this is particularly visible in the implementation of `plus` – `other` might not be a Point at all, so `other('x')` and `other('y')` might do anything; which i'

this is particularly visible in the implementation of `plus` – `other` might not be a Point at all, so `other('x')` and `other('y')` might do anything; which i'd say is textbook (ad-hoc) polymorphism. i remember reading this somewhere: "branching on values is the ultimate dynamic dispatch" :)