October 2013 - Haskell-Cafe

[ZipList Monad] Final answer?
by Etsuji Nakai 18 Oct '13

18 Oct '13

Hi, I found a few interesting discussions on how to construct ZipList Monad in the past (around 2009). For example, http://www.haskell.org/pipermail/haskell-cafe/2009-April/059079.html But there seems no final answer to it. After a good discussion with one of my Haskell friends, we finally came up with the following one: import Control.Monad newtype MyZipList a = MyZipList [a] deriving (Show) getBase :: MyZipList a -> [a] getBase (MyZipList xs) = xs instance Monad MyZipList where return x = MyZipList $ repeat x m >>= f = MyZipList $ bind (getBase m) (fmap getBase f) where bind :: [a] -> (a -> [b]) -> [b] bind [] f = [] bind (x:xs) f = case f x of [] -> [] y:_ -> y : bind xs (fmap tailOrNil f) tailOrNil :: [b] -> [b] tailOrNil [] = [] tailOrNil (x:xs) = xs This is fairly simple and looks to work with variable length lists. Do you think this could be the final answer? - Etsuji

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Building examples with Cabal
by Sven Panne 18 Oct '13

18 Oct '13

Is there a way to build examples in a Haskell package with Cabal without actually running them? "cabal test" and "cabal benchmark" don't really do what I want, I just want to check if e.g. all GLUT examples in https://github.com/haskell-opengl/GLUT/tree/master/examples still build after some API changes. Another requirement would be parallel builds, I want to actually use the 32 cores I have under my desk. ;-) Currently I use a recursive "make" infrastructure (https://github.com/haskell-opengl/GLUT/blob/master/examples/Makefile) which works OK, but it is quite a hack, is partly incorrect and, well, needs "make".

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Re: [Haskell-cafe] Xcode 5 support for GHC iOS
by Luke Iannini 18 Oct '13

18 Oct '13

Hi Dominick! Yes, this should work swimmingly on the 5S in 32bit mode. We'll have to wait for Apple to merge their Arm64 patches [1] before we can add full 64-bit support (I can do the 64bit simulator right now though : )). (though I just saw this! [2]) Cheers Luke [1] http://lists.cs.uiuc.edu/pipermail/llvmdev/2013-September/065480.html [2] http://lists.cs.uiuc.edu/pipermail/llvmdev/2013-September/065913.html On Wed, Oct 16, 2013 at 8:16 AM, Dominick Samperi <djsamperi(a)gmail.com>wrote: > Will this work with the new iPhone 5 S (64 bit ARM)? I assume that > it will work by running in 32 bit mode (requiring both 64 and 32 bit > libs to be loaded), but I'm not sure... > > Thanks, > Dominick > > > On Mon, Oct 14, 2013 at 3:48 PM, Luke Iannini <lukexipd(a)gmail.com> wrote: > >> Hi all, >> >> Just wanted to let you know I've finished updating GHC iOS to support >> Xcode 5. The new scripts are at >> https://github.com/ghc-ios/ghc-ios-scripts/tree/xcode5 and you'll find >> updated instructions at >> http://ghc.haskell.org/trac/ghc/wiki/Building/CrossCompiling/iOS . >> >> Please let me know if you have any trouble! >> Cheers >> Luke >> >> _______________________________________________ >> ghc-devs mailing list >> ghc-devs(a)haskell.org >> http://www.haskell.org/mailman/listinfo/ghc-devs >> >> >

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installing glib-0.12.4 on Mac
by Kazu Yamamoto 17 Oct '13

17 Oct '13

Hi, When I tried to install glib-0.12.3 on OS X 10.8.5 with GHC 7.6.3, I got the following error: ---- 1 of 2] Compiling Gtk2HsSetup ( Gtk2HsSetup.hs, dist/setup-wrapper/Gtk2HsSetup.o ) [2 of 2] Compiling Main ( SetupMain.hs, dist/setup-wrapper/Main.o ) Linking dist/setup-wrapper/setup ... Configuring glib-0.12.4... Building glib-0.12.4... Preprocessing library glib-0.12.4... gtk2hsC2hs: Error in C header file. /usr/include/dirent.h:147: (column 10) [FATAL] >>> Syntax error! The symbol `^' does not fit here. Failed to install glib-0.12.4 ---- I believe I could install it on 31 July 2013 and I don't think I changed anything. Does anyone know how to fix this? --Kazu

