C with a module system

In the history of the C language, have any experiments been done towards adding a module system?

I know about the C++ proposal which didn't make the latest standard. I'm thinking of开发者_Go百科 something more along the lines of particular implementations which added a module system as a non-standard feature.

By "module system" I mean something which at the very least allowed the user to write one file instead of a .h/.c pair.

D programming language is a C++-like language with a module system. I'm not aware of any module system designed for plain C.

Makeheaders is a related utility.

The creators of C did indeed explore these things in the languages (including extensions to C) developed for Plan 9. Check out Limbo.

Apple is working on adding a module system to the LLVM C++ implementation.