/*
 *  call-seq:
 *     term_doc_enum.doc -> doc_id
 *
 *  Move forward to the next document in the enumeration. Returns +true+ if
 *  there is another document or +false+ otherwise.
 */
static VALUE
frt_tde_next(VALUE self)
{
    TermDocEnum *tde = (TermDocEnum *)DATA_PTR(self);
    return tde->next(tde) ? Qtrue : Qfalse;
}