August 2009 - Haskell-Cafe

REMINDER: Next BostonHaskell meeting TOMORROW (August 18th) at MIT
by Ravi Nanavati 17 Aug '09

17 Aug '09

The full details of the event are here: http://groups.google.com/group/bostonhaskell/browse_thread/thread/71243e7d2… I'm just sending out this reminder to make sure more people hear about the event (especially as, with Brent on vacation, there wasn't a Haskell Weekly News this week). If you're planning to come please respond to our scheduling poll at: http://doodle.com/participation.html?pollId=x8rbbbprtezdtaan This will help us get a better count of attendees for refreshments (since my wife has volunteered to make more baked goodies). Please also respond to the poll if you're interested in BostonHaskell, but couldn't come this month because of scheduling or location constraints. That will help us improve planning for future meetings. I look forward to seeing many Boston-area Haskellers tomorrow! Thanks, - Ravi Nanavati

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Got problems with classes
by Grigory Sarnitskiy 17 Aug '09

17 Aug '09

Hello! I can't understand why the following dummy example doesn't work. {-# OPTIONS -XTypeSynonymInstances #-} {-# OPTIONS -XFlexibleInstances #-} module Main where import Data.Array.Unboxed class Particle p type ParticleC = (Double, Double, Double) instance Particle ParticleC class Configuration c where getParticleI :: (Particle p) => c -> Int -> p type Collection p = UArray (Int,Int) Double instance Configuration (Collection p) where getParticleI config i = (1,1,1) :: ParticleC

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Credit Suisse is hiring
by Sittampalam, Ganesh 17 Aug '09

17 Aug '09

Hi, Just to chime in with the spate of job advertisements, the Global Modelling and Analytics Group (GMAG) at Credit Suisse is once again looking to hire functional programmers. The group consists of about 130 people worldwide. The majority of the group are mathematicians engaged in developing mathematical models for financial products traded by the division. Approximately 20 people are primarily computing experts, based in the Architecture and Delivery (AD) subgroup within GMAG, and successful candidates will also be based in this group. We are already making heavy use of functional programming within the group, and we expect to increase this in the future. Some information about our Haskell projects can be found here: http://www.haskell.org/communities/05-2009/html/report.html#creditsuisse ; more recently we have adopted F# for implementing and deploying models on the .NET platform and we are currently ramping up our F# usage. Our team works closely with the modellers to help them leverage functional programming to improve the design of their code. Key requirements: At least one of: - An academic track record in functional programming. - Significant experience of "real-world" computing environments, preferably using functional programming. Excellent communication skills in order to convey new ideas to our modelling team. Location: London or New York Contact: Howard Mansell <howard.mansell(a)credit-suisse.com> Myself (Ganesh Sittampalam <ganesh.sittampalam(a)credit-suisse.com>) and Tobias Gedell <tobias.gedell(a)credit-suisse.com> will be attending ICFP 2009 and associated workshops in Edinburgh - if you'd like to discuss this in person, get in touch with us by email, or just grab one of us there. Background information: As one of the world's leading banks, Credit Suisse provides its clients with investment banking, private banking and asset management services worldwide. Founded in 1856, Credit Suisse has a long tradition of meeting the complex financial needs of a wide range of clients, offering advisory services, comprehensive solutions and innovative products to companies, institutional clients and high-net-worth private clients globally. Credit Suisse is active in over 50 countries and employs approximately 46,000 people. Further information can be found at www.credit-suisse.com. Cultural diversity is essential to our success. As such, we employ people from more than 100 countries. Credit Suisse empowers employees to work openly and respectfully with each other and with clients, ultimately striving to deliver superior results while offering initiatives and programs to assist employees achieve a healthy work-life balance. The Global Modelling and Analytics Group (GMAG) is responsible for producing state-of-the-art pricing, trading and risk management models for Credit Suisse. These models are used across a range of businesses in the Fixed Income and Equity departments. The group performs the full spectrum of quantitative work, from mathematical modelling through software implementation and delivery, to risk analysis of trades and existing portfolios. The group's mandate covers all major asset classes, including Credit Derivatives, Commodities, Emerging Markets, Equity Derivatives and Convertibles, Exotics, Foreign Exchange, Fund Linked Products, Interest Rate Products and Mortgage Derivatives. GMAG operates globally with members located in London, New York, Hong Kong, Tokyo, Zurich and São Paolo. Established in 1990, GMAG stands out as a unified quant group that has been covering all major product areas since its inception. The group has always enjoyed a strong relationship with Trading, Structuring and Sales, assisting them with trade pricing and risk management. As the group is based on the trading floor, it is ideally placed to respond to the financial modelling needs of the businesses it supports. The breadth of GMAG's mandate makes it uniquely positioned to leverage the skills and experience of its members, and to provide a consistent modelling approach across all areas. Over time, the group has developed an extensive suite of pricing models on a common platform with complete integration across all asset classes. Quantitative Analysts in GMAG carry out a range of activities which include the creation of sophisticated mathematical models for the valuation of complex derivatives, development of the technology platform used to deliver models and driving the use of these models throughout the bank. Our Quantitative Analysts typically hold an advanced quantitative degree, have excellent analytical and problem-solving skills, demonstrate creative thinking, have strong programming skills, and are confident communicators. =============================================================================== Please access the attached hyperlink for an important electronic communications disclaimer: http://www.credit-suisse.com/legal/en/disclaimer_email_ib.html ===============================================================================

