May 2009 - Haskell-Cafe

Qt declarative UI
by david48 13 May '09

13 May '09

I thought that it might interest some people : http://labs.trolltech.com/page/Projects/Graphics/Kinetic/DeclarativeUI

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caml build
by Vasili I. Galchin 13 May '09

13 May '09

Hello, I have forgotten whether I sent this posting out. Sorry if I did (I didn't see on Haskell cafe archive). I am building Swish and getting an error. I want to follow the progress of "swish build" ... I don't see an additional parameter like verbose mode that will tell which swish component is being built. ??? Regards, Vasili

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Stream-fusion without the lists
by Reiner Pope 13 May '09

13 May '09

Hi everyone, With stream-fusion, we can write functions which construct and destruct lists, such as (this is the main example from the Stream Fusion paper[1]) f :: Int -> Int f n = sum [k * m | k <- [1..n], m <- [1..k]] and the rewrite rules in stream-fusion replace these operations on lists with fusible operations on the Stream (non-recursive) datatype. In this example, the domain and codomain of the function don't mention the list datatype. There seem to be many functions like this: the lists are being used internally as composable loops rather than as data-structures. The Stream datatype seems to be much better suited to representing loops than the list datatype is. So, instead of programming with the lists, why don't we just use the Stream datatype directly? For example: In Data.Stream (from the stream-fusion package) we can find most of the Prelude list functions but with Stream in all the types instead of []. For example, Data.Stream.sum :: Num a => S.Stream a -> a Using this module, we can rewrite f without mentioning lists. We first need a Monad instance for Data.Stream.Stream: > import qualified Data.List.Stream as S > > instance Monad S.Stream where > return = S.return > (>>=) = S.concatMap Now we can write > f :: Int -> Int > f n = S.sum $ do > k <- S.enumFromToInt 1 n > m <- S.enumFromToInt 1 k > return (k*m) which is essentially the same as the original f, although lacking the syntactic sugar of the list comprehension. To me, it seems that Stream is more sensible data type to use than [] when the algorithm being expressed is just a loop (rather than something which needs a [] as a cache/buffer), for the following reasons: 1. If I am programming with lists and I need some function which I can't express with Prelude functions, I have to write it myself. I will probably lose fusion in this case, because I will write it recursively in terms of lists. On the other hand, if I am programming with Streams, I will write it myself in terms of Streams, and it should be easier to maintain fusion because it won't be recursive. 2. Holding on to a [] too long can cause a space leak. This is not the case for Stream, because a Stream only ever contains one "state". More generally, the memory use of Stream is more easily predictable than that of [], since "running" a Stream only holds on to one "state" at a time, and we often know how big the "state" is. 3. Fusion doesn't rely on rewrite rules firing. I consider this point less significant than the other two. So, thoughts? Do people program with Streams directly? What have I not considered? Cheers, Reiner [1] http://www.cse.unsw.edu.au/~dons/papers/stream-fusion.pdf

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Re: [Haskell-cafe] Functional Reactive Web Application Framework?
by Claus Reinke 13 May '09

13 May '09

oops, sorry, keyboard accident > >I assume you want to write FRP in a Haskell-embedded DSL and generate >>FRP'd JavaScript. If you wish to use Flapjax as a supporting library >>I'd be glad to help. > > I'm curious: how difficult is it nowadays for in-page JavaScript to > control the evolution of its surrouding page, FRP-style? I used to > do something like that, but with VRML+JavaScript instead of HTML > +JavaScript (there's a screencast for those without VRML viewer;-): > > http://community.haskell.org/~claus/FunWorlds/VRML/ > > and I found that mapping FRP style behaviours and events wasn't > the problem (though VRML has better support for this than HTML), > the problem was gaining the same advantages one would have from > embedding FRP in a functional language. Problems included scoping, > linking dynamically created material with enclosing scope (JavaScript > being in strings with scopes separate from the enclosing VRML, > VRML to be created dynamically also via strings, also in their own > scope) This became particularly obvious for dynamic recursion of reactive behaviours, somewhat like page n = <code involving n> `until` (keypress `then` (\key-> page n)) How are such things handled in Flapjax, if it follows the embedded compiler approach? Claus

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International Summer School on Advances in Programming Languages (precedes ICFP'09)
by Matthew Fluet (ICFP Publicity Chair) 13 May '09

