drvfail011.hs:8:1:
    No instance for (Eq a) arising from a use of ‘==’
    Possible fix: add (Eq a) to the context of the instance declaration
    In the expression: ((a1 == b1))
    In an equation for ‘==’: (==) (T1 a1) (T1 b1) = ((a1 == b1))
    When typechecking the code for  ‘==’
      in a derived instance for ‘Eq (T a)’:
      To see the code I am typechecking, use -ddump-deriv
    In the instance declaration for ‘Eq (T a)’