Gerd Stolpmann a écrit :
>>
>> 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(...)
> }

End_roots before caml_raise_with_arg? Why not after?

I mean, you do not do a CAMLreturn before a caml_raise_with_args, so why 
should't this be the same for End_roots()?

> The macros are only documented in memory.h.
> 
> So far I know, raising an exception from within Begin_roots/End_roots is
> not allowed.

It seems to me that the major issue is how caml_local_roots gets 
restored. With the CAMLparam/CAMLreturn macros, this is done by storing 
its original value in caml__frame and restoring it via CAMLreturn.

As it is written in memory.h

> Your function may raise an exception or return a [value] with the
> [CAMLreturn] macro.

I assume that caml_local_roots gets restored by a mechanism in the 'try' 
of the 'try / with' construct after the siglongjmp of caml_raise.

Therefore it should be OK to use caml_raise_with_args before End_roots().

Am I right, or is this plainly wild guessing?

-- 
      Guillaume Yziquel
http://yziquel.homelinux.org/