I'd like to add that with F# you get all the benefits of an extremely mature web stack with asp.net core and a huge eco system of very high quality libraries. Frameworks like Giraffe, Suave or Freya make it all possible to write your backend in a functional idiomatic way. Also a big plus for F# is the choice of top notch tooling. You've got Visual studio which works on Windows and Mac, then JetBrains Rider which is awesome and Visual studio code with the Ionide extension. I'd highly recommend anyone to go and check it all out!