- Haskell - Haskell.org

*** FORTHCOMING DEADLINE*** [CfP] 4th *OPEN* Answer Set Programming Competition 2013 - CALL FOR PARTICIPANTS
by Francesco Calimeri 30 Jan '13

30 Jan '13

[apologies for any cross-posting] ************************* *** IMMINENT DEADLINE *** ************************* ........................................................................ 4th OPEN Answer Set Programming Competition 2013 Call for Participant Systems University of Calabria - Vienna University of Technology Fall/Winter 2012/2013 http://aspcomp2013.mat.unical.it/ aspcomp2013(a)kr.tuwien.ac.at ........................................................................ The 4th Open Answer Set Programming (ASP) Competition is now in the Call for Participant Systems stage. +--------------------------------------------------------------------+ | The event is open to ASP systems and *any other* system based on a | | declarative specification paradigm. | +--------------------------------------------------------------------+ == Call for Participant Systems == Participants of the Answer Set Programming Competition will compete on a selected collection of benchmark problems, taken from a variety of benchmark problem domains as well as real world applications. These include, but are not limited to: * Classic and applicative graph problems * Scheduling, Timetabling, and other resource allocation problems * Sequential and Temporal Planning * Combinatorial Optimization Problems * Deductive database tasks on large data-sets * Puzzles and Combinatorics * Ontology reasoning * Automated Theorem Proving and Model Checking * Reasoning tasks over large propositional instances * Constraint Programming problems * Other AI problems The competition consists of two independent main tracks: * the Model & Solve Track invites any researcher and developer of declarative knowledge representation systems to participate in an open challenge for solving sophisticated AI problems with their tools of choice. Participants submit a solver based on an arbitrary input format and declarative specifications of the Competition's benchmark domains; * the System Track compares dedicated answer set solvers on ASP benchmarks. Participants compete with a solver for a standard ASP language. We encourage to submit parallel and portfolio systems exploiting multiple cores or multiple algorithms for solving the given instances. === About the Answer Set Programming Competition Series === Answer Set Programming is a well-established paradigm of declarative programming with close relationship to other declarative modelling paradigms and languages, such as SAT Modulo Theories, Constraint Handling Rules, FO(.), PDDL, CASC, and many others. The ASP Competition is a biannual event for evaluating declarative knowledge representation systems on hard and demanding AI problems. The 4th ASP Competition will be run in the first half of 2013 jointly at the University of Calabria (Italy) and the Vienna University of Technology (Austria). The event is the sequel to the ASP Competition series, held at the University of Potsdam (Germany) in 2006-2007, at the University of Leuven (Belgium) in 2009, and at University of Calabria (Italy) in 2011. The current competition takes place in cooperation with the 12th International Conference on Logic Programming and Nonmonotonic Reasoning (LPNMR 2013), where the results will be announced. The ASP competition is held as an open tournament. The "Model & Solve" competition track fosters the spirit of integration among communities, and is thus open to all types of solvers: ASP systems, SAT solvers, SMT solvers, CP systems, FOL theorem provers, Description Logics reasoners, planning reasoners, or any other. The "System" competition track is instead set up on a fixed language based on the answer set semantics. == Important Dates == * February 2nd, 2013: Participant registration deadline * March 1st, 2013: Participant system submission deadline * March 2nd, 2013: System freeze, the competition runs * September 15-19, 2013: Announcement of results and award presentation at LPNMR 2013 in Corunna, Spain For further information and submission instructions please visit the competition web site http://aspcomp2013.mat.unical.it/ or contact us by email: aspcomp2013(a)kr.tuwien.ac.at

