September 2012 - Haskell-Cafe

ANNOUCE: Haddock 2.10.0 and 2.11.0
by David Waern 09 Sep '12

09 Sep '12

-------------------------------------------- -- Haddock 2.10.0 and 2.11.0 -------------------------------------------- Two new versions of Haddock have been uploaded to Hackage: version 2.10.0 which comes with GHC 7.4.2 and 2.11.0 which comes with the new GHC 7.6.1! -------------------------------------------- -- Changes in version 2.12.0 -------------------------------------------- * Labeled URLs (e.g <http://example.net/ some label>) * Improved memory usage (new dependency: deepseq) -------------------------------------------- -- Changes in version 2.11.0 -------------------------------------------- * Show deprecation messages for identifiers * List identifiers declared on the same line (with a common type) separately * Don't crash on unicode strings in doc comments * Fix reporting of modules safe haskell mode * Fix a case where we were generating invalid xhtml * Improved --qual option (no crashes, proper error messages) * A new --qual option "aliased" which qualifies identifers by the module alias used in the source code * The Haddock API restores GHC's static flags after invocation * Access to unexported identifiers through the Haddock API again -------------------------------------------- -- Links -------------------------------------------- Homepage: http://www.haskell.org/haddock Hackage page: http://hackage.haskell.org/package/haddock-2.12.0 Bugtracker and wiki: http://trac.haskell.org/haddock Mailing list: haddock(a)projects.haskell.org Code repository: http://darcs.haskell.org/haddock.git -------------------------------------------- -- Contributors -------------------------------------------- The following people contributed patches to this release: Paolo Capriotti Simon Hengel Ian Lynagh Simon Peyton Jones Iavor S. Diatchki David Terei Henning Thielemann David Waern -------------------------------------------- -- Get Involved -------------------------------------------- We would be very happy to get more contributors. To get involved, start by grabbing the code: http://darcs.haskell.org/haddock.git Then take a look at the bug and feature tracker for things to work on: http://trac.haskell.org/haddock

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package categories
by Sergey Mironov 08 Sep '12

08 Sep '12

Hello list. Do we have a guideline for selecting correct category for a package being developed? I'd like to choose between Web.MyLib and Network.MyLib. Or probably just MyLib if I feel ambitious? Sergey.

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ANNOUNCE vkhs-0.0.3
by Sergey Mironov 08 Sep '12

08 Sep '12

I'm happy to announce a new package called VKHS: http://hackage.haskell.org/package/VKHS https://github.com/ierton/vkhs VKHS provides access to Vkontakte [1] (popular Russian social network) API methods. Library can be used to login into the network as a standalone application (OAuth implicit flow as they call it). Interaction with user is not required. For now, vkhs offers limited error detection and no captcha support. Here is an example code: import Web.VKHS.Login import Web.VKHS.Api main = do let client_id = "111111" -- application id, register first let user_of_interest = "222222" let e = env client_id "user(a)example.com" "password" [Photos,Audio,Groups] (Right at) <- login e (Right ans) <- api e at "users.get" [ ("uids",user_of_interest) , ("fields","first_name,last_name,nickname,screen_name") , ("name_case","nom") ] putStrLn ans Internally, library uses small curl-based HTTP automata and tagsoup for jumping over relocations and submitting various 'Yes I agree' forms. Sergey. [1] - http://vk.com

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Haskell with all the safeties off
by David Feuer 08 Sep '12

08 Sep '12

I have no plans to do such a thing anytime soon, but is there a way to tell GHC to allow nasal demons to fly if the program forces bottom? This mode of operation would seem to be a useful optimization when compiling a program produced by Coq or similar, enabling various transformations that can turn bottom into non-bottom, eliminating runtime checks in incomplete patterns, etc.

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ANN: LambdaCube 3D (purely functional rendering engine) is back in business
by Patai Gergely 08 Sep '12

08 Sep '12

Hello all, We recently rebooted the LambdaCube project, which aims to provide a purely functional interface for GPU programming. The details and the background are described in our new blog [1], while the code can be found on GitHub [2]. Cheers, Gergely [1] http://lambdacube3d.wordpress.com/ [2] https://github.com/csabahruska/lc-dsl -- http://www.fastmail.fm - The professional email service

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performance issues with popCount
by Harald Bögeholz 08 Sep '12

