[Haskell-beginners] Rose tree

[mike h]

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 <mike_k_houghton at yahoo.co.uk> 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