CombineReducer method in Kotlin

combineReducers.kt

//
// Reducer interface definition
//
typealias Reducer<ReducerStateType> = (action: Action, state: ReducerStateType?) -> ReducerStateType

//
// Combine reducers method
//
fun<T: StateType> combineReducers(vararg reducers: Reducer<T>): Reducer<T> {
    return { action, state ->
        var newState: T? = state
        reducers.forEach { reducer ->
            newState = reducer(action, newState)
        }
        newState!!
    }
}