htc_3_26.swift

func combine<State, Event>(_ reducers: (State, Event) -> State...) -> (State, Event) -> State {
    return { state, event in
        reducers.reduce(state) { state, reducer in
            reducer(state, event)
        }
    }
}
func transform<GlobalState, GlobalEvent, LocalState, LocalEvent>(
    localReducer: @escaping (LocalState, LocalEvent) -> LocalState,
    stateKeyPath: WritableKeyPath<GlobalState, LocalState?>,
    toLocalEvent: @escaping (GlobalEvent) -> LocalEvent?
) -> (GlobalState, GlobalEvent) -> GlobalState {
    return { globalState, globalEvent in
        guard
            let localEvent = toLocalEvent(globalEvent),
            let localState = globalState[keyPath: stateKeyPath]
            else { return globalState }
        var globalState = globalState
        globalState[keyPath: stateKeyPath] = localReducer(localState, localEvent)
        return globalState
    }
}