If anyone wants to try the flavour of Scheme used in the book, install Racket and use:

    #lang simply-scheme

Note that it doesn't get installed by default. You must download the package https://pkgs.racket-lang.org/package/simply-scheme

The easiest way is to go to inside DrRacket and open the menu File > Package Manager and add "simply-scheme".

Or if you prefer the command line, something like

  raco pkg install simply-sheme