Your main function does not return a Result. You need to do something with the error case. Probably something like function().expect("oh no! function() failed!!");, which will cause a panic and error exit in the unlikely event function() fails. expect() turns a Result into an A on success, and panics displaying a combination of your error message and the B on failure.
Or you could use Result::unwrap() which works similarly without adding an error message of your own, just using the error value of the Result.
