- Haskell-Cafe - Haskell.org

Removing mtl from the Haskell Platform
by roconnor＠theorem.ca 18 May '09

18 May '09

I wanted to pass this idea around the cafe to get some thoughts before submitting a trac on this topic. I'd like to see the mtl removed from the Haskell Platform. The mtl was a tremendous step forward when it was developed. However, we have learned a few things about monad transformers since the development of the mtl, and it is time that we moved forward. There are at least 3 significant problem with the mtl. 1) `pass' should not be a member functions of the MonadWriter class. It is my understanding that there is no `MonadWriter w m => MonadWriter w (ContT s m)' instance because the `pass' function cannot be implemented. I'm also highly suspicious of some other methods too (I'm looking at you `local'). 2) The `StateT s (Cont r a)' instance of callCC is wrong. The paper on modular monad transformers <http://www.cs.nott.ac.uk/~mjj/pubs/mmt/mmt.pdf> describes why this is wrong. 3) I am told by many people that the order of the state and value pair in `State' is backwards. Actually, I'm not entirely sure what the issue is here, but I trust the people who say this. I think that use of the mtl should be deprecated so that we move on to improved monad transformer libraries. Having the mtl in the Haskell Platform does the opposite by further entrenching its use, possibly to the point where we may not be able to get rid of it for years. If I had to recommend a replace library, I would pick monadLib. However, there are other libraries, such as the mmtl and transformers and it's related packages that I haven't looked at, and may also make fine replacements for the mtl. -- Russell O'Connor <http://r6.ca/> ``All talk about `theft,''' the general counsel of the American Graphophone Company wrote, ``is the merest claptrap, for there exists no property in ideas musical, literary or artistic, except as defined by statute.''

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community.haskell.org and code.haskell.org problems
by Neil Mitchell 18 May '09

18 May '09

Hi, I regularly (almost daily) have problems reaching both community and code.haskell.org, getting 500 server error messages. I've decided to make all my Haskell code available on community, which means that when it goes down, I can't access my repos - which is not great. Is there a reason for the poor reliability of these servers? Can anything be done to improve them? I'm very grateful for the availability of the service, but I know of servers running on Windows laptops which have far higher uptime :-) Thanks Neil

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TFM09: Last CFP (FMWeek, Eindhoven, November 6th 2009)
by J.N. Oliveira 18 May '09

18 May '09

TFM2009 2nd Int. FME Conference on Teaching Formal Methods "Widening Access to Formal Methods" Friday, November 6th 2009, co-located with FM2009 : 16th International Symposium on Formal Methods Eindhoven, the Netherlands, November 2 - November 6, 2009 CALL FOR PAPERS (URL: http://www.di.uminho.pt/tfm09) 1. About the conference ----------------------- Ten years after the First World Formal Methods Congress (FM'99) in Toulouse, formal methods communities from all over the world will once again have an opportunity to come together. As part of the First Formal Methods Week event surrounding the FM2009 conference in Eindhoven, Formal Methods Europe will be organizing TFM2009, the Second International Conference on Teaching Formal Methods. The conference will serve as a forum to explore the successes and failures of Formal Methods (FM) education, and to promote cooperative projects to further education and training in FMs. We would like to provide a forum for lecturers, teachers, and industrial partners to discuss their experience, present their pedagogical methodologies, and explore best practices. TFM2009 follows in a series of recent events on teaching formal methods, including: two BCS-FACS TFM workshops (Oxford in 2003, and London in 2006), the TFM 2004 conference in Ghent (with proceedings published as Springer LNCS Volume 3294), the FM-Ed 2006 workshop (Hamilton, co-located with FM'06), FORMED (Budapest, at ETAPS 2008), FMET 2008 (Kitakyushu 2008, co-located with ICFEM), etc. 2. Topics of interest --------------------- Formal methods (FM) have an important role to play in the development of complex computing systems - a role acknowledged in industrial standards such as IEC 61508 and ISO/IEC 15408, and in the increasing use of precise modeling notations, semantic markup languages, and model-driven techniques. There is a growing need for software engineers who can work effectively with simple, mathematical abstractions, and with practical notions of inference and proof. However, there is little clear guidance ? for educators, for managers, or for the engineers themselves ? as to what might comprise a basic education in FM. Neither the present IEEE/ACM Software Engineering Body of Knowledge (SWEBOK) nor the forthcoming Graduate Software Engineering Reference Curriculum (GSWERC) provide the kind of specific information that teachers and practitioners need to establish an adequate, balanced programme of learning in FM. Original contributions are solicited that provide insight, opinions, and suggestions for courses of action regarding the teaching FMs, including but not limited to the following aspects: * experiences of teaching FMs, both successful and unsuccessful; * educational resources including the use of books, case studies and the internet; * the education of weak and mathphobic students; * the integration, or otherwise, of FMs into the curriculum, including contributions to the definition of a Formal Methods Body of Knowledge (FMBOK); * the advantages of FM-trained graduates in the workplace; * changing attitudes towards FMs in students, academic staff and practitioners; * the necessary mathematical background. The conference proceedings will be published by Springer-Verlag in the LNCS series. Submissions may be up to 20 pages long using Springer's LNCS format. 3. Important dates ------------------ Please put the following dates in your diary: Submission deadline May 25, 2009 Notification of acceptance July 6, 2009 Final version August 3, 2009 4. How to submit ---------------- Papers for TFM2009 will be processed through the EasyChair conference management system. To submit your paper, please visit: http://www.easychair.org/conferences/?conf=tfm2009 5. Invited speakers ------------------- To be announced 6. Programme Committee ---------------------- Izzat Alsmadi (North Dakota State University, USA) Dines Bjorner (IIMM Institute, Denmark) Eerke Boiten (University of Kent, UK) Raymond Boute (Universiteit Gent, Belgium) Andrew Butterfield (Trinity College, Dublin) Jim Davies (University of Oxford, UK) David Duce (Oxford Brookes University, UK) John Fitzgerald (University of Newcastle upon Tyne, UK) Jeremy Gibbons (University of Oxford, UK) Randolph Johnson (National Security Agency, USA) Michael Mac an Airchinnigh (Trinity College, Dublin) Dino Mandrioli (Politecnico di Milano, Italy) Jose Oliveira (Universidade do Minho, Portugal) Kees Pronk (Technische Universiteit Delft, NL) Bernhard Schaetz (Tecnical University of Munique, Germany) Wolfgang Schreiner (Johannes Kepler University Linz, Austria) Simao Melo de Sousa (Universidade da Beira Interior, Portugal) Kenji Taguchi (National Institute of Informatics, Japan) Jeannette Wing (Carnegie-Mellon University, USA) 7. Sponsorship ---------------------- TFM2009 is supported by FME, the Formal Methods Europe Association

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ANNOUNCE: mathlink-2.0.0.3
by Tracy Wadleigh 18 May '09

18 May '09

Already posted to the Haskell list but dons suggested I post to the cafe, as well... All: mathlink is a library for writing Mathematica packages in Haskell. One simply writes some functions of type: (MLGet a, MLPut b) => a -> IO b and provides a package specification in a simple DSL that mimics that of Mathematica's mprep utility. The result is a program that exposes functions that can be called from Mathematica. This is a complete rewrite of my original implementation and more closely captures the functionality I originally intended. I've only tested it on my own platform (64-bit Linux), but I've taken pains to make sure the code should run on any platform. (The only real issue in the code is picking the right functions to call when marshaling Ints.) Please report any tweaks required to get it to work on your platform. (That is, of course, only if, in fact, there are any other users out there. Right now, as far as I know, I'm it.) I'd also just like to hear from any Haskellers out there that also use Mathematica on a regular basis. Ping me if you're one. --Tracy

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Re: [Haskell-cafe] Building a better dog house?
by michael rice 18 May '09

18 May '09

Hi Paul, I've been away from software design for more than a decade and have fallen behind on what's currently being used. I wasn't even aware of RUP. Thanks for the info. Michael --- On Sun, 5/17/09, Paul Johnson <paul(a)cogito.org.uk> wrote: From: Paul Johnson <paul(a)cogito.org.uk> Subject: Re: [Haskell-cafe] Building a better dog house? To: "michael rice" <nowgate(a)yahoo.com> Cc: haskell-cafe(a)haskell.org Date: Sunday, May 17, 2009, 3:26 PM michael rice wrote: > I was just looking at my UML (Unified Modeling Language) User Guide and discovered this: > > "The number of object-oriented methods increased from fewer than 10 to more than 50 during the period between 1989 and 1994." pg. xviii, Booch, Rumbaugh, Jacobson, 1999 > > Is there a modeling methodology recommended for functional languages? > > Michael > > UML of course is not a methodology, its a language. "Rational Unified Process" (RUP) is a methodology. There is no recommended methodology for functional programming, but large chunks of RUP and most similar methodologies have little to do with OO programming, and therefore could be used as-is. All the project planning, configuration management, requirements management and so on will work just fine. When it comes to the software design in functional languages I find it best to start by looking for a domain analysis of the problem (something that RUP includes as well, if I recall correctly). Then try to translate that domain analysis into an embedded domain specific language (EDSL). Ideally the EDSL should allow you to describe anything that is physically or logically possible in the domain, but nothing that is impossible. Then you can go ahead and create your software by translating the requirements directly into the EDSL. Paul.

