July 2014 - Haskell-Cafe

Haskell Weekly News: Issue 298
by Daniel Santa Cruz 03 Jul '14

03 Jul '14

Welcome to issue 298 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers from June 15 to 28, 2014 Quotes of the Week * Kinnison * imagines a radio station playing only things like 'Life tru a Lens', stuff by 'Dire States' or 'Monadonna' Top Reddit Stories * Today I published an introductory book on Haskell Data Analysis Domain: haskelldata.com, Score: 99, Comments: 26 Original: [1] http://goo.gl/R2kRFu On Reddit: [2] http://goo.gl/Ka0oP5 * Backpack: An ML-like module system for Haskell Domain: plv.mpi-sws.org, Score: 76, Comments: 44 Original: [3] http://goo.gl/7Zkxbg On Reddit: [4] http://goo.gl/78H37f * Cgrep, a context-aware grep for source code. Domain: awgn.github.io, Score: 67, Comments: 13 Original: [5] http://goo.gl/q1VdEA On Reddit: [6] http://goo.gl/2NNTrO * Teenage Haskell Domain: twdkz.wordpress.com, Score: 63, Comments: 7 Original: [7] http://goo.gl/cvJ0ap On Reddit: [8] http://goo.gl/aISHlG * GHC 7.10 gains -XBinaryLiterals language syntax extensions Domain: github.com, Score: 63, Comments: 14 Original: [9] http://goo.gl/qfWvAg On Reddit: [10] http://goo.gl/NOVgme * Haskelier - Haskell for the Advanced Layman Domain: haskelier.tumblr.com, Score: 59, Comments: 26 Original: [11] http://goo.gl/pLsRB1 On Reddit: [12] http://goo.gl/5HBSWD * Barely Functional: Writing a Real Program in Haskell Domain: ben.kirw.in, Score: 57, Comments: 36 Original: [13] http://goo.gl/4yWLuL On Reddit: [14] http://goo.gl/B1LX8f * hmatrix 0.16 now BSD3 and with static dimension checking Domain: github.com, Score: 51, Comments: 10 Original: [15] http://goo.gl/C5zKzk On Reddit: [16] http://goo.gl/A94AkD * Formatting: type-safe printf-like library by chrisdone Domain: hackage.haskell.org, Score: 51, Comments: 24 Original: [17] http://goo.gl/DHM0Yn On Reddit: [18] http://goo.gl/zUQN02 * Haskell 2014 accepted papers, with links (pull requests welcome) Domain: github.com, Score: 50, Comments: 5 Original: [19] http://goo.gl/B2f434 On Reddit: [20] http://goo.gl/XSmJGo * Real World Haskell - Outdated Parts? Domain: self.haskell, Score: 50, Comments: 12 Original: [21] http://goo.gl/5YhIOT On Reddit: [22] http://goo.gl/5YhIOT * I'm trying my hardest to learn this language and only get more and more discouraged. Domain: self.haskell, Score: 48, Comments: 111 Original: [23] http://goo.gl/9vuPBe On Reddit: [24] http://goo.gl/9vuPBe * Using f-algebras to produce a statically typed functional programming language Domain: burz.github.io, Score: 47, Comments: 19 Original: [25] http://goo.gl/9YCz4k On Reddit: [26] http://goo.gl/DvWBPS * 'ghc-make' released Domain: neilmitchell.blogspot.de, Score: 47, Comments: 19 Original: [27] http://goo.gl/JlMS1a On Reddit: [28] http://goo.gl/kO2FQP * A simple alternative to De Bruijn indexing, from ICFP 2013 Domain: pchiusano.io, Score: 46, Comments: 24 Original: [29] http://goo.gl/7PBIM2 On Reddit: [30] http://goo.gl/PGmQ6W * Haskoin: A Haskell implementation of the Bitcoin protocol. Domain: github.com, Score: 44, Comments: 0 Original: [31] http://goo.gl/n0eCEI On Reddit: [32] http://goo.gl/bvsE24 * What is the state of "The JavaScript Problem"? What is the currently preferred way to solve in a real world application? Domain: self.haskell, Score: 42, Comments: 55 Original: [33] http://goo.gl/dIww4i On Reddit: [34] http://goo.gl/dIww4i * ANNOUNCE: STM-Containers. A hash map and hash set for STM Domain: hackage.haskell.org, Score: 41, Comments: 13 Original: [35] http://goo.gl/6nuWAc On Reddit: [36] http://goo.gl/rAzIYr Top StackOverflow Questions * Why does flooring infinity does not throw some error? votes: 14, answers: 1 Read on SO: [37] http://goo.gl/f7gUB8 * How long can the name of a type constructor be? votes: 12, answers: 1 Read on SO: [38] http://goo.gl/mGiblp * Difference between $ and () votes: 11, answers: 5 Read on SO: [39] http://goo.gl/lTB24e * Need advice