- Haskell-Cafe - Haskell.org

Anyone familiar with Hpysics?
by Sven Bartscher 05 Sep '15

05 Sep '15

Greetings, I recently found the physic library/engine Hpysics. It looks really nice and would like to use it for a project, because it's more natural to use in Haskell, than Bullet is. The problem with the library, seems to be, that it doesn't seem, like it retrieved a lot of maintainer attention lately, e.g. after downloading it, I had to fix some type errors in the library (some incompatibility to GL floats), to get it working. The author field in the .cabal file lacks an email, so I can't contact him and ask if he still cares about the package. Given that there doesn't seem to be an active maintainer and I need the package, I would be willing to take over its maintenance. The documentation is not really verbose about most stuff, so there are some things, where I don't know how they are supposed to work. Is there maybe someone, who was involved in writing the library or maintaining it, or someone, who just used it and can help me, with getting it in shape again, or maybe someone, who still feels responsible for it and just didn't update it, because there was no interest? PS: The package can be found on http://code.haskell.org/hpysics/, but not on hackage (another reason, why I believe it's not actively mantained anymore). Regards Sven

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Physics engine for Haskell
by Sven Bartscher 05 Sep '15

05 Sep '15

Greetings, I'm looking for a game physics engine for Haskell. As Bullet is widely used in this field, I went to use the Haskell Bullet binding, but had to find, that it is very inconvenient to use, because of things like making optional parameters necessary in the binding. Is there any higher level binding to Bullet or some other Physics library that is more convenient to use on Haskell? Regards Sven

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GHC 7.8 undefined symbol
by Sven Bartscher 05 Sep '15

05 Sep '15

Greetings, I recently installed a library (namely Hpysics, not on hackage) with shared libraries (they were on by default). When trying to do some stuff with the library (program attached), I get a bunch of undefined symbol errors like this: $ ghc --make Main.hs Linking Main ... /home/sven/.cabal/lib/i386-linux-ghc-7.8.4/Hpysics-0.0/libHSHpysics-0.0.a(Body.o):(.text+0x46e): undefined reference to `Hpysicszm0zi0_PhysicsziHpysicsziBoundingSphere_constructBoundingSpherezugo_info' /home/sven/.cabal/lib/i386-linux-ghc-7.8.4/Hpysics-0.0/libHSHpysics-0.0.a(Body.o):(.text+0x4f9): undefined reference to `Hpysicszm0zi0_PhysicsziHpysicsziBoundingSphere_zdwlgo_info' /home/sven/.cabal/lib/i386-linux-ghc-7.8.4/Hpysics-0.0/libHSHpysics-0.0.a(Body.o):(.text+0xaca6): undefined reference to `Hpysicszm0zi0_PhysicsziHpysicsziBoundingSphere_constructBoundingSpherezugo_info' /home/sven/.cabal/lib/i386-linux-ghc-7.8.4/Hpysics-0.0/libHSHpysics-0.0.a(Body.o):(.text+0xad31): undefined reference to `Hpysicszm0zi0_PhysicsziHpysicsziBoundingSphere_zdwlgo_info Does anyone know, what this is about? PS: Hpysics can be found at http://code.haskell.org/hpysics/ Regards Sven

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ANN: stack-0.1.4.0 (and 0.1.4.1)
by Emanuel Borsboom 05 Sep '15

