John Carmack on mutable variables

After a 2 year Clojure stint I find it very hard to explain the clarity that comes with immutability for programmers used to trigger effects with a mutation.

I think it may be one of those things you have to see in order to understand.

Made a similar experience with Scheme. I could tell people whatever I wanted, they wouldn't really realize how much cleaner and easier to test things could be, if we just used functions instead of mutating things around. And since I was the only one who had done projects in an FP language, and they only used non-FP languages like Java, Python, JavaScript and TypeScript before, they would continue to write things based on needless mutation. The issue was also, that using Python it can be hard to write functional style code in a readable way too. Even JS seems to lend itself better to that. What's more is, that one will probably find oneself hard pressed to find the functional data structures one might want to use and needs to work around recursion due to the limitations of those languages.

I think it's simply the difference between the curious mind, who explores stuff like Clojure off the job (or is very lucky to get a Clojure job) and the 9 to 5 worker, who doesn't know any better and has never experienced writing a FP codebase.