Hi I've tried as an exercise to learn how to use the state monad to create a tree this way: module Main where import Control.Monad.State import Data.Tree import Random createTree :: Int -> Int -> (Tree Int, Int) createTree 4 = runState $ State $ \s -> (Node s [] , s+1) -- stop at level 4 createTree level = runState (do item <- State $ (\s -> (s,s+1)) forest <- State $ (\s -> foldr (\_ (for, n) -> let (l, n') = (createTree (level + 1) n) in (l:for,n')) ([], s) (replicate level ()) ) return $ Node item (reverse forest) ) main = do putStrLn $ drawTree $ fmap show $ fst $ createTree 2 0 ---- output ---------- 0 | +- 1 -- features: auto numbering and level n exists of n Nodes | | | +- 2 | | | +- 3 | | | `- 4 | `- 5 | +- 6 | +- 7 | `- 8 | | 2 3 ... Nodes per level I think this line is not very easy to understand.. the (replecate part is just a dummy to count the iterations) forest <- State $ (\s -> foldr (\_ (for, n) -> let (l, n') = (createTree (level + 1) n) in (l:for,n')) ([], s) (replicate level ()) ) Is there a better way to do this? This problem is similar to adding numbers to each tree item Marc