rose tree paths

tree paths

import Data.Maybe

data Tree a = Node a [Tree a] deriving (Show)

t = Node 1 [ Node 2 [ Node 3 [] ], Node 4 [], Node 5 [ Node 6 [] ] ]

paths :: Tree a -> [[a]]
paths (Node n []) = [[n]]
paths (Node n xs) = map ((:) n . concat . paths) xs

-- paths t 
-- [[1,2,3], [1,4], [1,5,6]]

filterPaths :: (a -> Bool) -> Tree a -> [[a]]
filterPaths f tree = catMaybes . map sequence $ g f tree
    where g f (Node n []) = case (f n) of 
                              True -> [[Just n]]
                              _    -> [[Nothing]]
          g f (Node n ns) = case (f n) of
                              True ->  map ((:) (Just n) . concat . (g f)) ns
                              _    -> [[Nothing]]

-- filterPaths (/= 2) t
-- [[1,4],[1,5,6]]