# Module Option

    module Option: sig .. end

Option values.

Option values explicitly indicate the presence or absence of a value.

- Since 4.08

## Options

    type 'a t = 'a option =

`|` | `None`
`|` | `Some of `'a``

The type for option values. Either `None` or a value `Some v`.

    val none : 'a option

`none` is `None`.

    val some : 'a -> 'a option

`some v` is `Some v`.

    val value : 'a option -> default:'a -> 'a

`value o ~default` is `v` if `o` is `Some v` and `default` otherwise.

    val get : 'a option -> 'a

`get o` is `v` if `o` is `Some v` and raise otherwise.

- Raises `Invalid_argument` if `o` is `None`.

    val bind : 'a option -> ('a -> 'b option) -> 'b option

`bind o f` is `f v` if `o` is `Some v` and `None` if `o` is `None`.

    val join : 'a option option -> 'a option

`join oo` is `Some v` if `oo` is `Some (Some v)` and `None` otherwise.

    val map : ('a -> 'b) -> 'a option -> 'b option

`map f o` is `None` if `o` is `None` and `Some (f v)` if `o` is `Some v`.

    val fold : none:'a -> some:('b -> 'a) -> 'b option -> 'a

`fold ~none ~some o` is `none` if `o` is `None` and `some v` if `o` is `Some v`.

    val iter : ('a -> unit) -> 'a option -> unit

`iter f o` is `f v` if `o` is `Some v` and `()` otherwise.

## Predicates and comparisons

    val is_none : 'a option -> bool

`is_none o` is `true` if and only if `o` is `None`.

    val is_some : 'a option -> bool

`is_some o` is `true` if and only if `o` is `Some o`.

    val equal : ('a -> 'a -> bool) -> 'a option -> 'a option -> bool

`equal eq o0 o1` is `true` if and only if `o0` and `o1` are both `None` or if they are `Some v0` and `Some v1` and `eq v0 v1` is `true`.

    val compare : ('a -> 'a -> int) -> 'a option -> 'a option -> int

`compare cmp o0 o1` is a total order on options using `cmp` to compare values wrapped by `Some _`. `None` is smaller than `Some _` values.

## Converting

    val to_result : none:'e -> 'a option -> ('a, 'e) result

`to_result ~none o` is `Ok v` if `o` is `Some v` and `Error none` otherwise.

    val to_list : 'a option -> 'a list

`to_list o` is `[]` if `o` is `None` and `[v]` if `o` is `Some v`.

    val to_seq : 'a option -> 'a Seq.t

`to_seq o` is `o` as a sequence. `None` is the empty sequence and `Some v` is the singleton sequence containing `v`.