[MLton] bool and MLton FFI
Wesley W. Terpstra
Fri, 23 Jun 2006 14:27:45 +0200
On Jun 23, 2006, at 4:52 AM, Stephen Weeks wrote:
> 1. No bool in the FFI.
> 2. C Bool in the FFI with manual conversion to/from SML bool.
> 3. Bool in the FFI with automatic conversion between C bool and SML
After more reflection, I think #2 is best.
> I think (2) will be slightly counter-intuitive to
> users, because all the other C types in the FFI have an SML type they
> are equivalent to (even C int is equivalent to some SML int type, even
> though it changes from platform to platform).
I disagree here. We should start encouraging users to use _import
_import "foo" : C_Int.t * C_Long.t * Int32.t-> C_Bool.t
for the function:
extern bool foo(int x, long y, int32_t z);
Otherwise their code won't be portable.
Requiring them to use the C_Bool type for FFI is then not so unusual.
The user-visible rule is: if it's not a fixed size, use C_X for type
X. You might need to convert types for int -> C_Int.t, but that's the
price you pay to interface with C. Plus, the conversion happens in
SML, with no C wrapper needed, and an overflow exception if you mess up.
As a tangental aside, it also makes C_Bool.t vector work insofar as
Vector.map C_Bool.fromBool v works.