Haskell-readFile捕获异常

2011-03-07 46 views 3 likes

我想读取Haskell中的文件，但捕获异常但无法正常工作。代码如下：Haskell-readFile捕获异常

 module Main where 
    import System.Environment 
    import System.IO 
    import System.Exit 

    main = do 
     x:xs <- getArgs 
     case length(x:xs) of 
      2 -> do catch (readFile x) 
         (\_ -> do putStrLn ("Error on reading file: " ++ x) 
            getLine 
            exitWith ExitSuccess) 
      _ -> do putStrLn ("Run this way: ./projekt inputFile RE") >> 
       exitFailure

而且我得到这个错误：

Couldn't match expected type `IO String 
           -> (ExitCode -> IO a) 
           -> ExitCode 
           -> IO String' 
     against inferred type `IO()' 
In the expression: 
    putStrLn 
     ("Error on reading file: " ++ x) getLine exitWith ExitSuccess 
In the expression: 
    do { putStrLn 
      ("Error on reading file: " ++ x) getLine exitWith ExitSuccess } 
In the second argument of `catch', namely 
    `(\ _ -> do { putStrLn 
        ("Error on reading file: " ++ x) getLine exitWith ExitSuccess })'

你能不能给我一个提示？感谢

来源

2011-03-07 Martin Pilch

http://www.haskell.org/ghc/docs/6.12.2/html/libraries/base-4.2.0.1/Control-Exception.html#5 – Jonke 2011-03-07 21:47:15

回答

您在第13行有一个额外的>>（或额外do）：

_ -> do putStrLn ("Run this way: ./projekt inputFile RE") >>

应该是：

_ -> do putStrLn ("Run this way: ./projekt inputFile RE")

或：

_ -> putStrLn ("Run this way: ./projekt inputFile RE") >> exitFailure

全码：

main = do 
[email protected](x:xs) <- getArgs 
case length l of 
    2 -> do catch (readFile x) $ \_ -> do 
      putStrLn $ "Error on reading file: " ++ x 
      getLine 
      exitWith ExitSuccess 
    _ -> do putStrLn $ "Run this way: ./projekt inputFile RE" 
      exitFailure

来源

2011-03-07 21:52:09 Alvivi

非常感谢，问题是这个问题 – 2011-03-08 06:18:04

检查您的缩进。

虽然您的代码在您粘贴时看起来不错，但错误消息表明getLine和exitWith ExitSuccess的缩进比上面的putStrLn更进一步。也许这是一个空格-v-标签问题？

来源

2011-03-07 22:34:37 dave4420

Haskell-readFile捕获异常

回答

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