May 2014 - Haskell-Cafe

ANN: loop - fast for loops
by Niklas Hambüchen 20 Jul '14

20 Jul '14

Announcing the first version of the loop package: http://hackage.haskell.org/package/loop This is for iterating over numeric or otherwise iteratable things in a fast fashion. Looks like C, runs like C. It's trivial, but very robust performance-wise and more independent of GHC smartness or non-smartness in regards to optimising alternatives like `forM_ [1..n]`. It comes with a lot of benchmarks. Contributions are very welcome.

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Re: [Haskell-cafe] ANN: set-cover solves Sudoku, Soma cube, 8 Queens etc.
by Johannes Waldmann 22 Jun '14

22 Jun '14

Henning Thielemann <lemming <at> henning-thielemann.de> writes: > .. package set-cover for solving exact set cover problems. > http://hackage.haskell.org/package/set-cover It's hard to evaluate whether one could use the library because there's essentially no visible documentation. E.g., what does Math.SetCover.Exact.search do? Its type refers to "State" which seems implementation-dependent, and hides the connection to the specification of the set cover problem. Putting some text and examples into the haddocks might help. But of course putting the specification there would be even better. Also, care to explain what algorithm your solver uses, and give some performance data (e.g., N-queens for N=10,20,40,..)? - J.W.

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ZuriHac 2014 - Updates
by Bas van Dijk 05 Jun '14

05 Jun '14

Dear (potential) ZuriHac 2014 attendees, I would like to make a few announcements regarding ZuriHac 2014, a Haskell hackathon taking place in Zurich from Friday 6 June 2014 to Sunday 8 June 2014. Besides hacking on Haskell projects with core members of the community you will hear talks by Simon Marlow and Edward Kmett. Note that this event is open to any experience level, from beginners to gurus. In fact, one of the goals is to bring beginners in contact with experts so that the former can get a quick start in the Haskell community and the latter more help with their projects. For more information see: http://www.haskell.org/haskellwiki/ZuriHac2014 Registration ------------ I'm happy and sad to inform you that we've almost reached capacity for ZuriHac 2014. Happy because it looks like this might be the biggest Haskell Hackathon ever. Sad because I soon have to start adding new registrations to a waiting list. So if you want to join us, and haven't registered already, then please do so soon at: http://bit.ly/ZuriHac2014. Also if you've already registered but know you won't be able to make it, please cancel by emailing me to make room for others. T-Shirt ------- Like last year, each attendee will get a free ZuriHac T-shirt. If you've already registered, please tell me which sizes and model you would like to have: Male: S, M, L, XL, XXL Female: S, M, L, XL, XXL Host ---- Erudify, the company which is hosting ZuriHac, recently changed its name to Better. Do note that we haven't changed location. See our new website on why we have rebranded: http://better.com/en/rebranding Regards, The ZuriHac 2014 organizers

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MacOS testing?
by Ian Ross 01 Jun '14

01 Jun '14

Hi all, Does anyone know of a good solution for MacOS testing that doesn't cost much? (Ideally, that costs nothing...) I've been getting a lot of MacOS-specific issues on the C2HS that I maintain and, since I don't have a Mac myself, testing and fixing these things is a bit of a problem. There is no equivalent of Amazon's EC2 for MacOS. There are some hosting services out there, but they're not all that practical, since they cost, they're set up for continuous hosting rather than intermittent use for bug-fixing, and you can't save a machine image snapshot once you've installed all the software you need (as you can on AWS) so you either need to keep your instance running or reinstall everything every time you want to test something. Any ideas? The only thought I've had so far was to try to do something horrible using Travis (Kiwamu Okabe has some slides about building and testing Haskell code on Travis: http://www.slideshare.net/master_q/20131109-kof2013-travisciosx) That's not a good solution for debugging though. Thanks for any thoughts you might have, Ian. -- Ian Ross Tel: +43(0)6804451378 ian(a)skybluetrades.net www.skybluetrades.net

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MonadRandom and traversing infinite streams
by Petr Pudlák 31 May '14

