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Odd behavior with Num instance for lists (was: f^n for functional iteration)
by Mark Fredrickson 13 Dec '13

13 Dec '13

On Fri, Dec 13, 2013 at 8:59 AM, Antonio Nikishaev <me(a)lelf.lu> wrote: > > http://hackage.haskell.org/package/NumInstances > The previous exchange prompted me to whip up a Num instance for lists: instance Num a => Num [a] where negate = fmap negate (+) = zipWith (+) (*) = zipWith (+) fromInteger x = [fromInteger x] abs = fmap abs signum = fmap signum It mostly behaves how one would expect: let a = [1,2,3] ghci> let b = [4,5,6,7] ghci> a + b [5,7,9] ghci> 1 + a [2] I was wondering whey `1 + a` succeeds. At first I thought it could be the `fromInteger` definition, but this explanation were true, I should be able to add integers and doubles freely, which I can't: ghci> fromInteger (1::Integer) + (1.0::Double) 2.0 ghci> (1::Integer) + (1.0::Double) <interactive>:30:17: Couldn't match expected type `Integer' with actual type `Double' In the second argument of `(+)', namely `(1.0 :: Double)' ... Thanks for enlightening me. -M

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Re: [Haskell-cafe] f^n for functional iteration
by Doug McIlroy 13 Dec '13

13 Dec '13

Agreeing with the analysis, I will sharpen my question. Is option 2 possible at all, regardless of sanity concerns (e.g. incomplete implementation of Num). Doug > On Tue, 10 Dec 2013 at 10:51 AM, Danny Gratzer <danny.gratzer(a)gmail.com> wrote > > Well (^) is already used for their traditional meaning and using this exact > operator would require > > 1. Shadowing (^) from prelude > 2. Making (a -> a) an instance of Num (impossible to do sanely) > > You can just use a different operator > > f .^. n = foldl (.) id $ replicate n f > > On Tue, Dec 10, 2013 at 10:45 AM, Doug McIlroy <doug(a)cs.dartmouth.edu>wrote: > > > Is there a trick whereby the customary notation f^n for iterated > > functional composition ((\n f -> foldl (.) id (replicate n f)) n f) can > > be defined in Haskell? > > > > Doug McIlroy

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Way to implement toFloat :: (Num a) => a -> Float
by EatsKittens 12 Dec '13

12 Dec '13

Is there a way to add a method to a typeclass like num to implement this concept? A function that converts any number to floats?

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ANN - csound-expression 3.1 library for electronic music
by Anton Kholomiov 12 Dec '13

12 Dec '13

I'm glad to announce the new version of the csound-expression [1] package. It's the library for electronic music and sound design. Here is a full description [2] In the new version it supports GUI-widgets. You can not only create sound instruments but update parameters onlne with sliders, knobs and buttons. There are many other widgets. You can find out the details in the quick start guide [3] and the examples [4]. Anton [1] http://hackage.haskell.org/package/csound-expression [2] https://github.com/anton-k/csound-expression [3] https://github.com/anton-k/csound-expression/blob/master/tutorial/QuickStar… [4] https://github.com/anton-k/csound-expression/tree/master/examples/Gui

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SENIOR HASKELL OPPORTUNITY
by Neena Singh 12 Dec '13

