[Caml-list] Possible to use optional args in external (C) calls?

[Caml-list] Possible to use optional args in external (C) calls?

[Richard Jones]

Is it possible to use optional or any labelled args in calls to C
code? I assume that optional args are passed as 'argtype option', but
what order do they appear to the C?

Rich.

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Re: [Caml-list] Possible to use optional args in external (C) calls?

[Eric C. Cooper]

On Sat, Oct 11, 2003 at 02:26:28PM +0100, Richard Jones wrote:
> Is it possible to use optional or any labelled args in calls to C
> code? I assume that optional args are passed as 'argtype option',
> but what order do they appear to the C?

The compiler accepts "external" declarations with labelled and
optional parameters, and a little experimentation with "ocaml
-dlambda" shows that the external function is called with the
arguments in the order specified by the "external" declaration.

-- 
Eric C. Cooper          e c c @ c m u . e d u

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Re: [Caml-list] Possible to use optional args in external (C) calls?

[Robert Roessler]

Richard Jones wrote:

> Is it possible to use optional or any labelled args in calls to C
> code? I assume that optional args are passed as 'argtype option', but
> what order do they appear to the C?

In order, yes, and as Eric says, in the "external" declaration order.

For example, the "OCaml-Win32" package from the "humps" makes use of 
both optional and labeled args.  The former show up as either 
"Val_int(0)" or a value of the type expected, while the latter are 
used in the specifications of C callbacks.

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