Comment by montmorency88

I'd highly recommend Erwigs FGL library in Haskell as a really nice example of a generally performant graph data structure that is easy to work with. The API feels like working with lists because you are essentially consing contexts(node, neighbours) into a list of contexts that form your graph. Many standard graph algorithms are then built up from depth or breadth first search and you can compose really succinct programs to manipulate the graph. Graphs are labelled with any Haskell data structure and there is a graphviz library complementary to FGL to generate dot files which can be rendered according to the data carried in the node labels. Often in an application you want to both perform computations on your graph and render a visualization simultaneously to the end user or for debugging and in FGL you minimise duplication of application and rendering logic.