Hi all, I'm working on a type-based side effect analysis for a Haskell-like language, and need to test it against some more higher order functions. The situation is a bit icky because it uses bounded quantification and various related issues (ie covariance vs contravariance) only come into play when dealing with functions of order >= 3. Trouble is, the vast majority of useful higher order functions that I can think of are of order 2. Oh, I can certainly invent toys like: order3 f = f succ order4 b f = if b then f else order3 .. and so on, but I'm left feeling unsatisfied. I vaguely remember a paper called something like "Is there any use for a seventh order function?", but I forget why they were used, and I can't find it on Google, or ACM or any of the other likely places. Does anyone have any examples of code (in whatever language) which usefully uses functions of order >= 3?? Preferably up to 5? Thanks, Ben.