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Re: [Haskell-cafe] [Haskell] ANNOUNCE: GHC version 7.8.1
by Ketil Malde 10 Apr '14

10 Apr '14

Austin Seipp <austin(a)well-typed.com> writes: > The (Interactive) Glasgow Haskell Compiler -- version 7.8.1 Congrats! > * Massive scalability improvements to the I/O manager Just a brief note from the front lines - I recompiled a heavily threaded program with (a recent pre-release) of 7.8.1 and got a 10% performance increase over 7.6.3. Nothing like free lunches - so thanks again for the great work! -k -- If I haven't seen further, it is by standing in the footprints of giants

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Haskell Weekly News: Issue 290
by Daniel Santa Cruz 10 Apr '14

10 Apr '14

Welcome to issue 289 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers from April 1 to 5, 2014 Quotes of the Week * edwardk: Zombies are expensive. Top Reddit Stories * foldl is broken! Domain: well-typed.com, Score: 148, Comments: 63 On Reddit: [1] http://goo.gl/LXmJTV Original: [2] http://goo.gl/viOG5O * A small Haskell extension Domain: augustss.blogspot.nl, Score: 76, Comments: 23 On Reddit: [3] http://goo.gl/buI46t Original: [4] http://goo.gl/LnAV9y * New GHC Features for 7.10.1 and Beyond Domain: haskell.org, Score: 74, Comments: 26 On Reddit: [5] http://goo.gl/DdXTfO Original: [6] http://goo.gl/g0FPBS * Libc considered harmful Domain: sylvain-henry.info, Score: 58, Comments: 28 On Reddit: [7] http://goo.gl/aq39Mf Original: [8] http://goo.gl/qdQDXm * Category Theory by Tom LaGatta Domain: youtube.com, Score: 58, Comments: 53 On Reddit: [9] http://goo.gl/oIzG1e Original: [10] http://goo.gl/DeLu5G * Idris 0.9.12 released with major laziness, codata, and documentation updates plus metavars in types Domain: idris-lang.org, Score: 55, Comments: 25 On Reddit: [11] http://goo.gl/4MtXJS Original: [12] http://goo.gl/3tXbqC * A cool paper I found on "Functional Programming and 3D Games". It discusses everything from collision detection to physics and texturing. [PDF] Domain: cse.unsw.edu.au, Score: 52, Comments: 3 On Reddit: [13] http://goo.gl/6PYB2e Original: [14] http://goo.gl/Tf6fa2 * Error reporting with locations Domain: augustss.blogspot.fr, Score: 47, Comments: 28 On Reddit: [15] http://goo.gl/ikaENm Original: [16] http://goo.gl/hntlJT * [ANN] Haste now has a website and a mailing list Domain: haste-lang.org, Score: 42, Comments: 7 On Reddit: [17] http://goo.gl/Ife2FA Original: [18] http://goo.gl/lRWmhv * Haskell in the Newsroom Domain: infoq.com, Score: 41, Comments: 5 On Reddit: [19] http://goo.gl/M4tehD Original: [20] http://goo.gl/bpvgLA * Haskell application architecture best practices Domain: self.haskell, Score: 32, Comments: 23 On Reddit: [21] http://goo.gl/XjHfNJ Original: [22] http://goo.gl/XjHfNJ Top StackOverflow Questions * Haskell - Is it possible to make pointfree functions more readable using different combinators than (.)? votes: 11, answers: 1 Read on SO: [23] http://goo.gl/5b036l * How to detect if a program has been compiled using -threaded? votes: 10, answers: 2 Read on SO: [24] http://goo.gl/Cr7pMA * What does the star mean in this haskell code? votes: 9, answers: 2 Read on SO: [25] http://goo.gl/qnolS7 * What about arrows? votes: 9, answers: 2 Read on SO: [26] http://goo.gl/b1wwp4 * Triggering a documentation update for a Hackage package votes: 8, answers: 1 Read on SO: [27] http://goo.gl/ErTVzf * Combining Data.Dynamic and type classes votes: 7, answers: 0 Read on SO: [28] http://goo.gl/n8qMo9 * Systematically applying a function to all fields of a haskell record votes: 6, answers: 3 Read on SO: [29] http://goo.gl/tNkLGu * Transforming a List of 2-Tuples in Haskell votes: 6, answers: 3 Read on SO: [30] http://goo.gl/dDe8QP * Error in ghci which I cannot reproduce in written haskell file votes: 6, answers: 1 Read on SO: [31] http://goo.gl/bg8DCw * Why can I call a monadic function without supplying a monad? votes: 6, answers: 1 Read on SO: [32] http://goo.gl/xZZ5iO * Deriving default instances using GHC.Generics votes: 6, answers: 1 Read on SO: [33] http://goo.gl/Autu6r Until next time, [34]+Daniel Santa Cruz References 1. http://www.well-typed.com/blog/90/ 2. http://www.reddit.com/r/haskell/comments/21wvk7/foldl_is_broken/ 3. http://augustss.blogspot.nl/2014/04/a-small-haskell-extension.html 4. http://www.reddit.com/r/haskell/comments/2239wh/a_small_haskell_extension/ 5. http://www.haskell.org/pipermail/haskell-cafe/2014-April/113373.html 6. http://www.reddit.com/r/haskell/comments/21wbme/new_ghc_features_for_7101_a… 7. http://sylvain-henry.info/blog/posts/2014-04-01-libc-considered-harmful.html 8. http://www.reddit.com/r/haskell/comments/220ae4/libc_considered_harmful/ 9. https://www.youtube.com/watch?v=o6L6XeNdd_k 10. http://www.reddit.com/r/haskell/comments/229scs/category_theory_by_tom_laga… 11. http://www.idris-lang.org/idris-0-9-12-released/ 12. http://www.reddit.com/r/haskell/comments/2284s5/idris_0912_released_with_ma… 13. http://www.cse.unsw.edu.au/~pls/thesis/munc-thesis.pdf 14. http://www.reddit.com/r/haskell/comments/21zush/a_cool_paper_i_found_on_fun… 15. http://augustss.blogspot.fr/2014/04/haskell-error-reporting-with-locations.… 16. http://www.reddit.com/r/haskell/comments/226otd/error_reporting_with_locati… 17. http://haste-lang.org/ 18. http://www.reddit.com/r/haskell/comments/21x4wm/ann_haste_now_has_a_website… 19. http://www.infoq.com/presentations/haskell-newsroom-nyt 20. http://www.reddit.com/r/haskell/comments/222i82/haskell_in_the_newsroom/ 21. http://www.reddit.com/r/haskell/comments/223i80/haskell_application_archite… 22. http://www.reddit.com/r/haskell/comments/223i80/haskell_application_archite… 23. http://stackoverflow.com/questions/22872098/haskell-is-it-possible-to-make-… 24. http://stackoverflow.com/questions/22839824/how-to-detect-if-a-program-has-… 25. http://stackoverflow.com/questions/22807728/what-does-the-star-mean-in-this… 26. http://stackoverflow.com/questions/22871648/what-about-arrows 27. http://stackoverflow.com/questions/22783637/triggering-a-documentation-upda… 28. http://stackoverflow.com/questions/22876370/combining-data-dynamic-and-type… 29. http://stackoverflow.com/questions/22807619/systematically-applying-a-funct… 30. http://stackoverflow.com/questions/22828259/transforming-a-list-of-2-tuples… 31. http://stackoverflow.com/questions/22839784/error-in-ghci-which-i-cannot-re… 32. http://stackoverflow.com/questions/22841899/why-can-i-call-a-monadic-functi… 33. http://stackoverflow.com/questions/22850983/deriving-default-instances-usin… 34. https://plus.google.com/105107667630152149014/about

