Module CCOption

Basic operations on the option type.

This module replaces `CCOpt`.

type +'a t = 'a option
val map : ('a -> 'b) -> 'a t -> 'b t

map f o applies the function f to the element inside o, if any.

val map_or : default:'b -> ('a -> 'b) -> 'a t -> 'b

map_or ~default f o is f x if o = Some x, default otherwise.

  • since 0.16
val map_lazy : (unit -> 'b) -> ('a -> 'b) -> 'a t -> 'b

map_lazy default_fn f o is f x if o = Some x, default_fn () otherwise.

  • since 1.2
val is_some : _ t -> bool

is_some (Some x) returns true otherwise it returns false.

val is_none : _ t -> bool

is_none None returns true otherwise it returns false.

  • since 0.11
val compare : ('a -> 'a -> int) -> 'a t -> 'a t -> int

compare comp o1 o2 compares two options o1 and o2, using custom comparators comp for the value. None is always assumed to be less than Some _.

val equal : ('a -> 'a -> bool) -> 'a t -> 'a t -> bool

equal p o1 o2 tests for equality between option types o1 and o2, using a custom equality predicate p.

val return : 'a -> 'a t

return x is a monadic return, that is return x = Some x.

val some : 'a -> 'a t

Alias to return.

  • since 3.5
val none : 'a t

Alias to None.

  • since 3.5
val flat_map : ('a -> 'b t) -> 'a t -> 'b t

flat_map f o is equivalent to map followed by flatten. Flip version of (>>=).

val flat_map_l : ('a -> 'b list) -> 'a t -> 'b list

flat_map_l f o is [] if o is None, or f x if o is Some x.

  • since 3.12
val bind : 'a t -> ('a -> 'b t) -> 'b t

bind o f is f v if o is Some v, None otherwise. Monadic bind.

  • since 3.0
val map2 : ('a -> 'b -> 'c) -> 'a t -> 'b t -> 'c t

map2 f o1 o2 maps 'a option and 'b option to a 'c option using f.

val iter : ('a -> unit) -> 'a t -> unit

iter f o applies f to o. Iterate on 0 or 1 element.

val fold : ('a -> 'b -> 'a) -> 'a -> 'b t -> 'a

fold f init o is f init x if o is Some x, or init if o is None. Fold on 0 or 1 element.

val filter : ('a -> bool) -> 'a t -> 'a t

filter f o returns Some x if o is Some x and f x is true, or None if f x is false or if o is None. Filter on 0 or 1 element.

  • since 0.5
val if_ : ('a -> bool) -> 'a -> 'a option

if_ f x is Some x if f x, None otherwise.

  • since 0.17
val exists : ('a -> bool) -> 'a t -> bool

exists f o returns true iff there exists an element for which the provided function f evaluates to true.

  • since 0.17
val for_all : ('a -> bool) -> 'a t -> bool

for_all f o returns true iff the provided function f evaluates to true for all elements.

  • since 0.17
val get_or : default:'a -> 'a t -> 'a

get_or ~default o extracts the value from o, or returns default if o is None.

  • since 0.18
val value : 'a t -> default:'a -> 'a

value o ~default is similar to the Stdlib's Option.value and to get_or.

  • since 2.8
val get_exn : 'a t -> 'a

get_exn o returns x if o is Some x or fails if o is None.

  • raises Invalid_argument

    if the option is None.

val get_exn_or : string -> 'a t -> 'a

get_exn_or msg o returns x if o is Some x or fails with Invalid_argument msg if o is None.

  • raises Invalid_argument

    if the option is None.

  • since 3.4
val get_lazy : (unit -> 'a) -> 'a t -> 'a

get_lazy default_fn o unwraps o, but if o is None it returns default_fn () instead.

  • since 0.6.1
val sequence_l : 'a t list -> 'a list t

sequence_l [x1; x2; …; xn] returns Some [y1; y2; …; yn] if every xi is Some yi. Otherwise, if the list contains at least one None, the result is None.

val wrap : ?handler:(exn -> bool) -> ('a -> 'b) -> 'a -> 'b option

wrap ?handler f x calls f x and returns Some y if f x = y. If f x raises any exception, the result is None. This can be useful to wrap functions such as Map.S.find.