1 0

CFP: EOOLT 2013: Extended Submission Deadline!
by Henrik Nilsson 30 Jan '13

30 Jan '13

Dear Haskellers, The included call for papers to the 5th international workshop on Equation-based Object-Oriented Languages and Tools (EOOLT) 2013 may be of interest to those interested in declarative domain-specific languages in the context of Haskell. Note that the deadlines have been extended: * Abstracts: 8 February * Full papers: 18 February Apologies for multiple copies! All the best, /Henrik -- Henrik Nilsson School of Computer Science The University of Nottingham nhn(a)cs.nott.ac.uk This message and any attachment are intended solely for the addressee and may contain confidential information. If you have received this message in error, please send it back to me, and immediately delete it. Please do not use, copy or disclose the information contained in this message or in any attachment. Any views or opinions expressed by the author of this email do not necessarily reflect the views of the University of Nottingham. 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

ANNOUNCE: GHC version 7.6.2
by Ian Lynagh 29 Jan '13

29 Jan '13

============================================================= The (Interactive) Glasgow Haskell Compiler -- version 7.6.2 ============================================================= The GHC Team is pleased to announce a new patchlevel release of GHC, 7.6.2. This release fixes a number of bugs relative to 7.6.1, so we recommend upgrading. Full release notes are here: http://www.haskell.org/ghc/docs/7.6.2/html/users_guide/release-7-6-2.html How to get it ~~~~~~~~~~~~~ The easy way is to go to the web page, which should be self-explanatory: http://www.haskell.org/ghc/ We supply binary builds in the native package format for many platforms, and the source distribution is available from the same place. Packages will appear as they are built - if the package for your system isn't available yet, please try again later. Background ~~~~~~~~~~ Haskell is a standard lazy functional programming language. GHC is a state-of-the-art programming suite for Haskell. Included is an optimising compiler generating good code for a variety of platforms, together with an interactive system for convenient, quick development. The distribution includes space and time profiling facilities, a large collection of libraries, and support for various language extensions, including concurrency, exceptions, and foreign language interfaces (C, whatever). GHC is distributed under a BSD-style open source license. A wide variety of Haskell related resources (tutorials, libraries, specifications, documentation, compilers, interpreters, references, contact information, links to research groups) are available from the Haskell home page (see below). On-line GHC-related resources ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Relevant URLs on the World-Wide Web: GHC home page http://www.haskell.org/ghc/ GHC developers' home page http://hackage.haskell.org/trac/ghc/ Haskell home page http://www.haskell.org/ Supported Platforms ~~~~~~~~~~~~~~~~~~~ The list of platforms we support, and the people responsible for them, is here: http://hackage.haskell.org/trac/ghc/wiki/Contributors Ports to other platforms are possible with varying degrees of difficulty. The Building Guide describes how to go about porting to a new platform: http://hackage.haskell.org/trac/ghc/wiki/Building Developers ~~~~~~~~~~ We welcome new contributors. Instructions on accessing our source code repository, and getting started with hacking on GHC, are available from the GHC's developer's site run by Trac: http://hackage.haskell.org/trac/ghc/ Mailing lists ~~~~~~~~~~~~~ We run mailing lists for GHC users and bug reports; to subscribe, use the web interfaces at http://www.haskell.org/mailman/listinfo/glasgow-haskell-users http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs There are several other haskell and ghc-related mailing lists on www.haskell.org; for the full list, see http://www.haskell.org/mailman/listinfo/ Some GHC developers hang out on #haskell on IRC, too: http://www.haskell.org/haskellwiki/IRC_channel Please report bugs using our bug tracking system. Instructions on reporting bugs can be found here: http://www.haskell.org/ghc/reportabug

1 0

Request for review of a GADT tutorial draft
by Anton Dergunov 28 Jan '13

28 Jan '13

Dear Haskell community, I have recently written an introductory-level tutorial article about GADTs in GHC (inspired by LASER 2012 summer school and to be submitted to their proceedings). I have already send this draft to the "Haskell Cafe" mailing list, but I was also advised to use these mailing lists, so I would like to ask for your feedback: http://anton-dergunov.ru/publications/gadts_draft_v4.pdf Any opinion about this article and any suggestions are very welcome! -- Best Regards, Anton Dergunov

