1.ml

let rec take n l =
  match n, l with
  | 0, [] -> []
  | _, [] -> raise (Invalid_argument "plop")
  | _, h::t when n < 0 -> raise (Invalid_argument "drop")
  | 0, _::_ -> []
  | _, h::t -> h :: take (n - 1) t;;
take 2 [1; 2; 3; 4];;
take 2 [];;