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package au.id.zancanaro;
import java.util.Arrays;
import java.util.Collections;
import java.util.Iterator;
import java.util.function.Function;
public class RoseTree<T> {
private final T value;
private final Iterable<RoseTree<T>> children;
public RoseTree(T value, Iterable<RoseTree<T>> children) {
this.value = value;
this.children = children;
}
public T getValue() {
return value;
}
public Iterator<RoseTree<T>> getChildren() {
return children.iterator();
}
public static <T> RoseTree<T> pure(T value) {
return new RoseTree<>(value, Collections.emptyList());
}
public static <T> RoseTree<T> join(RoseTree<RoseTree<T>> tree) {
return new RoseTree<>(
tree.getValue().getValue(),
() -> Iterators.concat(
Iterators.mappingIterator(RoseTree::join, tree.children.iterator()),
tree.getValue().children.iterator()));
}
public static <T> Iterator<RoseTree<T>[]> permutations(RoseTree<T>[] trees) {
return Iterators.flatten(Iterators.rangeIterator(trees.length, index ->
Iterators.mappingIterator(child -> {
@SuppressWarnings("unchecked")
RoseTree<T>[] result = (RoseTree<T>[]) new RoseTree[trees.length];
for (int i = 0; i < trees.length; ++i) {
result[i] = (i == index ? child : trees[i]);
}
return result;
}, trees[index].getChildren())
));
}
public static <T, R> RoseTree<R> zip(Function<T[], R> fn, RoseTree<T>[] trees) {
@SuppressWarnings("unchecked")
T[] heads = (T[]) new Object[trees.length];
for (int i = 0; i < trees.length; ++i) {
heads[i] = trees[i].getValue();
}
return new RoseTree<>(
fn.apply(heads),
() -> Iterators.mappingIterator(
roses -> RoseTree.zip(fn, roses),
RoseTree.permutations(trees)));
}
public <R> RoseTree<R> fmap(Function<T, R> f) {
return new RoseTree<>(
f.apply(this.value),
() -> Iterators.mappingIterator(tree -> tree.fmap(f), this.children.iterator()));
}
public <R> RoseTree<R> flatmap(Function<T, RoseTree<R>> f) {
return RoseTree.join(this.fmap(f));
}
}
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