# Module type Container_intf.Container.S0

    module type S0 = Container_intf.S0

    type t

    type elt

    val mem : ?equal:(elt -> elt -> bool) ->
           t -> elt -> bool

Checks whether the provided element is there using the default equality test, using the provided `equal` function if it is not

    val length : t -> int

    val is_empty : t -> bool

    val iter : t -> f:(elt -> unit) -> unit

`iter` must allow exceptions raised in `f` to escape, terminating the iteration cleanly. The same holds for all functions below taking an `f`.

    val fold : t ->
           init:'accum -> f:('accum -> elt -> 'accum) -> 'accum

`fold t ~init ~f` returns `f (... f (f (f init e1) e2) e3 ...) en`, where `e1..en` are the elements of `t`

    val exists : t -> f:(elt -> bool) -> bool

Returns `true` if and only if there exists an element for which the provided function evaluates to `true`. This is a short-circuiting operation.

    val for_all : t -> f:(elt -> bool) -> bool

Returns `true` if and only if the provided function evaluates to `true` for all elements. This is a short-circuiting operation.

    val count : t -> f:(elt -> bool) -> int

Returns the number of elements for which the provided function evaluates to true.

    val sum : (module Commutative_group.S with type t = 'sum) ->
           t -> f:(elt -> 'sum) -> 'sum

Returns the sum of `f i` for i in the container

    val find : t ->
           f:(elt -> bool) -> elt option

Returns as an `option` the first element for which `f` evaluates to true.

    val find_map : t -> f:(elt -> 'a option) -> 'a option

Returns the first evaluation of `f` that returns `Some`, and returns `None` if there is no such element.

    val to_list : t -> elt list

    val to_array : t -> elt array

    val min_elt : t ->
           cmp:(elt -> elt -> int) ->
           elt option

Returns a min (resp max) element from the collection using the provided `cmp` function. In case of a tie, the first element encountered while traversing the collection is returned. The implementation uses `fold` so it has the same complexity as `fold`. Returns `None` iff the collection is empty.

    val max_elt : t ->
           cmp:(elt -> elt -> int) ->
           elt option