1 0

Six PhD Studentships at St Andrews (tight deadline)
by Kevin Hammond 27 Jan '13

27 Jan '13

We have six funded PhD Studentships available. If you know any good applicants with an interest in functional programming, parallelism or related areas, I'd be pleased to hear from them. The deadline is tight (4th February), but the main thing is to get an application in. http://blogs.cs.st-andrews.ac.uk/csblog/2012/12/20/600th-anniversary-phd-sc… Best Wishes, Kevin -------- Kevin Hammond, Professor of Computer Science, University of St Andrews T: +44-1334 463241 F: +44-1334-463278 W: http://www.cs.st-andrews.ac.uk/~kh In accordance with University policy on electronic mail, this email reflects the opinions of the individual concerned, may contain confidential or copyright information that should not be copied or distributed without permission, may be of a private or personal nature unless explicitly indicated otherwise, and should not under any circumstances be taken as an official statement of University policy or procedure (see http://www.st-and.ac.uk) The University of St Andrews is a charity registered in Scotland : No SC013532

1 0

CFP WWV 2013
by Josep Silva Galiana 27 Jan '13

27 Jan '13

***************************************************************************** * * * WWV 2013 * * Automated Specification and Verification of Web Systems * * 9th International Workshop * * Call for Papers * * * ***************************************************************************** IMPORTANT DATES Abstract Submission March 22, 2013 Full Paper Submission March 29, 2013 Acceptance Notification May 3, 2013 Camera Ready (pre-proceedings) May 20, 2013 Workshop June 6, 2013 Camera Ready (post-proceedings) June 26, 2013 SCOPE The Workshop on Automated Specification and Verification of Web Systems (WWV, http://users.dsic.upv.es/grupos/elp/wwv/) is a yearly workshop that aims at providing an interdisciplinary forum to facilitate the cross-fertilization and the advancement of hybrid methods that exploit concepts and tools drawn from Rule-based programming, Software engineering, Formal methods and Web-oriented research. Nowadays, many companies and institutions have diverted their Web sites into interactive, completely-automated, Web-based applications for, e.g., e-business, e-learning, e-government and e-health. The increased complexity and the explosive growth of Web systems has made their design and implementation a challenging task. Systematic, formal approaches to their specification and verification can permit to address the problems of this specific domain by means of automated and effective techniques and tools. Topics of either theoretical or applied interest include, but are not limited to: - Rule-based approaches to Web system analysis, certification, specification, verification, and optimization. - Languages and models for programming and designing Web systems. - Formal methods for describing and reasoning about Web systems. - Model-checking, synthesis and debugging of Web systems. - Analysis and verification of linked data. - Abstract interpretation and program transformation applied to the semantic Web. - Intelligent tutoring and advisory systems for Web specifications authoring. - Middleware and frameworks for composition and orchestration of Web services. - Web quality and Web metrics. - Web usability and accessibility. - Testing and evaluation of Web systems and applications. AUDIENCE Participation to WWV is open. The workshop is intended for, but not limited to, researchers from the communities of Rule-based programming, Software engineering, Formal methods and Web-oriented research. SUBMISSION Submitted papers should present original unpublished