3 Dec
2007
3 Dec
'07
12:26 a.m.
On Mon, Dec 03, 2007 at 05:20:35AM +0000, PR Stanley wrote:
Hi data Tree = Leaf Int | Node Tree Int Tree
occurs :: Int -> Tree -> Bool occurs m (Leaf n) = m == n occurs m (Node l n r) = m == n || occurs m l || occurs m r
It works but I'd like to know if it can be improved in any way. Thanks, Paul
Note that occurs checks elements in pre-order; so it can be factored into preorder and elem, where elem is defined in the Prelude: preorder (Leaf n) = [n] preorder (Node l n r) = n : preorder l ++ preorder r occurs x = elem x . preorder --- Also, Tree can be made to work on any type of value as a type constructor: data Tree k = Leaf k | Node (Tree k) k (Tree k) -- definitions of preorder and occurs are the same as before Stefan