For completeness, here are the two conversion "opcode-"macros which
I've forgotten to show in my previous mail:
#define ___BEGIN_CFUN_SV_to_string_SCMOBJ(svp, obj) \
if ((___err = gperl__SV_to_string_SCMOBJ(svp, &obj)) == ___FIX(___NO_ERR)) {
#define ___END_CFUN_SV_to_string_SCMOBJ(svp, obj) }