unfold

[Stephen Weeks]

It's mostly a question of library consistency.  Since for lists, the old unfold
can be efficiently implemented in terms of the new unfold but not vice-versa, I
believe the new unfold should be in the LIST signature.  But I like functions
with the same name to have the same type (e.g. List.fold, Vector.fold, ...).
So, the question is, should the new unfold be called "unfold" or should the old
one (I would say old).  Assuming we keep the old one as unfold, what is the
right name for the new one.  The best I can think of is unfold'.