To generate partial application boxed closures I need to know the arity
of the expression to tell if more args will remain after the given args.
Right now I think I can recalculate the types if I have a symbol table
where I can look up every variable. I think this will be a lot of work
because I have to reimplement most of unification to deal with
collections, patterns, and type variables. And I currently don't know
how unification works.
