May 2014 - Haskell-Cafe

ANN: hcwiid-0.0.5 (wiimote, gaming)
by Ivan Perez 28 May '14

28 May '14

Hi cafe! We are happy to announce the release of Hcwiid 0.0.5, the Haskell bindings for cwiid, which provide a user-space driver for Nintendo's Wiimotes. The following new features have been made available recently: *- Infrared support*. This is essential if you want to use the sensor bar to detect what the wiimote is pointing at. *- Accelerometer support*. * - Improved API*. Access to all the key features, new auxiliary functions not present in cwiid, and a higher-level interface via the type system. *- Documentation*. An effort is being made to provide not only haddock documentation, but also several tests that demonstrate the features of this library. More information (including "What is a wiimote and how can I use it?" and "what can we expect next") can be found here: http://keera.co.uk/blog/2014/05/27/interacting-haskell-games-using-wiimote/ Hackage: https://hackage.haskell.org/package/hcwiid Github: https://github.com/ivanperez-keera/hcwiid I hope you all enjoy spicing up your applications a little bit with this library. All the best Ivan facebook: https://www.facebook.com/keerastudios twitter: @KeeraStudios

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Interfacing BTCe
by Miro Karpis 28 May '14

28 May '14

Hi cafe, I'm trying to interface BTCe and get my account info. I have found following peace of code, which I would like to build on top: http://pastebin.com/AfDt8jcs I have added to the request a POST method, but I'm still getting error from BTCe: "{\"success\":0,\"error\":\"*invalid nonce parameter; on key:0*, you sent:\"}" The API is documented here: https://btc-e.com/api/documentation In short: Authorization is performed by sending the following HTTP Headers: *Key* — API key *Sign* — POST data (?param=val&param1=val1) signed by a secret key according to HMAC-SHA512 method; Sent on *https://btc-e.com/tapi <https://btc-e.com/tapi>* . All requests must also include a special *nonce* POST parameter with increment integer. (>0) The method name is sent via POST parameter method. All the method parameters are sent via POST. {-# LANGUAGE OverloadedStrings #-} import Network.HTTP.Conduit import Network.HTTP.Types.Header import Data.Word import Data.ByteString.Lazy(pack) import qualified Data.ByteString.Char8 as B import Data.Digest.Pure.SHA import Data.Time.Clock.POSIX ------------------------------------------------------------------------------- toWord8 :: String -> [Word8] toWord8 = Prelude.map (fromIntegral . fromEnum) ------------------------------------------------------------------------------- key :: B.ByteString key = "key" secret :: String secret = "secret" url :: String url = "https://btc-e.com/tapi" ------------------------------------------------------------------------------- querystring :: Int -> String querystring nonce = "?method=getInfo&nonce=" ++ show nonce sign :: Int -> B.ByteString sign nonce = B.pack $ show $ hmacSha512 (pack $ toWord8 secret) (pack $ toWord8 $ querystring nonce) main :: IO () main = do nonce <- fmap floor getPOSIXTime putStrLn $ url ++ (querystring nonce) ticker <- parseUrl $ url ++ (querystring nonce) let request = ticker { secure = True , method = "POST" , requestHeaders = (requestHeaders ticker) ++ [ ("Content-Type", "application/x-www-form-urlencoded") , ("Host", "btc-e.com") , ("User-Agent", "Haskell Trading Robot") , ("Key", key) , ("Sign", sign nonce)]} putStrLn $ show request response <- withManager $ httpLbs request print $ responseBody response any ideas more than welcome cheers, miro

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Munich Haskell Meeting
by Heinrich Hördegen 27 May '14

27 May '14

Dear all, our next Haskell meeting in Munich is scheduled for the 29th of May, 19h30 at Cafe Puck. If you plan to join, please go to http://www.haskell-munich.de/dates and klick the button. With hope to see many of you, Heinrich

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Second Workshop on Haskell And Rewriting Techniques (HART 2014, co-located with ICFP 2014)
by Janis Voigtlaender 27 May '14

27 May '14

CALL FOR PAPERS Second Workshop on Haskell And Rewriting Techniques (HART 2014) http://www.program-transformation.org/HART14/ To be held on September 5, co-located with ICFP, the Haskell Symposium, etc., in Gothenburg. Haskell is an advanced purely-functional programming language. Pure functional programming is programming with equations, often defined by pattern-matching. Rewriting is the science of replacing equals by equals and thus a very powerful method for dealing with equations, often constructor-based. There are strong connections between Haskell (or generally, pure functional) programming and rewriting. The purpose of the HART workshop is to foster those connections. In addition to an invited talk by Oleg Kiselyov, we plan a half day of discussions, in an informal setting, on how Haskell (and related languages) and rewriting techniques and theories can cross-fertilize each other. Topics of interest are, for example: ==================================== - equational reasoning and other rewriting techniques for program verification and analysis; - lambda calculi and type systems for functional programs and higher-order rewrite systems; - rewriting of type expressions in the type checker; - rewriting of programs by refactoring tools, optimizers, code generators; - execution of programs as a form of graph rewriting (terms with sharing); - Template Haskell, generally introducing a rewriting-like macro language into the compilation process. This list of topics is non-exclusive. If you have a contribution that connects Haskell and rewriting, then submit. Also, the workshop is deliberately open for discussion of rewriting-related aspects of languages like Agda, Clean, ... When in doubt, please contact a member of the PC (see below). Dates: ====== July 2: deadline for submissions July 21: notification of acceptance September 5: workshop Submission and proceedings: =========================== We solicit two types of submissions: - Extended abstracts. Presenting original research, and also preliminary reports of work in progress. Will be included in the proceedings. - Presentation-only papers. Describing work recently published or submitted. Only abstract will be included in the proceedings. Papers should be at most 5 pages in length, and should use the easychair.cls style. Submission is electronically at https://www.easychair.org/conferences/?conf=hart2014 In line with the informal style of the workshop, the reviewing of submissions will be light. Proceedings will be made available electronically. Program committee: ================== Bertram Felgenhauer Carsten Fuhs Andy Gill Makoto Hamana Bastiaan Heeren Femke van Raamsdonk Tiark Rompf Kristoffer Rose (co-chair) Christian Sternagel Janis Voigtländer (co-chair) Johannes Waldmann

