> The best solution I have ever seen to global variables is definitely parameterize with Racket (https://docs.racket-lang.org/guide/parameterize.html). I don't think Racket was the first language to come up with this, but it was the first one I am aware of. The basic idea is that you define some global with a default value. However, you can call parameterize to change the value for the duration of some input function.

Isn't that basically Perl's `local`?