(* recursive version of factorial

   type

     #use "fact1.ml";;

   to load this file into ocaml *)

let fact n =
      let (* if n >= 0, then fct n returns n factorial *)

          rec fct n =
            if n = 0
            then 1
            else n * fct(n - 1)
      in if n < 0
         then -1
         else fct n

(* try: fact 6;; *)