Idea: Optics types, combining pattern types and view types

Here is a naive idea inspired by the optics (lens and prisms) in bidirectional transformation. Given the view types like lens that provides partial view and update for product types, and pattern types like prisms that provides partial view and update for sum types, the idea is to combine them together: the optics type that provides partial view and update for both product types and sum types. Here is the syntax sketch. struct Foo { x: i32, y: Bar, } enum Bar { A, B(i32), C...