Hi list, I have yet another question about folds. Reading here and there I encountered statements that foldr is more important than foldl, e.g. in this post on the list: http://www.haskell.org/pipermail/haskell-cafe/2012-May/101338.html I want to know are such statements correct and, if so, why? I am aware that foldl' can in some circumstances operate in constant space, while foldr can operate on infinite lists if the folding function is lazy in the second parameter. Is there more to this subject? Properties that I mentioned are more of technical nature, not theoretical ones. Are there any significant theoretical advantages of foldr? I read Bird's and Wadler's "Introduction to functional programming" and it seems to me that foldl and foldr have the same properties and in many cases are interchangeable. Greets, Janek