe/56573 23. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HCard 24. http://article.gmane.org/gmane.comp.lang.haskell.cafe/56444 25. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/SVGFonts 26. http://article.gmane.org/gmane.comp.lang.haskell.cafe/56374 27. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/network-bytestri… 28. http://article.gmane.org/gmane.comp.lang.haskell.general/17066 29. http://planet.haskell.org/ 30. http://haskell.org/haskellwiki/Blog_articles 31. http://www.poundstone.org/blog/?p=137 32. http://feedproxy.google.com/~r/splonderzoek/~3/KWqNCgsK1ww/latest-on-increm… 33. http://feedproxy.google.com/~r/splonderzoek/~3/0QNaK4byWhg/haskell-mode-for… 34. http://feedproxy.google.com/~r/splonderzoek/~3/4B0bHoeTCeQ/incremental-attr… 35. http://blog.human-constraints.com/?p=49 36. http://lhc-compiler.blogspot.com/2009/04/new-beginning.html 37. http://www.londonhug.net/2009/04/10/don-stewart-engineering-large-projects-… 38. http://ulissesaraujo.wordpress.com/2009/04/09/more-hylomorphisms-in-haskell/ 39. http://ulissesaraujo.wordpress.com/2009/04/08/anamorphisms-in-haskell/ 40. http://www.londonhug.net/2009/04/09/next-meeting-don-stewart-from-galois/ 41. http://lhc-compiler.blogspot.com/2009/04/hello-world.html 42. http://softwaresimply.blogspot.com/2009/04/adding-authentication-to-blog-ap… 43. http://blog.melding-monads.com/2009/04/07/polynomial-multiplication/ 44. http://lowlymath.net/2009/card-games-scorekeeping-and-associated-datatypes/ 45. http://softwaresimply.blogspot.com/2009/04/basic-happstack-blog-app.html 46. http://softwaresimply.blogspot.com/2009/04/standalone-auth-framework-for-ha… 47. http://lindstroem.wordpress.com/2008/05/03/introducing-wxgeneric/ 48. http://blog.happstack.com/2009/04/06/2-new-projects-that-use-happstack/ 49. http://bayern.stanford.edu/~brant/lightning/ 50. http://blog.melding-monads.com/2009/03/09/lloyd-allisons-corecursive-queues/ 51. http://www.haskell.org/mailman/listinfo/haskell 52. http://sequence.complete.org/ 53. http://planet.haskell.org/ 54. http://sequence.complete.org/node/feed 55. http://haskell.org/ 56. http://haskell.org/haskellwiki/HWN 57. http://code.haskell.org/~byorgey/code/hwn/

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seeking papers with good examples of the use of GADTs
by nr＠cs.tufts.edu 13 Apr '09

13 Apr '09

I have a class of beginning functional programmers; we're approaching end of term, and I'd like them to learn about GADTs. One of my goals in the class is to give students practice learning by reading papers, so I am asking for recommendations of papers that have good examples of GADTs in action. Papers I've used in the past have included Pottier and Gauthier 2005: Polymorphic Typed Defunctionalization and Concretization, in Higher-Order and Symbolic Computation Pottier and Régis-Gianas 2006: Towards Efficient, Typed LR Parsers, in Electr. Notes Theor. Comput. Sci and Peyton Jones et al. 2006: Simple unification-based type inference for GADTs, in the 11th ACM SIGPLAN International Conference on Functional Programming. Unfortunately the first two rely on concepts in which my students have little background (LR parsing and defunctionalization respectively), and the the third, while it opens with a nice example, is primarily about the (now obsolete) type-inference algorithm, rather than about how to use GADTs. I am hoping some of you may have suggestions about other papers that would be good tutorials in the use of GADTs. Norman

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how can I refer to a symbol in a module that is imported 'qualified'?
by nr＠cs.tufts.edu 12 Apr '09

12 Apr '09

I need to resolve a name clash between two different Haskell modules that want to use the same infix operator (<*>). The Haskell 98 report says that modid.varsym is permitted, but I can't get it to work. In their entirety here are Test.hs: module Test where import qualified Test2 as T three = T.<*> and Test2.hs: module Test2 where (<*>) = 3 But trying to compile results in an error message: Test.hs:6:12: parse error on input `T.<*>' I tried T.(<*>) but that doesn't work either (as indeed the Haskell 98 report says it should not). How can I refer to a symbolic name defined in a module imported by `import qualified`? Norman

