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[ANN] rtorrent-state 0.1.0.0
by Mateusz Kowalczyk 07 Aug '14

07 Aug '14

Hi, rtorrent-state is a library that allows working with rtorrent state files (SOMEHASH.torrent.rtorrent) placed in your session directory. If you're an rtorrent user and ever had to manually muck around with those files, you should be able to use this library to make your life easier. For example, you can stop all torrents in your session directory with just: “overFilesIn "rtorrent/session/dir" stopTorrent” The way it works is by parsing the session files, modifying the resulting data type and serialising it back into the file. I did not do optimisation but I had no problem with test sample of 100,000 files. I need to add IOException handling and maybe extra utility functions but otherwise I consider the library finished. Thanks -- Mateusz K.

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parsec: problem combining lookAhead with many1 (bug?)
by silly8888 07 Aug '14

07 Aug '14

Suppose that we have the following parser: p = lookAhead (char 'a') >> char 'b' If we use it like so parse p "" "a" we get the following error: Left (line 1, column 1): unexpected "a" expecting "b" What happened is that char 'a' succeeded by consuming the 'a' from the input and then lookAhead rewinded the input stream (as it does on success). Then, char 'b' tries to parse (again) the first character of the input and fails. Everything works as expected. Now let's slightly modify our parser: p' = lookAhead (many1 $ char 'a') >> char 'b' I've only added a many1. I was expecting this parser to give the same error as the previous one: many1 $ char 'a' will succeed consuming one 'a' and then lookAhead will rewind the input (as it does on success). Thus when we call char 'b' we are going to be in the beginning of the input again. Well, that doesn't happen: Left (line 1, column 2): unexpected end of input expecting "b" As you can see, lookAhead did not rewind the input as it was supposed to.

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Side-by-side pretty printing
by Michael Lazarev 07 Aug '14

07 Aug '14

Hi all, When looking into Text.PrettyPrint, I stumbled upon <> (beside) combinator. Is it true that multi-line documents can't be printed one beside other? E.g. this let doc1 = vcat $ map text ["This", "is", "a", "document"] in doc1 <> doc1 prints this: This is a documentThis is a document As well as if I would write `doc1 <> nest 50 doc1`. What I was expecting, was This This is is a a documentdocument Do I get it right that Text.PrettyPrint was not intended for such things?

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Haskell Weekly News: Issue 301
by Daniel Santa Cruz 07 Aug '14

