Hi - I am just learning Haskell and am far away from exception handling intricacies. However I just recently read an article of Herb Sutter about exception handling in C++ with some rules when to use exception handling - and perhaps these rules might be applicable to Haskell too (article: "When and How to Use Exceptions", Herb Sutter, C/C++ Users Journal August 2004, pp. 47 -- 51)? Herb Sutter gave these rules : An error is any failure that prevents a function from succeeding. Three main kind of errors: - a condition that prevents the function from meeting a precondition of another function that must be called (so to say: the caller has to check for preconditions while the function called my use C/C++ asserts to assert the correctness of its preconditions) - a condition that prevents a function from establishing one of its own postconditions (e.g. producing a (valid) return value) - a condition that prevents the function from reestablishing an invariant that it is responsible to maintain (special kind of postcondition mainly found in object oriented code). Any other condition is not an error and shouldn't be reported as one. The code that could cause an error is responsible for detecting and reporting the error otherwise this is a programming mistake. I am not sure if these rules apply to real functional programming but at least they seem to be useable. The point that the caller is responsible for checking the preconditions of functions it is calling is something I also found as a suggestion in using the object oriented language Eiffel. Cheers and best regards Bjoern