Hugs has data Exception = IOException IOError | HugsException HugsException where IOErrors are passed to a failure continuation and printed using Show. HugsExceptions are redexes that caused an error, triggering a longjmp. If not caught, they get printed by the internal printer, e.g. {primDivInt 1 0}. In my tree, I've switched over to the full Exception type (as in Control.Exception), with all Exceptions triggering a longjmp, caught by runAndShowError and printed using Show, e.g. "divide by zero" -- less information, but more friendly. Almost all of Control.Exception (all but throwTo/throwDynTo) then works with Hugs. The failure continuation in the IO type is then unused, though it's still there for now. A disadvantage is that the Exception types and Show instances move into Hugs.Prelude. It touches quite a few files, but it passes the test suite (appropriately modified), and I'm thinking of committing it. Anyone want to advise caution?