07 Aug '14

Welcome to issue 301 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers from July 27 to August 2, 2014 Quotes of the Week * bernalex: I used to have a problem then I used lens now I have an abstraction problem? * trap_exit: haskell is like the 'and they lived happily ever after' of programming languages Top Reddit Stories * The Comonad.Reader » Letter to a Young Haskell Enthusiast Domain: comonad.com, Score: 236, Comments: 56 Original: [1] http://goo.gl/Z5usp3 On Reddit: [2] http://goo.gl/CpPKnC * seL4 is now open source: the world's first end-to-end verified OS kernel Domain: github.com, Score: 87, Comments: 20 Original: [3] http://goo.gl/Uz50bj On Reddit: [4] http://goo.gl/EQK0MQ * FP Haskell Center now free for open projects Domain: fpcomplete.com, Score: 81, Comments: 23 Original: [5] http://goo.gl/ULc9ze On Reddit: [6] http://goo.gl/ZleWCk * -XOverlappingInstances and -XIncoherentInstances to be deprecated Domain: haskell.org, Score: 76, Comments: 64 Original: [7] http://goo.gl/dokkrY On Reddit: [8] http://goo.gl/0AyqA2 * First-Class "Statements": IO as data Domain: blog.jle.im, Score: 68, Comments: 32 Original: [9] http://goo.gl/JNj2D1 On Reddit: [10] http://goo.gl/h1v7yp * Foldable and Traversable in Haskell Domain: blog.jakubarnold.cz, Score: 61, Comments: 30 Original: [11] http://goo.gl/mgI6Mg On Reddit: [12] http://goo.gl/nvwj6j * Minimalist GUI toolkit in GHCi Domain: github.com, Score: 61, Comments: 7 Original: [13] http://goo.gl/9PvsUP On Reddit: [14] http://goo.gl/jQKyG7 * early adopters rejoyce! Haskell Platform 2014.2.0.0 Release Candidate 2 Domain: haskell.org, Score: 48, Comments: 27 Original: [15] http://goo.gl/AGl5po On Reddit: [16] http://goo.gl/ThS3Wc * The Modular, Functional Client Side Domain: stackbuilders.com, Score: 46, Comments: 3 Original: [17] http://goo.gl/eydkfz On Reddit: [18] http://goo.gl/z9q8hE * Beware of bracket Domain: ro-che.info, Score: 46, Comments: 18 Original: [19] http://goo.gl/UYA2mF On Reddit: [20] http://goo.gl/ksMQVV * Real World Haskell: Shipping "Carnival", a Blog Commenting Service Domain: robots.thoughtbot.com, Score: 44, Comments: 5 Original: [21] http://goo.gl/UmPyiL On Reddit: [22] http://goo.gl/4PRdpm * Flee traveller! Flee or you will be corrupted and devoured! Domain: github.com, Score: 41, Comments: 16 Original: [23] http://goo.gl/e3sA6X On Reddit: [24] http://goo.gl/RuAZ4o * Reading files from the /proc filesystem Domain: yesodweb.com, Score: 35, Comments: 4 Original: [25] http://goo.gl/mVfVyM On Reddit: [26] http://goo.gl/Bd2HBT * clckwrks CMS source now on github. A sad farewell to darcs and an optimistic look towards greater contributions from the community. Domain: clckwrks.com, Score: 33, Comments: 31 Original: [27] http://goo.gl/ZLqVWl On Reddit: [28] http://goo.gl/q0za2l * Introduction to GHC.TypeLits with base 4.7, including runtime conversion of symbols. Domain: ponies.io, Score: 32, Comments: 13 Original: [29] http://goo.gl/6FtdyO On Reddit: [30] http://goo.gl/PpmkOc * Converting Make to Shake Domain: neilmitchell.blogspot.com, Score: 23, Comments: 14 Original: [31] http://goo.gl/dOWVhV On Reddit: [32] http://goo.gl/cHYTmS * Learn Snap: Interactive Snap + Heist Examples Domain: learnsnap.chromaticleaves.com, Score: 21, Comments: 14 Original: [33] http://goo.gl/Opwt40 On Reddit: [34] http://goo.gl/06AneL * Hackage: ghc-server: A server interface to GHC. Domain: hackage.haskell.org, Score: 18, Comments: 14 Original: [35] http://goo.gl/ZjhScl On Reddit: [36] http://goo.gl/b9wBfP * Bloggy Badger: Homemade FRP: a study in following the types Domain: gelisam.blogspot.com, Score: 17, Comments: 1 Original: [37] http://goo.gl/T7ujN3 On Reddit: [38] http://goo.gl/HAV1mR Top StackOverflow Questions * IO/Monadic assign operator causing ghci to explode for infinite list votes: 16, answers: 1 Read on SO: [39] http://goo.gl/TC0Snn * A