Generating Function Prototypes

[Malcolm Wallace]

> > The effort of producing a header file is sufficient that ffi code
> > supplied without them will be very hard to port to ghc -fvia-C
> 
> Sure, it's a problem, a bug in GHC, whatever.  But I don't see a way
> around it!  We can't just generate prototypes because they might
> conflict with prototypes already in scope.

Here is nhc98's approach to solving the problem.  The usual case is for
the Haskell compiler to generate a C prototype for the FFI function
based solely on the Haskell type.  On the rare occasions where the
generated prototype conflicts with a #include'd prototype, you can
add the 'noproto' modifier to the Haskell FFI decl, and the prototype
is omitted.  This is both easy, and (I would guess) very portable.

Here's a real example from the nhc98 implementation of the standard
libraries:

    foreign import noproto rename :: CString -> CString -> IO Int

The 'noproto' is needed because <stdio.h> has

    extern int rename (__const char *__old, __const char *__new) __THROW;

(at least on Linux).  In fact, out of ~300 foreign imports in the
nhc98 libraries, this is the *only* occurrence of 'noproto', showing
that this really is a rare case.  Hence, generating prototypes by
default in the -fvia-C route could be a serious proposition.

Regards,
    Malcolm