demo.hs

instance LogType (IO a) where
  logn' arr = do
    -- Call putStr on all the elements in arr.
    mapM_ putStr arr -- functions that end in _ ignore their result
    -- Output a newline.
    putStrLn ""
    -- The "do" block must return something.
    return undefined

instance (Show a, LogType r) => LogType (a -> r) where
  logn' arr x = logn' (arr ++ [show x] ++ [" "])

logn :: (LogType t) => t -- Why doesn't () work in place of the last t?
logn = logn' []