Using expressions instead of statements

A statement is a block of code that doesn't return anything. An expression, on the other hand, returns a new value. Since statements produce no results, the only way for them to be useful is to mutate the state, whether that's changing a variable, changing a data structure, or performing some kind of IO.

Functional programming tries to avoid mutating the state as much as possible. Theoretically, the more we rely on expressions, the more our functions will be pure, with all the benefits of functional purity.

We've used the if expression many times already, so one of its benefits should be clear: it's less verbose and, for that reason, less error-prone than the if statement from other languages.

Pattern matching

The concept of pattern matching will seem like switch/case on steroids. We've already seen how the when expression can be used, which we explored in Chapter 1, Getting Started with Kotlin, so let&apos...