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www.galois.com' response to Heartbleed .... .
by Vasili I. Galchin 10 Apr '14

10 Apr '14

http://corp.galois.com/blog/2014/4/9/heartbleed-a-great-time-to-think-about… BTW I am always very careful when I use memcpy .. .hate that function ... read "buffer overrun" big time .....

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Automatically infer Newtype instance
by Dmitry Bogatov 09 Apr '14

09 Apr '14

Hello! I think, that Newtype instances are transitive, and there is only one sane definiton is (pack . pack). But in example below I have to use UndecidableInstances and they seems to loop somewhere (Context reduction stack overflow; size = 132). To my understanding, Ghc tries to prove, that exists only one type b, and somewhy fail at it(It is unclear, why), but is it any way to say to it that I take responsibility, that ANY b would be nice? I know about TH, but interested in more elegant solution. {-# LANGUAGE MultiParamTypeClasses #-} {-# LANGUAGE FunctionalDependencies #-} {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE UndecidableInstances #-} import Control.Newtype newtype A1 = A1 Int deriving (Eq, Show) newtype A2 = A2 A1 deriving (Eq, Show) instance Newtype A1 Int where pack = A1 unpack (A1 a) = a instance Newtype A2 A1 where pack = A2 unpack (A2 a) = a -- Here comes UndecidableInstances instance (Newtype a b, Newtype b c) => Newtype a c where pack = pack . pack unpack = unpack . unpack main = let foo :: A2 foo = pack "46" in print foo -- Best regards, Dmitry Bogatov <KAction(a)gnu.org>, Free Software supporter, esperantisto and netiquette guardian. git://kaction.name/rc-files.git GPG: 54B7F00D

