fj.data.TreeZipper Maven / Gradle / Ivy
Go to download
Show more of this group Show more artifacts with this name
Show all versions of functionaljava Show documentation
Show all versions of functionaljava Show documentation
Functional Java is an open source library that supports closures for the Java programming language
package fj.data;
import fj.*;
import fj.function.Booleans;
import java.util.Iterator;
import static fj.Equal.p3Equal;
import static fj.Equal.p4Equal;
import static fj.Equal.streamEqual;
import static fj.Equal.treeEqual;
import static fj.Function.compose;
import static fj.Function.curry;
import static fj.Function.flip;
import static fj.Function.uncurryF2;
import static fj.Show.p3Show;
import static fj.Show.p4Show;
import static fj.Show.streamShow;
import static fj.Show.treeShow;
import static fj.data.Option.none;
import static fj.data.Option.some;
import static fj.data.Stream.nil;
import static fj.data.Stream.unfold;
import static fj.data.Tree.node;
import static fj.data.Tree.unfoldTree;
/**
* Provides a zipper structure for rose trees, which is a Tree supplied with a location within that tree.
* Provides navigation, insertion, deletion, and memorization of visited locations within a tree.
*/
public final class TreeZipper implements Iterable> {
/**
* Returns an iterator of all the positions of this TreeZipper. Exists for use with the foreach syntax.
*
* @return An iterator of all the positions of this TreeZipper.
*/
public Iterator> iterator() {
return positions().toTree().iterator();
}
private final Tree tree;
private final Stream> lefts;
private final Stream> rights;
private final Stream>, A, Stream>>> parents;
private TreeZipper(final Tree tree,
final Stream> lefts,
final Stream> rights,
final Stream>, A, Stream>>> parents) {
this.tree = tree;
this.lefts = lefts;
this.rights = rights;
this.parents = parents;
}
/**
* Creates a new tree zipper given a currently selected tree, a forest on the left, a forest on the right,
* and a stream of parent contexts.
*
* @param tree The currently selected tree.
* @param lefts The selected tree's left siblings, closest first.
* @param rights The selected tree's right siblings, closest first.
* @param parents The parent of the selected tree, and the parent's siblings.
* @return A new zipper with the given tree selected, and the given forests on the left and right.
*/
public static TreeZipper treeZipper(final Tree tree,
final Stream> lefts,
final Stream> rights,
final Stream>, A, Stream>>> parents) {
return new TreeZipper<>(tree, lefts, rights, parents);
}
/**
* First-class constructor for tree zippers.
*
* @return A function that returns a new tree zipper, given a selected tree, left and right siblings,
* and a parent context.
*/
public static
F, F>, F>, F>, A, Stream>>>, TreeZipper>>>>
treeZipper() {
return curry(
TreeZipper::treeZipper);
}
/**
* Returns the product-4 representation of this zipper.
*
* @return the product-4 representation of this zipper.
*/
public P4, Stream>, Stream>, Stream>, A, Stream>>>> p() {
return P.p(tree, lefts, rights, parents);
}
/**
* A first-class function that returns the product-4 representation of a given zipper.
*
* @return a function that converts a given zipper to its product-4 representation.
*/
public static
F, P4, Stream>, Stream>, Stream>, A, Stream>>>>> p_() {
return TreeZipper::p;
}
/**
* An Equal instance for tree zippers.
*
* @param e An Equal instance for tree elements.
* @return An Equal instance for tree zippers.
*/
public static Equal> eq(final Equal e) {
return p4Equal(
treeEqual(e),
streamEqual(treeEqual(e)),
streamEqual(treeEqual(e)),
streamEqual(p3Equal(streamEqual(treeEqual(e)), e, streamEqual(treeEqual(e))))).contramap(TreeZipper.p_());
}
/**
* A Show instance for tree zippers.
*
* @param s A Show instance for tree elements.
* @return A Show instance for tree zippers.
*/
public static Show> show(final Show s) {
return p4Show(
treeShow(s),
streamShow(treeShow(s)),
streamShow(treeShow(s)),
streamShow(p3Show(streamShow(treeShow(s)), s, streamShow(treeShow(s))))).contramap(TreeZipper.p_());
}
private static Stream> combChildren(final Stream> ls,
final Tree t,
final Stream> rs) {
return ls.foldLeft(compose(flip(Stream.cons()), P.p1()), Stream.cons(t, P.p(rs)));
}
/**
* Navigates to the parent of the current location.
*
* @return A new tree zipper focused on the parent node of the current node,
* or none if the current node is the root node.
*/
public Option> parent() {
if (parents.isEmpty())
return none();
else {
final P3>, A, Stream>> p = parents.head();
return some(treeZipper(node(p._2(), combChildren(lefts, tree, rights)), p._1(), p._3(), parents.tail()._1()));
}
}
/**
* Navigates to the top-most parent of the current location.
*
* @return A new tree zipper focused on the top-most parent of the current node.
*/
public TreeZipper root() {
return parent().option(this, TreeZipper.root_());
}
/**
* A first-class version of the root function.
*
* @return A function that returns a new tree-zipper focused on the root of the given tree zipper's tree.
*/
public static F, TreeZipper> root_() {
return TreeZipper::root;
}
/**
* Navigates to the left sibling of the current location.
*
* @return A new tree zipper focused on the left sibling of the current node,
* or none if there are no siblings on the left.
*/
public Option> left() {
return lefts.isEmpty() ? Option.none()
: some(treeZipper(lefts.head(), lefts.tail()._1(), rights.cons(tree), parents));
}
/**
* Navigates to the right sibling of the current location.
*
* @return A new tree zipper focused on the right sibling of the current node,
* or none if there are no siblings on the right.