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Building a better dog house?
by michael rice 18 May '09

18 May '09

I was just looking at my UML (Unified Modeling Language) User Guide and discovered this: "The number of object-oriented methods increased from fewer than 10 to more than 50 during the period between 1989 and 1994." pg. xviii, Booch, Rumbaugh, Jacobson, 1999 Is there a modeling methodology recommended for functional languages? Michael

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Can't install happs-tutorial because syb-with-class fails to install
by Colin Paul Adams 17 May '09

17 May '09

Data/Generics/SYB/WithClass/Derive.hs:187:26: Couldn't match expected type `Pred' against inferred type `Type' Expected type: PredQ Inferred type: TypeQ In the first argument of `map', namely `dataCxt' In the first argument of `(++)', namely `map dataCxt dataCxtTypes' Data/Generics/SYB/WithClass/Derive.hs:198:36: Couldn't match expected type `Pred' against inferred type `Type' Expected type: Q Pred Inferred type: TypeQ In the expression: conT 'Data `appT` typ In the first argument of `map', namely `(\ typ -> conT 'Data `appT` typ)' Data/Generics/SYB/WithClass/Derive.hs:227:38: Couldn't match expected type `Name' against inferred type `TyVarBndr' Expected type: [Name] Inferred type: [TyVarBndr] In the expression: ps In the first argument of `return', namely `(n, ps, map conA cs)' cabal: Error: some packages failed to install: syb-with-class-0.5.1 failed during the building phase. The exception was: exit: ExitFailure 1 -- Colin Adams Preston Lancashire

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Haskell Weekly News: Issue 118 - May 16, 2009
by Brent Yorgey 17 May '09

17 May '09

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20090516 Issue 118 - May 16, 2009 --------------------------------------------------------------------------- Welcome to issue 118 of HWN, a newsletter covering developments in the [1]Haskell community. Welcome to the Google Summer of Code special edition! I asked each of the five students with accepted GSoC projects to describe what they plan to work on. You'll find their descriptions below, with links to their blogs. And keep watching this space: as I did last summer, I plan to provide readers of the HWN with weekly updates on the progress of the GSoC projects. Google Summer of Code Haddock improvements! Isaac Dupree is [2]working on improvements to [3]Haddock. "Besides the various inevitable small fixes/improvements, my specific projects are to make cross-package documentation work, and to refactor the comment-parsing out of GHC and into the Haddock code-base." EclipseFP. Thomas Ten Cate will be [4]working on EclipseFP: "Compared to more mainstream languages, Haskell has surprisingly poor IDE support, even though its static typing system allows for much more help from the IDE than in the case of dynamic languages. For the Java language, a very mature and powerful IDE exists in the form of Eclipse. A plugin for Haskell support in Eclipse, called EclipseFP, is in the works, but its development has been standing still for some time. I will bring EclipseFP to a more usable state. For this, I will use the Scion IDE library, which interfaces with the GHC API, so that more advanced features like type inference become possible. I will also add support for Cabal. Hopefully, this type of IDE support will lead to greater acceptance and use of Haskell, and be useful for development as well as education." Improving the Haskell space profiling experience. Gergely Patai's [5]project will be focused on space profiling: "At the present moment, heap profiling Haskell programs means analysing logs off-line, using conversion tools to visualise data. However, instead of generating graphs with hp2ps, it should be possible to present the data in a graphical application in real time, which is useful while developing interactive applications, and it should also be made easier to export profiler output in different formats. The aim of the project is to create a set of tools that make heap profiling of Haskell programs easier in various ways. In particular, the following components are planned: a library to process profiler output in an efficient way and make it easily accessible for other tools in the future; a real-time visualiser (most likely using OpenGL); some kind of history manager to keep track of profiling data and make it possible to perform a comparative analysis of performance between different versions of your program; a maintainable and extensible replacement for hp2ps; and converters to provide input for other profiling tools." haskell-src-exts -> haskell-src. Niklas Broberg: "My [6]project, dubbed 'haskell-src-exts -> haskell-src' is really two projects in one wrapping. The first milestone is to bring my haskell-src-exts library to the point where it can supersede the old haskell-src library as the de facto package for haskell source manipulation. The main problem that I need to solve is to implement a scheme that lets the user decide what extensions to recognize when parsing a source document. Currently, haskell-src-exts assumes all extensions are always on, which means that some valid H98 programs will be incorrectly parsed due to stolen syntax by e.g. Template Haskell. The second milestone is to extend the focus from source code to full source documents, and implement a scheme for handling comments as well. The ultimate goal here is to have (pretty . parse) == id, to allow haskell-src-exts to be run on source documents without changing them. This would open up for some really interesting applications, in particular refactoring tools that could automatically apply transformations to a source document while still preserving comments." darcs. Last but not least, Petr Rockai will be [7]working on improvements to [8]darcs: "My project revolves around the idea of fast darcs for medium and large repositories. Three are quite a few haskellers who use darcs in their day to day (haskell) work. A fair number of hackage packages is maintained in darcs. Even though many of these repositories are of a relatively modest size, there is a number of relatively large real-world darcs repositories out there. The primary target of the project is to improve scalability of darcs for large working trees. This should help those users with existing large darcs repositories, as well as encourage people to use darcs for larger projects, whenever the development model fits. I intend to make the darcs working tree handling comparably fast to git. And then, git is written in C, hand-tuned for a specific operating system. And unlike mercurial, I do not plan to introduce a C library for low level routines. So let's prove that Haskell is up to the challenge." Announcements 2009.2.1: version freeze for Haskell Platform approaching on Monday. Don Stewart [9]announced that the last chance to propose bug fix version bumps to be included in the first minor release (2009.2.1) of the [10]Haskell Platform is Monday. Please ensure that, as maintainer for one of the 2009.2.x series of packages, any bug fixes are in place by Monday, or they'll be bumped to the next platform release. OpenGL 2.2.3.0. Sven Panne [11]announced the release of a new version of the [12]OpenGL package. This is a feature release, containing a number of changes and additions. Programming in Haskell -- solutions to exercises. Graham Hutton [13]announced that solutions to the exercises from "Programming in Haskell" are now [14]available online. Bookshelf. Emil Axelsson [15]announced the first release of [16]Bookshelf, a simple document organizer with some wiki functionality. Documents in a directory tree are displayed as a set of HTML pages. Documents in Markdown format are converted to HTML automatically using Pandoc. Request for feedback: HaskellDB + HList. Brian Bloniarz [17]requested feedback on a branch of [18]HaskellDB which replaces the home-grown Record code with HList records. RESTng 0.1 + RedHandlers 0.1 (request handlers) + YuiGrids 0.1 (yahoo grids). Sergio Urinovsky [19]announced the release of three new packages developed for a RESTful web framework called RESTng: [20]RESTng, [21]redHandlers, and [22]yuiGrid. #haskell.pt IRC channel. Marco Túlio Gontijo e Silva [23]announced the formation of the #haskell.pt channel on irc.freenode.net for Portuguese-speaking Haskellers. Fun with type functions. Simon Peyton-Jones [24]requested feedback on a [25]draft tutorial paper about type families (aka associated data types, or type functions). Discussion conflicting variable definitions in pattern. Martin Hofmann [26]asked about the possibility of repeated variables in patterns, resulting in an interesting discussion. Removing mtl from the Haskell Platform. Russell O'Connor began a [27]discussion around the possibility of removing the mtl package from the Haskell Platform, and replacing it with something more modern. Jobs PhD position in Nottingham. vxc [28]announced the availability of a new PhD position in the Functional Programming Laboratory at the University of Nottingham. The topic of research for the project is "Programming and Reasoning with Infinite Structures": it consists in the theoretical study and development of software tools for coinductive types and structured corecursion. Blog noise [29]Haskell news from the [30]blogosphere. Blog posts from people new to the Haskell community are marked with >>>, be sure to welcome them! * Leif Frenzel: [31]EclipseFP is going to be reloaded. * Tom Schrijvers: [32]Dictionaries: Eager or Lazy Type Class Witnesses?. Can type class dictionaries be optimized by treating them strictly? * Real-World Haskell: [33]RWH Now In The Kindle Store. * JP Moresmau: [34]Adding a Writer Monad transformer. * Ketil Malde: [35]Using a phantom type to label different kinds of sequences. * Ivan Lazar Miljenovic: [36]Functions All The Way Down. Ivan's talk on lambda calculus. * Thomas M. DuBuisson: [37]Fun with Distributed Hash Tables. Distributed hash tables in Haskell. * Darcs: [38]darcs joins the Software Freedom Conservancy. * Mark Wassell: [39]Just Grapefruit. Mark's first impressions of the Grapefruit library. * Roman Cheplyaka: [40]LambdaCube accepted to JSSP. Jane Street is funding development of the LambdaCube 3D rendering engine. * >>> Joel Neely: [41]BuilderBuilder: The Model in Haskell. * Brandon Simmons: [42]directory-tree module released. * >>> Sadek Drobi: [43]Paul Hudak on Haskell. An interview with Paul Hudak. * >>> dayvan cowboy: [44]Blast from the past: a stochastic monad in Haskell. * Matthew Podwysocki: [45]Type Classes Are The Secret Sauce . * Remco Niemeijer: [46]Programming Praxis - Priority Queues. A priority queue implementation using a leftist heap. * >>> Y. Liang: [47]A Lambda Calculus Interpreter in Haskell. Quotes of the Week * seydar: what's the nick of the drug addict who wrote learn you a haskell? and i mean that in the best possible way. * roconnor: String is kinda a poor data type for strings. * kyevan: I had a haskell-related dream last night. Sorta. I was beaten up by some kids because I tried to go somewhere my type didn't match, apparently. * edwardk: Haskell 98 is the Windows 98 of standards ;) * PhilipWadler: I'm delighted to learn that "a monad is a monoid in the category of endofunctors"---anyone know where I can find a good tutorial? * David Leimbach: Don't play with your monads... eventually you'll go bind. About the Haskell Weekly News New editions are posted to [48]the Haskell mailing list as well as to [49]the Haskell Sequence and [50]Planet Haskell. [51]RSS is also available, and headlines appear on [52]haskell.org. To help create new editions of this newsletter, please see the information on [53]how to contribute. Send stories to byorgey at cis dot upenn dot edu. The darcs repository is available at darcs get [54]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://haddock2009.wordpress.com/ 3. http://www.haskell.org/haddock/ 4. http://eclipsefp.wordpress.com/ 5. http://just-bottom.blogspot.com/ 6. http://nibrofun.blogspot.com/ 7. http://web.mornfall.net/tag/darcs.html 8. http://darcs.net/ 9. http://article.gmane.org/gmane.comp.lang.haskell.libraries/11120 10. http://trac.haskell.org/haskell-platform/ 11. http://article.gmane.org/gmane.comp.lang.haskell.general/17194 12. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/OpenGL 13. http://article.gmane.org/gmane.comp.lang.haskell.general/17193 14. http://www.cs.nott.ac.uk/~gmh/book.html 15. http://article.gmane.org/gmane.comp.lang.haskell.general/17182 16. http://www.cs.chalmers.se/~emax/bookshelf/Manual.shelf.html 17. http://article.gmane.org/gmane.comp.lang.haskell.cafe/58615 18. http://haskelldb.sourceforge.net/ 19. http://article.gmane.org/gmane.comp.lang.haskell.cafe/58589 20. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/RESTng 21. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/redHandlers 22. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/yuiGrid 23. http://article.gmane.org/gmane.comp.lang.haskell.cafe/58581 24. http://article.gmane.org/gmane.comp.lang.haskell.cafe/58522 25. http://haskell.org/haskellwiki/Simonpj/Talk:FunWithTypeFuns 26. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/58560 27. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/58430 28. http://article.gmane.org/gmane.comp.lang.haskell.cafe/58526 29. http://planet.haskell.org/ 30. http://haskell.org/haskellwiki/Blog_articles 31. http://cohatoe.blogspot.com/2009/05/eclipsefp-is-going-to-be-reloaded.html 32. http://tomschrijvers.blogspot.com/2009/05/dictionaries-eager-or-lazy-type-c… 33. http://www.realworldhaskell.org/blog/2009/05/15/rwh-now-in-the-kindle-store/ 34. http://jpmoresmau.blogspot.com/2009/05/adding-writer-monad-transformer.html 35. http://blog.malde.org/index.php/2009/05/14/using-a-phantom-type-to-label-di… 36. http://ivanmiljenovic.wordpress.com/2009/05/14/functions-all-the-way-down/ 37. http://tommd.wordpress.com/2009/05/13/fun-with-distributed-hash-tables/ 38. http://blog.darcs.net/2009/05/darcs-joins-software-freedom.html 39. http://www.poundstone.org/blog/?p=165 40. http://physics-dph.blogspot.com/2009/05/lambdacube-accepted-to-jssp.html 41. http://joelneely.wordpress.com/2009/05/09/builderbuilder-the-model-in-haske… 42. http://coder.bsimmons.name/blog/2009/05/directory-tree-module-released/ 43. http://www.infoq.com/interviews/paul-hudak-haskell-Qcon-SF-08 44. http://dayvancowboy.org/2009/05/08/blast-from-the-past-a-stochastic-monad-i… 45. http://codebetter.com/blogs/matthew.podwysocki/archive/2009/05/08/type-clas… 46. http://bonsaicode.wordpress.com/2009/05/05/programming-praxis-priority-queu… 47. http://yiopposite.blogspot.com/2009/05/lambda-calculus-interpreter-in-haske… 48. http://www.haskell.org/mailman/listinfo/haskell 49. http://sequence.complete.org/ 50. http://planet.haskell.org/ 51. http://sequence.complete.org/node/feed 52. http://haskell.org/ 53. http://haskell.org/haskellwiki/HWN 54. http://code.haskell.org/~byorgey/code/hwn/

