I'd like to share something with you. I call it "the evil ******* function from hell": (Results xss) >>= f = Results $ map concat $ diagonalise $ map (foldr longZip [] . map (unpack . f)) xss If you attempt to comprehend how this function works, you WILL in fact loose your mind! However, it does in fact work completely correctly. It's just not possible to know why. :-D newtype Results t = Results [[t]] unpack (Results xss) = xss longZip = similar to zip (++) diagonalise = transform an infinite list of infinite lists into an infinite list of finite lists.