Re: C++ wrap

[Hans Aberg <haberg@math.su.se>]

I have experimented with adding C++ exception handling to the wrap. It  
seems, using gcc, that it works fine, as long as one does not try to  
pass a C++ exception through a C function call - then it calls the  
terminate handler.

So add an exception type to Guile which can hold the thrown data, a  
pair (key . args) with a predicate
   SCM_API int scm_is_exception(SCM x);
When there is an uncaught exception in a C function returning SCM, it  
should instead return this exception type with the thrown data. (So  
there would need to be some variable present, changing the behavior of  
these C-functions.)

Then write a function (object = C++ version of SCM)
   object rethrow(const object& x) {
     if (scm_is_exception(x))
       throw (exception)x;
     else
       return x;
   }

Then just add this rethrow() to the returns that might be an exception:
   number operator/(const number& x, const number& y) { return  
rethrow(scm_divide(x, y)); }
instead of
   number operator/(const number& x, const number& y) { return  
scm_divide(x, y); }

The code should then look normal:
   try {
     integer x = 1, y = 0;
     integer z = x/y;  // exception
   catch (exception& x) {
     out << "Exception: " << x << newline;
   }

I did some code using scm_internal_catch(), but it takes a body  
function of only one argument:
   SCM body(void *data);
So I guess one has to fiddle around with passing suitable structs  
using it. - May try it later.

   Hans