FP

I think that Functional Programming is almost as much of a hoax as Artificial Intelligence. I have yet to see an interesting piece of code that comes from these FP people.

...like in a video game or other types of simulations. It's most efficient to just update all the entities in place in a loop. You could make a copy of the entire world every frame and this could be optimized into something better by a very, very clever compiler, but there are other limitations as well. With mutations you can adopt models where components broadcast changes to other components. This isn't so easy to model in a functional way. And then there's concurrency used in ways other than parallel evaluation, like producer consumer pipes. All of these techniques invoke complexity but they are still very useful or the only way to go about solving some problems.