[Haskell-beginners] New style exceptions...

[Manfred Lotz]

On Wed, 10 Aug 2011 07:01:42 +0200
Manfred Lotz <manfred.lotz at arcor.de> 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