Re: [Haskell-cafe] Textbook example of instance Foldable ((,)a)

True. And their use in Arrow is a great example of pairs that do *not* work well as instances of Foldable as currently defined. Arrow is using pairs as abstract Cartesian products, and the natural isomorphism A×B≅B×A is used implicitly all the time. The Foldable definition for pairs breaks that symmetry inappropriately. Cheers, --Barak.