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Looking for maintainer of pwstore-fast
by Michael Snoyman 09 Apr '14

09 Apr '14

I just tried emailing Peter Scott, the maintainer of pwstore-fast[1], but the listed email address is no longer working. He also hasn't been responding to Github pings. Does anyone know how to get in touch with him? [1] http://hackage.haskell.org/package/pwstore-fast

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Heart Bleed bug in OpenSSL
by Vasili I. Galchin 09 Apr '14

09 Apr '14

http://heartbleed.com/ Ok .. I just scanned this .. but is this problem a "logic" bug in the OpenSSL C/C++ code or is a type correctness issue? Thanks, Vasili

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Re: [Haskell-cafe] ANNOUNCE: GHC version 7.8.1
by Felipe Lessa 09 Apr '14

09 Apr '14

Em 09-04-2014 11:23, Austin Seipp escreveu: > An updated SHA256SUMS.sig is attached. Thanks for Edsko de Vries for > pointing it out! If anybody is, like myself, trying to find a link for the SHA256SUMS file on the download page, here it is: https://www.haskell.org/ghc/dist/7.8.1/SHA256SUMS For some reason it seems that it's not linked anywhere on that page. Cheers, and thanks for the release! =) -- Felipe.

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Library for creating interactive diagrams?
by Kai Zhang 09 Apr '14

09 Apr '14

Hi cafe, Is there any active project about creating interactive diagrams, like D3js http://d3js.org/ ? The Diagrams library has already done a good job of making static images. Would it be possible to extend this library to support declaring interactive diagrams and then use JS and HTML as backend to draw them? Example: circle 1 $ with & hover .~ (change style) PS: I don't want a D3js binding.

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GHC Optimization seriously hurting performance by unsharing.
by Michael Karcher 09 Apr '14

09 Apr '14

Hello Haskell folks, Can you give me a hint whether the GHC optimizer behaviour demonstrated below should be considered a bug? If it is no bug, what should I keep in mind to make sure not to hit that trap again? This posting is (obviously) formatted as literal Haskell file, so feel free to try. This is a case where -O2 completely kills performance, because it unshares an object that should be shared. I stumbled across this behaviour of GHC 7.6.3 when trying to solve RMQ from hackerrank. Lets start with a typical header, the reason for the IORef module is discussed later. > module Main where > import Data.Set (member, fromAscList) > import Control.Monad (replicateM_) > import Data.IORef Now lets get to the code. > main = do The original problem statement requested to read a set of numbers from the standard input. To have this testcase self-contained, we use a "virtual file" instead, which is an (IORef String). The key point is that we need to get the string with the space-sperated test element from an IO operation, whereas it does not matter whether it is "getLine" or "readIORef" > ior <- newIORef $ unwords $ map show $ [1..20000] Now read the space-separated test input from an IO action. > testdata <- fmap (map read.words) $ readIORef ior and build a set from the number array we obtained to speed up membership queries. You don't want to search 20.000 numbers on each iteration. > let bigset = fromAscList testdata finally query the membership of the number 5 several times. This happens to be reasonably fast if compiled without optimization, but goes down to dog slow if compiled with optimization, as the set building process is hoisted into the loop and thus performed 10 times. > replicateM_ 10 . print . member 5 $ bigset this is the solution (or the workaround) to the problem. If you use this line, things get fast, because the loop gets created after evaluting the set to WHNF, thus forcing sharing replicateM_ 10 . print . member 5 $! bigset Enabling both of the replicateM_ lines also speeds up the first one, as the use of bigset in both lines prevents hoisting set construction into the first loop. Regards, Michael Karcher

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ANNOUNCE slot-lambda
by ducis 08 Apr '14

08 Apr '14

http://hackage.haskell.org/package/slot-lambda It lets your write lambdas with 'slots' without inventing names for the parameters. [s| ı + ı |] = \x y -> x+y The unicode character ı(305) representing a 'slot' can be input in vim with the digraph 'i.' . Use _ı to refer to the immediate left ı, and _0, _1, _2, ... to refer to the 1st, 2nd, 3rd, ... arguments respectively. e.g. [s| ı : ı : _ı : ı : _ı : _ı : _0 : [] |] 'a' 'b' 'c' = (\x y z -> x:y:y:z:z:z:x:[]) 'a' 'b' 'c' = "abbccca" I originally intended using '_' to represent the 'slots' but that doesn't parse as legal haskell. Actually I wonder how to achieve that without rolling my own haskell parser or forking haskell-src-exts.

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