- Haskell-Cafe - Haskell.org

haskell companies
by Andreas Kägi 21 Jun '06

21 Jun '06

hello i wonder if there are companies that use haskell in practice. i'm a computer science student from switzerland (europe) and need to do an internship. since i find haskell very interesting i thought these two things could maybe be combined.

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ACross
by Jenny678 20 Jun '06

20 Jun '06

Hello, Can somebody help me My Problem is to define a code for: >cross 7 -- means 7*7 >+++++++ >++ ++ >+ + + + >+ + + >+ + + + >++ ++ >+++++++ Another Example >cross 13 -- 13*13 >+++++++++++++ >++ ++ >+ + + + >+ + + + >+ + + + >+ + + + >+ + + >+ + + + >+ + + + >+ + + + >+ + + + >++ ++ >+++++++++++++ Can I use putString ??? Thanks for any help -- View this message in context: http://www.nabble.com/ACross-t1813549.html#a4943328 Sent from the Haskell - Haskell-Cafe forum at Nabble.com.

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Newbie question on iterating over IO list
by Taro Ikai 20 Jun '06

20 Jun '06

Here's a code fragment I have from working with Hal Daume's "Yet Another Haskell Tutorial". I cannot figure out how to iterate over the result from askForNumbers that returns "IO [Integer]", and print them. The "<-" operator seems to take IO off of the results from actions like getContents, which returns type "IO String", but I cannot seem to use it to take IO off of lists with it. What am I supposed to do? Also, as a side question, what should I be returning from the do function? >>>code>>>> module Main where import IO main = do hSetBuffering stdin LineBuffering s <- askForNumbers {-- This compiles --} map show s {-- But this doesn't. Why? --} {-- What expression should I be returning from do? --} askForNumbers = do putStrLn "Give me a number (or 0 to stop):" guess <- getLine let number = read guess if number == 0 then return [] else do rest <- askForNumbers return (number : rest) <<<code<<<< Thanks in advance. Taro Ikai

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Efficient way to edit a file
by Maurício 20 Jun '06

20 Jun '06

Hi, I need to edit big text files (5 to 500 Mb). But I just need to change one or two small lines, and save it. What is the best way to do that in Haskell, without creating copies of the whole files? Thanks, Maurício

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cabal-get and HXT?
by Greg Fitzgerald 20 Jun '06

20 Jun '06

I'd like to use a tool to automatically install Haskell XML Toolkit and its dependencies. What are my options? How's cabal-get coming? Thanks, Greg

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RE:[Haskell-cafe] A function using List and Tuple
by jotajota 19 Jun '06

19 Jun '06

Hi On 6/19/06, Sara Kenedy <sarakenedy(a)gmail.com> wrote: > Hello, > > I want to creat a function sumList as below examples: > sumList [("s1",2),("s2",4),("s3",3),("s4",2)] = ("#", 1/2 + 1/4 + 1/3 + 1/2) > sumList [("s1",2),("s2",4),("s3",3) = ("#", 1/2 + 1/4 + 1/3) > > I attempted it as following: > > sumList :: (Fractional a) => [(String,a)] -> (String, a) > sumList [] = ??? > sumList (x:xs) = ("#", 1/(snd x) + 1/snd(sumList xs)) > > I know this function cannot give the correct answer (even if I define > sumList []), but I did not find the right way. > If anyone can give me a suggestion, I really appereciate for that. Thanks. > Yo can use the foldr function: sumList a = ("#",foldr suma 0 a ) where suma (s,x) y = 1/x + y Juan Jose

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Parsec and destructuring HTML content
by Joel Reymont 19 Jun '06

19 Jun '06

Has anyone explored destructuring HTML with Parsec? Any other ideas on how to best do this? I'm looking to scrape bits of information from more or less unstructured HTML pages. I'm looking to structure, tag and classify the content afterwards. I think that developing HTML scrapers requires short tweak-compile- run cycles and is probably best done in Perl, Python, Ruby, i.e. dynamic languages but I wonder if someone has found otherwise. Thanks, Joel -- http://wagerlabs.com/

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A function using List and Tuple
by Sara Kenedy 19 Jun '06

19 Jun '06

Hello, I want to creat a function sumList as below examples: sumList [("s1",2),("s2",4),("s3",3),("s4",2)] = ("#", 1/2 + 1/4 + 1/3 + 1/2) sumList [("s1",2),("s2",4),("s3",3) = ("#", 1/2 + 1/4 + 1/3) I attempted it as following: sumList :: (Fractional a) => [(String,a)] -> (String, a) sumList [] = ??? sumList (x:xs) = ("#", 1/(snd x) + 1/snd(sumList xs)) I know this function cannot give the correct answer (even if I define sumList []), but I did not find the right way. If anyone can give me a suggestion, I really appereciate for that. Thanks. S.

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Fibonacci numbers generator in Haskell
by Vladimir Portnykh 19 Jun '06

19 Jun '06

Fibonacci numbers implementations in Haskell one of the classical examples. An example I found is the following: fibs :: [Int] fibs = 0 : 1 : [ a + b | (a, b) <- zip fibs (tail fibs)] To get the k-th number you do the following: Result = fibs !! k It is elegant but creates a list of all Fibonacci numbers less than k-th, and the code is not very readable :). I wrote my own Fibonacci numbers generator: fib :: Int -> [Int] fib 0 = [0,0] fib 1 = [1,0] fib n = [sum prevFib, head prevFib] where a = fib (n - 1) To get the k-th number you do the following: result = head (fib k) It does not generate full list of Fibonacci numbers, but keeps only 2 previous numbers, and has only one recursive call. Because the list always has only 2 elements using the functions head and sum is a bit overkill. Can we do better? _________________________________________________________________ Are you using the latest version of MSN Messenger? Download MSN Messenger 7.5 today! http://join.msn.com/messenger/overview

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take the keywords from a string
by Sara Kenedy 18 Jun '06

18 Jun '06

Hi everybody, I have a function: takeKeyword :: String -> [String] This function will take the input as a string and return a list of keywords taken from the input string and they are elements of ListOfKeywords. The order of the result list is sequenced as: the last keyword found is set as the first element of the list, and so on. For example, ListOfKeywords = ["expand, "limit", "diff"] takeKeyword :: String -> [String] takeKeyword limit(x + expand((x+3)^2), x=3) = ["expand", "limit"] takeKeyword limit(x -7, x= 3) =["limit"] If you have any suggestions for that, please share with me. Thanks in advance. S.

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