September 2017 - Haskell-Cafe

Re: [Haskell-cafe] EduHaskell
by erwig 25 Sep '17

25 Sep '17

Thanks for all the useful hints and suggestions! Maybe I should have explained the constraints (and where they come from) in more detail. First, the course is NOT an introduction to programming, but an introduction to computer science more generally and thus also discusses several topics not typically addressed by a programming course. Second, computing concepts are introduced with the help of stories, and programming will only take place in the second half of the course (more details about the approach can be found at web.engr.oregonstate.edu/~erwig/SBT) Thus the goal of minimizing the need for explaining advanced type system features. Also, we have already created Haskell code, so that's why Elm, although a really nice language, is currently not an option because of its different syntax. Code.world is also a cool system, but we do currently require a REPL. I definitely will take another look a Helium. Again, thanks for all the responses so far! I'm still wondering which, if any, of the existing alternative preludes would potentially be a good substitute for educational purposes. -- Martin

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(no subject)
by Vladyslav Nikolayevich 25 Sep '17

25 Sep '17

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deploy wxHaskell app on Windows
by Olaf Klinke 25 Sep '17

25 Sep '17

Dear Cafe, I need help deploying a wxHaskell application on Windows. (The gui(a)haskell.org list seems to be dormant, as is wxhaskell-users on sourceforge.) I am explicitly CC-ing some people who recently posted about wxHaskell on this list. TL;DR: How to deploy a wxHaskell application on several Windows machines? Option (a): Automate the installation of DLLs and tweaking of PATH Option (b): Build static libs of wxWidgets to be linked into a static binary. I don't know how to do either. I developed a GUI application based on wxWidgets. I love the wx package, since wxWidgets provides all the high-level dialogs I need, like file and date pickers. The necessary installations on my Linux development machine went like a charm. Next I tried a Windows 10 machine. I installed stack, which installed a ghc.exe in %HOME%/AppData/Local/Programs/.../bin/ and cabal and stack binaries in %HOME%/AppData/Roaming/local/bin/. I downloaded a wx-config.exe binary and placed it in the latter directory and added that to the PATH. I downloaded wxInstall-Achelanne-64.0.1 and after adding the above path to ghc.exe to it's Install.bat, the Installation completed. Install.bat suggested to add two directories to the PATH, which I did. I set WXWIN to wxInstall-Achelanne-64.0.1/wxWidgets and WXCFG to gcc_dll/mswu With this, wx-config outputs some flags if requested. Next, I added %WXWIN%/include to extra-include-dirs and %WXWIN%/lib/gcc_dll to extra-lib-dirs in my stack.yaml. I also added %WXWIN%/DLLs to the extra-lib-dirs in the .cabal file. %WXWIN%/include/wx/platform.h mentions wx/setup.h which is not there. Remedy: Copy %WXWIN%/include/wx/msw/setup.h to %WXWIN%/include/wx/setup.h I believe I did set SHARED=0 in the wxWidgets config but there are no .lib, only .dll files in %WXWIN%, so I can not use ghc -optl-static. Hence the binaries produced by stack need to be told the place of the DLLs via the PATH environment variable. This is something I'd like to avoid on all the machines. Any suggestions welcome. Olaf

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Re: [Haskell-cafe] EduHaskell
by Johannes Waldmann 24 Sep '17

24 Sep '17

Dear Martin, I use Haskell for teaching as well (not for beginners) [1]. I do use ghci in lab classes. For the problems you mention, I have these sort-of work-arounds: > Errors resulting from overloading numerical literals, arithmetical operators? avoid built-in (Prelude) numbers and the Num class. stuff that's been generalized from list to Foldable (e.g., length)? avoid built-in (Prelude) lists [2] > Errors due to undefined type class instances > (specifically, Eq and Show) I think these classes are somewhat easy to motivate - at least Eq is (we need "==" to notate and test properties of programs, not every type has decidable equality (functions have not), so we need to mark the types that do) For Show, it's not that nice (ghci uses "show" but implicitly - then why do we need to write the Show instance explicitly) Still, adding "deriving (Eq, Show)" after each data declaration is not too much of a burden. I agree it is a distraction. > Errors in the context of parametric polymorphism Well, it's an important concept to teach, so it is natural that it takes some time and work. (slightly tangential - I think it would already help if it would be easier to declare types of identifiers - to remove unwanted polymorphism. E.g., "\ (x::Bool) (y::Bool) -> x || y" currently requires a language pragma (!) whose name mentions type variables (!!) ) - Johannes. [1] https://www.imn.htwk-leipzig.de/~waldmann/talk/17/wflp [2] https://www.imn.htwk-leipzig.de/~waldmann/etc/untutorial/list-or-not-list/

