We quasi-did that with primitives. But as I recall, the discussion at the time acknowledged the ineffectiveness of the approach: The point of the platform is that if you compile against the platform, it should be stable - and there is really no effective way to keep people from compiling against them, or even warn them: We could hide them in the package database, but cabal will "unearth" them, without warning, if your project requires it.

I suppose this points at an interesting possible cabal enhancement: If it chooses a package that is hidden in the db, it warns you at configure time, even though at build time it is going to use it.

- Mark