persistent-vector based implementation

The original paper discusses an inductive `Graph` implementation based on "version tree" based arrays. I believe this was implemented in ML. Has there been any attempt to compare the performance of such an implementation in Haskell, perhaps using a library like this one? https://hackage.haskell.org/package/persistent-vector

Start by reviewing the original paper's version-tree array approach and the persistent-vector package linked in the issue. Then inspect fgl's current Graph representation and identify where a comparison or alternative implementation would belong; done would require an agreed scope and reproducible performance results.

Written by the indexing model from the issue text.