- Haskell-Cafe - Haskell.org

ANN: signed-multiset-0.1
by Stefan Holdermans 25 Apr '12

25 Apr '12

I am pleased to announce the first release of signed-multiset, which implements an abstract datatype for multisets with negative membership. The package can be obtained from http://hackage.haskell.org/package/signed-multiset-0.1 As always, feedback is welcome. Cheers, Stefan signed-multiset-0.1 ------------------- Multisets (or bags) are sets in which elements may occur more than once. The number of times an element occurs in a multiset is called its multiplicity. This package provides an efficient implementation of so-called signed multisets, which generalise multisets by allowing for negative membership. That is, elements in a signed multiset can have negative multiplicities. See also: Wayne D. Blizard. Negative membership. Notre Dame Journal of Formal Logic/, 31(3):346--368, 1990.

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JSON library suggestions?
by Jeff Shaw 25 Apr '12

25 Apr '12

Hello, Up until now I've been using Aeson, but I've found that its number type isn't going to work for me. I need to use decimal numbers while avoiding conversions from and to Double, which Aeson doesn't allow. There are quite a few more JSON libraries for Haskell, which all appear to use Rational for numbers, so I'm wondering if anyone can recommend one. Thanks, Jeff

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Haskell Weekly News: Issue 224
by Daniel Santa Cruz 25 Apr '12

