private static <A> Stream<String> drawSubTrees(final Show<A> s, final Stream<Tree<A>> ts) {
return ts.isEmpty()
? Stream.nil()
: ts.tail()._1().isEmpty()
? shift("`- ", " ", ts.head().drawTree(s)).cons("|")
: shift("+- ", "| ", ts.head().drawTree(s)).append(drawSubTrees(s, ts.tail()._1()));
}
/**
* Puts the elements of the tree into a Stream, in pre-order.
*
* @return The elements of the tree in pre-order.
*/
public Stream<A> flatten() {
final F2<Tree<A>, P1<Stream<A>>, Stream<A>> squish =
new F2<Tree<A>, P1<Stream<A>>, Stream<A>>() {
public Stream<A> f(final Tree<A> t, final P1<Stream<A>> xs) {
return cons(
t.root(),
t.subForest().map(Stream.<Tree<A>, Stream<A>>foldRight().f(curry()).f(xs._1())));
}
};
return squish.f(this, P.p(Stream.<A>nil()));
}
/**
* Creates a nullary tree.
*
* @param root The root element of the tree.
* @return A nullary tree with the root element in it.
*/
public static <A> Tree<A> leaf(final A root) {
return node(root, Stream.nil());
}