Module Core_kernel.Option

This module extends Base.Option with bin_io, quickcheck, and support for ppx_optional.

type 'a t = 'a Base.Option.t
include Bin_prot.Binable.S1 with type 'a t := 'a t
val bin_shape_t : Bin_prot.Shape.t -> Bin_prot.Shape.t
val bin_size_t : ('a, 'a t) Bin_prot.Size.sizer1
val bin_write_t : ('a, 'a t) Bin_prot.Write.writer1
val bin_read_t : ('a, 'a t) Bin_prot.Read.reader1
val __bin_read_t__ : ('a, int -> 'a t) Bin_prot.Read.reader1
val bin_writer_t : ('a, 'a t) Bin_prot.Type_class.S1.writer
val bin_reader_t : ('a, 'a t) Bin_prot.Type_class.S1.reader
val bin_t : ('a, 'a t) Bin_prot.Type_class.S1.t
include Typerep_lib.Typerepable.S1 with type 'a t := 'a t
val typerep_of_t : 'a Typerep_lib.Std_internal.Typerep.t -> 'a t Typerep_lib.Std_internal.Typerep.t
val typename_of_t : 'a Typerep_lib.Typename.t -> 'a t Typerep_lib.Typename.t
include module type of struct include Base.Option end with type 'a t := 'a option
val compare : ('a -> 'a -> int) -> 'a option -> 'a option -> int
val hash_fold_t : (Base.Hash.state -> 'a -> Base.Hash.state) -> Base.Hash.state -> 'a option -> Base.Hash.state
include Base.Sexpable.S1 with type 'a t := 'a option
val t_of_sexp : (Sexplib0.Sexp.t -> 'a) -> Sexplib0.Sexp.t -> 'a option
val sexp_of_t : ('a -> Sexplib0.Sexp.t) -> 'a option -> Sexplib0.Sexp.t
val t_sexp_grammar : Base.Sexp.Private.Raw_grammar.t
include Base.Container.S1 with type 'a t := 'a option
val mem : 'a option -> 'a -> equal:('a -> 'a -> bool) -> bool

Checks whether the provided element is there, using equal.

val length : 'a option -> int
val is_empty : 'a option -> bool
val iter : 'a option -> f:('a -> unit) -> unit
val fold : 'a option -> init:'accum -> f:('accum -> 'a -> '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 fold_result : 'a option -> init:'accum -> f:('accum -> 'a -> ('accum, 'e) Base.Result.t) -> ('accum, 'e) Base.Result.t

fold_result t ~init ~f is a short-circuiting version of fold that runs in the Result monad. If f returns an Error _, that value is returned without any additional invocations of f.

val fold_until : 'a option -> init:'accum -> f:('accum -> 'a -> ('accum, 'final) Base__Container_intf.Export.Continue_or_stop.t) -> finish:('accum -> 'final) -> 'final

fold_until t ~init ~f ~finish is a short-circuiting version of fold. If f returns Stop _ the computation ceases and results in that value. If f returns Continue _, the fold will proceed. If f never returns Stop _, the final result is computed by finish.

Example:

type maybe_negative =
  | Found_negative of int
  | All_nonnegative of { sum : int }

(** [first_neg_or_sum list] returns the first negative number in [list], if any,
    otherwise returns the sum of the list. *)
let first_neg_or_sum =
  List.fold_until ~init:0
    ~f:(fun sum x ->
      if x < 0
      then Stop (Found_negative x)
      else Continue (sum + x))
    ~finish:(fun sum -> All_nonnegative { sum })
;;

let x = first_neg_or_sum [1; 2; 3; 4; 5]
val x : maybe_negative = All_nonnegative {sum = 15}

let y = first_neg_or_sum [1; 2; -3; 4; 5]
val y : maybe_negative = Found_negative -3
val exists : 'a option -> f:('a -> 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 : 'a option -> f:('a -> 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 : 'a option -> f:('a -> bool) -> int

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

val sum : (module Base__Container_intf.Summable with type t = 'sum) -> 'a option -> f:('a -> 'sum) -> 'sum

Returns the sum of f i for all i in the container.

val find : 'a option -> f:('a -> bool) -> 'a option

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

val find_map : 'a option -> f:('a -> 'b option) -> 'b option

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

val to_list : 'a option -> 'a list
val to_array : 'a option -> 'a array
val min_elt : 'a option -> compare:('a -> 'a -> int) -> 'a option

Returns a minimum (resp maximum) element from the collection using the provided compare function, or None if the collection is empty. 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.

