Oh, then I think you'd find a lot to like about APL/J/K. It's not just that they contain genuinely new ideas worth learning; they're mindblowing in the way that Lisp and Forth are. I agree with silentbicycle that your best bet is probably the tutorials that ship with J (http://www.jsoftware.com/start.htm). The closest thing to a manifesto is Iverson's Turing award lecture Notation as a Tool of Thought (http://www.jsoftware.com/papers/tot.htm). But the really hardcore, beyond mindblowing stuff is Arthur Whitney's work on K, Q, and kdb. (Edit: the Q book is available online at https://code.kx.com/trac/wiki/QforMortals2/contents, user and pwd "anonymous").
I second what gruseom says: K (and Q, the newer version of K) is amazing. J seems more theoretically satisfyingly mathy to me, but K is a straight-up hacking language. It's really too bad that it's closed and oh-so expensive (but since it was made for real-time stock trading, and it works, I'm not surprised).
