99 bottles

bottles.hs

bottles :: Int -> String
bottles x | x == 0    = "No more bottles"
          | x == 1    = "1 more bottle"
          | x < 13    = show x ++ " more bottles"
          | otherwise = show x ++ " bottles"

verse :: Int -> String
verse x = line1 ++ "\n" ++ line2 ++ "\n\n"
    where line1  = bottles x ++ obotw ++ " " ++ bottles x ++ ob
          line2  = todpia ++ bottles (x-1) ++ obotw
          obotw  = " of beer on the wall."
          ob     = " of beer."
          todpia = "Take one down, pass it around. "

main :: IO ()
main = mapM_ putStr $ map verse [99,98..1]