Validar en F#

validar.fs

let validar tam accion =
    let cars = [for c in accion -> c]
    if List.exists (fun c -> not (Char.IsDigit c)) cars then List.empty<int>
    else 
        let org = List.map (fun c -> (int c) - (int '0')) cars
        let num = List.distinct org
        if (List.length org <> List.length num) || (List.length num <> tam) then List.empty<int>
        else num