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Haskell Weekly News: Issue 260
by Daniel Santa Cruz 01 Mar '13

01 Mar '13

Welcome to issue 260 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers the week of February 17 to 23, 2013. Quotes of the Week * danharaj: zygohistobfuscatory maintainomorphism * merijn: after a week you can delete 80% of your code and replace it with whatever edwardk wrote that day ;-) * merijn: If Oleg is the unit of type hackery I propose Edward as the unit of haskell productivity. * edwardk: the merijn is the unit for the number of distinct units you've named * elliott: If you encounter an edwardk in the wild: nod reassuringly when he talks about something you understand. Under NO circumstances EVER give your GitHub account name Top Reddit Stories * An awesome Haskell Valentines card, from my non-programmer girlfriend. Domain: i.imgur.com, Score: 127, Comments: 32 On Reddit: [1] http://goo.gl/5Cxwr Original: [2] http://goo.gl/BeksW * Announcing SmallCheck 1.0 Domain: ro-che.info, Score: 61, Comments: 16 On Reddit: [3] http://goo.gl/R0gvO Original: [4] http://goo.gl/7b5Dq * Intro to FRP and purely functional games: live-coding the basics of Mario in ~30 lines in Elm [video] Domain: ustream.tv, Score: 50, Comments: 12 On Reddit: [5] http://goo.gl/E22PW Original: [6] http://goo.gl/q7r8e * Reflections After a Hard Day in Haskell GUI Land Domain: fluffynukeit.com, Score: 49, Comments: 53 On Reddit: [7] http://goo.gl/xQv8i Original: [8] http://goo.gl/0hvT6 * Duncan Coutts on Parallelism and Concurrency with Haskell, Distributed Programming with Cloud Haskell Domain: infoq.com, Score: 44, Comments: 5 On Reddit: [9] http://goo.gl/jU9EH Original: [10] http://goo.gl/UkRDk * A Game of Type-Safe Tic-Tac-Toe Domain: github.com, Score: 42, Comments: 20 On Reddit: [11] http://goo.gl/SrIEx Original: [12] http://goo.gl/dFIyd * The Algebra of Algebraic Data Types, Part 3 Domain: chris-taylor.github.com, Score: 36, Comments: 7 On Reddit: [13] http://goo.gl/NQI8S Original: [14] http://goo.gl/CPkiV * Write Yourself a Haskell... in Lisp Domain: gergo.erdi.hu, Score: 36, Comments: 3 On Reddit: [15] http://goo.gl/YqdSl Original: [16] http://goo.gl/E3yzO * Overloading record fields with Lens Domain: statusfailed.com, Score: 31, Comments: 19 On Reddit: [17] http://goo.gl/oF7zN Original: [18] http://goo.gl/SOEz4 * On partial functions in Idris Domain: edwinb.wordpress.com, Score: 29, Comments: 3 On Reddit: [19] http://goo.gl/0HquS Original: [20] http://goo.gl/OaO2r * Who's using Haskell commercially? New collection of real-world case studies from FP Complete. Domain: fpcomplete.com, Score: 26, Comments: 12 On Reddit: [21] http://goo.gl/IM2rb Original: [22] http://goo.gl/zsf4c * Making 'Super Nario Bros.' in Haskell Domain: youtube.com, Score: 26, Comments: 11 On Reddit: [23] http://goo.gl/2Hg7o Original: [24] http://goo.gl/9Bb5t Top StackOverflow Questions * Why is there no implicit parallelism in Haskell? votes: 29, answers: 4 Read on SO: [25] http://goo.gl/n6VkF * Why is (a,b,c,d) not sugar for (a,(b,(c,(d,()))))? votes: 26, answers: 2 Read on SO: [26] http://goo.gl/aW6K2 * How can I understand “(.) . (.)”