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class variable dynamic inference
by Hugo Pacheco 14 Jun '07

14 Jun '07

Hi, I have defined some functors (with respective Functor instances) and a class that derives the equivalent non-functor representation class (Functor f) => Rep f a b | f a -> b My problem is that I need to define another class class (Functor f,Rep f d c) => FunctorOf f d | d -> f where in'' :: c -> d out'' :: d -> c where the variable c would be implicit and dynamically derived from the (f d) context. Of course this is not allowed as long as the variable c is not in the class context. Is there any way I can hack this around? defining the class functions like in'' :: Rep f d c => c -> d doesn't solve my problem as well. Thanks in advance, hugo

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Who pays for *.haskell.org machines?
by Malcolm Wallace 14 Jun '07

14 Jun '07

The haskell.org Summer-of-Code mentors are pleased to announce that money earned from the 2006 Google SoC (by the organisation, separately from student earnings) is now being spent for the community's benefit in maintaining the www.haskell.org web server. Previously, the server was kindly supported by Paul Hudak's academic grants at Yale. The server continues to be hosted at Yale, but is now being paid for directly by us, the Haskell language community. In addition, we are in the process of setting up a separate server called code.haskell.org which will offer project hosting to the Haskell world at large, along similar lines to darcs.haskell.org except open to anyone, and again funded by our Summer-of-Code activity. The details are still being finalised, so watch out for a fuller announcement. We are again participating in the 2007 GSoC, which will generate more income, which will eventually of course also go to furthering the Haskell community's aims. Many thanks to Galois for handling the SoC financial arrangements, not to mention that they also host darcs.haskell.org out of their own pocket. Regards, Malcolm

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PhD student on Real-life datatype-generic programming
by Johan Jeuring 13 Jun '07

13 Jun '07

=================================================== Vacancy PhD student on Real-life datatype-generic programming Software Technology, Utrecht University, The Netherlands. =================================================== Within the Software Technology group of the Information and Computing Sciences department of Utrecht University there is a vacancy for a PhD student to work on Real-life datatype-generic programming. The position is funded by NWO, the Netherlands Organisation for Scientific Research. ------------------------------------------------------------------------ ----------------- Project summary: Datatype-generic programming has been around for more than 10 years now. We think a lot of progress has been made in the last decade. As an example, there are more than 10 proposals for generic-programming libraries or language extensions just for the lazy functional- programming language Haskell. Although generic programming has been applied in several applications, it lacks users for real-life projects. This is understandable. Developing a large application takes a couple of years, and choosing a particular approach to generic programming for such a project involves a risk. Few approaches that have been developed over the last decade are still supported, and there is a high risk that the chosen approach will not be supported anymore, or that it will change in a backwards-incompatible way in a couple of years time. We propose to create an environment that supports developing real- life applications using generic-programming techniques. We will focus on developing: - a library or a mixture of a library with a language extension for which we will guarantee continuing support. - an example of a real-life application fundamentally using generic- programming techniques. This application will serve as a showcase for generic-programming support for software development and evolution. - generic-programming design patterns. The usage of the generic- programming techniques in real-life projects will exhibit recurrent patterns, and will give valuable advice for and help with developing other applications using generic-programming techniques. Thus we will show how generic programming can be used to develop powerful tools in little time, and that the resulting tools are easy to maintain, adapt, and reuse. ------------------------------------------------------------------------ ----------------- Requirements: Master degree in Computer Science, or equivalent. Good knowledge of functional programming, and several advanced computer science techniques. Knowledge of Haskell, parsing, rewriting, strategies, generic programming, etc. will be useful. Terms of employment: the PhD student should start as soon as possible, but no later than January 1, 2008. The position is for four years (after one year there will be an evaluation), full-time. Gross salary starts with € 1956,-- per month in the first year and increases to € 2502,-- in the fourth year of employment. The salary is supplemented with a holiday bonus of 8% and an end-of-year bonus of 3%. In addition we offer: a pension scheme, partially paid parental leave, facilities for child care, flexible employment conditions in which you may trade salary for vacation days or vice versa. Conditions are based on the Collective Employment Agreement of the Dutch Universities. More information about the project can be found on http:// www.cs.uu.nl/~johanj/publications/nwo-ew2006.pdf More information about the Software Technology group on http:// www.cs.uu.nl/wiki/Center More information about the Information and Computing Sciences department on http://www.cs.uu.nl/ More information about this vacancy can be obtained from Johan Jeuring (johanj(a)cs.uu.nl, http://www.cs.uu.nl/~johanj/, +31 6 40010053). Send your application in pdf (or another non-proprietary format) to SciencePenO(a)uu.nl with a cc to johanj(a)cs.uu.nl. on or before July 31, 2007. We expect to arrange interviews in September. Mention vacancy nr 62712.

