static boolean prefixMatches(Tree target, Tree pattern) {
if (pattern.isEmpty()) return true;
if (target.isEmpty() || target.value() != pattern.value()) return false;
return prefixMatches(target.left(), pattern.left())
&& prefixMatches(target.right(), pattern.right());
}
/**
* Search the tree for the first instance of `pattern`, giving preference to the left child.
*
* <p>`pattern` is a tree, representing a pattern of nodes. `NilNode`s should be considered
* wildcards.
*
* <p>Example patterns ---------------- `Tree()` Matches any tree.
*
* <p>`Tree(3)` Matches any tree where the root node has a value of `3`.
*
* <p>`Tree(3, Tree(2), Tree())` Matches any tree where the root node has a value of `3`, and a
* left sub-tree with a root value of `2`, and any (or no) right sub-tree.
*/
static Optional<Tree> find(Tree target, Tree pattern) {
if (pattern.isEmpty()) return Optional.of(target);
if (target.isEmpty()) return Optional.empty();
if (prefixMatches(target, pattern)) return Optional.of(target);
Optional<Tree> leftMatch = find(target.left(), pattern);
if (leftMatch.isPresent()) return leftMatch;
return find(target.right(), pattern);
}
@SuppressWarnings("unchecked")
static <T, U> Tree<U> apply(
Node<T> node, Function<? super T, ? extends Iterable<? extends U>> mapper) {
final Tree<U> mapped = Tree.ofAll(mapper.apply(node.getValue()));
if (mapped.isEmpty()) {
return Tree.empty();
} else {
final List<Node<U>> children =
(List<Node<U>>)
(Object)
node.getChildren()
.map(child -> FlatMap.apply(child, mapper))
.filter(Tree::isDefined);
return Tree.of(mapped.getValue(), children.prependAll(mapped.getChildren()));
}
}
@Override
public String toString() {
if (LeftSubTree.isEmpty() && RightSubTree.isEmpty()) return NodeValue.toString();
return "(" + NodeValue + " " + LeftSubTree + " " + RightSubTree + ")";
}