? votes: 21, answers: 5 Read on SO: [27] http://goo.gl/kqbcO * Are there any advantages of using Rank2Types in favor of RankNTypes? votes: 18, answers: 2 Read on SO: [28] http://goo.gl/V5naQ * What's the closest thing to Haskell's typeclasses in OCaml? votes: 16, answers: 4 Read on SO: [29] http://goo.gl/AWvgl * Why does ghci give me a type for “1 ++ 2” instead of ragequitting? votes: 16, answers: 2 Read on SO: [30] http://goo.gl/66Pti * Is (>>) supposed to discard all left-side output? votes: 11, answers: 2 Read on SO: [31] http://goo.gl/wvnLJ * Find inferred type for local function votes: 11, answers: 3 Read on SO: [32] http://goo.gl/WFCz1 * STUArray s i e - space leak only when i == Int? votes: 11, answers: 2 Read on SO: [33] http://goo.gl/fbyPE * Connecting to the System GHC votes: 10, answers: 1 Read on SO: [34] http://goo.gl/FGVN5 * Correctness of implicit lifting votes: 10, answers: 2 Read on SO: [35] http://goo.gl/5s8pR Until next time, +Daniel Santa Cruz References 1. http://i.imgur.com/P0d7v7z.jpg 2. http://www.reddit.com/r/haskell/comments/18q510/an_awesome_haskell_valentin… 3. http://ro-che.info/articles/2013-02-19-smallcheck.html 4. http://www.reddit.com/r/haskell/comments/18uhfy/announcing_smallcheck_10/ 5. http://www.ustream.tv/recorded/29330499 6. http://www.reddit.com/r/haskell/comments/190n1t/intro_to_frp_and_purely_fun… 7. http://fluffynukeit.com/2013/02/reflections-after-a-hard-day-in-haskell-gui… 8. http://www.reddit.com/r/haskell/comments/18p0nu/reflections_after_a_hard_da… 9. http://www.infoq.com/interviews/coutts-haskell 10. http://www.reddit.com/r/haskell/comments/18zvk2/duncan_coutts_on_parallelis… 11. https://github.com/leonidas/codeblog/blob/master/2013/2013-02-19-typesafe-t… 12. http://www.reddit.com/r/haskell/comments/18tys6/a_game_of_typesafe_tictacto… 13. http://chris-taylor.github.com/blog/2013/02/13/the-algebra-of-algebraic-dat… 14. http://www.reddit.com/r/haskell/comments/18p3p5/the_algebra_of_algebraic_da… 15. http://gergo.erdi.hu/blog/2013-02-17-write_yourself_a_haskell..._in_lisp/ 16. http://www.reddit.com/r/haskell/comments/18pm7r/write_yourself_a_haskell_in… 17. http://statusfailed.com/blog/2013/02/19/overloading-record-fields-with-lens… 18. http://www.reddit.com/r/haskell/comments/18t2n7/overloading_record_fields_w… 19. http://edwinb.wordpress.com/2013/02/19/on-partial-functions-in-idris/ 20. http://www.reddit.com/r/haskell/comments/18tbkj/on_partial_functions_in_idr… 21. http://fpcomplete.com/announcing-case-studies/ 22. http://www.reddit.com/r/haskell/comments/18p5n4/whos_using_haskell_commerci… 23. http://www.youtube.com/watch?v=gVLFGQGRsDw 24. http://www.reddit.com/r/haskell/comments/18v4ep/making_super_nario_bros_in_… 25. http://stackoverflow.com/questions/15005670/why-is-there-no-implicit-parall… 26. http://stackoverflow.com/questions/14973459/why-is-a-b-c-d-not-sugar-for-a-… 27. http://stackoverflow.com/questions/15029843/how-can-i-understand 28. http://stackoverflow.com/questions/15020428/are-there-any-advantages-of-usi… 29. http://stackoverflow.com/questions/14934242/whats-the-closest-thing-to-hask… 30. http://stackoverflow.com/questions/15041581/why-does-ghci-give-me-a-type-fo… 31. http://stackoverflow.com/questions/14953032/is-supposed-to-discard-all-left… 32. http://stackoverflow.com/questions/15034392/find-inferred-type-for-local-fu… 33. http://stackoverflow.com/questions/15038386/stuarray-s-i-e-space-leak-only-… 34. http://stackoverflow.com/questions/14918453/connecting-to-the-system-ghc 35. http://stackoverflow.com/questions/14928302/correctness-of-implicit-lifting 36. https://plus.google.com/105107667630152149014/about

