Earlier this year I mentioned a nice library adding a number of useful function programming methods to Swift call Dollar.$swift.
Here’s a nice guide from iJoshSmith where he demonstrates taking a problem, and solving that problem in the familiar imperative style, and then solves the same problem using functional programming in Swift.
The tutorial does a nice job explaining the thinking behind the changes made.
You can find the tutorial on the iJoshSmith blog.
A nice little tutorial on that will get you thinking if you’re just starting with functional programming.