open System

let rec sorted = function
    | (x :: xs) ->
        let left, right = List.partition (fun i -> i < x) xs
        let sleft = sorted left
        let sright = sorted right
        sleft @ (x :: sright)
    | [] -> []

let rnd = new Random()
let l = [for i in [1 .. 100] -> rnd.Next(1, 1000)]

printfn "%A" l
printfn "%A" <| sorted l