util.ml

let rec zip l1 l2 =
    match (l1, l2) with
    | h1 :: l1, h2 :: l2 -> (h1, h2) :: zip l1 l2
    | [], [] -> []
    | _ -> raise @@ Invalid_argument "lists that zip takes must be same length"

let rec zip3 l1 l2 l3 =
    match (l1, l2, l3) with
    | h1 :: l1, h2 :: l2, h3 :: l3 -> (h1, h2, h3) :: zip3 l1 l2 l3
    | [], [], [] -> []
    | _ ->
        raise @@ Invalid_argument "lists  that zip3 takes must be same length"

let rec zip4 l1 l2 l3 l4 =
    match (l1, l2, l3, l4) with
    | h1 :: l1, h2 :: l2, h3 :: l3, h4 :: l4 ->
        (h1, h2, h3, h4) :: zip4 l1 l2 l3 l4
    | [], [], [], [] -> []
    | _ ->
        raise @@ Invalid_argument "lists  that zip3 takes must be same length"

let rec unzip = function
    | [] -> ([], [])
    | (a, b) :: remain ->
        let a', b' = unzip remain in
        (a :: a', b :: b')

let rec unzip3 = function
    | [] -> ([], [], [])
    | (a, b, c) :: remain ->
        let a', b', c' = unzip3 remain in
        (a :: a', b :: b', c :: c')

let rec unzip4 = function
    | [] -> ([], [], [], [])
    | (a, b, c, d) :: remain ->
        let a', b', c', d' = unzip4 remain in
        (a :: a', b :: b', c :: c', d :: d')

let rec drop n l =
    match (n, l) with
    | 0, l -> l
    | n, h :: l -> drop (n - 1) l
    | _ -> raise @@ Invalid_argument "cannot drop"

let rec uniq = function
    | x :: remain -> x :: (uniq @@ List.filter (( <> ) x) remain)
    | [] -> []

let fst (x, _, _) = x

let snd (_, x, _) = x

let trd (_, _, x) = x