class Magic a where
  conjure :: String -> [a]
  magikStorage :: [a] -> String

-- Use return type
doMagik :: Magic a => Int -> [a]
doMagik n = concat $ replicate n res
  where
    res = conjure $ magikStorage res -- Must be lazy in res !!!!

-- Pass dummy parameter
anotherMagic :: Magic a => Int -> [a]
anotherMagic n = concat $ replicate n $ go []
  where
    go :: Magic a => [a] -> [a]
    go x = conjure $ magikStorage x