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MissingH status and thanks
by John Goerzen 08 Dec '06

08 Dec '06

Since the MissingH discussion took place on this list, I thought I should update you all on the status. First off, MissingH now has a new Trac-based homepage, complete with wiki, Darcs repository information, source browser, bug tracker, etc. It's at http://software.complete.org/missingh Secondly, the MissingH modules have been renamed as we discussed here. And finally, various pieces of MissingH have been split off already into separate packages. (See the announcements on haskell@h.o) The full list of changes -- planned and executed -- is at http://software.complete.org/missingh/wiki/TransitionPlanning Thanks to all for your valuable feedback. I hope that these changes will make this set of code more useful to everyone. -- John

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"computational time" always 0.0 in this example...
by Lennart 08 Dec '06

08 Dec '06

Hi, with the following code, I want to measure the time being needed to execute the algorithm. But the result is always 0.0. import Char (toLower) import Maybe import List ( delete, sort, intersect ) import System.CPUTime import Control.Exception import Debug.Trace fromInt = fromIntegral wordList2 :: [String] wordList2 = ["Sam J Chapman", "Samuel Chapman", "S Chapman", "Samuel John Chapman", "John Smith", "Richard Smith", "aaaa mnop zzzz", "bbbb mnop yyyy", "aa mnop zzzzzz", "a ", "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa", "aaaa bcdefgh mmmmmmmm stuvwx zzzzzz", "jjjj bcdefgh qqqqqqqq stuvx yyyyyy", "aaaaa bcdefgh stuvwx zzzzzz", "aaaaa aaaaa aaaaa zzzzzz", "aaaaa aaaaa"] time :: IO t -> IO t time a = do start <- getCPUTime v <- a end <- getCPUTime let diff = (fromIntegral (end - start)) / (10^12) -- let diff = (fromIntegral (end - start)) putStrLn "Computation time:" print (diff :: Double) return v main = do putStrLn "Starting..." time $ doTest wordList2 wordList2 `seq` return () putStrLn "Done." test3 = let loop = getCPUTime >>= print >> loop in loop doTest :: [String] -> [String] -> [ Double ] doTest [] _ = [] doTest (x:xs) [] = doTest xs xs doTest (x:xs) (y:ys) = result : (doTest (x:xs) (ys)) where result = qGramMetrics2 x y qGramMetrics2:: String -> String -> Double qGramMetrics2 t1 t2 = let i = intersect (qGramList (map toLower t1) 3) (qGramList (map toLower t2) 3) il = fromInt (length i) ml = fromInt ((max (length t1) (length t2)) - 1 ) in (il / ml ) -- list of chars within list of qgrams qGramList :: String -> Int -> [[Char]] qGramList [] _ = [] qGramList (x:[]) _ = [] qGramList (x:xs) i1 = (x: take (i1 - 1) xs):(qGramList xs i1) -- list of chars within list of qgrams numberedQgramListWithStart :: String -> Int -> [(Int, [Char])] numberedQgramListWithStart x i1 = let prefix = replicate (i1-1) '#' suffix = replicate (i1-1) '$' in numberedQgramList (prefix++(x++suffix)) i1 0 numberedQgramList :: String -> Int -> Int -> [(Int, [Char])] numberedQgramList [] _ _ = [] numberedQgramList (x:xs) i1 i2 -- add the dollar-sign | (length xs) < i1 && x=='$'= [] | otherwise = (i2,(x: take (i1 - 1) xs)):(numberedQgramList xs i1 (i2+1)) Am using ghci 6.6 under a Kubuntu 6.10 Linux. time $ product [1..1000] `seq` return () instead of time $ doTest wordList2 wordList2 `seq` return () works fine. things like time $ print (doTest wordList2 wordList2) `seq` return () or time $ length (doTest wordList2 wordList2) `seq` return () or time $ trace (doTest wordList2 wordList2) `seq` return () didn't work. Am desperated... Lennart

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STUArray's newArray_ breaks referential transparency
by Stefan O'Rear 08 Dec '06

