F# Uppercase String

namespace Program

open System

module Toup =

    let uppercase (n:string) =
        match n with
        | n when n.Length > 0 ->
            string(n.[0]).ToUpper() + n.Substring(1)
        | _ -> n

    type System.String with
        member this.Capitalize = uppercase this

module Main =
    open Toup
    [<EntryPoint>]
    let main args =
        printfn "%s" (uppercase "hello")
        printfn "%s" (uppercase "h")
        printfn "%s" (uppercase "")
        printfn "%s" "bb".Capitalize
        0