08 Sep '12

Dear Haskell Cafe, I am struggling with the performance of the popCount function from Data.Bits. To be more precise: I downloaded the Haskell Platform 2012.2.0.0 from http://hackage.haskell.org/platform/ (64 bit, Mac OS X). In this version I found the popCount function to be broken. If I look in the online documentation at http://hackage.haskell.org/packages/archive/base/4.5.1.0/doc/html/src/Data-… it is already fixed, but included with my Haskell Platform was the broken version. Anyway, I tried this version popCount :: Integer -> Int popCount = go 0 where go c 0 = c go c w = go (c+1) (w .&. (w - 1)) and profiling showed that my program spent 80 % of its time counting bits. So I thought I'm clever and implement a table-based version like this: popCount' :: Integer -> Int popCount' = go 0 where go c 0 = c go c w = go (c+1) (w .&. (w - 1)) popCountN = 10 popCountMask :: Integer popCountMask = shift 1 popCountN - 1 popCountTable :: Array Integer Int popCountTable = listArray (0, popCountMask) $ map popCount' [0 .. popCountMask] popCount :: Integer -> Int popCount 0 = 0 popCount x = popCountTable ! (x .&. popCountMask) + popCount (x `shiftR` popCountN) turns out this is even slower ... now my program spends 90 % of its time counting bits :-(. Any hints? Thanks -- Harald Bögeholz <bo(a)ct.de> (PGP key available from servers) Redaktion c't Tel.: +49 511 5352-300 Fax: +49 511 5352-417 http://www.ct.de/ int f[9814],b,c=9814,g,i;long a=1e4,d,e,h; main(){for(;b=c,c-=14;i=printf("%04d",e+d/a),e=d%a) while(g=--b*2)d=h*b+a*(i?f[b]:a/5),h=d/--g,f[b]=d%g;} (Arndt/Haenel) Affe Apfel Vergaser /* Heise Zeitschriften Verlag GmbH & Co. KG * Karl-Wiechert-Allee 10 * 30625 Hannover * Registergericht: Amtsgericht Hannover HRA 26709 * Persönlich haftende Gesellschafterin: Heise Zeitschriften Verlag * Geschäftsführung GmbH * Registergericht: Amtsgericht Hannover, HRB 60405 * Geschäftsführer: Ansgar Heise, Dr. Alfons Schräder */

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parsing ghc type errors
by Semen Trygubenko 07 Sep '12

07 Sep '12

Dear Haskell-cafe, When dealing with ghc type errors I often see messages like Couldn't match expected type `ghc-prim:GHC.Types.IO{tc 32I} MyTypeNameHere{tc r1d8}' with actual type `ghc-prim:GHC.Types.IO{tc 32I} MyOtherTypeNameHere{tc r1d8}' Could you please help me understand the meaning of the entities in {} and why are they useful, or point to a source of information about them? Messages where familiar types are referenced are easy to read, but occasionally I get messages of the sort with actual type `[( b0{tv t3p} [tau] :: ghc-prim:GHC.Prim.*{(w) tc 34d} )]' How do I go about reading the type [( b0{tv t3p} [tau] :: ghc-prim:GHC.Prim.*{(w) tc 34d} )] ? E.g., where the names 'b0' and '[tau]' come from? What does '(w)' in '{(w) tc 34d}' mean? Thank you, Semen -- Семен Тригубенко

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ANNOUNCE: haskell-src-exts 1.13.5
by Niklas Broberg 07 Sep '12

07 Sep '12

Fellow Haskelleers, I'm pleased to announce the release of haskell-src-exts-1.13.5! * On hackage: http://hackage.haskell.org/package/haskell-src-exts * Via cabal: cabal install haskell-src-exts * Darcs repo: http://code.haskell.org/haskell-src-exts There are two primary reasons for this release: 1) to add the requested support for UHC's 'js' FFI calling convention (in 1.13.4), and 2) to export a stand-alone token stream lexer (in 1.13.5). NOTE: If after reading the above, you think "wow, a token stream lexer, I'll use that for some kind of refactoring tool", then you're most likely wrong. Please contact me in that case and I'll tell you why. :-) A probably unnecessary warning: This release may fail to parse some files that were previously possible to parse, if they included RULES pragmas using 'forall' as a varid. I really doubt any such exist, and they would not have been accepted by GHC if they did, so I sincerely doubt that anyone will be effected by this. Changelog: 1.13.4 --> 1.13.5 =============== * Expose Language.Haskell.Exts.Lexer, which implements a standalone token stream lexer. The module is re-exported both by Language.Haskell.Exts and by Language.Haskell.Exts.Annotated. 1.13.3 --> 1.13.4 =============== * Fix bug where operators starting with # written in parentheses would not be parsed when UnboxedTuples is turned on. Now works. * Allow 'family' and 'forall' as (non-type) varid's. This adds one more shift/reduce conflict to the parser, and its resolution means that '{-# RULES "name" forall = ... #-}' is not allowed. * Complete the set of FFI calling conventions from the Haskell 2010 report (even if no compiler implements them). Also include the 'js' calling convention, supported by UHC. Cheers, /Niklas

