I had a different read on that but I am familiar with the link to Haskell zippers. People seem to assume if someone wrote something about Haskell they must be s

I had a different read on that but I am familiar with the link to Haskell zippers. People seem to assume if someone wrote something about Haskell they must be smart. Their "derivative" of trees implicitly assumes the cartesian product A x B is isomorphic to B x A. Just like the Frechet derivative for non-commutative Banach spaces, the derivative of T^2 is not 2 T dT, it is T dT + dT T.