What is a program without side effects? A program that does nothing.
Complementing our code with functional code with unavoidable side-effects can be called "mostly functional programming." Using multiple paradigms in the same codebase and applying them where they are most optimal is the best approach. Mostly functional programming is how even the pure, traditional functional programs are modelled: keep most of the logic in pure functions and interface with imperative code.
And this is how we're going to write a little application of our own.
In this example, we have a boss that tells us that we need a web application for our company that tracks the status of the employees' availability. All the employees at this fictional ...