That's an awesome website! I made it through the first three puzzles using F#. It's too bad that there's nothing like IntelliSense there, but you can use Visual Studio or www.tryfsharp.org for typing and CodinGame for testing. It looks neat, but might not be the best for learning a new language. You can see some clever solutions after solving a puzzle at least. How familiar are you with F# and functional programming?