T12170a.hs:20:35: error: [GHC-83865]
    • Couldn't match type ‘Ref m0’ with ‘IORef’
      Expected: IORef (f0 ()) -> m0 (f0 ())
        Actual: Ref m0 (f0 ()) -> m0 (f0 ())
        The type variable ‘m0’ is ambiguous
    • In the second argument of ‘(.)’, namely ‘readRef’
      In the second argument of ‘(>>=)’, namely ‘join . readRef’
      In the expression: newRef (pure ()) >>= join . readRef