On Sun, 18 Oct 2009, Michael Snoyman wrote:
While working on the next release of data-object, I wanted to represent some operations that might fail. The typical candidates were:
1) Maybe 2) Either 3) Monad
Monad is always iffy because of the often times poorly defined fail. Maybe doesn't provide any means of reporting what the problem was. Either is not defined as a Monad in the base library. Also, the usual candidate of Either String only provides for an error message. It would be nice to have more in-depth information available.
So I've put together a package I call "attempt". It defines a data type called (surprise) Attempt with a Success and Failure constructor.
Does the explicit-exception package provide what you need? http://hackage.haskell.org/package/explicit-exception