io.c:3742
static VALUE
argf_seek_m(argc, argv, self)
    int argc;
    VALUE *argv;
    VALUE self;
{
    if (!next_argv()) {
	rb_raise(rb_eArgError, "no stream to seek");
    }
    ARGF_FORWARD();
    return rb_io_seek_m(argc, argv, current_file);
}
