One can do this sort of thing in Ur i believe, which uses system F-omega with row polymorphic types, http://www.impredicative.com/ur/ http://www.impredicative.c

One can do this sort of thing in Ur i believe, which uses system F-omega with row polymorphic types, http://www.impredicative.com/ur/ http://www.impredicative.com/ur/