on optimising Haskell data processing votes: 11, answers: 3 Read on SO: [40] http://goo.gl/NnEqgn * Reconciling lens usage with database access votes: 11, answers: 1 Read on SO: [41] http://goo.gl/Zczjjf * Why constraints on data are a bad thing? votes: 11, answers: 3 Read on SO: [42] http://goo.gl/l0WXtP * Can I use template haskell to define missing functions? votes: 10, answers: 2 Read on SO: [43] http://goo.gl/AFFS2T * Is there a reason we can't populate types with DataKinds? votes: 10, answers: 2 Read on SO: [44] http://goo.gl/1gpZej * Why is a built-in function applied to too few arguments considered to be in weak head normal form? votes: 10, answers: 2 Read on SO: [45] http://goo.gl/6iFG8a Until next time, [46]+Daniel Santa Cruz References 1. http://haskelldata.com/ 2. http://www.reddit.com/r/haskell/comments/296l80/today_i_published_an_introd… 3. http://plv.mpi-sws.org/backpack/ 4. http://www.reddit.com/r/haskell/comments/28v6c9/backpack_an_mllike_module_s… 5. http://awgn.github.io/cgrep/ 6. http://www.reddit.com/r/haskell/comments/28moo0/cgrep_a_contextaware_grep_f… 7. http://twdkz.wordpress.com/2014/06/26/teenage-haskell/ 8. http://www.reddit.com/r/haskell/comments/29abyz/teenage_haskell/ 9. https://github.com/ghc/ghc/commit/1c0b5fdc9f2b6ea8166cc565383d4cd20432343c 10. http://www.reddit.com/r/haskell/comments/29b2jj/ghc_710_gains_xbinarylitera… 11. http://haskelier.tumblr.com/ 12. http://www.reddit.com/r/haskell/comments/28d7ma/haskelier_haskell_for_the_a… 13. http://ben.kirw.in/2014/06/24/barely-functional-1-rlp/ 14. http://www.reddit.com/r/haskell/comments/28zwoc/barely_functional_writing_a… 15. https://github.com/albertoruiz/hmatrix 16. http://www.reddit.com/r/haskell/comments/28peug/hmatrix_016_now_bsd3_and_wi… 17. http://hackage.haskell.org/package/formatting 18. http://www.reddit.com/r/haskell/comments/291wel/formatting_typesafe_printfl… 19. https://github.com/yallop/haskell2014-papers 20. http://www.reddit.com/r/haskell/comments/28yu1f/haskell_2014_accepted_paper… 21. http://www.reddit.com/r/haskell/comments/2938yb/real_world_haskell_outdated… 22. http://www.reddit.com/r/haskell/comments/2938yb/real_world_haskell_outdated… 23. http://www.reddit.com/r/haskell/comments/288egd/im_trying_my_hardest_to_lea… 24. http://www.reddit.com/r/haskell/comments/288egd/im_trying_my_hardest_to_lea… 25. http://burz.github.io/2014/06/15/feval.html 26. http://www.reddit.com/r/haskell/comments/28rbwr/using_falgebras_to_produce_… 27. http://neilmitchell.blogspot.de/2014/06/announcing-ghc-make.html 28. http://www.reddit.com/r/haskell/comments/28tttf/ghcmake_released/ 29. http://pchiusano.io/2014-06-20/simple-debruijn-alternative.html 30. http://www.reddit.com/r/haskell/comments/28vfd0/a_simple_alternative_to_de_… 31. https://github.com/haskoin/haskoin 32. http://www.reddit.com/r/haskell/comments/28y454/haskoin_a_haskell_implement… 33. http://www.reddit.com/r/haskell/comments/28o7my/what_is_the_state_of_the_ja… 34. http://www.reddit.com/r/haskell/comments/28o7my/what_is_the_state_of_the_ja… 35. http://hackage.haskell.org/package/stm-containers 36. http://www.reddit.com/r/haskell/comments/295lbr/announce_stmcontainers_a_ha… 37. http://stackoverflow.com/questions/24338673/why-does-flooring-infinity-does… 38. http://stackoverflow.com/questions/24335869/how-long-can-the-name-of-a-type… 39. http://stackoverflow.com/questions/24271129/difference-between-and 40. http://stackoverflow.com/questions/24278006/need-advice-on-optimising-haske… 41. http://stackoverflow.com/questions/24462070/reconciling-lens-usage-with-dat… 42. http://stackoverflow.com/questions/24465586/why-constraints-on-data-are-a-b… 43. http://stackoverflow.com/questions/24233346/can-i-use-template-haskell-to-d… 44. http://stackoverflow.com/questions/24439618/is-there-a-reason-we-cant-popul… 45. http://stackoverflow.com/questions/24447324/why-is-a-built-in-function-appl… 46. https://plus.google.com/105107667630152149014/about