  • parameter handler

    the exception handler, which returns true if the exception is to be caught.

val wrap2 : ?handler:(exn -> bool) -> ('a -> 'b -> 'c) -> 'a -> 'b -> 'c option

wrap2 ?handler f x y is similar to wrap but for binary functions.

Applicative

val pure : 'a -> 'a t

pure x is an alias to return.

Alternatives

val or_ : else_:'a t -> 'a t -> 'a t

or_ ~else_ o is o if o is Some _, else_ if o is None.

  • since 1.2
val or_lazy : else_:(unit -> 'a t) -> 'a t -> 'a t

or_lazy ~else_ o is o if o is Some _, else_ () if o is None.

  • since 1.2
val choice : 'a t list -> 'a t

choice lo returns the first non-None element of the list lo, or None.

val flatten : 'a t t -> 'a t

flatten oo transforms Some x into x.

  • since 2.2
val return_if : bool -> 'a -> 'a t

return_if b x applies Some or None depending on the boolean b. More precisely, return_if false x is None, and return_if true x is Some x.

  • since 2.2

Infix Operators

module Infix : sig ... end
include module type of Infix
val (>|=) : 'a t -> ('a -> 'b) -> 'b t

o >|= f is map f o.

val (>>=) : 'a t -> ('a -> 'b t) -> 'b t

o >>= f is the monadic bind.

val (<*>) : ('a -> 'b) t -> 'a t -> 'b t

f <*> o returns Some (f x) if o is Some x and None if o is None.

val (<$>) : ('a -> 'b) -> 'a t -> 'b t

f <$> o is like map f o.

val (<+>) : 'a t -> 'a t -> 'a t

o1 <+> o2 is o1 if o1 is Some _, o2 if o1 is None.

Let operators on OCaml >= 4.08.0, nothing otherwise

  • since 2.8
val let+ : 'a t -> ('a -> 'b) -> 'b t
val and+ : 'a t -> 'b t -> ('a * 'b) t
val let* : 'a t -> ('a -> 'b t) -> 'b t
val and* : 'a t -> 'b t -> ('a * 'b) t

Conversion and IO

val to_list : 'a t -> 'a list

to_list o returns [x] if o is Some x or the empty list [] if o is None.

val of_list : 'a list -> 'a t

of_list l returns Some x (x being the head of the list l), or None if l is the empty list.

val to_result : 'e -> 'a t -> ('a, 'e) Stdlib.result

to_result e o returns Ok x if o is Some x, or Error e if o is None.

  • since 1.2
val to_result_lazy : (unit -> 'e) -> 'a t -> ('a, 'e) Stdlib.result

to_result_lazy f o returns Ok x if o is Some x or Error f if o is None.

  • since 1.2
val of_result : ('a, _) Stdlib.result -> 'a t

of_result result returns an option from a result.

  • since 1.2
type 'a iter = ('a -> unit) -> unit
type 'a gen = unit -> 'a option
type 'a printer = Stdlib.Format.formatter -> 'a -> unit
type 'a random_gen = Stdlib.Random.State.t -> 'a
val random : 'a random_gen -> 'a t random_gen
val choice_iter : 'a t iter -> 'a t

choice_iter iter is similar to choice, but works on iter. It returns the first Some x occurring in iter, or None otherwise.

  • since 3.0
val choice_seq : 'a t Stdlib.Seq.t -> 'a t

choice_seq seq works on Seq.t. It returns the first Some x occurring in seq, or None otherwise.

  • since 3.0
val to_gen : 'a t -> 'a gen

to_gen o is o as a gen. Some x is the singleton gen containing x and None is the empty gen.

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

to_seq o is o as a sequence Seq.t. Some x is the singleton sequence containing x and None is the empty sequence. Same as Stdlib.Option.to_seq Renamed from to_std_seq since 3.0.

  • since 3.0
val to_iter : 'a t -> 'a iter

to_iter o returns an internal iterator, like in the library Iter.

  • since 2.8
val pp : 'a printer -> 'a t printer

pp ppf o pretty-prints option o using ppf.