12 Dec '13

Hello, I have been retained by a leading Hedge Fund who are looking for an experienced Haskell developer to join their highly regarded front office technology team. This is a great opportunity for a passionate technologist to join a group working very closely with the trading floor on advanced Haskell projects. Previous finance experience is not a pre-requisite however a passion for Haskell is a must. If you are interested learning more about this opportunity and potential salary ranges please call me on 020 7871 4482 or email me Neena.singh(a)henlowgroup.com<mailto:Neena.singh@henlowgroup.com>. I look forward to hearing from you, Regards, Neena Neena Singh Analyst Henlow Recruitment Group +44(0)20 7871 1834 neena.singh(a)henlowgroup.com<mailto:neena.singh@henlowgroup.com> www.henlowgroup.com<http://www.henlowgroup.com/> [cid:image017.jpg@01CECB15.783A6E10]<https://twitter.com/Henlow_Group> [cid:image019.png@01CECB15.783A6E10] <http://www.linkedin.com/profile/view?id=300878083&authType=OUT_OF_NETWORK&a…> [cid:image005.png@01CEDA27.B1142430] <http://www.linkedin.com/profile/view?id=300878083&authType=OUT_OF_NETWORK&a…> This e-mail contains proprietary information some or all of which may be legally privileged. It is for the intended recipient only. If an address or transmission error has misdirected this email, please notify the author by replying to this e-mail. If you are not the intended recipient you must not use, disclose, distribute, copy, print, rely on or retain this e-mail. This email and any attached files have been scanned for the presence of computer viruses, however you are advised that you open any attachments at your own risk. All e-mails including CV's are subject to our standard terms and conditions of business. The acceptance of any CV's constitutes the acceptance of our standard terms and conditions of business unless there has been written prior agreement. Any views or opinions presented here may be solely those of the originator and are not necessarily those of Henlow Recruitment Group. Henlow Recruitment Group reserves the right to share information between companies within our group. Please read Henlow Recruitment Groups' privacy policy at http://www.henlowgroup.com/privacy-policy to understand how Henlow Recruitment Group uses and protects the information you provide.

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GLFW/GLFW-b ambiguity
by Vlad Lopatin 12 Dec '13

12 Dec '13

Hey guys, I am messing with OpenGL and here's the question: GLFW-b is supposed to be based on GLFW and extend it. How come GLFW-b naming is ambiguous with GLFW? GLFW-b main module is named the same as GLFW (import Graphics.UI.GLFW), making it necessary to hide one of the libraries via ghc-pkg hide, or to use a language extension in order to solve ambiguity. I am tempted to consider it a bug, unless somebody knows a good reason for it to be called a feature. Am I missing something? Regards, Vladimir

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Haskell Weekly News: Issue 287
by Daniel Santa Cruz 12 Dec '13