13 May '09

International Summer School on Advances in Programming Languages 25th-28th August, 2009 Heriot-Watt University, Edinburgh, Scotland http://www.macs.hw.ac.uk/~greg/ISS-AiPL Overview ~~~~~~~~ This four-day residential International Summer School on Advances in Programming Languages has a major theme of Concurrency, Distribution, and Multicore. Intended primarily for postgraduate research students, the School offers lectures and practical sessions on an engaging blend of cutting edge theoretical and practical techniques from international experts. The Summer School is supported by the Scottish Informatics and Computer Science Alliance (http://www.sicsa.ac.uk/) a Scottish Funding Council Research Pool. Participants from SICSA member institutions may attend at no cost. Confirmed Topics/Speakers * Static and dynamic languages, Prof Philip Wadler, University of Edinburgh * Compiler technology for data-parallel languages, Dr Sven-Bodo Scholz, University of Hertfordshire * New applications of parametricity, Dr Janis Voigtlander, Technical University of Dresden * Automatic vectorising compilation, Dr Paul Cockshott, University of Glasgow * Foundational aspects of size analysis, Prof Marko van Eekelen / Dr Olha Shakaravska, Radboud University Nijmegen * Context oriented programming, Dr Pascal Costanza, Vrije Universiteit Brussels * Multi-core programming, Dr Phil Trinder, Heriot-Watt University * Multi-core compilation, Dr Alastair Donaldson, Codeplay Software Ltd * Principles and Applications of Refinement Types, Dr Andrew D. Gordon, Microsoft Research, Cambridge * Resource aware programming in Hume, Prof Greg Michaelson, Heriot-Watt University / Prof Kevin Hammond, University of St Andrews * Haskell concurrency & parallelism, Dr Satnam Singh, Microsoft Research, Cambridge Location ~~~~~~~~ The Summer School is at Heriot-Watt University's Riccarton campus, set in pleasant parkland to the west of Edinburgh, with easy access to the airport, city and central Scotland (http://www.hw.ac.uk/welcome/directions.htm) The Summer School immediately precedes the 2009 International Conference on Functional Programming (http://www.cs.nott.ac.uk/~gmh/icfp09.html) and takes place during the Edinburgh International Festival (http://www.eif.co.uk/) , and the associated Edinburgh Festival Fringe (http://www.edfringe.com/) and Edinburgh International Book Festival (http://www.edbookfest.co.uk/) Steering Committee ~~~~~~~~~~~~~~~~~~ Prof Prof Greg Michaelson, Heriot-Watt University (Convenor), <G.Michaelson(a)hw.ac.uk> Prof Kevin Hammond, University of St Andrews Dr Patricia Johann, University of Strathclyde Prof Philip Wadler, University of Edinburgh Fee ~~~ Full rate: £400; (free for SICSA students) Includes: four nights single room, en-suite accommodation with breakfast, lunch and dinner, plus coffee breaks and session materials. Day rate: £200; (free for SICSA students) Includes: lunch, coffee breaks, session materials Registration of Interest ~~~~~~~~~~~~~~~~~~~~~~~~ If you are interested in attending the International Summer School, please complete the form available from (http://www.macs.hw.ac.uk/~greg/ISS-AiPL/ISS-AiPL%20register.doc) or below, and return it to: <ISS-AiPL-register(a)macs.hw.ac.uk> ********** International Summer School on Advances in Programming Languages 25th-28th August, 2009 Heriot-Watt University, Edinburgh, Scotland Registration of Interest Name: Address: Email: Phone: SICSA Uni: Yes / No Rate: Full / Day Accessibility requirements: Dietary requirements: Return to: ISS-AiPL-register(a)macs.hw.ac.uk **********

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2nd Call For Papers: APLAS 2009 (Korea, Dec 14-16, 2009)
by Janis Voigtlaender 13 May '09

