Comment by simoncion

> Lets count the number of comercial sucesful released games that don't use mutability or object orientation....

1) I suspect game engines that Carmack designed towards the end of his career are built in a largely-functional style. He's on record [0] as thinking that writing code in a functional style is generally a good thing to do.

2) Running on the BEAM doesn't mean that you give up mutability. In my experience with Erlang, functions that return updated state are very, very, very common. Similarly, functions that mutate state external to the function [1] are also common... it's rare that a program that has no visible effect on the outside world is useful.

It's generally quite a lot easier to understand what your program does when most or nearly all of its functions take input and return output without mutating external state as a side effect.

[0] There's some Twitter thread of his that I CBA to find saying -in effect- "Writing in a functional style makes your code much easier to understand. Obviously, if you're writing a video game, you have to pass around pointers for efficiency reasons, but that doesn't preclude writing most of your code in a functional style."

[1] Such as in an ETS table, a external database, with a network call to a remote system, or even writing data to disk.