> I don't think Racket was the first language to come up with this.
Racket's parameters are just dynamically scoped variables. Most Lisps have them. The older Lisps actually predate lexically scoped variables and had dynamically scoped variables exclusively! Emacs Lisp is not even that old and only had dynamic scope until relatively recently.
> Racket's parameters are just dynamically scoped variables.
More or less. Racket's parameters also work with multiple threads and cooperates with continuations.
In Scheme it is common to see `fluid-let` to handle classic dynamically scoped variables.
I think most Common Lisp implementations that provide threads, make dynamically-scoped variables (called "special variables" in Common Lisp) thread-local.
Racket's parameters are just dynamically scoped variables. Most Lisps have them. The older Lisps actually predate lexically scoped variables and had dynamically scoped variables exclusively! Emacs Lisp is not even that old and only had dynamic scope until relatively recently.