performance conundrum votes: 14, answers: 1 Read on SO: [40] http://goo.gl/b910ez * Does an unused let binding have any effect in Haskell? votes: 12, answers: 3 Read on SO: [41] http://goo.gl/KEl13j * In Haskell, are guards or matchers preferable? votes: 12, answers: 1 Read on SO: [42] http://goo.gl/LiXDjk * If MonadPlus is the “generator” class, then what is the “consumer” class? votes: 12, answers: 2 Read on SO: [43] http://goo.gl/eqRu3a * Why would using head/tail instead of pattern matching make evaluation terminate? votes: 12, answers: 3 Read on SO: [44] http://goo.gl/LOjX0V Until next time, [45]+Daniel Santa Cruz References 1. http://comonad.com/reader/2014/letter-to-a-young-haskell-enthusiast/ 2. http://www.reddit.com/r/haskell/comments/2cbbgf/the_comonadreader_letter_to… 3. https://github.com/seL4/seL4 4. http://www.reddit.com/r/haskell/comments/2c1bnp/sel4_is_now_open_source_the… 5. https://www.fpcomplete.com/business/blog/fp-haskell-center-going-free/ 6. http://www.reddit.com/r/haskell/comments/2c9u0g/fp_haskell_center_now_free_… 7. http://www.haskell.org/pipermail/ghc-devs/2014-July/005830.html 8. http://www.reddit.com/r/haskell/comments/2c136i/xoverlappinginstances_and_x… 9. http://blog.jle.im/entry/first-class-statements 10. http://www.reddit.com/r/haskell/comments/2byuhj/firstclass_statements_io_as… 11. http://blog.jakubarnold.cz/2014/07/30/foldable-and-traversable.html 12. http://www.reddit.com/r/haskell/comments/2c8b87/foldable_and_traversable_in… 13. https://github.com/divipp/lensref/wiki 14. http://www.reddit.com/r/haskell/comments/2cge6f/minimalist_gui_toolkit_in_g… 15. http://www.haskell.org/pipermail/haskell/2014-July/024276.html 16. http://www.reddit.com/r/haskell/comments/2c0ep4/early_adopters_rejoyce_hask… 17. http://www.stackbuilders.com/news/the-modular-functional-client-side 18. http://www.reddit.com/r/haskell/comments/2c21j0/the_modular_functional_clie… 19. http://ro-che.info/articles/2014-07-30-bracket.html 20. http://www.reddit.com/r/haskell/comments/2c4li4/beware_of_bracket/ 21. http://robots.thoughtbot.com/ship-you-a-haskell 22. http://www.reddit.com/r/haskell/comments/2cfdms/real_world_haskell_shipping… 23. https://github.com/haskell/bytestring/blob/2530b1c28f15d0f320a84701bf507d56… 24. http://www.reddit.com/r/haskell/comments/2cbgpz/flee_traveller_flee_or_you_… 25. http://www.yesodweb.com/blog/2014/07/reading-files-proc-filesystem 26. http://www.reddit.com/r/haskell/comments/2buufk/reading_files_from_the_proc… 27. http://www.clckwrks.com/page/view-page-slug/12/clckwrks-now-on-github 28. http://www.reddit.com/r/haskell/comments/2cd26w/clckwrks_cms_source_now_on_… 29. http://ponies.io/posts/2014-07-30-typelits.html 30. http://www.reddit.com/r/haskell/comments/2c8bfi/introduction_to_ghctypelits… 31. http://neilmitchell.blogspot.com/2014/07/converting-make-to-shake.html 32. http://www.reddit.com/r/haskell/comments/2bukaj/converting_make_to_shake/ 33. http://learnsnap.chromaticleaves.com/ 34. http://www.reddit.com/r/haskell/comments/2cdc36/learn_snap_interactive_snap… 35. http://hackage.haskell.org/package/ghc-server-1.0 36. http://www.reddit.com/r/haskell/comments/2c17zz/hackage_ghcserver_a_server_… 37. http://gelisam.blogspot.com/2014/07/homemade-frp-study-in-following-types.h… 38. http://www.reddit.com/r/haskell/comments/2c0vg4/bloggy_badger_homemade_frp_… 39. http://stackoverflow.com/questions/24986296/io-monadic-assign-operator-caus… 40. http://stackoverflow.com/questions/25089668/a-performance-conundrum 41. http://stackoverflow.com/questions/24984661/does-an-unused-let-binding-have… 42. http://stackoverflow.com/questions/25000929/in-haskell-are-guards-or-matche… 43. http://stackoverflow.com/questions/25070740/if-monadplus-is-the-generator-c… 44. http://stackoverflow.com/questions/25078598/why-would-using-head-tail-inste… 45. https://plus.google.com/105107667630152149014/about

