November 2012 - Haskell

ANNOUNCE: The Algebra of Algebraic Data Types @ London Haskell user group (28-Nov-12)
by Derek Wright 23 Nov '12

23 Nov '12

The London Haskell user group has a talk next week: The Algebra of Algebraic Data Types Speaker: Chris Taylor Haskell's types are "algebraic data types". But what's so 'algebraic' about algebraic types? This talk explains what types have to do with algebra, starting with counting and type equations (Maybe x = 1 + x) and maybe getting as far as the calculus of types, divided types and what the hell it means to take the exponential of a type. No assumptions on any maths background beyond what you learned at school. Wednesday 28-Nov-2012 6-30pm City University, College Building, St John Street, London. EC1V 4PB http://www.meetup.com/London-HUG/events/88524182/ Link on Reddit: http://redd.it/13nry4 The talk will be followed by a discussion of a potential London Haskell coding project: http://www.meetup.com/London-HUG/events/92459312/ Other news, the video <http://www.youtube.com/watch?v=3q8xYFDYLeI>, code <https://github.com/londonhaskell/londonhaskell-2012-10-24-why-do-monads-mat…> and slides <http://files.londonhaskell.org/2012/10/24/WhyDoMonadsMatter-WithAnimations.…> from the last meeting (Why Do Matter Matter?) have been uploaded. Video = http://www.youtube.com/watch?v=3q8xYFDYLeI Code = https://github.com/londonhaskell/londonhaskell-2012-10-24-why-do-monads-mat… PDF with animations (for on-screen viewing) = http://files.londonhaskell.org/2012/10/24/WhyDoMonadsMatter-WithAnimations.… PDF (with most of the animations removed for printing) = http://files.londonhaskell.org/2012/10/24/WhyDoMonadsMatter.pdf PowerPoint Presentation (with all the animations!) = http://files.londonhaskell.org/2012/10/24/WhyDoMonadsMatter.pptx <http://files.londonhaskell.org/2012/10/24/WhyDoMonadsMatter.pptx>Hope to see you there. Yours, Derek. http://www.meetup.com/London-HUG/ <http://www.meetup.com/London-HUG/>

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CFP: EOOLT 2013
by Henrik Nilsson 23 Nov '12

23 Nov '12

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. Please consider to contribute! Also, if you could forward to colleagues who might be interested, I would be much obliged. 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.

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CFP: EOOLT 2013
by Henrik Nilsson 23 Nov '12

23 Nov '12

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. 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.

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Leaving Microsoft
by Simon Marlow 22 Nov '12

22 Nov '12

Today I'm announcing that I'm leaving Microsoft Research. My plan is to take a break to finish the book on Parallel and Concurrent Haskell for O'Reilly, before taking up a position at Facebook in the UK in March 2013. This is undoubtedly a big change, both for me and for the Haskell community. I'll be stepping back from full-time GHC development and research and heading into industry, hopefully to use Haskell. It's an incredibly exciting opportunity for me, and one that I hope will ultimately be a good thing for Haskell too. What does this mean for GHC? Obviously I'll have much less time to work on GHC, but I do hope to find time to fix a few bugs and keep things working smoothly. Simon Peyton Jones will still be leading the project, and we'll still have support from Ian Lynagh, and of course the community of regular contributors. Things are in a reasonably stable state - there haven't been any major architectural changes in the RTS lately, and while we have just completed the switchover to the new code generator, I've been working over the past few weeks to squeeze out all the bugs I can find, and I'll continue to do that over the coming months up to the 7.8.1 release. In due course I hope that GHC can attract more of you talented hackers to climb the learning curve and start working on the internals, in particular the runtime and code generators, and I'll do my best to help that happen. Cheers, Simon

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Haskell Weekly News: Issue 251
by Daniel Santa Cruz 22 Nov '12

