I've recently had a resurgence in my interests with regards to functional programming, and have decided that I want to dive deeper. More specifically, I'm looking to purchase a set of authoritative texts on the subject.
I'm moderately familiar Haskell and ML, and a bit more so with LISP (Scheme and Common). I've also toyed with F#, but only just enough to be dangerous. I'm more interested in the core fundamentals and theory of functional programming versus a specific language or how-to focus, although discussions on the historical evolution of languages is cool, too. Hardcore math and textbook style reading is welcome.
Any suggestions?