Option

t

type t('a) = option('a);

some

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

Wraps the given value in Some()

RE
Js.Option.some(1066) == Some(1066);

isSome

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

Returns true if the argument is Some(value); false if the argument is None.

isSomeValue

let isSomeValue: ((. 'a, 'a) => bool, 'a, option('a)) => bool;

The first argument to isSomeValue is an uncurried function eq() that takes two arguments and returns true if they are considered to be equal. It is used to compare a plain value v1(the second argument) with an option value. If the option value is None, isSomeValue() returns false; if the third argument is Some(v2), isSomeValue() returns the result of calling eq(v1, v2).

RE
let clockEqual = (. a, b) => (a mod 12 == b mod 12);
Js.Option.isSomeValue(clockEqual, 3, Some(15)) == true;
Js.Option.isSomeValue(clockEqual, 3, Some(4)) == false;
Js.Option.isSomeValue(clockEqual, 3, None) == false;

isNone

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

Returns true if the argument is None; false otherwise.

getExn

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

If the argument to getExn() is of the form Some(value), returns value. If given None, it throws a getExn exception.

equal

let equal: ((. 'a, 'b) => bool, option('a), option('b)) => bool;

The first argument to equal is an uncurried function eq() that takes two arguments and returns true if they are considered to be equal. The second and third arguments are option values.

If the second and third arguments are of the form:

• Some(v1) and Some(v2): returns eq(v1, v2)

• Some(v1) and None: returns false

• None and Some(v2): returns false

• None and None: returns true

RE
let clockEqual = (. a, b) => (a mod 12 == b mod 12);
Js.Option.equal(clockEqual, Some(3), Some(15)) == true;
Js.Option.equal(clockEqual, Some(3), Some(16)) == false;
Js.Option.equal(clockEqual, Some(3), None) == false;
Js.Option.equal(clockEqual, None, Some(15)) == false;
Js.Option.equal(clockEqual, None, None) == true;

andThen

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

The first argument to andThen() is an uncurried function f() that takes a plain value and returns an option result. The second argument is an option value. If the second argument is None, the return value is None. If the second argument is Some(v), the return value is f(v).

RE
let reciprocal = (. x) => (x == 0) ? None : Some(1.0 /. (float_of_int(x)));
Js.Option.andThen(reciprocal, Some(5)) == Some(0.2);
Js.Option.andThen(reciprocal, Some(0)) == None;
Js.Option.andThen(reciprocal, None) == None;

map

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

The first argument to map() is an uncurried function f() that takes a plain value and returns a plain result. The second argument is an option value. If it is of the form Some(v), map() returns Some(f(v)); if it is None, the return value is None, and function f() is not called.

RE
let square = (. x) => (x * x);
Js.Option.map(square, Some(3)) == Some(9);
Js.Option.map(square, None) == None;

getWithDefault

let getWithDefault: ('a, option('a)) => 'a;

The first argument to getWithDefault() is a default value. If the second argument is of the form Some(v), getWithDefault() returns v; if the second argument is None, the return value is the default value.

RE
Js.Option.getWithDefault(1066, Some(15)) == 15;
Js.Option.getWithDefault(1066, None) == 1066;

default

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

See: getWithDefault

filter

let filter: ((. 'a) => bool, option('a)) => option('a);

The first argument to filter() is an uncurried function that takes a plain value and returns a boolean. The second argument is an option value.

If the second argument is of the form Some(v) and f(v) is true, the return value is Some(v). Otherwise, the return value is None.

RE
let isEven = (. x) => {x mod 2 == 0};
Js.Option.filter(isEven, Some(2)) == Some(2);
Js.Option.filter(isEven, Some(3)) == None;
Js.Option.filter(isEven, None) == None;

firstSome

let firstSome: (option('a), option('a)) => option('a);

The firstSome() function takes two option values; if the first is of the form Some(v1), that is the return value. Otherwise, firstSome() returns the second value.

RE
Js.Option.firstSome(Some("one"), Some("two")) == Some("one");
Js.Option.firstSome(Some("one"), None) == Some("one");
Js.Option.firstSome(None, Some("two")) == Some("two");
Js.Option.firstSome(None, None) == None;