open System
 
type AP = | Alpha of string | Punkt of string
    with static member cons (isPunct, s) = if not isPunct then Alpha s else Punkt s
 
[<EntryPoint>]
let main argv = 
    let s = "The quick brown   fox hmm fox, jumps over the lazy dog dog."
    printfn "Source : %A" (s)
    let chartest x = Char.IsPunctuation x || Char.IsSeparator x || Char.IsWhiteSpace x
    let dict = set [] |> ref
    let xs = seq {  let isChar = ref <| chartest s.[0]
                    let a = ref 0
                    for i in 0 .. s.Length - 1 do 
                        if chartest s.[i] = !isChar then ()
                        else yield AP.cons(!isChar, s.[!a .. i - 1])
                             a := i
                             isChar := chartest s.[i]
                    yield AP.cons(!isChar, s.[!a .. s.Length - 1]) } |> Seq.toList
    let rec loop xs acc = 
        match xs with
        | [] -> List.rev acc
        | Punkt s :: Alpha a :: t when Set.contains a !dict -> loop t acc
        | Punkt s :: t                                      -> loop t (s :: acc)
        | Alpha a :: t when Set.contains a !dict    -> loop t acc
        | Alpha a :: t                              -> dict := Set.add a !dict; loop t (a :: acc)
    let xs = String.Join("", loop xs [] |> List.toArray)
 
    printfn "Result : %A" (xs)
    0
 

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