ambiguous_method_2.m:030: In declaration for function `e'/0:
ambiguous_method_2.m:030:   error in type class constraints: type variable `E'
ambiguous_method_2.m:030:   occurs in the constraints, but is not determined by
ambiguous_method_2.m:030:   the function's argument or result types.
For more information, recompile with `-E'.