05 Sep '15

See README <https://github.com/commercialhaskell/stack#how-to-install> for installation and upgrade instructions. Note: while stack-0.1.4.1 is on Hackage, the only change is to a comment so that stack’s haddocks build. Therefore, no new binaries were generated. Functionally, v0.1.4.0 is identical to v0.1.4.1. Note: we have stopped uploading new versions to the Fedora 20 repository, since that version of Fedora has reached end of life <https://fedoraproject.org/wiki/End_of_life>. If you are using Fedora 20, use stack upgrade or download the general Linux binary <https://github.com/commercialhaskell/stack/wiki/Downloads#linux>. Major changes: - You now have more control over how GHC versions are matched, e.g. “use exactly this version,” “use the specified minor version, but allow patches,” or “use the given minor version or any later minor in the given major release.” The default has switched from allowing newer later minor versions to a specific minor version allowing patches. For more information, see #736 <https://github.com/commercialhaskell/stack/issues/736> and #784 <https://github.com/commercialhaskell/stack/pull/784>. - Support added for compiling with GHCJS - stack can now reuse prebuilt binaries between snapshots. That means that, if you build package foo in LTS-3.1, that binary version can be reused in LTS-3.2, assuming it uses the same dependencies and flags. #878 <https://github.com/commercialhaskell/stack/issues/878> Other enhancements: - Added the --docker-env argument, to set environment variables in Docker container. - Set locale environment variables to UTF-8 encoding for builds to avoid “commitBuffer: invalid argument” errors from GHC #793 <https://github.com/commercialhaskell/stack/issues/793> - Enable translitation for encoding on stdout and stderr #824 <https://github.com/commercialhaskell/stack/issues/824> - By default, stack upgrade automatically installs GHC as necessary #797 <https://github.com/commercialhaskell/stack/issues/797> - Added the ghc-options field to stack.yaml #796 <https://github.com/commercialhaskell/stack/issues/796> - Added the extra-path field to stack.yaml - Code page changes on Windows only apply to the build command (and its synonyms), and can be controlled via a command line flag (still defaults to on) #757 <https://github.com/commercialhaskell/stack/issues/757> - Implicitly add packages to extra-deps when a flag for them is set #807 <https://github.com/commercialhaskell/stack/issues/807> - Use a precompiled Setup.hs for simple build types #801 <https://github.com/commercialhaskell/stack/issues/801> - Set —enable-tests and —enable-benchmarks optimistically #805 <https://github.com/commercialhaskell/stack/issues/805> - --only-configure option added #820 <https://github.com/commercialhaskell/stack/issues/820> - Check for duplicate local package names - Stop nagging people that call stack test #845 <https://github.com/commercialhaskell/stack/issues/845> - --file-watch will ignore files that are in your VCS boring/ignore files #703 <https://github.com/commercialhaskell/stack/issues/703> - Add --numeric-version option Bug fixes: - stack init --solver fails if GHC_PACKAGE_PATH is present #860 <https://github.com/commercialhaskell/stack/issues/860> - stack solver and stack init --solver check for test suite and benchmark dependencies #862 <https://github.com/commercialhaskell/stack/issues/862> - More intelligent logic for setting UTF-8 locale environment variables #856 <https://github.com/commercialhaskell/stack/issues/856> - Create missing directories for stack sdist - Don’t ignore .cabal files with extra periods #895 <https://github.com/commercialhaskell/stack/issues/895> - Deprecate unused --optimizations flag - Truncated output on slow terminals #413 <https://github.com/commercialhaskell/stack/issues/413>

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Foreign calls and periodic alarm signals
by Phil Ruffwind 04 Sep '15

04 Sep '15

TL;DR: Does 'foreign import safe' silence the periodic alarm signals? I received a report on this rather strange bug in 'directory': https://github.com/haskell/directory/issues/35#issuecomment-136890912 I've concluded based on the dtruss log that it's caused by the timer signal that the GHC runtime emits. Somewhere inside the guts of 'realpath' on Mac OS X, there is a function that does the moral equivalent of: while (statfs64(…) && errno == EINTR); On a slow filesystem like SSHFS, this can cause a permanent hang from the barrage of signals. The reporter found that using 'foreign import safe' mitigates the issue. What I'm curious mainly is that: is something that the GHC runtime guarantees -- is using 'foreign import safe' assured to turn off the periodic signals for that thread? I tried reading this article [1], which seems to be the only documentation I could find about this, and it didn't really go into much depth about them. (I also couldn't find any info about how frequently they occur, on which threads they occur, or which specific signal it uses.) I'm also concerned whether there are other foreign functions out in the wild that could suffer the same bug, but remain hidden because they normally complete before the next alarm signal. [1]: https://ghc.haskell.org/trac/ghc/wiki/Commentary/Rts/Signals

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Private packages on hackage
by Alan & Kim Zimmerman 04 Sep '15

04 Sep '15

Hi all I had a chat with Duncan Coutts of Well-Typed about the possibility of an extension to hackage which would allow private packages to be uploaded and managed by hackage, for a fee. The idea is that it operates in a similar fashion to GitHub, where public packages are free, but there is a monthly fee for hosting private packages. This would give commercial organisations wanting to get started with Haskell a simple way to host their packages, so that members of the organisation could see the private and public packages when logged in, and cabal install would work as expected with the superset. Duncan is worried about the up-front effort required vs an uncertain return. Personally I think that this could be a good way to fund the hackage infrastructure. So the question is, apart from me, would anyone be interested in such a feature? Regards Alan

