[Caml-list] Exceptions and C

[Caml-list] Exceptions and C

[Mitchell N Charity]

I rather expected this to raise an exception...

$ cat test1.ml 
let plus_f  x y = x +. y;;
Callback.register "plus_f" plus_f;;

$ cat test2.c
#include <caml/mlvalues.h>
#include <caml/memory.h>
#include <caml/callback.h>
#include <stdio.h>

int main (int argc, char **argv) {
  char * args[2] = { "fake_name", NULL };
  caml_startup(args);

  {
    CAMLparam0();
    CAMLlocal2(f,res);
    value the_args[3];
    the_args[0] = copy_double(32.1);
    the_args[1] = copy_string("go boom"); /** incorrect type **/
    f = *(caml_named_value("plus_f"));
    res = callbackN_exn(f,2,the_args);
    if(Is_exception_result(res)) {
      fprintf(stderr,"OCaml exception raised.\n");
      exit(1);
    }
    fprintf(stderr,"No exception.\n");
    fprintf(stderr,"%lf\n",Double_val(res));
  }
}

$ gcc -c test2.c -I/usr/local/lib/ocaml
$ ocamlopt test2.o test1.ml
$ ./a.out 
No exception.
32.100000

But it doesn't.

Any thoughts?

I gather run-time type checking is not occurring.  Can I at least
count on avoiding a segfault, or is behavior completely undefined if
callback arguments are incorrectly typed?

Thanks,
Mitchell Charity
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[Caml-list] Exceptions and C

[Basile STARYNKEVITCH]

>>>>> "Mitchell" == Mitchell N Charity <mcharity@vendian.org> writes:

    Mitchell> I gather run-time type checking is not occurring.  Can I
    Mitchell> at least count on avoiding a segfault, or is behavior
    Mitchell> completely undefined if callback arguments are
    Mitchell> incorrectly typed?

Behavior is undefined. For details, read the Chapter 18 "Interfacing C
with Objective Caml" of the reference manual. To understand what is
happening, read the section 18.2 (the value type) - or read the source
of the runtime system.

And there is a reason for that. The whole philosophy of Ocaml is
static typing, which the OCaml team pushes to the extreme (for
instance by refusing dynamic casting or class checking for objects).

I miss more dynamic ability of the object part of Ocaml (even if this
means having a tree of classes, not a forest, and reject multiple
inheritance).



-- 

Basile STARYNKEVITCH         http://starynkevitch.net/Basile/ 
email: basile<at>starynkevitch<dot>net 
alias: basile<at>tunes<dot>org 
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