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Re: [Haskell-cafe] Data.FiniteMap deprecrated
by Vasili I. Galchin 17 May '09

17 May '09

Yevgeni, I am specifying "base" as a Cabal dependency ... dumb question ... I have forgotten whether I need to import Data.Map also? Vasili On Sat, May 16, 2009 at 1:05 AM, Eugene Kirpichov <ekirpichov(a)gmail.com>wrote: > It's Data.Map. It's in the base package. > > 2009/5/16 Vasili I. Galchin <vigalchin(a)gmail.com>: > > Hello, > > > > > http://hackage.haskell.org/cgi-bin/hackage-scripts/package/FiniteMap > > ... since this is deprecated what is the orthodox way to implement > "finite > > map"?? > > > > Thanks, > > > > Vasili > > > > _______________________________________________ > > Haskell-Cafe mailing list > > Haskell-Cafe(a)haskell.org > > http://www.haskell.org/mailman/listinfo/haskell-cafe > > > > > > > > -- > Eugene Kirpichov > Web IR developer, market.yandex.ru >

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Request for feedback: HaskellDB + HList
by Brian Bloniarz 17 May '09

17 May '09

Hi, It's come time to share something that I've been playing around with recently: a branch of HaskellDB which replaces the home-grown Record code with HList records. It's definitely not ready for primetime, but I thought it'd be a good time to post the code and solicit some feedback from the community. HaskellDB the concept is very promising, but IMHO the code still falls short of that promise. Hopefully this is a small step in the right direction -- the advantages of using HList: * Shared implementation of extensible records * Additional features from HList * Better error messages for record misuse * "Lacks" predicates * Simpler code As an example of how this can be better, a DB insert looks like so: > insert db table $ constantRecord $ > film .=. "Munchie" .*. > director .=. Just "Jim Wynorski" .*. > emptyRecord The columns need not appear in the same order as in the database. If you forget a column, you'll get "error: No instance for (Fail (FieldNotFound (Proxy Director)))" rather than an opaque error. Using the new "insertOpt" function, Maybe columns will default to Nothing rather than needing to be specified. The details: I haven't updated everything, but there's enough to run test/TestCases.hs under Postgresql. TestCases is probably the best place to look for examples of the new syntax for now. HList had name conflicts with HaskellDB's SQL expression language ((.*.), (.++.), etc.) My temporary band-aid is to move the expression functions to Database.HaskellDB.SqlExpr, and require people to import qualified. The Attr type is gone, columns labels are untyped now. I also replaced a few instances of primitive type-level recursion with HMap/HMapOut. This makes the code simpler, and the type signatures more complex -- type families would help a lot here, I think. Feedback welcome! You can find my darcs tree at: http://mysite.verizon.net/vzewxzuh/sitebuildercontent/sitebuilderfiles/hask… It also requires minor changes to HList, available at: http://mysite.verizon.net/vzewxzuh/sitebuildercontent/sitebuilderfiles/hlis… I'll talk to the HList people about getting those merged. Thanks! Brian Bloniarz _________________________________________________________________ Hotmail® has a new way to see what's up with your friends. http://windowslive.com/Tutorial/Hotmail/WhatsNew?ocid=TXT_TAGLM_WL_HM_Tutor…

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Graphs and graph algorithms?
by Cory Knapp 17 May '09

17 May '09

Hey, Besides fgl, are there any graph libraries in Haskell that are still maintained? Are there other papers (or books) besides Erwig's that I could use to understand how graph algorithms have been implemented in functional languages? Has anything even been published on the topic since Erwig's paper? Thanks, Cory

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typeclasses comprehension problems: situation classes?
by Belka 17 May '09

17 May '09

Hello, cafe visitors! I'm trying to learn Haskell typeclasses, - about how to use them, - but can't handle some conceptiual problems, which confuses me a lot. I took one real problem (ErrorInfo gragual gathering), to tackle it in my studies: I have a class of situations: there is an object, and it gets cumulatively filled (or updated) with content. The code is in the end - it consists of 3 versions: 1. My first try. Fast written, based on intuitive understanding. Failed. 2. The second try - exploring an open world assumption. I hoped this would set me on the right path. Failure. 3. Surrendered to compiler - statisfied all it's requirements. This code looks absurd to me: parameter-never-to-be-used, unwanted-defaults. Compiler accepted this one though. Problems: 1. How to define *fillerRole* correctly, so that it depends on the type-value of "src_t"? 2. How to define *initFillable* correctly, so that it depends only on the type-value "filled_t", which is specified by the context of evaluation? 3. What are my misconcepts in the use of Haskell typeclasses here? 4. Maybe I should distinguish *situation class* (as this one), as something unavailable in Haskell? This assumption is the last one to make... I'd rather belive, that there is something I'm not aware of (for a considerably long time already) in Haskell. A lack of some programming technique Please, Help! Regards, Belka ==TRY=1===DOESN'T=COMPILE================================================== {-# LANGUAGE MultiParamTypeClasses #-} class FillsConsideringRoles src_t filled_t role_t where initFillable :: filled_t fillerRole :: role_t fill :: src_t -> filled_t -> filled_t ------------------------------------------------------------ data Role = Role1 | Role2 deriving (Show) data FillableObject = FillableObject { foData1 :: Maybe (Int, Role) , foData2 :: Maybe (Int, Role) } deriving (Show) newEmptyFillableObject :: FillableObject newEmptyFillableObject = FillableObject Nothing Nothing data Constructor1 = Constructor1 Int data Constructor2 = Constructor2 Int instance FillsConsideringRoles Constructor1 FillableObject Role where initFillable = newEmptyFillableObject fillerRole = Role1 fill c fo = let (Constructor1 i) = c in fo { foData1 = Just (i, fillerRole) } instance FillsConsideringRoles Constructor2 FillableObject Role where initFillable = newEmptyFillableObject fillerRole = Role2 fill c fo = let (Constructor2 i) = c in fo { foData2 = Just (i, fillerRole) } main = putStrLn $ show $ fill c2 $ fill c1 initFillable where c1 = Constructor1 76 c2 = Constructor2 43 ==TRY=1==[END]=================================================== ==TRY=2===DOESN'T=COMPILE======================================== {-# LANGUAGE MultiParamTypeClasses #-} {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE OverlappingInstances #-} class FillsConsideringRoles src_t filled_t role_t where initFillable :: filled_t fillerRole :: role_t fill :: src_t -> filled_t -> filled_t ---------------------------------------------------------------------- data Role = DefaultRole | Role1 | Role2 deriving (Show) data FillableObject = FillableObject { foData1 :: Maybe (Int, Role) , foData2 :: Maybe (Int, Role) } deriving (Show) newEmptyFillableObject :: FillableObject newEmptyFillableObject = FillableObject Nothing Nothing data Constructor1 = Constructor1 Int data Constructor2 = Constructor2 Int instance FillsConsideringRoles filler_t filled_t Role where fillerRole = DefaultRole instance FillsConsideringRoles Constructor2 filled_t Role where fillerRole = Role2 instance FillsConsideringRoles Constructor1 filled_t Role where fillerRole = Role1 instance FillsConsideringRoles filler_t FillableObject role_t where initFillable = newEmptyFillableObject instance FillsConsideringRoles Constructor1 FillableObject Role where fill c fo = let (Constructor1 i) = c in fo { foData1 = Just (i, fillerRole) } instance FillsConsideringRoles Constructor2 FillableObject Role where fill c fo = let (Constructor2 i) = c in fo { foData2 = Just (i, fillerRole) } main = putStrLn $ show $ fill c2 $ fill c1 initFillable where c1 = Constructor1 76 c2 = Constructor2 43 ==TRY=2==[END]=================================================== ==TRY=3===WORKS================================================= {-# LANGUAGE MultiParamTypeClasses #-} class FillsConsideringRoles src_t filled_t role_t where initFillable :: ((),src_t, role_t) -> filled_t fillerRole :: ((),src_t, filled_t) -> role_t fill :: ((),role_t) -> src_t -> filled_t -> filled_t ------------------------------------------------------------ data Role = DefaultRole | Role1 | Role2 deriving (Show) data FillableObject = FillableObject { foData1 :: Maybe (Int, Role) , foData2 :: Maybe (Int, Role) } deriving (Show) newEmptyFillableObject :: FillableObject newEmptyFillableObject = FillableObject Nothing Nothing data Constructor1 = Constructor1 Int data Constructor2 = Constructor2 Int instance FillsConsideringRoles Constructor1 FillableObject Role where initFillable _ = newEmptyFillableObject fillerRole _ = Role1 fill _ c fo = let (Constructor1 i) = c in fo { foData1 = Just (i, fillerRole ((), c, fo)) } instance FillsConsideringRoles Constructor2 FillableObject Role where initFillable _ = newEmptyFillableObject fillerRole _ = Role2 fill _ c fo = let (Constructor2 i) = c in fo { foData2 = Just (i, fillerRole ((), c, fo)) } main = putStrLn $ show $ fill ((), DefaultRole) c2 $ fill ((), DefaultRole) c1 ((initFillable ((), Constructor1 (-1), DefaultRole)) :: FillableObject) where c1 = Constructor1 76 c2 = Constructor2 43 ==TRY=3==[END]=================================================== -- View this message in context: http://www.nabble.com/typeclasses-comprehension-problems%3A-situation-class… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

