let mapping =
    Map.ofList [
        'A', ".-";   'B', "-..."; 'C', "-.-."; 'D', "-..";  'E', ".";
        'F', "..-."; 'G', "--.";  'H', "...."; 'I', "..";   'J', ".---";
        'K', "-.-";  'L', ".-.."; 'M', "--";   'N', "-.";   'O', "---";
        'P', ".--."; 'Q', "--.-"; 'R', ".-.";  'S', "...";  'T', "-";
        'U', "..-";  'V', "...-"; 'W', ".--";  'X', "-..-"; 'Y', "-.--";
        'Z', "--.."; ' ', "/"
    ]

[<EntryPoint>]
let main _ =
    let message = "THIS IS A TEST"
    let asMorse =
        message.ToUpper()
        |> Seq.choose (fun x -> mapping.TryFind x)
        |> Seq.map string
        |> String.concat " "
    printfn "%s" asMorse
    0