htc_4_1.swift

enum State {
    case initial
    case loading
    case loaded(data: [String])
}
enum Event {
    case dataLoaded(data: [String])
    case loadData
}
extension State {
    static func reduce(state: State, event: Event) -> State {
        var state = state
        switch event {
        case .dataLoaded(let data):
            state = .loaded(data: data)
        case .loadData:
            state = .loading
        }
        return state
    }
}