(* 目的：自然数 n の階乗を求める *) 
(* fac : int -> int *) 
let rec fac n = 
  if n = 0 then 1 
           else n * fac (n - 1) 
 
(* テスト *) 
let test1 = fac 0 = 1 
let test2 = fac 1 = 1 
let test3 = fac 2 = 2 
let test4 = fac 3 = 6 
let test5 = fac 4 = 24 
let test6 = fac 10 = 3628800