At 2002-05-13 08:44, Simon Marlow wrote:

Prelude.catch catches IO exceptions only, because this is what the Haskell report specifies.

OK

The idea is that if you want to use Exceptions in their full glory, you: ... import qualified Exception

I've noticed something a bit unusual about Exception.catch. It seems it can't catch "return undefined" by itself. Consider these values of type "IO String": iouPure :: IO String; iouPure = undefined; iouError :: IO String; iouError = error "error"; These aren't even an IO actions, they're simply bottom. Straightforward enough. But they _will_ be caught by Exception.catch. iouFail :: IO String; iouFail = fail "failure"; iouEvaluate :: IOString; iouEvaluate = Exception.evaluate undefined; These two are IO actions that "fail" when executed. They will also be caught by Exception.catch. iouReturn :: IO String; iouReturn = return undefined; This one is an IO action that "succeeds" when executing. It _won't_ be caught by Exception.catch, which will instead simply return the undefined value. I'm not sure what to make of this... -- Ashley Yakeley, Seattle WA