Conor McBride gives a talk at the Bay Area Haskell Users Group about writing containers in Haskell. A container is a functor with a "shapes and positions" presentation: the contained values are given as the image of a function from positions, but the type of positions depends on the value of the shape. Some container theory will be live-coded using many GHC language extensions.

Conor has a post on his blog about this topic as well: https://pigworker.wordpress.com/2015/06/06/hasochistic-containers-a-first-attempt/

Also available on YouTube: https://youtu.be/dGv9zJfTf58