John Meacham:
It is my understanding that the FFI foreign imports declare an ABI and not an API, meaning the exact way to make the foreign call should be completely deterministic based on just what is in the haskell file proper. Otherwise, obviously, direct to assembly implementations would be impossible.
In this sense, include files are always potentially optional, however, due to the oddness of the C langauge, one cannot express certain calls without proper prototypes, current haskell implementations take the straightforward path of relying on the prototypes that are contained in the system headers, which also incidentally provides some safety net against improperly specified FFI calls. However, it would also be reasonable for an implementation to just generate its own prototypes, or use inline assembly or any other mechanism to implement the FFI ABI calls properly.
Exactly! The FFI Addendum specifically leaves the compiler complete freedom as to which method to choose. I regard this property of the specification as important and we should keep it for Haskell'. Manuel