- Haskell-Cafe - Haskell.org

Proposal: Non-recursive let
by oleg＠okmij.org 02 Aug '13

02 Aug '13

Here is a snippet from a real code that could benefit from non-recursive let. The example is notable because it incrementally constructs not one but two structures (both maps), ast and headers. The maps are constructed in a bit interleaved fashion, and stuffing them into the same State would be ungainly. In my real code -- Add an update record to a buffer file do_update :: String -> Handle -> Parsed -> [Parsed] -> IO () do_update "TAF" h ast asts@(_:_) = do rv <- reflect $ get_trange "TRange" ast headers0 <- return . M.fromList =<< sequence (map (\ (n,fld) -> reflect (fld ast) >>= \v -> return (n,v)) fields_header) let headers = M.insert "_report_ranges" (format_two_tstamps rv) headers0 foldM write_period (rv,headers,(snd rv,snd rv)) asts return () where write_period (rv,headers,mv) ast = do pv@(p_valid_from,p_valid_until) <- reflect $ get_trange "TRange" ast check_inside pv rv let prevailing = M.lookup "PREVAILING" ast (mv,pv) <- case prevailing of Just _ -> return (pv,pv) -- set the major valid period -- Make sure each VAR period occurs later than the prevailing -- period. If exactly at the same time add 1 min Nothing -> case () of _ | fst mv < p_valid_from -> return (mv,pv) _ | fst mv == p_valid_from -> return (mv,(p_valid_from + 60, p_valid_until)) _ -> gthrow . InvalidData . unwords $ [ "VAR period begins before prevailing:", show ast, "; prevailing TRange", show mv] let token = maybe (M.findWithDefault "" "VAR" ast) id prevailing let ast1 = M.insert "_token" token . M.insert "_period_valid" (format_two_tstamps pv) . M.unionWith (\_ x -> x) headers $ ast let title = M.member "Title" ast let headers1 = if title then headers else M.delete "_limit_to " . M.delete "_limit_recd" $ headers write_fields h ast1 fields return (rv,headers1,mv)

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Getting the 'ThreadId' of the calling thread
by Nikita Karetnikov 02 Aug '13

02 Aug '13

(I'm trying to update a package that was written with GHC 6.10.4 in mind.) I feel that a 'myThreadId' action, which is defined in this module [1], is useless, but I'm not sure. I think it will always return the "Map.find: element not in the map" exception because a 'threadMap' contains an empty 'ThreadMap'. Is it right, or am I missing something? [1] https://gitweb.torproject.org/tordnsel.git/blob/HEAD:/src/TorDNSEL/Control/…

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[ANNOUNCE] fficxx : haskell-C++ FFI binding generator
by Ian-Woo Kim 02 Aug '13

02 Aug '13

Dear Haskellers, Hello. I am very happy to announce the first version of fficxx (http://ianwookim.org/fficxx, also, please look at http://github.com/wavewave/fficxx ) fficxx is a haskell Foreign Function Interface (FFI) generator to C++. This tool automatically generates haskell FFI package for a given C++ class structure. It has been used for generating my haskell binding to the ROOT library [1] called HROOT [2]. Now I made it as a separate tool to benefit everyone trying to make a haskell-C++ binding. I am going to explain how to use the library/tool one by one in my blog ( http://ianwookim.org/blog ). Currently, in the fficxx cabal package, I provide a very simple sample in the sample directory. If interested, please try this and give me some comments on it in the discussion mailing list: http://ianwookim.org/fficxx/discuss.html I hope that this is useful to many haskellers. Have fun with it! Thanks, Ian-Woo Kim (wavewave) [1] : http://root.cern.ch [2] : http://ianwookim.org/HROOT

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Hoogle problems?
by Andrew Butterfield 01 Aug '13

01 Aug '13

I've just tried using Hoogle, but either get a 404 not found (http://haskell.org/hoogle/) or else I find I get a ELF 64-bit LSB executable being downloaded If I search using Google and click on the first link (shown as www.haskell.org/hoogle/ I get the following (spaces deliberately added to make it less dangerous) https://www.goo gle.com/url?sa=t&rct=j&q=&esrc=s&sou rce=web&cd=1&cad=rja&ved=0CC8QFjAA&url=http%3A%2F%2Fwww.haskell.org%2Fhoogle%2F&ei=y_njUdZAhY 7sBsGpgNAK&usg=AFQjCNFljq5Oyb4LT7VF-I5MUotq512AQg&sig2 =SVRE_6nF3bhho7-NKqEaCw&bvm=bv.487 05608,d.ZGU Using Mac OS X 10.6, Chrome and Safari Is it me, or is there a wider problem ? -------------------------------------------------------------------- Andrew Butterfield Tel: +353-1-896-2517 Fax: +353-1-677-2204 Lero@TCD, Head of Foundations & Methods Research Group Director of Teaching and Learning - Undergraduate, School of Computer Science and Statistics, Room G.39, O'Reilly Institute, Trinity College, University of Dublin http://www.scss.tcd.ie/Andrew.Butterfield/ --------------------------------------------------------------------

