Functional Kotlin

Recursive functions

Recursive functions are functions that invoke themselves, with some sort of condition to stop the execution. In Kotlin, a recursive function maintains a stack but can be optimized with a tailrec modifier.

Let's look at an example, an implementation of a factorial function.

First, let's take a look at a typical imperative implementation, loops, and state change in the following code snippet:

fun factorial(n: Long): Long {   var result = 1L   for (i in 1..n) {      result *= i   }   return result}

It's nothing fancy nor particularly elegant. Now, let's take a look at a recursive implementation, no loops, and no state change:

fun functionalFactorial(n: Long): Long {   fun go(n: Long, acc: Long): Long {      return if (n <= 0) {         acc      } else