tree-view is a package for rendering trees as foldable HTML and Unicode art.
http://hackage.haskell.org/package/tree-view
Example:
*Data.Tree.View> drawTree $ Node "Add" [Node "Sub" [Node "3" [], Node
"Mul" [Node "1" [], Node "2" []]], Node "4" []]
Add
├╴Sub
│ ├╴3
│ └╴Mul
│ ├╴1
│ └╴2
└╴4
/ Emil