Solving the Monty Hall problem in Clojure

At this week's Bristol Clojurians meetup we decided to give the Monty Hall problem a go as described in the cyber dojo problem set. Here's the solution I (eventually) came up with:

This turned out to be a lot trickier than it looks. I ended up spending way more time than necessary hacking emoji support into Emacs to display little car and goat icons. Important things first, right?