work and cannot be under review for publication elsewhere. Each paper will undergo a thorough evaluation by at least three reviewers, chosen by the Program Committee. Contributions should be submitted through the EasyChair online submission system in PDF format, and should be prepared in LaTeX using the EPTCS-style format and should not exceed 15 pages (typeset 11 points). Submission is a firm commitment that at least one of the authors will attend the workshop, if the paper is accepted. PUBLICATION Accepted papers will be included in the pre-proceedings, which will be made available in electronic form through the WWV web site. After the workshop, authors of accepted papers will be asked to prepare, by incorporating insights gathered during the event, a final version of their paper to be published in the post-proceedings. We plan to publish the workshop post-proceedings as a volume of the EPTCS series. STEERING COMMITTEE Maria Alpuente Technical University of Valencia, Spain (co-Chair) Demis Ballis University of Udine, Italy Santiago Escobar Technical University of Valencia, Spain Moreno Falaschi University of Siena, Italy (co-Chair) Laura Kovacs Vienna University of Technology, Austria Temur Kutsia Johannes Kepler University Linz, Austria Massimo Marchiori University of Padova, Italy Rosario Pugliese University of Florence, Italy Josep Silva Technical University of Valencia, Spain Francesco Tiezzi IMT Institute for Advanced Studies Lucca, Italy WORKSHOP CO-CHAIRS Antònio Ravara New University of Lisbon, Portugal Josep Silva Universidad Politécnica de Valencia, Spain PROGRAM COMMITTEE Jesús Almendros University of Almeria, Spain Maria Alpuente Universitat Politècnica de València, Spain Demis Ballis University of Udine, Italy Daniela Da Cruz Universidade do Minho, Portugal Raymond Hu Imperial College London, United Kingdom Ivan Lanese University of Bologna/INRIA, Italy Anders Møller Aarhus University, Denmark Elie Najm Telecom ParisTech, France Kostis Sagonas University of Uppsala, Sweden Francesco Tiezzi IMT, Institute for Advanced Studies Lucca, Italy Emilio Tuosto University of Leicester, United Kingdom WORKSHOP FORMAT One full day meeting, including 1 or 2 invited talks and about 8 refereed contributions. PAST WORKSHOP EDITIONS Started in 2005, the series of this workshop established itself as a lively, friendly event with many interactions and discussions. 1. WWV'05 in Valencia, Spain; March 14-15, 2005 homepage: http://users.dsic.upv.es/workshops/wwv05/ 2. WWW'06 in Paphos, Cyprus; November 19, 2006 homepage: http://users.dsic.upv.es/workshops/wwv06/ 3. WWV'07 in Venice, Italy; December 14, 2007 homepage: http://wwv07.dimi.uniud.it/ 4. WWV'08 in Siena, Italy; July 4, 2008 homepage: http://wwv08.dimi.uniud.it/ 5. WWV'09 in Castle of Hagenberg, Austria; July 17, 2009 homepage: http://www.risc.uni-linz.ac.at/about/conferences/wwv09/ 6. WWV'10 in Vienna, Austria; July 30-31, 2010 homepage: http://www.complang.tuwien.ac.at/WWV2010/ 7. WWV'11 in Reykjavik, Iceland; June 9, 2011 (as part of DisCoTec 2011) homepage: http://rap.dsi.unifi.it/wwv2011/ 8. WWV'12 in Stockholm, Sweden; June 16, 2012 (as part of DisCoTec 2012) homepage: http://users.dsic.upv.es/~jsilva/wwv2012/ The previous 7 editions of WWV attracted high quality papers that were published in ENTCS (WWV'05, WWV'07, WWV'08), IEEE (WWV'06) and EPTCS (WWV'11,WWV'12). After WWV'09, a special issue of the Journal of Symbolic Computation on the topics of the WWV has been organized. Similarly, a special issue of the Journal of Applied Logic has been organized after WWV'10, and a special issue of the Journal of Logic and Algebraic Programming is being organized after WWV'11 and WWV'12.

