private static TreeZipper GoDown(TreeZipper zipper)
{
if (zipper == null || !zipper.Focus.Children.Any())
{
return(null);
}
var focus = zipper.Focus;
var children = focus.Children;
var newCrumb = new TreeCrumb(focus.Value, Array.Empty <Tree>(), children.Skip(1).ToArray());
return(new TreeZipper(children.First(), new[] { newCrumb }.Concat(zipper.Crumbs)));
}
private static TreeZipper GoRight(TreeZipper zipper)
{
if (zipper == null || !zipper.Crumbs.Any() || !zipper.Crumbs.First().Right.Any())
{
return(null);
}
var crumbs = zipper.Crumbs;
var firstCrumb = crumbs.First();
var newCrumb = new TreeCrumb(firstCrumb.Value, firstCrumb.Left.Concat(new[] { zipper.Focus }).ToArray(), firstCrumb.Right.Skip(1).ToArray());
return(new TreeZipper(firstCrumb.Right.First(), new[] { newCrumb }.Concat(crumbs.Skip(1))));
}