08 Dec '06

newArray_ allocates an array full of garbage. > import Control.Monad.ST > import Data.Array.ST > import Data.Array > > tickle :: Int > tickle = runST (do { > x <- newArray_ (0,100) ; > (readArray :: STUArray s Int Int -> Int -> ST s Int) x 3 > })

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Hac 2007 : Haskell Hackathon - extended registration
by dons＠cse.unsw.edu.au 07 Dec '06

07 Dec '06

------------------------------------------------------------------------ Hac 2007 The 2007 Haskell Hackathon January 10-12, 2007 Oxford University Computing Laboratory http://haskell.org/haskellwiki/Hac_2007 ------------------------------------------------------------------------ The deadline for registration for Hac 2007, the Haskell Hackathon, has passed, and some places are still available, on a first-come first-served basis. The current attendee list is up at: http://haskell.org/haskellwiki/Hac_2007/Attendees If you want to attend the hackathon, and hack on Haskell infrastructure, tools, libraries and compilers, please register, and get ready to hack those lambdas! Follow the instructions on the registration page: http://haskell.org/haskellwiki/Hac_2007/Registration Numbers for the hackathon are limited to 20. The organisers, Duncan Coutts Ian Lynagh Don Stewart Attached is the initial announcement: ------------------------------------------------------------------------ Hac 2007 The 2007 Haskell Hackathon January 10-12, 2007 Oxford University Computing Laboratory http://haskell.org/haskellwiki/Hac_2007 ------------------------------------------------------------------------ Following the success of the GHC Hackathon at ICFP, we are pleased to announce the inaugural Haskell Hackathon, Hac 2007! The event will be held over 3 days, January 10-12 2007, at the Oxford University Computing Laboratory, in the UK. The plan is to hack on Haskell infrastructure, tools, libraries and compilers. To attend please register, and get ready to hack those lambdas! Code to hack on: * Hackage * Cabal * Porting foreign libraries * Porting compilers * Bug squashing * Performance improvements to compilers * You decide! Registration: We ask that you register you interest. Follow the instructions on the registration page: http://haskell.org/haskellwiki/Hac_2007/Registration Numbers for the hackathon are limited to 20, due to room size constraints. Should space be available after the registration period ends, additional attendees may register on a first-come first-served basis. Important dates: Registration deadline: December 6th, 2006 Confirmation: December 10th, 2006 Hackathon: January 10-12, 2007 Organisers: Duncan Coutts Ian Lynagh Don Stewart

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How to get subset of a list?
by Huazhi (Hank) Gong 07 Dec '06

07 Dec '06

Like given a string list s="This is the string I want to test", I want to get the substring. In ruby or other language, it's simple like s[2..10], but how to do it in Haskell? -- View this message in context: http://www.nabble.com/How-to-get-subset-of-a-list--tf2735647.html#a7631994 Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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File locked unnecessarily
by Arie Peterson 06 Dec '06

06 Dec '06

Hi, After a partial rewrite of my webserver, it is suffering from locked files: /path/to/file: openBinaryFile: resource busy (file is locked) The file in question really shouldn't be locked: - Only my server knows of the file's existence. - Only one thread accesses the file. - The thread accesses the file multiple times in quick succession, opening and closing it each time, but debugging statements show that it is properly closed before it is reopened. I tried opening, reading/writing and closing a file continuously for some time in an isolated environment, and that works without problems. Also, my server did not have this file locking problem before the rewrite, and the rewrite did not touch the part of the code that accesses the file. This suggests that the locking is somehow triggered by the specific access pattern of my code, if that is even possible. Does anyone know what could cause this locking and/or how to prevent it? I'm using ghc 6.4 on gentoo linux (amd64). Thanks and greetings, Arie

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GADT vs Arrows for parsers/FSMs/etc.
by S. Alexander Jacobson 06 Dec '06

06 Dec '06

It seems like Haskell has two emerging idioms for parsing and fsms: GADTs and Arrows. I am thinking about using one of these idioms to represent server structure in a future version of HAppS but I'm not sure where to start. Why would one choose one or the other? -Alex- ______________________________________________________________ S. Alexander Jacobson tel:917-770-6565 http://alexjacobson.com

