John Carmack on mutable variables

On a similar note, I’ve always liked the idea of being able to mark functions as pure (for some reasonable definition of pure).

The principle of reducing state changes and side-effects feels a good one.

For what it's worth, I was experimenting with this idea for Python (in an almost completely vibe-coded fashion) here: https://github.com/jlmcgraw/pure-function-decorators

Whether it's of any actual utility is debatable