val max_elt : 'a option -> compare:('a -> 'a -> int) -> 'a option
include Base.Equal.S1 with type 'a t := 'a option
val equal : 'a Base.Equal.equal -> 'a option Base.Equal.equal
include Base.Invariant.S1 with type 'a t := 'a option
val invariant : ('a -> unit) -> 'a option -> unit

Options form a monad, where return x = Some x, (None >>= f) = None, and (Some x >>= f) = f x.

include Base.Monad.S with type 'a t := 'a option
val (>>=) : 'a option -> ('a -> 'b option) -> 'b option

t >>= f returns a computation that sequences the computations represented by two monad elements. The resulting computation first does t to yield a value v, and then runs the computation returned by f v.

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

t >>| f is t >>= (fun a -> return (f a)).

module Monad_infix : sig ... end
val bind : 'a option -> f:('a -> 'b option) -> 'b option

bind t ~f = t >>= f

val return : 'a -> 'a option

return v returns the (trivial) computation that returns v.

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

map t ~f is t >>| f.

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

join t is t >>= (fun t' -> t').

val ignore_m : 'a option -> unit option

ignore_m t is map t ~f:(fun _ -> ()). ignore_m used to be called ignore, but we decided that was a bad name, because it shadowed the widely used Caml.ignore. Some monads still do let ignore = ignore_m for historical reasons.

val all : 'a option list -> 'a list option
val all_unit : unit option list -> unit option

Like all, but ensures that every monadic value in the list produces a unit value, all of which are discarded rather than being collected into a list.

module Let_syntax : sig ... end

These are convenient to have in scope when programming with a monad:

val is_none : 'a option -> bool

is_none t returns true iff t = None.

val is_some : 'a option -> bool

is_some t returns true iff t = Some x.

val value_map : 'a option -> default:'b -> f:('a -> 'b) -> 'b

value_map ~default ~f is the same as function Some x -> f x | None -> default.

val map2 : 'a option -> 'b option -> f:('a -> 'b -> 'c) -> 'c option

map2 o f maps 'a option and 'b option to a 'c option using ~f.

val call : 'a -> f:('a -> unit) option -> unit

call x f runs an optional function ~f on the argument.

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

value None ~default = default

value (Some x) ~default = x

val value_exn : ?here:Caml.Lexing.position -> ?error:Base.Error.t -> ?message:string -> 'a option -> 'a

value_exn (Some x) = x. value_exn None raises an error whose contents contain the supplied ~here, ~error, and message, or a default message if none are supplied.

val some : 'a -> 'a option
val both : 'a option -> 'b option -> ('a * 'b) option
val first_some : 'a option -> 'a option -> 'a option
val some_if : bool -> 'a -> 'a option
val merge : 'a option -> 'a option -> f:('a -> 'a -> 'a) -> 'a option

merge a b ~f merges together the values from a and b using f. If both a and b are None, returns None. If only one is Some, returns that one, and if both are Some, returns Some of the result of applying f to the contents of a and b.

val filter : 'a option -> f:('a -> bool) -> 'a option
val try_with : (unit -> 'a) -> 'a option

try_with f returns Some x if f returns x and None if f raises an exception. See Result.try_with if you'd like to know which exception.

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

try_with_join f returns the optional value returned by f if it exits normally, and None if f raises an exception.

val validate : none:unit Base.Validate.check -> some:'a Base.Validate.check -> 'a option Base.Validate.check
include Comparator.Derived with type 'a t := 'a t
type 'cmp comparator_witness
val comparator : ('a, 'cmp) Comparator.comparator -> ('a t, 'cmp comparator_witness) Comparator.comparator
include Quickcheckable.S1 with type 'a t := 'a t
val quickcheck_generator : 'a Base_quickcheck.Generator.t -> 'a t Base_quickcheck.Generator.t
val quickcheck_observer : 'a Base_quickcheck.Observer.t -> 'a t Base_quickcheck.Observer.t
val quickcheck_shrinker : 'a Base_quickcheck.Shrinker.t -> 'a t Base_quickcheck.Shrinker.t
module Stable : sig ... end
module Optional_syntax : Optional_syntax.S1 with type 'a t := 'a t and type 'a value := 'a

You might think that it's pointless to have Optional_syntax on options because OCaml already has nice syntax for matching on options. The reason to have this here is that you might have, for example, a tuple of an option and some other type that supports Optional_syntax. Since Optional_syntax can only be opted into at the granularity of the whole match expression, we need this Optional_syntax support for options in order to use it for the other half of the tuple.