(*---------------------------------------------------------

    YOUR NAME:

    STUDENT ID:

  ---------------------------------------------------------*)




let rec foldl f x l =
  match l with
  | []     -> x
  | hd::tl -> foldl f (f x hd) tl

let rec foldr f x l =	
  match l with
  | []     -> x
  | hd::tl -> f hd (foldr f x tl)

let subt x y = x - y

let d1 = [ 10; 20; 30; 40; 50]

(*---------------------------------------------------------
   QUESTION #1: What is the output of the statement below?
   ANSWER:

  ---------------------------------------------------------*)
let _ =
let ans = foldl subt 0 [ 10; 20; 30; 40; 50] in
  print_int ans



(*---------------------------------------------------------
   QUESTION #2: What is the output of the statement below?
   ANSWER:

  ---------------------------------------------------------*)
let _ =
let ans = foldr subt 0 [ 10; 20; 30; 40; 50] in
  print_int ans



(*---------------------------------------------------------
   QUESTION #3: What is the output of the statement below?
   ANSWER:

  ---------------------------------------------------------*)
let _ =
let ans = foldl subt 1 [ 10; 20; 30; 40; 50] in
  print_int ans



















(*---------------------------------------------------------
   QUESTION #4: Complete the last line of the function
                "for_all" below using foldl() or foldr().
   ---------------------------------------------------------*)

let for_all f l =
  let fn x e = x && (f e) in

  __________________________

let _ =
  let d = [ 2; 4; 6; 8; 10] in
  let f x = x mod 2 == 0 in
  let ans = for_all f d in
  print_string (string_of_bool ans)  (***** true ******)


(*---------------------------------------------------------
   QUESTION #5: Change the above function "for_all" to
                "there_exists" such that the second statement
                outputs false.
  ---------------------------------------------------------*)

let there_exists f l =

   _______________________

   _______________________

let _ =
  let d = [ 2; 4; 6; 8; 10] in
  let f x = x mod 2 == 1 in
  let ans = there_exists f d in
  print_string (string_of_bool ans)  (***** false ******)


(*---------------------------------------------------------
   QUESTION #6: Given a very long list, which would you use,
                foldl or foldr?  Why?
   ANSWER:




















  ---------------------------------------------------------*)