player.fs

open FSharpx.Option

module String20 =
    open System.Text.RegularExpressions
    type T = String20 of string

    let createWithCont success failure (s: string) = 
        if Regex.IsMatch(s,@"^\w{1,20}$") 
        then success (String20 s)
        else failure "string length is more than 20"
    let create = 
        createWithCont Some (fun _ -> None)

module Player =
    type T = 
        { NickName  : String20.T
          FirstName : String20.T }

    let create nickName firstName = maybe {
        let! nick = String20.create nickName
        let! fn   = String20.create firstName
        return 
            { NickName  = nick
              FirstName = fn }
    }