You might be thinking that this is all very well, but you don’t write mathematical functions as part of your daily job.
But functional programming isn’t about mathematical functions.
Functions are things that transform data. The trig function sin transforms the value 90 degrees to the value 1.0. And that’s the hint.
Programming is not about data. It’s about transforming data. Every program we write takes some input and transforms it into some output. The input could be a web request, some command-line parameters, or the weather in Boise. Whatever it is, our code takes it and transforms it multiple times on the way to producing the desired result.
And that’s why I think functional programming is a natural successor ...