unwrapping.hs

-- unwrapping exercise, the goal is to print the contents of the IO

newtype MyActionThing a 
    = MyActionThing 
    { runMyActionThing :: IO a 
    }
action :: MyActionThing Int
newtype ExceptT e m a 
    = ExceptT
    { runExceptT :: m (Either e a)
    }
newtype ReaderT r m a
    = ReaderT
    { runReaderT :: r -> m a
    }
-- >>> :t runReaderT
-- runReaderT :: ReaderT r m a -> r -> m a

newtype StateT s m a 
  = StateT 
  { runStateT :: s -> m (a, s)
  }

x 
    :: ReaderT Int 
        (ExceptT Double 
            (StateT Char 
                IO)
        ) 
        String
x = do
    i <- ask
    when (i == 0) $ throwError 2.3
    pure (replicate i 'a')
main :: IO ()
main = do
    let a :: Int -> ExceptT Double (StateT Char IO) String
        a = runReaderT x
        b :: ExceptT Double (StateT Char IO) String
        b = y 3
        c :: (StateT Char IO) (Either Double String)
        c = runExceptT w
        d :: Char -> IO (Either Double String, Char)
        d = runStateT z
        e :: IO (Either Double String, Char)
        e = q 'a'
    res <- r
    case res of
        (Left d, c) -> print d -- print out some number as an error
        (Right s, c) -> print s -- big success!