- Haskell-Cafe - Haskell.org

api-tools questions
by Karsten Gebbert 25 Sep '14

25 Sep '14

Hi All, I have a question concerning the api-tools package. Its not clear from the tests, sources or the tutorial how I can use other date/time formats that the default `utc` type can handle. I'm trying to wrap a JSON API that is not under my control, so I have to adhere to whatever I get back from it. Could anybody with experience with the package point me to some example, relevant bits in the sources or a tip how to do it? I'm planning to create some more documentation around the package to contribute back once I figured out a few more details, because I think its quite a useful abstraction when dealing with (foreign) APIs IMO. Thanks already for any hints, karsten

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Replacement for Ptr () in FFI declaration?
by Howard B. Golden 25 Sep '14

25 Sep '14

Hi, Apparently, before GHC 7.8, it was possible to specify FFI declarations using Ptr (). However, it now gets an error message: This is from com-1.2.3.1 when I try to compile it: ------ message follows ----- [12 of 21] Compiling System.Win32.Com.Automation.TypeLib ( System\Win32\Com\Automation\TypeLib.hs, dist\build\System\Win 32\Com\Automation\TypeLib.o ) System\Win32\Com\Automation\TypeLib.hs:1379:1: Unacceptable argument type in foreign declaration: Ptr () When checking declaration: foreign import stdcall safe "dynamic" prim_System_Win32_Com_Automation_TypeLib_setGuid :: Ptr () -> Ptr () -> Ptr GUID -> IO Int32 ------ end of message ----- What is the proper declaration to use instead of Ptr () ? Thanks. Howard B. Golden

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Haskell Weekly News: Issue 307
by Daniel Santa Cruz 25 Sep '14