3 2

Foldable for BNFC generated tree
by Deniz Dogan 17 May '09

17 May '09

Hi I have a bunch of data types which are used to represent a JavaScript program. The data types and a lexer and a parser have all been generated using BNFC. So basically an entire JavaScript program is represented as a tree using these data types. Ideally I'd like to be able to "fold" over this data structure, but I can't instantiate Foldable for my data types, since the data types all have kind *, if I'm not completely lost. Here's an example data type: data Statement = StmtFunDecl JIdent [JIdent] ExprOrBlock | StmtVarDecl [VarDecl] | StmtLetDecl [VarDecl] | StmtWhile Expr Statement | ... So, basically I'd like some sort of folding functionality for these data types, without having to hack the lexer/parser myself (parameterising the data types), because as I said they're being generated by BNFC. I noticed that you can make BNFC generate GADTs instead of normal ADTs, which would allow me to instantiate Foldable, but I'm not entirely sure that this is the best way to do this. Any help is appreciated, Deniz Dogan

3 3

Building 'text-icu-0.1' on Windows
by Serge LE HUITOUZE 17 May '09

17 May '09

Hi there, I fail to build text-icu-0.1 on Windows, and would appreciate some help... Thanks in advance! Let me describe what I've done so for, and what results I got: First, I got a version of ICU on my machine, specifically unzipping the file "icu4c-4_0_1-Win32-msvc8.zip" from <http://icu-project.org/download/4.0.html> http://icu-project.org/download/4.0.html. This made me having ICU stuff at location "C:\HaskellStuff\icu\icu", as witnessed below: >> C:\HaskellStuff\icu\icu>dir << 30/04/2009 16:08 <REP> . << 30/04/2009 16:08 <REP> .. << 30/04/2009 16:51 <REP> bin << 30/04/2009 16:08 <REP> include << 30/04/2009 16:36 <REP> lib << 14/01/2009 22:48 2 032 license.html After downloading and untaring "text-icu-0.1", I tried to configure, typing in: >> C:\HaskellStuff\pkg\text-icu-0.1>runhaskell Setup configure << Configuring text-icu-0.1... << Setup: Missing dependencies on foreign libraries: << * Missing C libraries: icui18n, icuuc, icudata << This problem can usually be solved by installing the system packages that << provide these libraries (you may need the "-dev" versions). If the libraries << are already installed but in a non-standard location then you can use the << flags --extra-include-dirs= and --extra-lib-dirs= to specify where they are. OK, let's restart with appropriate values for said flags! >> C:\HaskellStuff\pkg\text-icu-0.1>runhaskell Setup configure >> --extra-include-dirs=C:\HaskellStuff\icu\icu\include >> --extra-lib-dirs=C:\HaskellStuff\icu\icu\lib << Configuring text-icu-0.1... And then proceed with the building per se: >> C:\HaskellStuff\pkg\text-icu-0.1>runhaskell Setup build << Preprocessing library text-icu-0.1... << In file included from C:/HaskellStuff/icu/icu/include/unicode/umachine.h:47, << from C:/HaskellStuff/icu/icu/include/unicode/utypes.h:36, << from Data\Text\ICU\Error.hsc:148: << C:/HaskellStuff/icu/icu/include/unicode/pwin32.h:120: << error: redefinition of typedef 'int8_t' << C:/ghc/ghc-6.10.1/include/mingw/stdint.h:27: << error: previous declaration of 'int8_t' was here << ... << ... (a bunch of similar messages for other type aliases, e.g. 'uint8_t') << ... << compiling dist\build\Data\Text\ICU\Error_hsc_make.c failed << command was: C:\ghc\ghc-6.10.1\gcc.exe -c -BC:\ghc\ghc-6.10.1\gcc-lib << -IC:\ghc\ghc-6.10.1\include\mingw -D__GLASGOW_HASKELL__=610 << -IC:\HaskellStuff\icu\icu\include << -IC:\ghc\ghc-6.10.1\bytestring-0.9.1.4\include << -IC:\ghc\ghc-6.10.1\base-4.0.0.0\include << -IC:\ghc\ghc-6.10.1/include << -IPAPI_INCLUDE_DIR dist\build\Data\Text\ICU\Error_hsc_make.c << -o dist\build\Data\Text\ICU\Error_hsc_make.o << << C:\HaskellStuff\pkg\text-icu-0.1> The "mingw/stdint.h" file contains a series of lines of this style: << << typedef signed char int8_t; Whereas, the "unicode/pwin32.h" file contains contains stuff like: << << /* Define whether inttypes.h is available */ << #ifndef U_HAVE_INTTYPES_H << #define U_HAVE_INTTYPES_H 0 << #endif << ... << << /* Determines whether specific types are available */ << #ifndef U_HAVE_INT8_T << #define U_HAVE_INT8_T U_HAVE_INTTYPES_H << #endif << ... << << /* If your platform does not have the <inttypes.h> header, you may << need to edit the typedefs below. */ << #if U_HAVE_INTTYPES_H << #include <inttypes.h> << #else /* U_HAVE_INTTYPES_H */ << << #if ! U_HAVE_INT8_T << typedef signed char int8_t; << #endif << ... << #endif So, do I need to explicitely change the icu include file? And in which way? Any other solution/suggestion? Best regards. --Serge

3 4

Re: [Haskell-cafe] Decoupling OpenAL/ALUT packages from OpenGL
by Tillmann Vogt 16 May '09

16 May '09

Sven Panne schrieb: > > * a tiny "ObjectName" package, consisting only of OpenGL's ObjectName class > (In "Data.ObjectName"? I'm not very sure about a good place in the hierarchy > here.) How about Data.GraphicsObjects ? > > * a package containing most of the data types/newtypes in OpenGL's > VertexSpec module (Vertex{2,3,4}, Color{3,4}, etc.) plus instances for the > base classes like Eq, Ord, Show, etc. I really don't know a good name for this > package and what a good place in the hierarchy would be (probably something > like "Data.Foo", but what is Foo?) Now that you mention it. I just looked through haskell hierachical libraries and there seems to be no standard data types for vector math. Am I getting something wrong or is every library that is using linear algebra stuff using its own data types? So if I use a numeric library for matrices inside HOpenGL I have to convert around? I think it would be nice to have data types and functions for dot produkt, scalar product, norms, ... together with HOpenGL types. Currently I am trying to embed a triangulation library from a ten year old diploma thesis (http://www.dinkla.net/fp/cglib.html) in my libary (I know that glu has tesselation). The author has developed a quite big and abstract type structure for all sorts of computer graphics algorithms and I didn't wanted to copy this into my library just for triangulation. But it is reasonable. It could be combined with HOpenGL types to maybe Data.VectorMath or Data.LinearAlgebra . I would favour the second. > > The point is: The first two package would be very small. Would this be OK? > Does anybody see other alternatives? What would be good names for those > packages and where in the naming hierarchy should they really go? > > Cheers, > S. > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe

5 7

conflicting variable definitions in pattern
by Martin Hofmann 16 May '09

16 May '09

It is pretty clear, that the following is not a valid Haskell pattern: foo (x:x:xs) = x:xs My questions is _why_ this is not allowed. IMHO, the semantics should be clear: The pattern is expected to succeed, iff 'x' is each time bound to the same term. Isn't this allowed, because this would require a strict evaluation of the 'x' variables? Thanks, Martin

11 16

help :type class?
by yu yang 16 May '09

16 May '09

Does anyone have an idea how to use an instance to list all the functions of type? Thank you! ___________________________________________________________ 好玩贺卡等你发，邮箱贺卡全新上线！ http://card.mail.cn.yahoo.com/

3 2

Data.FiniteMap deprecrated
by Vasili I. Galchin 16 May '09

16 May '09

Hello, http://hackage.haskell.org/cgi-bin/hackage-scripts/package/FiniteMap ... since this is deprecated what is the orthodox way to implement "finite map"?? Thanks, Vasili

2 1

Re: [Haskell-cafe] Example code won't compile
by michael rice 16 May '09

16 May '09

OK. Thanks, everyone. Michael --- On Fri, 5/15/09, Krzysztof Skrzętnicki <gtener(a)gmail.com> wrote: From: Krzysztof Skrzętnicki <gtener(a)gmail.com> Subject: Re: [Haskell-cafe] Example code won't compile To: "michael rice" <nowgate(a)yahoo.com> Cc: "Lennart Augustsson" <lennart.augustsson(a)gmail.com>, "haskell-cafe(a)haskell.org" <haskell-cafe(a)haskell.org> Date: Friday, May 15, 2009, 9:55 PM The one important line is > import Control.Monad.Error It adds dependancy on mtl package, which is not used by default (contrary to 'base' package, which includes Monad, System and IO modules). With --make GHC adds it automatically. Therefore $ ghc -package mtl ex14.hs compiles fine. I'd recommend using --make. In rare occasions when there is a namespace clash between packages one can simply hide offending packages or specify preferred ones. Best regards Christopher Skrzętnicki