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Haskell Workshop Deadline is approaching
by Gabriele Keller 13 Jun '07

13 Jun '07

Just a reminder that the deadline for the Haskell Workshop is this Friday, 15th of June! More info: http://www.cse.unsw.edu.au/~keller/haskellws/HaskellWorkshop.html Cheers, Gabriele

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Fwd: Mutually dependent functions
by Michael Speer 13 Jun '07

13 Jun '07

The code I reference is located at : http://michaelspeer.blogspot.com/2007/06/impossible-is-only-possible-someti… In the code I am building a parser for regular expressions. I know it is possible with ghc to have a function that accepts its own output as its input so long as it does not utilize that piece of output in generating itself. E.g. test x y = ( "World" , x , x ++ " " ++ y ) main = let ( a , b , c ) = test "Hello" a in do print $ ( a , b , c ) -- emits ("World","Hello","Hello World") This contrived example works properly. A more complex example can be found in the linked-to function `aexn' ( and-extracted-nodes ). It seems though, if you try this same trick with two different functions that rely on each others input and output, that the compiler will generate code, but the generated program causes the stack to overflow as each function tries to force the other one to evaluate first and neither bows out releasing an output of promises so that the two functions can resolve. They seem to encounter a lack of laziness. Well, more a duplication of effort. I specifically refer to the linked function `oexn' ( or-extracted-function-nodes ) that performs this feat. Or would if the program worked after being compiled. If the compiler were forced to only make the function call once and mark all variables generated by it immediately with either proper values or promises than the second functions call would receive the promises in place of the empty variables it feels the need to call the original function to fill. Are the promises added to the stack before or after the call? If after, then putting them on before may resolve this. It would likely make the implementation slower to do so however. Is this a known problem that will one day be resolved, or is it considered beyond the scope of the language? As I only use ghc, I am unfamiliar if one of the other implementations could handle this. I have seen nothing referring to it though out my searches regarding the matter. - michael speer

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ANNOUNCE: Harpy -- run-time code generation library
by Dirk Kleeblatt 12 Jun '07

12 Jun '07

Hi everybody, we're pleased to announce the first release of Harpy. Harpy is a library for run-time code generation of x86 machine code. It provides not only a low level interface to code generation operations, but also a convenient domain specific language for machine code fragments, a collection of code generation combinators and a disassembler. Harpy homepage: http://uebb.cs.tu-berlin.de/harpy/ Kind regards, Martin Grabmüller and Dirk Kleeblatt

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CfP: 2nd CEFP Functional Programming School, June 23-30, 2007
by HORVATH Zoltan 11 Jun '07

