May 2007 - Haskell - Haskell.org

ANNOUNCE: AGI library (Asterisk Gateway Interface)
by Jeremy Shaw 13 May '07

13 May '07

Hello, I have uploaded a simple AGI interface to hackage. It is still very alpha, but that has never stopped me before :) http://hackage.haskell.org/cgi-bin/hackage-scripts/package/AGI-1.0 darcs get http://www.n-heptane.com/nhlab/repos/haskell-agi/ The best way to understand how to use it is to: 1. Refer to the documentation for AGI: http://www.voip-info.org/wiki-Asterisk+AGI 2. Look at GuessingGame in the examples directory. The guessing game is just a simple game where you try to guess a number between 0 and 9. It is not very exciting to play, but it does demonstrate how to use the library. j.

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Newbie help with type-classes
by Ryan Ingram 11 May '07

11 May '07

Here's a test case for the problem I'm having; I'm using runhaskell from ghc v6.6. Problem #1) Without -fallow-undecidable-instances, I get the following error: Constraint is no smaller than the instance head in the constraint: ConvertToInt a (Use -fallow-undecidable-instances to permit this) In the instance declaration for `ConvertToIntList a' Problem #2) With -fallow-undecidable-instances, I get this error instead: Overlapping instances for ConvertToIntList () arising from use of `convl' at testcase.hs:28:6-15 Matching instances: instance (ConvertToInt a) => ConvertToIntList a -- Defined at testcase.hs:15:0 instance ConvertToIntList () -- Defined at testcase.hs:18:0 In the expression: convl [()] In the definition of `xl2': xl2 = convl [()] I don't understand why there is an overlapping instances error; () is not an instance of ConvertToInt so how could that instance ever apply? Is there something basic about type-classes that I'm not understanding here? My actual problem is more complicated than this, but this test-case covers the basic issue; something being an instance of class A means that I can derive an instance of class B for it, but I want to implement other instances of class B as well. Code below: {-# OPTIONS -fglasgow-exts -fallow-undecidable-instances #-} module TestCase where class ConvertToInt a where conv :: a -> Int class ConvertToIntList a where convl :: [a] -> [Int] instance ConvertToInt Int where conv = id instance ConvertToInt a => ConvertToIntList a where convl = map conv instance ConvertToIntList () where convl x = [] x :: Int x = 5 xl :: [Int] xl = convl [x] xl2 :: [Int] xl2 = convl [()]

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Integrated Formal Methods 2007: Call for participation
by Jeremy.Gibbons＠comlab.ox.ac.uk 09 May '07

09 May '07

IFM2007: INTEGRATED FORMAL METHODS CALL FOR PARTICIPATION 2nd to 5th July 2007 St Anne's College, Oxford, UK www.ifm2007.org The design and analysis of computing systems presents a significant challenge: systems need to be understood at many different levels of abstraction, and examined from many different perspectives. Formal methods - languages, tools, and techniques with a sound, mathematical basis - can be used to develop a thorough understanding, and to support rigorous examination. Further research into effective integration is required if these methods are to have a significant impact outside academia. The IFM series of conferences seeks to promote that research, to bring together the researchers carrying it out, and to disseminate the results of that research among the wider academic and industrial community. This is the sixth IFM conference. It will be held in the historic university town of Oxford, at St Anne's College - one of the larger colleges of the University, with excellent new conference facilities. Oxford is easily reached from most UK cities, and is 70 minutes from the country's largest airport. Earlier conferences in the series were held at York (1999), Schloss Dagstuhl (2000), Turku (2002), Kent (2004), and Eindhoven (2005). The conference runs for three full days, 3rd to 5th July. Invited speakers include Jifeng He on "UTP Semantics for Web Services" and Daniel Jackson on "Recent Advances in Alloy"; a third invited speaker is yet to be confirmed. There are 32 contributed papers, including a special session on Unifying Theories of Programming. In addition, there are four satellite events, taking place on 2nd and 3rd July - three workshops: * Refinement Workshop * C/C++ Verification * MeMoT (Methods, Models and Tools for Fault Tolerance) and a tutorial: * KeY (Integrating OO Design and Deductive Verification of Software) The full programme is available at: http://www.ifm2007.org/programme-ifm.html Registration for the conference is now open, at: http://www.ifm2007.org/registration.html Special early-registration fees apply until 1st June 2007. For more information, visit the conference web page: http://www.ifm2007.org/ or contact the local organisers: Jim Davies http://www.softeng.ox.ac.uk/Jim.Davies Jeremy Gibbons http://www.softeng.ox.ac.uk/Jeremy.Gibbons

