Option

catchMap

Takes a function that returns an option. It returns the output of the function if source option is None.

Example

RESCRIPT
Some(42)->Option.catchMap(() => 100) // => Some(42)
None->Option.catchMap(() => 100) //=> Some(100)

chain

Takes a function 'a => option<'b> and applies that function to the value inside the option and returns another option.

Example

RESCRIPT
Some(42)->Option.chain(t => t < 100 ? Some(t) : None) // => Some(42)
Some(400)->Option.chain(t => t < 100 ? Some(t) : None) // => None
None->Option.chain(t => t < 100 ? Some(t) : None) // => None

filter

Convert to None if predicate function return falsy value, otherwise return the same Just.

Example

RESCRIPT
Some(42)->Option.filter(n => n == 42) // => Some(42)
Some(42)->Option.filter(n => n != 42) // => None
None->Option.filter(n => n != 42) // => None

fold

Takes a (lazy) default value, a function, and an Option value, if the Option value is None the default value is returned, otherwise the function is applied to the value inside the Some and the result is returned.

Example

RESCRIPT
Some(42)->Option.fold(() => "no number", t => "the number is " ++ t->Js.Int.toString) // => "the number is 42"

forEach

Invoke a function applying a side-effect on the contents of the option if any.

Example

RESCRIPT
Some(42)->Option.forEach(Js.Console.log) // => logs 42 to the console

getOrElse

Extracts the value out of the structure, if it exists. Otherwise returns the given default value.

Example

RESCRIPT
Some(42)->Option.getOrElse(() => 100) // => 42
None->Option.getOrElse(() => 100) // => 100

isNone

Returns true if the option is None, false otherwise.

Example

RESCRIPT
Some(42)->Option.isNone // => false
None->Option.isNone // => true

isSome

Returns true if the option is Some, false otherwise.

Example

RESCRIPT
Some(42)->Option.isNone // => false
None->Option.isNone // => true

liftA1

converts a function ('a) => 'b to (option<'a>) => option<'b>

Example

RESCRIPT
let increment = n => n + 1
let liftedIncrement = Option.liftA1(increment)
Some(42)->liftedIncrement // => Some(43)

liftA2

converts a function ('a, 'b) => 'c to (option<'a>, option<'b>) => option<'c>

Example

RESCRIPT
let sum = (n1, n2) => n1 + n2
let liftedSum = Option.liftA2(sum)
liftedSum(Some(100), Some(42)) // => Some(142)

liftA3

converts a function ('a) => 'b to (option<'a>) => option<'b>

Example

RESCRIPT
let sum = (n1, n2, n3) => n1 + n2 + n3
let liftedSum = Option.liftA3(sum)
liftedSum(Some(100), Some(42), Some(100)) // => Some(242)

map

Takes a function 'a => 'b and applies that function to the value inside the option and returns another option.

Example

RESCRIPT
Some(42)->Option.map(n => n + 10) // => Some(52)
None->Option.map(n => n + 10) // => None

map2

Takes a function ('a, 'b) => 'c and applies that function to the values inside the options and returns another option.

Example

RESCRIPT
let sum = (n1, n2) => n1 + n2
Some(42)->Option.map2(Some(100), sum) // => Some(142)

map3

Takes a function ('a, 'b, 'c) => 'd and applies that function to the values inside the options and returns another option.

Example

RESCRIPT
let sum = (n1, n2, n3) => n1 + n2 + n3
Some(42)->Option.map3(Some(100), Some(100), sum) // => Some(242)

orElseRun

Invoke a parameterless side-effecting function if the option is None.

Example

RESCRIPT
None->Option.orElseRun(() => Js.Console.log(42)) // => logs 42 to the console