August 2014 - Haskell-Cafe

local mins
by Закиров Марат 16 Aug '14

16 Aug '14

Some time ago we have a discussion and now I am ready to present my algorithm for counting local mins. It is liniar for imperative case and in functially too (I hope). I spent hours of debugging on it... -- | Main entry point to the application. module Main where str = [5, 6, 7, 1, 0, 5, 3] norm :: ([a],[a]) -> ([a],[a]) norm (x,[]) = (take l1 x, take l2 $ reverse x) where l1 = length x `div` 2 l2 = length x - l1 norm ([],x) = (take l2 $ reverse x, take l1 x) where l1 = length x `div` 2 l2 = length x - l1 norm x = x insert :: (Ord a, Show a) => [a] -> Int -> ([(a, Int)],[(a, Int)]) -> ([(a, Int)],[(a, Int)]) insert [] _ x = x insert x p ([],[]) = ([(head x, p)],[]) insert x p (y,[]) = insert x p (norm (y,[])) insert x p (ys,z:zs) = if head x >= fst z then (ys,(head x, p):z:zs) else insert x p (ys,zs) delete :: (Ord a, Show a) => Int -> Int -> ([(a, Int)],[(a, Int)]) -> ([(a, Int)],[(a, Int)]) False = undefined delete p r ([],x) = delete p r (norm ([],x)) delete p r (x:xs,y) = if p > (snd x + r) then (xs,y) else (x:xs,y) getmin :: (Ord a, Show a) => ([(a, Int)],[(a, Int)]) -> a getmin ([],[]) = error "Getmin error" getmin ([],x) = getmin (norm ([],x)) getmin (x:xs,y) = fst x pass :: (Ord a, Show a) => [a] -> [a] pass [] = [] pass (x:xs) = xs minn :: Ord a => [a] -> [a] -> [a] minn x y = [] lmini :: (Ord a, Show a) => Int -> Int -> ([(a, Int)],[(a, Int)]) -> [a] -> [a] -> [a] lmini _ _ _ [] _ = [] lmini p r deq c l = if p < r then lmini (p+1) r (insert l p deq) c (pass l) else getmin deqn : lmini (p+1) r deqn (pass c) (pass l) where deqn = if p < (r*2) then insert l p deq else insert l p (delete (p-1) r deq) lmin :: (Ord a, Show a) => Int -> [a] -> [a] lmin r x = lmini 0 r ([],[]) x x main :: IO () main = do putStrLn "Min for list" putStrLn $ show str -- Regards, Marat. С уважением Марат.

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ANNOUNCE: BOB Conference 2015 Berlin
by Matthias Fischmann 15 Aug '14

15 Aug '14

BOB Conference 2015 Berlin 23.1.2015 http://bobkonf.de/2015/ CALL FOR CONTRIBUTIONS English: http://bobkonf.de/2015/cfp.html German: http://bobkonf.de/2015/cfp.html Deadline: September 30, 2014 You drive advanced software engineering methods, implement ambitious architectures and are open to cutting-edge innovation? Attend this conference, meet people that share your goals, and get to know the best software tools and technologies available today. We strive to offer you a day full of new experiences and impressions that you can use to immediately improve your daily life as a software developer. If you share our vision and want to contribute, submit a proposal for a talk or tutorial! We are looking for talks about best-of-breed software technology, e.g.: - functional programming - reactive programming - micro-service architectures - persistent data structures and databases - everything really that isn’t mainstream, but you think should be. Presenters should provide the audience with information that is practically useful for software developers. This could take the form of e.g.: - experience reports - introductory talks on technical background - demos and how-tos We accept proposals for presentations of 45 minutes (40 minutes talk + 5 minutes questions), as well as 90 minute tutorials for beginners. The language of presentation should be either English or German. - questions to bobkonf at active minus group dot de - proposal deadline: September 30, 2014 - notification: October 15, 2014 - program: October 2014, 2014 For more info, visit http://bobkonf.de/2015/ Looking forward to your submissions, and to seeing you there! cheers, matthias

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Functional Programming Job Opportunities
by stephen.t.west＠barclays.com 15 Aug '14

15 Aug '14

The Risk & Analytics team at Barclays currently has opportunities for functional programmers with experience of investment banking technology and quantitative analytics. If you're interested, please contact me (stephen dot t dot west at barclays dot com). Regards, Stephen. _______________________________________________ This message is for information purposes only, it is not a recommendation, advice, offer or solicitation to buy or sell a product or service nor an official confirmation of any transaction. It is directed at persons who are professionals and is not intended for retail customer use. Intended for recipient only. This message is subject to the terms at: www.barclays.com/emaildisclaimer. For important disclosures, please see: www.barclays.com/salesandtradingdisclaimer regarding market commentary from Barclays Sales and/or Trading, who are active market participants; and in respect of Barclays Research, including disclosures relating to specific issuers, please see http://publicresearch.barclays.com. _______________________________________________

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Using `jack` on Windows, sounds realistic?
by Alois Cochard 15 Aug '14