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GLUT under Windows using ghc 7.8.2?
by Dominick Samperi 03 Jul '14

03 Jul '14

It appears that The Haskell Platform includes libglut32.a and other important libs, so it is self-contained, provided users can work with the version of ghc that is provided: currently 7.6.3 under Windows. In particular, 'cabal install glut' works fine with the default version of ghc. But if I try using ghc-7.8.2 I get: Configuring GLUT-2.5.1.1... cabal: Missing dependencies on a foreign library: * Missing C library: glut32 ... All of the following do not change the result: 1. Adding --extra-lib-dirs=c:\glut-3.7.6-bin to the command line. 2. Using freeglut instead of glut 3. Copying libglut.a from The Haskell Package mingw/lib directory to c:\ghc-3.8.2\mingw\lib (dangerous because I am mixing architectures here). How does cabal decide that the C library glut32 is missing? Where is it looking? Why doesn't it look in the places I specify? Thanks, Dominick

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handling non-string command line arguments
by Johan Larson 02 Jul '14

02 Jul '14

I've been looking at choices for parsing command line arguments, including getOpt. The examples I can find focus on string arguments, whereas I am interested in numbers. In the application at hand, it is particularly important to issue clear error messages when arguments don't parse as numbers or are out of range. I could use getOpt as a first pass with string arguments and then turn the strings into validated numbers in a second pass, but that's a bit awkward. Alternately I could use the options records with Options -> IO Options functions. But both of these solutions treat type mismatches differently from other options errors. Has anyone found a cleaner solution? -- Johan Larson -- Toronto, Canada

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Problem with type in a function
by Leza Morais Lutonda 02 Jul '14

02 Jul '14

Hi, I have the following function plotf :: Ploteable a => ([a] -> IO ()) -> (a -> a) -> [a] -> IO () plotf plot fn xs = plot $ map fn xs that compiles correctly, but when I use it with: plotf win sin [1..100::Double] -- where win :: [Double] -> IO () I'm geting the error: No instance for (Ploteable Double) arising from a use of ‘plotf’ In the expression: plotf win sin [1 .. 100 :: Double] In an equation for ‘it’: it = plotf win sin [1 .. 100 :: Double] What am I missing? Thanks! 50 Aniversario de la Cujae. Inaugurada por Fidel el 2 de diciembre de 1964 http://cujae.edu.cu

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haskell in several upcoming live performances in the UK
by Renick Bell 02 Jul '14

