gistfile1.txt

class (Show a, Read a) => PlainTextDB a where
  get :: IO a
  get = fmap read $ readFile "db.txt"
  set :: a -> IO ()
  set x = return (show x) >>= writeFile "db.txt"

instance PlainTextDB Int

main = do
  set (4 :: Int)
  (get :: IO Int) >>= putStrLn . show