I like to write loops where they follow the functional map/filter/reduce paradigm where they don’t mutate anything except some initial variables you “fold” over

I like to write loops where they follow the functional map/filter/reduce paradigm where they don’t mutate anything except some initial variables you “fold” over (defined immediately prior to the loop) and which are treated immutable (or uniquely owned) after the loop. I find this has good readability and by containing the mutation you can reason about it “at a distance” quite simply since further away it’s for-intents-and-purposes pure code. What you might lose are the compiler-enforced guarantees that a functional language gives you. Some languages give you the best of both worlds - with rust you could put this in a pure function (immutable inputs, owned outputs) and the borrow checker even reasons about things like this within a function body.