Let us consider some of the functions that Foldable actually provides for tuples: length Useless and wrong. Unless "length" means "the number of items which fmap will operate over", in which case it's just useless and misleading. maximum Useless and wrong/misleading. minimum Useless and wrong/misleading. product Useless and wrong/misleading. sum Useless and wrong/misleading. etc It may be that some of the Foldable methods for tuples happen to be useful, but this does not mean that tuples are foldable. It means that there are some potentially useful helper methods which could be defined for tuples, and included in the Prelude. It may be that the same methods are applicable to Either, in which case there could be a new class ApplyFunctionToArbitraryPreDeterminedComponent. It may even make sense for this class to be a super-class of Foldable. But it does not make sense for tuples or Either to be instances of Foldable, because they aren't foldable. -- View this message in context: http://haskell.1045720.n5.nabble.com/Proposal-Add-conspicuously-missing-Func... Sent from the Haskell - Libraries mailing list archive at Nabble.com.