mod47.hs:6:10: error:
    • Could not deduce ‘Num a’
        arising from the superclasses of an instance declaration
      from the context: (Eq a, Enum a)
        bound by the instance declaration at mod47.hs:6:10-34
      Possible fix:
        add (Num a) to the context of the instance declaration
    • In the instance declaration for ‘Bar [a]’