why-lazy.hs

foldRight' ::
  (b -> z -> z)
  -> (a -> b)
  -> z
  -> [a]
  -> z
foldRight' _ _ z [] =
  z
foldRight' k f z (x:xs) =
  k (f x) (foldRight' k f z xs)

map' ::
  (([a] -> [a]) -> [b] -> [b]) -> (c -> a) -> [c] -> [b]
map' k f =
  foldRight' k ((:) . f) []

program' ::
  (([Int] -> [Int]) -> [a] -> [a])
  -> [a]
program' k =
  take 10 (map' k (+1) [1..])

terminates ::
  [Int]
terminates =
  program' id

doesNotTerminate ::
  [Int]
doesNotTerminate =
  program' ($!)