topologicalOrder :: PackageInstalled a => PackageIndex a -> [a]
topologicalOrder index = map toPkgId
                       . Graph.topSort
                       $ graph
  where (graph, toPkgId, _) = dependencyGraph index
topologicalOrder :: PackageInstalled a => PackageIndex a -> [a]
topologicalOrder index = map toPkgId
                       . Graph.topSort
                       $ graph
  where (graph, toPkgId, _) = dependencyGraph index
topologicalOrder index = map toPkgId
                       . Graph.topSort
                       $ graph
  where (graph, toPkgId, _) = dependencyGraph index