31 May '14

Hi Brent and Wouter, looking at SO questions http://stackoverflow.com/q/14494648/1333025 http://codereview.stackexchange.com/q/52149/15600 threre are monads and applicative functors that support ``` sequenceInf :: S.Stream (f a) -> f (S.Stream a) ``` that is, allow lazy traversals of streams (infinite lists). Namely those that don't produce any additional output. And instances of MonadRandom seem to have valid implementations of `sequenceInf`, which would allow to produce lazy infinite randomized lists (basically a generalization of `getRandoms`). My proposal is to add ``` class Applicative f => LazyApplicative f where sequenceInf :: S.Stream (f a) -> f (S.Stream a) sequenceInf = traverseInf id traverseInf :: (a -> f b) -> S.Stream a -> f (S.Stream b) traverseInf f = sequenceInf . S.map f ``` to a module in Stream package (for example `Control.Applicative.Lazy`), and add its instances into `MonadRandom`. What do you think? I'd be willing to send patches. Best regards, Petr

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Self-contained GHC for Mac
by Bob Ippolito 30 May '14

30 May '14

After seeing some demand for packaged Haskell for Mac for the IHaskell project and by word of mouth at BayHac I decided to take a stab at it. Here you go: http://ghcformacosx.github.io/ (currently GHC 7.8.2 and cabal-install 1.20.0.1) Why? It can be a bit cumbersome to use the GHC builds from haskell.org on Mac, because they don't come "fully baked", you have to ./configure --prefix=/some/path to get them installed and the installation is not relocatable, if you move it the scripts will break and the package.conf.d files will go stale. It also doesn't ship with cabal-install, which is cumbersome as well, especially for new users. How does it work? In https://github.com/ghcformacosx/ghc-dot-app I have a Main.hs script which downloads/builds/etc. all of the prerequisites. Then it patches the shell scripts to use a path relative to themselves (after following symlinks) rather than hard-coding an installation location. It also patches the package.conf.d files to use ${pkgroot} relative paths. Separately, there's an Xcode project that includes all of the metadata to make it look like a real Mac app bundle (icons, Info.plist) and a small Cocoa application that has a button to open the docs and provides instructions for adding it to the PATH in .bashrc. Due to the heuristics in Mac OS X's man, this will automatically make man pages work as well. Using Xcode here also makes it produce a signed build (which I do, since I am already paying for the $99/year license). -bob

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Local .ghci_history
by João Cristóvão 29 May '14

29 May '14

Hello, I raised this on trac ( https://ghc.haskell.org/trac/ghc/ticket/9089 ), but it seems it did not get much attention, but surelly I'm not the only one who finds this useful. With this little change, if there is a .ghci_history in the folder where you launch ghci it will use it instead of the global ~/.ghc/ghci_history. So, if you keep jumping from one project folder to the other, you can have a project specific history on each one (if you want). If you do not create a local .ghci_history file on that folder, the behaviour is exactly the same as it was before. Thus, this is somewhat identical to the local .ghci file. This, coupled with finally discovering the well hidden possibility of increasing the history size: http://trac.haskell.org/haskeline/wiki/UserPrefs Has vastly improved my ghci workflow. What do you think? João

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Haskell in Org Mode Babel
by Chris Warburton 29 May '14

29 May '14

Hello, I'm wondering if anyone's had success using Haskell in "Babel", the literate programming system in Emacs's Org Mode? I'm trying it with a blog post, but am getting mixed results. For those who don't know, Org Mode is an Emacs mode for editing text files, which has a bunch of features controlled by markup in the file. Babel is a feature which allows source code in various languages to be included in-line and executed. For example, I can write some Haskell like this: #+begin_src haskell [1..10] #+end_src Cheers, Chris

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Haskell Weekly News: Issue 295
by Daniel Santa Cruz 28 May '14

