Module Stdlib.Option

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

type t('a) = option('a) = 
  | None
  | Some('a)
;

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

val none : 'a option

let none: option('a);

none is None.

val some : 'a -> 'a option

let some: 'a => option('a);

some v is Some v.

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

let value: option('a) => default:'a => 'a;

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

val get : 'a option -> 'a

let get: option('a) => '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

let bind: option('a) => ('a => option('b)) => option('b);

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

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

let join: option(option('a)) => option('a);

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

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

let map: ('a => 'b) => option('a) => option('b);

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

val product : 'a option -> 'b option -> ('a * 'b) option

let product: option('a) => option('b) => option(('a, 'b));

product o0 o1 is Some (v0, v1) if o0 is Some v0 and o1 is Some v1 and None otherwise.

since 5.5

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

let fold: none:'a => some:('b => 'a) => option('b) => '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

let iter: ('a => unit) => option('a) => unit;

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

val blend : ('a -> 'a -> 'a) -> 'a option -> 'a option -> 'a option

let blend: ('a => 'a => 'a) => option('a) => option('a) => option('a);

blend f o1 o2 is o1 if o2 is None, o2 if o1 is None, and Some (f v1 v2) if o1 is Some v1 and o2 is Some v2.

since 5.5

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

let for_all: ('a => bool) => option('a) => bool;

for_all p behaves like List.for_all p on a list of zero or one element:

• for_all p None is true,
• for_all p (Some v) is p v. since 5.5

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

let exists: ('a => bool) => option('a) => bool;

exists p behaves like List.exists p on a list of zero or one element:

• exists p None is false,
• exists p (Some v) is p v. since 5.5

Predicates and comparisons

val is_none : 'a option -> bool

let is_none: option('a) => bool;

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

val is_some : 'a option -> bool

let is_some: option('a) => bool;

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

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

let equal: ('a => 'a => bool) => option('a) => option('a) => 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

let compare: ('a => 'a => int) => option('a) => option('a) => 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

let to_result: none:'e => option('a) => result('a, 'e);

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

val to_list : 'a option -> 'a list

let to_list: option('a) => list('a);

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

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

let to_seq: option('a) => Seq.t('a);

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

Syntax

module Syntax : sig ... end

module Syntax: { ... };

Binding operators. See manual section 12.23 for details.