August 2014 - Haskell-Cafe

Does the lambda calculus have provisions for I/O? State can be done with free variables.
by KC 14 Aug '14

14 Aug '14

Hi: Does the lambda calculus have provisions for I/O? State can be done with free variables. -- -- Sent from an expensive device which will be obsolete in a few months! :D Casey

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ANNOUNCE: hayland 0.1.0.0
by Auke Booij 14 Aug '14

14 Aug '14

I just pushed the first release of the Haskell bindings to Wayland I've been working on to Hackage. SHAMELESS SPAM ----- I'm looking for a PhD position in (mathematical) type theory (preferably in Europe). Contact me for my (interesting!) background. What is Wayland? ----- For those of you who have been living under a rock, X11 is probably going to be ditched soon (porting work for GNOME, KDE, and E is already well underway), and the graphics stack reworked, in favor of "wayland". There will no longer be a monolithic server between the compositor (aka window manager) and the window clients. In the new design, the compositor *is* the central server. The new architecture allows for proper isolation of clients (a HUGE security improvement over X11), as well as major cleanups of code (enabling embedded use). Why bind to C code? ----- In theory, wayland should only be a protocol specification (which happens to have a reference implementation) which could be implemented in Haskell. However, the current state of the matter is that for EGL implementation reasons, one is forced to bind to this reference implementation. (More precisely, the EGL libraries need to be able to configure wayland - and such code would have to be written for every wayland implementation.) So in practice, one can't write a pure Haskell implementation, and that's why I made bindings for the C library. Where's the code? ----- https://github.com/tulcod/haskell-wayland Wait, why are you even binding to Wayland? ----- Not sure, but it's pretty foundational stuff so I'm sure it'll be of use to someone, somewhere. Maybe someone wants to write a window manager for the new ecosystem (I'm looking at you XMonad)? Wow, I've never seen a module expose this many symbols ----- Yes, if anyone has ideas on how to reorganize and/or clean up the symbols exposed by the various part of the library, I am most interested. The problem here is that I'm generating a lot of code using template haskell, and TH does not give you control over which symbols you want to expose and how. I could write this list to a haskell source file at configure time instead (which might be useful for other reasons as well), but ideally I would like to split up the library into the various "interfaces" wayland offers - but these interfaces are unknown at dev time time, and I don't think there is remotely any mechanism to generate /modules/ at compile time. I'm interested to hear what you guys think about controlling the symbol exposure of TH-generated code. TemplateHaskell /and/ GeneralizedNewtypeDeriving? Are you /trying/ to derive bottom? ----- Well I sacrificed some Safety in favor of exposing nice Haskelly types. Feedback is welcome. Final note ----- By the way, I also wrote bindings to xkbcommon a while ago, although they need some attention. Anyway, my point is that with hayland and xkbcommon in place (both in a semi-usable state), there should be plenty of groundwork ready for you to get started with Wayland on Haskell. (xkbcommon is the de facto standard library to work with keyboard layouts in wayland. It translates keyboard events ("which key did you press") into Unicode symbols ("what letter should appear on the screen"), using the right keyboard layout.)

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Visualising Haskell function execution
by Jan Paul Posma 13 Aug '14

13 Aug '14

Hey all, Last weekend my friend Steve and I did a small project for visualising Haskell function execution in the browser. It's meant to be used in education, and uses a tiny custom parser. I figured it could be of interest for anyone here learning or teaching Haskell: https://stevekrouse.github.io/hs.js/ To see it in action, scroll a bit down to the red bordered box, and click on "map", and then keep clicking on each new line. I hope it can be useful to someone. Cheers, JP

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Openings for brilliant Haskell devs for exciting project "as close to a space station as you can get" @ Swedish spinoff, DSLs/safety-critical/embedded software, and more
by Johan Glimming 13 Aug '14

