May 2015 - Haskell-Cafe

PSA: How to use the cabal-version field in cabal files
by Adam Bergmark 02 May '15

02 May '15

The cabal-version field seems pretty mysterious. Recommendation: Set it no higher than >= 1.10, Cabal will warn you if it's too low. This field contains the format of the cabal file, the number corresponds to the Cabal release. Hence this version is incremented more often than the format actually changes. There have been no significant changes between 1.10 and 1.20. The Cabal source is surprisingly helpful as a changelog: https://github.com/haskell/cabal/blob/641e854ae663e2b34f34ecc11ba663ac3a9bd… By setting it too high you risk users getting errors like "The package 'foo' requires Cabal library version -any && >=1.14 but no suitable version is installed." This can be problematic for anyone using an older GHC or if there are Cabal releases outside of the GHC release cycle. You may get this error even if you have a newer Cabal if it doesn't ship with GHC. Happy hacking, Adam

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Import hiding module
by amindfv＠gmail.com 01 May '15

01 May '15

It's possible to write e.g. module A (module A.B, x) where To reexport everything from A.B And we can import A hiding (x) Is there a way to also import A hiding (module A.B) ? Thanks

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Swapping type arguments
by Alexey Uimanov 01 May '15

01 May '15

This question probably asked already. I have a type data T m b a = T (m (b, a)) and it should be instance of `Bifunctor` and `MonadTrans` same time. But there is a problem: instance Bifunctor (T m) is ok, but instance MonadTrans (T ... is not, because first argument is `m` but we need `b`. Type can be rewritten like data T b m a = T (m (b, a)) and instance of MonadTrans is ok: instance MonadTrans (T b) but how to define Bifunctor? instance Bifunctor (T ... I did not found how to workaround this. Is there any type magic for such cases?

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Haskell Weekly News
by Kim-Ee Yeoh 01 May '15

