Factorial in Haskell

Example for versions GHC 6.10.4

This example uses the Prelude function product, which computes the product of a list of numbers. When the list is empty, it returns 1 (the multiplicative identity), so this works for 0 too. 

module Main where

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

line x = putStrLn $ show x ++ "! = " ++ factorial x

main = mapM_ line [0..16]