Hello, I would like to get some advice about state monad (or any other monad I guess) and CPS. Let's take a simple exemple (see the code below) 'walk' is a function written in CPS that compute the number of nodes & leaves in a tree. It use a counter which is explicitly passed through calls. 'walk2' is does the same using the state monad but is not written in CPS Is it possible to write a function 'walk3' written in CPS and using the state monad? Thank you Regards J-C module M where import Control.Monad.State data Node = Node (Node, Int, Node) |Leaf Int |Empty deriving (Show) walk Empty acc k = k acc walk (Leaf _) acc k = k (acc+1) walk (Node (l, _, r)) acc k = let k1 acc = walk r acc k in walk l (acc+1) k1 nb = Node (Leaf 1, 2, Leaf 3) nd = Node (nb, 4, Empty) nh = Node (Empty, 8, Leaf 9) ng = Node (Leaf 6, 7, nh) ne = Node (nd, 5, ng) r = walk ne 0 id walk2 Empty = return () walk2 (Leaf _ ) = do acc <- get put (acc+1) return () walk2 (Node (l, _, r)) = do acc <- get put (acc+1) walk2 l walk2 r return () r2 = runState (walk2 ne) 0