About implementing classes of type Haskell

Question

Several presentations by Simon Peyton Jones have a page that shows the history of type classes:

There is a lot of material for understanding type classes from a programmer’s view, such as typeclassopedia article and many other tutorials. However, its implementation and overhead are rarely described.

I am wondering what the problems were during the implementations and their solutions (I think there must be academic publications for the solution).

In other words, I'm looking for materials, such as inside a C ++ object model, but for the Haskell language.