Base.Option
Option type.
val hash_fold_t : (Hash.state -> 'a -> Hash.state) -> Hash.state -> 'a t -> Hash.state
include Sexpable.S1 with type 'a t := 'a t
val t_of_sexp : (Sexplib0.Sexp.t -> 'a) -> Sexplib0.Sexp.t -> 'a t
val sexp_of_t : ('a -> Sexplib0.Sexp.t) -> 'a t -> Sexplib0.Sexp.t
val t_sexp_grammar : Sexp.Private.Raw_grammar.t
include Container.S1 with type 'a t := 'a t
val mem : 'a t -> 'a -> equal:('a -> 'a -> bool) -> bool
Checks whether the provided element is there, using equal
.
val length : 'a t -> int
val is_empty : 'a t -> bool
val iter : 'a t -> f:('a -> unit) -> unit
val fold : 'a t -> 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 t -> init:'accum -> f:('accum -> 'a -> ('accum, 'e) Result.t) ->
('accum, 'e) 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 t -> 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 t -> 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 t -> 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 t -> 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 t -> f:('a -> 'sum) -> 'sum
Returns the sum of f i
for all i
in the container.
val find : 'a t -> f:('a -> bool) -> 'a option
Returns as an option
the first element for which f
evaluates to true.
val find_map : 'a t -> 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 t -> 'a list
val to_array : 'a t -> 'a array
val min_elt : 'a t -> 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 t -> compare:('a -> 'a -> int) -> 'a option
include Equal.S1 with type 'a t := 'a t
val equal : 'a Equal.equal -> 'a t Equal.equal
include Invariant.S1 with type 'a t := 'a t
val invariant : ('a -> unit) -> 'a t -> unit
Options form a monad, where return x = Some x
, (None >>= f) = None
, and (Some x
>>= f) = f x
.
include Monad.S with type 'a t := 'a t
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
.
module Monad_infix : sig ... end
val return : 'a -> 'a t
return v
returns the (trivial) computation that returns v.
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.
module Let_syntax : sig ... end
These are convenient to have in scope when programming with a monad:
val is_none : 'a t -> bool
is_none t
returns true iff t = None
.
val is_some : 'a t -> bool
is_some t
returns true iff t = Some x
.
val value_map : 'a t -> default:'b -> f:('a -> 'b) -> 'b
value_map ~default ~f
is the same as function Some x -> f x | None -> default
.
map2 o f
maps 'a option
and 'b option
to a 'c option
using ~f
.
val call : 'a -> f:('a -> unit) t -> unit
call x f
runs an optional function ~f
on the argument.
val value : 'a t -> default:'a -> 'a
value None ~default
= default
value (Some x) ~default
= x
val value_exn : ?here:Caml.Lexing.position -> ?error:Error.t -> ?message:string -> 'a t -> '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 t
val some_if : bool -> 'a -> 'a t
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 try_with : (unit -> 'a) -> 'a t
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.
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 Validate.check -> some:'a Validate.check -> 'a t Validate.check