Date: Fri, 18 Sep 2009 13:07:20 -0400
   From: David Van Horn <xxxxxx@cs.brandeis.edu>

   I could add conversion functions if that seems useful (they are trivial
   to define in terms of the folds given).  In a system that really
   embraces the random-access pair type as fundamental, these would just be
   identities.

I think this would be good: otherwise programs would not be able to
portably exploit systems that embrace random-access lists.