> For instance, here is the piece of code that executes R code ad catches 
> errors. I've tried to follow guidelines available on the net, and 
> inspired myself from pcre.
> 
> > CAMLprim value r_eval_sxp (value sexp_list) {
> >   CAMLparam0();
> >   CAMLlocal2(ml_error_call, ml_error_message);
> >   SEXP e;
> >   int error = 0;
> >   PROTECT(e = R_tryEval(Sexp_val(sexp_list), R_GlobalEnv, &error));
> >   UNPROTECT(1);
> >   if (error) {
> >     ml_error_call = Val_sexp(error_call);
> >     error_call = NULL;
> >     ml_error_message = caml_copy_string(error_message);
> >     error_message = NULL;
> >     value error_result = caml_alloc_small(2, 0);
> >     Store_field(error_result, 0, ml_error_call);
> >     Store_field(error_result, 1, ml_error_message);
> >     raise_with_arg(*caml_named_value("OCaml-R generic error"), error_result);
> >   }
> >   CAMLreturn(Val_sexp(e));
> > }
> 
> Do you see GC / allocation / threading problems with it?
> 
> Would it be legitimate to include CAMLlocal2 inside the error-handling 
> braces?

No. You would start a new context for local roots, and there is no way
to end it (CAMLreturn ends the context).

There are the macros Begin_roots<n> and End_roots that should be used in
this case, e.g.

if (error) {
  value ml_error_call = Val_unit;
  value ml_error_message = Val_unit;

  Begin_roots2(ml_error_call, ml_error_message);
  ...
  End_roots();

  raise_with_arg(...)
}

The macros are only documented in memory.h.

So far I know, raising an exception from within Begin_roots/End_roots is
not allowed.

Gerd
-- 
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Gerd Stolpmann, Bad Nauheimer Str.3, 64289 Darmstadt,Germany 
gerd@gerd-stolpmann.de          http://www.gerd-stolpmann.de
Phone: +49-6151-153855                  Fax: +49-6151-997714
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