let rec filter func list =
        match list with
        | x::xs when func xs -> x::(filter func xs)
        | _::xs -> filter func xs
        | [] -> []

    let rec count list =
        match list with
        | [] -> 0
        | x::xs -> 1 + count xs

    let first list =
        match list with
        | [] -> null
        | x::xs -> x

    let rec reverse list =
        match list with
        | [] -> []
        | x::xs -> reverse xs @ [x]

    let last list =
        match list with
        | [] -> null
        | x -> first (reverse x)

    let rec take list takeVal =
        match list, takeVal with
        | [], _ -> []
        | _, 0 -> []
        | x::xs, t -> x::(take xs (t - 1))

    let rec skip list skipVal =
        match list, skipVal with
        | x, s when s < 0 -> x
        | [], _ -> []
        | x, 0 -> x
        | x::xs, s -> skip xs (s - 1)

    let addToEnd list token =
        list @ [token]

    let addToBegin list token =
        token::list

    let removeAt list token =
        list |> filter (fun x -> x = token)

    let addToPosition list token position =
        (list |> take position) @ [token] @ (list |> skip position)