February 2010 - Beginners

Draft paper submission deadline is extended: MULTICONF-10, Orlando, USA
by John Edward 14 Feb '10

14 Feb '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. Draft paper submission deadline is extended: MULTICONF-10, Orlando, USA 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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distinguished types
by Rick Murphy 14 Feb '10

14 Feb '10

Greetings and thanks in advance for all the great work on this list. Being new Haskell I hope someone could help me clarify the use of the term *distinguished type* in relation to Haskell 98 as well as confirm my understanding of the construction of a distinguished type in GHC. I understand from [1] that a distinguised type is defined as a type with only one non-bottom value and that value is in fact identical to the name of the type. [1] provides the unit type () as an example of a Haskell distinguished type. Would it be accurate to say that an approach to creating distinguished types in Haskell is to create data types with a single constructor whose name is identical to the data type name? More specifically, would > data F = F deriving (Show) create a distinguished type F in Haskell? I've searched the Haskell Report, but there's no indication that the report recognizes distinguished types. Is that true and if so why ? 1. http://okmij.org/ftp/Scheme/misc.html -- Rick cell: 703-201-9129 web: http://www.rickmurphy.org blog: http://phaneron.rickmurphy.org

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running HGL on Mac OSX
by Vojtěch Knyttl 13 Feb '10

13 Feb '10

Hello, I am having difficulties running HGL on Mac OSX, Snow Leopard. Here is what I've done: –– 1. Installed X11 for OSX ("About" dialog says: The X Window System, XQuartz 2.3.4 (xorg-server 1.4.2-apple45)) –– 2. Got X11 from Hackage – configured, built and installed – however, there where quite a lot of warnings: … [ 8 of 25] Compiling Graphics.X11.Xlib.Color ( Graphics/X11/Xlib/Color.hs, dist/build/Graphics/X11/Xlib/Color.o ) Graphics/X11/Xlib/Color.hs:38:0: Warning: The import of `Foreign.C.Types' is redundant except perhaps to import instances from `Foreign.C.Types' To import instances alone, use: import Foreign.C.Types() [ 9 of 25] Compiling Graphics.X11.Xlib.Font ( dist/build/Graphics/X11/Xlib/Font.hs, dist/build/Graphics/X11/Xlib/Font.o ) Graphics/X11/Xlib/Font.hsc:167:1: Warning: A do-notation statement discarded a result of type CInt. Suppress this warning by saying "_ <- xTextExtents font_struct c_string (fromIntegral nchars) direction_return font_ascent_return font_descent_return overall_return", or by using the flag -fno-warn-unused-do-bind … and so on. –– 3. Got HGL package, built and installed with some warnings like: … [ 1 of 27] Compiling Graphics.HGL.Internals.Flag ( Graphics/HGL/Internals/Flag.hs, dist/build/Graphics/HGL/Internals/Flag.o ) Graphics/HGL/Internals/Flag.hs:1:0: Warning: Module `Prelude' is deprecated: You are using the old package `base' version 3.x. Future GHC versions will not support base version 3.x. You should update your code to use the new base version 4.x. … –– Now, when I try to run simple program like: main = runGraphics $ withWindow_ "Hello World Window" (300, 200) $ \ w -> do drawInWindow w $ text (100, 100) "Hello World" drawInWindow w $ ellipse (100, 80) (200, 180) getKey w it says: $ ghci graphics.hs GHCi, version 6.12.1: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Loading package ffi-1.0 ... linking ... done. Ok, modules loaded: Main. Prelude Main> main Loading package syb-0.1.0.2 ... linking ... done. Loading package X11-1.5.0.0 ... can't load .so/.DLL for: X11 (dlopen(libX11.dylib, 9): image not found) Prelude Main> Just to precise, I have X11 running (it can be seen in the OSX dock) Thanks

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Regular expressions in case
by legajid 13 Feb '10

13 Feb '10

Hi, is it possible to write regular expressions in case .. of ? I tried it, with no success. a x = case x of "a1" -> "A1" "a2" -> "A2" "a*" -> "A*" "b1" -> "B1" _ -> "_" for x="a3", result is _, instead of A* that i wanted. Thks, Didier

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Data.Tree computation
by Gabi 12 Feb '10

12 Feb '10

Hi guys, I've tried to use Data.Tree as a computation tree (each node is numerical function, each leaf is a terminal) It kinda works, but the code seems very verbose. How can it made more concise ? I am sure I missed a lot of shortcuts and idioms. -- file t.hs import qualified Data.Tree as T data Term = TInt Int| TDouble Double deriving (Show, Eq) data Func = Plus | Minus | Mult | Div deriving (Show, Eq) data ANode = GFunc Func | GTerm Term deriving (Show, Eq) fNode :: Func -> T.Forest ANode-> T.Tree ANode fNode f = T.Node (GFunc f) tNode:: Term -> T.Tree ANode tNode t = T.Node (GTerm t) [] calc :: T.Tree ANode -> Double calc (T.Node (GTerm (TInt n))[]) = fromIntegral n :: Double calc (T.Node (GFunc Plus) xs ) = foldl1 (+) (map calc xs) calc (T.Node (GFunc Minus) xs ) = foldl1 (-) (map calc xs) calc (T.Node (GFunc Mult) xs ) = foldl1 (*) (map calc xs) calc (T.Node (GFunc Div) xs ) = foldl1 (/) (map calc xs) -- (/ (+ 5 5 (- 10 100)) 10) - calc Should return -8.0 aTree = fNode Div [fNode Plus [tNode $ TInt 5,tNode $ TInt 5, fNode Minus [tNode $ TInt 10,tNode $ TInt 100]], tNode (TInt 10)] Regards, Gabi http://bugspy.net