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Job Opportunity
by Luke Evans 07 May '07

07 May '07

The Open Quark team at Business Objects is hiring. This is an opportunity to be working on and with the framework that includes the CAL language, a Haskell-like lazy functional language for the Java platform. Details of Open Quark can be found on the following page: http://labs.businessobjects.com/cal The position is located in Vancouver, Canada. The official job listing is here: http://www.recruitingcenter.net/clients/businessobjects/publicjobs/canada/co ntroller.cfm?jbaction=JobProfile&Job_Id=16831&esid=az Applications should be submitted via this page.

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The Monad.Reader - Call for copy
by Wouter Swierstra 07 May '07

07 May '07

Call for Copy The Monad.Reader - Issue 8 I would like to welcome articles for the next issue of The Monad.Reader. * The Monad.Reader * The Monad.Reader is a electronic magazine about all things Haskell. It is less-formal than journal, but somehow more enduring than a wiki- page. There have been a wide variety of articles, including: exciting code fragments, intriguing puzzles, book reviews, tutorials, and even half-baked research ideas. * Submission Details * Get in touch with me if you intend to submit something -- the sooner you let me know what you're up to, the better. Please submit articles for the next issue by e-mail (wss at cs.nott.ac.uk) to me before ** July 27, 2007 ** Articles should be written according to the guidelines available from http://www.haskell.org/haskellwiki/The_Monad.Reader Please submit your article in PDF, together with any source files you used. The sources will be released together with the magazine under a BSD license. If you would like to submit an article, but have trouble with LaTeX please let me know and we'll sort something out. Looking forward to your submission, Wouter This message has been checked for viruses but the contents of an attachment may still contain software viruses, which could damage your computer system: you are advised to perform your own checks. Email communications with the University of Nottingham may be monitored as permitted by UK legislation.

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Fwd: CfP: Scheme and Functional Programming 2007
by Simon Marlow 07 May '07

