Hendrik Tews <tews@tcs.inf.tu-dresden.de> wrote

[...]
>Has anybody tried to include parts of an interface into an
>implementation (for instance by means of a preprocessor)?

I've seen SML programs written using NoWeb, a variant of Knuth's
literate programming tool Web. The tool acts as a preprocessor and
makes it easy to write type declarations only once, and use them in
signatures and structures.

-Manuel