Advanced Exercism • fsharp

Two Fer

Challenge Overview

Create a sentence of the form "One for X, one for me.".

Visit the two-fer exercise on Exercism to read the full instructions and download the exercise files.

Dig Deeper

Option.defaultValue

`Option.defaultValue`

let twoFer (nameOpt: string option): string =
    let name = Option.defaultValue "you" nameOpt
    $"One for {name}, one for me."

We use the Option.defaultValue function which either returns the value within the Option<T> value passed to it, or else returns the default value we pass to it ("you").

We then use string interpolation to build the return string where {name} is replaced with the name we just found.

String formatting

The string formatting article discusses alternative ways to format the returned string.

Pattern matching

module TwoFer

let twoFer (nameOpt: string option): string =
    let name =
        match nameOpt with
        | Some name -> name
        | None -> "you"

    $"One for {name}, one for me."

We use pattern matching to get the name we need to use in our greeting:

Some name matches when a name was specified. In this case, we’ll just return that name
None matching when no name was specified. We’ll return "you" in this case

We then use string interpolation to build the return string where {name} is replaced with the name we just found.

String formatting

The string formatting article discusses alternative ways to format the returned string.

Source: Exercism fsharp/two-fer