Option

t

type t<'a> = option<'a>

some

let some: 'a => option<'a>

Wraps the given value in Some()

RES
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).

RES
let clockEqual = (. a, b) => mod(a, 12) == mod(b, 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

RES
let clockEqual = (. a, b) => mod(a, 12) == mod(b, 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).

RES
let reciprocal = (. x) => x == 0 ? None : Some(1.0 /. Belt.Int.toFloat(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.

RES
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.

RES
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.

RES
let isEven = (. x) => mod(x, 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.

RES
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