[Haskell-cafe] functional graphs

Hi, Given a complete graph as a list of nodes whose edge labels are given by a function over two nodes: data CGraph a b = CGraph [a] (a -> a -> b) Can I define an instance for the fgl Graph class? import Data.Graph.Inductive.Graph instance Graph CGraph where empty = CGraph [] -- and now? I had no idea how to define empty (except using undefined). I thought of requiring a context for the node labels of type a, but this type is not mentioned in the class header. So it looked to me like the impossibility to define sets (requiring an Ord) as monads. (i.e. instance Monad Data.Set.Set) Any working proposals for my graph problem? Cheers Christian