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ANN xmobar-0.9.2
by Andrea Rossato 11 Apr '09

11 Apr '09

Hi, I'm glad to announce xmobar-0.9.2. What's new: - Norbert Zeh tracked and fixed a longstanding bug that made xmobar leak X resources. This alone makes it worth this release and its public announcement, with the advice to users to upgrade.[*] - Norbert also overhauled the template parser to allow nested color definitions; - Norbert, once again, added the possibility to add color definitions in the monitors' templates. Many thanks to Norbert!! I've read that xmobar lists in the top 25 most downloaded Hackage packages. This is very cool: thanks to all the xmobar users. Hope you'll enjoy. Andrea [*] I tend to believe the same issue affects xmonad, even though it should be visible only after a huge number of restarts. Things get far worse when it comes to the xmonad-contrib library, especially if you use fancy decorations in your layouts: if you see colors you are probably leaking them.

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Hac5 is almost upon us!
by Sean Leather 11 Apr '09

11 Apr '09

In six days, tens of crazy/obsessed, type-safe, functional programmers will be converging on Utrecht to commence execution of... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The 5th Haskell Hackathon April 17 - 19, 2009 Utrecht, The Netherlands ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The local organizing team welcomes you all and looks forward to all of the new developments that come out of everyone's undying quest to write more and better code. As always, you can find lots of useful information on the wiki: http://haskell.org/haskellwiki/Hac5 == Sponsors == We have sponsors! The following companies were very gracious to provide us with support during these tough economic times. * Galois - http://galois.com/ * Microsoft Research - http://research.microsoft.com/ * Tupil - http://tupil.com/ The organizers are incredibly grateful to Galois, MSR, and Tupil for helping to encourage and promote more Haskell hacking. == More To Come == Hopefully, you have already registered, booked your room, and bought your ticket. If not, don't forget that you can keep in touch with the attendees via IRC on Freenode: #haskell-hac5 All registered attendees will soon be receiving an email with more details. Let us know if you have any questions. Happy Hacking! == 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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Re: Hi-res/vector version of logo?
by Brian Sniffen 11 Apr '09

11 Apr '09

> Sure, I'm happy to convert the PSDs (available in the src/ directory, > here [1]) into SVG, but I will have to do so through tracing them in > InkScape unless somebody has another solution. Many of those are on one basic template. I have no expertise to advice on the choice of greys, but I do like MetaPost. I have created a basic metapost encoding of your logo7, and placed it at <http://evenmere.org/~bts/haskell-logo/>. I'm not entirely thrilled with its use of explicit constants to end the equal sign or place the groin of the lambda, but this'll do for a first draft. A PDF generated from that MetaPost file is there as logo-0.pdf for easy evaluation. I experimented with the PDF-to-SVG converter at <http://www.tlhiv.org/MetaPost/tools/mptosvg/>, but do not expect anyone to be thrilled with the results who must edit them. I also experimented with potrace. The results will are wiggly. They may be inspected at .../potrace/. -Brian -- Brian T. Sniffen bts(a)alum.mit.edu or brian.sniffen(a)gmail.com http://www.evenmere.org/~bts

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Ann: Yogurt-0.4
by Martijn van Steenbergen 10 Apr '09

10 Apr '09

Bonsoir café, It is my pleasure to announce version 0.4 of Yogurt, a functional MUD client. Version 0.4 makes Yogurt available as a standalone executable that is able to dynamically load and reload Yogurt scripts. Here is a small example of such a script: > module Minimal where > > import Network.Yogurt > > newmoon :: Session > newmoon = session > { hostName = "eclipse.cs.pdx.edu" > , portNumber = 7680 > , mudProgram = \reload -> do > mkCommand "reload" reload > } Valid scripts define at least one session which is used to connect to the MUD. mudProgram fields are provided with a reload action that when invoked reloads the script without interrupting the MUD connection. Of course, Yogurt also still offers hooks, timers, logging, variables and more. The executable is released as a separate package so that developers wishing to use just the "pure" machinery can do that without inheriting dependencies on the GHC API or readline library. To install the executable, run: $ cabal update $ cabal install Yogurt -freadline $ cabal install Yogurt-Standalone Yogurt's new home page can be found at: http://code.google.com/p/yogurt-mud/ And on hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Yogurt http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Yogurt-Standalone I would love to hear your feedback! Suggestions, complaints, comments, bug reports, experiences et cetera are all welcome. Kind regards, Martijn.

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