Swift Rx based pager (inspired from https://gist.github.com/mttkay/24881a0ce986f6ec4b4d)

Pager.swift

import RxSwift

// MARK: globals 

private var noOp: () -> Void = { _ in }

// MARK: Pager

public class Pager<T> {
  public typealias PagingFunction = ([T]) -> Observable<[T]>
  private let pagingFunction: PagingFunction
  private let pages: PublishSubject<[T]>

  lazy private var nextDelegate: () -> Void = { _ in self.pages.onNext([]) }

  public init(pageSize: Int, pagingFunction: PagingFunction) {
    self.pagingFunction = pagingFunction
    pages = PublishSubject<[T]>()
  }

  public func next() {
    nextDelegate()
  }

  public func page() -> Observable<[T]> {
    return pages
      .asObservable()
      .doOnNext { _ in self.nextDelegate = noOp }
      .flatMap { return self.pagingFunction($0) }
      .doOnNext { list in
        if list.count == 0 {
          self.pages.onCompleted()
        } else {
          self.nextDelegate = { _ in self.pages.onNext(list) }
        }
      }
      .filter { $0.count > 0 }
  }
}

// MARK: Usage

let pager = Pager<Int>() { previousPage in
  let last = previousPage.last ?? 0
  if last > 10 { return Observable.just([]) }

  let timer: Observable<Int> =  Observable.timer(0.1, scheduler: MainScheduler.instance)

  return timer
    .take(1)
    .map { _ in [last + 1, last + 2, last + 3].filter { $0 <= 10 } }
}

let stream = pager
  .page()
  .scan([Int](), accumulator: +)
  .shareReplay(1)

stream.subscribeNext { print($0) }
stream.subscribeCompleted { print("completed") }

// should print [1, 2, 3], [1, 2, 3, 4, 5, 6], ...
delay(0.2) { pager.next() }
delay(0.4) { pager.next() }
delay(0.6) { pager.next() }
delay(0.8) { pager.next() }
delay(1.0) { pager.next() }