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From monads to monoids in a small category
by Alberto G. Corona 06 Sep '12

06 Sep '12

"Monads are monoids in the category of endofunctors" This Monoid instance for the endofunctors of the set of all elements of (m a) typematch in Haskell with FlexibleInstances: instance Monad m => Monoid (a -> m a) where mappend = (>=>) -- kleisly operator mempty = return The article can be found here: http://haskell-web.blogspot.com.es/2012/07/from-monads-to-monoids-in-small.… I would appreciate some comments.

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Haskell Weekly News: Issue 234
by Daniel Santa Cruz 05 Sep '12

05 Sep '12

Welcome to issue 243 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers the week of August 26 to September 01, 2012. Quotes of the Week * companion_cube: "I don't understand this article at all" edwardk: "Well, when you finish reading it, here's a follow-up article" Top Reddit Stories * Parsing with Haskell and Attoparsec Domain: newartisans.com, Score: 64, Comments: 8 On Reddit: [1] http://goo.gl/rrlQG Original: [2] http://goo.gl/aHlTJ * FRP - Release of reactive-banana-0.7. Finally features dynamic event switching! Domain: apfelmus.nfshost.com, Score: 48, Comments: 21 On Reddit: [3] http://goo.gl/5QnBl Original: [4] http://goo.gl/8dnLg * Combinatorrent - Writing Haskell Code for Fun and Profit [InfoQ] Domain: infoq.com, Score: 46, Comments: 14 On Reddit: [5] http://goo.gl/FE4OF Original: [6] http://goo.gl/feU7U * Putting it all together -- Example project that pulls together Snap, Blaze, OpenId, IxSet, AcidState, and Sessions. Domain: self.haskell, Score: 34, Comments: 3 On Reddit: [7] http://goo.gl/huFaI Original: [8] http://goo.gl/huFaI * Invert the Inversion of Control Domain: thev.net, Score: 32, Comments: 30 On Reddit: [9] http://goo.gl/1uO5a Original: [10] http://goo.gl/89UnF * A follow up on my initial experience and why there's still something immensely attractive about Haskell Domain: binarysculpting.com, Score: 27, Comments: 19 On Reddit: [11] http://goo.gl/3RLNO Original: [12] http://goo.gl/81YF2 * Haskim -- a convenient Haskell VIM distribution Domain: github.com, Score: 25, Comments: 19 On Reddit: [13] http://goo.gl/9sJ3O Original: [14] http://goo.gl/Wq0Rq * Introducing Perdure: persistence for acyclic immutable data Domain: hackage.haskell.org, Score: 23, Comments: 12 On Reddit: [15] http://goo.gl/ACWDi Original: [16] http://goo.gl/CSi57 * Existential types and data abstraction Domain: iveselov.info, Score: 22, Comments: On Reddit: [17] http://goo.gl/K6JGl Original: [18] http://goo.gl/GBYlW * I just realized that running monads is applying a left monad action Domain: self.haskell, Score: 20, Comments: 63 On Reddit: [19] http://goo.gl/Geus4 Original: [20] http://goo.gl/Geus4 Top StackOverflow Questions * How can I recover sharing in a GADT? votes: 14, answers: 2 Read on SO: [21] http://goo.gl/I3cuW * Constructing efficient monad instances on `Set` (and other containers with constraints) using the continuation monad votes: 13, answers: 2 Read on SO: [22] http://goo.gl/Ys4Uy * Numbers as multiplicative functions (weird but entertaining) votes: 12, answers: 1 Read on SO: [23] http://goo.gl/yN8KN * Game server in Haskell votes: 10, answers: 3 Read on SO: [24] http://goo.gl/QV9de * Why doesn't sortBy take (a -> a -> Bool)? votes: 10, answers: 5 Read on SO: [25] http://goo.gl/Y7EzD * Default type instances referring to each other votes: 9, answers: 1 Read on SO: [26] http://goo.gl/6cUG7 * Applying a fixed-length-vector-function to the inital part of a longer