This mentions and :: Foldable t => t Bool -> Bool as an example of "abstract nonsense". Well, I will run into teaching this soon myself, though not to freshmen - my students had some Java before but not Haskell. With regards to the type of "and", I will first have them write "data List a = ..." and a concrete "and :: List Bool -> Bool" from scratch. Later, to explain the type of "the true and" I will claim that the corresponding Java method would have type "static Boolean and (Iterable<Boolean> xs)" where Iterable<> is an interface (that the students should know). That's not too bad: xs.iterator() corresponds to toList xs (a lazy stream). "toList" would even be a complete definition for the Foldable instance? (since foldr f z = foldr f z . toList ) So perhaps "Foldable \approx Iterable \approx Enumerable" is a useful guideline. (Yes, there is a difference between a one-argument type class and an interface. But they have some common use cases.) - J.W.