In this chapter, we will further improve “Jarvis” to have better UI and user experience and then will add a basic web access layer on top. This will drive an important discussion on how to use mutable variables in Haskell (it’s amazing that we did so much without ever needing them!) as well as a pick under the hood of GHC – for those who are more technically inclined and want to understand how functional machinery works, which may help in optimizing your code for production use.