We present a new foreign-function interface for SML/NJ. It is based on
the idea of data-level interoperability -- the ability of ML programs
to inspect as well as manipulate C data structures directly.

The core component of this work is an encoding of the almost complete
C type system in ML types. The encoding makes extensive use of a
"folklore" typing trick, taking advantage of ML's polymorphism, its
type constructors, its abstraction mechanisms, and even functors. A
small low-level component which deals with C struct and union
declarations as well as program linkage is hidden from the
programmer's eye by a simple program-generator tool that translates C
declarations to corresponding ML glue code.