Again: FFI syntax

[Fergus Henderson]

On 31-May-2001, Manuel M. T. Chakravarty <chak at cse.unsw.edu.au> wrote:
> Fergus Henderson <fjh at cs.mu.oz.au> wrote,
> > Making the semantics of a particular construct implementation-dependent is
> > a good thing if the semantics that you want are implementation-dependent.
> > Doing this allows the code to work correctly on different implementations
> > without modifying the code.
> > 
> > That is the case here, I believe.  In particular, "ccall" is not abstract
> > enough to use as a default.  The default calling convention -- the one that
> > you normally want -- is "whatever the corresponding C implementation uses".
> > But on x86, "ccall" means a *particular* calling convention (args passed
> > on stack, caller pops, return value in EAX, etc.) which may not match
> > the one that your C implementation uses.  If you have a C implementation
> > which always passes args in registers, as is certainly allowed by the C
> > standard, then you want to the default calling convention to be passing
> > args in registers, otherwise nothing that uses the default will work.
> 
> How about saying that `ccall' means "whatever the
> corresponding C implementation uses" on any platform?

I would be fine to say that some other name, e.g. `c', means that.
But `ccall' already has an existing meaning, and it would be
terribly confusing if e.g. MSVC and GNU C used `ccall' to mean one thing,
while Haskell used it to mean something different.

> (Nevertheless, the question of how the Haskell system
> figures out what the C implementation uses, especially if
> there are multiple C implementations with multiple
> conventions is not, and cannot be handled.)

"The ``corresponding'' C implementation is implementation-defined."

Or in more verbose but probably clearer words:

"The Haskell implementation must document which C
implementation the `c' calling convention corresponds to."

> > It would be nicer to make this explicit in the grammar.
> 
> By having
> 
>   callconv -> ccall | stdcall | cplusplus | jvm | dotnet |
> 	    | <implementation-specific conventions>
> 
> ?

Exactly.

-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "I have always known that the pursuit
                                    |  of excellence is a lethal habit"
WWW: <http://www.cs.mu.oz.au/~fjh>  |     -- the last words of T. S. Garp.