[plt-scheme] Binary tree Traversals

In post-order you use append in the wrong way.
In in-order you use list, but you should use append here too.
What type of arguments does append expect in order to act as you want?
Jos

----- Original Message ----- 
From: "Shrutarshi Basu" <technorapture at gmail.com>
To: <plt-scheme at list.cs.brown.edu>
Sent: Friday, October 10, 2008 3:40 AM
Subject: [plt-scheme] Binary tree Traversals


> I've written some scheme code for traversing binary trees. Here is my 
> code:
>
>
> (define (atom? x)
>  (not (pair? x)))
>
>
> ;;Functions to manipulate a binary tree
> (define (leaf? node) (atom? node))
> (define (left node) (cadr node))
> (define (right node) (caddr node))
> (define (label node) (if (leaf? node) node (car node)))
>
> ;; Preorder Traversal
>
> (define (pre-order node)
>  (cons
>   (label node)
>   (if (leaf? node)
>       '()
>       (append
> (pre-order (left node))
> (pre-order (right node))))))
>
> ;;Post-order traversal
> (define (post-order node)
>  (list
>   (if (leaf? node) '()
>       (append
> (post-order (left node))
> (post-order (right node))))
>   (label node)))
>
> ;;in-order traversal
> (define (in-order node)
>  (if (leaf? node) (label node)
>      (list
>       (in-order (left node))
>       (cons
> (label node)
> (in-order (right node))))))
>
> (define tree '(A (B C D)(E (F G H) I)))
> (pre-order tree)
> (post-order tree)
> (in-order tree)
>
>
>
> Though they do work, the post and in-order traversals output as deeply
> nested lists and not a simple flat list. Can someone how to get
> results in flattened lists (without running a separate flatten routine
> on the returned results)?
> Thanks
> Basu
>
> -- 
> The ByteBaker :
> http://www.bytebaker.com
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