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Haskell.org committee self-nomination time
by Jason Dagit 17 Oct '13

17 Oct '13

Dear Haskellers, Another year of the haskell.org committee is drawing to a close and it is therefore time to seek replacements for those members whose term is expiring. This year three members are retiring, Edward Z. Yang, Vo Minh Thu, and Mark Lentczner. The rest of the committee would like to thank them for their excellent service. To nominate yourself, please send an e-mail to committee at haskell.org by 29 October 2013. The retiring members are eligible to re-nominate themselves. Please feel free to include any information about yourself that you think will help us to make a decision. Being a member of the committee does not require a significant amount of time, but committee members should aim to be responsive during discussions when the committee is called upon to make a decision. Strong leadership, communication, and judgement are very important characteristics for committee members. The role is about setting policy, providing direction/guidance for the Haskell.org infrastructure, planning for the long term, and being fiscally responsible with the Haskell.org funds (and donations). As overseers for policy regarding the open source side of Haskell, committee members must also be able to set aside personal or business related bias and make decisions with the good of the open source Haskell community in mind. More details about the committee's roles and responsibilities are on http://www.haskell.org/haskellwiki/Haskell.org_committee If you have any questions about the process, please feel free to e-mail us at committee at haskell.org or to contact one of us individually. Regards, Jason

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Eternal Compatibility in Theory
by Corentin Dupont 17 Oct '13

17 Oct '13

Hi Café, I've read the Eternal Compatibility in Theory article [1], is anyone actually using it? I don't see it discussed very much on the internet. My biggest concern about it is that it would be a real pollution in the code, because you must import every module with its version number, i.e. * * *import Data.Maybe_1* instead of * **import Data.Maybe* Thus poluting a lot with version numbers, which are not relevant to what the source code should aim at: help the reader understand it. Secondly, does it means that, as the developper of a package, I have to leave all the previous versions of a module in that package? I.e: Maybe_1.hs, Maybe_2.hs would have to stay in my package? This seems to be very polluting and redundant. So the proposition seems to be "versionning and dependency management are a problem, so let's remove the problem by leaving all previous versions in the package". Did I misunderstood something? Cheers, Corentin [1] http://www.haskell.org/haskellwiki/The_Monad.Reader/Issue2/EternalCompatibi…

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Embarrassed Haskeller -- why is Read so bad? What are alternatives?
by Ryan Newton 17 Oct '13

17 Oct '13

We have great tools for [de]serializing both to binary and to JSON (binary, cereal, json, aeson, etc). But we have rather weak support for [de]serializing to human readable Haskell-ish external formats. Read instances are both (1) slow, because they take Strings, and (2) they don't allow sensible error messages! (Historical decision choosing Maybe rather than Either.) Right now I'm working on a project with a Racketeer who is trying to read a 6000 line file as a single list data structure. The derived Read instance is just telling him it won't parse, with NO error information, line number etc. To someone used to Scheme readers, that's rather poor. I wish I had something better to tell him! I am not aware of a library to recommend other than switching to JSON format on disk. OR manually kludging together a parsing hack that, for example, puts one element of the list on each line and makes much smaller calls to "read". Argh!, -Ryan

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Haskell Weekly News: Issue 283
by Daniel Santa Cruz 16 Oct '13