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Cabal, tar and uploading to Hackage
by Magnus Therning 26 May '14

26 May '14

Lately my attempts at creating tar-balls for uploading to Hackage have been failing. I use the standard `./Setup.hs sdist` method to generate tar-balls, but apparently that uses `/usr/bin/tar` (GNU tar), which defaults to the 'gnu' format, while Hackage requires the 'ustar' format. Is there some way to pass arguments to `tar` when using `./Setup.hs sdist`? /M -- Magnus Therning OpenPGP: 0xAB4DFBA4 email: magnus(a)therning.org jabber: magnus(a)therning.org twitter: magthe http://therning.org/magnus Heuristic is an algorithm in a clown suit. It’s less predictable, it’s more fun, and it comes without a 30-day, money-back guarantee. -- Steve McConnell, Code Complete

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How to write fast for loops
by Niklas Hambüchen 26 May '14

26 May '14

As you probably now, `forM_ [1..n]` is incredibly slow in Haskell due to lack of list fusion [1]; a manually written loop is 10x faster. How do you people work around this? I keep defining myself something like loop :: (Monad m) => Int -> (Int -> m ()) -> m () loop bex f = go 0 where go !n | n == bex = return () | otherwise = f n >> go (n+1) Is there a function for this somewhere already? Or do you have another way to deal with this problem? Thanks! [1]: https://ghc.haskell.org/trac/ghc/ticket/8763

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New Functional Programming Job Opportunities
by Functional Jobs 26 May '14

26 May '14

Here are some functional programming job opportunities that were posted recently: Haskell Developer at skedge.me http://functionaljobs.com/jobs/8712-haskell-developer-at-skedgeme Cheers, Sean Murphy FunctionalJobs.com

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Chan with priorities
by Bulat Ziganshin 26 May '14

26 May '14

Hello Haskell-cafe, can you please point me to any OSS implementation of IO Channels with priorities - i.e. data pushed to the Chan using high priority should be read prior to the data pushed with lower priority: pushChan ch 1 'x' pushChan ch 2 'y' readChan ch >>= print -- prints 'y' i've found only STM implementations - i don't know STM enough, may be i just need to convert STM to IO operations? i don't expect strong guarantees, my algorithm will remain correct anyway. and i don't have lot of objects, it's just a few dozens -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com

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Job opening: Anchor Hosting, Sydney - Linux Haskell Developers
by Christian Marie 25 May '14

25 May '14

Anchor hosting is hiring Haskell developers! ============================================ Anchor hosting has job opportunities for two entry-to mid-level developers. We will be building an open source cloud hosting platform built upon Ceph and OpenStack in Haskell. This will involve experience across diverse fields, such as: Linux systems development, distributed systems, metric storage, data analysis, monitoring, tool development, REST API design and development, to name a few. We have two positions available; if you can't make your mind up, feel free to ask about them. Linux Systems Developer / Wizard ================================ You will work alongside sysadmins and developers on the Systems Team. This developer will be cutting a lot of Linux systems automation code, and will probably build a distributed system by the time you're done. A proven track record with Haskell and Linux is a must. Knowledge of type theory and language design would be a bonus. A working knowledge of C and basic algorithms is expected. You'll get to work on a Cloud hosting framework with interesting technologies, doing some cool things that nobody has done before. Data engineer ============= Part of our Analytics team, this role is fundamentally about helping our engineers make evidence-based decisions. You would be writing code to take numbers (such as the CPU usage of a set of machines) and convert them into more useful numbers (such as the probability of those servers catching fire in the next week, or the usage we should be billing the customer for). In addition to a working knowledge of Haskell and UNIX programming, experience working with large datasets, computational stats or machine learning would be a big plus. Applicants ========== Please send a resume along with a link to your Github account to pingu(a)anchor.com.au. Perks ===== Why Anchor should be your home away from home: * Our kick-ass office is on Hyde park, with Town Hall station just minutes away. * Well-stocked drinks fridge. * Catered lunch every Friday. * Pizza and board games every Tuesday night. * Transparent, no-nonsense and trusting environment – if we hire you we know you’ll do the right thing. * Company account with a great coffee shop across the road means your daily caffeination is free of charge! -- Christian Marie - Sparkly Code Princess

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wanted: Function to break circular data dependencies
by Job Vranish 24 May '14

24 May '14

Is a function like the following possible?: avoidCircularDataDependency :: a -> a -> a avoidCircularDataDependency a b = ? I want avoidCircularDataDependency to evaluate 'a', but if in the process of evaluating 'a' its own result is demanded (which normally would result in an infinite loop) it returns 'b' otherwise it returns 'a' . I've often found myself wanting a function like this. It would make certain kinds of knot-tying/cycle detection _much_ easier. Is there any reason why this function can't/shouldn't exist? - Job

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