22 Nov '12

Welcome to issue 251 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers the week of November 4 to 17, 2012. Quotes of the Week * Ralith: [why some people don't use conduits/pipes] also, I think at least some people are waiting for edwardk to write his version. * edwardk: f -| g means that f a -> b is isomorphic to a -> g b (for arrows in the appropriate categories) * edwardk: @type (^.) lambdabot: s -> Getting a s t a b -> a byorgey: I would not like to be getting a stab, thank you * edwardk: I mean we're so oop even our member accessors have diagrams explaining their member accessors. * shapr: hylo! That's the category theorist greeting. * shachaf: type AbstractAlgebra a = Abstract a -> a * nicoo: Yet many Writers concern themselves with issues of State, imaginary or real * rwbarton: when you learn C, watch out for the keyword "return", it doesn't do what you'd expect * Oleg: We show how to program with the law of excluded middle. We specifically avoid call/cc, which is overrated. Top Reddit Stories * Haskell Platform 2012.4.0.0 is out Domain: self.haskell, Score: 89, Comments: 21 On Reddit: [1] http://goo.gl/BPno4 Original: [2] http://goo.gl/BPno4 * A Khan Academy style tutorial on generalized algebraic data types Domain: apfelmus.nfshost.com, Score: 56, Comments: 7 On Reddit: [3] http://goo.gl/kXQ0a Original: [4] http://goo.gl/NWn3B * Cartesian Closed Comic #17: Typing Domain: ro-che.info, Score: 53, Comments: 24 On Reddit: [5] http://goo.gl/6c4Uy Original: [6] http://goo.gl/dZeDx * Cartesian Closed Comic #18: Equality Domain: ro-che.info, Score: 53, Comments: 8 On Reddit: [7] http://goo.gl/8Qf9d Original: [8] http://goo.gl/XCyuB * Natural Language Processing for the Working Programmer (in Haskell!) Domain: nlpwp.org, Score: 50, Comments: 17 On Reddit: [9] http://goo.gl/3yLTZ Original: [10] http://goo.gl/BleWX * Waiting for garbage collection can kill parallelism? Domain: ics.p.lodz.pl, Score: 50, Comments: 7 On Reddit: [11] http://goo.gl/iUPlD Original: [12] http://goo.gl/N0kiV * foldr is made of monoids Domain: byorgey.wordpress.com, Score: 47, Comments: 12 On Reddit: [13] http://goo.gl/Y0mz5 Original: [14] http://goo.gl/IxKov * Solving Cabal Hell: vetted packages, multiple hackages Domain: yesodweb.com, Score: 46, Comments: 67 On Reddit: [15] http://goo.gl/dkzMz Original: [16] http://goo.gl/lDjuj * Parallel falling sand game with Repa Domain: github.com, Score: 45, Comments: 16 On Reddit: [17] http://goo.gl/G6MGG Original: [18] http://goo.gl/cP1zH * Agda, Epigram or Idris. Which one to learn Domain: self.haskell, Score: 38, Comments: 61 On Reddit: [19] http://goo.gl/3PGVo Original: [20] http://goo.gl/3PGVo * Fun with Fay - A ring oscillator Domain: skybluetrades.net, Score: 38, Comments: 6 On Reddit: [21] http://goo.gl/mGvcZ Original: [22] http://goo.gl/bJxCI * Introduction to Category Theory 1: Course Overview Domain: youtube.com, Score: 37, Comments: 6 On Reddit: [23] http://goo.gl/fbfYR Original: [24] http://goo.gl/Nx5SH * HALO: Haskell to Logic through Denotational Semantics [PDF] Domain: research.microsoft.com, Score: 35, Comments: 6 On Reddit: [25] http://goo.gl/V0RWs Original: [26] http://goo.gl/oCzUw * How to write Python in Haskell: State and Either Domain: stackoverflow.com, Score: 34, Comments: 25 On Reddit: [27] http://goo.gl/Z80yb Original: [28] http://goo.gl/W933i * What is foldr made of? Domain: web.jaguarpaw.co.uk, Score: 30, Comments: 22 On Reddit: [29] http://goo.gl/LdS9X Original: [30] http://goo.gl/I2uzX * How to shoot yourself in the foot with Haskell Domain: ics.p.lodz.pl, Score: 29, Comments: 34 On Reddit: [31] http://goo.gl/CcvZB Original: [32] http://goo.gl/SJYvd * Happstack, Fay, & Acid-State: Shared Datatypes are Awesome Domain: happstack.com, Score: 29, Comments: 8 On Reddit: [33] http://goo.gl/AUtj6 Original: [34] http://goo.gl/cYQr1 * ANN: OpenGL packages update Domain: haskell.org, Score: 28, Comments: 7 On Reddit: [35] http://goo.gl/0SN7O Original: [36] http://goo.gl/PbtlT * How can I cleanly/consistently work with 3 different Exception-raising schemes? Domain: self.haskell, Score: 28, Comments: 22 On Reddit: [37] http://goo.gl/Xf4sq Original: [38] http://goo.gl/Xf4sq Top StackOverflow Questions * What are paramorphisms? votes: 39, answers: 1 Read on SO: [39] http://goo.gl/V6rXq * In pure functional languages, is there an algorithm to get the inverse