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Call for papers (Deadline Extended): MULTICONF-10, USA, July 2010
by John Edward 24 Mar '10

24 Mar '10

It would be highly appreciated if you could share this announcement with your colleagues, students and individuals whose research is in computer science, computer engineering, information science and related areas. Call for papers (Deadline Extended): MULTICONF-10, USA, July 2010 The 2010 multi-conference (MULTICONF-10) (website: http://www.PromoteResearch.org ) will be held during July 12-14, 2010 in Orlando, Florida, USA. The primary goal of MULTICONF is to promote research and developmental activities in computer science, information technology, control engineering, and related fields. Another goal is to promote the dissemination of research to a multidisciplinary audience and to facilitate communication among researchers, developers, practitioners in different fields. The following conferences are planned to be organized as part of MULTICONF-10. • International Conference on Artificial Intelligence and Pattern Recognition (AIPR-10) • International Conference on Automation, Robotics and Control Systems (ARCS-10) • International Conference on Bioinformatics, Computational Biology, Genomics and Chemoinformatics (BCBGC-10) • International Conference on Computer Communications and Networks (CCN-10) • International Conference on Enterprise Information Systems and Web Technologies (EISWT-10) • International Conference on High Performance Computing Systems (HPCS-10) • International Conference on Information Security and Privacy (ISP-10) • International Conference on Image and Video Processing and Computer Vision (IVPCV-10) • International Conference on Software Engineering Theory and Practice (SETP-10) • International Conference on Theoretical and Mathematical Foundations of Computer Science (TMFCS-10) MULTICONF-10 will be held at Imperial Swan Hotel and Suites. It is a full-service resort that puts you in the middle of the fun! Located 1/2 block south of the famed International Drive, the hotel is just minutes from great entertainment like Walt Disney World® Resort, Universal Studios and Sea World Orlando. Guests can enjoy free scheduled transportation to these theme parks, as well as spacious accommodations, outdoor pools and on-site dining — all situated on 10 tropically landscaped acres. Here, guests can experience a full-service resort with discount hotel pricing in Orlando. Please see the website http://www.PromoteResearch.org for more details. Sincerely John Edward

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web
by Dupont Corentin 24 Mar '10

24 Mar '10

Hello, what would you use to grab data displayed on a web site (several pages hyper-linked)? And then to compute and display statistics over that data? Thanks, Corentin

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Applicative functors and trees
by Darryn Reid 23 Mar '10

23 Mar '10

Hi, I'm playing around with Functors in Haskell with the aim of understanding more structured functors, particularly applicative functors and traversable and foldable. I'm using the standard binary tree type to play around with this, as follows: data Tree a = Empty | Leaf a | Node (Tree a) a (Tree a) I think I understand Functor fine: instance Functor Tree where fmap f Empty = Empty fmap f (Leaf x) = Leaf (f x) fmap f (Node l x r) = Branch (fmap f l) (f x) (fmap f r) (with (<$>) being a synonym for fmap). This satisfies the laws for Functor (I'll omit details). Likewise, I think I'm fine with Foldable, for Tree a over any monoid a: instance Foldable Tree foldMap f Empty = mempty foldMap f (Leaf x) = f x foldMap f (Node l x r) = foldMap f l `mappend` f x `mappend` foldMap f r Where I'm stuck is with Applicative: class (Functor f) => Applicative f where pure :: a -> f a (<*>) :: f (a -> b) -> f a -> f b I understand that pure lifts a value into the applicative functor, so this one is easy: pure = Leaf but I cannot see what <*> should look like. I know that <*> is essentially application ($) lifted into the functor, so if the functor were also a monad then <*> would be liftM2 ($), I suppose. But I want a "direct" implementation, without monads floating about, but I cannot see what to do. I think then I would be able to define an instance for traversable as something like this: instance Traversable Tree traverse f Empty = pure Empty traverse f (Leaf x) = Leaf `fmap` f x traverse f (Node l x r) = Node `fmap` traverse f (l <*> f x <*> traverse f r) (I think that <*> must be associative). Can anyone advise what <*> should look like, please? Thanks in advance for your help. Darryn.

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How to print the name of a variable
by John Velman 20 Mar '10

20 Mar '10

I have a number of variables (whose values are computed in my program) of the same type, and in ghci I want to be able to call a function to print something computed from the value of one or more of these to a file. I want the file name to reflect the name of the variable. This is probably not clear, but conceptually the function to do the output would look something like this: someFunction :: MyTypeVariable -> String writeFileFor :: MyTypeVariable -> IO () writeFileFor v = do nameOfV <- someFunction v outh <- openFile nameOfV ++ ".txt" WriteMode outputstring = calculationsFrom v hPutStr outh outputstring hClose outh Is there any such "someFunction", or is there a way to build one? Thanks, John Velman

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ghci parse error on input
by Rick Murphy 20 Mar '10

