Immutable map
val mem : _ Key.t ‑> t ‑> boolval find : 'a Key.t ‑> t ‑> 'a optionval find_exn : 'a Key.t ‑> t ‑> 'a- Raises Not_found: if the key is not in the table.
val iter : (pair ‑> unit) ‑> t ‑> unitval add_list : t ‑> pair list ‑> tval of_list : pair list ‑> tval to_list : t ‑> pair list