Io is the language in Seven Languages that I never would have picked up on my own. But it was one of the funnest.
I compare Io to Ferris Bueller. He’s a young guy, razor sharp, who knows how to get stuff done. He breaks the rules and has a blast doing it.
The concurrency strategy in the language is rock solid. Actors, message passing, immutability where it counts. Futures, coroutines—everything you want.
But there’s that element of being a little dangerous. Say you get a message with an argument that is nil. You don’t want it to be nil, so you take the inbound arguments, grab the sender, and modify the object attribute that caused the problem… after the fact, and without the knowledge of the calling object.
Things that make you go “hmmmmmm….” bueller? bueller? anyone?