20 Mar '10

Hello All: Using GHCi, I am working from an existing example which surprisingly contains a parse error in an export statement. I have reproduced the parse error as follows: > module Export > ( > (^) > , (#) > ) > where > import Prelude hiding ((^)) GHCi reports: parse error on input (# I read 5.2 Export Lists in the Haskell Report, but the syntax above does not appear to contradict the Haskell Report. I have eliminated the following solutions: 1. Add (#) to the hiding list. 2. Swap the (#) and (^). 3. Load as non-literate file. Would anyone be able to provide advice on how to avoid this parse error? -- Rick blog: http://phaneron.rickmurphy.org

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Recursion/dynamic programming optimization
by ivovnenko 20 Mar '10

20 Mar '10

Hi. I tried to solve one of the google code jam's problems using haskel http://code.google.com/codejam/contest/dashboard?c=90101#s=p2: w :: Eq a => [a] -> [a] -> Int w text str = w' (reverse text) (reverse str) w' :: Eq a => [a] -> [a] -> Int -- Init w' _ [] = 0 w' [] _ = 0 -- For one symbol string w' text [a] = if head text == a then w' (tail text) [a] +1 else w' (tail text) [a] -- General case w' text str = if head str == head text then w' (tail text) (tail str) + w' (tail text) str else w' (tail text) str and it worked great on small inputs, not on large: w "viwiwhiuwwwgxzseebneesgzxiekzeeyivrbbhzrlllccxczyurxfhhccghkzvxusfbcucyvncpzpvfvccxcvbqnqogobzoiorxrbikyzzbobpmmmmpmvrzyivpfmmuzxixhqpeebyekkxffeyexeiukuebgbrukzefeu rkxy z h x vkq fsyp iy tfyzbptygtsrkhbytvruztzbttnoxuquokipyyqoik ib xu gxchcnccuccyfcccccsczccskifcprgovryxuxoozqoozsvudyfkdpkkxyhdvfsrnvpnpzvrhqhbduidkdpdysinyxnuxnxipddevqhgeufxeepyyezbekyviieeeryiexynevbzfeezryizvepynefffy y v zuzrbpzn sz y vzirkxjniuqvjjbjgubnjkujhjpiyanaabrqagzqqvspqpkvqyuhrgupbaiaasxybiygmmfimyvykkmrzum" "welcome to code jam" Can you please advice how to optimize this solution? Thanks. Regards, Ivan Vovnenko

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Simple lookahead with Parsec
by Derek Thurn 19 Mar '10

19 Mar '10

Hello. I'm just starting out with Parsec and Haskell, and I want to parse a very simple grammar with it. I think I may not understand how to use try correctly. Here's a simplified version of my grammar: myType = try (primitiveType) <|> arrayType primitiveType = do {reserved "int"; return "primitive"} arrayType = do { primitiveType; symbol "["; symbol "]"; return "array"} Basically, I want to use lookahead to produce the result "array" on inputs like "int[]" and the result "primitive" on inputs like "int". However, no matter what I do with the try function, I am not able to get what I expect. When I run this code using the runLex function described in the Parsec documentation, it chokes on "int[]", saying that the '[' character was unexpected. I've discovered that switching the order of primitiveType and arrayType solves this, which makes sense, but I still expected it to be possible to use try() in this manner to resolve the error with lookahead. Am I doing something wrong? (I've got some boilerplate code form the Parsec documentation defined as well, but I didn't include it for brevity's sake. Reserved and symbol are defined how you'd expect.)

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Getting into a Haskell project?
by Duncan Mortimer 19 Mar '10

19 Mar '10

Hi All, I'm very new to both Haskell, and open source development (well... really, development of any kind...). However, I'm really interested in getting good at both. I was wondering whether anyone has any suggestions about good open source Haskell projects I could cut my teeth on, and any advice in general in getting into this stuff more deeply? Thanks! Duncan

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how long it will take to install Haskell
by love_pku 18 Mar '10

18 Mar '10

Dear Sir or Madam: I met problems when install haskell. Following are the interface after do the command 'make',and it stay at the state 'Linking Setup'for a long time. So I am wondering how long it will take to finish 'linking setup'. #make scripts/build.sh Platform package mtl-1.1.0.2 is already installed. Skipping... Building "/usr/local/bin/ghc" "--make" "Setup" "-o" "Setup" "-package" "Cabal-1.6.0.3" Linking Setup ...

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about installation of Haskell
by love_pku 18 Mar '10

18 Mar '10

Dear Sir or Madam:: Sorry to trouble you! I am a beginner of Haskell and I just run into problems to install it. Things went smoothly when I do ./configure,but when I do the command 'make',errors appeared. The errors are as follows(red font): $make scripts/build.sh Building "/usr/bin/ghc" "--make" "Setup" "-o" "Setup" "-package" "Cabal" Linking Setup ... "./Setup" "configure" "--package-db=../../packages/package.conf.inplace" "--prefix=/usr/local" "--with-compiler=/usr/bin/ghc" "--with-hc-pkg=/usr/bin/ghc-pkg" "--with-hsc2hs=/usr/bin/hsc2hs" "--enable-library-profiling" Setup: Unrecognised flags: --package-db=../../packages/package.conf.inplace Error: Configuring the mtl-1.1.0.2 package failed make: *** [build.stamp] Error 2 So I do hope you can give me some suggestions. Thank you very much! Best wishes, Yours, juan

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