Can I improve this tree mutator ?

[Dimitar Georgiev]

I've a function in my project that looks like this:

static <A> Tree<A> adhocEndoBottomUp(Tree<A> tree, F<Tree<A>, Tree<A>> endo)
{
    Stream<Tree<A>> newChildren = tree.subForest().f().map(endo);
    return endo.f(Tree.node(tree.root(), newChildren));

}

It maps each subtree, bottom up, to another one of the same type. Finally it maps the root with all the mapped children.

A sample usecase is to remove all intermediate nodes that have a single child that is a leaf, and replace those

nodes with their respective single childs:

Tree<String> trimmed = adhocEndoBottomUp(tree, x -> {
    List<Tree<String>> childList = x.subForest().f().toList();

    if (childList.isSingle())
    {
        Tree<String> theChild = childList.head();
        if (theChild.isLeaf())
        {
            return theChild;  
        }

    }

    return x;
});

(For example the input is a filesystem tree, where a subtree has nothing in it but a number of subdirectories,

only containing one single file at the leaf. The transformed result will skip the intermediate empty subdirs)

This adhocEndoBottomUp of mine is, I think, a totally unlawless operation. After all, in the general case there exists

no relation between the original tree and the result. I might for example pass a function which maps the tree

to a single leaf (provided I have some pointed set for A).

Therefore I was wondering if there is a canonical way in which to achieve this sample usecase of "collapsing",

using FJ, or in general.

Excuse the handwaviness. This is the best I could do considering my poor undestanding of the essence of the problem.

Regards, Dimitar
  

[Tony Morris]

Does a tree zipper (TreeZipper) help?

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[Dimitar Georgiev]

Thanks! I considered, and tried that, and failed miserably since I have no experience working with zippers, and could not find any examples, at least for fj. I'll give it anoher shot.