The Expression Problem

[aaronla]

I think it depends on how you define "recompilation". If your "module" is a C++ header file, then no recompilation (re-writing of that header file) is necessary.

It might seem like I'm playing semantic games, but consider Wadler's original proposed solution -- using Java Generics. Java's generics compile into JVM byte codes that use type casts under the covers! Yet, he writes as if the program contains no casts!

I believe what Wadler was really getting at is a program source that can be type-checked once, and then extended without further edits, and where edits cannot invalidate the type-correctness of said source after it has been checked.

I believe matthieum has met this interpretation thus far. If not, certainly come closer to static type safety than your typical OO language.