1 0

Haskell Weekly News: Issue 255
by Daniel Santa Cruz 24 Jan '13

24 Jan '13

Welcome to issue 255 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers the weeks of January 06 to 19, 201. Quotes of the Week * ky3: Indexed monads are just categories in the category of endofunctors, what's the problem? * tac: I guess I'm just living in a fantasy world where the docs tell you how to use such a basic API :P * shachaf: 3.0 is an edwardk phase, not just a version number. It's like Picasso's Blue Period. * cmccann: Clearly the reason why edwardk uses Haskell now is because every C++ compiler has a restraining order against him. * shachaf: I'm not sure what your question is, but maybe lens is the answer. * cmccann: * cmccann has concluded that lenses are just a category whose objects are english prepositions and whose morphisms are all unsafeCoerce * shachaf: Some people, when asking about a problem in #haskell, get a link to okmij.org. Now they have two problems. * quicksilver: It returns undefined for convenience. I'm not really sure it's that convenient, but that's why. * edwardk: cmccann: let me get this straight you are saying that someone [mm_freak] who by their very nick admits to being a freak did something freakish? Top Reddit Stories * LiquidHaskell: Refinement Types in Haskell via SMT Domain: goto.ucsd.edu, Score: 71, Comments: 22 On Reddit: [1] http://goo.gl/PE2nf Original: [2] http://goo.gl/P3Gm9 * Hakyll 4.0 released Domain: jaspervdj.be, Score: 59, Comments: 19 On Reddit: [3] http://goo.gl/IQAXq Original: [4] http://goo.gl/AbLnM * When Haskell is faster than C Domain: paulspontifications.blogspot.co.uk, Score: 52, Comments: 23 On Reddit: [5] http://goo.gl/3rj8J Original: [6] http://goo.gl/N2cbA * I'm teaching an introductory 12-week class on Haskell. Join in for a journey! Domain: reddit.com, Score: 45, Comments: 15 On Reddit: [7] http://goo.gl/TsnQ5 Original: [8] http://goo.gl/EMMVR * Subtractable values are torsors Domain: ro-che.info, Score: 42, Comments: 15 On Reddit: [9] http://goo.gl/4IcMp Original: [10] http://goo.gl/6YJrY * Chordify: extract chord sequences from MP3's using HarmTrace Domain: chordify.net, Score: 42, Comments: 8 On Reddit: [11] http://goo.gl/8J7rA Original: [12] http://goo.gl/ySfR5 * Getting Started with Haskell Domain: bob.ippoli.to, Score: 41, Comments: 8 On Reddit: [13] http://goo.gl/4Evnb Original: [14] http://goo.gl/nzg9o * Using AngularJS with Haskell Snap Domain: nurpax.github.com, Score: 40, Comments: 19 On Reddit: [15] http://goo.gl/SH8e1 Original: [16] http://goo.gl/0lSyN * Down with kinds: adding dependent heterogeneous equality to to FC Domain: cis.upenn.edu, Score: 38, Comments: 14 On Reddit: [17] http://goo.gl/iEvyI Original: [18] http://goo.gl/cH0Eo * Fixing GADTs : Generic recursion schemes for GADTs using fixed points of higher-order functors Domain: timphilipwilliams.com, Score: 38, Comments: 25 On Reddit: [19] http://goo.gl/dEMq9 Original: [20] http://goo.gl/vnjhp * What's the importance of Category Theory in Haskell? Is it worth really studying? Domain: self.haskell, Score: 37, Comments: 60 On Reddit: [21] http://goo.gl/T430r Original: [22] http://goo.gl/T430r * Parsing Markdown with Parsec: How Pandoc does it Domain: youtube.com, Score: 35, Comments: 13 On Reddit: [23] http://goo.gl/TN9TJ Original: [24] http://goo.gl/zpX7f * Clckwrks, from the creator of Happstack, is developing into a clean alternative to Wordpress Domain: clckwrks.com, Score: 34, Comments: 7 On Reddit: [25] http://goo.gl/L9WXx Original: [26] http://goo.gl/FZRpU * pipes-safe-1.0 - Resource management and exception handling for pipes Domain: haskellforall.com, Score: 32, Comments: 27 On Reddit: [27] http://goo.gl/HeLWz Original: [28] http://goo.gl/1hTFc Top StackOverflow Questions * values, types, kinds,… as an infinite sequence? votes: 36, answers: 1 Read on SO: [29] http://goo.gl/lyyYc * Why is this a useful warning in Haskell when pattern matching? “Defined but not used” votes: 17, answers: 3 Read