25 Sep '14

Welcome to issue 307 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers from September 14 to 20, 2014 Quotes of the Week * Qfwfq: I seq what you mean. * trap_exit_: if haskell makes programmers 10x more productive, then why are there not better haskell ides? :-) Fuuzetsu: trap_exit_: because you don't need one when you're 10x more productive already ;P * joshcough: im just surprised when im looking for something and i dont find a package by ed kmett. Top Reddit Stories * Wayward Tide is Being Written in Haskell Domain: blog.chucklefish.org, Score: 131, Comments: 30 Original: [1] http://goo.gl/00xr22 On Reddit: [2] http://goo.gl/kJBqTe * Hython: The simplest possible language Domain: callcc.io, Score: 82, Comments: 16 Original: [3] http://goo.gl/T95xQ3 On Reddit: [4] http://goo.gl/LBKTks * Hey /r/haskell, we're hiring! Domain: blog.chucklefish.org, Score: 79, Comments: 49 Original: [5] http://goo.gl/93gW3N On Reddit: [6] http://goo.gl/zULSci * hindent: A Haskell indenter Domain: chrisdone.com, Score: 58, Comments: 18 Original: [7] http://goo.gl/4XlJpL On Reddit: [8] http://goo.gl/SCXxOS * Reflecting strictness in Haskell types Domain: h2.jaguarpaw.co.uk, Score: 51, Comments: 27 Original: [9] http://goo.gl/lfPkYD On Reddit: [10] http://goo.gl/hx6XtM * Towards Shake 1.0 Domain: neilmitchell.blogspot.com, Score: 49, Comments: 7 Original: [11] http://goo.gl/RPlddo On Reddit: [12] http://goo.gl/ckKD2m * Formatting in Haskell (Chris Done) Domain: chrisdone.com, Score: 49, Comments: 11 Original: [13] http://goo.gl/eq7hAF On Reddit: [14] http://goo.gl/f1Amec * Haskell Dice of Doom - Part 1 Domain: derekmcloughlin.github.io, Score: 39, Comments: 6 Original: [15] http://goo.gl/oF3ot3 On Reddit: [16] http://goo.gl/oLz2Fv * Beginner error messages in C++ vs Haskell Domain: izbicki.me, Score: 39, Comments: 65 Original: [17] http://goo.gl/j05AXH On Reddit: [18] http://goo.gl/ZOLvZW * Blog: GHC Weekly News - 2014/09/15 Domain: ghc.haskell.org, Score: 28, Comments: 0 Original: [19] http://goo.gl/8Dt0e8 On Reddit: [20] http://goo.gl/P4uz3y * Let's Build a Browser Engine in Haskell: part 3 Domain: hrothen.github.io, Score: 27, Comments: 8 Original: [21] http://goo.gl/0ckGRH On Reddit: [22] http://goo.gl/vZXZOy * ANN: best-haskell - haskell download ranking Domain: best-haskell.herokuapp.com, Score: 24, Comments: 11 Original: [23] http://goo.gl/9RtgrI On Reddit: [24] http://goo.gl/3zO7SN * ICFP "The Ghost of Church" - writeup by Olle Fredriksson who was the first to solve it! Domain: reddit.com, Score: 23, Comments: 3 Original: [25] http://goo.gl/9j7hG3 On Reddit: [26] http://goo.gl/nDxc4T * What is wrong with the Monoid instance for Maybe? Domain: self.haskell, Score: 21, Comments: 21 Original: [27] http://goo.gl/kgVlFf On Reddit: [28] http://goo.gl/kgVlFf * Inferring Algebraic Effects Domain: lmcs-online.org, Score: 20, Comments: 0 Original: [29] http://goo.gl/Wjklhq On Reddit: [30] http://goo.gl/PBJY7N * Are typeclasses essential? (includes Luke Palmer's view on it) Domain: stackoverflow.com, Score: 19, Comments: 30 Original: [31] http://goo.gl/5rh2dq On Reddit: [32] http://goo.gl/RuX5i7 * Built on Haskell: Findmelike - visual search for art Domain: findmelike.com, Score: 19, Comments: 1 Original: [33] http://goo.gl/MgM69t On Reddit: [34] http://goo.gl/Vzrc6R * Let's Build a Browser Engine in Haskell: setting up tests Domain: hrothen.github.io, Score: 17, Comments: 9 Original: [35] http://goo.gl/qwLXRq On Reddit: [36] http://goo.gl/mUqX6w Top StackOverflow Questions * Are typeclasses essential? votes: 20, answers: 4 Read on SO: [37] http://goo.gl/5rh2dq * Ambigous instance resolution in Haskell votes: 14, answers: 2 Read on SO: [38] http://goo.gl/KzV5jC * Understanding the casts involved in patterns matching a datatype that is indexed over a user defined kind votes: 11, answers: 1 Read on SO: [39] http://goo.gl/TppaAg * What does fixIO do? votes: 10, answers: 2 Read on SO: [40] http://goo.gl/yECrrk Until next time, [41]+Daniel Santa Cruz References 1. http://blog.chucklefish.org/?p=154 2. http://www.reddit.com/r/haskell/comments/2glk10/wayward_tide_is_being_writt… 3. http://callcc.io/hython-the-simplest-possible-language/ 4. http://www.reddit.com/r/haskell/comments/2go4v6/hython_the_simplest_possibl… 5. http://blog.chucklefish.org/?p=322 6. http://www.reddit.com/r/haskell/comments/2gyn1w/hey_rhaskell_were_hiring/ 7. http://chrisdone.com/posts/hindent 8. http://www.reddit.com/r/haskell/comments/2gyaw7/hindent_a_haskell_indenter/ 9. http://h2.jaguarpaw.co.uk/posts/strictness-in-types/ 10. http://www.reddit.com/r/haskell/comments/2gk51p/reflecting_strictness_in_ha… 11. http://neilmitchell.blogspot.com/2014/09/towards-shake-10.html 12. http://www.reddit.com/r/haskell/comments/2gnat7/towards_shake_10/ 13. http://chrisdone.com/posts/formatting 14. http://www.reddit.com/r/haskell/comments/2gyrvp/formatting_in_haskell_chris… 15. http://derekmcloughlin.github.io/2014/09/13/Haskell-Dice-Of-Doom-Part-1/ 16. http://www.reddit.com/r/haskell/comments/2gg3um/haskell_dice_of_doom_part_1/ 17. https://izbicki.me/blog/error-messages-in-ghc-vs-g++.html 18. http://www.reddit.com/r/haskell/comments/2go92u/beginner_error_messages_in_… 19. https://ghc.haskell.org/trac/ghc/blog/weekly20140915 20. http://www.reddit.com/r/haskell/comments/2gia13/blog_ghc_weekly_news_201409… 21. http://hrothen.github.io/2014/09/19/lets-build-a-browser-engine-in-haskell-… 22. http://www.reddit.com/r/haskell/comments/2gw2bw/lets_build_a_browser_engine… 23. http://best-haskell.herokuapp.com/ 24. http://www.reddit.com/r/haskell/comments/2gsjk0/ann_besthaskell_haskell_dow… 25. http://www.reddit.com/r/theghostofchurch/comments/2fccjw/i_found_this_trink… 26. http://www.reddit.com/r/haskell/comments/2gkjij/icfp_the_ghost_of_church_wr… 27. http://www.reddit.com/r/haskell/comments/2guo44/what_is_wrong_with_the_mono… 28. http://www.reddit.com/r/haskell/comments/2guo44/what_is_wrong_with_the_mono… 29. http://www.lmcs-online.org/ojs/viewarticle.php?id=1469 30. http://www.reddit.com/r/haskell/comments/2gdl31/inferring_algebraic_effects/ 31. http://stackoverflow.com/questions/25855507/are-typeclasses-essential 32. http://www.reddit.com/r/haskell/comments/2gjqop/are_typeclasses_essential_i… 33. http://findmelike.com/ 34. http://www.reddit.com/r/haskell/comments/2gn81y/built_on_haskell_findmelike… 35. http://hrothen.github.io/2014/09/14/lets-build-a-browser-engine-in-haskell-… 36. http://www.reddit.com/r/haskell/comments/2ge7om/lets_build_a_browser_engine… 37. http://stackoverflow.com/questions/25855507/are-typeclasses-essential 38. http://stackoverflow.com/questions/25854072/ambigous-instance-resolution-in… 39. http://stackoverflow.com/questions/25934209/understanding-the-casts-involve… 40. http://stackoverflow.com/questions/25876042/what-does-fixio-do 41. https://plus.google.com/105107667630152149014/about