1 0

Re: [Haskell-cafe] Example code won't compile
by michael rice 16 May '09

16 May '09

This example compiles fine without --make. What's the difference? Michael ================== {- Author: Jeff Newbern Maintainer: Jeff Newbern <jnewbern(a)nomaware.com> Time-stamp: <Wed Jul 2 18:11:36 2003> License: GPL -} {- DESCRIPTION Example 13 - Using the List monad Usage: Compile the code and execute the resulting program with various arguments. Each argument will produce a list of possible parses of the argument as a decimal number, a hexadecimal number or a word. Try: ./ex13 34 f3 bean ./ex13 food f00d ./ex13 beef 10 "n!" ./ex13 "why?" "(punctuation)" -} import Monad import System import Char -- we can parse three different types of terms data Parsed = Digit Integer | Hex Integer | Word String deriving Show -- attempts to add a character to the parsed representation of a hex digit parseHexDigit :: Parsed -> Char -> [Parsed] parseHexDigit (Hex n) c = if isHexDigit c then return (Hex ((n*16) + (toInteger (digitToInt c)))) else mzero parseHexDigit _ _ = mzero -- attempts to add a character to the parsed representation of a decimal digit parseDigit :: Parsed -> Char -> [Parsed] parseDigit (Digit n) c = if isDigit c then return (Digit ((n*10) + (toInteger (digitToInt c)))) else mzero parseDigit _ _ = mzero -- attempts to add a character to the parsed representation of a word parseWord :: Parsed -> Char -> [Parsed] parseWord (Word s) c = if isAlpha c then return (Word (s ++ [c])) else mzero parseWord _ _ = mzero -- tries to parse the digit as a hex value, a decimal value and a word -- the result is a list of possible parses parse :: Parsed -> Char -> [Parsed] parse p c = (parseHexDigit p c) `mplus` (parseDigit p c) `mplus` (parseWord p c) -- parse an entire String and return a list of the possible parsed values parseArg :: String -> [Parsed] parseArg s = do init <- (return (Hex 0)) `mplus` (return (Digit 0)) `mplus` (return (Word "")) foldM parse init s -- show the original string and all possible parses for the string showResult :: String -> IO () showResult s = do putStr s putStr ": " print (parseArg s) -- prints possible parsed values for command-line arguments main :: IO () main = do args <- getArgs mapM_ showResult args -- END OF FILE --- On Fri, 5/15/09, Lennart Augustsson <lennart.augustsson(a)gmail.com> wrote: From: Lennart Augustsson <lennart.augustsson(a)gmail.com> Subject: Re: [Haskell-cafe] Example code won't compile To: "michael rice" <nowgate(a)yahoo.com> Cc: "haskell-cafe(a)haskell.org" <haskell-cafe(a)haskell.org> Date: Friday, May 15, 2009, 7:25 PM --make -- Lennart (iPhone)

2 1

Example code won't compile
by michael rice 16 May '09

16 May '09

Why won't this code compile? Michael ======================= {- Author: Jeff Newbern Maintainer: Jeff Newbern <jnewbern(a)nomaware.com> Time-stamp: <Thu Aug 14 09:53:53 2003> License: GPL -} {- DESCRIPTION Example 14 - Using the IO monad Usage: Compile the code to produce a poor replacement for the standard Unix "tr" command. Try: cat file | ./ex14 "aeiou" "X" cat file | ./ex14 " " "_" ./ex14 "abc" -} import Monad import System import IO import Control.Monad.Error -- translate char in set1 to corresponding char in set2 translate :: String -> String -> Char -> Char translate [] _ c = c translate (x:xs) [] c = if x == c then ' ' else translate xs [] c translate (x:xs) [y] c = if x == c then y else translate xs [y] c translate (x:xs) (y:ys) c = if x == c then y else translate xs ys c -- translate an entire string translateString :: String -> String -> String -> String translateString set1 set2 str = map (translate set1 set2) str usage :: IOError -> IO () usage e = do putStrLn "Usage: ex14 set1 set2" putStrLn "Translates characters in set1 on stdin to the corresponding" putStrLn "characters from set2 and writes the translation to stdout." -- translates stdin to stdout based on commandline arguments main :: IO () main = (do [set1,set2] <- getArgs contents <- hGetContents stdin putStr $ translateString set1 set2 contents) `catchError` usage -- END OF FILE ===================================== [michael@localhost ~]$ ghc ex14.hs -o ex14 ex14.o: In function `rF8_info': (.text+0x48): undefined reference to `mtlzm1zi1zi0zi2_ControlziMonadziError_zdf17_closure' ex14.o: In function `sGp_info': (.text+0x861): undefined reference to `mtlzm1zi1zi0zi2_ControlziMonadziError_zdf17_closure' ex14.o: In function `sGp_info': (.text+0x91d): undefined reference to `__stginit_mtlzm1zi1zi0zi2_ControlziMonadziError_' ex14.o: In function `rF8_info': (.text+0x50): undefined reference to `mtlzm1zi1zi0zi2_ControlziMonadziErrorziClass_zdp1MonadError_info' ex14.o: In function `sGp_info': (.text+0x869): undefined reference to `mtlzm1zi1zi0zi2_ControlziMonadziErrorziClass_catchError_info' ex14.o: In function `rF8_srt': (.data+0x0): undefined reference to `mtlzm1zi1zi0zi2_ControlziMonadziError_zdf17_closure' ex14.o: In function `Main_main_srt': (.data+0x6c): undefined reference to `mtlzm1zi1zi0zi2_ControlziMonadziError_zdf17_closure' collect2: ld returned 1 exit status [michael@localhost ~]$

2 1

GSoC project for EclipseFP
by Thomas ten Cate 16 May '09

16 May '09

Hi all, I'm happy to announce that my Google Summer of Code project proposal, titled "Extend EclipseFP functionality for Haskell", has been accepted! This means that I will be working on EclipseFP during the upcoming months. For the uninitiated, EclipseFP is a plugin for the Eclipse IDE that makes Haskell support possible. Currently it is fairly limited, but I hope to bring it to a state in which I can start using it for some larger projects of my own. "Live" type checking and type inference, and all that jazz. This will be powered by the Scion library by Thomas Schilling (nominolo), who is also my GSoC mentor. More information is on my new blog: http://eclipsefp.wordpress.com/ Cheers, Thomas

3 2

ANN: RESTng 0.1 + RedHandlers 0.1 (request handlers) + YuiGrids 0.1 (yahoo grids)
by Sergio Urinovsky 16 May '09

16 May '09

I'd like to announce the release of 3 new packages in hackage developed for a RESTful web framework called RESTng. They are experimental, the framework is incomplete and we are currently not actively developing it. There are several interesting features so we have decided to release them to share the ideas. *RESTng:* A framework for writing RESTful applications. Features that may be of interest are: * Resource presentation with annotations (implemented with Grids): Resources are annotated with related data and all ends in boxes using grids. i.e., an annotation for a book resource could be its author (the author resource), and also their comments, so the book, the author and their comments are shown in boxes. Annotations can have arbitrary data, but there are some generic ones already available. * Hierarchical URLs are automatically handled. i.e.: Can easily define that a book resource "has many" chapters, then these actions are defined: GET http://site/book/3/chapter/1 (get the chapter 1 of book with id 3) GET http://site/book/3/chapter/new (get a form for filling data for the new chapter for book with id 3) POST http://site/book/3/chapter/new (create a new chapter for the book with id 3) and so on for updates, list and delete actions * ORM generates tables from haskell records (currently only PostgreSQL is supported in the ORM). * Associations "has many" defined for models. Making available functions to query for the parent and children so you don't have to make the SQL query. * Associations can be polymorphic so a comment can be associated to different resources types. A record for a comment on a book, another for a comment on a post. * Tags, Ratings, Comments, Users and login and CMS-like form fields validations supported. *YuiGrids:* * Containers and boxes with layout hints are specified. i.e: - Box A: in left side bar, near the bottom, with this content .... - Container B: in the main part of the page, near the top, with 3 columns and these let's say 14 boxes inside ... (including Box C) - Box C: in the left column of three, with this other content ... * Tries to satisfy the layout hints. Not allways possible, i.e: if every box has layout hint to go near the bottom, some of them will go at the top. * Boxes can have CSS specifications. * All is rendered into Yahoo grids (http://developer.yahoo.com/yui/grids) Currently, the YuiGrids uses own contextual html combinators are also implemented in this package (called CxML here) instead of Text.XHtml for keeping track of html parts like inline CSSs to be rendered at the head. This can be improved to use the standard Text.XHtml library. *RedHandlers:* It is another HTTP request handlers library to build standalone web apps. * They deal with request data as usual. * There are also combinators for mapping part of the URL to public folders in the file system. * And one for sending files efficiently in the response (a fork of the HTTP library was necessary for this, included here).

1 0

Don't play with your monads...
by David Leimbach 16 May '09

16 May '09

eventually you'll go bind. Sorry couldn't resist.

2 1

I have forgotten .. my bad
by Vasili I. Galchin 16 May '09

16 May '09

Hello, darcs get --init ....?????? I want to pull down Data.FiniteMap. I have forgotten the path to Hackage .. I tried .... sudo darcs get http://hackage.haskell.org/ Data.FiniteMap [sudo] password for vigalchin: Invalid repository: http://hackage.haskell.org darcs failed: Failed to download URL http://hackage.haskell.org/_darcs/inventory : HTTP error (404?) ?? Obviously the code I am cabalizing needs to be "upgraded"(i.e. not using deprecated packages) but first I want it to build! Thanks, Vasili

4 4

TFM09: Last CFP (Formal Methods Week, Eindhoven, November 6th 2009)
by J.N. Oliveira 16 May '09

