FFI proposal: allow some control over the scope of C headerfiles

[Duncan Coutts]

On Tue, 2006-04-25 at 10:16 +0100, Simon Marlow wrote:
> On 25 April 2006 09:51, John Meacham wrote:
> 
> > On Tue, Apr 25, 2006 at 09:40:58AM +0100, Simon Marlow wrote:
> >> Admittedly I haven't tried this route (not including *any* external
> >> headers at all when compiling .hc files).  It might be possible, but
> >> you lose the safety net of compiler-checked calls.
> > 
> > yeah, perhaps a hybrid approach of some sort, when building the
> > package, use the system headers, but then include generated
> > prototypes inside the package-file and don't propagate #includes once
> > the package is built. 
> > 
> > or just an intitial conformance check against the system headers
> > somehow (?), but then only use your own generated ones when actually
> > compiling haskell code. It would be nice to never need to include
> > external headers in .hc files.
> 
> Hmm, the more I think about it, the more I like this idea.  It means we
> could essentially forget about the public/private header file stuff, we
> don't need the extra pragmas, and there would be no restrictions on
> inlining of foreign calls.

That would be nice. If the module that imports the C functions were
compiled via-C with the headers (or some other check like c2hs does)
then we'd get the safety check. Then other client modules could be
compiled without a prototype at all (or one generated by the Haskell
compiler).

As you say, it is a bit of a pain that users of Haskell bindings libs
need to install the development versions of C libraries. For example
Gtk2Hs users on windows need the full dev version of Gtk+ which is
considerably larger than the runtime version.

One downside would be that we would only be able to call C functions
which conform to the standard platform ABI. As it is at the moment
(perhaps somewhat by accident) we can call C functions that have
non-standard ABI annotations in their prototype, eg:

int foo (int) __attribute__((regparam(3)))

ok that's a silly example, bu there are more sensible examples of ABI
weirdness - especially on arches like mips which seem to support half a
dozen different ABIs. Perhaps we don't care, I'm not sure I do.

Duncan