07 May '07

[ posting on behalf of Danny Dubé <danny.dube(a)ift.ulaval.ca> ] [Apologies of you receive multiple copies of this message] > (for-papers) ; call for papers 2007 Workshop on Scheme and Functional Programming http://sfp2007.ift.ulaval.ca/ Freiburg, Germany --- 30 September 2007 The 2007 Scheme Workshop is a forum for discussing experience with and future development of the Scheme programming language. The scope of the workshop includes all aspects of the design, implementation, theory, and application of Scheme. We encourage everyone interested in Scheme to participate. This workshop forms part of the 2007 International Conference on Functional Programming (ICFP) as an associated, ACM SIGPLAN sponsored event. Topics of interest for technical papers include (but are not limited to): Design. Language critiques and extensions, concurrency and distribution, components and composition, language embedding, object systems, type systems, exception handling, syntactic abstraction, module systems and libraries, multiparadigm programming, scripting. Implementation. Compilers, interpreters, runtime systems, virtual machines, resource management, program analysis and transformation, partial evaluation, compile-time and run-time optimization, foreign function and operating system interfaces, embedded systems. Development tools. Profilers, tracers, debuggers, program development environments, program understanding tools, performance and conformance test suites. Theory. Formal semantics, correctness of analyses and transformations, lambda calculus, continuations, program verification. Education. Teaching Scheme, teaching with Scheme. Topics of interest for experience papers include (but are not limited to): Applications. Domain-specific languages, graphical user interfaces, web programming, network applications, multimedia programming, systems programming, symbolic computing, large systems, use of Scheme as a scripting language. Practice and experience. Experience with Scheme in education and industry. Scheme pearls. Elegant, instructive uses of Scheme. Experience papers need not necessarily report original research results; they may instead report practical experience that will be useful to others, re-usable programming idioms, or elegant new ways of approaching a problem. The key criterion for such a paper is that it makes a contribution from which other practitioners can benefit. It is not enough simply to describe a program! System Demonstrations. Authors of both technical and experience papers are invited to describe, in an appendix, proposals for system demonstrations to be given during the workshop. Panel Discussions. We also invite proposals for panel discussions on topics of interest to the Scheme community. Authors of accepted proposals will give a brief presentation on the topic and then moderate the discussion that follows. For submission details, please see http://sfp2007.ift.ulaval.ca/. Program committee John Clements (Cal Poly) Danny Dubé, chairman (Laval University) Martin Gasbichler (Zühlke Engineering) Aubrey Jaffer (ClearMethods Inc.) Christian Queinnec (University Paris 6) Chung-chieh Shan (Rutgers University) Steering committee William D. Clinger (Northeastern University) Marc Feeley (University of Montréal) Robby Findler (University of Chicago) Dan Friedman (Indiana University) Christian Queinnec (University Paris 6) Manuel Serrano (INRIA Sophia Antipolis) Olin Shivers (Northeastern University) Mitchell Wand (Northeastern University) Submission deadline June 22, 2007 Author notification August 3, 2007 Final paper due September 7, 2007 Workshop September 30, 2007

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Haskell Weekly News: May 07, 2007
by dons＠cse.unsw.edu.au 07 May '07

