generalizes ppx_import by allowing a whole module to be imported with all its types, possibly with annotations.

module overriding: mechanization of Gabriel Scherer's post on Gagallium blog http://gallium.inria.fr/blog/overriding-submodules/

type rewriting: types can be systematically annotated, substituted, renamed, or removed. Transformations such as those that are described in the comments of ast/ast.ml in ppxlib sources can be mechanized.