28 May '14

Welcome to issue 294 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers from May 4 to 24, 2014 Quotes of the Week * dalaing: going from doing a fair bit of haskell recently to doing javascript today... sigh... it feels like the difference between typing at a keyboard and typing with a pair of those sporting-event-foam-hands-with-a-pointing-finger on * monochrom: to be blunt, I believe that "I do X for a living" means nothing. politicians do politics for a living too, what is the result? * Cale: Java seems like it was designed especially to be a strawman for people who hate static type systems * ReinH: Every so often edwardk goes up to the mountain of CT and brings us some new tablets edwardk: hear that dolio? we're going to start calling you the mountain. Top Reddit Stories * #haskell is welcoming and troll resistent (just found this by accident) Domain: gist.github.com, Score: 172, Comments: 19 Original: [1] http://goo.gl/TCiMW On Reddit: [2] http://goo.gl/JZNY3M * $7.5m DoD grant to develop Homotopy Type Theory Domain: cmu.edu, Score: 117, Comments: 70 Original: [3] http://goo.gl/EmSlbE On Reddit: [4] http://goo.gl/sKjGIl * Understanding the Stack Domain: well-typed.com, Score: 102, Comments: 13 Original: [5] http://goo.gl/qo9m5O On Reddit: [6] http://goo.gl/MVvaQn * Elm 0.12.3 - efficient 3D rendering with WebGL Domain: elm-lang.org, Score: 82, Comments: 19 Original: [7] http://goo.gl/iATfSi On Reddit: [8] http://goo.gl/QJ5ttp * An example of a Real World Haskell Application Architecture Domain: self.haskell, Score: 68, Comments: 36 Original: [9] http://goo.gl/ZTcr1x On Reddit: [10] http://goo.gl/ZTcr1x * ezyang: “try a <|> b” considered harmful Domain: blog.ezyang.com, Score: 67, Comments: 29 Original: [11] http://goo.gl/BEkC6W On Reddit: [12] http://goo.gl/3oql5l * 9m URL Shortener (Written in Haskell) Domain: 9m.no, Score: 67, Comments: 27 Original: [13] http://goo.gl/E0NoYv On Reddit: [14] http://goo.gl/n4cyN5 * Announce: JHC 0.8.1 IS OUT Domain: notanumber.net, Score: 66, Comments: 14 Original: [15] http://goo.gl/n6qAcf On Reddit: [16] http://goo.gl/wSMrva * Haskell for Mac OS X, self-contained relocatable GHC builds Domain: ghcformacosx.github.io, Score: 64, Comments: 35 Original: [17] http://goo.gl/CvsYC7 On Reddit: [18] http://goo.gl/WcIBw5 * Binary serialisation: better, stronger, faster (PDF, Duncan Coutts, March 2014) Domain: code.haskell.org, Score: 63, Comments: 39 Original: [19] http://goo.gl/r4xShZ On Reddit: [20] http://goo.gl/xhJRbg * CS240h lecture notes Domain: scs.stanford.edu, Score: 61, Comments: 8 Original: [21] http://goo.gl/F39zHe On Reddit: [22] http://goo.gl/AQqrUj * Haskell-mode documentation Domain: chrisdone.com, Score: 58, Comments: 28 Original: [23] http://goo.gl/XzKMCk On Reddit: [24] http://goo.gl/DZBQtO * PSA: you can now visit status.haskell.org Domain: status.haskell.org, Score: 58, Comments: 19 Original: [25] http://goo.gl/oRHfsn On Reddit: [26] http://goo.gl/Ye9YU2 * Once more into the teach, dear friends Domain: serpentine.com, Score: 57, Comments: 11 Original: [27] http://goo.gl/L8Csnm On Reddit: [28] http://goo.gl/AyF2Fs * What Features Would You Like to Find in a Haskell IDE? Domain: self.haskell, Score: 57, Comments: 90 Original: [29] http://goo.gl/Pvo32I On Reddit: [30] http://goo.gl/Pvo32I * Adventure with Types in Haskell - Simon Peyton Jones [1:33:36] Domain: youtu.be, Score: 57, Comments: 10 Original: [31] http://goo.gl/L9wGWe On Reddit: [32] http://goo.gl/sL3u8i * Ars Technica has Haskell as one of three potential heirs to Fortran's scientific computing throne Domain: arstechnica.com, Score: 56, Comments: 78 Original: [33] http://goo.gl/lxWcdK On Reddit: [34] http://goo.gl/kCxUS9 Top StackOverflow Questions * Why does Haskell's “do nothing” function, id, consume tons of memory? votes: 72, answers: 1 Read on SO: [35] http://goo.gl/8awkSk * Are Ana-/Catamorphisms just slower? votes: 29, answers: 2 Read on SO: [36] http://goo.gl/wcmkQw * Code becomes slower as more boxed arrays are allocated votes: 22, answers: 2 Read on SO: [37] http://goo.gl/qfKo2a * Which part of Real World Haskell is now obsolete or considered bad practise? votes: 22, answers: 1 Read on SO: [38] http://goo.gl/EtT51x Until next time, [39]+Daniel Santa Cruz References 1. https://gist.github.com/quchen/5280339 2. http://www.reddit.com/r/haskell/comments/2516e4/haskell_is_welcoming_and_tr… 3. http://www.cmu.edu/news/stories/archives/2014/april/april28_awodeygrant.html 4. http://www.reddit.com/r/haskell/comments/24rs73/75m_dod_grant_to_develop_ho… 5. http://www.well-typed.com/blog/94/ 6. http://www.reddit.com/r/haskell/comments/2641x0/understanding_the_stack/ 7. http://elm-lang.org/blog/announce/0.12.3.elm 8. http://www.reddit.com/r/haskell/comments/261abs/elm_0123_efficient_3d_rende… 9. http://www.reddit.com/r/haskell/comments/24y6ls/an_example_of_a_real_world_… 10. http://www.reddit.com/r/haskell/comments/24y6ls/an_example_of_a_real_world_… 11. http://blog.ezyang.com/2014/05/parsec-try-a-or-b-considered-harmful/ 12. http://www.reddit.com/r/haskell/comments/25ulsv/ezyang_try_a_b_considered_h… 13. http://9m.no/ 14. http://www.reddit.com/r/haskell/comments/267evu/9m_url_shortener_written_in… 15. http://notanumber.net/archives/178/jhc-haskell-0-8-1-released 16. http://www.reddit.com/r/haskell/comments/25o33n/announce_jhc_081_is_out/ 17. http://ghcformacosx.github.io/ 18. http://www.reddit.com/r/haskell/comments/26bx5n/haskell_for_mac_os_x_selfco… 19. http://code.haskell.org/~duncan/binary-experiment/binary.pdf 20. http://www.reddit.com/r/haskell/comments/25ch8v/binary_serialisation_better… 21. http://www.scs.stanford.edu/14sp-cs240h/slides/ 22. http://www.reddit.com/r/haskell/comments/25i99i/cs240h_lecture_notes/ 23. http://chrisdone.com/posts/haskell-mode-docs 24. http://www.reddit.com/r/haskell/comments/2583sm/haskellmode_documentation/ 25. http://status.haskell.org/ 26. http://www.reddit.com/r/haskell/comments/2653kp/psa_you_can_now_visit_statu… 27. http://www.serpentine.com/blog/2014/05/13/once-more-into-the-teach-dear-fri… 28. http://www.reddit.com/r/haskell/comments/25iqk7/once_more_into_the_teach_de… 29. http://www.reddit.com/r/haskell/comments/25sqvk/what_features_would_you_lik… 30. http://www.reddit.com/r/haskell/comments/25sqvk/what_features_would_you_lik… 31. http://youtu.be/6COvD8oynmI 32. http://www.reddit.com/r/haskell/comments/25vj62/adventure_with_types_in_has… 33. http://arstechnica.com/science/2014/05/scientific-computings-future-can-any… 34. http://www.reddit.com/r/haskell/comments/250558/ars_technica_has_haskell_as… 35. http://stackoverflow.com/questions/23746852/why-does-haskells-do-nothing-fu… 36. http://stackoverflow.com/questions/23664197/are-ana-catamorphisms-just-slow… 37. http://stackoverflow.com/questions/23462004/code-becomes-slower-as-more-box… 38. http://stackoverflow.com/questions/23727768/which-part-of-real-world-haskel… 39. https://plus.google.com/105107667630152149014/about

