Josh Abernathy just open-sourced his take on ReactNative, Few.swift:
Few.swift lets us express UIs as stateless, composable, immutable-ish values of their state. When their state changes, Few.swift calls a function to render the UI for that state, and then intelligently applies any changes.
To put it another way, the state is the necessary complexity of the app. The view is a mapping from state to its representation.
This is super cool because the only thing that's mutating is the state. Few.swift is in charge of making an in-place changes to the UI when the state changes.