#!/usr/bin/runghc

module Recursion02Factorial where

import Data.List

-- Four different versions of Factorial(n):

factInf :: Int -> Integer
factInf n = product (take n [1 ..])

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

factTail :: Integer -> Integer -> Integer
factTail 0 sum = sum
factTail n sum = factTail (n - 1) (n * sum)

factFoldl :: Integer -> Integer
factFoldl n = foldl' (*) 1 [1 .. n]

main :: IO ()
main = do
  print (factInf 5)
  print (factInf 10)

  print (factRec 5)
  print (factRec 10)

  print (factTail 5 1)
  print (factTail 10 1)

  print (factFoldl 5)
  print (factFoldl 10)