Overview

In this post, we'll create a new F# project from the command line.

We'll walk through creating two different kinds of apps:

• Console App - Good for libraries, command line utilities, or just running simple scripts
• Web App - Good for starting a web project (with APIs, etc)

Pre-Requisites

We'll be using the official dotnet CLI tool which will get you set up with a lean, up-to-date project skeleton to start building with F#.

• .NET SDK - The only thing we need for this tutorial is the .NET SDK installed on your machine which will give us access to the dotnet command.
  • Install: Download .NET

Create a Console Application

First let's create a console application. This is typically the simplest kind of application - it's invokable via command line, it runs some code, it exits.

Create a console app command:

dotnet new console -lang f#

This will create a project with a few files:

• YOUR_APP_NAME.fsproj - This contains metadata about your project like what files to include and what dependencies it has. This is similar to a package.json in javascript / npm
• Program.fs - This is your "main" file. This will be run like a script, top-to-bottom.
• obj/ - This contains build artifacts, you'll typically want to .gitignore this

My Program.fs looks like this:

Program.fs

printfn "Hello from F#"

We can run it with:

dotnet run

When I run this, it outputs:

Hello from F#

More resources:

• This example is availabe on GitHub: fsharp-docker-console-example
• If you want to run F# in a container, read: Run F# / .NET in Docker

Create a Web Application

Console apps are useful, but typically you'll want to write something that's invokable via the web. The standard framework for web in F# / .NET land is ASP.NET base with optional frameworks built on top.

Covering all web options is out of scope for this post but you can get started with sane defaults using CloudSeed - a fullstack F# project boilerplate - and see a list of officially endorsed options in Web Programming with F#

Create a web project command:

dotnet new web -lang f#

This will create a project with a few files:

• YOUR_APP_NAME.fsproj - (Same as console app) A file listing metadata about your project and how to build it
• Program.fs - A simple main function that initializes ASP.NET, creates a minimal API endpoint at / that returns Hello World!, then starts the server

Program.fs

open System
open Microsoft.AspNetCore.Builder
open Microsoft.Extensions.Hosting

[<EntryPoint>]
let main args =
    let builder = WebApplication.CreateBuilder(args)
    let app = builder.Build()

    app.MapGet("/", Func<string>(fun () -> "Hello World!")) |> ignore

    app.Run()

    0 // Exit code

We can start the web server with:

dotnet run

This should print some info to console including what port it's listening on. Mine says:

info: Microsoft.Hosting.Lifetime[14]
      Now listening on: https://localhost:7055
info: Microsoft.Hosting.Lifetime[14]
      Now listening on: http://localhost:5127

If I go to the http://* link, I see Hello World! returned from my server.

Next Steps

You should now have a working skeleton for a console app and a web app.

Further reading:

• Run F# / .NET in a Docker container
• Full stack boilerplate for F# / SvelteKit: CloudSeed