on SO: [30] http://goo.gl/iQLFq * Why are getArgs and getProgName IO actions? votes: 16, answers: 3 Read on SO: [31] http://goo.gl/5ZPYO * Can GADTs be used to prove type inequalities in GHC? [duplicate] votes: 14, answers: 2 Read on SO: [32] http://goo.gl/fDdha * Applying Denotational Semantics to design of Programs [migrated] votes: 14, answers: 0 Read on SO: [33] http://goo.gl/KLOCX * Examples where compiler-optimized functional code performs better than imperative code votes: 14, answers: 1 Read on SO: [34] http://goo.gl/Fzqdx * Why is there only one non-strict function from Int to Int? votes: 12, answers: 2 Read on SO: [35] http://goo.gl/KXcAy * Dependency injection in Haskell: solving the task idiomatically votes: 12, answers: 3 Read on SO: [36] http://goo.gl/xTcYc * What does a Haskell comment starting with `{- |` generally mean? votes: 11, answers: 1 Read on SO: [37] http://goo.gl/zNikw * Is operational really isomorphic to a free monad? votes: 10, answers: 3 Read on SO: [38] http://goo.gl/AJlgH Until next time, [39]+Daniel Santa Cruz References 1. http://goto.ucsd.edu/~rjhala/liquid/haskell/blog/blog/2013/01/01/refinement… 2. http://www.reddit.com/r/haskell/comments/16w3hp/liquidhaskell_refinement_ty… 3. http://jaspervdj.be/posts/2013-01-16-hakyll-4.0.html 4. http://www.reddit.com/r/haskell/comments/16ojtv/hakyll_40_released/ 5. http://paulspontifications.blogspot.co.uk/2013/01/when-haskell-is-faster-th… 6. http://www.reddit.com/r/haskell/comments/16tryo/when_haskell_is_faster_than… 7. http://www.reddit.com/r/UniversityofReddit/comments/169jfe/class_introducti… 8. http://www.reddit.com/r/haskell/comments/169k67/im_teaching_an_introductory… 9. http://ro-che.info/articles/2013-01-08-torsors.html 10. http://www.reddit.com/r/haskell/comments/166iju/subtractable_values_are_tor… 11. http://chordify.net/pages/how-to-use-chordify/ 12. http://www.reddit.com/r/haskell/comments/16u44u/chordify_extract_chord_sequ… 13. http://bob.ippoli.to/archives/2013/01/11/getting-started-with-haskell/ 14. http://www.reddit.com/r/haskell/comments/16fegr/getting_started_with_haskel… 15. http://nurpax.github.com/posts/2013-01-13-angularjs-and-haskell.html 16. http://www.reddit.com/r/haskell/comments/16iaiq/using_angularjs_with_haskel… 17. http://www.cis.upenn.edu/~eir/papers/2013/jmnokinds/jmnokinds.pdf 18. http://www.reddit.com/r/haskell/comments/167c21/down_with_kinds_adding_depe… 19. http://www.timphilipwilliams.com/posts/2013-01-16-fixing-gadts.html 20. http://www.reddit.com/r/haskell/comments/16qr6q/fixing_gadts_generic_recurs… 21. http://www.reddit.com/r/haskell/comments/16i322/whats_the_importance_of_cat… 22. http://www.reddit.com/r/haskell/comments/16i322/whats_the_importance_of_cat… 23. http://www.youtube.com/watch?v=nCwG9ijQMuQ&t=01m22s 24. http://www.reddit.com/r/haskell/comments/16kf0j/parsing_markdown_with_parse… 25. http://www.clckwrks.com/ 26. http://www.reddit.com/r/haskell/comments/168j2w/clckwrks_from_the_creator_o… 27. http://www.haskellforall.com/2013/01/pipes-safe-10-resource-management-and.… 28. http://www.reddit.com/r/haskell/comments/16mban/pipessafe10_resource_manage… 29. http://stackoverflow.com/questions/14401689/values-types-kinds-as-an-infini… 30. http://stackoverflow.com/questions/14309396/why-is-this-a-useful-warning-in… 31. http://stackoverflow.com/questions/14295582/why-are-getargs-and-getprogname… 32. http://stackoverflow.com/questions/14273235/can-gadts-be-used-to-prove-type… 33. http://stackoverflow.com/questions/14349232/applying-denotational-semantics… 34. http://stackoverflow.com/questions/14357918/examples-where-compiler-optimiz… 35. http://stackoverflow.com/questions/14262014/why-is-there-only-one-non-stric… 36. http://stackoverflow.com/questions/14327327/dependency-injection-in-haskell… 37. http://stackoverflow.com/questions/14270500/what-does-a-haskell-comment-sta… 38. http://stackoverflow.com/questions/14263363/is-operational-really-isomorphi… 39. https://plus.google.com/105107667630152149014/about