16 Oct '13

Welcome to issue 283 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers the week of October 06 to 12, 2013. Quotes of the Week * elliott: haskell programs allocate a lot because they can't do much else * spj: [on pointfree style] It has a certain eccentric charm all of its own. * acowley: When we pick a random number, we stick to it. Top Reddit Stories * Simon Peyton Jones on Lenses at the Haskell eXchange Skillscast now available! Domain: skillsmatter.com, Score: 127, Comments: 107 On Reddit: [1] http://goo.gl/V6J6dR Original: [2] http://goo.gl/Kc1zEf * Why I don’t like the lens library Domain: fvisser.nl, Score: 99, Comments: 104 On Reddit: [3] http://goo.gl/Xz6p6C Original: [4] http://goo.gl/ZzxSOU * Cartesian Closed Comic #23: Picking a lens library Domain: ro-che.info, Score: 85, Comments: 8 On Reddit: [5] http://goo.gl/mXXUQw Original: [6] http://goo.gl/Bi2UIW * The core flaw of pipes and conduit Domain: yesodweb.com, Score: 45, Comments: 101 On Reddit: [7] http://goo.gl/tfSZ2Z Original: [8] http://goo.gl/5CpF2I * How to reimplement the conduit parsing API in pipes Domain: haskellforall.com, Score: 43, Comments: 16 On Reddit: [9] http://goo.gl/xQ9f93 Original: [10] http://goo.gl/iqFxfs * pipes resource problems Domain: yesodweb.com, Score: 40, Comments: 74 On Reddit: [11] http://goo.gl/9FpIwz Original: [12] http://goo.gl/tj0LbW * Beginners cheatsheet to the lens library Domain: haskell.org, Score: 40, Comments: 59 On Reddit: [13] http://goo.gl/I2i2or Original: [14] http://goo.gl/Y8znDQ * Demo: Ariadne, go-to-definition for Haskell Domain: youtube.com, Score: 39, Comments: 35 On Reddit: [15] http://goo.gl/KC1D5m Original: [16] http://goo.gl/0lqLPh * Do Extraterrestrials Use Functional Programming? Domain: justtesting.org, Score: 39, Comments: 39 On Reddit: [17] http://goo.gl/FZos1f Original: [18] http://goo.gl/RaIEZF * Haskell for all: Manual proofs for the `pipes` laws Domain: haskellforall.com, Score: 37, Comments: 55 On Reddit: [19] http://goo.gl/rhLmBC Original: [20] http://goo.gl/cmiDln * Unique PDFs linked in #haskell Domain: ircbrowse.net, Score: 36, Comments: 13 On Reddit: [21] http://goo.gl/mNNkM7 Original: [22] http://goo.gl/7Sj2si * Andres Löh on free monads Domain: skillsmatter.com, Score: 36, Comments: 15 On Reddit: [23] http://goo.gl/2sRcxC Original: [24] http://goo.gl/fvLiRn * Simpler conduit core (aka part 3 of 3) Domain: fpcomplete.com, Score: 36, Comments: 23 On Reddit: [25] http://goo.gl/V3FutZ Original: [26] http://goo.gl/4qYkRj * Proposal for Applicative do-notation Domain: ghc.haskell.org, Score: 36, Comments: 50 On Reddit: [27] http://goo.gl/skxmph Original: [28] http://goo.gl/st8iOp * So I (kind of) made a Haskell clone of the business card Ray Tracer Domain: github.com, Score: 35, Comments: 14 On Reddit: [29] http://goo.gl/tZZMnH Original: [30] http://goo.gl/G1hzjt * Call to Action - Fay FFI Bindings for AngularJS Domain: haskell.org, Score: 35, Comments: 16 On Reddit: [31] http://goo.gl/en6th1 Original: [32] http://goo.gl/g5T8TJ * The Haxl project at Facebook: concise, efficient access to diverse data sources Domain: skillsmatter.com, Score: 34, Comments: 9 On Reddit: [33] http://goo.gl/vEKNKb Original: [34] http://goo.gl/HKaMmn * Rethinking Supercompilation [PDF] Domain: community.haskell.org, Score: 34, Comments: 17 On Reddit: [35] http://goo.gl/IVwvdi Original: [36] http://goo.gl/BuaaXW * Musings on Lens Domain: gist.io, Score: 31, Comments: 9 On Reddit: [37] http://goo.gl/akld2Z Original: [38] http://goo.gl/CdPtlT Top StackOverflow Questions * Functions of possibly cyclic data structures votes: 12, answers: 1 Read on SO: [39] http://goo.gl/SBPV2t * How can I improve my understanding of the Haskell Type system? votes: 11, answers: 2 Read on SO: [40] http://goo.gl/HLsynN * Haskell: how to tell hlint not to: `Warning: Use string literal` votes: 7, answers: 1 Read on SO: [41] http://goo.gl/pf5d5O * How are uncurry and fanin related in category theory? votes: 7, answers: 1 Read on SO: [42] http://goo.gl/mo9150 * Haskell