Get started with F# with the .NET CLI

This article covers how you can get started with F# on any operating system (Windows, macOS, or Linux) with the .NET CLI. It goes through building a multi-project solution with a class library that is called by a console application.

Prerequisites

To begin, you must install the latest .NET SDK.

This article assumes that you know how to use a command line and have a preferred text editor. If you don't already use it, Visual Studio Code is a great option as a text editor for F#.

Build a simple multi-project solution

Open a command prompt/terminal and use the dotnet new command to create a new solution file called FSharpSample:

dotnet new sln -o FSharpSample

The following directory structure is produced after running the previous command:

FSharpSample
    ├── FSharpSample.sln

Write a class library

Change directories to FSharpSample.

Use the dotnet new command to create a class library project in the src folder named Library.

dotnet new classlib -lang "F#" -o src/Library

The following directory structure is produced after running the previous command:

└── FSharpSample
    ├── FSharpSample.sln
    └── src
        └── Library
            ├── Library.fs
            └── Library.fsproj

Replace the contents of Library.fs with the following code:

module Library

open System.Text.Json

let getJson value =
    let json = JsonSerializer.Serialize(value)
    value, json

Add the Library project to the FSharpSample solution using the dotnet sln add command:

dotnet sln add src/Library/Library.fsproj

Run dotnet build to build the project. Unresolved dependencies will be restored when building.

Write a console application that consumes the class library

Use the dotnet new command to create a console application in the src folder named App.

dotnet new console -lang "F#" -o src/App

The following directory structure is produced after running the previous command:

└── FSharpSample
    ├── FSharpSample.sln
    └── src
        ├── App
        │   ├── App.fsproj
        │   ├── Program.fs
        └── Library
            ├── Library.fs
            └── Library.fsproj

Replace the contents of the Program.fs file with the following code:

open System
open Library

[<EntryPoint>]
let main args =
    printfn "Nice command-line arguments! Here's what System.Text.Json has to say about them:"

    let value, json = getJson {| args=args; year=System.DateTime.Now.Year |}
    printfn $"Input: %0A{value}"
    printfn $"Output: %s{json}"

    0 // return an integer exit code

Add a reference to the Library project using dotnet reference add.

dotnet add src/App/App.fsproj reference src/Library/Library.fsproj

Add the App project to the FSharpSample solution using the dotnet sln add command:

dotnet sln add src/App/App.fsproj

Restore the NuGet dependencies with dotnet restore and run dotnet build to build the project.

Change directory to the src/App console project and run the project passing Hello World as arguments:

cd src/App
dotnet run Hello World

You should see the following results:

Nice command-line arguments! Here's what System.Text.Json has to say about them:
Input: { args = [|"Hello"; "World"|] year = 2021 }
Output: {"args":["Hello","World"],"year":2021}

Next steps

Next, check out the Tour of F# to learn more about different F# features.