I think you’re after something other than immutability then.

You’re allowed to rebind a var defined within a loop, it doesn’t mean that you can’t hang on to the old value if you need to.

With mutability, you actively can’t hang on to the old value, it’ll change under your feet.

Maybe it makes more sense if you think about it like tail recursion: you call a function and do some calculations, and then you call the same function again, but with new args.

This is allowed, and not the same as hammering a variable in place.