I was a little surprised he took until the final paragraph to mention Racket. If he had played around with it then I think the article might have read differently.

  " Racket is a Lisp dialect that’s specifically designed for creating
  new languages (a technique sometimes referred to as
  language-oriented programming). I haven’t had time to play around
  much with Racket myself, but it looks like a very suitable tool for
  creating 'little languages'."