You could have checked exceptions with more flexibility than Java had, and it might work out well (or might break down for other reasons). "How do you write a

You could have checked exceptions with more flexibility than Java had, and it might work out well (or might break down for other reasons). "How do you write a 'map' function that can accept a callback, where the callback may want to communicate back one of several distinct kinds of error?" With Java style checked exceptions, you don't, and that's for sure a problem. However, one approach would be to say that map is polymorphic in the exceptions that may be raised from within it. But that set is not entirely unbounded - it is precisely the set that can be raised by its function argument, unioned with any that might be raised during traversal of its container argument.