Even if you use AI, there's a certain point where it's not clear that an AI would make you faster. F# is my favorite language, and I've been programming in it so long (since 2012) that I feel like I think in F#. Asking an AI for something can be faster if I can state my requirements informally; but if I need to specify many things precisely to an AI... why not just write the code in F#? Part of the beauty of good functional designs is that they are declarative, not imperative, so in some sense you're really just stating what you want, at finer and finer granularities, until what you want is trivial.

Even when I want code written in a different language (e.g., C/C++), I often still start by making a prototype in F#. This helps me nail down the logic without having to worry about things like allocation or layouts. Perhaps I could ask an AI to do this second step for me, and then use the F# implementation as an oracle. Anyway.

Yes! That's exactly how you should do it while working with a language that doesn't have a compiler that will aggressively analyze, and rewrite and optimize your code for you. (So, most languages with "heavy runtimes" that support a bunch of dynamic stuff and JITs)

There are basically two points to programming with immutable-first data. One, eliminate certain classes of data race concurrency bugs. Two, less mutable state in a given context makes it easier to reason about.

So, if you're inside a function scope and you aren't launching any concurrent operations from inside that function, you don't have to worry about benefit #1. If you're inside a function (and you're not reaching out for global mutable state), then the context you need to keep in your working memory is likely fairly small, so a few local mutable variables doesn't significantly harm "understandability" of the implementation (in most cases). So, you really don't have to worry about #2, either. Make your functions black boxes with solid "APIs" (type signatures), and let the inside do whatever it needs to make it work the best.

Just because premature optimization is the root of all evil, it doesn't mean we need to jump right to premature pessimization...

I wonder at what point even a still functioning device no longer looks the same?

I've been going through a lot of very old stuff recently and a lot of it is well preserved in a way but given enough years everything changes.

I don't think any original Gameboys have been made in twenty years or more.

Yeah I did see that part. Although he mentioned his Chip8 emulator which was fully immutable. Still interesting so see when people use the mutability escape hatches.