01 May '15

*Top Picks:* - Haskell wins a bumper crop of 18 accepted Google Summer of Code proposals <http://www.reddit.com/r/haskell/comments/342rvp/google_summer_of_code_18_pr…>. Mentor offers total 44, another thumpin' sign of life. Kudos to Edward Kmett, Johan Tibell, Shachaf Ben-Kiki, and Gershom Bazerman. Gloria Haskella sine labore nulla. - Reddit Haskell celebrates <http://www.reddit.com/r/haskell/comments/33wnf1/20k_rhaskell_subscribers_ni…> 20k subscribers. It's the 7th largest PL community on reddit <https://www.reddit.com/r/programming/wiki/faq#wiki_what_language_reddits_ar…> after python, javascript, java, php, ruby, c++, in that order. - Matthew Griffith <http://mechanical-elephant.com/thoughts/2015-04-20-becoming-productive-in-h…> migrates away from Python: "I do most of my web prototyping in Haskell now." A journey vividly logged and much loved on Hacker News <https://news.ycombinator.com/item?id=9431944>. And also on Proggit <http://www.reddit.com/r/programming/comments/33oyx9/becoming_productive_in_…> and Reddit Haskell <http://www.reddit.com/r/haskell/comments/33mnlc/becoming_productive_in_hask…> . - A web developer migrates away from Rails to Haskell and explains on HN the 10x advantage <https://news.ycombinator.com/item?id=9419601#up_9420448> he reaps. - Fancy Python in Haskell dress? Check out Dogelang <http://pyos.github.io/dg/>, charmingly defiant: "With Haskell's syntax but none of its type system, dg is the best way to make fans of static typing shut up already." Proggit kibbitzing here <http://www.reddit.com/r/programming/comments/33kleg/dg_its_a_python_no_its_…>, HN there <https://news.ycombinator.com/item?id=9432383>. - Caio Rordrigues copiously illustrates <https://github.com/caiorss/Functional-Programming> Haskell programming. Pretty: a tax bracket tool <https://github.com/caiorss/Functional-Programming#tax-brackets> and a coffee shop Point-of-Sale DSL <https://github.com/caiorss/Functional-Programming#small-dsl-domain-specific…>. It's almost a whole book! - Christian Marie starts the ball rolling on library cheatsheets <https://github.com/anchor/haskell-cheat-sheets/> to guide your way through the jungle of hackage. Moar, moar! <http://www.reddit.com/r/haskell/comments/33sc98/haskell_cheat_sheets_for_co…> - Got a C library you'd love Haskell bindings for? Remember Ian Ross and his new C2HS release <http://haskell.1045720.n5.nabble.com/Haskell-Weekly-News-td5768107.html>? Well, Ian's happy <http://haskell.1045720.n5.nabble.com/Tutorial-Ideas-td5808049.html> to do it for you. Provisos <http://www.skybluetrades.net/blog/posts/2015/04/27/c2hs-tutorial-request.ht…> apply. - Olle Fredriksson announces a combinator-based Earley parsing library <https://github.com/ollef/Earley> which accepts context-free but not context-sensitive (monadic parsing) grammars. Discussion <https://www.reddit.com/r/haskell/comments/33l9cr/ann_earley_parsing_library/> reveals that "one enormously important difference for this library is that it reports all possible parses." - Another Lennart, last name Spitzner, creates another genie that turns type signatures into programs. Unlike Djinn, Exference <http://haskell.1045720.n5.nabble.com/ANN-exference-a-different-djinn-td5807…> makes no promises over termination. "Your wish is my command even at the expense of closure." - Like Agda? You can now enjoy the hole-driven development style in Haskell, brought to you courtesy of Mote by Izaak Meckler <https://github.com/imeckler/mote>. Discussion here <https://www.reddit.com/r/haskell/comments/33v4nm/ann_mote_a_tool_bringing_h…> . <http://tomassetti.me/an-erd-web-server-generation-entity-diagrams-from-a-te…> - Federico Tomassetti <http://tomassetti.me/an-erd-web-server-generation-entity-diagrams-from-a-te…> creates a web-based interface to Andrew Gallant's erd tool <https://github.com/BurntSushi/erd>. Entity-Relationship Diagrams (ERD) come from the database world and help visualize {one,many} to {one,many} relationships. Federico's web app enables him to use erd everywhere without having to install the tool chain multiple times. - Mark Dominus gives a beginner spin <http://blog.plover.com/prog/haskell/monad-search.html> to the chestnut of SEND + MORE = MONEY <https://en.wikipedia.org/wiki/Verbal_arithmetic>. This puzzle site <http://programmingpraxis.com/2012/07/31/send-more-money-part-1/> has comparisons with other languages. - Got a number system? Flip it into a data structure <https://www.fpcomplete.com/user/edwardk/fibonacci/leonardo>. Re-flip it into an efficient search algorithm <https://www.fpcomplete.com/user/edwardk/fibonacci/search>. Edward Kmett shows you how. Respective discussion here <http://www.reddit.com/r/haskell/comments/342s31/edward_kmett_leonardo_rando…> and here <http://www.reddit.com/r/haskell/comments/346b6t/edward_kmett_openended_fibo…> . *In Memoriam* - A key founder of Haskell, Professor Paul Hudak, completed <http://yaledailynews.com/blog/2015/04/30/hudak-spirited-saybrugian-and-cs-p…> his end-of-life plan <http://www.caringbridge.org/visit/hudak/journal/view/id/5538f5cea589b4216c0…> after a five-year encounter with leukemia. He stays <https://news.ycombinator.com/item?id=9431017> in the thoughts <https://news.ycombinator.com/item?id=9465999> of all <http://www.reddit.com/r/haskell/comments/33oe4b/holding_on_and_letting_go/> who cherish <http://www.reddit.com/r/haskell/comments/34exz3/prof_hudak_passed_away_last…> his gifts <http://www.reddit.com/r/programming/comments/34f19q/paul_hudak_creator_of_h…> from the heart. *Quotes of the Week* - A type system flattens the cost of change curve <http://www.agilemodeling.com/essays/costOfChange.htm>. -- Chad Austin <http://chadaustin.me/2015/04/the-long-term-problem-with-dynamically-typed-l…> - The MLs and Haskell remind me of Brian Eno's line about how the first Velvet Underground album only sold 30,000 copies, but "everyone who bought one of those 30,000 copies started a band". -- Source <https://news.ycombinator.com/item?id=9431944#up_9437017> - On the value of Haskell <https://news.ycombinator.com/item?id=9445968#up_9448988>: I find I'm able to accomplish tasks which would otherwise be beyond my skill and intelligence. For example, even though C was the first language I learned, I can't imagine writing a parser in C after discovering the simplicity & readability of monadic parsing in Haskell. - Haskell's level of abstraction is so crazy that they can actually swap out their entire I/O system for another one without changing any application interfaces, this one blew my mind, it's the change that makes GHC 7.8 run the Warp webserver twice as fast. ... All of this without changing a line in Warp, they just transparently made every traditional Haskell use modern I/O principles. Academics man, they're smart ;) -- Source <https://news.ycombinator.com/item?id=9419601#up_9432564> - An old man loved is winter with flowers. -- Edgar Z. Friedenberg *Cool Beans of the Week* - Ravi Chugh and his fine team at U. Chicago just concluded stateside's first ever FRP-based FP course for undergrads using Elm. Check out the student projects <https://www.classes.cs.uchicago.edu/archive/2015/winter/22300-1/Showcase.ht…> for inspiration on FRP architecture. Over in Bonn, Janis Voigtländer also gave such a course <https://groups.google.com/d/msg/elm-discuss/Qjs6sp3lZq0/8aa5bvYcdDYJ> that completed this year. Paul's legacy lives on. p.s. Coming soon: Cabal Hell -- Kim-Ee

