let create: int => t('a);
let clear: t('a) => unit;
let reset: t('a) => unit;
let add: t('a) => 'a => unit;
let remove: t('a) => 'a => unit;
let mem: t('a) => 'a => bool;
let iter: t('a) => ('a => unit) => unit;
let to_list: t('a) => list('a);
let length: t('a) => int;