We wanted to finish up Conal's [Compiling to Categories](http://conal.net/papers/compiling-to-categories/) paper before moving on to automatic differentiation. The reverse-mode autodiff stuff has some overlap with Fong and Spivak's Chapter 2 as they both tackle related concepts.

I can try and read the automatic differentiation paper now, if you like. But could you post the code in particular you are wondering about so I can know what to focus on when I read?