last_two

last_two.fsx

// selfmade :/ not yet...
let rec last_two = function 
    | [] -> None
    | [x] -> None
    | x::xs -> 
        if xs.Length > 1 then
            last_two xs
        else
            Some (x, xs.Head)

// better from solution
let rec last_two = function 
    | [] -> None
    | [x] -> None
    | [x;xs] -> Some (x, xs)
    | x::xs -> last_two xs

last_two [ "a" ; "b" ; "c" ; "d" ];;
// (string * string) option = Some ("c", "d")
last_two [ "a" ];;
// (string * string) option = None