16 May '09

TFM2009 2nd Int. FME Conference on Teaching Formal Methods "Widening Access to Formal Methods" Friday, November 6th 2009, co-located with FM2009 : 16th International Symposium on Formal Methods Eindhoven, the Netherlands, November 2 - November 6, 2009 CALL FOR PAPERS (URL: http://www.di.uminho.pt/tfm09) 1. About the conference ----------------------- Ten years after the First World Formal Methods Congress (FM'99) in Toulouse, formal methods communities from all over the world will once again have an opportunity to come together. As part of the First Formal Methods Week event surrounding the FM2009 conference in Eindhoven, Formal Methods Europe will be organizing TFM2009, the Second International Conference on Teaching Formal Methods. The conference will serve as a forum to explore the successes and failures of Formal Methods (FM) education, and to promote cooperative projects to further education and training in FMs. We would like to provide a forum for lecturers, teachers, and industrial partners to discuss their experience, present their pedagogical methodologies, and explore best practices. TFM2009 follows in a series of recent events on teaching formal methods, including: two BCS-FACS TFM workshops (Oxford in 2003, and London in 2006), the TFM 2004 conference in Ghent (with proceedings published as Springer LNCS Volume 3294), the FM-Ed 2006 workshop (Hamilton, co-located with FM'06), FORMED (Budapest, at ETAPS 2008), FMET 2008 (Kitakyushu 2008, co-located with ICFEM), etc. 2. Topics of interest --------------------- Formal methods (FM) have an important role to play in the development of complex computing systems - a role acknowledged in industrial standards such as IEC 61508 and ISO/IEC 15408, and in the increasing use of precise modeling notations, semantic markup languages, and model-driven techniques. There is a growing need for software engineers who can work effectively with simple, mathematical abstractions, and with practical notions of inference and proof. However, there is little clear guidance ? for educators, for managers, or for the engineers themselves ? as to what might comprise a basic education in FM. Neither the present IEEE/ACM Software Engineering Body of Knowledge (SWEBOK) nor the forthcoming Graduate Software Engineering Reference Curriculum (GSWERC) provide the kind of specific information that teachers and practitioners need to establish an adequate, balanced programme of learning in FM. Original contributions are solicited that provide insight, opinions, and suggestions for courses of action regarding the teaching FMs, including but not limited to the following aspects: * experiences of teaching FMs, both successful and unsuccessful; * educational resources including the use of books, case studies and the internet; * the education of weak and mathphobic students; * the integration, or otherwise, of FMs into the curriculum, including contributions to the definition of a Formal Methods Body of Knowledge (FMBOK); * the advantages of FM-trained graduates in the workplace; * changing attitudes towards FMs in students, academic staff and practitioners; * the necessary mathematical background. The conference proceedings will be published by Springer-Verlag in the LNCS series. Submissions may be up to 20 pages long using Springer's LNCS format. 3. Important dates ------------------ Please put the following dates in your diary: Submission deadline May 25, 2009 Notification of acceptance July 6, 2009 Final version August 3, 2009 4. How to submit ---------------- Papers for TFM2009 will be processed through the EasyChair conference management system.To submit your paper, please visit: http://www.easychair.org/conferences/?conf=tfm2009 5. Invited speakers ------------------- To be announced 6. Programme Committee ---------------------- Izzat Alsmadi (North Dakota State University, USA) Dines Bjorner (IIMM Institute, Denmark) Eerke Boiten (University of Kent, UK) Raymond Boute (Universiteit Gent, Belgium) Andrew Butterfield (Trinity College, Dublin) Jim Davies (University of Oxford, UK) David Duce (Oxford Brookes University, UK) John Fitzgerald (University of Newcastle upon Tyne, UK) Jeremy Gibbons (University of Oxford, UK) Randolph Johnson (National Security Agency, USA) Michael Mac an Airchinnigh (Trinity College, Dublin) Dino Mandrioli (Politecnico di Milano, Italy) Jose Oliveira (Universidade do Minho, Portugal) Kees Pronk (Technische Universiteit Delft, NL) Bernhard Schaetz (Tecnical University of Munique, Germany) Wolfgang Schreiner (Johannes Kepler University Linz, Austria) Simao Melo de Sousa (Universidade da Beira Interior, Portugal) Kenji Taguchi (National Institute of Informatics, Japan) Jeannette Wing (Carnegie-Mellon University, USA) 7. Sponsorship ---------------------- TFM2009 is supported by FME, the Formal Methods Europe Association

1 0

Re: Data.Binary and little endian encoding
by John Lato 16 May '09

16 May '09

leimy2k: > On Thu, May 14, 2009 at 8:46 PM, Don Stewart <dons(a)galois.com> wrote: > >> leimy2k: >> > >> > >> > On Thu, May 14, 2009 at 8:40 PM, Don Stewart <dons(a)galois.com> wrote: >> > >> > leimy2k: >> > > I actually need little endian encoding... wondering if anyone else >> hit >> > this >> > > with Data.Binary. (because I'm working with Bell Lab's 9P protocol >> which >> > does >> > > encode things on the network in little-endian order). >> > > >> > > Anyone got some "tricks" for this? >> > >> > Yes! >> > There are big, little and host-endian primitives in the Get/Put >> monads. >> > >> > >> http://hackage.haskell.org/packages/archive/binary/0.5.0.1/doc/html/ >> > Data-Binary-Put.html#v%3AputWord16le >> > >> > You can use these to build encoders directly. >> > >> > >> > Cool... I just have to write my own encoder and decoder now. >> > >> > As a request could we get encodeLe decodeLe for a later version of this >> > library? :-) That'd be totally awesome. >> >> Oh, you mean entirely different instances for all the current ones, that >> use LE encodings? >> > > Well the library is leaning towards "Network Byte Order" in that it has > encode/decode that only encode/decode for Big Endian. > > Us folks who have to do little endian all now have to write our own > encoding/decoding :-) > > I'm speaking specifically of the encode/decode functions. I have no idea > how they're implemented. The encode/decode functions just call the runGet/runPut functions for whatever is being encoded or decoded to combined with the get/put functions from the Binary instance. The endian-ness is entirely determined by the Binary instance for the data type you're encoding/decoding, not anything in the encode/decode functions themselves. For data types you define, you can make the Binary instance LE standard (although it may not be a good idea) by using the little-endian primitives Don mentioned. For built-in types, if you want to use a different endian-ness, you can make new get/put functions then call runGet/runPut on those directly. You won't be able to redefine the Binary instances, but if you'll be doing this with a lot of different types you could make your own BinaryLE class like this: class BinaryLE t where putLE :: t -> Put getLE :: Get t encodeLE :: BinaryLE a => a -> ByteString encodeLE = runPut . putLE decodeLE :: BinaryLE a => ByteString -> a decodeLE = runGet getLE I've done some work with Binary and little-endian, and this bias never really bothered me (I think it's actually a host-endian bias, could be mistaken). I was using my own data types so I had to make my own custom Binary instances, which I would have had to do anyway. The data format specified little-endian, so making the Binary instance LE-standard seemed appropriate. You'd only need to re-make custom get/put functions if you're using types that already have Binary instances, and you intend to manipulate the data outside of Haskell. Does that describe your situation? John

2 1

ICFP09 Accepted Papers
by Matthew Fluet (ICFP Publicity Chair) 15 May '09

15 May '09

Accepted Papers ICFP 2009: International Conference on Functional Programming Edinburgh, Scotland, 31 August - 2 September 2009 http://www.cs.nott.ac.uk/~gmh/icfp09.html The ICFP 2009 Program Chair and Committee are pleased to announce that the following papers have been accepted for the conference. Additional information regarding the final program, invited speakers, and registration will be forthcoming. However, the Local Arrangements Co-Chairs would like to remind participants of the following: * ICFP'09 coincides with the final week of the Edinburgh International Festival, one of the premier arts and cultural festivals in the world. The opportunity to attend the Festival is a plus! Due to the popularity of Edinburgh during the festival period, we recommend booking accommodation early. More details regarding accommodation may be obtained from the ICFP 2009 Local Arrangements webpage: http://www.haskell.org/haskellwiki/ICFP_2009_Local_Arrangements Accepted papers ~~~~~~~~~~~~~~~ A CONCURRENT ML LIBRARY IN CONCURRENT HASKELL Avik Chaudhuri A THEORY OF TYPED COERCIONS AND ITS APPLICATIONS Nikhil Swamy, Michael Hicks and Gavin Bierman A UNIVERSE OF BINDING AND COMPUTATION Daniel Licata and Robert Harper ATTRIBUTE GRAMMARS FLY FIRST-CLASS: HOW TO DO ASPECT ORIENTED PROGRAMMING IN HASKELL Marcos Viera, S. Doaitse Swierstra and Wouter S. Swierstra AUTOMATICALLY RESTFUL WEB APPLICATIONS OR, MARKING MODULAR SERIALIZABLE CONTINUATIONS Jay McCarthy BEAUTIFUL DIFFERENTIATION Conal Elliott BIORTHOGONALITY, STEP-INDEXING AND COMPILER CORRECTNESS Nick Benton and Chung-Kil Hur CAUSAL COMMUTATIVE ARROWS AND THEIR OPTIMIZATION Hai Liu, Eric Cheng and Paul Hudak COMPLETE AND DECIDABLE TYPE INFERENCE FOR GADTS Tom Schrijvers, Simon Peyton Jones, Martin Sulzmann and Dimitrios Vytiniotis CONTROL-FLOW ANALYSIS OF FUNCTION CALLS AND RETURNS BY ABSTRACT INTERPRETATION Jan Midtgaard and Thomas P. Jensen EDUCATIONAL PEARL: FUN FOR FRESHMEN KIDS Matthias Felleisen, Robert Bruce Findler, Matthew Flatt and Shriram Krishnamurthi EFFECTIVE INTERACTIVE PROOFS FOR HIGHER-ORDER IMPERATIVE PROGRAMS Adam Chlipala, Gregory Malecha, Greg Morrisett, Avraham Shinnar and Ryan Wisnesky EXPERIENCE REPORT: EMBEDDED, PARALLEL COMPUTER-VISION WITH A FUNCTIONAL DSL Ryan Newton and Teresa Ko EXPERIENCE REPORT: HASKELL IN THE REALWORLD Curt Sampson EXPERIENCE REPORT: OCAML FOR AN INDUSTRIAL-STRENGTH STATIC ANALYSIS FRAMEWORK Pascal Cuoq and Julien Signoles EXPERIENCE REPORT: OCSIGEN, A WEB PROGRAMMING FRAMEWORK Vincent Balat, Jérôme Vouillon and Boris Yakobowski EXPERIENCE REPORT: SEL4 -- FORMALLY VERIFYING A HIGH-PERFORMANCE MICROKERNEL Gerwin Klein, Philip Derrin and Kevin Elphinstone FINDING RACE CONDITIONS IN ERLANG WITH QUICKCHECK AND PULSE Koen Claessen, Michal Palka, Nicholas Smallbone, John Hughes, Hans Svensson, Thomas Arts and Ulf Wiger FREE THEOREMS INVOLVING TYPE CONSTRUCTOR CLASSES Janis Voigtlaender GENERIC PROGRAMMING WITH FIXED POINTS FOR MUTUALLY RECURSIVE DATATYPES Alexey Rodriguez, Stefan Holdermans, Andres Löh and Johan Jeuring IDENTIFYING QUERY INCOMPATIBILITIES WITH EVOLVING XML SCHEMAS Pierre Geneves, Nabil Layaida and Vincent Quint IMPLEMENTING FIRST-CLASS POLYMORPHIC DELIMITED CONTINUATIONS BY A TYPE-DIRECTED SELECTIVE CPS-TRANSFORM Tiark Rompf, Ingo Maier and Martin Odersky LA TOUR D'HANOï Ralf Hinze NON-PARAMETRIC PARAMETRICITY Georg Neis, Derek Dreyer and Andreas Rossberg OXENSTORED: AN EFFICIENT HIERARCHICAL AND TRANSACTIONAL DATABASE USING FUNCTIONAL PROGRAMMING WITH REFERENCE CELL COMPARISONS Thomas Gazagnaire and Vincent Hanquez PARALLEL CONCURRENT ML John Reppy, Claudio Russo and Yingqi Xiao PARTIAL MEMOIZATION OF CONCURRENCY AND COMMUNICATION Suresh Jagannathan, KC Sivaramakrishnan and Lukasz Ziarek PURELY FUNCTIONAL LAZY NON-DETERMINISTIC PROGRAMMING Sebastian Fischer, Oleg Kiselyov and Chung-chieh Shan RUNTIME SUPPORT FOR MULTICORE HASKELL Simon Marlow, Simon Peyton Jones and Satnam Singh SAFE FUNCTIONAL REACTIVE PROGRAMMING THROUGH DEPENDENT TYPES Neil Sculthorpe and Henrik Nilsson SCRIBBLE: CLOSING THE BOOK ON AD HOC DOCUMENTATION TOOLS Matthew Flatt, Eli Barzilay and Robert Bruce Findler USING OBJECTIVE CAML TO DEVELOP SAFETY-CRITICAL EMBEDDED TOOL IN A CERTIFICATION FRAMEWORK Bruno Pagano, Olivier Andrieu, Thomas Moniot, Benjamin Canou, Emmanuel Chailloux, Philippe Wang, Pascal Manoury and Jean-Louis Colaco