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Re: [Haskell] ANNOUNCE: GLUT 2.2.1.0
by Rafael Gustavo da Cunha Pereira Pinto 17 Aug '09

17 Aug '09

Thanks Sven! BTW, as an enhancement for 2.2.2.0, you could treat unnamed mouse buttons. Mouses with more axis and more buttons are becoming increasingly common, and "unmarshalMouseButton" is not prepared to accept them!! Here are exceptions I caught, playing with my Genius Traveler 515 mouse: unmarshalMouseButton: illegal value 5 unmarshalMouseButton: illegal value 6 unmarshalMouseButton: illegal value 7 unmarshalMouseButton: illegal value 8 Anyway, keep the good work! Best Regards, Rafael On Sun, Aug 16, 2009 at 13:12, Sven Panne <Sven.Panne(a)aedion.de> wrote: > A new version of the GLUT package has been uploaded to Hackage. > > * The package is now autoconf-free. API entries are resolved dynamically > at > runtime, just like the OpenGLRaw and GLURaw packages. > > * Support for sRGB framebuffers has been added, just use SRGBMode with > initialDisplayMode. To use this functionality, you need the upcoming > freeglut > 2.6.0 library, older versions and "classic" GLUT do not support this > feature. > > * Support for context profiles has been added via initialContextProfile. > Again, this works with the upcoming freeglut 2.6.0 library only. > > Cheers, > S. > _______________________________________________ > Haskell mailing list > Haskell(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell > -- Rafael Gustavo da Cunha Pereira Pinto

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Elerea/GLFW Tetris
by jean legrand 17 Aug '09

17 Aug '09

Hi Haskellers, Here is my first real program in Haskell. http://hpaste.org:80/fastcgi/hpaste.fcgi/view?id=8211 In fact, I'm not fully responsible because it's just an adapted version of a Tetris Creighton Hogg had written for Reactive/GLUT. As the first version, it's a very simple game (no levels, no points ...) but it's playable ! The major problem is when the board is full, the program sadly stops for an empty list : indeed, I wasn't interested in that part and I prefered dealing with the signals. As the frame is the same as the breakout frame, it is also possible to launch the game with ./Tetris --dump-dot | dot -Tsvg -o tetris.svg in order to get an svg showing a graph of the signals. Any help is welcome to understand this graph ! Every comment is welcome (especially about the first 170 lines). Enjoy!

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Getting highest sum of list elements with Map
by gwern0＠gmail.com 17 Aug '09

