namespace Sanchime.DataStructures.Lists

module Link = 

    exception EmptyList

    type LinkList<'T> =
        | Cons of 'T * 'T LinkList
        | Nil

    let first = function
        | Nil -> raise EmptyList
        | Cons(value, _) -> value

    let last = function
        | Nil -> Nil
        | Cons(_, tail) -> tail

    let length list =
        let rec loop list count =
            match list with
            | Nil -> count
            | Cons(_, tail) -> loop tail (count + 1)
        loop list 0

    let rec map mapper = function
        | Nil -> Nil
        | Cons(head, tail) -> Cons(mapper head, map mapper tail)

    let rec append left right =
        match left with
        | Nil -> right
        | Cons(head, tail) -> Cons(head, append tail right)

    let empty = function
        | Nil -> true
        | Cons(_, _) -> false