So I work with files, and I need to know the largest line in file X. Using Unix awk results in a Int that I m looking for. But in Haskell how can I return that value and save it to a variable?
I tried define something with IO [Int] -> [Int]
maxline = do{system "awk { if ( length > x ) { x = length } }END{ print x } filename";}
工作原因:
Couldn t match expected type Int ,against inferred type IO GHC.IO.Exception.ExitCode
这是因为。 这些行动使你指挥的撤离状态得以恢复,不能改成<代码>。 Int 。 您应使用
> readProcess "date" [] []
"Thu Feb 7 10:03:39 PST 2008
"
请注意,<条码>翻新/编码>没有将指挥系统直接运行。 第二个参数是指挥的论点应当去哪里。 因此,应当举出你的例子。
readProcess "awk" [" { if ( length > x ) { x = length } }END{ print x }", "/home/basic/Desktop/li11112mp/textv"] ""
您可使用 readProcess/a>获取另一个方案产出。 您将无法将由此产生的<编码>IO String转换成纯粹的<代码>String;然而,您可以撤销预期的的职能。 将<规定为预期职能:IO Strings。 我的两篇关于与IO(和其他各种mon子) m合的正面文章是:草原精彩的博客, and The IO Monad for People who Simply Don t Care.
对于这一特殊问题,我强烈建议寻找一种纯粹的Haskell解决办法(即,不要夸张)。 http://hackage.haskell.org/ Packages/archive/base/latest/doc/html/Prelude.html#v:readFile”rel=“noretinger”>readFile , :code/code><>>>>>>>>>/>>>>>a>和
I m trying my hand at Euler Problem 4 in Haskell. It asks for that largest palindrome formed by multiplying two three-digit numbers. The problem was simple enough, and I thought my Haskell-fu was up ...
Can anybody explain how does foldr work? Take these examples: Prelude> foldr (-) 54 [10, 11] 53 Prelude> foldr (x y -> (x+y)/2) 54 [12, 4, 10, 6] 12.0 I am confused about these executions....
How can I efficiently implement a list data structure where I can have 2 views to the head and end of the list, that always point to a head a tail of a list without expensive calls to reverse. i.e: ...
I am doing problem 61 at project Euler and came up with the following code (to test the case they give): p3 n = n*(n+1) `div` 2 p4 n = n*n p5 n = n*(3*n -1) `div` 2 p6 n = n*(2*n -1) p7 n = n*(5*n -3)...
I ve just started learning about Functional Programming, using Haskel. I m slowly getting through Erik Meijer s lectures on Channel 9 (I ve watched the first 4 so far) and in the 4th video Erik ...
The type of the Prelude function flip is: flip :: (a -> b -> c) -> b -> a -> c I.e., it takes one binary function and two arguments. The type of the Prelude function id is: id :: a -...
group :: Ord a => [(a, [b])] -> [(a, [b])] I want to look up all pairs that have the same fst, and merge them, by appending all the list of bs together where they have the same a and discarding ...
I want to do a popen() / python s subprocess.communicate from Haskell - start a program, give it stdin, and get its stdout/stderr. What s the most direct / Haskellish way to do this?