Module Make.Option

Option values.

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

Options

type 'a t = 'a option =
  1. | None
  2. | 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 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) is 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 iff o is None.

val is_some : 'a option -> bool

is_some o is true iff o is Some o.

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

equal eq o0 o1 is true iff 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) Pervasives.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 (>>=) : 'a option -> ('a -> 'b option) -> 'b option

x >>= f is an infix notation for apply ~f x

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

x >>| f is an infix notation for map ~f x

val first_some : 'a option -> 'a option -> 'a option

First input of form Some x, or None if both are None

val pp : ?default:string -> (Format.formatter -> 'a -> unit) -> Format.formatter -> 'a option -> unit

pp ~default pp fmt x pretty-print value x using pp or default ("None" by default) string if there is no value.