Iterate over 2d list, filter, output 1d list votes: 7, answers: 6 Read on SO: [43] http://goo.gl/h47C9e * Haskell why does “Num x” require “Show x”? votes: 7, answers: 3 Read on SO: [44] http://goo.gl/ORddsf * How to avoid creating an orphan FromJSON instance for Data.Tree votes: 7, answers: 1 Read on SO: [45] http://goo.gl/5MAI2k * State Monad with multiple state values votes: 6, answers: 3 Read on SO: [46] http://goo.gl/iuutId * Difference between Print and putStrLn in Haskell votes: 6, answers: 2 Read on SO: [47] http://goo.gl/GqUunm Until next time, [48]+Daniel Santa Cruz References 1. http://skillsmatter.com/podcast/scala/lenses-compositional-data-access-and-… 2. http://www.reddit.com/r/haskell/comments/1o1z8x/simon_peyton_jones_on_lense… 3. http://fvisser.nl/post/2013/okt/11/why-i-dont-like-the-lens-library.html 4. http://www.reddit.com/r/haskell/comments/1o6iqs/why_i_dont_like_the_lens_li… 5. http://ro-che.info/ccc/23 6. http://www.reddit.com/r/haskell/comments/1obeom/cartesian_closed_comic_23_p… 7. http://www.yesodweb.com/blog/2013/10/core-flaw-pipes-conduit 8. http://www.reddit.com/r/haskell/comments/1o1ink/the_core_flaw_of_pipes_and_… 9. http://www.haskellforall.com/2013/10/how-to-reimplement-conduit-parsing-api… 10. http://www.reddit.com/r/haskell/comments/1o3viw/how_to_reimplement_the_cond… 11. http://www.yesodweb.com/blog/2013/10/pipes-resource-problems 12. http://www.reddit.com/r/haskell/comments/1nw7ji/pipes_resource_problems/ 13. http://www.haskell.org/haskellwiki/LensBeginnersCheatsheet 14. http://www.reddit.com/r/haskell/comments/1oa9qx/beginners_cheatsheet_to_the… 15. https://www.youtube.com/watch?v=-sbGijbhxAc 16. http://www.reddit.com/r/haskell/comments/1nvauj/demo_ariadne_gotodefinition… 17. http://justtesting.org/post/63457249417/here-is-the-video-of-my-yow-lambda-… 18. http://www.reddit.com/r/haskell/comments/1nz5j5/do_extraterrestrials_use_fu… 19. http://www.haskellforall.com/2013/10/manual-proofs-for-pipes-laws.html 20. http://www.reddit.com/r/haskell/comments/1nw7yt/haskell_for_all_manual_proo… 21. http://ircbrowse.net/pdfs/haskell/unique 22. http://www.reddit.com/r/haskell/comments/1o23nf/unique_pdfs_linked_in_haske… 23. http://skillsmatter.com/podcast/scala/monads-for-free 24. http://www.reddit.com/r/haskell/comments/1o38fa/andres_l%C3%B6h_on_free_mon… 25. https://www.fpcomplete.com/user/snoyberg/blog-posts/simpler-conduit-core 26. http://www.reddit.com/r/haskell/comments/1o494w/simpler_conduit_core_aka_pa… 27. http://ghc.haskell.org/trac/ghc/wiki/ApplicativeDo 28. http://www.reddit.com/r/haskell/comments/1o7lpm/proposal_for_applicative_do… 29. https://github.com/RommelVR/RayTracer 30. http://www.reddit.com/r/haskell/comments/1nuhze/so_i_kind_of_made_a_haskell… 31. http://www.haskell.org/pipermail/haskell-cafe/2013-October/218522.html 32. http://www.reddit.com/r/haskell/comments/1o4x3m/call_to_action_fay_ffi_bind… 33. http://skillsmatter.com/podcast/home/simon-marlow 34. http://www.reddit.com/r/haskell/comments/1o2mqe/the_haxl_project_at_faceboo… 35. http://community.haskell.org/~ndm/temp/supero.pdf 36. http://www.reddit.com/r/haskell/comments/1o8ksw/rethinking_supercompilation… 37. http://gist.io/6923187 38. http://www.reddit.com/r/haskell/comments/1o63ww/musings_on_lens/ 39. http://stackoverflow.com/questions/19337153/functions-of-possibly-cyclic-da… 40. http://stackoverflow.com/questions/19247753/how-can-i-improve-my-understand… 41. http://stackoverflow.com/questions/19237695/haskell-how-to-tell-hlint-not-t… 42. http://stackoverflow.com/questions/19262581/how-are-uncurry-and-fanin-relat… 43. http://stackoverflow.com/questions/19308845/haskell-iterate-over-2d-list-fi… 44. http://stackoverflow.com/questions/19327792/haskell-why-does-num-x-require-… 45. http://stackoverflow.com/questions/19336569/how-to-avoid-creating-an-orphan… 46. http://stackoverflow.com/questions/19227418/state-monad-with-multiple-state… 47. http://stackoverflow.com/questions/19288652/difference-between-print-and-pu… 48. https://plus.google.com/105107667630152149014/about

