haskell - 不在范围 : `catch' 内

Question

我正在阅读“向你学习 Haskell”，但当我阅读输入和输出章节中的异常部分时，我遇到了“不在范围内:‘catch’”的错误

这是我的代码:

import System.Environment  
import System.IO  
import System.IO.Error  

main = toTry `catch` handler  

toTry :: IO ()  
toTry = do (fileName:_) <- getArgs  
           contents <- readFile fileName  
           putStrLn $ "The file has " ++ show (length (lines contents)) ++ " lines!"  

handler :: IOError -> IO ()  
handler e = putStrLn "Whoops, had some trouble!"  

我收到此错误消息:

Not in scope: `catch'

Answer 1

catch 由 Control.Exception 模块导出。

import Control.Exception