1 0

#haskell.pt IRC channel
by Marco Túlio Gontijo e Silva 15 May '09

15 May '09

Hello, I'd like to invite all Portuguese speakers haskellers to join #haskell.pt in irc.freenode.net. I added it to the list in http://www.haskell.org/haskellwiki/IRC_channel . Greetings. -- marcot http://marcot.iaaeee.org/

1 0

Pretty printing a tree
by José Romildo Malaquias 15 May '09

15 May '09

Hello. I would like to pretty print a tree in a way that its structure is easily perceived. For instance, consider the declarations: data Node a = Node a [Node a] type Tree a = [ Node a ] t = [ Node "a" [ Node "b" [] , Node "c" [ Node "c1" [] , Node "c2" [] ] , Node "d" [ Node "d1" [ Node "d1a" [] ] , Node "d2" [] ] ] ] Then the resulting of pretty printing the given tree would be something like the following: a | +-------------+ | | | b c d | | +---+ +---+ | | | | c1 c2 d1 d2 | d1a There is the module Text.PrettyPrint.HughesPJ, but it lacks examples on how to use the pretty print combinators, and it is not well docomented. I would like to see solutions for this problem, or clues on how to solve it. Regards, José Romildo

5 4

looking for suggestion on pattern matching problem
by Daryoush Mehrtash 15 May '09

15 May '09

I am trying to analyze a list of items (say integers) for longest matches on patterns and their location on the list. One catch is that pattern may be defined in terms of other patterns. Example of patterns would be the any sequence of increasing numbers, or sequence of increasing numbers followed by upto 5 zeros then followed by any odd digits. I don't know much about the actual patterns, but would like to be able to define EDSL for composing the patterns and an execution environment to actually find the patterns. I like to find out various ways I can structure the problem and its trade offs. I appreciate any books, articles, suggestions, papers, etc on this type of problems. Thanks, Daryoush

3 2

"hiddenness"
by Vasili I. Galchin 15 May '09

15 May '09

Hello, When I am compiling a module, I get "Could not find module 'Control.Module.State': it is a member of package mtl-1.1.0.2, which is hidden" 1) What is the efficacy of "hiddenness"? 2) I have forgotten what tool I run to expose a package. ?? 3) In another vein, the code is using Data.Finitemap ... so I guess I must "darcs" install this? Regards, Vasili

2 2

Recommending "Design concepts in programming languages"
by Eugene Kirpichov 15 May '09

15 May '09

Hi. To all those people who are in any sense interested in PL theory I'd like to recommend the book "Design concepts in programming languages", because I am extremely impressed with it and because I, surprisingly, have not heard much about it. So, the book is about various concepts encountered in various kinds of programming languages: denotational and operational (BOS/SOS) semantics, issues of state and control, type systems, modules, modeling effects and compilation. Every concept is introduced by defining the semantics of a language that has this concept and exploring the design dimensions and issues of this concept and language. Concepts are gradually accumulated, and by the time you reach the chapter on modules you've got a CBV language with records, mutable state, polymorphic algebraic data types, a System F type system with type inference and a hint of dependent types, abstract data types and first-class dynamically loadable modules. The tools used for description are of course the good old denotational and operational semantics and typing judgements and derivation trees; but each element of those is clearly and succintly described in text; it happens to me all the time that I am reading a type reconstruction algorithm and wondering, "why does this rule have that restriction?" and it immediately turns out that in the next paragraph, the authors focus attention on why this rule has that restriction; just like if they were reading my thoughts. That's why this book feels very comfortable to me: I am absolutely sure that I won't encounter a point where I am lost and buried under the notation; but there is also not a single boring moment. I've been interested in functional programming and PL theory for 2-3 years already, and here's a brief list of the *new* things that I have learned, at least: - What do SOS and BOS mean, and why one should care, and what properties a SOS might posess (confluence and normalization, for instance) - How many features of languages can be defined in terms of simply desugaring, and how in some cases they can't - How one might use monadic style in the semantics metalanguage to greatly simplify the semantic rules for monadic concepts like state, control and error handling (the authors mention the word "monad" only once, but they use return- and bind-like operators in their semantics) - How powerful records are, and of what use are operators like "conceal" - What use is subtyping outside of OOP - How does one define CPS-style semantics and how such a style allows to add state, control and errors with minimal changes - How small yet powerful an OOP language core can be - How algebraic datatypes can be very useful in a language without static typing - How pattern matching can be desugared into CPS-style deconstructors - How many caveats are there in defining typing rules, and how a small change in them can lead to very big changes in language expressiveness - How HM type inference actually works - Why purity is important for certain polymorphism issues - What let-polymorphism means - What effect systems are - How effect reconstruction works and how it is different from type reconstruction in nature - How effect inference can prove the external purity of certain internally impure programs That's where I finished my reading for now. The remaining looks even more intriguing; for example, I don't (yet) know how functional languages are compiled and how register allocation is done. I'm afraid to sound like a salesman, but this is absolutely the best-written technical book I have ever seen in my life, and probably the most influential one for me, excluding probably SICP. Here you can check out its table of contents: http://cs.wellesley.edu/~fturbak/pubs/6821/current/contents-nov22.pdf I was impressed with the TOC even before buying the book, but turned out that I was greatly under-estimating it. Well, that's it :) -- Eugene Kirpichov Web IR developer, market.yandex.ru

8 12

Structural sharing in haskell data structures?
by Andrew Wagner 15 May '09

15 May '09

So I've been reading a lot about a (relatively) new language called Clojure. One of its goals is to make concurrency easier via a built-in home-grown STM. Anyway, one of the ways it tries to do this is to have completely immutable data structures. Every time I read a tutorial about this in Clojure, it says "...yes, it sounds awful to think that your whole data structure gets copied every time you want to make a change to it, but it's sane because of a technique called structural sharing". Yet every time I hear immutability talked about in Haskell, what I hear is "...yes, it sounds awful to think that your whole data structure gets copied every time you want to make a change to it, but it's sane because of laziness...unless you need the whole data structure...". So I'm just curious, does GHC use structural sharing or something similar? Do other implementations? Does it matter?

8 16

hsffig and duplicate typedef declarations
by Dimitry Golubovsky 15 May '09

15 May '09

Dean, I am not sure how HSFFIG would deal with duplicate typedefs (I'm afraid you get error from gcc when processing hsc2hs output). In case you haven't seen this, I put a repo for HSFFIG here recently: http://code.haskell.org/hsffig/ Before running "cabal install" run make at the toplevel of the repo first. I have fixed some glitches recently, and adjusted both hsffig and ffipkg to work with contemporary GHC and Cabal (at least 1.6.0.x). I'd be glad to get any feedback on HSFFIG. E-mail me to "golubovsky at gmail dot com". Thanks. -- Dimitry Golubovsky Anywhere on the Web

1 0

RE: [Haskell-cafe] Developing 3 dimensional interactive environments/functional objects
by paulfrancis＠friendbliss.com 14 May '09

14 May '09

1 0

PhD position in Nottingham
by vxc＠Cs.Nott.AC.UK 14 May '09

14 May '09

PhD position in Type Theory at Nottingham ----------------------------------------- A new PhD position is available in the Functional Programming Laboratory at the University of Nottingham. The topic of research for the project is "Programming and Reasoning with Infinite Structures": it consists in the theoretical study and development of software tools for coinductive types and structured corecursion. The candidate must be a UK resident with an excellent degree in Computer Science or Mathematics at MSc (preferred) or BSc level (first class or equivalent). The applicant should have a good background in mathematical logic, theoretical computer science or functional programming. (S)he should be interested doing research in type theory, constructive mathematics, category theory and foundations of formal reasoning. We offer: PhD place with living expenses (standard UK level) for 3 years. The grants also provide laptops and travel expenses for conference and workshop visits. Nottingham University provides a vibrant research environment in the Functional Programming Laboratory. Deadline for applications: 20 June 2009. Send a cover letter and your CV to Venanzio Capretta (vxc(a)cs.nott.ac.uk) Please contact me for any additional information that you need. 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.