25 Apr '12

Welcome to issue 224 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers the week of April 15 to 21, 2012. Announcements Some of these announcements are a bit behind, for which I apologize. Better late than never... The long awaited version of cabal-install is out! [1] http://goo.gl/LlO7s Janis Voigtlander is looking for contributors for the May 2012 edition of the Haskell Comunities and Activities Report. If you have anything Haskell related that you have been working on, make sure to send Janis a note. The deadline is May 1st. [2] http://goo.gl/AW3gR Jeremy O'Donoghue announced the release of wxHaskell 0.90. "his release represents a significant milestone for us as it includes support for wxWidgets 2.9.x." [3] http://goo.gl/vTYTp Janis Voigtlander also issued a call for papers for the Haskell Symposium 2012, Copenhagen, Denmark on 13th September, 2012, directly after ICFP. [4] http://goo.gl/fR2hB Eric Kow released the 9th edition of the Parallel Haskell Digest. [5] http://goo.gl/gBIhK Quotes of the Week * TSC: The type families might have little type children * mm_freak: i'd love to have an embeddable Agda type checker and evaluator mm_freak: that would make a great scripting language for haskell programs * shachaf: You can't spell "-funsafe" without "fun" and "safe". * elliott: By the way, I find the inclusion of a package named "colour" in a section titled "Color" offensive :) * elliott: I don't think Haskell can ever hope to enter the enterprise if we can't model non-standard colourblind observers with it. * danharaj:oh hey this looks nice. Mathnerd314: every open-source math library under the sun glued together into a Python framework danharaj: nevermind o_o * elliott: What do we do with people who paste code blocks on IRC? We yell at them. * acowley: I am a bull in a math shop * elliott: I like how edwardk's answer to every question always goes "most abstract solution to the problem possible --> microoptimisation details". elliott: I swear I've seen him go from category theory to unboxed types and unsafeCoerce in a single line of IRC. * shachaf: It is a sobering thought that by the time Galois was my age, he had been dead for almost two months. Top Reddit Stories * Why do Monads Matter? (or it's Monad tutorial season again) Domain: cdsmith.wordpress.com, Score: 64, Comments: 27 On Reddit: [6] http://goo.gl/DCJYV Original: [7] http://goo.gl/8glhF * Ur/Web records: can we apply lessons from them to Haskell? Domain: blog.ezyang.com, Score: 53, Comments: On Reddit: [8] http://goo.gl/9m3Sw Original: [9] http://goo.gl/dNcET * Blank Canvas - a new Haskell graphics library based on HTML5 and <canvas> Domain: ittc.ku.edu, Score: 42, Comments: 10 On Reddit: [10] http://goo.gl/H3SMB Original: [11] http://goo.gl/if7kG * Client Side Yesod, an FRP-inspired approach Domain: yesodweb.com, Score: 41, Comments: 44 On Reddit: [12] http://goo.gl/gECTq Original: [13] http://goo.gl/Rn0LS * Understanding Haskell Kinds Domain: softwaresimply.blogspot.com, Score: 38, Comments: 18 On Reddit: [14] http://goo.gl/XxiwQ Original: [15] http://goo.gl/xaqDM * Adding SIMD Support to Data Parallel Haskell Domain: ghc-simd.blogspot.co.uk, Score: 35, Comments: 8 On Reddit: [16] http://goo.gl/R8M9L Original: [17] http://goo.gl/ZeJ7e * Working With HTML In Haskell Domain: adit.io, Score: 31, Comments: 24 On Reddit: [18] http://goo.gl/4NMBc Original: [19] http://goo.gl/EOvM1 * Descending the level ladder Domain: monoidal.blogspot.com, Score: 26, Comments: 13 On Reddit: [20] http://goo.gl/9IYZL Original: [21] http://goo.gl/TJm0D * Why is Haskell so large? Domain: self.haskell, Score: 25, Comments: 29 On Reddit: [22] http://goo.gl/KQnbj Original: [23] http://goo.gl/KQnbj * Parallel Haskell Digest 9: GSoC, STM, SIMD, and the Downfall of Imperative Programming? Domain: well-typed.com, Score: 25, Comments: 1 On Reddit: [24] http://goo.gl/Z5bF3 Original: [25] http://goo.gl/eLnVs * blaze-html 0.5 released Domain: jaspervdj.be, Score: 25, Comments: 3 On Reddit: [26] http://goo.gl/7XtMD Original: [27] http://goo.gl/RkbR7 * Four Tips for New Haskell Programmers Domain: softwaresimply.blogspot.com, Score: 22, Comments: 72 On Reddit: [28] http://goo.gl/GQ4O1 Original: [29] http://goo.gl/Ye57L * Check for interest - an argument/option parser using type level strings Domain: self.haskell, Score: 22, Comments: 13 On Reddit: [30] http://goo.gl/eOtE5 Original: [31] http://goo.gl/eOtE5 * New Cabal feature: cabal bench Domain: blog.johantibell.com, Score: 22, Comments: 3 On Reddit: [32] http://goo.gl/ClkjJ Original: [33] http://goo.gl/sA3aD Top StackOverflow Questions * The Pause monad votes: 20, answers: 5 Read on SO: [34] http://goo.gl/DNIo1 * To what extent are macros “functions in reverse?” votes: 15, answers: 6 Read on SO: [35] http://goo.gl/ZoEht * Curry-Howard isomorphism votes: 13, answers: 3 Read on SO: [36] http://goo.gl/1pzKd * How does Djinn work? votes: 12, answers: 3 Read on SO: [37] http://goo.gl/RnEny * How is co-recursion handled? votes: 12, answers: 2 Read on SO: [38] http://goo.gl/DXtj1 * Distinction between typeclasses MonadPlus, Alternative, and Monoid? votes: 11, answers: 1 Read on SO: [39] http://goo.gl/4LZd7 * Why can't Existential Types use record syntax? votes: 11, answers: 2 Read on SO: [40] http://goo.gl/4Gn96 * Given a Haskell type signature, is it possible to generate the code automatically? votes: 11, answers: 4 Read on SO: [41] http://goo.gl/7Xff3 * Is it possible to force a type to a class in Haskell? votes: 10, answers: 6 Read on SO: [42] http://goo.gl/SeFpb * Haskell concurrency - is forkIO really nondeterministic? votes: 10, answers: 2 Read on SO: [43] http://goo.gl/z2q9Y * Where to find programming exercises for applicative functors? votes: 9, answers: 4 Read on SO: [44] http://goo.gl/CXOYU Until next time, Daniel Santa Cruz References 1. http://permalink.gmane.org/gmane.comp.lang.haskell.general/19239 2. http://www.haskell.org/pipermail/haskell/2012-April/023244.html 3. http://permalink.gmane.org/gmane.comp.lang.haskell.wxhaskell.general/1178 4. http://permalink.gmane.org/gmane.comp.science.types.announce/2949 5. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/97851 6. http://cdsmith.wordpress.com/2012/04/18/why-do-monads-matter/ 7. http://www.reddit.com/r/haskell/comments/sfvbu/why_do_monads_matter_or_its_… 8. http://blog.ezyang.com/2012/04/how-urweb-records-work-and-what-it-might-mea… 9. http://www.reddit.com/r/haskell/comments/sjoh5/urweb_records_can_we_apply_l… 10. http://ittc.ku.edu/csdl/fpg/Tools/BlankCanvas 11. http://www.reddit.com/r/haskell/comments/seppr/blank_canvas_a_new_haskell_g… 12. http://www.yesodweb.com/blog/2012/04/client-side 13. http://www.reddit.com/r/haskell/comments/sm72n/client_side_yesod_an_frpinsp… 14. http://softwaresimply.blogspot.com/2012/04/less-travelled-monad-tutorial-pa… 15. http://www.reddit.com/r/haskell/comments/scagx/understanding_haskell_kinds/ 16. http://ghc-simd.blogspot.co.uk/2012/04/adding-simd-support-to-data-parallel… 17. http://www.reddit.com/r/haskell/comments/sfxck/adding_simd_support_to_data_… 18. http://adit.io/posts/2012-04-14-working_with_HTML_in_haskell.html 19. http://www.reddit.com/r/haskell/comments/sbxhb/working_with_html_in_haskell/ 20. http://monoidal.blogspot.com/2012/04/descending-level-ladder.html 21. http://www.reddit.com/r/haskell/comments/scq1q/descending_the_level_ladder/ 22. http://www.reddit.com/r/haskell/comments/sb80y/why_is_haskell_so_large/ 23. http://www.reddit.com/r/haskell/comments/sb80y/why_is_haskell_so_large/ 24. http://www.well-typed.com/blog/65 25. http://www.reddit.com/r/haskell/comments/sjbgv/parallel_haskell_digest_9_gs… 26. http://jaspervdj.be/posts/2012-04-21-blaze-html-0.5.html 27. http://www.reddit.com/r/haskell/comments/sl6ps/blazehtml_05_released/ 28. http://softwaresimply.blogspot.com/2012/04/four-tips-for-new-haskell-progra… 29. http://www.reddit.com/r/haskell/comments/sarkz/four_tips_for_new_haskell_pr… 30. http://www.reddit.com/r/haskell/comments/sbpmz/check_for_interest_an_argume… 31. http://www.reddit.com/r/haskell/comments/sbpmz/check_for_interest_an_argume… 32. http://blog.johantibell.com/2012/04/cabal-bench.html 33. http://www.reddit.com/r/haskell/comments/sfhv3/new_cabal_feature_cabal_benc… 34. http://stackoverflow.com/questions/10236953/the-pause-monad 35. http://stackoverflow.com/questions/10249110/to-what-extent-are-macros-funct… 36. http://stackoverflow.com/questions/10212660/curry-howard-isomorphism 37. http://stackoverflow.com/questions/10217931/how-does-djinn-work 38. http://stackoverflow.com/questions/10257326/how-is-co-recursion-handled 39. http://stackoverflow.com/questions/10167879/distinction-between-typeclasses… 40. http://stackoverflow.com/questions/10192663/why-cant-existential-types-use-… 41. http://stackoverflow.com/questions/10205793/given-a-haskell-type-signature-… 42. http://stackoverflow.com/questions/10211664/is-it-possible-to-force-a-type-… 43. http://stackoverflow.com/questions/10247555/haskell-concurrency-is-forkio-r… 44. http://stackoverflow.com/questions/10239630/where-to-find-programming-exerc…

