In the author's example of the geometric mean, shouldn't the function return an error if any of the numbers were negative? Because the program shouldn't be sending negative numbers to that function to begin with so he/she should maybe get some hint that one of those functions producing said numbers isn't working properly. And if there are no positives, I sure as hell don't want a divide by zero error bringing the program to a complete stop when I could just simply display "Could not calculate geometric mean, check the inputs" to the user.
The functions in the article are not the geometric_mean. They are functions which first filter the list and then take the geometric mean. I only misnamed them that way for the sake of exposition. The only true geometric_mean in there is the J version
