FFI progress

[Simon Peyton-Jones]

| I propose the following (basically my last proposal plus
| suggestions made by others):
| 
|   foreign import "gtk.h:foo" foo :: <type>
| 
| corresponds to a `#include "gtk.h"' and
| 
|   foreign import "<gtk.h>:foo" foo :: <type>
| 
| corresponds to a `#include <gtk.h>'.  The former allows to
| have a custom `gtk.h' "lying around" as suggested above.
| The filename may of course be a path.
| 
| As suggested by SimonM, we also allow multiple includes
| seperated by comma
| 
|   foreign import "<sys/types.h>,<sys/sockets.h>:socket" 
| socket :: <type>

Do we really need this?  Surely it's not so hard to have one
header file per package living in a standard place that collects
the headers needed for a particular package, including whether
they are <..> or "...", etc.    

Its easy to add features and nigh impossible to remove them. 
I suggest we have just

	"gtk:foo"

(no ".h") meaning 
	#include "gtk.h"

Now we can sensibly interpret "gtk:foo" as meaning "foo from package
gtk";
and in concrete terms import a suitable header file.  But I could
imagine
a clever compiler could also use to add gtk.a to the link line etc
(hence no .h).

Let's see if simplicity  is too painful.  I can't imagine it will be.

Simon