May 2014 - Haskell-Cafe

Re: [Haskell-cafe] ANN: hsqml-0.3.0.0 supports Qt 5
by Robin KAY 10 May '14

10 May '14

Dear Andrew, On 09/05/14 16:42, Andrew Voron wrote: [snip] > I've tryed to compile sample project on windows - it compiles good, but > outputs: > Segmentation fault/access violation in generated code > when I'm trying to start executables. As described in the installation section on my web-site [1], this problem is most likely caused by an incompatibility between the MinGW tool-chains shipped with the Haskell Platform and with the Qt binaries. In fact, writing that in the docs was probably too coy, as the latest Haskell Platform and the latest official Qt SDK for Windows will not work together. In the past, this was not the case but the respective copies of MinGW/gcc must now be too far out of step with each other. A relatively simple fix I have found to work is to modify the GHC settings file to point to the version of gcc.exe inside the Qt SDK distribution rather than GHC's. Otherwise, you could build your own Qt binaries using GHC's MinGW but that is rather more involved. [1] http://www.gekkou.co.uk/software/hsqml/#installation Regards, -- Robin KAY

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Haddock issue tracker is now on GitHub.
by Mateusz Kowalczyk 10 May '14

10 May '14

Greetings, The Haddock issue tracker now lives at [1]. The reasoning is that a lot of people have a GitHub account already and signing up just for Trac is tedious. Hopefully this will also allow people to see more easily what's going on. This also removes the maintenance load from Haskell infrastructure: the Trac instance has been bitrotting quite a bit and recently even sending out e-mail about tickets stopped working. Old issues have been migrated over so the ticket numbers still correspond. Please file any new issues or make issue comments on GitHub. If you do not wish to use GitHub (which is fairly understandable) then please send me the report directly and I will create one for you. Thanks. [1]: https://github.com/haskell/haddock/issues?state=open -- Mateusz K.

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Templates as typeclasses?
by Mike Meyer 09 May '14

09 May '14

In going over yet again the many failings of template frameworks for building web apps, I recalled some of the features of the best of the lot, and wondered if those features might be useful in a Haskell template framework. Python's Cheetah tool makes templates almost fully functional members of Python's OO system. A template can inherit from a Python class or another template, and a Python class can inherit from a template. Which makes me wonder if something similar might not be useful in a Haskell template framework. Possibly have each template create an appropriate datatype and make it as an instance of the Template typeclass (and possibly others). Is there already a Haskell web framework that does something like this? Would it actually add value to a framework? Thanks, Mike

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[TFPIE2014] final call for participation
by Peter Achten 09 May '14

09 May '14

[FINAL CALL FOR PARTICIPATION] 3rd International Workshop on Trends in Functional Programming in Education (TFPIE 2014) May 25, 2014 Utrecht University Soesterberg, The Netherlands (http://www.cs.uwyo.edu/~jlc/tfpie14/) The 3rd International Workshop on Trends in Functional Programming in Education, TFPIE 2014, will be co-located with the Symposium on Trends in Functional Programming (TFP 2014) at Soesterberg, at the “Kontakt der Kontinenten” hotel in the Netherlands on Sunday, May 25th. TFP will follow from May 26-28. The goal of TFPIE is to gather researchers, teachers and professionals that use, or are interested in the use of, functional programming in education. TFPIE aims to be a venue where novel ideas, classroom-tested ideas and work-in-progress on the use of functional programming in education are discussed. The one-day workshop will foster a spirit of open discussion by having a review process for publication after the workshop. The program chair of TFPIE 2014 will screen submissions to ensure that all presentations are within scope and are of interest to participants. Potential presenters are invited to submit an extended abstract (4-6 pages) or a draft paper (up to 16 pages) in EPTCS style. The authors of accepted presentations will have their preprints and their slides made available on the workshop's website/wiki. Visitors to the TFPIE 2014 website/wiki will be able to add comments. This includes presenters who may respond to comments and questions as well as provide pointers to improvements and follow-up work. After the workshop, presenters will be invited to submit (a revised version of) their article for review. The PC will select the best articles for publication in the journal Electronic Proceedings in Theoretical Computer Science (EPTCS). Articles not selected for presentation and extended abstracts will not be formally reviewed by the PC. TFPIE workshops have previously been held in St Andrews, Scotland (2012) and in Provo Utah, USA (2013). ** Invited Speaker ** TFPIE is pleased to announce that professor Johan Jeuring of Utrecht University and Open University, both in The Netherlands is giving an invited talk entitled: "Automatic tutoring and assessing functional programs". ** Program Committee ** James Caldwell, (Program Chair) University of Wyoming Peter Achten, Radboud University, Nijmgen Edwin Brady, University of St Andrews, St Andrews Jurriaan Hage, Universiteit Utrecht Philip Holzenspies, University of Twente Daniel R. Licata, Wesleyan University Marco T Morazan, Seton Hall University Christian Skalka, University of Vermont David Van Horn, Northeastern University ** Program ** The preliminary program of TFPIE 2014 is available at the home site of TFPIE 2014 and the TFPIE wiki (http://wiki.science.ru.nl/tfpie/Main_Page) This year's edition features 14 talks. The program is closed with a plenary discussion. ** Important Dates ** * 1 February 2014: TFPIE submissions open on easychair. * 14 April 2014: Early registration for TFP closes * 21 April 2014: Submission deadline for draft TFPIE papers and abstracts * 27 April 2014: Notification of acceptance for presentation * 15 May 2014: Registration for TFPIE closes - as does late registration for TFP * 25 May 2014: Presentations in Soesterberg, Netherlands * 29 June 2014: Full papers for EPTCS proceedings due * 16 August 2014: Notification of acceptance for proceedings * 8 September 2014: Camera ready copy due for EPTCS Submission of an abstract implies no obligation to submit a full paper; abstracts with no corresponding full versions by the full paper deadline will be considered as withdrawn. At least one author from each accepted presentation must attend the workshop.

