Dear Robert:

I recently read about your work with your student Mark Lillibridge.
From your POPL '94 abstract:
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A Type-Theoretic Approach to Higher-Order Modules with Sharing. 
Robert Harper and Mark Lillibridge. 

The design of a module system for constructing and maintaining large programs
is a difficult task that raises a number of theoretical and practical issues.
A fundamental issue is the management of the flow of information between
program units at compile time via the notion of an interface.  Experience has
shown that fully opaque interfaces are awkward to use in practice since too
much information is hidden, and that fully transparent interfaces lead to
excessive interdependencies, creating problems for maintenance and separate
compilation.  The ``sharing'' specifications of Standard ML address this issue
by allowing the programmer to specify equational relationships between types
in separate modules, but are not expressive enough to allow the programmer
complete control over the propagation of type information between modules.
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Our work on Adaptive Programming (AP) addresses a similar issue.
Our interfaces use graphs (they are pattern graphs defining
a family of graphs) which specify at a high level of abstraction
how the internals of the module should look like. Given a concrete data
structure C (again as a graph) for the module, we can check whether C 
matches the pattern graph in the interface.

In this sense we have also more transparent interfaces _without_
creating excessive dependencies between the modules.
In our case, the dependencies between structure and behavior
get even significantly reduced compared to non-adaptive modules.

We have developed the concept of traversal strategy graphs
as a theoretical foundation for AP (with Boaz Patt-Shamir).
http://www.ccs.neu.edu/research/demeter/biblio/strategies.html

An applications paper which appears at OOPSLA '98 is at:
http://www.ccs.neu.edu/research/demeter/biblio/components.html

Best regards,
-- Karl Lieberherr
http://www.ccs.neu.edu/home/lieber/demeter.html