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Taking over the thrift package.
by Sean Parsons 24 Sep '14

24 Sep '14

Hi there. As per the instructions on the Haskell wiki I'm posting here as I'm interested in either taking over the thrift package or helping out with getting more recent builds uploaded as it's wildly out of date: https://hackage.haskell.org/package/thrift Does anyone have any contact details for the current maintainer? Thanks, Sean.

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Combining LoggingT with another library's monad
by Joe Fiorini 24 Sep '14

24 Sep '14

As I've been learning Haskell, I've found I constantly get tripped up on combining monads with transformers to form stacks. This seems to be very common in web development, which is my primary use case for Haskell. I'm using the Wheb framework as it's been the simplest to understand of all the frameworks I've seen. To get a better understanding of monad transformers, I'm trying to implement logging in a small app I wrote. I'm attempting to use Control.Monad.Logger to add LoggingT to my monad stack, that way I can use runStdoutLoggingT to log straight to stdout (without having to deal with implementing my own monadLoggerLog method). I added LoggingT to the top of my monad stack, but ran into lots of problems and moved the LoggingT type to one of my route handlers (you can see my latest attempt & the compiler error here https://gist.github.com/joefiorini/9e89bdf86e28e6b98bf0) I'm at a point now where I believe my problem is either a) I'm just not understanding something about how monad transformers work, in which case I just need to do some more reading or b) the LoggingT transformer is simply not "compatible" with the WhebT transformer, in which case I need to completely change my approach. I'm not looking for someone to solve my problem for me; I'm just trying to get a little guidance. Am I heading in the right direction here or should I change up my approach? If the latter, can anyone give me a little direction as to where to look? Thanks!