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Templates as typeclasses?
by oleg＠okmij.org 09 May '14

09 May '14

Tobias Dammers wrote: > You can do similar things with Haskell EDSL-style template systems such > as Blaze... > > Still, the big picture with these is that template building blocks are > language elements, and template code and regular code can be mixed > freely. The `h1` function from Blaze is just another Haskell function; > it takes a MarkdownM () value and returns a MarkdownM (), and because > MarkdownM happens to be a Monad, you can use do notation to sequence > HTML elements. MarkdownM () is also an instance of IsString, so if you > enable -XOverloadedStrings, you can use string literals to produce HTML > text nodes. This means that you can write, in plain Haskell: > > h1 $ do > span "Hello, " > span "world!" > > ...and it'll produce <h1><span>Hello, </span><span>world!</span></h1>. In this regard it is worth mentioning HSXML http://okmij.org/ftp/Scheme/xml.html#typed-SXML The document in HSXML is a monoid rather than a monad. It is hard to find a good reason for the document be a monad except for using a do notation, which is not needed in HSXML. The above "Hello, World!" example looks in HSXML as h1 (span "Hello") (span "world!") (Note that we don't need the space after `Hello'.) This produces the desired output (in plain text, HTML or XML). If we don't need span, we can just write h1 "Hello" "world!" The main difference from Blaze shows up if we attempt h1 (p "Hello") "world!" It will be a type error. The error message says No instance for (Build (DC CT_inline d0) (DC CT_block d0) t) arising from a use of `h1' No instance for (Build (DC CT_inline d0) (DC CT_block d0) (DC CT_inline d0)) arising from a use of `p' That is, (p "Hello") produces block-level content and h1 requires its children to be inline-level. HSXML thus implements the block/inline content model of HTML. Arbitrary many content content-level tags may be defined (in fact, HSXML, besides block/inline elements uses document-, attribute-, and table-level elements). It is possible for the same element to be usable in different contexts (e.g., 'title' can be either an attribute or an element used within 'head'). It is rendered differently in different contexts. Although the document itself is just a monoid rather than a monad, rendering a document can be in a monad. For instance, one of the rendering engines works in an IO monad so it can validate local links as the document is rendered. The resulting document does not have dead local links. > For the common case where you have a "master" template and an > incarnation, you could write a master template that takes its inner > blocks as arguments, e.g.: It is very easy to do that in HSXML. Here is an example, the top template for the ChangeLog: toHTML :: MDoc d => CLHead d -> DC CT_root d toHTML (CLHead attrs updates) = document (head (title (cdata (ha_title attrs))) (meta_tag (description (cdata (ha_description attrs)))) author_address (meta_tag (pub_date (ha_DateRevision attrs))) (head_link LR_top (href (ha_top attrs)) (title "All you can find here")) ) (body (h1 "Log of changes on" (aref (ha_top attrs) "this site")) (p nbsp) updates (change_log_prev (ha_history_first attrs)) (change_log_prev (ha_history_last attrs)) ) (One could omit many parentheses using $, but I like parentheses in this context).

