I worked a lot in F# and loved it. I love that it has a lot of great functional ideas without being too pedantic about being 100% functional all the time. (You can have mutating state or just call arbitrary C#.) I took a lot of its insights into my daily python code too. I especially love match.

There's no need to be functional 100% of the time, and it's not pedantry.

You mark your functions and non-functions as such, so the compiler can get your back.