let drop list n =

    let rec aux i = function

      | [] -> []

      | h :: t -> if i = n then aux 1 t else h :: aux (i+1) t  in

    aux 1 list

​

​

let drop2 list n =

  list

  |> List.mapi (fun i x -> if (n > 0) && (i % n = n - 1) then None else Some(x))

  |> List.choose id

​

​

let drop3 list n =

  let list = List.mapi (fun i x -> (i,x)) list

  [ for (i,x) in list do if not ((n > 0) && (i % n = n - 1)) then yield x ]

​

​

let test f1 f2 =

    [ for len in 0..9 do

        let v = List.replicate len "x"

        for skip in -10..10 do

          let same = (f1 v skip) = (f2 v skip)

          yield same

          if same = false then

            printfn "len = %A  skip = %A" len skip

            printfn "%A" v

            printfn "%A" (f1 v skip)

            printfn "%A\n" (f2 v skip)

    ]

    |> List.forall ((=) true)

    |> function true -> "Passed" | false -> "Failed"

    |> printfn "%s"

​

​

​

test drop drop2

test drop drop3

​