07 May '07

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20070507 Issue 62 - May 07, 2007 --------------------------------------------------------------------------- Welcome to issue 62 of HWN, a weekly newsletter covering developments in the [1]Haskell community. This week sees the release of Atom, a hardware description language embedded in Haskell, along with the usual suite of new libraries and tools. In addition, The Monad.Reader Issue 7 was released, and the hackage upload festival continues unabated. 1. http://haskell.org/ Announcements Atom: Hardware Description in Haskell. Tom Hawkins [2]announced the release of [3]Atom, a high-level hardware description language embedded in Haskell, compiles conditional term rewriting systems into conventional HDL. 2. http://article.gmane.org/gmane.comp.lang.haskell.general/15209 3. http://www.funhdl.org/ The Monad.Reader: Issue 7. Wouter Swierstra [4]announced the latest issue of [5]The Monad.Reader. The Monad.Reader is a quarterly magazine about functional programming. It is less-formal than journal, but somehow more enduring than a wiki page or blog post. 4. http://article.gmane.org/gmane.comp.lang.haskell.cafe/22038 5. http://www.haskell.org/haskellwiki/The_Monad.Reader HDBC: Haskell Database Connectivity. John Goerzon [6]announced that [7]HDBC 1.1.2 is now released. HDBC provides an abstraction layer between Haskell programs and SQL relational databases. This lets you write database code once, in Haskell, and have it work with any number of backend SQL databases. 6. http://article.gmane.org/gmane.comp.lang.haskell.general/15227 7. http://software.complete.org/hdbc FileManip: Expressive Filesystem Manipulation. Bryan O'Sullivan [8]announced the [9]FileManip package provides expressive functions and combinators for searching, matching, and manipulating files. 8. http://article.gmane.org/gmane.comp.lang.haskell.cafe/22090 9. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/FileManip-0.1 photoname: manipulate photos using EXIF data. Dino Morelli [10]announced the release of [11]photoname, a command-line utility for renaming and moving photo image files. The new folder location and naming are determined by two things: the photo shoot date information contained within the file's EXIF tags and the usually-camera-assigned serial number, often appearing in the filename. 10. http://article.gmane.org/gmane.comp.lang.haskell.general/15187 11. http://ui3.info/d/proj/photoname.html RSA-Haskell: Command-line Cryptography. David Sankel [12]announced the release of [13]RSA-Haskell, a collection of command-line cryptography tools and a cryptography library written in Haskell. It is intended to be useful to anyone who wants to secure files or communications or who wants to incorporate cryptography in their Haskell application. 12. http://article.gmane.org/gmane.comp.lang.haskell.general/15207 13. http://www.netsuperbrain.com/rsa-haskell.html Haskell modes for Vim. Claus Reinke [14]summarised the various Haskell/Vim support currently available 14. http://article.gmane.org/gmane.comp.lang.haskell.general/15180 French Translation of Gentle Introduction to H98. The haskell-fr team [15]announced a completed a [16]translation into French of the 'Gentle Introduction to Haskell'. 15. http://article.gmane.org/gmane.comp.lang.haskell.general/15193 16. http://gorgonite.developpez.com/livres/traductions/haskell/gentle-haskell/ Haskell' This section covers the [17]Haskell' standardisation process. * [18]Polymorphic strict fields 17. http://hackage.haskell.org/trac/haskell-prime 18. http://thread.gmane.org/gmane.comp.lang.haskell.prime/2192 Hackage This week's new libraries in [19]the Hackage library database. 19. http://hackage.haskell.org/ * BitSyntax-0.2. Adam Langley. [20]A simple function for the construction of binary data. 20. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/BitSyntax-0.2 * filepath-1.0. Neil Mitchell. [21]Library for manipulating FilePath's in a cross platform way. 21. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/filepath-1.0 * Chart-2007.3.5. Tim Docker [22]A library for generating 2D Charts and Plots. 22. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Chart-2007.3.5 * FileManip-0.1. Bryan O'Sullivan [23]A Haskell library for working with files and directories. 23. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/FileManip-0.1 * hsns-0.5.2. Austin Seipp [24]A network sniffer written in a purely fun language. 24. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hsns-0.5.2 * template-0.1. Johan Tibell [25]Simple string substitution library that supports dollar-based substitution. 25. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/template-0.1 * ASN1-0.0.1. Dominic Steinitz [26]ASN.1 suppport for X.509 identity and attribute certificates, PKCS8, PKCS1v15. 26. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/ASN1-0.0.1 Discussion The Proper Definition of (evaluate :: a -> IO a). Isaac Dupree [27]described a variant of evaluate with modified semantics to the current implementation. 27. http://article.gmane.org/gmane.comp.lang.haskell.libraries/6858 Why is Data.Set not a monad?. Dan Doel [28]documented the reasons why Data.Set is not currently an instance of Monad. 28. http://article.gmane.org/gmane.comp.lang.haskell.libraries/6861 Chaos. Andrew Coppin [29]announced chaos, a fun image generating mystery program. 29. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/22177 The Functional Pearls. Don Stewart [30]collected the functional pearls known to be available online, on to a single page on the Haskell wiki. 30. