[Haskell-beginners] Type Tree variables

[Ozgur Akgun]

Hi,

On 11 March 2012 13:36, bahadýr altan <doaltan at yahoo.co.uk> wrote:

> ... my function works on just first three nodes of  a binary tree, but
> the tree is bigger, I don't care the other nodes. Like this :
>
> function Node a (Node b Subtree Subtree)  (Node c Subtree Subtree)
>

Assuming you use the following declaration for your data type:

data Tree a = Leaf | Node a (Tree a) (Tree a)

The syntax you are looking for is the following; where x, y and z are
pattern variables.

f :: Tree a -> (a,a,a)
f (Node x (Node y _ _) (Node z _ _)) = (x,y,z)

The above function is obviously partial. It would throw an exception if you
apply it to anything which doesn't have the 'proper' shape. (e.g. "f Leaf")

I don't know your background, but I'd suggest reading some introductory
material if you are having trouble understanding the above snippets. LYAH
is a pretty fun read: http://learnyouahaskell.com

Hope this helps,
Ozgur
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