It's extracted, not contrived. Updating nested attributes on a tree of objects as a nice one-liner. The most contrived bits were that I didn't use the built in

It's extracted, not contrived. Updating nested attributes on a tree of objects as a nice one-liner. The most contrived bits were that I didn't use the built in tree type so I had to define more stuff explicitly. Traverse comes from Data.Traverable but is exported with lens as lens can be seen as a generalization of traverse.