Question on tree-walking and mutually-recursive types

[Daniel Berlin]

On Jun 28, 2004, at 11:22 PM, Richard Kenner wrote:

>     Yes walk using a hashtable saying you already walked the tree.
>     walk_tree_without_duplicates is what you want.
>
> Well, I figured out a way to perhaps keep the cost under control but 
> still
> handle the pathalogical case.   I used what was below and it works,
> but YUCK!
>

I'm confused.
Why can't you just use walk_tree_without_duplicates to do your tree 
walk in the caller, instead of polluting walk_tree?

Or is this common code that requires a walk_tree instead (it's not 
clear), and if so, what code exactly?