tcfail165.hs:18:17: error: [GHC-83865]
    • Couldn't match type: forall a. Show a => a -> String
                     with: b0 -> String
      Expected: IO (MVar (b0 -> String))
        Actual: IO (MVar (forall a. Show a => a -> String))
    • In a stmt of a 'do' block:
        var <- newEmptyMVar :: IO (MVar (forall a. Show a => a -> String))
      In the expression:
        do var <- newEmptyMVar ::
                    IO (MVar (forall a. Show a => a -> String))
           putMVar var (show :: forall b. Show b => b -> String)
      In an equation for ‘foo’:
          foo
            = do var <- newEmptyMVar ::
                          IO (MVar (forall a. Show a => a -> String))
                 putMVar var (show :: forall b. Show b => b -> String)