Extremely-newbie questions: Is there any way to know if a list is finite or infinite, other than doing: length l and waiting forever? :) I ask because I was learning Haskell by writing some pretty naive implementation of surreal numbers, where I used lists for left and right surreal sets, and I wanted to do some operations on the sets (like finding the maximum/minimum), but obviously just on finite sets. I vaguely suspect the answer is going to be: "No, because lists are lazy (at least when they are :) and there's no general way to know beforehand how many elements they're going to have". But still, if I write x = [1..5] the compiler knows pretty well x is not going to grow any new member... (Unrelated) Is there any standard function to do: interleave [] _ = [] interleave _ [] = [] interleave (x:xs) (y:ys) = x : y : interleave xs ys It's pretty easy to implement as shown or via zipWith, but given that Haskell 98 already includes some "basic" functions (like cycle, iterate, etc.) I wonder if I've missed this one somehow. Thanks, /L/e/k/t/u