I remember having a great deal with trouble dealing with the lack of immutable cyclic data structures in Clojure, and not wanting to use an atom with atoms for the recursive parts, though there's probably more ways to make it work that I wasn't clever enough to think of :)
It reminds me of my own (tiny) roguelike-in-clojure experiment: http://thomcc.github.com/dunjeon/
I remember having a great deal with trouble dealing with the lack of immutable cyclic data structures in Clojure, and not wanting to use an atom with atoms for the recursive parts, though there's probably more ways to make it work that I wasn't clever enough to think of :)