GraphViz pretty-printing

http://hackage.haskell.org/package/prettyprinter-graphviz

Just some simple utility functions for hooking up the Haskell libraries graphviz and prettyprinter.

Given a Doc, you can use render to transform it to a GraphViz Label. If you are using a different annotation type (eg. something more abstract), then you can define a mapping to GraphViz HTML attributes, and fmap it over your Doc.