What's new in purely functional data structures since Okasaki?

I took his Programming Languages and Translators class at Columbia where he basically taught how to rip apart languages and build some crazy things. Postscript compilers, Lambda Calculus interpreters, Regex parsers using lazy evaluation in Haskell, and other mad scientist stuff.

You were dazed and confused by much of the material (he'd expect you to learn a new language and a new way of thinking almost every assignment). At the end of the semester though, it would be hard finding something that intimidates you. I actually TAed the class the next time he taught it, just so I could interact with the material some more.

He's over at West Point now, which might be a better fit for him anyway (most of us tended to whine about how hard the assignments were :)).