On Wed, 2 Mar 2011, Rouan van Dalen wrote:
I would like to know what is the preferred Haskell mechanism for handling exceptions in the IO monad? I am not concerned with mechanisms such as Maybe / Either, but would like to know about exception mechanisms inside the IO monad.
The 2 I know of are: o) throwDyn o) ioError and catch
I do need the exceptions to be extendable. So which is the preferred way to handle exceptions in Haskell for new libs?
For my taste there is nothing I can really recommend. I cannot recommend the exceptions that are implicit in IO, since if you have an IO action you cannot know on what exceptions you have to react. Can the action throw a FileDoesNotExist or AudioBufferCouldNotBeAllocated? You don't know, because the type does not tell you. I think the mechanisms like IO (Either ErrorMsg a) are the better solution, since they explicitly tell you, what exceptions you have to expect and when you forgot to handle a particular exception. I think the control-monad-exception package is the most advanced one, but it requires some type extensions. I have written explicit-exceptions which is Haskell 98, and you can use more advanced types of exceptions (such as those from control-monad-exception) on top of it.