1 0

Fun with type functions
by Simon Peyton-Jones 14 May '09

14 May '09

Friends Ken, Oleg, and I have been working on a tutorial paper about type families (aka associated data types, or type functions). It's in draft at the moment, and we'd really appreciate feedback that would help us improve it. Here it is: http://haskell.org/haskellwiki/Simonpj/Talk:FunWithTypeFuns Thank you! Simon

1 0

Functional Reactive Web Application Framework?
by Petr Pudlak 14 May '09

14 May '09

Hi, I've been learning Haskell for a few months, and it has influenced my thinking about programs quite a lot. Most of my current work is creating complex web applications. Naturally, I was thinking about how to make rich internet applications (and GUI apps in general) in an (utmost :-)) functional way. Recently I found out the concepts of functional reactive programming <http://www.haskell.org/haskellwiki/Functional_Reactive_Programming>, which supersede and generalize my ideas. My question is: "Is there a FRP web application framework, or perhaps an effort to create one?" If not, I'd be willing to start such a project, but since I'm not very experienced Haskell programmer, I'd most likely need some help from somebody more experienced. If somebody would be interested, my ideas go as follows: Handling events in GUI/RIA applications can be very tedious, especially for complex applications. Instead, I'd prefer something like that: 1) Abstract what a user wants to see using a structured datatype, specifically tailored for the application. You may imagine it as something like a structured URL. This can be then viewed as a FRP behavior -- a function of the user's request depending on time. 2) The data that will be displayed on the page are a function of this structured user request and an environment, which is usually database. This is again a behavior. 3) Finally, the resulting page is a function of the data (again a behavior). 4) User actions that change the application state (update the database) could be viewed as FRP events. So instead of handling tons of events, the programmer would construct the application mostly by composing behaviors. Only state-changing user actions would be handled as events. Does anybody see these ideas as useful? Constructive criticism is welcomed. Best regards, Petr

6 7

[ANNOUNCE] Bindings for libguestfs
by Richard W.M. Jones 14 May '09

14 May '09

I added some partial bindings for libguestfs[1] here: http://git.et.redhat.com/?p=libguestfs.git;a=blob;f=haskell/Guestfs.hs;hb=H… Some very simple example programs which use these bindings: http://git.et.redhat.com/?p=libguestfs.git;a=tree;f=haskell;hb=HEAD Any comments welcome. My Haskell skills are pretty terrible, so I'm sure there are many ways these can be improved. If someone wants to look at binding the rest of the API, then please send me some patches. (Note that the Guestfs.hs file is automatically generated). BTW, I found the documentation on writing FFIs very contradictory and incomplete. For example, I was completely defeated trying to find ways to do simple stuff like passing in integers or returning booleans. *Potentially* Haskell's FFI seems like it might be one of the best out of the languages I've used so far, but it needs way more documentation and examples. Rich. [1] http://et.redhat.com/~rjones/libguestfs/ -- Richard Jones, Emerging Technologies, Red Hat http://et.redhat.com/~rjones virt-df lists disk usage of guests without needing to install any software inside the virtual machine. Supports Linux and Windows. http://et.redhat.com/~rjones/virt-df/

4 7

Darcs as undo/redo system?
by Peter Verswyvelen 14 May '09

14 May '09

If you work with a text editor like Microsoft Visual Studio (maybe also Eclipse, don't know), each text editor has its own undo/redo history. However, when you perform refactoring - like renaming a function - this becomes an undo/redo on multiple files together, so in a sense these changes are part of a global history. You can combine these two different kinds of mutations, and undo/redo still works as expected. I don't know how hard this is to implement, but it looks like this problem is somehow is related to Darcs theory of patches (which I don't know yet :-)

9 9

IO trouble
by Xiao-Yong Jin 14 May '09

14 May '09

Hi, I can't really describe it in the subject. So let me try to do it here. I have two functions > f :: a -> b > g :: (a -> b) -> c -> d and I use them as > gf :: c -> d > gf = g f Now I want to handle exceptions in f and redefine f as in f' > f' :: a -> IO (Either e b) So my question is how to define gf' now to use f' instead of f? > gf' :: c -> IO (Either e d) Thanks in advance. Xiao-Yong -- c/* __o/* <\ * (__ */\ <

3 3

hsffig and duplicate typedef declarations
by Dean Herington 14 May '09

14 May '09

I have a large body of C/C++ code at work that I'd like to be able to access from Haskell via FFI. Because the interface to this code is broad, hsffig would seem to be ideal for the task. I've run across one serious hitch, though. The existing #include file graph is complicated and ends up declaring some typedefs multiple times (albeit in consistent ways). While gcc (for example) rejects such practice, the Windows C compiler we're using accepts it. Does anyone know how feasible it would be to get hsffig to accept such practice as well? I've started looking at the hsffig code (and discovered that the C grammar hsffig uses seems to get confused by duplicate typedefs), but thought I'd ask the list in parallel with my further study. Thanks. Dean

2 4

question on the Prelude .. vis-a-vis
by Vasili I. Galchin 14 May '09

14 May '09

Hello, I am seriously punching my way to build Swish via .cabal ... My head is totally to the wall .... punch .. punch ..... Graham Lyle has written some seriously beautiful code .... I am trying to get to adhere to contemporary Haskell namespace convention ..... I still awaiting response from Graham vis-a-vis posting on Hackage ... I strongly think that in bioinformatics and also oil/gas industry(<< I am stuck here everyday ;^)) that Swish is a strong arena of discussion! In any case .. there are some issues: 1) I strongly suspect that in Swish 0.2.1 that some of Graham's libaries are already superseded by the Haskell prelude , e.g. HUnit, Parsec(!!!), his Sort directory/library .. Don ...please 2) Graham wrote a deterministic finite automaton ..... which is giving some grieve namespace-wise ..... please see following Swish/HaskellRDF/Dfa/Dfa.lhs:1:0: Failed to load interface for `Prelude': it is a member of package base, which is hidden vigalchin here is a fragement of Dfa.lhs: > {-# OPTIONS -fglasgow-exts #-} > {-# OPTIONS -fallow-undecidable-instances #-} > module Swish.HaskellRDF.Dfa.Dfa ( > Re(..), > matchRe, > matchRe2 > ) where > {- ???? > import Control.Monad.Identity > import Control.Monad.Reader > import Control.Monad.State > import Data.FiniteMap > import List > import Data.Array > -} import IOExts The type of a regular expression. > data Re t "Dfa.lhs" 609 lines, 18871 characters Very kind regards, Vasili

4 4

ANN: Bookshelf
by Emil Axelsson 14 May '09

14 May '09

This is the first release of Bookshelf, a simple document organizer with some wiki functionality. Documents in a directory tree are displayed as a set of HTML pages. Documents in Markdown format are converted to HTML automatically using Pandoc. The manual http://www.cs.chalmers.se/~emax/bookshelf/Manual.shelf.html describes the full functionality. Bookshelf is available on Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Bookshelf or through its Darcs repository: http://www.cs.chalmers.se/~emax/darcs/Bookshelf/ I'm not aware of any bugs. I hope it works on Windows, but I haven't tested. Cheers, / Emil

2 3

forall vs "=>"
by Daryoush Mehrtash 14 May '09

14 May '09

What is the difference between forall as in: runST<http://www.haskell.org/ghc/docs/6.10-latest/html/libraries/base/Control-Mon…>:: ( forall s. ST<http://www.haskell.org/ghc/docs/6.10-latest/html/libraries/base/Control-Mon…>s a) -> a and the "=>" as in evalStateT<http://www.haskell.org/ghc/docs/6.6/html/libraries/mtl/Control-Monad-State.…>:: Monad<http://www.haskell.org/ghc/docs/6.6/html/libraries/base/Control-Monad.html#…>m => StateT<http://www.haskell.org/ghc/docs/6.6/html/libraries/mtl/Control-Monad-State.…>s m a -> s -> m a thanks daryoush

4 3

ANN: priority-sync-0.1.0.1: Cooperative task prioritization.
by Christopher Lane Hinson 14 May '09

14 May '09

http://hackage.haskell.org/cgi-bin/hackage-scripts/package/priority-sync $ cabal install priority-sync git clone http://www.downstairspeople.org/git/priority-sync.git Feedback will be greatly appreciated. This package is a spin-off from my work on roguestar, where I need to do significant background processing while retaining enough resources to perform smooth animation. The following is the front-page documentation for the package. In a simple use case, we want to run some expensive tasks in prioritized order, so that only one task is running on each CPU (or hardware thread) at any time. For this simple case, four operations are needed: simpleTaskPool, schedule, claim, and startQueue. let expensiveTask = threadDelay 1000000 pool <- simpleTaskPool forkIO $ claim Acquire (schedule pool 1) $ putStrLn "Task 1 started . . ." >> expensiveTask >> putStrLn "Task 1 completed." forkIO $ claim Acquire (schedule pool 3) $ putStrLn "Task 3 started . . ." >> expensiveTask >> putStrLn "Task 3 completed." forkIO $ claim Acquire (schedule pool 2) $ putStrLn "Task 2 started . . ." >> expensiveTask >> putStrLn "Task 2 completed." threadDelay 100000 -- contrive to wait for all tasks to become enqueued putStrLn "Starting pool: " startQueue pool threadDelay 4000000 -- contrive to wait for all tasks to become dequeued A TaskPool combines Rooms and Queues in an efficient easy-to-use-interface. Rooms provide fully reentrant synchronization to any number of threads based on arbitrary resource constraints. For example, the Room from a simpleTaskPool is constrained by GHC.numCapabilities. Queues provide task prioritization. A Queue systematically examines (to a configurable depth) all waiting threads with their priorities and resource constraints and wakes the most eagerly prioritized thread whose constraints can be satisfied. TaskPools are not thread pools. The concept is similar to IO Completion Ports. There are no worker threads. If a number of threads are waiting, the thread that is most likely to be processed next is woken and temporarily serves as a working thread. Rooms, Queues, and TaskPools are backed by carefully written STM (software transactional memory) transactions. A salient feature is that, because any thread can participate, a TaskPool supports both bound threads and threads created with forkOnIO. Friendly, --Lane

2 2

List of exports of a module - are there alternatives?
by Maurício 14 May '09

14 May '09

Hi, When we want to list which declarations are exported by a module we do: module Mod ( list of exports ) where ... Are there propositions to alternatives to that (I could not find one)? Like, say, add a "do export" or "do not export" tag to declarations we want to (not) export? (I think something like that could be nice when we have modules with 200 declarations and just a few are (not) going to be exported.) Thanks, Maurício

8 9

Fundep Curiosity
by Christopher Lane Hinson 14 May '09

14 May '09

I've noticed that a large majority of fundeps I see in other people's libraries are written: class C a b | b -> a Where the dependent parameter appears first in the MPTC. Is there a reason for this? AFAIK, there isn't any semantic significance to the order of parameters in an MPTC. Why do many haskellers find this configuration more intuitive? Friendly, --Lane

4 3

Data.Map.Map Pattern Matching
by Nico Rolle 14 May '09

14 May '09

Hi I tried this but it diddn't work in ghci: import qualified Data.Map as Map test :: Map.Map [Int] [[Int]] -> Bool test (fromList[((i:is), (j:js))]) = [i] == j i get the : "Parse error in pattern Failed." error. regards

3 2