不在范围内:`catch'

本文介绍了不在范围内:`catch'的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我正在阅读，以了解您对haskell的极大兴趣，但是当我阅读输入&的异常部分时，我遇到了Not in scope:`catch'的错误.输出章节

I am reading learn you a haskell for great good but i faced an error of Not in scope: `catch' when I read the exception section in input & output chapter

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'

推荐答案

catch 由 Control.Exception 模块导出.

import Control.Exception