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[ANN] cartel - specify Cabal files using Haskell
by Omari Norman 28 May '14

28 May '14

The Cabal file format works very well for small projects. However, in big projects with a library, many executables, and test suites, some irritations emerge. You need to specify dependencies in multiple places, leading to redundancy. You also have to manually add in new modules, make sure you list all modules (a real pain with executables, as problems may arise only after you build a distribution tarball), and update your module lists when you refactor. Specifying your Cabal files in Haskell rather than in a plain-text file format helps deal with a lot of these problems. You have the full power of Haskell to make definitions in one place and then reuse them. You can also dynamically read a tree of modules and use the result, thus avoiding the need to manually update your module lists. A disadvantage to Cartel is that it can be a bit more verbose than a vanilla Cabal file. In addition, you also have to remember to generate the new Cabal file whenever you change the script that generates your Cabal file. Cabal already has an AST that it uses. Cartel could, perhaps, have re-used these structures. Cartel does not do this for three reasons. First, the Cabal API is a bit untidy, partially because it has to do things that Cartel doesn't have to worry about, but also because the comments in the Cabal modules themselves indicate that the whole thing could use a refactoring. Second, the Cabal developers make no commitment to keep that API stable. Third, the Cartel API tries only to replicate format of the plain-text Cabal file, which will be much more stable than the Cabal API. Hackage: http://hackage.haskell.org/package/cartel Github: https://github.com/massysett/cartel

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