Hi, I've written some code and was wondering if there was a better way to write it in terms of readability, brevity and/or efficiency. The function concerned is pathsToForest which takes a list of paths (ie. [[String]]) and converts it into a tree structure where the individual nodes are the names in the path. Siblings with the same name are merged. For instance: prettyPrint $ mergeForest $ pathsToForest [["a", "b", "c"], ["c", "b", "a"], ["a", "b", "d"]] gives: a b d c c b a Thanks -John import Data.Tree import Control.Monad data ArcData = ArcData { name :: String } deriving Show type ArcTree = Tree ArcData type ArcForest = Forest ArcData pathsToForest :: [[String]] -> ArcForest pathsToForest paths = mergeForest $ concat $ map pathToTree paths mergeForest :: ArcForest -> ArcForest mergeForest [] = [] mergeForest (x:xs) = merge x (mergeForest xs) where merge :: ArcTree -> ArcForest -> ArcForest merge tree [] = [tree] merge tree (y:ys) = if sameTreeName tree y then merge tree { subForest = mergeForest ((subForest tree) ++ (subForest y)) } ys else (y:merge tree ys) treeName :: ArcTree -> String treeName tree = name $ rootLabel $ tree sameTreeName :: ArcTree -> ArcTree -> Bool sameTreeName treeLeft treeRight = treeName treeLeft == treeName treeRight pathToTree :: [String] -> ArcForest pathToTree [] = [] pathToTree (name:subpath) = [ Node { rootLabel = ArcData { name = name } , subForest = pathToTree subpath } ] prettyPrint' :: ArcForest -> [String] prettyPrint' [] = [] prettyPrint' (x:xs) = [name $ rootLabel $ x] ++ (map (" " ++) (prettyPrint' $ subForest x)) ++ prettyPrint' xs prettyPrint :: ArcForest -> IO () prettyPrint forest = do forM_ (prettyPrint' forest) putStrLn