Jonathan Bryant writes:
 > Has anybody ever come up with a way of doing these things (HOFs,
 > functors, partial application, module types, parametric polymorphism) in
 > UML or any kind of modeling language? 

In Norman  Ramsey's nice  paper "ML Module  Mania" you'll find  such a
diagram for a complex combination of signatures, modules and functors:
see

  http://www.eecs.harvard.edu/nr/pubs/maniaws-abstract.html 

There  are similar  diagrams in  Philippe Narbel's  recent  book about
Ocaml, but unfortunately  this book is only printed  in French (if I'm
right).

Hope this helps,
-- 
Jean-Christophe Filliâtre (http://www.lri.fr/~filliatr)