let rec fold (combine: 'a -> 'b -> 'b) (base: 'b) (l: 'a list) : 'b =
  begin match l with
  | [] -> base
  | x :: xs -> combine x (fold combine base xs)
  end

let test () : bool =
  not (for_all (fun x -> x > 0) [1; 2; -5; -33; 2])
;; run_test "for_all: multiple elements; returns false" test

let  for_all (pred: 'a -> bool) (l: 'a list) : bool =
fold (fun(x:'a)(acc: bool)->  _?_&&_?_  )false l