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/22171 Blog noise [31]Haskell news from the blogosphere. * [32]HUG: Nested Data Parallelism in Haskell * [33]HUG: London Haskell User Group * [34]New York Functional Programmers meeting: roundup * [35]Python-style string split in Haskell * [36]Thinking in types * [37]Using the Haskell package system * [38]Fixed precision, an update * [39]Use of Text.XHtml.Strict for Outputting XHTML * [40]Idiom: Plan for Currying * [41]Bowling in Haskell * [42]The Trivial Monad * [43]Homeland Security Threat Level Monad * [44]Monads as universe helpers * [45]Understanding comonads * [46]Coding in Haskell: conciseness * [47]Functional programming in Wall Street * [48]Phantom Types for Real Problems * [49]Haskell rocks * [50]Advertising the ICFP Programming Contest * [51]Haskell wikibook * [52]Roll Your Own Window Manager: Part 1: Defining and Testing a Model * [53]Haskell and the Type Calculus: or, the Good -> Bad -> Ugliness of Types * [54]FileManip, an expressive Haskell library for manipulating files * [55]Programming in Haskell * [56]Parsing JSON in Haskell * [57]Namespace confusion * [58]A Scheme parser in Haskell * [59]Simple performance analysis * [60]Playing with Haskell unsafely * [61]repeat and sequence * [62]Haskell and C: functions returning more than one value 31. http://planet.haskell.org/ 32. http://www.londonhug.net/2007/05/01/hug-update-nested-data-parallelism-in-h… 33. http://www.phildawes.net/blog/2007/05/02/london-haskell-user-group/ 34. http://privosoft.blogspot.com/2007/05/new-york-functional-programmers-meeti… 35. http://gimbo.org.uk/blog/2007/04/20/splitting-a-string-in-haskell/ 36. http://totherme.livejournal.com/3845.html 37. http://gimbo.org.uk/blog/2007/04/27/haskell-packages-gotcha-global-vs-per-u… 38. http://augustss.blogspot.com/2007/04/fixed-precision-update-so-i-was-bit.ht… 39. http://www.movethemarkets.com/richard/2007/04/14/use-of-textxhtmlstrict-for… 40. http://www.movethemarkets.com/richard/2007/04/28/functional-programming-idi… 41. http://www.randomhacks.net/articles/2007/04/28/bowling-in-haskell 42. http://sigfpe.blogspot.com/2007/04/trivial-monad.html 43. http://sigfpe.blogspot.com/2007/04/homeland-security-threat-level-monad.html 44. http://gelisam.blogspot.com/2006/10/monads-as-universe-helpers.html 45. http://gelisam.blogspot.com/2007/04/i-understand-comonads.html 46. http://defowl.blogspot.com/2007/04/coding-in-haskell.html 47. http://codemiscellany.blogspot.com/2007/04/functional-programming-in-wall-s… 48. http://neilmitchell.blogspot.com/2007/04/phantom-types-for-real-problems.ht… 49. http://errantember.livejournal.com/50627.html 50. http://johanjeuring.blogspot.com/2007/05/advertising-icfp-programming-conte… 51. http://koweycode.blogspot.com/2007/05/haskell-wikibook-now-featured.html 52. http://cgi.cse.unsw.edu.au/~dons/blog/2007/05/01#xmonad_part1_model 53. http://disparatemathematician.blogspot.com/2007/05/haskell-and-type-calculu… 54. http://www.serpentine.com/blog/2007/05/01/filemanip-an-expressive-haskell-l… 55. http://www.regdeveloper.co.uk/2007/05/03/programming_haskell/ 56. http://notes-on-haskell.blogspot.com/2007/05/parsing-json.html 57. http://notes-on-haskell.blogspot.com/2007/05/namespaces-confusion.html 58. http://sami.samhuri.net/articles/2007/05/03/a-scheme-parser-in-haskell-part… 59. http://syntaxfree.wordpress.com/2007/05/04/lra/ 60. http://therning.org/magnus/archives/249 61. http://therning.org/magnus/archives/269 62. http://therning.org/magnus/archives/280 Quotes of the Week * Oleg K: So, `bind' is `let' and monadic programming is equivalent to programming in the A-normal form. That is indeed all there is to monads * kc5tja: Premature evil is the root of all optimization * Tommah: Remember, kids: if you program in a language with side effects, the terrorists win. * ndm: Comments are for people who can't sense what their code does from the indentation * jcreigh: GHC has lots of interesting features above Haskell98, I've noticed. 'You can take the red pill or the blue pill...' 'Hmm. What's the green pill?' 'What? Oh. That's GHC.' * schluehk: It's about a variant of the other big Haskell credo: once it compiles it works. Once you have written a prototype you have also a spec. If this is not agile I don't know what? It is a quite remarkable inversion. Formerly people wanted tools that are so versatile that they let them express almost everything with great ease and where they didn't care a lot about speed optimizations and corner cases in the early iterations. Now people want tools that restricts intentionally their expressivity to let them do big upfront design as source code. They want to be guided to initial perfection. Let's face it: Haskell has quite some momentum in the dialectic move. Code Watch Notable new features and bug fixes to the Haskell compilers. Thu May 3 06:19:55 PDT 2007. Simon Marlow. [63]Add history/trace functionality to the GHCi debugger. The debugger can now log each step of the evaluation without actually stopping, keeping a history of the recent steps (currently 50). When a (real) breakpoint is hit, you can examine previous steps in the history (and their free variables) using the :history, :back and :forward commands. 63. http://article.gmane.org/gmane.comp.lang.haskell.cvs.ghc/20551 Wed May 2 09:34:57 PDT 2007. Simon Peyton-Jones. [64]Make records work properly with type families. This fixes Trac #1204. There's quite a delicate interaction of GADTs, type families, records, and in particular record updates. 64. http://article.gmane.org/gmane.comp.lang.haskell.cvs.ghc/20522 About the Haskell Weekly News Each week, new editions are posted to [65]the Haskell mailing list as well as to [66]the Haskell Sequence and [67]Planet Haskell. [68]RSS is also available, and headlines appear on [69]haskell.org. Headlines are available as [70]PDF. To help create new editions of this newsletter, please see the [71]contributing information. Send stories to dons at cse.unsw.edu.au. The darcs repository is available at darcs get [72]http://www.cse.unsw.edu.au/~dons/code/hwn 65. http://www.haskell.org/mailman/listinfo/haskell 66. http://sequence.complete.org/ 67. http://planet.haskell.org/ 68. http://sequence.complete.org/node/feed 69. http://haskell.org/ 70. http://www.cse.unsw.edu.au/~dons/code/hwn/archives/20070507.pdf 71. http://haskell.org/haskellwiki/HWN 72. http://www.cse.unsw.edu.au/~dons/code/hwn

