Re: [Haskell-beginners] New style exceptions...

10 Aug 2011


      On Wed, 10 Aug 2011 07:01:42 +0200
Manfred Lotz  wrote:
...
Hi there,
Exception handling in RWH is called old-style and deprecated. I didn't
find a tutorial telling how to do the new style.
Here I created two examples both dealing with an exception when
creating a directory.
I would like to know if the way I did is ok or not.
Improvements resp. corrections are most welcome
First way:
<--------------snip------------------------------------>
{-# LANGUAGE ScopedTypeVariables #-}
module Main where
import System.Exit
import System.Directory
import Control.Exception
import Prelude hiding ( catch, readFile )
main :: IO ()
main = do 
  handle (\(e :: SomeException) -> print $ show e) $ do
    createDirectoryIfMissing True "/tmr/a/b/c/d"
    _ <- exitWith $ ExitFailure 1
    return ()
  print "Directory created successfully"
<--------------snap------------------------------------>
This was stupid. Should be like this:


main :: IO ()
main = do 
  handle (\(e :: SomeException) -> do print $ show e
                                      _ <- exitWith $ ExitFailure 1
                                      return ()
         ) $ do
    createDirectoryIfMissing True "/tmr/a/b/c/d"
  print "Directory created successfully"


-- 
Manfred