[lostcolony]

That's actually one of the more reasonable uses for OO; have an interface that defines 'apply_tax_rate', and a bunch of implementations for each, so you only have a single line in your function (instance).apply_tax_rate. Of course, that leads to your actual implementing code being scattered in different classes, and that can be a pain, too.

If a functional language, I'd prefer each being its own function, with the case matching in a single, standalone file that returns the appropriate function based on whatever. That way you still get just apply_tax_rate(type, amount) in your main calculation function.