1 0

ANN: monad-bool 0.1
by John Wiegley 23 Jan '13

23 Jan '13

monad-bool implements a pair of Boolean monoids and monads, to support short-circuiting, value-returning computations similar to what Python and Ruby offer with their native && and || operators. For example, in Python you might see this: x = [1,2,3,0] print x[1] || x[3] -- prints "2" With this library, you can now mirror such code in Haskell: let x = [1,2,3,0] print $ (x !! 1) ||? (x !! 3) -- prints "Success 2" "Booleanness" is based on each type having an instance of the 'Control.Conditional.ToBool' type, for which only the basic types are covered (Bool, Int, Integer, Maybe a, Either a b, [a], Attempt a). If you wish to define a truth value for your own types, simply provide an instance for ToBool: instance ToBool MyType where toBool = ... The And/Or monoids use the Attempt library so that the actual type of the successful results depends on case analysis. It could be a list, a Maybe, an Either, or an exception in the IO Monad. The monad variants, AndM, AndMT, OrM and OrMT provide short-circuiting behavior in a Monad, which returns the last value returned before truth was determined. Here are two examples: Use 'onlyIf' with AndM and AndMT to guard later statements, which are only evaluated if every preceding 'onlyIf' evaluates to True. For example: foo :: AndM Int foo = do onlyIf (True == True) return 100 onlyIf (True == True) return 150 onlyIf (True == False) return 200 When run with `evalAndM foo (-1)` (where (-1) provides a default value), 'foo' returns 150. Use 'endIf' with OrM and OrMT to chain statements, which are only executed if every preceding 'endIf' evaluated to False. For example: bar :: OrM Int bar = do endIf (True == False) return 100 endIf (True == False) return 150 endIf (True == True) return 200 When run with `evalOrM bar (-1)` (where (-1) again provides a default value), 'bar' returns 150. And please, somebody let me know if this has already been done. A search for likely candidates did not turn up anything obvious in Hoogle, but as my knowledge of the whole of Hackage is minimal, I would appreciate any wiser minds that can inform me. Thank you, -- John Wiegley FP Complete Haskell tools, training and consulting http://fpcomplete.com johnw on #haskell/irc.freenode.net

1 0

[ANNOUNCE] JuicyPixels 3.0
by Vincent Berthoux 20 Jan '13

20 Jan '13

Hello haskellers, I'm presenting the third version of JuicyPixels. As the version number indicate, this is a major version with backward compatibility break. The major reason behind this breakage is the introduction of High Dynamic Range images. High Dynamic Range images are used in photography, and in some APIs like OpenGL and DirectX for some fancy effects. Version 3.0 changelog : - Simplification of the 'Pixel' typeclass, removed many unused part. - Removal of some Storable instances for pixel types. - Amelioration of the documentation. - Support for High Dynamic range images. - Support for the Radiance file format (or RGBE, file extension .pic and .hdr). - Dropped the cereal library in favor of the last version of Binary, present in the Haskell platform. Every dependencies are now present in the platform. As usual, this version is available in Hackage and on GitHub : - Hackage : http://hackage.haskell.org/package/JuicyPixels - GitHub : https://github.com/Twinside/Juicy.Pixels Thanks Vincent Berthoux

