Yes, I've already been thinking about constraining type parameters to an interface. Internally, the type-checker considers type parameters to have underlying ty

Yes, I've already been thinking about constraining type parameters to an interface. Internally, the type-checker considers type parameters to have underlying type interface {}. A constraint on a type parameter should be as straightforward as changing it's underlying type to a specific named interface instead of an empty one. The only tricky bit I can see is thinking about how this would work with generic interfaces or whether we should allow other kinds of type constraints (e.g., union types).