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Unicode Haskell source -- Yippie!
by Rustom Mody 09 May '14

09 May '14

I'm mighty pleased to note that the following is valid Haskell code! Do others find this useful/appealing? Any possibilities on making the commented out parts work? [Pragmatics about typing this at the same speed and facility as we do with Ascii is a separate and (IMHO) solvable problem though its not the case at the moment] -------------------- import qualified Data.Set as Set -- Experimenting with Unicode in Haskell source -- Numbers x ≠ y = x /= y x ≤ y = x <= y x ≥ y = x >= y x ÷ y = divMod x y x ⇑ y = x ^ y x × y = x * y -- readability hmmm !!! π = pi -- ⌊ x = floor x -- ⌈ x = ceiling x -- Lists xs ⤚ ys = xs ++ ys -- Bools x ∧ y = x && y x ∨ y = y || y -- ¬x = not x -- Sets x ∈ s = x `Set.member` s -- or keep ∈ for list elem? s ∪ t = s `Set.union` t s ∩ t = s `Set.intersection` t s ⊆ t = s `Set.isSubsetOf` t s ⊂ t = s `Set.isProperSubsetOf` t s ⊈ t = not (s `Set.isSubsetOf` t) -- ∅ = Set.null

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Announcement: First Dutch FinTech Hackaton
by Han Joosten 09 May '14

09 May '14

Hi all, Always wanted to show the industry what Functional Programming can do? Have a look at http://dutchfintechhackathon.nl/ for this is a great opportunity to do so! please spread the word, I think it would be very cool if a FP-team would participate. Cheers! Han Joosten

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ML Family Workshop -- Last call for presentations
by oleg＠okmij.org 09 May '14

