Removing side effects can improve composition... The Red Book helps me see code from a different perspective so I wrote about it: https://lordraydenmk.github.io//2019/side-effects-and-composition/

small typo

The return type is Pair<List<Coffee, Charge>> containing a list of purchased coffees and a single charge for all of them.

-> Pair<List<Coffee>, Charge>

Will fix, thanks