exception Empty_list
let fold fn = function
    | [] -> raise Empty_list
    | head :: tail -> List.fold_left fn head tail

let list_min ls = fold Stdlib.min ls
let list_max ls = fold Stdlib.max ls

let rec repeat n a =
    if n <= 0
    then []
    else a :: repeat (n - 1) a

let empty ls = (ls = [])

let rec zip l1 l2 =
    match (l1, l2) with
    | ([], _) -> []
    | (_, []) -> []
    | (h1 :: t1, h2 :: t2) -> (h1, h2) :: zip t1 t2

let rec transpose = function
    | [] :: _ -> []
    | ls -> List.(map hd ls) :: transpose List.(map tl ls)

let flip f a b = f b a

let rot_right ls = List.(rev ls |> transpose)
let rot_left ls  = List.(transpose ls |> rev)

let saturating_sub b a =
    if a < b then 0
    else a - b