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Numerals in input vs numerals in source
by Doug McIlroy 24 Sep '14

24 Sep '14

Consider e1 = read "1" :: Integer e2 = read "1" :: Rational e3 = read "1" :: Double e1 and e3 evaluate to 1 and 1.0 respectively e2 produces an error: "Prelude.read: no parse" Yet (1::Integer, 1::Rational, 1::Double) evaluates to (1, 1%1, 1.0) Is the inconsistent parsing defensible, or just an (irrational!) fact? I believe a reconciliation would break nothing. Doug McIlroy

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code.haskell.org down
by Henning Thielemann 24 Sep '14

24 Sep '14

code.haskell.org seems to be down :-(

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Re: [Haskell-cafe] [ANN] Declarative Game Programming & haskanoid (FRP, SDL, Android)
by Ivan Perez 24 Sep '14

24 Sep '14

Hi Mikolaj, (CC haskell-cafe) Thanks, Mikolaj! Indeed, the original links to the slides were broken (deployment env vs production env, yikes!). That has been fixed now. Bitbucket seeems to be taking some time to refresh the page, though. In the meantime: http://fplab.bitbucket.org/uploads/ppdp2014-tutorial.pdf http://fplab.bitbucket.org/uploads/ppdp2014-tutorial-4up.pdf Best Ivan On 24 September 2014 10:27, Mikolaj Konarski <mikolaj.konarski(a)gmail.com> wrote: > > * Announcement and slides: > > > http://fplab.bitbucket.org/posts/2014-09-23-declarative-game-programm.html > > Hi! Thank you for the post. Both slides links are dead for me, though. >

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Nottingham Research Fellowships (deadline 20th October)
by Graham Hutton 24 Sep '14

24 Sep '14

Dear all, The University of Nottingham is seeking applications for a number of Nottingham Research Fellowships: http://tinyurl.com/notts-fellows These are highly prestigious three-year fellowships, which are normally expected to lead into permenant academic positions. Candidates should have no more than 8 years postdoctoral experience, and fellowships normally start in October 2015. The deadline for submission of initial Expressions of Interest is ** 20th October 2014 **. Applicants in the area of the Functional Programming (FP) lab would be most welcome. The FP lab is keen to receive applications from outstanding candidates with an excellent publication record, experience in combining theory with practice, and the ability to secure external funding to support their research. Further information about the FP lab is available from http://fp.cs.nott.ac.uk As an approximate guideline, candidates in the area of the FP lab would normally be expected to have at least 3 years postdoc experience, and a number of strong publications in leading international venues such as ICFP, POPL, LICS, JFP, Haskell Symposium, etc. Best wishes, Graham Hutton -- Prof Graham Hutton Functional Programming Lab School of Computer Science University of Nottingham, UK http://www.cs.nott.ac.uk/~gmh This message and any attachment are intended solely for the addressee and may contain confidential information. If you have received this message in error, please send it back to me, and immediately delete it. Please do not use, copy or disclose the information contained in this message or in any attachment. Any views or opinions expressed by the author of this email do not necessarily reflect the views of the University of Nottingham. This message has been checked for viruses but the contents of an attachment may still contain software viruses which could damage your computer system, you are advised to perform your own checks. Email communications with the University of Nottingham may be monitored as permitted by UK legislation.

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[ANN] Declarative Game Programming & haskanoid (FRP, SDL, Android)
by Ivan Perez 24 Sep '14

24 Sep '14

Hi Café A few weeks ago Henrik Nilsson gave a tutorial at PPDP 14 on Declarative Game Programming, demoing an SDL game using the FRP implementation Yampa. Additional material has been made available now: * Announcement and slides: http://fplab.bitbucket.org/posts/2014-09-23-declarative-game-programm.html * Game: http://github.com/ivanperez-keera/haskanoid The game includes wiimote support, SDL graphics and sound. We have other versions working with a kinect, if anyone is particularly interested. This is, IMHO, very fun to play, since you have to actually run around the room. Also, Keera Studios (my company) is working on an Android version of the game and a video of an early demo running on a Galaxy Tab is available ( http://keera.co.uk/blog/2014/09/24/game-programming-videos-code/ <http://keera.co.uk/blog/?p=690&preview=true>). Our internal, latest version runs now much faster than the ones in either video (new videos will be released soon). I hope we can soon give you a great excuse to be playing games at the office ;) All the best Ivan

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