PaginateOperator.swift

extension ObservableType {
   func paginate<O: ObservableType>(nextPageTrigger: O,
                 hasNextPage: E -> Bool,
                 nextPageFactory: E -> Observable<E>) -> Observable<E> {
      return flatMap { page -> Observable<E> in
         if !hasNextPage(page) {
            return Observable.just(page)
         }
         return [
            Observable.just(page),
            Observable.never().takeUntil(nextPageTrigger),
            nextPageFactory(page)
         ].concat()
      }
   }
}