[MLton] cvs commit: Improved FFI.

Wesley W. Terpstra wesley@terpstra.ca
Sun, 24 Jul 2005 15:40:20 +0200

On Sat, Jul 23, 2005 at 04:55:44AM -0700, Matthew Fluet wrote:
>   Incorporated Wesley's patch for improved FFI.  After the discussion on
>   the list regarding C pointers, I went ahead and eliminated _address
>   infavor of _symbol, which provides the address, getter, and setter.
>   So, the FFI system now looks like:
>   _symbol "symbol" [define] : ptrTy, cbTy;  ==> ptrTy * (unit -> cbTy) * (cbTy -> unit)
>   _symbol * : ptrTy, cbTy;  ==> (ptrTy -> cbTy) * (ptrTy * cbTy -> unit)

I think this was a mistake.

There is now no way to take the address of a function.
Which means you can't pass a MLton function to a C method that takes
a function pointer. I'm sorry I didn't object earlier; I had no net

I realize that you could lie:

val () = _export "foo": int -> int; (fn x => x)
val ptr = #1 _symbol "foo": MLton.Pointer.t, int;

However, I think this is worse than not having a type with address
in the first place. I added it so we could encourage people to 
provide the extra information against future problems. The new API
encourages people to provide wrong information...

Wesley W. Terpstra