Point = Class {x = Int; y = Int}, Impl: Add() and Eq()
Point.
    new x, y = Self::__new__ {x; y}
    norm &self = self::x**2 + self::y**2
    @Impl Add()
    `+` self, other =
        Self.new(self::x + other::x, self::y + other::y)

p = Point.new 1, 2
q = Point.new 3, 4
r = p + q
assert r == Point.new 4, 6
assert r.norm() == 52