@neauoire A classic! Alone the opening statement is gold:
"For those of you concerned with theorems and proofs, I apologize, today is going to be a very bad day."
If you haven't done so yet, also recommend checking out his dissertation: "A foundation for typed concatenative languages"
https://www2.ccs.neu.edu/racket/pubs/dissertation-kleffner.pdf
@toxi I hadn't seen this one! thanks. Reading it now :)