[grogers]

Another good introduction to zippers that helped me understand them in plain terms is: http://blog.ezyang.com/2010/04/you-could-have-invented-zippe...

[eru]

And for those who like their math hard to understand (and rigorous): "The Derivative of a Regular Type is its Type of One-Hole Contexts" (http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.22.8...)

It's cited as "Conor's paper" in your article. But the link there doesn't work.