moveAl :: [Point] -> [Point]
moveAl [] = []
moveAl ((x, y) : xs)= (x, y - 1) : moveAl xs

moveAliens :: (MonadState Game m) => m ()
moveAliens = do
  game <- get
  let naliens (x:xs) = _getAliens (_aliens game)
      naliens [] = []
      naliens (x:xs) = do
        moveAl x
        naliens xs
  aliens .= naliens

=================================================================================================================
Couldn't match expected type ‘Aliens’
                  with actual type ‘[[Point]] -> [Point]’
    • Probable cause: ‘naliens’ is applied to too few arguments
      In the second argument of ‘(.=)’, namely ‘naliens’
      In a stmt of a 'do' block: aliens .= naliens
      In the expression:
        do game <- get
           let naliens (x : xs) = _getAliens (_aliens game)
               naliens [] = []
               naliens (x : xs) = ...
           aliens .= naliens
    |