you cannot catch exceptions anywhere but the IO monad, in Haskell 98 this is clear since only IO actions may throw exceptions. With imprecise exceptions as implemented by ghc the reasoning is that what exeption is thrown depends on the evaluation order of a given implementation. imagine: throw (userException "foo") + throw (userException "bar") without defining an evaluation order you cannot know which exepction is to be thrown. catching the exception in the IO monad makes this 'okay' since IO actions can depend on things other than its arguments (like the evaluation order of a given implementation) John On Mon, Dec 09, 2002 at 11:35:54AM +1100, Thomas L. Bevan wrote:
Hi,
I'm writing a little command line app, but I have a question about error handling. The code will go something like,
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? Ideally, I think I would like to use the ErrorT monad as a means of handling a potentially fairly complex set of inputs, but I can see no way of handling these errors neatly within that monad.
Tom
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