13 May '09

=============================================================== CALL FOR PAPERS The Seventh Asian Symposium on Programming Languages and Systems (APLAS 2009) Seoul, December 14-16, 2009 http://ropas.snu.ac.kr/aplas09/ =============================================================== APLAS aims at stimulating programming language research by providing a forum for the presentation of recent results and the exchange of ideas and experience in topics concerned with programming languages and systems. APLAS is based in Asia, but is an international forum that serves the worldwide programming languages community. The APLAS series is sponsored by the Asian Association for Foundation of Software (AAFS), which has recently been founded by Asian researchers in cooperation with many researchers from Europe and the USA. The past formal APLAS symposiums were successfully held in Bangalore (2008, India), Singapore (2007), Sydney (2006, Australia), Tsukuba (2005, Japan), Taipei (2004, Taiwan) and Beijing (2003, China) after three informal workshops held in Shanghai (2002, China), Daejeon (2001, Korea) and Singapore (2000). Proceedings of the past symposiums were published in Springer-Verlag's LNCS 2895, 3302, 3780, 4279, and 5356. TOPICS: The symposium is devoted to both foundational and practical issues in programming languages and systems. Papers are solicited on, but not limited, to the following topics: * semantics, logics, foundational theory * type systems, language design * program analysis, optimization, transformation * software security, safety, verification * compiler systems, interpreters, abstract machines * domain-specific languages and systems * programming tools and environments INVITED SPEAKERS: TBA IMPORTANT DATES: Abstract Deadline: June 8 (Monday), 2009 Paper Submission Deadline: 24:00 AM (in Samoan Time), June 15 (Monday), 2009 Author Notification: August 17, 2009 Camera Ready: September 14, 2009 Conference: December 14-16, 2009 SUBMISSIONS INFORMATION: Papers should be submitted electronically online via the conference submission web page at URL <http://www.easychair.org/conferences/?conf=aplas2009>. Acceptable formats are PostScript or PDF, viewable by Ghostview or Adobe Reader. Submissions should not exceed 16 pages in LNCS format, including bibliography and figures. Submitted papers will be judged on the basis of significance, relevance, correctness, originality, and clarity. They should clearly identify what has been accomplished and why it is significant. Submitted papers must be unpublished and not submitted for publication elsewhere. The proceedings of the symposium is planned to be published as a volume in Springer-Verlag's Lecture Notes in Computer Science series. Authors of selected papers will be invited after the symposium to submit a full version for publication in a special issue of New Generation Computing. GENERAL CHAIR Kwangkeun Yi (Seoul National University, Korea) PROGRAM CHAIR Zhenjiang Hu (National Institute of Inforamtics, Japan) PROGRAM COMMITTEE Manuel M. T. Chakravarty (University of New South Wales, Australia) Wei-Ngan Chin (National University of Singapore, Singapore) Nate Foster (University of Pennsylvania, USA) Ralf Hinze (Oxford University, United Kingdom) Zhenjiang Hu (National Institute of Informatics, Japan), Chair Ik-Soon Kim (Electronics and Telecommunications Research Institute, Korea) Julia Lawall (DIKU, Denmark) Sebastian Maneth (NICTA and University of New South Wales, Australia) Sungwoo Park (Pohang University of Science and Technology, Korea) G. Ramalingam (Microsoft Research, India) Peter Thiemann (University of Freiburg, Germany) Kazushige Terui (Kyoto University, Japan) Janis Voigtländer (Technical University of Dresden, Germany) Chung-chieh Shan (Rutgers University, USA) Kazunori Ueda (Waseda University, Japan) Bow-Yaw Wang (Academia Sinica, Taiwan) Jianjun Zhao (Shanghai Jiaotong University, China) POSTER SESSION CHAIR Kiminori Matsuzaki (University of Tokyo, Japan)

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haskell & cuda?
by Dan 13 May '09

13 May '09

Hi, Does anyone know if there's a compiler from Data-Parallel Haskell to GPU code? I saw a paper on it a while back, but Google hasn't turned up any code. Cheers, - Dan

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Kind of confusing
by Anton van Straaten 12 May '09

12 May '09

GHC amused me today with this error (context omitted): Couldn't match kind `(* -> *) -> * -> *' against `?? -> ? -> *' When matching the kinds of `t :: (* -> *) -> * -> *' and `(->) :: ?? -> ? -> *' It was a silly mistake: I had used 'lift' where I intended to use 'liftM'. But I'm thinking Haskell compilers should have some sort of option which, when the ratio of punctuation to alphanumerics in an error message exceeds a certain level, just responds to the user with a more readily comprehensible message such as "WTF, dude?" Serious question: what is the significance of the question mark and double question marks in those signatures, or better yet, where can I read about it? Anton

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Main function error
by applebiz89 12 May '09

12 May '09

I have compiled each function independently and they have compiled the only problem is the main function.. I keep getting the error 'films not defined' and I am not sure why [code] type Title = String type Director = String type Year = Int type Fan = String data Film = Film Title Director Year [Fan] deriving Show -- List of films testDatabase :: [Film] testDatabase = [ (Film "Casino Royale" "Martin Campbell" 2006 ["Garry", "Dave", "Zoe"])] -- Function filmsInGivenYear :: Year -> [Film] -> [String] filmsInGivenYear year' films = [ title | (Film title director year fans) <- films, year == year'] doFilmsInGivenYear :: [Film] -> IO () doFilmsInGivenYear films = do putStrLn "which year?" text <- getLine let year' = read text :: Int let answer = filmsInGivenYear year' films print answer main :: IO () main = do doFilmsInGivenYear films main [/code] if the other functions are compiling without this error im not sure as to why the main function does not compile because of the films...any light on this? Thanks -- View this message in context: http://www.nabble.com/Main-function-error-tp23506481p23506481.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Developing 3 dimensional interactive environments/functional objects
by paulfrancis＠friendbliss.com 12 May '09

12 May '09

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