RE: [Sml-implementers] extensions to SML: Foreign function interf ace

[David M. <Dav...@pr...>]

On Sunday, September 16, 2001 3:19 PM, Dave Berry
[SMTP:da...@ta...] wrote:
> At 16:03 14/09/2001, Stephen Weeks wrote:
> If you have a standard interface to C and a standard for compilation
> management, then it becomes much easier to write libraries.  Any SML
> programmer will be able to write libraries that run on any SML
compiler.
> That seems a "base level" that everyone on this list should aim for.
> 
> I suggest an IDL interface for the C FLI.  People should not have to
write
> any C themselves.  I know SML/NJ were working on this, as were the
MLWorks
> team.  

Dave,
Have you looked at the foreign function interface that Nick Chapman did
for Poly/ML several year ago? (See
http://www.lfcs.ed.ac.uk/software/polyml/docs/CInterface.html ).  It's
been used for several projects but particularly the Windows interface
which has several hundred functions in it.  It works for dynamic
libraries in Unix or DLLs in Windows and doesn't require the SML
programmer to write anything but ML.

As an example, the following code creates a function to put up a message
box using the Windows MessageBox function.  MessageBoxA is a function
within the user32 DLL and is normally called from C or Visual Basic code
but it's just as easy to give it an ML type and call it with ML
arguments. 

local
	open CInterface
	fun userDLL name = load_sym (load_lib "user32.dll") name
in
	val MB_OKCANCEL           = 0x00000001
	val MessageBox = call4 (userDLL "MessageBoxA") (INT, STRING,
STRING, INT) INT
end;

MessageBox is now a function with type    int * string * string * int ->
int  and can be called as
MessageBox(0, "Is this OK?", "The title", MB_OKCANCEL);

The converters INT and STRING are defined in the library but it's easy
to define new converters for arbitrary types.

David.