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Typeclass question
by Jonathan Tang 06 Dec '06

06 Dec '06

I've got what's probably a beginner's question, but I'm out of ideas for solving it. It looks like it tripped me up in "Write Yourself a Scheme..." too, since the code there seems like it's arranged so I never ran into it... I've got a couple functions: binop :: (AmbrosiaData -> AmbrosiaData -> AmbrosiaM AmbrosiaData) -> AmbrosiaM () binop operator = do second <- popStack first <- popStack result <- operator first second pushStack result numNumOp :: Num a => (a -> a -> a) -> AmbrosiaData -> AmbrosiaData -> AmbrosiaM AmbrosiaData numNumOp op (Number val1) (Number val2) = return $ Number $ op val1 val2 numNumOp op (Float val1) (Float val2) = return $ Float $ op val1 val2 numNumOp op _ _ = throwError . TypeMismatch $ "Number" the intention being that I can define primitive operations for an interpreter with ("+", binop $ numNumOp (+)). In the Number case, val1 & val2 are Integers, while in the Float case, they're Floats. However, when I try to compile, I get: ./Primitives.hs:82: Cannot unify the type-signature variable `a' with the type `Integer' Expected type: Integer Inferred type: a In the application `op val1 val2' In the second argument of `($)', namely `op val1 val2' This makes no sense to me, since Integer is an instance of Num and op is defined as type Num a => a -> a -> a. Shouldn't the typechecker be able to instantiate 'a' with Integer and give the resulting type Integer -> Integer -> Integer, and then pass the final Integer to Number? Is my understanding of typeclasses off somehow? Any help would be appreciated. Regards, Jonathan

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Would someone explain this code to me?
by Justin Bailey 06 Dec '06

06 Dec '06

I'm reading Chris Okasaki's "Purely Functional Data Structures", and some of his Haskell is confusing me. He defines the type Color and RedBlackSet as: data Color = R | B data RedBlackSet a = E | T Color (RedBlackSet a) a (RedBlackSet a) and then later he defines a function insertSet: insertSet x s = T B a y b where ins E = T R E x E ... T _ a y b = ins s What I don't understand is his use of the "T" constructor, both at insertSet x s = T B a y b and in the where statement: T _ a y b = ins s Is "T" being redefined, so the "T" called in the first line is a new function that happens to be called "T" which is defined in the where statement? If that was the case, I would expect this to work: insertSet x s = foo B a y b where ins E = foo R E x E ... foo _ a y b = ins s but it does not. If anyone can explain what's going on here, I'd appreciate it. Thank you! Justin

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[Haskell] Defining Cg, HLSL style vectors in Haskell
by Slavomir Kaslev 06 Dec '06

06 Dec '06

Hello, I have to define a couple of float2, float3, float4 Cg, HLSL style vectors in Haskell. At first I was tempted to make them instances of Num, Floating, RealFrac, etc. but some of the functions defined in those classes have no sense for vectors. One such example is signum from class Num. There are several workarounds for this. One may come up with some meaning for vectors of such functions, for example: instance Num Float3 where ..... signum a | a == Float3 0 0 0 = 0 | otherwise = 1 This is silly. Other option, which I prefer, is to leave such functions undefined (that is signum=undefined, not just not defining them). Is this ok? Are there any other options? Another bugging thing is that some of the functions do have meaning for vectors but they need different signatures. For example (**) :: Floating a => a -> a -> a, for vectors should be (**) :: (Floating a, Vector v) => v -> a -> v, that is (**) applied for every component of the vector. Any workarounds for that? I know that I can scrap all those Num, Floating, RealFrac, etc. classes and define class Vector from scratch, but I really don't want to come up and use different names for +, -, etc. that will bloat the code. Last question: Does haskell have something like C++ templates? For example, some time in the future I may need types like int2, short3, etc., that behave just like float2, float3, but use different types for their components. I really, really wouldn't like to copy-paste the definitions of floatn and manually change their types to intn respectfully. Cheers. -- Slavomir Kaslev

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