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ghc problem
by jean verdier 11 Feb '10

11 Feb '10

Trying to compile sources gives me: ghc: internal error: evacuate(static): strange closure type 34 (GHC version 6.10.4 for i386_unknown_linux) Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug This already occured to me some times before and a cleanup and recompile would work. This time i am stuck as i can't compile anymore. The ghc version i use is the 6.10.4 from the ghc home page binary distribution i think. uname -a gives : Linux localhost.localdomain 2.6.29.4-167.fc11.i586 #1 SMP Wed May 27 17:14:37 EDT 2009 i686 athlon i386 GNU/Linux The command line is: ghc -fwarn-incomplete-patterns -fno-warn-unused-binds -fno-warn-unused-matches -fno-warn-unused-imports -fno-warn-missing-signatures -fno-glasgow-exts -Werror -outputdir /tmp/mfk/build -package ghc -i/tmp/mfk/gensrc --make common/MFK/Common/SrcGen.hs common/MFK/Common/Conf.hs Any hints ?

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HackageDB - How to browse by development status
by Gabi 11 Feb '10

11 Feb '10

Thanks Stephen This is really useful link. At least now I can guess what package is "popular" what is esoteric. -- Regards, Gabi http://bugspy.net

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HackageDB - How to browse by development status
by Gabi 11 Feb '10

11 Feb '10

Hi I really miss the option browsing this big DB by development status (.e.g. alpha,beta,stable,mature,inactive) It is very common (in other langs at least) to have some approx development status. Otherwise it is really hard to choose. How can I know if a package is considered stable enough for production ? -- Regards, Gabi http://bugspy.net

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let expression
by John Moore 11 Feb '10

11 Feb '10

Hi All, Trying to get this to work, keeps telling me there a parse error on right in the let expression. Can anyone see where the problem is and be able to explain it to me. import Maybe data Expression = Val Double | Add Expression Expression | Subtract Expression Expression | Multiply Expression Expression | Divide Expression Expression | Var String | Let String Expression Expression deriving Show demo1 = (Add(Multiply(Divide(Subtract(Val 25)(Val 5))(Val 10))(Val 7))(Val 30)) type Dict =[(String,Expression)] emptyDict :: Dict emptyDict = [] addEntry :: String->Expression ->Dict -> Dict addEntry n e d = (n,e): d lookupEntry :: String -> Dict -> Maybe Expression lookupEntry n [] = Nothing lookupEntry n (x:xs) = if (n == k) then (Just v) else lookupEntry n xs where (k,v) = x evalStep :: Dict -> Expression -> Expression evalStep d(Val x)= (Val x) evalStep d(Add x y) = case x of (Val a) -> case y of (Val b) -> Val (a+b) left -> Add x (evalStep d y) right -> Add (evalStep d x)y evalStep d(Subtract x y) = case x of (Val a) -> case y of (Val b) -> Val (a-b) left -> Subtract x (evalStep d y) right -> Subtract (evalStep d x)y evalStep d(Multiply x y) = case x of (Val a) -> case y of (Val b) -> Val (a*b) left -> Multiply x (evalStep d y) right -> Multiply (evalStep d x)y evalStep d (Divide x y) = case x of (Val a) -> case y of (Val b) -> Val (a/b) left -> Divide x (evalStep d y) right -> Divide (evalStep d x)y evalStep d (Let n e1 e2) = case e1 of (Val a) -> case e2 of (Val b)-> Val (Let e1 e2) left -> Let e1 (evalStep d e2) right -> Let (evalStep d e1) e2 evaluate :: Dict-> [Expression] -> Expression -> IO() evaluate d(x:xs) e = do putStrLn (show e) putStrLn "Do another step (y/n) or rollback (r)? :" c <- getLine case c of "y" -> let e'= (evalStep d e)in evaluate d (e:x:xs) e'-- build up history "r" -> case (x:xs) of (x:xs)-> evaluate d xs x []-> do { putStrLn "Empty" ;evaluate d(x:xs) e } "n" -> putStrLn $ "Ok you said no :" ++ c John

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Re: Simplifying code
by edgar klerks 10 Feb '10

10 Feb '10

Hello all, I have a very interesting alternative solution of the problem. First I generate a tree with all the permutations: eg if I want to find al permutations of ao, I get the following tree [a @] | | [o 0] [o 0] Then I walk trough the tree so I can print it. There is only one ugly thing. Showtree' returns a string (in our example aoa0@o@0). To make it a list i put a \n between a left and right node and then use lines to make it a list of strings. Can someone point me in the right direction how to beautify it a bit? I also have an annoying problem with gmail and firefox. It seems it doesn add my posts to the current thread, but starts a new one. Oh well think I switch to evolution. I will review all yours solutions tomorrow. I saw some very beautifull things. With kind regards, Edgar Klerks module Main where import Data.Char data WordTree = Chain (Char,WordTree) | Choice (Char, WordTree) (Char, WordTree) | Stop instance Show WordTree where show = unlines.showTree type Rule = (Char, Char) type Rules = [Rule] infixl 4 ==> a ==> b = (a,b) rules :: Rules rules = [ 'a' ==> '@', 'l' ==> '|'] buildTree :: String -> Rules -> WordTree buildTree [] r = Stop buildTree (c:cs) r = case lookup c r of Just a -> Choice (a, buildTree cs r) (c, buildTree cs r) Nothing -> Chain (c, buildTree cs r) showTree a = lines $ showTree' a [] showTree' (Chain (a,b)) p = a : showTree' b p showTree' (Choice (a,b) (c,d)) p = c : showTree' d p ++ "\n" ++ (a : showTree' b p) showTree' (Stop) p = p

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