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Sublime Text
by Graham Berks 16 Oct '13

16 Oct '13

Anyone using sublime haskell with sublime repl and have the cabal integration working ? >From what I understand, you can get ghci loaded with the modules / reps from the cabal file. But I can't seem to get this to work. Thanks

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Announce: HDBI-1.3 and friends
by Alexey Uimanov 16 Oct '13

16 Oct '13

Hello haskellers! HDBI is the fork of HDBC but reworked. It supports SQlite3 and Postgresql for now. It also supports streaming with coduits. There is TH deriving mechanism to map database rows to Haskell structures and back. HDBI is trying to become simple but still powerfull and flexible database interface. It must be suitable to become the common RDBMS interface for higher level interfaces like persistent or haskelldb. The documentation is not very good, while I have no enough time to make some. In this version changed typeclass signatures of Connection and Statement. Now methods `run` and `execute` get any instance of `ToRow` and method `fetch` return an instance of `FromRow`. Note that [SqlValue] is also an instance of `FromRow` and `ToRow` typeclasses so you do not loose the control. Methods `fromRow` and `toRow` for [SqlValue] are just `id`. SQlite and Postgresql drivers are fixed as well as hdbi-conduit. There is also new helper functions, like `onei :: Integer -> [SqlValue]` which helps you to execute queries with one parameter or execute many queries consistinf of one parameter. Prelude Database.HDBI Database.HDBI.SQlite> :set -XScopedTypeVariables Prelude Database.HDBI Database.HDBI.SQlite> :set -XOverloadedStrings Prelude Database.HDBI Database.HDBI.SQlite> c <- connectSqlite3 ":memory:" Prelude Database.HDBI Database.HDBI.SQlite> runRaw c "create table test(val integer)" Prelude Database.HDBI Database.HDBI.SQlite> withTransaction c $ runMany c "insert into test(val) values (?)" $ map one [1..1000] <interactive>:7:76: Warning: Defaulting the following constraint(s) to type `Integer' ......... Prelude Database.HDBI Database.HDBI.SQlite> r :: (Maybe Integer) <- runFetchOne c "select sum(val) from test" () Prelude Database.HDBI Database.HDBI.SQlite> r Just 500500 Note here that the empty set is used as a parameter of query in `runFetchOne`. Empty set is an instance of `FromRow` and `ToRow` and return an empty list of [SqlValue]. Use empty list as a parameters is bad idea, because we could instantiate some another list of things, suppose the [Integer] as `FromRow` and `ToRow` instance. So it would lead to ambigous type because [SqlValue] is also a list instantiating `FromRow` and `ToRow`.

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