list pattern arbitrary sublist.fsx

let (|Contains|_|) xs input =
    let rec contains xs' input' acc =
        match xs', input' with
        | [], after -> 
            let length = List.length acc - List.length xs
            let before = acc |> List.rev |> Seq.take length |> List.ofSeq
            Some (before, after)
        | _, [] -> None
        | h1 :: t1, h2 :: t2 when h1 = h2 ->
            contains t1 t2 (h2 :: acc)
        | h1 :: t1, h2 :: t2 ->
            contains xs t2 (h2 :: acc)
    
    contains xs input []

match [0;0;7;6;7;1;3;7;6;7;0;0] with
| Contains [7;6;7] (before,after) -> printfn "before: %A; after: %A" before after
| _ -> printfn "does not contain"