While this isn't exactly the same, the convention of appending "!" in scheme/racket to denote a function that mutates a value is helpful in my opinion. You don'

While this isn't exactly the same, the convention of appending "!" in scheme/racket to denote a function that mutates a value is helpful in my opinion. You don't absolutely need it, but reading through your code and easily identifying where your values can change is nice.