factorial.hs

import System.Environment
import Data.List

main :: IO()
main = fmap factorialize getArgs >>= putStrLn 

factorialize :: [String] -> String
factorialize = toStr . factorials . toIntegers

toIntegers :: [String] -> [Integer]
toIntegers = map read

toStr :: [Integer] -> String
toStr = unwords . map show

factorials :: [Integer] -> [Integer]
factorials = map factorial

factorial :: Integer -> Integer
factorial 0 = 1
factorial num = factAcc [1..num]

factAcc :: [Integer] -> Integer
factAcc = foldl' (*) 1