It's an interesting paper that I intend to dig into more carefully, but I kind of wish that a paper "for the Working Programmer" used a language like Python rather than Haskell. I'm aware that Haskell has a very nice type system for doing things like this -- and I'm a language nerd myself, so It's not that -- but it just seems like it would be more practical in something more "mainstream."
That said, it is interesting from what I've read so far.