13 Aug '14

Dear All, I’d like to share this exciting job opportunity (formatted text below), as this forum might be right for the very skilled developers we are looking for here. The LinkedIn posting is on the following webpage, e.g. in case the email does not display correctly: https://www.linkedin.com/today/post/article/20140812174919-547525-openings-… … Best wishes, Johan Glimming @ LinkedIn: http://se.linkedin.com/in/glimming — Openings for brilliant Haskell devs for exciting project "as close to a space station as you can get" @ Swedish spinoff, DSLs/safety-critical/embedded software, and more As we grow our business further we look for extraordinary Haskell developers to further strengthen our exceptionally skilled teams in our spinoff and startup Functor Group AB, Kista/Stockholm, Sweden, with subsidiaries. www.functorgroup.com @functors +FunctorGroups You would have an impressive background in computer science, with industrial experience and first-class academic education including certainly advanced functional programming. Compiler design skills are valued highly. Experience of static code analysis (tools and/or research) and safety-critical software and embedded software development are all relevant to this startup and spinoff. You would be part of a team with extraordinary skills and work with other talented individuals which, for those with the right mindset, is extremely rewarding. It's relevant with skill sets that include AFP, EDSLs, type systems, Martin-Löf type theory, dependent types, formal methods, standard-type static analysis tools (as we offer a new kind that adds dependent types to the abstract interpretation approach), experience from tools form e.g. Coverity, Klocwork, MathWorks,, Spec#, Coq, Agda, Epigram, Twelf or other such tools, LLVM, ANSI / ISO C, MISRA C, software testing, various programming languages and their implementation, domain-specific languages, DDD, language-based programming turned into our emerging method named language-driven development, logical frameworks, meta languages, operational semantics, logic, theorem provers. (Learn more atwww.functor.se.) You should be able to contribute to very demanding, challenging, creative teamwork as it manifests itself in a pioneering high-tech spinoff. This all means great responsibility, important contributions to be made, with multiple and varying roles in our highly dynamic work environment where you would be working with other exceptional talents and contribute with your passion for functional programming. You are assumed to share our enthusiasm for and commitment to the new constructive programming paradigm, and recognise the value and great importance of our research foundation, our core technology, being made available in the industry. You would share and nourish our vision for the future of the software industry with the new constructive programming paradigm based on type theory research and the next level of functional programming with EDSL integrated in programming as never done before. But most important is of course your documented talent and experience in Haskell development at an industrial level as well as great teamwork skills and enthusiasm about relevant technologies, and being aligned with our mission (for which see www.functorgroup.com) Several of our developers have higher academic degrees such as a PhD in computer science, logic or mathematics, including two of our Research Engineers, who are professors. (and two more in our Advisory Board, both with own spinoffs, plus an extensive network to leading researchers that we work closely with now and in the future). Your experience may include software development in segments such as safety-critical software and embedded software, hardware modelling, advanced DSL implementation, compiler design and compiler technologies, GPU applications, implementing software testing tools and tools for formal methods. We do not expect you to have all these listed skills, but we expect you to be exceptionally talented and contribute to the success and further growth of Functor Group and its subsidiaries. We are now in an extremely interesting but demanding phase as a spinoff eg with one extraordinarily high-profile customer. You will be part of that project and other very exciting customer projects where we deploy unmatched new technology that brings a new programming paradigm to the software industry, with customers internationally, and an exciting journey into a future where research progress is finally bring aligned with best-practices also in software engineering in a world where software drives innovation and much of growth, but where our technology opens up for much needed improvements in the way software is being developed, designed and tested. Mail your application with resumé with references etc to jobs(a)functor.se. www.functorgroup.com Posted by Dr Johan Glimming at Functor Group AB and Functor AB —

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ANNOUNCE: wxHaskell 0.91.0.0
by Henk-Jan van Tuyl 12 Aug '14

