utop[9]> let sum_list l =
  let rec aux l s =
    match l with
      [] -> s
    | e :: t -> aux t (e + s)
  in aux l 0;;
val sum_list : int list -> int = <fun>
utop[10]> let l = List.tl (iota 11);;
val l : int list = [1; 2; 3; 4; 5; 6; 7; 8; 9; 10]
utop[11]> sum_list l;;
- : int = 55
utop[12]> List.fold_right;;
- : ('a -> 'b -> 'b) -> 'a list -> 'b -> 'b = <fun>
utop[14]> let sum_list l =
  List.fold_right ( + ) l 0;;
val sum_list : int list -> int = <fun>
utop[15]> ( + );;
- : int -> int -> int = <fun>
utop[16]> fun x y -> x + y;;
- : int -> int -> int = <fun>
utop[17]> 1 + 4;;
- : int = 5
utop[18]> ( + );;
- : int -> int -> int = <fun>
utop[19]> List.fold_left;;
- : ('a -> 'b -> 'a) -> 'a -> 'b list -> 'a = <fun>
utop[20]> let sum_list l =
  List.fold_left ( + ) 0 l;;
val sum_list : int list -> int = <fun>
utop[21]> List.append;;
- : 'a list -> 'a list -> 'a list = <fun>
utop[22]> ( @ );;
- : 'a list -> 'a list -> 'a list = <fun>
utop[23]> let conc_list lists =
  List.fold_right ( @ ) lists [];;
val conc_list : 'a list list -> 'a list = <fun>
utop[24]> conc_list [[1;2]; [3;4]];;
- : int list = [1; 2; 3; 4]
utop[25]> 
let map f l =
  List.fold_right (fun e l -> f e :: l)  l [];;
val map : ('a -> 'b) -> 'a list -> 'b list = <fun>
utop[26]> map (fun x -> x * x) l;;
- : int list = [1; 4; 9; 16; 25; 36; 49; 64; 81; 100]
utop[27]> l;;
- : int list = [1; 2; 3; 4; 5; 6; 7; 8; 9; 10]
utop[28]>