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Haskell Weekly News: Issue 274
by Daniel Santa Cruz 01 Aug '13

01 Aug '13

Welcome to issue 274 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers the week of July 14 to 27, 2013. Quotes of the Week * knuth: To help the reader drowning in a sea of abstraction, the following example may serve as a concrete life preserver >From the mail bag * Haskell for schools in Argentina [1] http://goo.gl/EAPHXx Top Reddit Stories * Parallel and Concurrent Programming in Haskell available now in ebook formats, print version can be preordered Domain: shop.oreilly.com, Score: 94, Comments: 14 On Reddit: [2] http://goo.gl/426HB0 Original: [3] http://goo.gl/anqIi * Lenses in pictures Domain: adit.io, Score: 84, Comments: 51 On Reddit: [4] http://goo.gl/e8Bc0N Original: [5] http://goo.gl/1kmqf * Monads made difficult Domain: stephendiehl.com, Score: 70, Comments: 11 On Reddit: [6] http://goo.gl/sQAmVD Original: [7] http://goo.gl/35EDt * Helm - FRP Game Engine Inspired by Elm Domain: github.com, Score: 67, Comments: 19 On Reddit: [8] http://goo.gl/1lJEIB Original: [9] http://goo.gl/4wDcHN * Ian Lynagh leaves GHC HQ Domain: haskell.org, Score: 64, Comments: 4 On Reddit: [10] http://goo.gl/XCnjrA Original: [11] http://goo.gl/Ox5KXW * Yesod in Production Domain: joelt.io, Score: 61, Comments: 13 On Reddit: [12] http://goo.gl/jlhvvm Original: [13] http://goo.gl/7pSCJ * A Comparison Between Perl and Haskell Domain: ocharles.org.uk, Score: 60, Comments: 22 On Reddit: [14] http://goo.gl/cwYXb0 Original: [15] http://goo.gl/P46D4e * Backpack: Retrofitting Haskell with Interfaces (Kilpatrick, Dreyer, SPJ, Marlow) [link to pdf] Domain: mpi-sws.org, Score: 58, Comments: 63 On Reddit: [16] http://goo.gl/sjjAE Original: [17] http://goo.gl/C06Ly * Parallel and Concurrent Programming in Haskell (online version, part of Atlas beta) Domain: chimera.labs.oreilly.com, Score: 56, Comments: 35 On Reddit: [18] http://goo.gl/x5dhf5 Original: [19] http://goo.gl/H7MeFa * Why Haskell at School matters Domain: sawafaso.blogspot.com.ar, Score: 52, Comments: 18 On Reddit: [20] http://goo.gl/2LHlsn Original: [21] http://goo.gl/8Dwy4R * Measuring the Haskell Gap :: PDF Domain: leafpetersen.com, Score: 49, Comments: 13 On Reddit: [22] http://goo.gl/6b4xdx Original: [23] http://goo.gl/nqDJZd * Automatic SIMD Vectorization for Haskell by Leaf Petersen, Dominic Orchard and Neal Glew [ICFP13][PDF] Domain: leafpetersen.com, Score: 47, Comments: 13 On Reddit: [24] http://goo.gl/dPCPio Original: [25] http://goo.gl/gDBajX * IRC Browse Domain: chrisdone.com, Score: 43, Comments: 12 On Reddit: [26] http://goo.gl/OPXVQK Original: [27] http://goo.gl/IOoJgT * How to Help Develop Hackage2 Domain: self.haskell, Score: 40, Comments: 46 On Reddit: [28] http://goo.gl/NQGmY Original: [29] http://goo.gl/NQGmY Top StackOverflow Questions * Can someone explain to me why the app function of ArrowApply makes them as powerful as monads? votes: 13, answers: 2 Read on SO: [30] http://goo.gl/V6I0fK * Haskell newtype with parentheses votes: 12, answers: 2 Read on SO: [31] http://goo.gl/k9A7YU * GHC: insert compilation date votes: 11, answers: 2 Read on SO: [32] http://goo.gl/MbWGqH * How can Haskell function guards operate on other values than the functions parameters? votes: 10, answers: 2 Read on SO: [33] http://goo.gl/sgI9i8 * Can Haskell functions be serialized? votes: 10, answers: 3 Read on SO: [34] http://goo.gl/fVsPvv * Calling Haskell library from C++ votes: 10, answers: 1 Read on SO: [35] http://goo.gl/6V2zqb * Debugging compile time performance issues caused by GHC's constraint solver votes: 10, answers: 1 Read on SO: [36] http://goo.gl/XPAqAy * Haskell performance when using classes and instances votes: 10, answers: 2 Read on SO: [37] http://goo.gl/EZNVMS * Could not deduce (m ~ m1) votes: 9, answers: 1 Read on SO: [38] http://goo.gl/vW0x6D * Running a subexpression once votes: 9, answers: 2 Read on SO: [39] http://goo.gl/MdRgkZ Until next time, [40]+Daniel Santa Cruz References 1. http://sawafaso.blogspot.com.ar/2013/07/why-haskell-at-school-matters.html?… 2. http://shop.oreilly.com/product/0636920026365.do 3. http://www.reddit.com/r/haskell/comments/1ioorw/parallel_and_concurrent_pro… 4. http://adit.io/posts/2013-07-22-lenses-in-pictures.html 5. http://www.reddit.com/r/haskell/comments/1isryj/lenses_in_pictures/ 6. http://www.stephendiehl.com/posts/monads.html 7. http://www.reddit.com/r/haskell/comments/1iafky/monads_made_difficult/ 8. https://github.com/z0w0/helm 9. http://www.reddit.com/r/haskell/comments/1j1fd8/helm_frp_game_engine_inspir… 10. http://www.haskell.org/pipermail/ghc-devs/2013-July/001677.html 11. http://www.reddit.com/r/haskell/comments/1ikc91/ian_lynagh_leaves_ghc_hq/ 12. http://joelt.io/entries/yesod-in-production 13. http://www.reddit.com/r/haskell/comments/1inf8a/yesod_in_production/ 14. http://ocharles.org.uk/blog/posts/2013-07-26-a-comparison-between-perl-and-… 15. http://www.reddit.com/r/haskell/comments/1j3jgd/a_comparison_between_perl_a… 16. http://www.mpi-sws.org/~skilpat/backpack/ 17. http://www.reddit.com/r/haskell/comments/1id0p7/backpack_retrofitting_haske… 18. http://chimera.labs.oreilly.com/books/1230000000929/index.html 19. http://www.reddit.com/r/haskell/comments/1iwr7x/parallel_and_concurrent_pro… 20. http://sawafaso.blogspot.com.ar/2013/07/why-haskell-at-school-matters.html 21. http://www.reddit.com/r/haskell/comments/1j3k19/why_haskell_at_school_matte… 22. http://www.leafpetersen.com/leaf/publications/hs2013/haskell-gap.pdf 23. http://www.reddit.com/r/haskell/comments/1j2k4a/measuring_the_haskell_gap_p… 24. http://www.leafpetersen.com/leaf/publications/icfp2013/vectorization-haskel… 25. http://www.reddit.com/r/haskell/comments/1izyok/automatic_simd_vectorizatio… 26. http://chrisdone.com/posts/ircbrowse 27. http://www.reddit.com/r/haskell/comments/1iy8nv/irc_browse/ 28. http://www.reddit.com/r/haskell/comments/1iki8p/how_to_help_develop_hackage… 29. http://www.reddit.com/r/haskell/comments/1iki8p/how_to_help_develop_hackage… 30. http://stackoverflow.com/questions/17668452/can-someone-explain-to-me-why-t… 31. http://stackoverflow.com/questions/17853232/haskell-newtype-with-parentheses 32. http://stackoverflow.com/questions/17796521/ghc-insert-compilation-date 33. http://stackoverflow.com/questions/17650866/how-can-haskell-function-guards… 34. http://stackoverflow.com/questions/17785916/can-haskell-functions-be-serial… 35. http://stackoverflow.com/questions/17815804/calling-haskell-library-from-c 36. http://stackoverflow.com/questions/17822539/debugging-compile-time-performa… 37. http://stackoverflow.com/questions/17834802/haskell-performance-when-using-… 38. http://stackoverflow.com/questions/17765690/could-not-deduce-m-m1 39. http://stackoverflow.com/questions/17900495/running-a-subexpression-once 40. https://plus.google.com/105107667630152149014/about