12 Dec '13

Welcome to (the "I'm not dead yet") issue 287 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers the very long span of time from November 10 to December 07, 2013. Quotes of the Week * chrisdone: monads are like a finger pointing away to the moon. *smack* don't look at the finger or you will miss all that heavenly glory * quchen: A group with an associative law is called a group. * chrisdone: i swim in a sea of parens and it warms me like rays of the sun * zomg: my client tells me weekly how I've saved his company. Then I goto haskell and I'm like "I have no idea what I'm doing lul" * pigworker: The usual style is to write as if everything is inductive, and if it still works on infinite data, to pat ourselves on the back for using Haskell rather than ML. Top Reddit Stories * Honorary Doctorate for Simon Peyton Jones - On December 3 2013 Simon Peyton Jones was honoured by the University of Glasgow with the honorary degree of Doctor of Science. Domain: dcs.gla.ac.uk, Score: 166, Comments: 18 On Reddit: [1] http://goo.gl/XLezZO Original: [2] http://goo.gl/WqC2EN * Hell: A Haskell shell Domain: github.com, Score: 114, Comments: 53 On Reddit: [3] http://goo.gl/6ogD6n Original: [4] http://goo.gl/YCzNT3 * Löb and möb: strange loops in Haskell Domain: github.com, Score: 95, Comments: 35 On Reddit: [5] http://goo.gl/8bF5Op Original: [6] http://goo.gl/GqzuP0 * Explanation of the new Haskell records extension Domain: well-typed.com, Score: 88, Comments: 70 On Reddit: [7] http://goo.gl/419sYv Original: [8] http://goo.gl/g24kLB * FP Complete IDE now free for community use. Give it a try! Domain: fpcomplete.com, Score: 86, Comments: 65 On Reddit: [9] http://goo.gl/OJh2Oz Original: [10] http://goo.gl/2FYHa * The Haskell Cast #4 - Simon Marlow on Parallelism and Concurrency Domain: haskellcast.com, Score: 82, Comments: 13 On Reddit: [11] http://goo.gl/kzNEz3 Original: [12] http://goo.gl/yrUDXL * 24 Days of Hackage: scotty Domain: ocharles.org.uk, Score: 74, Comments: 16 On Reddit: [13] http://goo.gl/CoUanr Original: [14] http://goo.gl/a83HZg * Idris 0.9.10 released Domain: idris-lang.org, Score: 73, Comments: 21 On Reddit: [15] http://goo.gl/0OnlPV Original: [16] http://goo.gl/MKtbxu * 24 Days of Hackage: threepenny-gui Domain: ocharles.org.uk, Score: 68, Comments: 4 On Reddit: [17] http://goo.gl/vSTpc0 Original: [18] http://goo.gl/Hmjqzq * 24 Days of Hackage: linear Domain: ocharles.org.uk, Score: 66, Comments: 43 On Reddit: [19] http://goo.gl/dcFHGg Original: [20] http://goo.gl/R9c0bh * 24 Days of Hackage: tasty Domain: ocharles.org.uk, Score: 65, Comments: 4 On Reddit: [21] http://goo.gl/xIwvgk Original: [22] http://goo.gl/aUJGLJ * 24 Days of Hackage: 2013 in Review Domain: ocharles.org.uk, Score: 64, Comments: 11 On Reddit: [23] http://goo.gl/ideT63 Original: [24] http://goo.gl/DQYDar * Hacking Haskell in nightclubs (x-post from /r/programming) Domain: vice.com, Score: 60, Comments: 30 On Reddit: [25] http://goo.gl/ezuhIJ Original: [26] http://goo.gl/bD3vnN * 24 Days of Hackage: extensible-effects Domain: ocharles.org.uk, Score: 60, Comments: 25 On Reddit: [27] http://goo.gl/5T2brL Original: [28] http://goo.gl/q2hVM0 * From Object Oriented Programming to Functional Programming - Inheritance and the Expression Problem Domain: github.com, Score: 58, Comments: 62 On Reddit: [29] http://goo.gl/fFldOR Original: [30] http://goo.gl/n5nHYo * I've been working on a small roguelike in Haskell Domain: github.com, Score: 56, Comments: 26 On Reddit: [31] http://goo.gl/mojdIu Original: [32] http://goo.gl/fT9DLB * Chordify: Get the chords to any song, using Haskell ! Domain: chordify.net, Score: 55, Comments: 19 On Reddit: [33] http://goo.gl/YfcHEu Original: [34] http://goo.gl/19apd * Merging, Folding, Monoids, and Foldable Domain: mtnviewmark.wordpress.com, Score: 53, Comments: 5 On Reddit: [35] http://goo.gl/GtoDKp Original: [36] http://goo.gl/QJsd7L * 24 Days of Hackage: persistent & esqueleto Domain: ocharles.org.uk, Score: 49, Comments: 14 On Reddit: [37] http://goo.gl/97eeUF Original: [38] http://goo.gl/TL8P7V * Haskell From Scratch - Series about making a non-trivial app from the ground up. Domain: youtube.com, Score: 46, Comments: 2 On Reddit: [39] http://goo.gl/sPV7rs Original: [40] http://goo.gl/KslDE4 Top StackOverflow Questions * What does (f .) . g mean in Haskell? votes: 17, answers: 2 Read on SO: [41] http://goo.gl/2i3GNc * LaTeX natural deduction proofs using Haskell votes: 13, answers: 0 Read on SO: [42] http://goo.gl/uH1K2u * Lazily Tying the Knot for 1 Dimensional Dynamic Programming votes: 13, answers: 4 Read on SO: [43] http://goo.gl/1kZQkK * What does Clojure borrow from Haskell? [on hold] votes: 12, answers: 0 Read on SO: [44] http://goo.gl/DsqKhp * Meaning of `<-` in do block in Haskell votes: 10, answers: 4 Read on SO: [45] http://goo.gl/JOJiFy * Why is function composition in Haskell right associative? votes: 10, answers: 1 Read on SO: [46] http://goo.gl/mURUDZ * Is there a library or typeclass for getting the transformer version of a monad? votes: 9, answers: 1 Read on SO: [47] http://goo.gl/k81E1h * How to implement B+ tree in Haskell? votes: 9, answers: 2 Read on SO: [48] http://goo.gl/lkwh8Z * Delimiting the IO monad votes: 9, answers: 2 Read on SO: [49] http://goo.gl/x3RlXO Until next time, [50]+Daniel Santa Cruz References 1. http://www.dcs.gla.ac.uk/~muffy/SPJ_oration.pdf 2. http://www.reddit.com/r/haskell/comments/1sbfmb/honorary_doctorate_for_simo… 3. https://github.com/chrisdone/hell 4. http://www.reddit.com/r/haskell/comments/1r755t/hell_a_haskell_shell/ 5. https://github.com/quchen/articles/blob/master/loeb-moeb.md 6. http://www.reddit.com/r/haskell/comments/1qwjk6/l%C3%B6b_and_m%C3%B6b_stran… 7. http://www.well-typed.com/blog/84 8. http://www.reddit.com/r/haskell/comments/1rpte3/explanation_of_the_new_hask… 9. https://www.fpcomplete.com/ 10. http://www.reddit.com/r/haskell/comments/1qzioh/fp_complete_ide_now_free_fo… 11. http://www.haskellcast.com/episode/004-simon-marlow-on-parallelism-and-conc… 12. http://www.reddit.com/r/haskell/comments/1rexqq/the_haskell_cast_4_simon_ma… 13. http://ocharles.org.uk/blog/posts/2013-12-05-24-days-of-hackage-scotty.html 14. http://www.reddit.com/r/haskell/comments/1s65bl/24_days_of_hackage_scotty/ 15. http://www.idris-lang.org/idris-0-9-10-released/ 16. http://www.reddit.com/r/haskell/comments/1rn4d6/idris_0910_released/ 17. http://ocharles.org.uk/blog/posts/2013-12-07-24-days-of-hackage-threepenny-… 18. http://www.reddit.com/r/haskell/comments/1sc67q/24_days_of_hackage_threepen… 19. http://ocharles.org.uk/blog/posts/2013-12-02-24-days-of-hackage-linear.html 20. http://www.reddit.com/r/haskell/comments/1rximk/24_days_of_hackage_linear/ 21. http://ocharles.org.uk/blog/posts/2013-12-03-24-days-of-hackage-tasty.html 22. http://www.reddit.com/r/haskell/comments/1s0t1f/24_days_of_hackage_tasty/ 23. http://ocharles.org.uk/blog/posts/2013-12-01-24-days-of-hackage-intro.html 24. http://www.reddit.com/r/haskell/comments/1rv45n/24_days_of_hackage_2013_in_… 25. http://www.vice.com/read/algorave-is-the-future-of-dance-music-if-youre-an-… 26. http://www.reddit.com/r/haskell/comments/1riror/hacking_haskell_in_nightclu… 27. http://ocharles.org.uk/blog/posts/2013-12-04-24-days-of-hackage-extensible-… 28. http://www.reddit.com/r/haskell/comments/1s3oba/24_days_of_hackage_extensib… 29. https://github.com/Dobiasd/articles/blob/master/from_oop_to_fp_-_inheritanc… 30. http://www.reddit.com/r/haskell/comments/1quhrl/from_object_oriented_progra… 31. https://github.com/dvolk/hoodie 32. http://www.reddit.com/r/haskell/comments/1r248j/ive_been_working_on_a_small… 33. http://chordify.net/ 34. http://www.reddit.com/r/haskell/comments/1r7sh1/chordify_get_the_chords_to_… 35. https://mtnviewmark.wordpress.com/2013/12/02/mfmf/ 36. http://www.reddit.com/r/haskell/comments/1rz8cn/merging_folding_monoids_and… 37. http://ocharles.org.uk/blog/posts/2013-12-06-24-days-of-hackage-persistent-… 38. http://www.reddit.com/r/haskell/comments/1s9fyb/24_days_of_hackage_persiste… 39. https://www.youtube.com/playlist?list=PLxj9UAX4Em-Ij4TKwKvo-SLp-Zbv-hB4B 40. http://www.reddit.com/r/haskell/comments/1s48bm/haskell_from_scratch_series… 41. http://stackoverflow.com/questions/20279306/what-does-f-g-mean-in-haskell 42. http://stackoverflow.com/questions/19919431/latex-natural-deduction-proofs-… 43. http://stackoverflow.com/questions/20159269/lazily-tying-the-knot-for-1-dim… 44. http://stackoverflow.com/questions/20411148/what-does-clojure-borrow-from-h… 45. http://stackoverflow.com/questions/19961941/meaning-of-in-do-block-in-haske… 46. http://stackoverflow.com/questions/20342860/why-is-function-composition-in-… 47. http://stackoverflow.com/questions/20066858/is-there-a-library-or-typeclass… 48. http://stackoverflow.com/questions/20309501/how-to-implement-b-tree-in-hask… 49. http://stackoverflow.com/questions/20318936/delimiting-the-io-monad 50. https://plus.google.com/105107667630152149014/about