1 0

Re: [Haskell] [Haskell-cafe] ANNOUNCE: MFlow 0.2
by Alberto G. Corona 18 Jan '13

18 Jan '13

The blog has a dynamic template. and I´m afraid that it needs javascript. Sorry. I will paste the rest of the blog entry: [Continue from the first message] .... Statefulness means that the flow of execution is right in front of the eyes of the programmer, rather that in the spaghetti code of the event-handling model, the goto of the XXI century. it also means that the entire session is in a procedure, so the session data need no trickery. But, like in the stateless case, any page in the flow could have a direct URL.<http://haskell-web.blogspot.com/2013/01/stateful-but-stateless-at-last-than…> [1] Event sourcing in combination with statefulness means automatic logging of all the events and automatic recovery of the execution state of the server procedure and its data, thanks to the Workflow monad transformer<http://hackage.haskell.org/package/Workflow> [2]. So the server procedure can be stopped after timeout and restarted by the application server when the user invokes it. The programmer can determine the timeout and for how long the state is stored. Back button management: the flow of execution can run back<http://haskell-web.blogspot.com.es/2012/03/failback-monad.html> when the back button is pressed [3]. Thanks to a monad transformer. In combination with event sourcing, this means automatic rollback of user session data. So if the user want to undo his last item in the shopping cart, he only has to press the back button. User interface: It is made of self contained pieces called widgets, made around the formlet concept, so they compose gracefully with applicative operators and other extra operators. A MFlow widget is more like the widgets of XWindows, ASP.NET or JavaServer Faces: they have their own HTML formatting, their own behaviours and interact with the server via AJAX, they execute actions when activated and they return statically typed data. They declare their required scripts, CSS links and server procedures in the form of requirements to the requirement service. They include the server and client code in the same piece of text. Being self contained and typed, they can be shared and plugged with a minimum of configuration and instructions. The URL links are also widgets or elements of widgets and return data to the same flow, so no spaguetty event handling occur, unless the programmer need out-of-flow links. This versions <http://haskell-web.blogspot.com.es/2013/01/now-example-of-use-of-active-wid…>includes some active widgets with server-side controls for creating them [4]. Bindings: wai-warp, blaze-html, xhtml, HSP, hack. Persistence and transactions: Global data can be transacted with any kind of persistence framework. MFlow internally uses TCache [5], which provides with persistent STM references (DBRefs). Their serialization can be configured. For rapid prototyping, they have default persistence in files. Just add a Read-Show or a Binary instance for your data and you can have a persistent, transactional DBRef to it. Use them like you use TVars. TCache can index text and register fields. It has a simple query language. Data can be accessed by key or by any indexed field. EXAMPLE: The human mind learn by examples. There is a online demo<http://haskell-web.blogspot.com.es/2013/01/online-example-of-mflow.html> for some of the features that you can play with and you can download the code [6] [0] http://hackage.haskell.org/package/MFlow [1] http://haskell-web.blogspot.com/2013/01/stateful-but-stateless-at-last-than… [2] http://hackage.haskell.org/package/Workflow [3] http://haskell-web.blogspot.com.es/2012/03/failback-monad.html [4] http://haskell-web.blogspot.com.es/2013/01/now-example-of-use-of-active-wid… [5] http://hackage.haskell.org/package/TCache [6] http://81.169.134.95:8081 2013/1/18 Ertugrul Söylemez <es(a)ertes.de> > Heinrich Apfelmus <apfelmus(a)quantentunnel.de> wrote: > > > For some reason, your blog posts are not displayed in my browser > > (Chrome). I block all cookies and I'm using adblock, though. > > Blogger.com blogs often need JavaScript to display anything at all. > > > Greets, > Ertugrul > > -- > Not to be or to be and (not to be or to be and (not to be or to be and > (not to be or to be and ... that is the list monad. > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > > -- Alberto.

1 0