12 Aug '14

L.S., I am happy to announce a new version of wxHaskell. This version binds to both wxWidgets 2.9 and 3.0 [0]. As wxWidgets 3.0 is significantly better, I advice everyone, who is already using wxHaskell, to upgrade to wxWidgets 3.0.1 What is it? ----------- wxHaskell[1] is a portable and native GUI library for Haskell. The goal of the project is to provide an industrial strength GUI library for Haskell, but without the burden of developing (and maintaining) one ourselves. wxHaskell is therefore built on top of wxWidgets – a comprehensive C++ library that is portable across all major GUI platforms; including GTK, Windows, X11, and MacOS X. Furthermore, it is a mature library (in development since 1992) that supports a wide range of widgets with the native look-and-feel. What's new? ----------- - Accept both wxWidgets 2.9 and 3.0, with a preference for 3.0 - Added bindings for wxGraphicsContext::CreatePath - Use the same custom hook for `cabal copy` in wxc/Setup.hs - Many updates in definitions of constants and some 'deprecated' annotations - samples/wx/TestTaskBarIcon.hs now displays an icon in the taskbar - Parsec.hs can now handle lines starting with "//" properly (package wxdirect) - Fixed build issue that was caused by not having both the 2.9 and 3.0 versions of wxWidgets installed - Made samples/test/STCEvent.hs compilable - Solved warnings about deprecated methods and duplicate constant definition - Added -Wl to options for compiling wxc.dll - Adapted upper limit for packages process and array - Solved "deprecated" warning from GHC 7.8.2 Links ----- See the homepage of wxHaskell for more information: https://www.haskell.org/haskellwiki/WxHaskell The packages are: - wxc https://hackage.haskell.org/package/wxc - wxdirect https://hackage.haskell.org/package/wxdirect - wxcore https://hackage.haskell.org/package/wxcore - wx https://hackage.haskell.org/package/wx Regards, Henk-Jan van Tuyl [0] https://www.wxwidgets.org [1] https://www.haskell.org/haskellwiki/WxHaskell -- Folding@home What if you could share your unused computer power to help find a cure? In just 5 minutes you can join the world's biggest networked computer and get us closer sooner. Watch the video. http://folding.stanford.edu/ http://Van.Tuyl.eu/ http://members.chello.nl/hjgtuyl/tourdemonad.html Haskell programming --

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Updating code to work with vinyl 0.4
by Mateusz Kowalczyk 12 Aug '14

12 Aug '14

Hi, I'm looking for some help in helping to migrate to vinyl-0.4 from earlier version. I'll first outline how I currently have things set up and then ask a few questions. For reference the whole project is at [1]. You can just skip to questions in the end if you want to. I have a small project which goes out to a few sites, fetches some similar XML data, parses some fields and returns a data type. My original attempt was to generate a data type per site but that was very ugly: couldn't reuse functions, accessors, anything. So I then turned to vinyl and have the following solution: I have a bunch of common fields defined like this: -- file_url ∷ "file_url" ::: String file_url = Field parent_id ∷ "parent_id" ::: Maybe Integer parent_id = Field -- and so on. I'm using HXT to process the XML I get from each site so I have created many HXT arrows creating each field like this: -- parent_idA ∷ (Functor (cat XmlTree), ArrowXml cat) ⇒ cat XmlTree (PlainRec '["parent_id" ::: Maybe Integer]) parent_idA = (parent_id =:) . readMaybe <$> getAttrValue "parent_id" -- Then for each site I define records like this -- type GelbooruPost = PlainRec '[ "height" ::: Integer , "score" ::: Integer , "file_url" ::: String , "parent_id" ::: Maybe Integer , … ] -- and create the final HXT arrow which will parse and run my value parsers on the whole output -- parsePost ∷ (Functor (cat XmlTree), ArrowXml cat) ⇒ cat XmlTree GelbooruPost parsePost = hasName "post" >>> heightA <:+> scoreA <:+> file_urlA <:+> parent_idA <:+> sample_urlA <:+> sample_widthA <:+> sample_heightA <:+> preview_urlA <:+> ratingA <:+> tagsA <:+> idA <:+> widthA <:+> changeA <:+> md5A <:+> creator_idA <:+> has_childrenA <:+> created_atA <:+> statusA <:+> sourceA <:+> has_notesA <:+> has_commentsA <:+> preview_widthA <:+> preview_heightA -- This works OK: I have similar records for each site and vinyl let me use the same accessors to work over the data from each site without much hassle even though they all return slightly different things. But now vinyl-0.4 is out and I have to update but I'm struggling. As per tutorial I converted all my fields to this format: -- data Fields = Height | Score | FileUrl | ParentId | SampleUrl | … -- Then generated singletons and made universe: -- genSingletons [ ''Fields ] makeUniverse' ''Fields "ElF" semantics ''ElF [ 'Height :~> ''String , 'Score :~> ''Integer , 'FileUrl :~> ''String , 'ParentId :~> ''Integer -- Maybe Integer , 'SampleWidth :~> ''Integer , 'SampleHeight :~> ''Integer , 'PreviewUrl :~> ''String , 'Rating :~> ''Rating , 'Tags :~> ''String -- [String] -- As you can see I have a problem here already: I don't know how to specify ‘Maybe Integer’ or ‘[String]’ in the way that is accepted. Previously I would just do "tags ::: [String]" and it worked. I also wonder what things like: -- PlainRec '["parent_id" ::: Maybe Integer]) -- now become. “PlainRec ElF (ParentId ': '[])” works but is ugly, is there a shorthand for singletons? This is assuming I can convince the ParentId field to be Maybe Integer. Lastly I'd like to know why trivial examples such as this -- a ∷ PlainRec ElF (Score ': '[]) a = SScore =: 7 -- require a type signature. While I put down the signatures anyway, I wonder if there's a way to skip them. I suppose using the field in an annotated record somewhere might let me do this. I imagine the problem here is that we need to specify ElF. Perhaps I am meant to approach this whole thing differently which is why I laid out the structure a bit rather than just asking about syntax. I have watched the video at [2] and while the new records do sound better, I can't find a good guide on how to use them. The tutorial on GitHub[3] is rather lacking. If someone knows about more guides then I'd love to hear about that too. Thanks! [1]: http://github.com/Fuuzetsu/h-booru [2]: http://vimeo.com/102785458 [3]: https://github.com/VinylRecords/Vinyl/blob/master/tests/Intro.lhs -- Mateusz K.

