Question: unrestricted list functions

[treeowl]

Do we have functions that can conveniently implement these?

foo :: Ur [a] %1-> [Ur a]
bar :: [Ur a] %1-> Ur [a]

[aspiwack]

I assume foo would be a traverse function, but we haven't got around to design the traversable hierarchy see #220 .

I don't have any generic mechanism for bar in mind.