17 Aug '09

(Full source attached; or alternately, grab it: darcs get http://community.haskell.org/~gwern/hcorpus ) So I have this little program which hopefully will help me learn French by picking, from a textfile/corpus the most 'valuable' word to learn - the word that will complete or bring closer to completion the most sentences in that corpus. It's a relatively straightforward problem, but efficiency is an issue. It can handle up to a book in length just fine, but at 10x that, it eats all my RAM and seems as if it will run indefinitely. (I haven't let it run long enough to find out.) The profiling fingers the method I would expect, one 'ranks' at ~80% of runtime, but it doesn't get any more specific than that, alas. The inner loop goes: fidiv :: (Integral a, Fractional b) => a -> a -> b fidiv = (/) `on` fromIntegral swap :: (a, b) -> (b, a) swap = uncurry (flip (,)) ranks :: (NFData v, Ord k, Ord v) => Map.Map k (Set.Set v) -> Maybe (Rational, v) ranks s = listToMaybe . sortBy (flip compare) . pmap swap . Map.toList . Map.fromListWith (+) $ [(word, 1 `fidiv` Set.size wrds) | (_sentenceId, wrds) <- Map.toList s , word <- Set.toList wrds] approximation :: (NFData v, Ord k, Ord v) => Map.Map k (Set.Set v) -> Int -> [v] approximation _ 0 = [] approximation s n = case ranks s of Nothing -> [] Just (_value, word) -> let withoutWord = Map.map (Set.delete word) s in word : approximation withoutWord (n-1) The inside of 'ranks' is generating a list which will look like [("foo", 0.2), ("bar", 0.0), ("foo", 0.5)...]; we insert into an empty Map, using the word as the key, and incrementing the existing value (so with that example we'd have {"foo" -> 0.7, "bar" -> 0.0}, and then we immediately convert *back* to a list, swap the tuple elements, and sort the whole blessed thing. I can't help but think that this is rather inefficient, and not the most straightforward way to go about it. But poring through Data.Map, I can't figure out what the right thing to do is. Obviously I only want to pull out the key/string with the maximum Rational value, but all the min/max functions work only on the *key*, not the value. Am I missing something, or am I using the wrong data structure, or what? -- gwern

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Request for comments - hdnsomatic
by Jesús Alberto Sánchez Pimienta 17 Aug '09

17 Aug '09

Hello haskellers, I just finished my first useful haskell program and I'd be glad if you make me some comments http://hpaste.org/fastcgi/hpaste.fcgi/view?id=8244#a8244 Thank you, and sorry for my english. "Piensa y trabaja" Jesús Alberto Sánchez Pimienta Estudiante de la Lic. en Estudios Políticos y Gobierno Universidad de Guadalajara

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Re: [Haskell-beginners] Ambigous Types with Haskell Functional Graph Library
by Max Desyatov 17 Aug '09

17 Aug '09

Joe <joesmoe10(a)gmail.com> writes: > I tried using ucycle directly from Data.Graph.Inductive.Example by > itself. > > I didn't realize there were two instances of Graph. How would you use the > PatriciaTree Graph instance in the ucycle type signature? > > ucycle :: Graph gr => Int -> gr () () You must have that Graph instance in scope. I can't give any more suggestions as I don't see the code in which you use `ucycle`.

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ANNOUNCE: compose-trans-0.0
by Miguel Mitrofanov 17 Aug '09

17 Aug '09

Just uploaded compose-trans-0.0 to Hackage. 'compose-trans' is a small library intended to make monad transformers composable. It provides a class TransM, derived from MonadTrans, which is closed under composition - that is, if t1 and t2 are instances of TransM, then (t2 :. t1) is also an instance of TransM (and, therefore, an instance of MonadTrans), and the type ((t2 :. t1) m x) is isomorphic to (t2 (t1 m) x). It's fairly easy to make a new transformer an instance of TransM; it only takes one short line of code. There are also TransP and TransF classes, that help dealing with MonadPlus and MonadFix instances.

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Calling function with unknown number and type arguments
by Maciej Piechotka 17 Aug '09

17 Aug '09

I have to write a function which calls a function with unknown (i.e. given in runtime) number and type of arguments. 1. Use closure implementation from Gtk2Hs. Pros: Written Cons: Not in haskell 2. Use unsafeCoerce. Something like: f a b = return (a + b) f' = unsafeCoerce (f :: Int -> Int -> IO Int) :: IO () unsafeCoerce (unsafeCoerce ((unsafeCoerce f' :: Int -> IO ()) 5) :: Int -> IO ()) 4 :: IO Int (of course it is an example in fact it will be not only Int etc.) Personally I'd prefere in-haskell solution as: - Rts API used by Gtk2Hs is 'semi-public' - It is GHC-specific (?) but I'm not sure if my solution is safe. Regards

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