Error Handling

[Andrew J Bromage]

G'day all.

On Mon, Dec 09, 2002 at 11:35:54AM +1100, Thomas L. Bevan wrote:

> main = do	(a:b:cs) <- getArgs
> 		i <- return (read a :: Int)
> 		j <- return (read b :: Int)
> 		putStr $ i + j
> 
> How can I catch any possible cast exception?

How about this?

readM :: (Read a, Monad m) => String -> m a
readM s
  = case readEither s of
	Left err -> fail err
	Right x  -> return x

main = runErrorT main'

main' = do	(a:b:cs) <- liftIO getArgs
		(i::Int) <- readM a
		(j::Int) <- readM b
		liftIO (putStr $ i + j)

Cheers,
Andrew Bromage