Thanks for mentioning Pyret, I've searched for it and it made me laugh discovering the extension of the files is .arr (some would say I'm really easily amused).
I've been watching the videos from 2012, and the professor sprinkles that humor throughout the lectures, and done well in that its not annoying (to me at least).
Update: seems the author talks about Pyret/Racket in this thread https://news.ycombinator.com/item?id=6702563