These are Racket bindings for the SoftPosit library for implementing posit arithmetic. More info on posits and the SoftPosit library is available at https://posithub.org/.
You can download this library through the Racket package manager by running
raco pkg install softposit-rkt; more information on the package is available at https://pkgs.racket-lang.org/package/softposit-rkt.
Documentation is available at http://docs.racket-lang.org/softposit-rkt/index.html.