2.5 Recursion instead of an explicit loop state
Functional programs don’t rely on loops and the associated overhead of tracking the state of loops. Instead, functional programs try to rely on the much simpler approach of recursive functions. In some languages, the programs are written as recursions, but Tail-Call Optimization (TCO) in the compiler changes them to loops. We’ll introduce some recursion here and examine it closely in Chapter 6, Recursions and Reductions.
We’ll look at an iteration to test whether a number is a prime number. Here’s a definition from https://mathworld.wolfram.com/PrimeNumber.html: “A prime number ... is a positive integer p > 1 that has no positive integer divisors other than 1 and p itself.” We can create a naive and poorly performing algorithm to determine whether a number has any factors between 2 and the number. This is called the Trial Division algorithm. It has the advantage of simplicity; it works acceptably...
