Introduction

Key points

Microsoft language family on the .NET platform

• Designer: Don Syme @ Microsoft Research

• ≃ OCaml implementation for .NET

• ≃ Inspired by Haskell (Version 1.0 in 1990)

• dotnet new -lang F♯

• Interoperability between C♯ and F♯ projects/assemblies

Multi-paradigm language Functional-first and very concise

Whereas C♯ is imperative/objective-oriented-first and rather verbose (even if it's inspired by F♯ to become more succinct and functional)

History

Date	C♯	F♯	.NET	Visual Studio
2002	C♯ 1.0		.NET Framework 1.0	VS .NET 2002
2005	C♯ 2.0	F♯ 1.x	.NET Framework ?.?	VS 2005
2007	C♯ 3.0		.NET Framework 3.5	VS 2008
2010	C♯ 4.0	F♯ 2.0	.NET Framework 4	VS 2010
...	...	...	...	...
2019	C♯ 8.0	F♯ 4.7	.NET Core 3.x	VS 2019
2020	C♯ 9.0	F♯ 5.0	.NET 5.0	VS 2019
...	...	...	...	...
2024	C♯ 13.0	F♯ 9.0	.NET 9.0	VS 2022

🔗 Versions details: https://learn.microsoft.com/en-us/dotnet/fsharp/whats-new/

Editors / IDE

• VsCode + Ionide → ☝ More a boosted text editor than a full IDE → ☝ Permissive: does not always report all compilation errors → 🔗 Fantastic F♯ and Azure Developer Extensions for VSCode by Compositional IT
• Visual Studio / Rider → ☝ Less refactoring capabilities than for C♯

• Try F♯: https://try.fsharp.org/ → Online REPL with some examples

F♯ interactive (FSI)

• REPL available in VS, Rider, vscode + dotnet fsi

• Usage : instantly test a snippet

  • 💡 In the FSI console, enter ;; at the end of an expression to evaluate it

Example from vscode with ionide:

FSI: Send Selection

💡 In the FSI console, enter ;; at the end of an expression to evaluate it

☝️ Notes:

• C♯ interactive is more recent (VS 2015 Update 1). The FSI was there from the get go.

• Alternative worth trying, also working for C#: LINQPad

File types

4 file types: .fs, .fsi, .fsx, .fsproj

⚠️ Single language : for F♯ only

Standalone file

• Script file .fsx

  • Executable (hence the final x) using the FSI

  • Independent but can reference other files, DLLs, NuGet packages

Project files

• In C♯ : .sln contains .csproj projects that contains .cs files

• In F♯ : .sln contains .fsproj projects that contains .fs(i) code files

💡 Easy Interop = Combine both .csproj and .fsproj projects in the same .sln

.fsi are signature files (i for interface)

• Associated with a .fs file of the same name

• Optional and rather rare in codebases

• Usages

  • Reinforces encapsulation (like .h in C)

  • Separate long documentation (xml-doc)

• More info : MSDN

F♯ Project

Creation in the IDE or using the CLI dotnet:

• dotnet new -l : list supported project types

• dotnet new console --language F♯ -o MyFSharpApp

  • Création of a console project named MyFSharpApp

  • --language F♯ is key to specify the language, by default in C#

• dotnet build : to build the project

• dotnet run : to build the project and run the underlying executable