[Haskell-cafe] about the concatenation on a tree

[Henk-Jan van Tuyl]

On Wed, 31 Dec 2008 17:19:09 +0100, Max cs <max.cs.2009 at googlemail.com>  
wrote:

> Hi Henk-Jan van Tuyl,
>
> Thank you very much for your reply!
>
> I think the concatenation should be different to thhe
>
> treeConcat :: Tree a -> Tree a -> Tree a
>
> the above is a combination of two trees instead of a concatenation, so
> I think the type of treeConcat should be:
>
> treeConcat :: Tree (Tree a) -> Tree a
>
> instead. How do you think? : ) I tried to implement it .. but it seems
> confusing.. to me
>
> Thanks
>
> Max

Hello Max,

The function
   treeConcat :: Tree (Tree a) -> Tree a
cannot be created, as it has an infinite type;
you can however, define a function that replaces leafs with trees,
for example treeConcat' in the following module, that replaces all leaves  
that contains a one with a given tree:

> module TreeConcat where

> data Tree a = Leaf a | Branch (Tree a) (Tree a)
>   deriving Show

> treeConcat' :: Num a => Tree a -> Tree a -> Tree a
> treeConcat' (Leaf 1)     tree = tree
> treeConcat' (Leaf x)     _    = Leaf x
> treeConcat' (Branch x y) tree = Branch (treeConcat' x tree) (treeConcat'  
> y tree)

> main :: IO ()
> main = print $ treeConcat' (Branch (Leaf 1) (Leaf 2)) (Branch (Leaf 3)  
> (Leaf 4))

This displays:
   Branch (Branch (Leaf 3) (Leaf 4)) (Leaf 2)

If this doen't help you either, I need to know more about what you are  
trying to do.

Regards,
Henk-Jan van Tuyl


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>
>
> On Wed, Dec 31, 2008 at 3:33 PM, Henk-Jan van Tuyl  
> <hjgtuyl at chello.nl>wrote:
>
>> Hi Max,
>>
>> A simple way to do this:
>>
>>  module TreeConcat where
>>>
>>
>>  data Tree a = Leaf a | Branch (Tree a) (Tree a)
>>>  deriving Show
>>>
>>
>>  treeConcat :: Tree a -> Tree a -> Tree atreeConcat xs ys = Branch xs ys
>>>
>>
>>  main :: IO ()
>>> main = print $ treeConcat (Leaf 1) (Leaf 2)
>>>
>>
>> But perhaps you want a certain ordering? Have a look at:
>>
>> http://hackage.haskell.org/packages/archive/AvlTree/4.2/doc/html/Data-Tree-AVL.html#44
>>
>>
>> --
>> Regards,
>> Henk-Jan van Tuyl
>>
>>
>> --
>> http://functor.bamikanarie.com
>> http://Van.Tuyl.eu/
>> --
>>
>>
>>



--