fixed-length-vector votes: 9, answers: 2 Read on SO: [27] http://goo.gl/03KcE * Haskell: example of function of type a -> a, besides the identity votes: 9, answers: 5 Read on SO: [28] http://goo.gl/q2UDW * Stack overflow when using Haskell sort function votes: 8, answers: 2 Read on SO: [29] http://goo.gl/D31Ku * How to navigate up inside a HUET Zipper votes: 7, answers: 2 Read on SO: [30] http://goo.gl/X7dE3 * Haskell : reference to previously updated elements of list within the update function votes: 7, answers: 6 Read on SO: [31] http://goo.gl/0yRIo * Is there any way to make parsec report “shift-reduce” conflicts? votes: 7, answers: 1 Read on SO: [32] http://goo.gl/LQeDG * Haskell: how to write a monadic variadic function, with parameters using the monadic context votes: 7, answers: 1 Read on SO: [33] http://goo.gl/ThniY * Haskell parMap and parallelism votes: 7, answers: 1 Read on SO: [34] http://goo.gl/3qQHu Until next time, Daniel Santa Cruz References 1. http://newartisans.com/2012/08/parsing-with-haskell-and-attoparsec/ 2. http://www.reddit.com/r/haskell/comments/z2lir/parsing_with_haskell_and_att… 3. http://apfelmus.nfshost.com/blog/2012/08/26-frp-banana-0-7.html 4. http://www.reddit.com/r/haskell/comments/yv6ku/frp_release_of_reactivebanan… 5. http://www.infoq.com/presentations/Combinatorrent-Haskell-casestudy 6. http://www.reddit.com/r/haskell/comments/yzdyr/combinatorrent_writing_haske… 7. http://www.reddit.com/r/haskell/comments/z4iay/putting_it_all_together_exam… 8. http://www.reddit.com/r/haskell/comments/z4iay/putting_it_all_together_exam… 9. http://www.thev.net/PaulLiu/invert-inversion.html 10. http://www.reddit.com/r/haskell/comments/z4inb/invert_the_inversion_of_cont… 11. http://binarysculpting.com/2012/09/01/theres-something-about-haskell/ 12. http://www.reddit.com/r/haskell/comments/z6idz/a_follow_up_on_my_initial_ex… 13. https://github.com/jejansse/haskim 14. http://www.reddit.com/r/haskell/comments/z3orc/haskim_a_convenient_haskell_… 15. http://hackage.haskell.org/package/perdure-0.1.2 16. http://www.reddit.com/r/haskell/comments/z2sc6/introducing_perdure_persiste… 17. http://iveselov.info/posts/2012-08-30-existential-types.html 18. http://www.reddit.com/r/haskell/comments/z1ojj/existential_types_and_data_a… 19. http://www.reddit.com/r/haskell/comments/ytovd/i_just_realized_that_running… 20. http://www.reddit.com/r/haskell/comments/ytovd/i_just_realized_that_running… 21. http://stackoverflow.com/questions/12230088/how-can-i-recover-sharing-in-a-… 22. http://stackoverflow.com/questions/12183656/constructing-efficient-monad-in… 23. http://stackoverflow.com/questions/12133932/numbers-as-multiplicative-funct… 24. http://stackoverflow.com/questions/12134097/game-server-in-haskell 25. http://stackoverflow.com/questions/12152561/why-doesnt-sortby-take-a-a-bool 26. http://stackoverflow.com/questions/12199324/default-type-instances-referrin… 27. http://stackoverflow.com/questions/12221080/applying-a-fixed-length-vector-… 28. http://stackoverflow.com/questions/12230820/haskell-example-of-function-of-… 29. http://stackoverflow.com/questions/12203380/stack-overflow-when-using-haske… 30. http://stackoverflow.com/questions/12129300/how-to-navigate-up-inside-a-hue… 31. http://stackoverflow.com/questions/12144973/haskell-reference-to-previously… 32. http://stackoverflow.com/questions/12170780/is-there-any-way-to-make-parsec… 33. http://stackoverflow.com/questions/12175912/haskell-how-to-write-a-monadic-… 34. http://stackoverflow.com/questions/12224842/haskell-parmap-and-parallelism

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