I got nerd sniped to write a function that takes an n, and prints all strings of length n containing only 'X' and 'Y'

PrintXY.hs

import Data.Bits
printXY n = mapM_ print (gen n)
  where gen 0 = [""]
        gen n = map (f n) [0..2^(n-1)]
        f :: Int -> Integer -> String
        f n i = map (toXY . testBit i)  [0..(n-1)]
        toXY c = if c then 'X' else 'Y'
        genRec n = (map ('X':) smaller) ++ (map ('Y':) smaller)
          where smaller = genRec (n-1)

printXYRec n = mapM_ print (genRec n)
  where
    genRec 0 = [""]
    genRec n = (map ('X':) smaller) ++ (map ('Y':) smaller)
      where smaller = genRec (n-1)

printXYM n = mapM_ . print . replicateM n "XY"