09 May '14

Important dates Monday May 19 (any time zone): Abstract submission Monday June 30: Author notification Thursday September 4, 2014: ML Family Workshop Higher-order, Typed, Inferred, Strict: ACM SIGPLAN ML Family Workshop Thursday September 4, 2014, Gothenburg, Sweden (immediately following ICFP and preceding OCaml Users and Developers Workshop) Call For Papers http://okmij.org/ftp/ML/ML14.html ML is a very large family of programming languages that includes Standard ML, OCaml, F#, SML#, Manticore, MetaOCaml, JoCaml, Alice ML, Dependent ML, Flow Caml, and many others. All ML languages, beside the great deal of syntax, share several fundamental traits. They are all higher-order, strict, mostly pure, and typed, with algebraic and other data types. Their type systems inherit from Hindley-Milner. The development of these languages has inspired a significant amount of computer science research and influenced a number of programming languages, including Haskell, Scala and Clojure, as well as Rust, ATS and many others. ML workshops have been held in affiliation with ICFP continuously since 2005. This workshop specifically aims to recognize the entire extended ML family and to provide the forum to present and discuss common issues, both practical (compilation techniques, implementations of concurrency and parallelism, programming for the Web) and theoretical (fancy types, module systems, metaprogramming). The scope of the workshop includes all aspects of the design, semantics, theory, application, implementation, and teaching of the members of the ML family. We also encourage presentations from related languages (such as Scala, Rust, Nemerle, ATS, etc.), to exchange experience of further developing ML ideas. The ML family workshop will be held in close coordination with the OCaml Users and Developers Workshop. Format Since 2010, the ML workshop has adopted an informal model. Presentations are selected from submitted abstracts. There are no published proceedings, so any contributions may be submitted for publication elsewhere. We hope that this format encourages the presentation of exciting (if unpolished) research and deliver a lively workshop atmosphere. Each presentation should take 20-25 minutes, except demos, which should take 10-15 minutes. The exact time will be decided based on the number of accepted submissions. The presentations will likely be recorded. Post-conference proceedings The post-proceedings of selected papers from the ML Family and the OCaml Users and Developers workshops will be published in the Electronic Proceedings in Theoretical Computer Science (EPTCS). The Program Committee shall invite interested authors of selected presentations to expand their abstract for inclusion in the proceedings. The submissions are to be reviewed according to the EPTCS standards. Coordination with the OCaml Users and Developers Workshop The OCaml workshop is seen as more practical and is dedicated in significant part to the OCaml community building and the evolution of the OCaml system. In contrast, the ML family workshop is not focused on any language in particular, is more research oriented, and deals with general issues of the ML-style programming and type systems. Yet there is an overlap, which we are keen to explore in various ways. The authors who feel their submission fits both workshops are encouraged to mention it at submission time or contact the Program Chairs. Scope We acknowledge the whole breadth of the ML family and aim to include languages that are closely related (although not by blood), such as Rust, ATS, Scala, Typed Clojure. Those languages have implemented and investigated run-time and type system choices that may be worth considering for OCaml, F# and other ML languages. We also hope that the exposure to the state of the art ML might favorably influence those related languages. Specifically, we seek research presentations on topics including but not limited to * Design: concurrency, distribution and mobility, programming for the web and embedded systems, handling semi-structured data, facilitating interactive programming, higher forms of polymorphism, generic programming, objects * Implementation: compilation techniques, interpreters, type checkers, partial evaluators, runtime systems, garbage collectors, etc. * Type systems: fancy types, inference, effects, overloading, modules, contracts, specifications and assertions, dynamic typing, error reporting, etc. * Applications: case studies, experience reports, pearls, etc. * Environments: libraries, tools, editors, debuggers, cross-language interoperability, functional data structures, etc. * Education: ML and ML-like languages in college or high-school, in general or computer science curriculum. Four kinds of submissions will be accepted: Informed Positions, Research Presentations, Experience Reports and Demos. * Informed Positions: A justified argument for or against a language feature. The argument must be substantiated, either theoretically (e.g., by a demonstration of (un)soundness, an inference algorithm, a complexity analysis), empirically or by a substantial experience. Personal experience is accepted as justification so long as it is extensive and illustrated with concrete examples. * Research Presentations: Research presentations should describe new ideas, experimental results, or significant advances in ML-related projects. We especially encourage presentations that describe work in progress, that outline a future research agenda, or that encourage lively discussion. These presentations should be structured in a way which can be, at least in part, of interest to (advanced) users. * Experience Reports: Users are invited to submit Experience Reports about their use of ML and related languages. These presentations do not need to contain original research but they should tell an interesting story to researchers or other advanced users, such as an innovative or unexpected use of advanced features or a description of the challenges they are facing or attempting to solve. * Demos: Live demonstrations or short tutorials should show new developments, interesting prototypes, or work in progress, in the form of tools, libraries, or applications built on or related to ML. (You will need to provide all the hardware and software required for your demo; the workshop organizers are only able to provide a projector.) Submission Submissions should be at most two pages, in PDF format, and printable on US Letter or A4 sized paper. A submission should have a synopsis (2-3 lines) and a body between 1 and 2 pages, in one- or two-column layout. The synopsis should be suitable for inclusion in the workshop program. Submissions must be uploaded to the workshop submission website before the submission deadline (Monday May 19, 2014). For any question concerning the scope of the workshop or the submission process, please contact the program chair. Program Committee Kenichi Asai Ochanomizu University, Japan Matthew Fluet Rochester Institute of Technology, USA Jacques Garrigue Nagoya University, Japan Dave Herman Mozilla, USA Stefan Holdermans Vector Fabrics, Netherlands Oleg Kiselyov (Chair) Monterey, CA, USA Keiko Nakata Tallinn University of Technology, Estonia Didier Remy INRIA Paris-Rocquencourt, France Zhong Shao Yale University, USA Hongwei Xi Boston University, USA

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reactive-banana GLFW-b event register example
by Vlad Lopatin 08 May '14

08 May '14

Hello List, I am trying to make the following quasi-code example work: registerMouseButton :: IO (Event MouseButton) registerMouseButton = do(addHandler, fire) <- newAddHandler setMouseButtonCallback $ \button _ -> fire button fromAddHandler addHandler According to http://stackoverflow.com/questions/8631816/reactive-banana-how-to-create-an… looks like it should be something straightforward. Can somebody show an example of a functional code that registers a key or a mouse event? Thanks, Vladimir

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Need pointer to explain CPU usage
by Robin Palotai 08 May '14

08 May '14

Hello List, I have a tiny scotty-based application, which when compiled and started in profiling mode, consumes 10x CPU it does in normal mode. Interestingly, if I fire a request on the app, CPU usage drops to minimal after finishing the request for a while. But after a few minutes it starts consuming 10x CPU again. First I would have suspected scotty, however collecting time profiling info with -p, -P or -Pa doesn't reveal much. That still not rules scotty out however. To make matters worse, I inspect strange time profiling tick count I can't explain - the .prof file says "2 ticks @ 1000 us", while the application was clearly running idle for a good few seconds. Any ideas what am I missing? Thanks, Robin

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