May 2008 - Haskell - Haskell.org

looking for interesting examples with recursion + state in which you'd want to prove termination
by Byron Cook 20 May '08

20 May '08

Hi Haskell folks, I'm looking for interesting recursive functions (i.e. not tail-recursive) that make use of state in the state monad. I'd like to prove them terminating with a new method I'm developing (or, of course, perhaps disprove termination....). If you have examples in this class that you wouldn't mind sharing, please send them to me. - Byron http://research.microsoft.com/~bycook

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release manager needed for Gtk2Hs
by Axel Simon 17 May '08

17 May '08

Good morning all, the Gtk2Hs library, one of the two major GUI libraries for Haskell, is in need of a release manager. With the upcoming HACR, I have realised that we haven't released in a long time despite the fact that there are many new developments in the darcs repository (the ListStore and TreeStore implemented in Haskell are now usable from all relevant widgets, e.g., ComboBox, IconView). Duncan has been busy working on Cabal which will allow us to swap Gtk2Hs' autoconf-based infrastructure to Cabal one day. I myself have relocated and very limited access to the various platforms that Gtk2Hs runs on. So while I'm still pushing towards a 1.0 release by working on Gtk2Hs, I don't have the resources to do the releases. Helping us releasing Gtk2Hs does not imply a long-term commitment. For now, we'd be very grateful for somebody helping us out with the next two releases (now and around Xmas). Ideally you have: - Access to a Linux, Windows, Sun and MacOS machine (no biggie if you don't have a Mac). - Root access to the Linux and Windows machine. - Experience using autoconf, possibly automake. - Knowledge of darcs. - Experience of how broken sed on Solaris is. - Machines that have a really ancient versions of Gtk installed. - One machine that has the latest Gtk installed as well as the SourceView widget, one of the HTML browser widgets, libglade, svgcairo, gconf, gnomevfs, glext and gstreamer libraries. What we would like you to do is: - Fix configuration issues that people have reported. - Build the library on all platforms mentioned above. - Build a source release. - Produce a binary installer on Windows. - Put the documentatio online. - Make announcements. What would be great: - Build a binary installer for Mac using the Aqua port of Gtk+. - Make the library build documentation using the new haddock. What you get out of it: - Experience working with a 82 kLoc Haskell project. - Mentioned in the Hall of Fame on our webpage. - Eternal gratefulness from us and our growing community of users. - A beer from me or Duncan when the situation arises. If you're interested, please send an email to me or Duncan. Cheers, Axel.

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Translation of the "Haskell Tutorial for C Programmers"
by Gorgonite 13 May '08

13 May '08

Hello, I don't know if there are French-speaking people reading this mailing-list, but we at haskell-fr have some great news today ! We didn't find any French translation of the "Haskell Tutorial for C Programmers", thus we decide to write it. Today, I would like to announce that we have completed a translation into French, that it can be read by following the link : http://corentin-dupont.developpez.com/tutoriels/haskell/haskell-for-c-progr…<http://gorgonite.developpez.com/livres/traductions/haskell/gentle-haskell/> It is currently available as a set of HTML pages and PDF file. Please send your comments and suggestions to the French Haskell mailing list haskell-fr(a)haskell.org Best regards,

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Announce: SCC, Streaming Component Combinator library
by Mario Blazevic 09 May '08

09 May '08

I'm pleased to announce the 0.1 release of Streaming Component Combinators in Haskell, based on my earlier work done in OmniMark and published in paper Mario Blažević, Streaming component combinators, Extreme Markup Languages, 2006. http://www.idealliance.org/papers/extreme/proceedings/html/2006/Blazevic01/… The release consists of the following: - Yet another monad transformer with coroutine functionality. Its central feature is the function pipe :: forall context x m r1 r2. Monad m => Producer m x r1 -> Consumer m x r2 -> Pipe context m (r1, r2) - Based on the above, streaming component types Transducer and Splitter are defined, as well as a number of primitive component instances. - Next are component combinators that can be used to synthesize larger components. - Finally, there is a rudimentary executable, shsh (Streaming Haskell SHell), that exposes most of the above within a command-line shell. It's useful for experiments and testing of new components. Here are a few simple command examples: wc -c count | show | concatenate wc -l foreach line then substitute x else suppress end | count | show | concatenate grep "foo" foreach line having substring "foo" then append "\n" else suppress end sed "s:foo:bar:" foreach substring "foo" then substitute "bar" end sed "s:foo:[\\&]:" foreach substring "foo" then prepend "[" | append "]" end The SCC library and shell are available on Hackage, at http://hackage.haskell.org/cgi-bin/hackage-scripts/package/scc-0.1