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3rd International Workshop on Real World Domain Specific Languages (RWDSL'18)
by Rob Stewart 22 Sep '17

22 Sep '17

CALL FOR PAPERS ================================= 3rd International Workshop on Real World Domain Specific Languages https://sites.google.com/site/realworlddsl In conjunction with The International Symposium on Code Generation and Optimisation 2018. http://cgo.org/cgo2018/ Vienna, Austria, 24 February, 2018 ==================================== As the use of computers proliferates, the complexity and variety of systems continues to grow. As a result, it is becoming increasingly inflexible to "hard wire" behaviours into software. Software developers can enable more control over their software configurations by exploiting Domain Specific Languages (DSLs). Such DSLs provide a systematic way to structure the underlying computational components: to coin a phrase, a DSL is a library with syntax. There is an enormous variety of DSLs for a very wide range of domains. Most DSLs are highly idiosyncratic, reflecting both the specific natures of their application domains and their designers' own preferences. This workshop will bring together constructors of DSLs for "real world" domains; that is, DSLs intended primarily to aid in building software to solve real world problems rather than to explore the more theoretical aspects of language design and implementation. We are looking for submissions that present the motivation, design, implementation, use and evaluation of such DSLs. ================================= Key Dates: ---------------- Paper submission deadline : 15th December2017 Author notification: 26th January 2018 Final manuscript due: 9th February 2018 Workshop: 24th February 2018 ---------------- Submission Instructions: The EasyChair submission page for this workshop is: https://easychair.org/conferences/?conf=rwdsl18 We anticipate that accepted submissions will be published in the ACM Digital Library within its International Conference Proceedings Series, as were RWSDL'16 and RWDSL'17. Submissions should be 8-10 pages in ACM double-column format. Authors should follow the information for formatting ACM SIGPLAN conference papers, which can be found at http://www.acm.org/publications/proceedings-template. Full submission details are on the workshop web page. ================================= Program Chairs Rob Stewart, Heriot-Watt University, UK Greg Michaelson, Heriot-Watt University, UK PC Members Riyadh Baghdadi, MIT, USA Allin Cottrell, Wake Forest University, USA Nina Dethlefs, University of Hull, UK And Gill, X - The Moonshot Factory, USA Kevin Hammond, University of St Andrews, UK Patrick Maier, University of Glasgow, UK Mathijs Schuts, Phillips Healthcare, Netherlands Simon Thompson, University of Kent, UK Phil Trinder, University of Glasgow, UK Contact Please email inquiries concerning the workshop to: R.Stewart(a)hw.ac.uk

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Munich Haskell Meeting, 2017-09-25 @ 19:30
by Christian Neukirchen 22 Sep '17

22 Sep '17

Dear all, Next week, our monthly Munich Haskell Meeting will take place again on Monday, September 25 at Max Emanuel Brauerei at 19h30. For details see here: http://muenchen.haskell.bayern/dates.html If you plan to join, please add yourself to this dudle so we can reserve enough seats! It is OK to add yourself to the dudle anonymously or pseudonymously. https://dudle.inf.tu-dresden.de/haskell-munich-sep-2017/ Everybody is welcome! cu, -- Christian Neukirchen <chneukirchen(a)gmail.com> http://chneukirchen.org

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Curious why there's no ioe_description accessor in System.IO.Error?
by Viktor Dukhovni 21 Sep '17

21 Sep '17

The IOError type re-exported from GHC.IO.Exception by System.IO.Error has accessors for some of the error elements fields, but is notably missing an accessor for ioe_description, which is only available as "ioeGetErrorString" for UserError, for all other errors you just get the string form of the error type: ioeGetErrorType :: IOError -> IOErrorType ioeGetErrorString :: IOError -> String ioeGetLocation :: IOError -> String ioeGetHandle :: IOError -> Maybe Handle ioeGetFileName :: IOError -> Maybe FilePath ioeGetErrorString ioe | isUserErrorType (ioe_type ioe) = ioe_description ioe | otherwise = show (ioe_type ioe) the real ioe_description for other error types can only be brought into scope by importing GHC.IO.Exception instead, or alternatively via the System.IO.Error.Lens: -- | Error type specific information. description :: Lens' IOException String description f s = f (ioe_description s) <&> \e -> s { ioe_description = e } {-# INLINE description #-} I am curious why ioeGetDescription was left out of System.IO.Error, and/or why it should not be added? Somehow it feels "wrong" to import GHC.IO.Exception instead of System.IO.Error just to get at the specific error text... Is it the case that, given all the other language extensions my code depends on, I should not have any qualms about importing GHC.* modules? Or perhaps is it the case that one should just start using lens, and so adding "missing" record accessors just delays migration to the right way and is no longer a priority? -- Viktor.