function? votes: 35, answers: 9 Read on SO: [40] http://goo.gl/wBtqv * What are free monads? votes: 26, answers: 5 Read on SO: [41] http://goo.gl/NAx8n * What's the status of current Functional Reactive Programming implementations? votes: 23, answers: 3 Read on SO: [42] http://goo.gl/FmRYF * What does the “world” mean in functional programming world? votes: 22, answers: 7 Read on SO: [43] http://goo.gl/dyM8c * Type-safe difference lists votes: 20, answers: 1 Read on SO: [44] http://goo.gl/TlvF4 * Is it possible to annotate a function's special properties (e.g. surjectivity)? votes: 12, answers: 3 Read on SO: [45] http://goo.gl/uzanF * Under what circumstances are monadic computations tail-recursive? votes: 12, answers: 2 Read on SO: [46] http://goo.gl/lPJef * Should I use new Haskell language extensions in favour of the old ones? votes: 12, answers: 2 Read on SO: [47] http://goo.gl/xkc78 Until next time, Daniel Santa Cruz References 1. http://www.reddit.com/r/haskell/comments/12pxiq/haskell_platform_2012400_is… 2. http://www.reddit.com/r/haskell/comments/12pxiq/haskell_platform_2012400_is… 3. http://apfelmus.nfshost.com/blog/2010/06/01-gadts-video.html 4. http://www.reddit.com/r/haskell/comments/12ou1p/a_khan_academy_style_tutori… 5. http://ro-che.info/ccc/17.html 6. http://www.reddit.com/r/haskell/comments/12nm3w/cartesian_closed_comic_17_t… 7. http://ro-che.info/ccc/18.html 8. http://www.reddit.com/r/haskell/comments/138crz/cartesian_closed_comic_18_e… 9. http://nlpwp.org/book/ 10. http://www.reddit.com/r/haskell/comments/13a0ut/natural_language_processing… 11. http://ics.p.lodz.pl/~stolarek/blog/2012/11/waiting-for-garbage-collection-… 12. http://www.reddit.com/r/haskell/comments/13cpm3/waiting_for_garbage_collect… 13. http://byorgey.wordpress.com/2012/11/05/foldr-is-made-of-monoids/ 14. http://www.reddit.com/r/haskell/comments/12prpr/foldr_is_made_of_monoids/ 15. http://www.yesodweb.com/blog/2012/11/solving-cabal-hell 16. http://www.reddit.com/r/haskell/comments/1306wn/solving_cabal_hell_vetted_p… 17. https://github.com/tranma/falling-turnip 18. http://www.reddit.com/r/haskell/comments/133nja/parallel_falling_sand_game_… 19. http://www.reddit.com/r/haskell/comments/132kg0/agda_epigram_or_idris_which… 20. http://www.reddit.com/r/haskell/comments/132kg0/agda_epigram_or_idris_which… 21. http://www.skybluetrades.net/blog/posts/2012/11/13/fay-ring-oscillator/inde… 22. http://www.reddit.com/r/haskell/comments/134tr6/fun_with_fay_a_ring_oscilla… 23. http://www.youtube.com/watch?v=eu0rj5C2Otg 24. http://www.reddit.com/r/haskell/comments/12vvn2/introduction_to_category_th… 25. http://research.microsoft.com/en-us/people/dimitris/hcc-popl.pdf 26. http://www.reddit.com/r/haskell/comments/12wovt/halo_haskell_to_logic_throu… 27. http://stackoverflow.com/a/13432926/208257 28. http://www.reddit.com/r/haskell/comments/13cz6b/how_to_write_python_in_hask… 29. http://web.jaguarpaw.co.uk/~tom/blog/posts/2012-11-04-what-is-foldr-made-of… 30. http://www.reddit.com/r/haskell/comments/12mnhu/what_is_foldr_made_of/ 31. http://ics.p.lodz.pl/~stolarek/blog/2012/11/how-to-shoot-yourself-in-the-fo… 32. http://www.reddit.com/r/haskell/comments/12rlgt/how_to_shoot_yourself_in_th… 33. http://www.happstack.com/c/view-page-slug/15/happstack-fay-acid-state-share… 34. http://www.reddit.com/r/haskell/comments/1375q0/happstack_fay_acidstate_sha… 35. http://www.haskell.org/pipermail/haskell-cafe/2012-November/104329.html 36. http://www.reddit.com/r/haskell/comments/12mk7h/ann_opengl_packages_update/ 37. http://www.reddit.com/r/haskell/comments/12relk/how_can_i_cleanlyconsistent… 38. http://www.reddit.com/r/haskell/comments/12relk/how_can_i_cleanlyconsistent… 39. http://stackoverflow.com/questions/13317242/what-are-paramorphisms 40. http://stackoverflow.com/questions/13404208/in-pure-functional-languages-is… 41. http://stackoverflow.com/questions/13352205/what-are-free-monads 42. http://stackoverflow.com/questions/13341937/whats-the-status-of-current-fun… 43. http://stackoverflow.com/questions/13340458/what-does-the-world-mean-in-fun… 44. http://stackoverflow.com/questions/13346200/type-safe-difference-lists 45. http://stackoverflow.com/questions/13281316/is-it-possible-to-annotate-a-fu… 46. http://stackoverflow.com/questions/13379060/under-what-circumstances-are-mo… 47. http://stackoverflow.com/questions/13422610/should-i-use-new-haskell-langua…

