Just to add to the discussion of these two language levels, there is a new research language called 1ML that unifies both levels: http://www.mpi-sws.org/~rossb

Just to add to the discussion of these two language levels, there is a new research language called 1ML that unifies both levels: http://www.mpi-sws.org/~rossberg/1ml/ http://www.mpi-sws.org/~rossberg/1ml/ "a redesign of ML in which modules are truly first-class values, and core and module layer are unified into one language. In this "1ML", functions, functors, and even type constructors are one and the same construct; likewise, no distinction is made between structures, records, or tuples."