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HGamer3D - version 0.4
by Peter Althainz 12 Aug '14

12 Aug '14

You will find version 0.4 of HGamer3D on github and hackage now. It also comes with some updated introductions on http://www.hgamer3d.org . best regards Peter (uotbw)

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Any tips on "doing it right" for a small program?
by Bram Neijt 12 Aug '14

12 Aug '14

Dear reader, I'm still new to haskell, and decided to convert a simple bash script to a full-on-bells-and-whistles Haskell program (as a learning experience). As you might guess I could use some help. The program is very simple, in Bash it reads: CMDPATTERN="$@" while [[ "`pgrep --count --full "$CMDPATTERN"`" -gt 1 ]]; do sleep 5 done AKA: while there is a command running with the given string, loop. I called this script "after" and use it on the commandline to chain commands from different terminals. The Haskell version is available at https://github.com/bneijt/after What I have done: - Add Travis CI - Add a first test case using test-framework - Add commandline option parsing using "options" - Implement a fork-join behavior using parallel-io What I would like help with: - How to add a --version that reflects the after.cabal version? - Is there a library for what I'm doing in Process.hs (listing running processes, etc.)? - How to add "-p <pid>" support, so I can do "after -p 129 -p 402" (after both pids) - Should I move from exitcode-stdio-1.0 to detailed-1.0? - Any and all other hints you might have Also if you have projects you want to point to for inspiration, I'd be happy to take a look. Greetings, Bram

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New Functional Programming Job Opportunities
by Functional Jobs 11 Aug '14

11 Aug '14

Here are some functional programming job opportunities that were posted recently: Big Data Engineer / Data Scientist at Recruit IT http://functionaljobs.com/jobs/8731-big-data-engineer-data-scientist-at-rec… Cheers, Sean Murphy FunctionalJobs.com

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Irritating Referential Transparency behavior?
by martin 10 Aug '14

10 Aug '14

Hello all, I came across something strange: This code compiles: ------------------------------------------------------------ data LProcess a = LP {lstep :: Writer [String] (Event a -> ([Event a], LProcess a))} ------------------------------------------------------------ exProcess2 :: ProcState -> Location -> LProcess EvtData exProcess2 pState loc = LP {lstep = xxx} where xxx = myStep pState myStep _ = return $ \(E t l _) -> ([E (t+1) l Wakeup], (proc' pState)) proc' state = exProcess2 (trc state) loc but when I replace xxx by myStep pState as in exProcess2 pState loc = LP {lstep = myStep pState} where xxx = myStep pState myStep _ = return $ \(E t l _) -> ([E (t+1) l Wakeup], (proc' pState)) proc' state = exProcess2 (trc state) loc I get No instance for (Monad m0) arising from a use of `myStep' The type variable `m0' is ambiguous Possible fix: add a type signature that fixes these type variable(s) It compiles again when I remove the xxx = line. Why is that so?

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