I found a nice idiom for a graph algorithm where the pairs of nodes representing links could be merged into node lists by something like:

    ns = nub $ map fst  g    --head nodes

    ne = nub $ map snd g   -- tail nodes

And found a nicer approach:

   (ns,ne) = (nub***nub) unzip g

Or perhaps:

   (ns.ne) = bimap nub nub $ unzip g    -- from Control.Bifunctor

The SO reference I saw described bimap as a way to map a function over a pair, and it seemed like a great match, but I cannot find the bimap function, and cabal reports no package Control.Bifunctor.

??

-------------------------------------------------------