What are some good references, not very dense, to understand the underlying math and computability aspects of the notion of "functional programming"? I'd like to have something that talks about it from a math point of view and if/when I learn a functional programming language I can have the necessary "aha" moments when seeing the ideas being implemented.
I've read SICP, but that's Scheme specific and is a dense read. I don't really "get" functional programming after reading it and was looking for something more sublime and closer to the underlying math and computability points of views.