pool_result_set
pool_elem_t *(*prs_next)(struct pool_result_set *);
pool_elem_t *(*prs_prev)(struct pool_result_set *);
pool_elem_t *(*prs_first)(struct pool_result_set *);
pool_elem_t *(*prs_last)(struct pool_result_set *);
int (*prs_set_index)(struct pool_result_set *, int);
int (*prs_get_index)(struct pool_result_set *);
int (*prs_close)(struct pool_result_set *);
int (*prs_count)(struct pool_result_set *);