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[ANN] gtk2hs-0.12.4
by wagnerdm＠seas.upenn.edu 21 Nov '12

21 Nov '12

Today, we welcome into the world version 0.12.4 of Gtk2Hs[1], a set of Haskell bindings to many of the libraries included in the Gtk+/Gnome platform. Gtk+ is an extensive and mature multi-platform toolkit for creating graphical user interfaces. GUIs written using Gtk2Hs use themes to resemble the native look on Windows. Gtk is the toolkit used by Gnome, one of the two major GUI toolkits on Linux. On Mac OS programs written using Gtk2Hs are run by Apple's X11 server but may also be linked against a native Aqua implementation of Gtk. This release is primarily a GHC-7.6 compatibility release, thanks in large part to John Lato. In addition to releases of the core packages, this release includes point updates to gconf and gstreamer. The release has been tested on Linux and Windows with a variety of combinations of Gtk+ and GHC versions. Installation ------------ Assuming you have the necessary Gtk+ base libraries already installed, you can get the basic set of Haskell bindings with these two commands: cabal install gtk2hs-buildtools cabal install gtk Other available packages include gconf, glade, gnomevfs, gstreamer, gtkglext, gtksourceview2, soegtk, svgcairo, vte, and webkit. There are longer-winded instructions that include pointers on getting the Gtk+ base libraries installed on the website [2]. Features -------- * Automatic memory management (unlike some other C/C++ GUI libraries, Gtk+ provides proper support for garbage-collected languages) * Unicode support * High quality vector graphics using Cairo * Extensive reference documentation * An implementation of the ``Haskell School of Expression'' graphics API Community --------- You can keep up with the latest developments on the mailing lists: * gtk2hs-users [3]: discussions about writing code that uses Gtk2Hs * gtk2hs-devel [4]: discussions about modifying the Gtk2Hs bindings * gtk2hs-commit [5]: a read-only mailing list with announcements of every patch to hit the darcs repository Check out the latest code via darcs: darcs get http://code.haskell.org/gtk2hs/ Or complain on the bug tracker [6]. This code was brought to you by: Duncan Coutts Axel Simon Andy Stewart Peter Gavin Jens Petersen John Obbele Hans van Thiel Daniel Wagner Bertram Felgenhauer John Lato ...and many, many more [1] http://projects.haskell.org/gtk2hs/ [2] http://code.haskell.org/gtk2hs/INSTALL [3] https://lists.sourceforge.net/lists/listinfo/gtk2hs-users [4] https://lists.sourceforge.net/lists/listinfo/gtk2hs-devel [5] https://lists.sourceforge.net/lists/listinfo/gtk2hs-commit [6] http://hackage.haskell.org/trac/gtk2hs/

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Tech Mesh alternative programming - London
by Andra Dinu 20 Nov '12

20 Nov '12

Check out the Tech Mesh alternative programming event- London 4th - 6th December: Topics include: · Haskell: practical as well as cool - Co-inventors of Haskell Simon Peyton Jones, Philip Wadler and John Hughes will do a joint keynote about three distinctive aspects of Haskell that might make it worth the bother. · 183 Years of Programming - Co-inventors of Erlang Joe Armstrong, Robert Virding and Mike Williams will be sharing their experience in a joint keynote · The Database as a Value: Rethinking fundamentals of database architecture, in light of the principles of functional programming - Rich Hickey is the author of the Clojure programming language and designer of the Datomic database system · Implementing Riak in Erlang Benefits and Challenges - The choice of using Erlang has resulted in both benefits and challenges to the Basho team and Riak community. Basho Technologies architect Steve Vinoski will tell you all about the process Over 50 speakers will be giving talks on Haskell, Erlang, OTP, Scala, Akka, Raspberry Pi, F#, Go, OCaml and much more. We also have tutorials on Erlang, Scala , Akka and OTP. See the full schedule here: http://techmeshconf.com/techmesh-london-2012/schedule/index.jsp You can get a ticket for Tech Mesh at a 20% discount. All you need to do is register through our website and enter the promotion code TECHMESH_FRIEND. Register here: https://secure.trifork.com/techmesh-london-2012/registration/registration.j… -- Andra Dinu Marketing executive ERLANG SOLUTIONS LTD New Loom House 101 Back Church Lane London, E1 1LU United Kingdom Tel +44(0)2076550344 Mob +44(0)7983484387 www.erlang-solutions.com