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[Haskell-cafe] Help with polymorphic functions
by Wei Yuan Cai 09 May '08

09 May '08

Hello, I'm having some trouble with a polymorphic function using another polymorphic function within. A simplified code of what I'm trying to do is as follows: main = print $ test 1 8 test :: a -> Int -> a test x n = shift x n I get the following compilation error: Could not deduce (Data.Bits.Bits a) from the context () arising from a use of `shift' at test.hs:8:11-19 Possible fix: add (Data.Bits.Bits a) to the context of the type signature for `test' In the expression: shift x n In the definition of `test': test x n = shift x n shift is defined as "a -> Int -> a" What am I doing wrong here? Thanks, Weiyuan

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REMINDER: Haskell Communities and Activities Report
by Janis Voigtlaender 09 May '08

09 May '08

Dear Haskellers, It is not yet too late to contribute to the 14th edition of the HC&A Report. The deadline is this weekend, Saturday, 10 May 2008. If you haven't already, please write an entry for your new project or update your old entry. Please mail your entries to <hcar at haskell dot org> in plain text or LaTeX format. More information can be found in the original Call for Contributions at http://www.haskell.org/pipermail/haskell/2008-April/020378.html We look forward to receiving your contributions. Thanks a lot, Andres and Janis. -- Dr. Janis Voigtlaender http://wwwtcs.inf.tu-dresden.de/~voigt/ mailto:voigt@tcs.inf.tu-dresden.de

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Re: [Haskell] [Haskell-cafe] Help with polymorphic functions
by Wei Yuan Cai 08 May '08

08 May '08

Thank you all for the help. This was most helpful. Regards, Weiyuan On Fri, May 9, 2008 at 8:16 AM, Brett G. Giles <brett.giles(a)ucalgary.ca> wrote: > Hi Wei > > Haskell needs to know that it can legally apply the function "shift". > So, as requested, you need to add context to the typing of "test". > > if you define your function as: > > test :: (Data.Bits.Bits a) => a -> Int -> a > test x n = shift x n > > you should be fine. > > On Fri, 2008-05-09 at 03:10 +0800, Wei Yuan Cai wrote: > > Hello, > > > > I'm having some trouble with a polymorphic function using another > > polymorphic function within. A simplified code of what I'm trying to > > do is as follows: > > > > main = print $ test 1 8 > > > > test :: a -> Int -> a > > test x n = shift x n > > > > I get the following compilation error: > > > > Could not deduce (Data.Bits.Bits a) from the context () > > arising from a use of `shift' at test.hs:8:11-19 > > Possible fix: > > add (Data.Bits.Bits a) to the context of > > the type signature for `test' > > In the expression: shift x n > > In the definition of `test': test x n = shift x n > > > > > > shift is defined as "a -> Int -> a" > > > > What am I doing wrong here? > > > > Thanks, > > Weiyuan > > _______________________________________________ > > Haskell mailing list > > Haskell(a)haskell.org > > http://www.haskell.org/mailman/listinfo/haskell > >

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Workshop on Generic Programming: Call for Papers (co-located w/ ICFP08)
by Matthew Fluet (ICFP Publicity Chair) 08 May '08