11 Jun '07

2nd Central-European Functional Programming School CEFP 2007 Cluj-Napoca, June 23-30, 2007 http://cs.ubbcluj.ro/cefp2007/ First Announcement - Call for participation - Call for PhD student presentation Aims and Scopes: The Central-European Functional Programming School (CEFP) is an intensive summer school series in the field of functional programming. The main goal is to bring together computer scientists, researchers, graduate and especially PhD students. The school would like to promote the research and the education of the functional programming languages, software technologies and programming methodologies. The second CEFP school will be organized by the Babeş-Bolyai University (Cluj-Napoca / Kolozsvár / Klausenburg) between 23-30 June, 2007. The previous school was held in Budapest, Hungary, July, 2005. The invited lecturers are prominent researchers in the field, and they will present state-of-the-art functional programming techniques. Beside the lectures practical courses will be held. The school includes a workshop for PhD students to present their work and get feed-back from the lecturers. Invited Lecturers: Rinus Plasmeijer (Radboud University Nijmegen, The Netherlands): iTasks: Defining Interactive Workflows for the Web Werner Kluge (Christian-Albrechts-Universität zu Kiel, Germany): Abstract Lambda Calculus Machines Marko van Eekelen (Radboud University Nijmegen, The Netherlands): Proving Properties of Lazy Functional Programs Tim Sheard (Portland State University, USA): The Omega Programming Language Ralf Hinze (Universität Bonn, Germany): Generics Three additional short courses will be given: Zoltán Horváth (Eötvös Loránd University, Budapest, Hungary): Refactoring Erlang Programs Zoltán Csörnyei (Eötvös Loránd University, Budapest, Hungary): Lambda-Calculus Horia F. Pop (Babeş-Bolyai University, Cluj-Napoca, Romania): A Tutorial on Object Orientedness in Functional Programming Submissions: PhD students are invited to submit the abstract of their presentations to be included in the workshop programme. Each presentation can be of max. 25 minutes. The full paper version can be submitted after the summer school. It is under negotiation to publish the revised lectures and the selected and reviewed papers in LNCS Volume. Venue: Cluj-Napoca / Kolozsvár / Klausenburg, formerly the capital of Transylvania, is one of the most beautiful medieval cities with a huge multicultural and historical inheritance. Surrounded by marvelous hills and mountains, the city provides fascinating environment for experiencing the unique ambience of a diversified culture, society and nature. Registration and costs: The registration fee (260 Euro) includes the course materials distributed during the school, the post-school volume, lunches, the excursion and the summer school banquet. For further information, accommodation possibilities and registration please visit the web-page of the event: http://www.cs.ubbcluj.ro/cefp2007. The deadline for registration and submissions is 1 June 2007.

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Bug in the HXT: Data.Char.UTF8.decodeOne
by Uwe Schmidt 11 Jun '07

11 Jun '07

I've got a bug report concerning the UTF decoding in HXT. I've copied the source containing the bug from the Haskell Internationalisation Working Group. I guess this source is also used in other projects, e.g. darcs. My question: Is this really a bug or is it a feature. My knowlege so far was, the intervall from E000 to FFFF is not legal in unicode. ---------- Forwarded Message ---------- Subject: Bug in the HXT: Data.Char.UTF8.decodeOne Date: Sunday 10 June 2007 07:40 From: PHO <phonohawk(a)ps.sakura.ne.jp> To: hxmltoolbox(a)fh-wedel.de Hello, I've found a bug in Data.Char.UTF8.decodeOne that it fails to decode UTF-8 letters from U+E000 to U+FFFF. Here is the patch: { hunk ./src/Data/Char/UTF8.hs 248 - | b1 < 0xEE = decodeOne_threebyte bs + | b1 < 0xF0 = decodeOne_threebyte bs } -------------------------------------------------------------- here is the source http://darcs.fh-wedel.de/hxt/src/Data/Char/UTF8.hs Any suggestions? Uwe Schmidt

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ANNOUNCE: Atom 2007.06
by Tom Hawkins 11 Jun '07

11 Jun '07

Atom is a high-level hardware description language embedded in Haskell that compiles conditional term rewriting systems into conventional HDL. New in this release: - User guided rule scheduling to help the compiler build the optimal scheduler. - Rule schedule visualization with Graphviz. gray edges: sequential composable rules red edges: feedback arcs (bad) blue edges: user defined scheduling constraints - Bug fix affecting "alwayActiveWhenEnabled" performance constraint. Enjoy! http://www.funhdl.org/ -Tom

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Please help!!!
by AVG 09 Jun '07

09 Jun '07

What's wrong?? greatest common divisor code: mdc :: Int-> Int -> Int mdc _ 1 = 1 mdc 1 _ = 1 mdc x y |x > y = mdc (x-y) y |y > x = mdc (y-x) x |x==y = x mdcl :: [Int]-> [Int] mdcl []=[] mdcl l = mdcl ([mdc (tira(take 1 l)) (tira(take 1 (drop 1 l)))]++ drop 2 l) gcdl :: [Int] -> Int gcdl l = tira l tira :: [Int] -> Int tira []=0 tira [x]=x -- View this message in context: http://www.nabble.com/Please-help%21%21%21-tf3895195.html#a11042870 Sent from the Haskell - Haskell mailing list archive at Nabble.com.

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