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striping non-alphanumericals
by Joerg Fritsch 11 Dec '13

11 Dec '13

I have the following code snippet: import System.IO import Data.String.Utils main = withFile "test.txt" ReadMode $ \handle -> do xs <- getwords handle sequence_ $ map putStrLn (escapeRe xs) getwords :: Handle -> IO [String] getwords h = hGetContents h >>= return . words What I want to to there is to get i.e. "word," or "word!" etc. and arrive at "word". I understand that escapeRe may do this. However, I always get some sort of mismatch errors like this: test.hs:6:38: Couldn't match type `Char' with `[Char]' Expected type: [String] Actual type: String In the return type of a call of `escapeRe' In the second argument of `map', namely `(escapeRe xs)' In the second argument of `($)', namely `map putStrLn (escapeRe xs)' test.hs:6:47: Couldn't match type `[Char]' with `Char' Expected type: String Actual type: [String] In the first argument of `escapeRe', namely `xs' In the second argument of `map', namely `(escapeRe xs)' In the second argument of `($)', namely `map putStrLn (escapeRe xs)' Now I have three questions: 1. Is escapeRe the right function to use here? 2. What do I do wrong? 3. I read in the Real World Haskell book that actually all these file/string operations are very very slow. The recommendation is to work with bytestrings instead. Is there any (fast) way to strip non-alphanumericals from bytestrings? Thanks, --Joerg

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Re: [Haskell-cafe] Does anyone use ghc-mod with Yesod?
by Carlo Hamalainen 11 Dec '13

11 Dec '13

On 11/12/13 01:36, Curtis Carter wrote: > I believe you just need to install that lib. It's not in the main > dependencies but in the test ones. That did the trick. I thought that yesod-test would be installed automatically when I ran cabal install in the Yesod project directory. I can confirm that ghc-mod works fine on a Yesod project via ghcmod-vim. Thanks, -- Carlo Hamalainen http://carlo-hamalainen.net

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ANN: tasty-0.5
by Roman Cheplyaka 11 Dec '13

11 Dec '13

The new version of Tasty, a modern and extensible testing framework for Haskell, is out. The major new feature in this release is resources, described in detail in the article http://ro-che.info/articles/2013-12-10-tasty-resources.html Although I haven't posted here since the very first release of tasty, there have been many small improvements and some new big features, such as resources and ingredients. The core Tasty packages are now part of Stackage, which means that you can use them in FP Haskell Center™ and School of Haskell. It's also great to see third-party packages appearing, which was the main motivation behind Tasty's extensible design: http://hackage.haskell.org/package/tasty-th, by Benno Fünfstück http://hackage.haskell.org/package/tasty-hspec, by Mitchell Rosen http://hackage.haskell.org/package/tasty-ant-xml, by Oliver Charles To learn more about Tasty, please see: http://documentup.com/feuerbach/tasty — the README http://hackage.haskell.org/package/tasty-0.5.1/docs/Test-Tasty.html — the haddock documentation https://github.com/feuerbach/tasty/blob/master/CHANGES.md — the changelog http://ocharles.org.uk/blog/posts/2013-12-03-24-days-of-hackage-tasty.html — this year's «24 days of Hackage» article about Tasty Roman

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