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Template Haskell and Haddock
by Jose A. Lopes 31 Jul '13

31 Jul '13

Hi, Is there a way to access docstrings through Template Haskell ? For example, access the docstring of a function declaration ? Best regards, Jose

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ANN: Angel 0.4.4
by Michael Xavier 31 Jul '13

31 Jul '13

I'm pleased to announce the release of Angel 0.4.4. angel is a daemon that runs and monitors other processes. It is similar to djb's daemontools or the Ruby project god. It's goals are to keep a set of services running, and to facilitate the easy configuration and restart of those services. New in 0.4.4 * Add env option to config to specify environment variables. * Inject ANGEL_PROCESS_NUMBER environment variable into processes started with count. This is intended for the purpose of logging, port enumeration, etc. Homepage: https://github.com/michaelxavier/angel HackageDB: http://hackage.haskell.org/package/angel -- Michael Xavier http://www.michaelxavier.net

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ANNOUNCE: hdbi-1.0.0 and hdbi-postgresql-1.0.0
by Alexey Uimanov 31 Jul '13

31 Jul '13

Hello, haskellers. This is the first release of HDBI (Haskell Database Independent interface). It is the fork of HDBC. HDBI has some improvements in design, it also has better testing and performance (mainly because of using Text instead of String anywhere). HDBI designed to be more flexible and correct database interface. You can find out more information in the documentation. http://hackage.haskell.org/package/hdbi http://hackage.haskell.org/package/hdbi-postgresql I am planning to implement MySql and Sqlite drivers as well https://github.com/s9gf4ult/hdbi https://github.com/s9gf4ult/hdbi-postgresql Issues and pull requests are welcome, as well as collaboration.

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ForeignPtr and Garbage Collection
by satvik chauhan 30 Jul '13

30 Jul '13

Hi Cafe, Is it guaranteed that the value of `ForeignPtr` will not be changed (for example due to compaction etc) by haskell garbage collector until it goes out of scope and finalizer is run. -Satvik

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Call for talks: Haskell Implementors Workshop 2013, Sept 22, Boston
by Ryan Newton 30 Jul '13

30 Jul '13

Please pass on this announcement! The deadline is in two weeks.* * * * * Call for Talks* ACM SIGPLAN Haskell Implementors' Workshop http://haskell.org/haskellwiki/HaskellImplementorsWorkshop/2013 Boston, USA, September 22th, 2013 The workshop will be held in conjunction with ICFP 2013 http://www.icfpconference.org/icfp2013/ *Important dates* Proposal Deadline: *13th August 2013 (by midnight, any timezone)* Notification: 27th August 2013 Workshop: 22th September 2013 The Haskell Implementors' Workshop is to be held alongside ICFP 2013 this year in Boston. There will be no proceedings; it is an informal gathering of people involved in the design and development of Haskell implementations, tools, libraries, and supporting infrastructure. This relatively new workshop reflects the growth of the user community: there is a clear need for a well-supported tool chain for the development, distribution, deployment, and configuration of Haskell software. The aim is for this workshop to give the people involved with building the infrastructure behind this ecosystem an opportunity to bat around ideas, share experiences, and ask for feedback from fellow experts. We intend the workshop to have an informal and interactive feel, with a flexible timetable and plenty of room for ad-hoc discussion, demos, and impromptu short talks. Scope and target audience ------------------------- It is important to distinguish the Haskell Implementors' Workshop from the Haskell Symposium which is also co-located with ICFP 2013. The Haskell Symposium is for the publication of Haskell-related research. In contrast, the Haskell Implementors' Workshop will have no proceedings -- although we will aim to make talk videos, slides and presented data available with the consent of the speakers. In the Haskell Implementors' Workshop, we hope to study the underlying technology. We want to bring together anyone interested in the nitty-gritty details behind turning plain-text source code into a deployed product. Having said that, members of the wider Haskell community are more than welcome to attend the workshop -- we need your feedback to keep the Haskell ecosystem thriving. The scope covers any of the following topics. There may be some topics that people feel we've missed, so by all means submit a proposal even if it doesn't fit exactly into one of these buckets: * Compilation techniques * Language features and extensions * Type system implementation * Concurrency and parallelism: language design and implementation * Performance, optimisation and benchmarking * Virtual machines and run-time systems * Libraries and tools for development or deployment Talks ----- At this stage we would like to invite proposals from potential speakers for a relatively short talk. We are aiming for 20 minute talks with 10 minutes for questions and changeovers. We want to hear from people writing compilers, tools, or libraries, people with cool ideas for directions in which we should take the platform, proposals for new features to be implemented, and half-baked crazy ideas. Please submit a talk title and abstract of no more than 200 words. Submissions should be made via EasyChair. The website is: https://www.easychair.org/conferences/?conf=hiw2013 If you don't have an account you can create one here: https://www.easychair.org/account/signup.cgi Because the submission is an abstract only, please click the "abstract only" button when you make your submission. There is no need to attach a separate file. We will also have a lightning talks session which will be organised on the day. These talks will be 2-10 minutes, depending on available time. Suggested topics for lightning talks are to present a single idea, a work-in-progress project, a problem to intrigue and perplex Haskell implementors, or simply to ask for feedback and collaborators. Organisers ---------- * Ryan Newton (Indiana University) * Neal Glew (Intel Labs) * Edward Yang (Stanford University) * Thomas Schilling (University of Kent) * Geoffrey Mainland (Drexel University)

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