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Split and substitution using regex-pcre
by Simon Marechal 28 Feb '13

28 Feb '13

I could not find the perl-equivalents of these functions on Hackage, so I quickly wrote mine. Code is there: https://github.com/bartavelle/pcre-utils It should behave like perl (not really tested actually), and do strange things like : > splitCompile "a" "aaaab" Right ["","","","","b"] > splitCompile "a" "aaaabaaa" Right ["","","","","b"] This will go on Hackage as I need it for the language-puppet package, but I am interested in comments, especially concerning the namespaces: * is the name of this package OK ? * is the name of the package OK ? * should I work with the regex-pcre maintainer to try to merge it ?

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How to return a network connection to C
by C K Kashyap 28 Feb '13

28 Feb '13

Hi, I am using Network.Connection to connect to gmail in my Haskell module - that's compiled to DLL and invoked from C. I need a mechanism to return the connection handle to C so that it can pass it in the subsequent calls. How can I achieve this? Regards, Kashyap

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Question about forkIO
by C K Kashyap 28 Feb '13

28 Feb '13

Hi All, Say I have a haskell function 'f' that does a forkIO and starts an action "a". I create a DLL of this haskell code and inovke "f" from C. Can I expect the "a" to continue to run once "f" has returned to C? Regards, Kashyap

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How does one create an input handle bound to a string instead of a file?
by John D. Ramsdell 28 Feb '13

28 Feb '13

How does one create a value of type System.IO.Handle for reading that takes its input from a string instead of a file? I'm looking for the equivalent of java.io.StringReader in Java. Thanks in advance. John

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Implementing name-mangling in GHC?
by Ismael Figueroa Palet 28 Feb '13

28 Feb '13

Hi café, I'm working on a small project, and I need to rename all ocurrences of a data type in a module. For instance, if the program is module Foo where data Bar fun :: Bar -> Bar fun = ... I'd like that during compilation the module looks as if it was written like: module Foo where data _BarXZY fun :: _BarXZY -> _BarXZY fun ... I think the simplest way to do this is using TH to define a special $data splice, which directly mangles the name. But then I'd need another splice every time I want to use the type. I've read other options like implementing a GHC compiler plugin ( http://www.haskell.org/ghc/docs/7.2.1/html/users_guide/compiler-plugins.html ) is it possible to perform the renaming by modifying the ModGuts structure in a compiler pass? Can you please give more pointers on how to perform this task? Thanks -- Ismael

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Problem accessing Hackage
by Roman Cheplyaka 28 Feb '13

28 Feb '13

I have this weird problem accessing hackage, when the first response gets delayed by 30 seconds: http://superuser.com/q/557271/53951 Does anyone else experience it? (No need to reply with "works for me" — I know that it works for most people.) Any clues about what can be the problem? Roman

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Re: [Haskell-cafe] The state of binary (de)serialization
by wren ng thornton 28 Feb '13

28 Feb '13

On 2/27/13 2:17 AM, Vincent Hanquez wrote: > Two major problems of lazy bytestrings is that: > > * you can't pass it to a C bindings easily. > * doing IO with it without rewriting the chunks, can sometimes (depending > how the lazy bytestring has been produced) result in a serious degradation of > performance calling syscalls on arbitrary and small chunks (e.g. socket's 'send'). If you're on a POSIX system, you can always make use of unix-bytestring[1]. In particular, for lazy ByteStrings the function you want is System.Posix.IO.ByteString.Lazy.fdWritev which performs a single syscall to write all the chunks, and without manually concatenating them. [1] http://hackage.haskell.org/package/unix-bytestring -- Live well, ~wren

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ANN: cabal-dev 0.9.2 - sandboxed haskell builds
by Rogan Creswick 28 Feb '13

28 Feb '13

The (ever growing) cabal-dev team is happy to announce v. 0.9.2! Cabal-dev is a tool to test development libraries by creating a sandboxed package and dependency build environment. Executing `cabal-dev install` will create a sandbox, named cabal-dev in the current directory, and populate it with the project dependencies, which are built and installed into a package database within the sandbox. This is a bug-fix/maintenance release, but it's worth noting that it is now possible to build cabal-dev from hackage with a recent GHC. We've also decided to focus our efforts to provide support for the current release of GHC, the current Haskell Platform, and the previous Haskell Platform. This is the long-awaited version that actually builds with recent GHC's (7.6, in particular). A great deal of thanks for this release to go to active members of the community who've patiently directed other Haskell users to the github repo for a working cabal-dev, and in particular to the dozens (!) of you who've submitted bug reports and patches that resulted in this release (in particular: Bob Ippolito for not only fixing a race condition that caused the test suite to fail. Thanks Bob!)). Urls: * Hackage: http://hackage.haskell.org/package/cabal-dev * Issue tracker: http://github.com/creswick/cabal-dev/issues * Github repo: http://github.com/creswick/cabal-dev --Rogan

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Help to write type-level function
by Dmitry Kulagin 27 Feb '13

27 Feb '13

Hi, I try to implement typed C-like structures in my little dsl. I was able to express structures using type-level naturals (type Ty is promoted): > data Ty = TInt | TBool | TStruct Symbol [Ty] That allowed to implement all needed functions, including type-level function: > type family Get (n :: Nat) (xs :: [Ty]) :: Ty But it is not very convenient to identify struct's fields using naturals, and I wanted to change Ty definition to: > data Ty = TInt | TBool | TStruct Symbol [(Symbol, Ty)] It is much closer to how C-struct looks, but I was unable to implement required type function: > type family Find (s :: Symbol) (xs :: [(Symbol,Ty)]) :: Ty Which just finds a type in a associative list. Could someone give me a hint, how to do it? Or perhaps, is it just impossible thing to do? Thanks!

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