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Traversable instance for ((->) a)?
by David Banas 20 Sep '17

20 Sep '17

Is there a Traversable instance for ((->) a)? -db

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Re: [Haskell-cafe] Why is Haskell so slow (comparing to Java/Scala)?
by Saurabh Nanda 20 Sep '17

20 Sep '17

Intresting. Wont using "void" or "_ <- forM blah" have the same effect? Why not? On 20-Sep-2017 9:37 PM, "Nick Smallbone" <nick(a)smallbone.se> wrote: Hi Stanislav, Станислав Черничкин <schernichkin(a)gmail.com> writes: > I've wrote simple Haskell benchmark program, which populated primitive vector > from vector package: > > ... > void $ for [0..1000000 - 1] $ flip (P.unsafeWrite v) (1 :: Int) 'for' is a variant of 'map' - it returns a list of results (in this case a list of a million () values). Instead you should use 'forM_' (note the underscore) from Control.Monad, which discards the result - that cuts the runtime by a huge amount when I try it. (And make sure to compile with -O too.) Nick _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

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Call for Contributions: BOB 2018 - Berlin, Feb 23, 2018
by Matthias Fischmann 20 Sep '17

20 Sep '17

BOB Conference 2018 "What happens when we use what's best for a change?" http://bobkonf.de/2018/en/cfp.html Berlin, February 23 Call for Contributions Deadline: October 29, 2017 You are actively engaged in advanced software engineering methods, implement ambitious architectures and are open to cutting-edge innovation? Attend this conference, meet people that share your goals, and get to know the best software tools and technologies available today. We strive to offer a day full of new experiences and impressions that you can use to immediately improve your daily life as a software developer. If you share our vision and want to contribute, submit a proposal for a talk or tutorial! Topics ------ We are looking for talks about best-of-breed software technology, e.g.: - functional programming - persistent data structures and databases - types - formal methods for correctness and robustness - abstractions for concurrency and parallelism - metaprogramming - probabilistic programming - math and programming - controlled side effects - beyond REST and SOAP - effective abstractions for data analytics - ... everything really that isn’t mainstream, but you think should be. Presenters should provide the audience with information that is practically useful for software developers. We’re especially interested in experience reports. But this could also take other forms, e.g.: - introductory talks on technical background - overviews of a given field - demos and how-tos Requirements ------------ We accept proposals for presentations of 45 minutes (40 minutes talk + 5 minutes questions), as well as 90 minute tutorials for beginners. The language of presentation should be either English or German. Your proposal should include (in your presentation language of choice): - an abstract of max. 1500 characters. - a short bio/cv - contact information (including at least email address) - a list of 3-5 concrete ideas of how your work can be applied in a developer’s daily life - additional material (websites, blogs, slides, videos of past presentations, ...) Submit here: https://docs.google.com/forms/d/e/1FAIpQLSdjgwulSMpaITJ6q6cK_ndrfR1FlEs_HQl… Organisation - direct questions to contact at bobkonf dot de - proposal deadline: October 29, 2017 - notification: November 13, 2017 - program: December 1, 2017 NOTE: The conference fee will be waived for presenters, but travel expenses will not be covered. Speaker Grants -------------- BOB has Speaker Grants available to support speakers from groups under-represented in technology. We specifically seek women speakers and speakers who are not be able to attend the conference for financial reasons. Details are here: http://bobkonf.de/2018/en/speaker-grants.html Shepherding ----------- The program committee offers shepherding to all speakers. Shepherding provides speakers assistance with preparing their sessions, as well as a review of the talk slides. Program Committee ----------------- (more information here: http://bobkonf.de/2018/en/programmkomitee.html) - Matthias Fischmann, zerobuzz UG - Matthias Neubauer, SICK AG - Nicole Rauch, Softwareentwicklung und Entwicklungscoaching - Michael Sperber, Active Group - Stefan Wehr, factis research Scientific Advisory Board - Annette Bieniusa, TU Kaiserslautern - Torsten Grust, Uni Tübingen - Peter Thiemann, Uni Freiburg

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