reducer.kt

private fun reducer(state: State, event: Event): State = when (event) {
    is Event.TodoCheckedEvent -> {
        val todos = state.todos.map { todo ->
            if (todo.id == event.id) todo.copy(completed = event.completed)
            else todo
        }
        state.copy(todos = todos)
    }
    is Event.DbUpdateEvent -> state.copy(todos = event.todos)
    is Event.NewTodoEvent -> state.copy(
            todos = state.todos + TodoEntity(0L, event.text, false)
    )
    else -> state
}