08 May '08

CALL FOR PAPERS Workshop on Generic Programming 2008 Victoria, Canada, 20th September 2008 http://www.comlab.ox.ac.uk/ralf.hinze/wgp2008/cfp.{html,pdf,ps,txt} The Workshop on Generic Programming is sponsored by ACM SIGPLAN and forms part of ICFP 2008. Previous Workshops on Generic Programming have been held in Marstrand (affiliated with MPC), Ponte de Lima (affiliated with MPC), Nottingham (informal workshop), Dagstuhl (IFIP WG2.1 Working Conference), Oxford (informal workshop), Utrecht (informal workshop), and Portland (affiliated with ICFP). Scope ----- 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, but only recently have generic programming techniques become a specific focus of research in the functional and object-oriented programming language communities. This workshop will bring together leading researchers in generic programming from around the world, and feature papers capturing the state of the art in this important emerging area. We welcome contributions on all aspects, theoretical as well as practical, of o adaptive object-oriented programming, o aspect-oriented programming, o component-based programming, o generic programming, o meta-programming, o polytypic programming, o programming with modules, and so on. Submission details ------------------ Deadline for submission: 30th June 2008 Notification of acceptance: 14th July 2008 Final submission due: 28th July 2008 Workshop: 20th September 2008 Authors should submit papers, in PostScript or PDF format, formatted for A4 paper, to Ralf Hinze (ralf.hinze(a)comlab.ox.ac.uk) or Don Syme (Don.Syme(a)microsoft.com) by 30th June 2008. The length should be restricted to 12 pages in standard (two-column, 9pt) ACM. Accepted papers are published by the ACM and will additionally appear in the ACM digital library. Programme committee ------------------- Ralf Hinze (co-chair) University of Oxford Patrik Jansson Chalmers University Andrew Lumsdaine Indiana University Conor McBride University of Nottingham Adriaan Moors Universiteit Leuven Fritz Ruehr Willamette University Tim Sheard Portland State University Don Syme (co-chair) Microsoft Research Todd Veldhuizen University of Waterloo

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The Monad.Reader (11) - Call for Copy
by Wouter Swierstra 07 May '08

07 May '08

Call for Copy The Monad.Reader - Issue 11 Please consider writing something for the next issue of The Monad.Reader. The deadline for Issue 11 is ** August 1, 2008 ** It doesn't matter if you're a respected researcher or if you have only just started learning Haskell, get your thoughts together and write an article for The Monad.Reader! The Monad.Reader is a electronic magazine about all things Haskell. It is less formal than journal, but more enduring than a wiki-page or blog. There have been a wide variety of articles, including: exciting code fragments, intriguing puzzles, book reviews, tutorials, and even half-baked research ideas. * Submission Details * Get in touch with me 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 (wss at cs.nott.ac.uk). 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. If you would like to submit an article, but have trouble with LaTeX please let me know and we'll sort something out. All the best, Wouter This message has been checked for viruses but the contents of an attachment may still contain software viruses, which could damage your computer system: you are advised to perform your own checks. Email communications with the University of Nottingham may be monitored as permitted by UK legislation.

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ANN: SmallCheck 0.3
by Colin Runciman 06 May '08

06 May '08

SmallCheck 0.3: another lightweight testing library in Haskell -------------------------------------------------------------- A new version of SmallCheck can be obtained from: http://www.cs.york.ac.uk/fp/smallcheck0.3.tar Main differences from 0.2: * existential quantifiers now have unique variants for which two witnesses are reported when uniqueness fails; * the over-generating coseries method for functions of functional arguments has been replaced; * additional examples; * test counters are now Integers, not Ints! SmallCheck is similar to QuickCheck (Claessen and Hughes 2000-) but instead of testing for a sample of randomly generated values, SmallCheck tests properties for all the finitely many values up to some depth, progressively increasing the depth used. Folk-law: if there is any case in which a program fails, there is almost always a simple one. Corollary: if a program does not fail in any simple case, it almost never fails. Other possible sales pitches: * write test generators for your own types more easily * be sure any counter-examples found are minimal * write properties using existentials as well as universals * establish complete coverage of a defined test-space * display counter-examples of functional type Comments and suggestions welcome. Colin Runciman

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