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"desactivate" my Show instance implementations temporarily
by TP 25 Apr '12

25 Apr '12

Hello, I have a module where I have made several types as instances of the Show typeclass. For debugging purpose, I would like to use the default implementation for Show (the one obtained when using "deriving", which shows all the constructors). Is there some option to do that, or have I to comment all the Show instances of my code, and add "Show" in "deriving (...)" for each of my types? If this is the only possibility, is there some script around here to do that automatically? Thanks in advance, TP

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Multi-site haddock documentation with proper links?
by Ryan Newton 25 Apr '12

25 Apr '12

Hello cafe, For various reasons, some packages don't build documentation on hackage: http://hackage.haskell.org/package/accelerate Therefore I want to locally install documentation for a set of packages like this and host them on a separate website. I want all of these ~ten packages' haddock documentation to be properly interlinked with eachother, but also to link to Hackage for types and classes defined in other modules. Is this possible? Hackage haddocks are all interlinked, but that is simply because hackage is one giant local install, right? If it's not possible (and it seems not) do any haddock devs have pointers on how to implement this? Thanks, -Ryan P.S. Someone recommended to me the following simple hack -- just use sed to rewrite the links after haddock generates the html. I think I'll do that for the time being unless someone has a better suggestion.

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atomicModifyMutVar and casMutVar
by Thomas Bereknyei 25 Apr '12

25 Apr '12

I have seen some push to take advantage of the new primop casMutVar, yet I see that atomicModifyMutVar hasn't been used yet either. For example, modifySTRef is just a read followed by a write. I've been unable to create a version that does not allocate with something as simple as modifySTRef ref (+1). There is a package Data.Ref.Unboxed that allows ST to use an unboxed STURef, but even though I can see the Core using Int#, any use of modifySTURef, or any version I've been able to make will excessively box/rebox. Should I instead be using something like modifySTURef ref (GHC.Prim.+#) or can this be automatically done by the compiler?

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static linking with ghc?
by Johannes Waldmann 24 Apr '12

24 Apr '12

Hi. I want to produce a statically linked executable. I am trying 'ghc --make -fforce-recomp -static -optl-static Main' but it gives lots of errors like (.text+0xfa): undefined reference to `pthread_mutex_unlock' collect2: ld returned 1 exit status A similar thing is mentioned here (see Caveat) http://www.haskell.org/haskellwiki/Web/Literature/Static_linking The ghc user guide talks a great length about shared libs http://www.haskell.org/ghc/docs/latest/html/users_guide/using-shared-libs.h… but I don't see anything on how to switch this off. - J.W.

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I am having trouble with the type declaration for creating an identity matrix.
by KC 24 Apr '12

24 Apr '12

initIdentityMat :: Int -> ST s (STUArray s (Int,Int) ((Int, Int), Double)) initIdentityMat m = newListArray ((1,m),(1,m)) ([((i,j), if i == j then 1.0 else 0.0) | i <- [1..m], j <- [1..m]] :: [((Int,Int), Double)]) Doesn't seem to compile, nor do minor variations of the type declaration. -- -- Regards, KC

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Is protocol-buffers package maintainer reachable?
by Paul Graphov 24 Apr '12

24 Apr '12

Hello Cafe! I am using protocol-buffers and hprotoc packages but they fail to compile with recent GHC due to trivial errors. Hackage names Christopher Edward Kuklewicz as their maintainer. I've sent him patches more than a month ago but neiter they were applied nor I got any response. It's quite inconvenient to keep patched versions all the time. Does anybody know if he is still interested in maintaining those packages? Is it possible to contact him? And what should I do if he is unreachable? Thanks! Links: http://hackage.haskell.org/package/protocol-buffers http://hackage.haskell.org/package/hprotoc

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Offer to mirror Hackage
by Dan Knapp 24 Apr '12

24 Apr '12

With Hackage down, now seemed like a good time to push this issue again. It's such an important site to us that it's really rather a shame there are no mirrors of it. I have a personal-and-business server in a data center in Newark, with a fair chunk of bandwidth, which I'd like to offer for a permanent mirror. Is there interest in this? Who do I need to talk to for it to happen? Strategy-wise, I think the best approach is round-robin DNS, since that's transparent to the end user - everything would still appear at the URL it's at now, but behind-the-scenes magic would let things keep working when one or the other site is down. I haven't personally set up such a system before but I'm willing to take on the burden of figuring it out. So I have a better idea of what I'm signing up for, can anyone tell me how much disk space and how much bandwidth per month Hackage uses? I have a fair chunk of both, as I say, but I'd like to know in advance to ensure that things go smoothly. As for what I'd want in return for this, really nothing. I wouldn't say no to an unobtrusive mention somewhere on the site, but I'd be happy just knowing I'd given something back to the Haskell community, which has given a lot to me. -- Dan Knapp "An infallible method of conciliating a tiger is to allow oneself to be devoured." (Konrad Adenauer)

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