02 Jul '14

Hello everyone. I hope the Haskell Cafe will tolerate this musical interruption. I suppose it's not so often that you can hear two different performers use Haskell in their performances in one concert, but if you live in the UK you have several opportunities to do so in the next few days. Both Alex McLean and I will be playing at Algorave NIME on Thursday night in London at Corsica Studios. The event starts at 21:00. Alex will be playing in the duo Canute with Matthew Yee-King, and I will be playing a solo set. http://www.nime2014.org/public-events/concerts-and-installations/ After that, it's the UK algorave tour, with stops in Brighton (07/04), Sheffield (07/06), Leeds (07/07), Manchester (07/08), and York (07/09): http://algorave.com/ Both Alex and I will perform in Sheffield and Manchester. I will be playing all of the above dates. See Alex fling Haskell in Emacs and me in vim, tmux, and xmonad! If you haven't heard Alex's music recently, he did a great track the other day: https://soundcloud.com/yaxu/at-last There's this set he did in Antwerp in May: https://www.youtube.com/watch?v=fgRDKxkHCSw My sets are likely to resemble this one that I did last Friday in Portugal: https://soundcloud.com/renick/live-at-xcoax-2014-porto-portugal-june-27-2014 Or this one from the Linux Audio Conference in May: https://soundcloud.com/renick/live-at-the-linux-audio-conference-2014-karls… If you come to one of the performances, please come up and say hello. I really want to meet the UK Haskell crew! Hope to see you there, dancing to Haskell or just relaxing and enjoying the music. Best, Renick -- Renick Bell - http://renickbell.net - http://twitter.com/renick - http://the3rd2nd.com

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use of -Werror
by Johan Larson 02 Jul '14

02 Jul '14

Is there a consensus within the Haskell community on the use of -Werror in packages uploaded to Cabal? Most places where I've worked, building with -Werror has been considered a laudable ideal, but fixing all the old warnings in the codebase was too much work, so it wasn't done. I suppose -Werror could cause problems in heterogeneous build environments. -- Johan Larson -- Toronto, Canada

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Haskell Wiki user account creation
by Haitham Gad 01 Jul '14

01 Jul '14

Hi, I read the following note at the log-in page of haskell wiki: NOTE: Automatic wiki account creation has been disabled. If you would like an account please email "nominolo" (at the email service from Google) or on the haskell-cafe mailing list. Does anyone know the exact email address I should be sending to (is it nominolo(a)gmail.com)? Thanks, Haitham

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Need help - my haskell code is over 50 times slower than equivalent perl implementation
by C K Kashyap 01 Jul '14

01 Jul '14

Dear cafe, I have created a reproducible app here - https://github.com/ckkashyap/haskell-perf-repro Essentially I am trying to open a number of files and printing out their sized by reading them in and computing it's length. I have the equivalent perl program also there. I'd appreciate it very much if someone could take a look at my Haskell implementation and point out what I am doing wrong. Since it's over 50 times slower than the perl code, I assume I am doing something obviously incorrect. Regards, Kashyap

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Algorithm for labeling same-colored regions in a 2D array?
by Steve Trout 01 Jul '14

01 Jul '14

(Apparently joining the list through the Google Groups interface doesn't work, but the post still shows up there. Sorry if you see this twice!) For fun, I'm writing a rules engine for the board game Go (in Haskell obviously). I have a board, which is a grid of spaces that can contain a black piece, a white piece, or nothing. Part of what i need to do is to detect regions of the same "color" (black, white, or empty) and get information about them like their size, the color of the bordering spaces, etc. Regions are bounded by other colors or the board edges in cardinal directions. I'm just starting on this so I haven't picked my data structures yet, but Vector (Vector _) or Map (Int, Int) _ are what I've toyed with. I have a vague idea of how I would go about this in an imperative language with mutation. I'd iterate over the board, keeping lists of points contained in the same region, combining (relabeling) regions if they happen to connect later on. (I realize there are probably better algorithms in those languages, but that would be my first attempt.) I know i could cobble something like this together in the State monad, but I have a feeling that there ought to be a better (more "Haskellish"/pure-functional) way. What would a Haskellish algorithm for this kind of thing look like? I wouldn't mind a complete answer or just a nudge in the right direction. Thanks, -Steve

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