main = print (fact1 3)


fact1 :: Integer -> Integer 
fact1 n  =  if n == 0 then 
		1 
	    else
		n * fact1 (n-1)

fact2 :: Integer -> Integer 
fact2 n 
  | n == 0    = 1 
  | otherwise = n * fact2 (n-1)

fact3 :: Integer -> Integer 
fact3 0 = 1 
fact3 n = n * fact3 (n-1)

fact4 :: Integer -> Integer 
fact4 n 
  | n == 0 =  1 
  | n >= 1 =  n * fact4 (n-1)

-- fact5 :: Integer -> Integer 
-- fact5 0	    = 1 
-- fact5 (n+1) = (n+1) * fact5 n

fact6 :: Integer -> Integer  
fact6 n = product [1..n]