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[TFP'15] call for participation
by Peter Achten 01 May '15

01 May '15

----------------------------- L A S T C A L L F O R P A R T I C I P A T I O N ----------------------------- ======== TFP 2015 =========== 16th Symposium on Trends in Functional Programming June 3-5, 2015 Inria Sophia Antipolis, France http://tfp2015.inria.fr/ The symposium on Trends in Functional Programming (TFP) is an international forum for researchers with interests in all aspects of functional programming, taking a broad view of current and future trends in the area. It aspires to be a lively environment for presenting the latest research results, and other contributions (see below). Authors of draft papers will be invited to submit revised papers based on the feedback receive at the symposium. A post-symposium refereeing process will then select a subset of these articles for formal publication. The selected revised papers will be published as a Springer Lecture Notes in Computer Science (www.springer.com/lncs) volume. TFP 2015 will be the main event of a pair of functional programming events. TFP 2015 will be accompanied by the International Workshop on Trends in Functional Programming in Education (TFPIE), which will take place on June 2nd. The TFP symposium is the heir of the successful series of Scottish Functional Programming Workshops. Previous TFP symposia were held in * Edinburgh (Scotland) in 2003; * Munich (Germany) in 2004; * Tallinn (Estonia) in 2005; * Nottingham (UK) in 2006; * New York (USA) in 2007; * Nijmegen (The Netherlands) in 2008; * Komarno (Slovakia) in 2009; * Oklahoma (USA) in 2010; * Madrid (Spain) in 2011; * St. Andrews (UK) in 2012; * Provo (Utah, USA) in 2013; * and in Soesterberg (The Netherlands) in 2014. For further general information about TFP please see the TFP homepage. (http://www.tifp.org/) == INVITED SPEAKERS == TFP is pleased to announce talks by the following two invited speakers: * Laurence Rideau is a researcher at INRIA and is interested in the semantics of programming languages , the formal methods, and the verification tools for programs and mathematical proofs. She participated in the beginnings of the Compcert project (certified compiler), and is part of the Component Mathematical team in the MSR-INRIA joint laboratory, who performed the formalization of the Feit-Thompson theorem successfully. Thirty years ago, computers barged in mathematics with the famous proof of the Four Color Theorem. Initially limited to simple calculation, their role is now expanding to the reasoning whose complexity is beyond the capabilities of most humans, as the proof of the classification of finite simple groups. We present our large collaborative adventure around the formalization of the Feit-Thompson theorem (http://en.wikipedia.org/wiki/Feit%E2%80%93Thompson_theorem) that is a first step to the classification of finite groups and that uses a palette of methods and techniques that range from formal logic to software (and mathematics) engineering. * Anil Madhavapeddy == SCOPE == The symposium recognizes that new trends may arise through various routes. As part of the Symposium's focus on trends we therefore identify the following five article categories. High-quality articles are solicited in any of these categories: Research Articles: leading-edge, previously unpublished research work Position Articles: on what new trends should or should not be Project Articles: descriptions of recently started new projects Evaluation Articles: what lessons can be drawn from a finished project Overview Articles: summarizing work with respect to a trendy subject Articles must be original and not simultaneously submitted for publication to any other forum. They may consider any aspect of functional programming: theoretical, implementation-oriented, or experience-oriented. Applications of functional programming techniques to other languages are also within the scope of the symposium. Topics suitable for the symposium include: Functional programming and multicore/manycore computing Functional programming in the cloud High performance functional computing Extra-functional (behavioural) properties of functional programs Dependently typed functional programming Validation and verification of functional programs Debugging and profiling for functional languages Functional programming in different application areas: security, mobility, telecommunications applications, embedded systems, global computing, grids, etc. Interoperability with imperative programming languages Novel memory management techniques Program analysis and transformation techniques Empirical performance studies Abstract/virtual machines and compilers for functional languages (Embedded) domain specific languages New implementation strategies Any new emerging trend in the functional programming area If you are in doubt on whether your article is within the scope of TFP, please contact the TFP 2015 program chair, Manuel Serrano. == BEST PAPER AWARDS == To reward excellent contributions, TFP awards a prize for the best paper accepted for the formal proceedings. TFP traditionally pays special attention to research students, acknowledging that students are almost by definition part of new subject trends. A student paper is one for which the authors state that the paper is mainly the work of students, the students are listed as first authors, and a student would present the paper. A prize for the best student paper is awarded each year. In both cases, it is the PC of TFP that awards the prize. In case the best paper happens to be a student paper, that paper will then receive both prizes. == SPONSORS == TFP is financially supported by Erlang Solutions. == PROGRAM == Please find the program at: http://tfp2015.inria.fr/program/ The program features two invited talks by Laurence Rideau and Anil Madhavapeddy and one comprehensive Dart tutorial by Florian Loitsch. == IMPORTANT DATES == Registration: May 4, 2015 TFP Symposium: June 3-5, 2015 == PROGRAM COMMITTEE == Janis Voigtländer University of Bonn, DE Scott Owens University of Kent, UK Neil Sculthorpe Swansea University, UK Colin Runciman University of York, UK Manuel Serrano Inria (PC chair), FR Rinus Plasmeijer University of Nijmegen, NL Tomas Petricek University of Cambridge, UK Marco T. Morazan Seton Hall University, USA Wolfgang De Meuter Vrije Universiteit Brussel, BE Michel Mauny Ensta ParisTech, FR Sam Lindley The University of Edinburgh, UK Daan Leijen Microsoft, USA Jurriaan Hage Utrecht University, NL Andy Gill University of Kansas, USA Thomas Gazagnaire University of Cambrige, UK Lars-Ake Fredlund Universidad Politécnica de Madrid, ES Jean-Christophe Filliatre Université Paris Sud Orsay, FR Marc Feeley Université de Montréal, CA Olaf Chitil University of Kent, UK Edwin Brady University of St Andrews, UK

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