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ANNOUNCE: Haskell Communities and Activities Report (23rd ed., November 2012)
by Janis Voigtländer 17 Nov '12

17 Nov '12

On behalf of all the contributors, I am pleased to announce that the Haskell Communities and Activities Report (23rd edition, November 2012) is now available in PDF and HTML formats: http://haskell.org/communities/11-2012/report.pdf http://haskell.org/communities/11-2012/html/report.html Many thanks go to all the people that contributed to this report, both directly, by sending in descriptions, and indirectly, by doing all the interesting things that are reported. I hope you will find it as interesting a read as I did. If you have not encountered the Haskell Communities and Activities Reports before, you may like to know that the first of these reports was published in November 2001. Their goal is to improve the communication between the increasingly diverse groups, projects, and individuals working on, with, or inspired by Haskell. The idea behind these reports is simple: Every six months, a call goes out to all of you enjoying Haskell to contribute brief summaries of your own area of work. Many of you respond (eagerly, unprompted, and sometimes in time for the actual deadline) to the call. The editor collects all the contributions into a single report and feeds that back to the community. When I try for the next update, six months from now, you might want to report on your own work, project, research area or group as well. So, please put the following into your diaries now: ======================================== End of April 2013: target deadline for contributions to the May 2013 edition of the HC&A Report ======================================== Unfortunately, many Haskellers working on interesting projects are so busy with their work that they seem to have lost the time to follow the Haskell related mailing lists and newsgroups, and have trouble even finding time to report on their work. If you are a member, user or friend of a project so burdened, please find someone willing to make time to report and ask them to "register" with the editor for a simple e-mail reminder in April (you could point me to them as well, and I can then politely ask if they want to contribute, but it might work better if you do the initial asking). Of course, they will still have to find the ten to fifteen minutes to draw up their report, but maybe we can increase our coverage of all that is going on in the community. Feel free to circulate this announcement further in order to reach people who might otherwise not see it. Enjoy! Janis Voigtlaender <hcar at haskell.org>

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ANN: hledger-web 0.19
by Simon Michael 17 Nov '12

17 Nov '12

I'm pleased to announce hledger-web 0.19, compatible with the latest hledger and Yesod. Release notes: * web: builds with yesod 1.1.3 * web: obeys command-line query options at startup again * the autogenerated session file is now a dot file (.hledger-web_client_session.aes) hledger is a command-line tool and haskell library for tracking financial transactions, which are stored in a human-readable plain text format. In addition to reporting, it can also help you record new transactions, or convert CSV data from your bank. Add-on packages include hledger-web, a web interface. hledger is inspired by and compatible with John Wiegley's Ledger. For more, see http://hledger.org . Install it: cabal update; cabal install hledger-web For more installation help, see http://hledger.org/MANUAL.html#installing . Or, sponsor a ready-to-run binary for your platform: http://hledger.org/DOWNLOAD.html .

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Announce: Agda 2.3.2
by Andreas Abel 13 Nov '12

13 Nov '12

I am pleased to announce the source release of Agda 2.3.2! http://wiki.portal.chalmers.se/agda/pmwiki.php?n=Main.Download If you have a recent Haskell Platform installed, you can get it with cabal update cabal install Agda agda-mode setup agda-mode compile (The last step is optional.) Highlights from the release-notes: http://wiki.portal.chalmers.se/agda/uploads/Main.Download/release-notes-2-3… * A new backend that produces highlighted LaTeX from a literate agda file. * Improved Emacs interaction mode: - No longer depends on GHCi. - Syntax highlighting is updated while buffer is type-checked. - You can case split on several variables simultaneously. * Syntax extensions: - Pattern synonyms. - Qualified mixfix operators. - Sections and instantiated module imports. * Enhancements of the type checker: - Improved coverage checking. - Improved constraint solving and instance search. Enjoy, Andreas (for the Agda team) -- Andreas Abel <>< Du bist der geliebte Mensch. Theoretical Computer Science, University of Munich Oettingenstr. 67, D-80538 Munich, GERMANY andreas.abel(a)ifi.lmu.de http://www2.tcs.ifi.lmu.de/~abel/

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