The factoria function using hylomorphism in Haskell.

fact.hs

import Data.List  --To enable unfoldr.
fact n =
  foldr
    (*) --Function input
    1   --Base case
    (unfoldr  --List input
      (\n -> if n==0 then Nothing else Just (n, n-1))
      n)

--Print out example results of the fact fn.
main = do
  print (fact 5)