We looked at optionally returning a value from a function. In the case of average it was an average value, or no value at all. In some more elaborate functions, the “no result” case needs some more explanation to the caller of the function. We may feel the need to communicate what went wrong, or for what reason. This gives the user the opportunity to pass better input next time, or fix some external issue that the program can’t fix itself (e.g. a file not being readable).