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platform 2014.2.0.0 for Windows
by Andrew Butterfield 03 Sep '15

03 Sep '15

Where do I download Haskell Platform 2014.2.0.0 for Windows? - the current (new?) Haskell Platform page doesn't link to old versions anymore (I want to build wxHaskell 0.92, but I gather it doesn't build with ghc 7.10 right now) Andrew Butterfield School of Computer Science & Statistics Trinity College Dublin 2, Ireland

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How to direct cabal to use an alternative ghc version, ala stack?
by David Banas 03 Sep '15

03 Sep '15

Hi all, How do I direct cabal to use an alternative (i.e. - not my system’s default) version of ghc, which I’ve installed, via stack? I tried this: stack exec cabal install ... but got this: cabal: Use of GHC's environment variable GHC_PACKAGE_PATH is incompatible with Cabal. Use the flag --package-db to specify a package database (it can be used multiple times). Thanks, -db

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Examples for Control.Lens.Plated?
by Andrey Chudnov 03 Sep '15

03 Sep '15

Hello Cafe, I'm considering porting some of my code that uses uniplate to lens. But Control.Lens.Plated is giving me headaches. So I'm looking for remedy. Has anyone used it and willing to share examples? I hope that seeing some of the combinators in action would help me understand the type signatures and documentation. What I'm particularly interested in is the following: 1) implementation of something like transformBi and rewriteBi using lens 2) usage of *On, *Off and *OnOff combinators (e.g., transformMOn, transformMOff, transformMOnOff). What I want to understand is the difference between the 3 variants. Also, what does it mean to "Transform every element in the tree in a region indicated by a supplied Traversal" and how exactly does the traversal define the region. 3) any recursive tree traversals/transformations using Plated that stop the recursion at a certain point (e.g., upon seeing a certain constructor) I hope this isn't too vague, but, please, let me know if it is. /Andrey

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JOB OPPORTUNITY_ IT Software Developer
by CREATE-NET Jobs 02 Sep '15

02 Sep '15

CREATE-NET is seeking a Software Developer passionate about web applications development and its latest technologies. You will be part of our Innovation IT team based in Trento, Italy and will contribute to the development and testing of our portfolio of specialized software products for supporting the promotion and education of Create-Net innovation result. *Technical skills* ● Working experience with HTML5, CSS, AJAX, JSON APIs, JavaScript ● Working experience with Ruby (on Rails) and PHP plus some knowledge about Java and Node.js ● Knowledge of Mobile application development (Native Android/iOs or PhoneGap/Cordova) and Responsive Web Design ● Knowledge or interest of functional programming languages (Haskell, Common Lisp, others) will be considered a strong plus ● Experience with relational DBMSs (PostgreSQL in particular) ● Experience with distributed version control systems such as Git ● Familiarity working with Linux environments (Redhat, Ubuntu) ● Experience and knowledge of agile methodologies, software design methods are also considered a plus. *Specific Job responsibilities will include:* ● Contribution to the maintenance and evolution of existing tools which support e-learning and virtual incubation (community portal, tasks management app, event mobile app, idea-incubation/learning platform) ● Contribution to the development of new solutions for software integration ● Contribution to technical support. *Organization skills* ● Autonomous thinking and problem solving skills; ● Prioritization, time management skills and capability to adapt to dynamic environments; ● Ability to work hands-on and with little supervision; ● Attitude to collaborative working. Applicants should have Bachelor's degree (or equivalent experience) in computing or other related disciplines and a proven experience in web software development. They should be enthusiastic about web applications technologies, open-minded and willing to share and expand their knowledge and skills on other technologies too. Please include any Github/Bitbucket or otherwise links to open source contributions you have made. *HOW TO APPLY:* Please send your resume/CV in English to careers(a)create-net.org, specifying in the email subject: “IT SOFTWARE DEVELOPER_HC”. Only applications submitted in English will be taken into consideration. *Important:* due to Italian Privacy Protection Law n.196/03 any resume not mentioning explicitly the following wording: “I authorize the use of my personal data in accordance with Italian Privacy Protection Law (30/06/2003, n.196/03)” will be automatically deleted from our database and consequently not taken into consideration. *Languages:* Excellent command of the English language (written and spoken) is essential. knowledge of the Italian language both spoken and written is not required, but can be helpful. *Working Place*: Povo (Trento), Italy

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