15 Aug '14

Hi all, I've been recently used the great `jack` library from Henning Thielemann (cc'ed) on my linux computer. It work like a charm, but I was wondering about Windows support? As I see Jack run on windows, I'm hoping I might be able to build my haskell application that use `jack` on windows as well, is that realistic? anyone have tried already? Thanks in advance Note: I plan to have an other backend using 'portaudio', which would allow me to be cross-platform anyway... but using Jack bring ASIO support, which is really need for my use case (real time synthesizer). -- *Λ\ois* http://twitter.com/aloiscochard http://github.com/aloiscochard

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Cannot install the Haskell Platform on GNU/Linux (possible Cabal issue)
by egarrulo 15 Aug '14

15 Aug '14

Hello guys, I cannot install the Haskell Platform 2014.2.0.0 on my GNU/Linux system: $ ./platform.sh \ > --prefix=/opt/haskell-platform/haskell-platform-2014.2.0.0 \ > ../ghc-7.8.3/ghc-7.8.3-i386-unknown-linux.tar.bz2 Warning: The following packages are likely to be broken by the reinstalls: haskell-platform-2013.2.0.0 Use --force-reinstalls if you want to install anyway. === pre-requisite packages for hptool are not installed run the following: cd hptool ; cabal install --only-dependencies However, the dependencies for *hptool* are already installed: $ cd hptool ; cabal install --only-dependencies Resolving dependencies... All the requested packages are already installed: Use --reinstall if you want to reinstall anyway. The existing Haskell system: - GHC 7.6.3 - Haskell Platform 2013.2.0.0 - cabal-install 1.16.0.2 (using Cabal library 1.16.0) Any help? Thank you.

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How to improve the zipwith's performance
by jun zhang 15 Aug '14

15 Aug '14

Dear All I write a code for Clustering with Data.Clustering.Hierarchical, but it's slow. I use the profiling and change some code, but I don't know why zipwith take so many time? (even I change list to vector) My code is as blow, Any one kindly give me some advices. ====================== main = do .... let cluster = dendrogram SingleLinkage vectorList getVectorDistance .... getExp2 v1 v2 = d*d where d = v1 - v2 getExp v1 v2 | v1 == v2 = 0 | otherwise = getExp2 v1 v2 tfoldl d = DV.foldl1' (+) d changeDataType:: Int -> Double changeDataType d = fromIntegral d getVectorDistance::(a,DV.Vector Int)->(a, DV.Vector Int )->Double getVectorDistance v1 v2 = fromIntegral $ tfoldl dat where l1 = snd v1 l2 = snd v2 dat = DV.zipWith getExp l1 l2 ======================================= build with ghc -prof -fprof-auto -rtsopts -O2 log_cluster.hs run with log_cluster.exe +RTS -p profiling result is log_cluster.exe +RTS -p -RTS total time = 8.43 secs (8433 ticks @ 1000 us, 1 processor) total alloc = 1,614,252,224 bytes (excludes profiling overheads) COST CENTRE MODULE %time %alloc getVectorDistance.dat Main 49.4 37.8 tfoldl Main 5.7 0.0 getExp Main 4.5 0.0 getExp2 Main 0.5 1.5

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HaskellWiki page about SDL
by Henk-Jan van Tuyl 15 Aug '14

15 Aug '14

L.S., Does the problem with SDL on OS X, as mentioned on the HaskellWiki page about SDL[0], still exist? This text is quite old and I would like to remove it. Regards, Henk-Jan van Tuyl [0] https://www.haskell.org/haskellwiki/SDL#Haskell-SDL_with_Mac_OS_X -- Folding@home What if you could share your unused computer power to help find a cure? In just 5 minutes you can join the world's biggest networked computer and get us closer sooner. Watch the video. http://folding.stanford.edu/ http://Van.Tuyl.eu/ http://members.chello.nl/hjgtuyl/tourdemonad.html Haskell programming --

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haskell (and beyond) in education
by Rustom Mody 15 Aug '14

15 Aug '14

I am collecting some data on FP used to introduce programming ie as a first course: http://blog.languager.org/2014/08/universities-starting-functional.html Naturally the haskell link is the first: http://www.haskell.org/haskellwiki/Haskell_in_education I was just wondering if there are more extremal cases of this: eg Are there any univs using Idris/Agda to *introduce* programming/math/proofs etc

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maintainer needed: extensible-effects
by Ben Foppa 15 Aug '14

15 Aug '14

Hey cafe, is there anybody interested in taking over maintainership of the extensible-effects package? I'm rather busy and not keeping a good eye on it.

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Closed Type Family Simplification
by Ian Milligan 14 Aug '14

14 Aug '14

When a closed type family has only one instance it seems like it should never fail to simplify. Yet this doesn't appear to be the case. When I defined (in GHC 7.8.3) the closed type family type family (:.:) f g a where (:.:) f g a = f (g a) I get errors such as 'Could not deduce (Object c3 ((:.:) f g a) ~ Object c3 (f (g a)))' (where Object is a Constraint family), indicating that f (g a) is not being substituted for (:.:) f g a as desired. Any idea why this happens?

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