tcfail001.hs:9:2: error:
    • Couldn't match expected type ‘[a]’
                  with actual type ‘[a0] -> [a1]’
    • The equation(s) for ‘op’ have one value argument,
        but its type ‘[a]’ has none
      In the instance declaration for ‘A [a]’
    • Relevant bindings include op :: [a] (bound at tcfail001.hs:9:2)