rose.hs

module Rose where

import Data.List (findIndex)

data Tree a = Node { value :: a, getSubForest :: [Tree a] } deriving Show

insertPath :: (Eq a ) => [a] -> Tree a -> Tree a
insertPath []     tree = tree
insertPath (x:xs) (Tree a subForest) = Tree a modifiedSubForest
  where
    maybeIndex =
      findIndex (\node -> value node == x) subForest

    subtree =
      case maybeIndex of
           Just index ->
             subForest !! index
           Nothing ->
             Node x []

    modifiedSubForest =
      case maybeIndex of
           Just index ->
             replaceAt index (insertPath xs subtree) subForest
           Nothing ->
             insertPath xs subtree : subForest

replaceAt :: Int -> a -> [a] -> [a]
replaceAt 0 a []       = [a]
replaceAt _ _ []       = []
replaceAt 0 a (_ : xs) = a : xs
replaceAt n a (x : xs) = x : replaceAt (n - 1) a xs