Chapter 4 covered some pieces of functional programming that can be hard to wrap your head around, but this chapter will be much simpler. We will just look at three general methods that are used in functional programming instead of loops and instead of explicitly writing recursive functions. They are really three different patterns for computing on sequences, and they come in different flavors in different functions, but just these three allow you do almost anything you would otherwise do with loops. Note the emphasis on almost!
These three functions do not replace everything you can do with ...
