[Haskell-cafe] Traversing a graph in STM

Hello Is there an elegant way of traversing a directed graph in STM? type Node nt et = TVar (NodeT nt et) type Edge et = TVar et data NodeT nt et = NodeT nt [(Node nt et, Edge et)] type MyGraph = Node String Int When implementing a simple depth first search we need a way to mark nodes (= TVars) as visited. In addition multiple concurrent searches should be possible. Is it possible to avoid passing around an explicit Set of visited nodes? And is there a better way of getting TVar identity than StableNames? - Einar Karttunen