UseTree.lhs

	Using the search tree ADT					
                                                                      
        (c) Simon Thompson, 1995, 1998.


>	module UseTree where

>	import Tree					
           
The size function  definable using the operations of the	
 	abstype.							
 

>       size :: Tree a -> Int
>       size t 
>         | isNil t 	= 0
>         | otherwise 	= 1 + size (leftSub t) + size (rightSub t)

 
Finding the nth element of a tree.				
 

>       indexT :: Int -> Tree a -> a

>       indexT n t 
>         | isNil t 	= error "indexT"
>         | n < st1 	= indexT n t1
>         | n == st1 	= v
>         | otherwise 	= indexT (n-st1-1) t2
>             where
>             v   = treeVal t
>             t1  = leftSub t
>             t2  = rightSub t
>             st1 = size t1