Option Module

The Option module in F# provides functions that operate on the Option type, allowing you to handle and transform options effectively.

Let’s consider the values:

let option1 = Some 42
let option2 = None

The Option.map function applies a transformation function to the value inside an option and returns a new option containing the transformed value.

Option.map (fun x -> x * 2) option1 

// => val it: int option = Some 84

The Option.filter function applies a predicate to the value inside an option and returns the option itself if the predicate is true, or None if the predicate is false.

Option.filter (fun x -> x < 50) option1 // => val it: int option = Some 42
Option.filter (fun x -> x > 50) option1 // => val it: int option = None

The Option.bind function, also known as the >>= operator, applies a transformation function to the value inside an option and returns a new option. It is useful for chaining computations that may return options.

let boundOption =
    Option.bind (fun x ->
        if x > 0 then Some (x * 3)
        else None
    ) option1 
    
// =>  val boundOption: int option = Some 126

The Option.defaultValue function takes an option and a default value. If the option is None, it returns the default value; otherwise, it returns the value inside the option.

Option.defaultValue 0 option1 // => val it: int = 42
Option.defaultValue 0 option2 // => val it: int = 0

The Option.contains function checks if an option contains a specific value and returns a boolean indicating the result.

let containsValue = Option.contains 42 option1 // => val it: bool = true

The Option.get function extracts the value from an option if it is Some, or throws an exception if it is None.

Option.get option1 // => val it: int = 42

The Option.orElse function combines two options. If the first option is Some, it returns the first option; otherwise, it returns the second option.

Option.orElse option1 option2 // => val it: int option = Some 42
Option.orElse option2 option1 // => val it: int option = Some 42

The Option.isSome function checks if an option contains a value (is Some) and returns a boolean indicating the result.

Option.isSome option1 // => val it: bool = true
Option.isSome option2 // => val it: bool = false

The Option.isNone function checks if an option is empty (is None) and returns a boolean indicating the result.

Option.isNone option1 // => val it: bool = false
Option.isNone option2 // => val it: bool = true