What we have here is a feature interaction problem. There's a combination of features (Foldable, Traversable, ((,) a), &c) each of which is sensible and useful, but which together give people a nasty surprise. We also have the combination of a language which is getting a lot of attention in terms of expressiveness, mathematical power, consistency and all manner of goodness BUT less attention with respect to beginners and bears of very little brain like me. If I write something that evaluates to length (2,3), it will quite definitely be unintentional. I'm reminded of a feature that Emacs used to have (and maybe still does): there were lots of commands that beginners were much more likely to type by accident than on purpose, so when you typed on, it would tell you something like "you just typed Ctrl-Meta-Explode, which does XYZ, are you sure you meant to do that?" and if you said yes, it remembered that and would let you use it again. That's one way to try to combine power for experts with safety for beginners. Again, if I remember correctly, PLT Scheme (now Racket) had similar support for beginners, where you could choose different language levels so that beginners didn't have to worry about major or even minor arcana. What I'm wondering here is if there's room in the Haskell world for something similar? Perhaps some sort of Profile: <profile name> pragma, where profiles can say things like "tuples are not Foldable". Does everyone have "beginner" days, or is it just me?