Data.Graph has always been a bit of an unloved module in containers. However, at GHC HQ the graph has always been a bit of an important data type, and we've been maintaining basically another version of the module under the name Digraph. I was refactoring this module to use Data.Graph and I noticed that there were a few functions which were conspicuously missing from the module proper. So here they are: For Data.Graph: - Generalized reachable :: Graph -> [Vertex] -> [Vertex] (compare to reachable :: Graph -> Vertex -> [Vertex] - Returns an undirected version of a graph which, for any edge a -> b, an edge b -> a also exists. undirected :: Graph -> Graph - Extract a list of groups of elements of a graph such that each group has no dependence except on nodes in previous groups (i.e. they may not depend on nodes in their own group) such that the groups are maximal. No solution exists for cyclic graphs vertexGroups :: Graph -> [[Vertex]] For Data.Tree - preorderF :: Forest a -> [a] (or perhaps flattenF, to keep naming consistent with existing flatten :: Tree a -> [a] which does a preorder) Furthermore, we have a few "low level" functions implementing algorithms for classifying edges, finding connected and biconnected components that were contributed by Sigbjorn Finne in 1997, although GHC does not use them. Finally, I think GHC's node-parametrized variant of graphs (to which it gives the name 'Graph', as opposed to Data.Graph style graphs which it calls 'IntGraph'; is far more useful to clients: data Graph node = Graph { gr_int_graph :: IntGraph, gr_vertex_to_node :: Vertex -> node, gr_node_to_vertex :: node -> Maybe Vertex } and I think it is well worth considering implementing this is the standard library. If no one else, GHC will happily use such an implementation. Thanks, Edward