(*  simple_factorial.ml
 *
 *  Author: W. M. Farmer
 *  Revised: December 1, 2009
 *  Description: Three simple implementations of the factorial function.
 *
 *)

let rec fact_rec n =
  if n = 0 
  then 1
  else (fact_rec (n - 1)) * n ;;

let fact_tail_rec n =
  let rec fact_tail_rec_aux n accum = 
    if n = 0 
    then accum
    else fact_tail_rec_aux (n - 1) (accum * n)
  in fact_tail_rec_aux n 1 ;;

let fact_iter n =
  let n' = ref n in
  let accum = ref 1 in
  while !n' <> 0 do
    accum := !accum * !n' ;
    n' := !n' - 1
  done ;
  !accum ;;