add :: Eq a => a -> a -> RoseTree a -> RoseTree a add x px (Node x' []) = Node x' [Node x []] add x px (Node x' trees) | px == x' = Node x' $ (Node x []):trees | otherwise = Node x' $ (add x px) <$> trees seems to be correct. :)

On 8 Jan 2017, at 20:06, mike h wrote:

Hi,

I’m rapidly descending into a spiral of confusion! :)

How do I add something to a rose tree?

I have

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

add :: Eq a => a -> a -> Tree a -> Tree a

and the first ‘a’ is the thing to add and the second is its parent node. i.e. add :: Eq a => a -> a -> Tree a -> Tree a add x px (Node x' []) = Node x' [Node x []] …..

I’ve tried various ways for the more general case but always seem to lose part of the tree.

Any advice would be very welcome.

Thanks

Mike