On 31-May-2001, Manuel M. T. Chakravarty <[EMAIL PROTECTED]> wrote:
> Fergus Henderson <[EMAIL PROTECTED]> 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 <[EMAIL PROTECTED]> | "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.
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