Best way to create a typeclass dependency graph?

I was doing some refactors for a project I’m working on, and I found myself in a situation where it would be really handy if I could get a graph of the project’s typeclass dependencies. Including cross-module dependencies. I did a bit of hacking, and managed to get something working using a GHC plugin and Prolog. The GHC plugin outputs the constraint information for each module into a single Prolog file, and then my Prolog script queries that file to make a Graphviz file for the part of the gra...