Animal and attribute

AnimalAttribute.hs

-- For haskell202

import Data.List (intercalate)

main :: IO ()
main = loop [] []
  where
    split = intercalate ", " . filter (not . null)
    loop animal attribute = do
      animal'    <- getLine
      attribute' <- getLine
      acc (split [animal, animal']) (split [attribute, attribute'])
        where
          acc :: String -> String -> IO ()
          acc [] [] = putStrLn "no data provided"
          acc an [] = do
            putStrLn "no attribute provided"
            loop an []
          acc [] at = do
            putStrLn "no animal provided"
            loop [] at
          acc an at = do
            putStrLn "done"
            putStrLn an
            putStrLn at

{-
ghci> main
dog
red
done
dog
red
ghci> main
dog

no attribute provided
cat
red
done
dog, cat
red
ghci> main

green
no animal provided
dog
yellow
done
dog
green, yellow
ghci> main


no data provided
-}