All, The containers library has a somewhat primitive but certainly useful Data.Graph library. Building a graph with this library simultaneously results in the lookup functions: m1 :: Vertex -> (node, key, [key]) m2 :: key -> Maybe Vertex (where 'key' is like FGL's 'label' but is assumed to be unique) This is exactly what I wanted when building and analyzing a call graph in FGL. To that end, I started making a graph type that tracked label to Node mappings, wrapping Data.Graph.Inductive.Gr, and assuming the labels are all unique. The classes for such a graph actually aren't possible. The ability to build a mapping from a node's 'label' to the 'Node' requires extra context (ex: Hashable, Ord, or at least Eq), but such context can not be provided due to the typeclass construction. Is there any chance we can change the Graph and DiaGraph classes to expose the type variables 'a' and 'b'? class Graph gr a b where ... class (Graph gr) => DynGraph gr a b where ... This would allow instances to provide the needed context: instance (Hashable a, Hashable b) => Graph UniqueLabel a b where ... buildGraph = ... some use of containers libraries that require context ... ... lookupNode :: Hashable a => UniqueLabel a b -> a -> Node -- etc Cheers, Thomas P.S. Please do educate me if I simply missed or misunderstood some feature of FGL.