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Dealing with encodings
by Dmitry Bogatov 06 Aug '14

06 Aug '14

Hello! How teach hxt to handle "KOI8-R" encoding of input file? And it seems that so many great packages (like hxt, feed, curl) uses String. Is it some work in progress to port them to Text? -- Best regards, Dmitry Bogatov <KAction(a)gnu.org>, Free Software supporter, esperantisto and netiquette guardian. GPG: 54B7F00D

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Applicative & Monad as interaction between categories
by Ruben Astudillo 05 Aug '14

05 Aug '14

Hi all, I recently came across of two blog posts[1][2] by Gabriel Gonzales where he shows motivation for writing compositional functions -- and thus why the concept of category is useful -- and motivation to write functors between them. I wanted to know if something similar for has been done to `Applicative' and `Monad' as design pattern and interaction between categories. I've searching but I always hit the Monad tutorials and more info on how to use them. Thanks in advance. Excuse my English. [1]: http://www.haskellforall.com/2012/08/the-category-design-pattern.html [2]: http://www.haskellforall.com/2012/09/the-functor-design-pattern.html -- Ruben Astudillo. pgp: 0x3C332311 , usala en lo posible :-) Crear un haiku, en diecisiete silabas, es complica...

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[ANN] Hayoo Relaunch
by Sebastian Philipp 05 Aug '14

05 Aug '14

Hi Cafe, Hayoo <http://hayoo.fh-wedel.de> has been relaunched. Hayoo is a search engine for Hackage packages, which allows you to search for functions, data types and packages. It is currently work in progress. Any feedback is greatly appreciated! Hayoo uses Hunt <https://github.com/hunt-framework> for indexing and searching, which is the successor of Holumbus. Hunt is a flexible, lightweight search platform with a powerful query language and JSON API. Example search requests are: * Function names: map <http://hayoo.fh-wedel.de/?query=map> * Function signatures: (a->b)->f a->f b <http://hayoo.fh-wedel.de/?query=%28a-%3Eb%29-%3Ef+a-%3Ef+b> * Module names: Control.Loop <http://hayoo.fh-wedel.de/?query=Control.Loop> Have a look at the examples on <http://hayoo.fh-wedel.de/examples> for some advances queries. The old Hayoo and Holumbus are still online at <http://holumbus-alt.fh-wedel.de/> -- Sebastian Philipp

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Fwd: Default stdout buffering of child process of createProcess
by Chris Myzie 05 Aug '14

05 Aug '14

I'm reposting this message because I think it only went to the google group and not the official haskell-cafe list: On Friday, August 1, 2014 10:06:32 AM UTC-4, Chris Myzie wrote: > > As a workaround, I am able to trick the child haskell process into > thinking it's running in an interactive terminal by wrapping it with > /usr/bin/script: > > createProcess (proc "/usr/bin/script" ["-qc","./A","/dev/null"]) { std_out > = CreatePipe } > > I still think haskell is using screwy defaults for stdout buffering.. > > On Thursday, July 31, 2014 3:24:47 PM UTC-4, Chris Myzie wrote: >> >> Hello, >> >> I'm trying to write a wrapper process that will be able to read any child >> process' stdout. The problem I'm running into is that unless I force the >> child's stdout to LineBuffering, it defaults to BlockBuffering. Is >> BlockBuffering really the default in this case? I don't want to have to >> modify all of the child processes that I want to use with this wrapper. >> >> Below is a simple test case. A.hs is the child process, and B.hs is the >> wrapper. If I run B.hs, I will get no output unless I uncomment the line >> in A.hs. >> >> Thanks, >> Chris >> >> >> ------------------------------ A.hs --------------------------- >> import Control.Concurrent >> import System.IO >> >> main :: IO () >> main = do >> -- hSetBuffering stdout LineBuffering >> putStrLn "test" >> threadDelay 1000000 >> main >> >> >> ------------------------------ B.hs --------------------------- >> import Control.Monad >> import System.IO >> import System.Process >> >> main :: IO () >> main = do >> (_,Just h,_,_) <- createProcess (proc "./A" []) { std_out = CreatePipe } >> hSetBuffering h LineBuffering >> forever $ hGetLine h >>= putStrLn >> >

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[ANN] StrappedTemplates - general purpose templates
by Kyle Hanson 04 Aug '14

04 Aug '14

Hello all, I found that I wasn't quite satisfied by the template offerings (Heist, Hastache, Shakespearean, etc..) of Haskell, so I built my own. The goal is to have simple syntax that non-haskellers would be comfortable using, resembles templates found in other languages (Jinja, Django, etc) and an interface to render them that I don't have to think very hard to use. Features include inheritance, logic, includes, functions, and relatively speedy rendering (much faster than interpreted templates like Heist-I and Hastache) . Its very much a work in progress, but I felt that it was enough for an initial release and get general feedback on it. Comments are appreciated. One thing that I want to improve is how functions are handled in the template and in the "InputBucket", extend the syntax to allow you to do more inside the template and be able to define your own block functions. These will probably be added next major release. http://hackage.haskell.org/package/StrappedTemplates https://github.com/hansonkd/StrappedTemplates Thanks! Kyle Hanson

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New Functional Programming Job Opportunities
by Functional Jobs 04 Aug '14

04 Aug '14

Here are some functional programming job opportunities that were posted recently: Pragmatic Haskell Developer at Anchor Systems http://functionaljobs.com/jobs/8729-pragmatic-haskell-developer-at-anchor-s… Cheers, Sean Murphy FunctionalJobs.com

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