Right, I'm not arguing that it's impossible to produce a difference, but I think that if you're defining the sequence of fibs, the most likely scenario might be that you're actually interested in a prefix, and more importantly, you can still, from the outside, force the prefix even if you're only interested in a particular element.
Three topics are repeatedly discussed among beginners in Japan: 1) fibs implemented with zipWith 2) simple quicksort 3) sieve of eratosthenes Some people use 1) with "!!" and say "it's slow, why?". Some people say 2) is not a true quicksort because it is not in-place. Some people say 3) is not the sieve of eratosthenes at all because, for example, 7 is divided by 5. These three examples are mis-leading. In my opinion, if we use them, we should - use them as is, but describe such opinions OR - use better implementations I don't know translations work well but you can find such discussions here: http://d.hatena.ne.jp/kazu-yamamoto/20100624 http://d.hatena.ne.jp/nishiohirokazu/20100622/1277208908 http://d.hatena.ne.jp/mkotha/20100623/1277286946 --Kazu