rebindable6.hs:109:17: error:
    Ambiguous type variable ‘t0’ arising from a do statement
    prevents the constraint ‘(HasSeq
                                (IO a -> t0 -> IO b))’ from being solved.
      (maybe you haven't applied a function to enough arguments?)
    Relevant bindings include
      g :: IO (Maybe b) (bound at rebindable6.hs:107:19)
      f :: IO a (bound at rebindable6.hs:107:17)
      test_do :: IO a -> IO (Maybe b) -> IO b
        (bound at rebindable6.hs:107:9)
    Probable fix: use a type annotation to specify what ‘t0’ should be.
    These potential instance exist:
      instance HasSeq (IO a -> IO b -> IO b)
        -- Defined at rebindable6.hs:55:18
    In a stmt of a 'do' block: f
    In the expression:
      do { f;
           Just (b :: b) <- g;
           return b }
    In an equation for ‘test_do’:
        test_do f g
          = do { f;
                 Just (b :: b) <- g;
                 return b }

rebindable6.hs:110:17: error:
    Ambiguous type variable ‘t1’ arising from a do statement
                                 with the failable pattern ‘Just (b :: b)’
    prevents the constraint ‘(HasFail
                                ([Char] -> t1))’ from being solved.
      (maybe you haven't applied a function to enough arguments?)
    Probable fix: use a type annotation to specify what ‘t1’ should be.
    These potential instance exist:
      instance HasFail (String -> IO a)
        -- Defined at rebindable6.hs:60:18
    In a stmt of a 'do' block: Just (b :: b) <- g
    In the expression:
      do { f;
           Just (b :: b) <- g;
           return b }
    In an equation for ‘test_do’:
        test_do f g
          = do { f;
                 Just (b :: b) <- g;
                 return b }

rebindable6.hs:111:17: error:
    Ambiguous type variable ‘t1’ arising from a use of ‘return’
    prevents the constraint ‘(HasReturn (b -> t1))’ from being solved.
      (maybe you haven't applied a function to enough arguments?)
    Relevant bindings include
      b :: b (bound at rebindable6.hs:110:23)
      g :: IO (Maybe b) (bound at rebindable6.hs:107:19)
      test_do :: IO a -> IO (Maybe b) -> IO b
        (bound at rebindable6.hs:107:9)
    Probable fix: use a type annotation to specify what ‘t1’ should be.
    These potential instance exist:
      instance HasReturn (a -> IO a) -- Defined at rebindable6.hs:45:18
    In a stmt of a 'do' block: return b
    In the expression:
      do { f;
           Just (b :: b) <- g;
           return b }
    In an equation for ‘test_do’:
        test_do f g
          = do { f;
                 Just (b :: b) <- g;
                 return b }