accessing a printf-like function from scheme

[Dan McMahill]

Hello,

I'm trying to provide scheme access to a C function which has the same 
interface a printf(). What I'd like to do in scheme is something like

(gschem-log
   "This is a %s message with %d args, pi is %g\n"
   "log"
   3
   3.14
)

so I've gotten as far as a function which takes a variable number of 
arguments and made it available from scheme but can't seem to figure out 
the last step which is how to get the elements from the :

SCM g_funcs_log(SCM s_num_list)
{
  SCM s_element;
  int length;
  int i;

  /* Check that the input is a list */
  SCM_ASSERT (SCM_NFALSEP (scm_list_p (s_num_list)),
              s_num_list,
              SCM_ARG1,
              "gschem-log");
  length = scm_num2int(scm_length(s_num_list), 0, "g_funcs_log()");

  if (length == 0)
     return SCM_BOOL_T;

  /* how to actully feed the data to s_log_message which
   * has a printf-like interface
   */
  s_log_message ("Hi there.  Length = %d\n", length);

  return SCM_BOOL_T;
}

scm_c_define_gsubr ("gschem-log", 0, 0, 1, g_funcs_log);



If it would be easier I can also write a

void s_log_messagev (const char * restrict format, va_list ap);

to complement the

void s_log_message(const char * restrict format, ...);

I tried to find some sort of scm_list2_c_va_list() but haven't found it yet.

Any suggestions?

Thanks
-Dan