These playgrounds were used in class demos teaching the basic priniciple of reactive programming for Swift in 67-443 F20. These playgrounds draw heavily from the book RxSwift: Reactive Programming with Swift v2.0 by Pillet, et al. I strongly recommend students interested in learning more about reactive programming buy the book, as there is a lot of material covered in the book that we cannot hope to cover in a single week.
Be aware that I could not get the code examples provided to work (kept getting a "error: Couldn't lookup symbols" message, so I rebuilt these from scratch and added some additional annotation and some modifications). I'm not sure if the issue is due to the transition to a new version of iOS (this was written from iOS 11, which is dated now) or some other issue, but I didn't get these to work. In order to get a playground to allow for the use of Cocoapods, I had to create them within a Xcode workspace, following the directions found at https://learnappmaking.com/cocoapods-playground-how-to/. Hopefully students using these playgrounds will not encounter the same frustration of them not working as I had with the original material.