I spent a long time working on a solution for an exercise in RWH: if you can, use foldr to mimic haskell's cycle function. At first, I wondered whether it was even possible. Then I worked on some ideas, and finally I came up with a solution. Surprisingly, my solution ended up being very simple: myCycle [] = [] myCycle xs = helperFunc xs [1..] where helperFunc ys foldrXs = foldr accFunc [] foldrXs where accFunc _ acc = ys ++ acc I tested it out, and it worked like a charm: *Main> let x = myCycle [1, 2, 3] *Main> take 2 x [1,2] *Main> take 10 x [1,2,3,1,2,3,1,2,3,1] *Main> take 30 x [1,2,3,1,2,3,1,2,3,1,2,3,1,2,3,1,2,3,1,2,3,1,2,3,1,2,3,1,2,3] After re-examining my solution, I decided that this line: --where accFunc _ acc = ys ++ acc read better like this: --where accFunc _ acc = acc ++ ys The altered function returns a list just fine. But when I use take on the list, I get a stack overflow. What is being thunked in both cases? Thanks.