I'd like to be able to say

{ case Good(whatever) => whatever }.andThen { case Even(num) => println("it's even!") }

But if I use this, although it makes a PartialFunction, it doesn't do what I want it to. In particular, it will tell me that it's defined at Good(3). This is because it inherits andThen from Function, and so it takes a Function as its argument.

I think overloading andThen to take a PartialFunction would be pretty disruptive, so I propose two better ways forward:

A. provide a compose method on the PartialFunction object (somewhat confusing because there is also a compose method on the PartialFunction instance, but its behavior is not what we want for composing two PFs)
B. change andThen to inspect the other function, and if it's a PartialFunction, upgrade its behavior. (this is a thrilling runtime change, and makes its behavior inconsistent).

What do you think?