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Monad and Monad transformer???
by Duong Thai Ha 07 May '07

07 May '07

hi I am a newbee to haskell so please forgive me if the question is not appropreate. I am trying to get the idea of using Monad and have to understand the following code. Can you please tell me is how different Monad and Monad transformer is? And what is mean by > newtype State s a = State { runState :: s -> (a, s) } --------------------------------- Define (State s) as a State monad > instance Monad (State s) where > return a = State $ \s -> (a,s) > m >>= k = State $ \s -> let (a,s') = runState m s in runState (k a) s' Thanks lot for your help I really do appreciate that Best regard

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Is Hackage becoming a centralistic approach?
by Wolfgang Jeltsch 03 May '07

03 May '07

Hello, on <http://haskell.org/haskellwiki/Hackage> I read that there is the idea to make Hackage support bug tracking and project pages. This looks like Hackage should provide complete hosting of Haskell projects at some time. Is this really intended? Since any reasonable Haskell project should use Hackage now, this would mean that a Haskell software developer cannot use another hosting provider or whatever to host his project. I think this would be very bad since the decision about how and where to host a project shouldn’t be based primarily on what programming language it uses. Any comments? Best wishes, Wolfgang

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ANN: HDBC 1.1.2
by John Goerzen 03 May '07

03 May '07

Hi everyone, I've made a few improvements to HDBC since the release of 1.1.0 yesterday. HDBC 1.1.2 is posted, with these updates: * New data type that "wraps" the IConnection class in a way that's easier to use in Haskell and more backwards-compatible. * Updated docs for correct URLs for HDBC info Also, on the HDBC website: * Posted migration to 1.1.x information * Posted API docs for the database backend drivers HDBC is at http://software.complete.org/hdbc -- John Goerzen Author, Foundations of Python Network Programming http://www.amazon.com/exec/obidos/tg/detail/-/1590593715

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