*/
public Option> right() {
return rights.isEmpty() ? Option.none()
: some(treeZipper(rights.head(), lefts.cons(tree), rights.tail()._1(), parents));
}
/**
* Navigtes to the first child of the current location.
*
* @return A new tree zipper focused on the first child of the current node, or none if the node has no children.
*/
public Option> firstChild() {
final Stream> ts = tree.subForest()._1();
return ts.isEmpty() ? Option.none()
: some(treeZipper(ts.head(), Stream.nil(), ts.tail()._1(), downParents()));
}
/**
* Navigtes to the last child of the current location.
*
* @return A new tree zipper focused on the last child of the current node, or none if the node has no children.
*/
public Option> lastChild() {
final Stream> ts = tree.subForest()._1().reverse();
return ts.isEmpty() ? Option.none()
: some(treeZipper(ts.head(), ts.tail()._1(), Stream.nil(), downParents()));
}
/**
* Navigates to the given child of the current location, starting at index 0.
*
* @param n The index of the child to which to navigate.
* @return An optional tree zipper focused on the child node at the given index, or none if there is no such child.
*/
public Option> getChild(final int n) {
Option> r = none();
for (final P2>, Stream>> lr
: splitChildren(Stream.nil(), tree.subForest()._1(), n)) {
r = some(treeZipper(lr._1().head(), lr._1().tail()._1(), lr._2(), downParents()));
}
return r;
}
/**
* Navigates to the first child of the current location, that satisfies the given predicate.
*
* @param p A predicate to be satisfied by the child node.
* @return An optional tree zipper focused on the first child node that satisfies the given predicate,
* or none if there is no such child.
*/
public Option> findChild(final F, Boolean> p) {
Option> r = none();
final F2>, Stream>, Option>, Tree, Stream>>>> split =
new F2>, Stream>, Option>, Tree, Stream>>>>() {
public Option>, Tree, Stream>>> f(final Stream> acc,
final Stream> xs) {
return xs.isNotEmpty()
? p.f(xs.head()) ? some(P.p(acc, xs.head(), xs.tail()._1()))
: f(acc.cons(xs.head()), xs.tail()._1())
: Option.none();
}
};
Stream> subforest = tree.subForest()._1();
if (subforest.isNotEmpty()) {
for (final P3>, Tree, Stream>> ltr
: split.f(Stream.nil(), subforest)) {
r = some(treeZipper(ltr._2(), ltr._1(), ltr._3(), downParents()));
}
}
return r;
}
private Stream>, A, Stream>>> downParents() {
return parents.cons(P.p(lefts, tree.root(), rights));
}
private static Option, Stream>> splitChildren(final Stream acc,
final Stream xs,
final int n) {
return n == 0 ? some(P.p(acc, xs))
: xs.isNotEmpty() ? splitChildren(acc.cons(xs.head()), xs.tail()._1(), n - 1)
: Option.none();
}
private static Stream>, A, Stream>>> lp3nil() {
return nil();
}
/**
* Creates a new tree zipper focused on the root of the given tree.
*
* @param t A tree over which to create a new zipper.
* @return a new tree zipper focused on the root of the given tree.
*/
public static TreeZipper fromTree(final Tree t) {
return treeZipper(t, Stream.nil(), Stream.nil(), TreeZipper.lp3nil());
}
/**
* Creates a new tree zipper focused on the first element of the given forest.
*
* @param ts A forest over which to create a new zipper.
* @return a new tree zipper focused on the first element of the given forest.
*/
public static Option> fromForest(final Stream> ts) {
return ts.isNotEmpty()
? some(treeZipper(ts.head(), Stream.nil(), ts.tail()._1(), TreeZipper.lp3nil()))
: Option.none();
}
/**
* Returns the tree containing this location.
*
* @return the tree containing this location.
*/
public Tree toTree() {
return root().tree;
}
/**
* Returns the forest containing this location.
*
* @return the forest containing this location.
*/
public Stream> toForest() {
final TreeZipper r = root();
return combChildren(r.lefts, r.tree, r.rights);
}
/**
* Returns the tree at the currently focused node.
*
* @return the tree at the currently focused node.
*/
public Tree focus() {
return tree;
}
/**
* Returns the left siblings of the currently focused node.
*
* @return the left siblings of the currently focused node.
*/
public Stream> lefts() {
return lefts;
}
/**
* Returns the right siblings of the currently focused node.
*
* @return the right siblings of the currently focused node.
*/
public Stream> rights() {
return rights;
}
/**
* Indicates whether the current node is at the top of the tree.
*
* @return true if the current node is the root of the tree, otherwise false.
*/
public boolean isRoot() {
return parents.isEmpty();
}
/**
* Indicates whether the current node is the leftmost tree in the current forest.
*
* @return true if the current node has no left siblings, otherwise false.
*/
public boolean isFirst() {
return lefts.isEmpty();
}
/**
* Indicates whether the current node is the rightmost tree in the current forest.
*
* @return true if the current node has no siblings on its right, otherwise false.
*/
public boolean isLast() {
return rights.isEmpty();
}
/**
* Indicates whether the current node is at the bottom of the tree.
*
* @return true if the current node has no child nodes, otherwise false.
*/
public boolean isLeaf() {
return tree.subForest()._1().isEmpty();
}
/**
* Indicates whether the current node is a child node of another node.
*
* @return true if the current node has a parent node, otherwise false.
*/
public boolean isChild() {
return !isRoot();
}
/**
* Indicates whether the current node has any child nodes.
*
* @return true if the current node has child nodes, otherwise false.
*/
public boolean hasChildren() {
return !isLeaf();
}
/**
* Replaces the current node with the given tree.
*
* @param t A tree with which to replace the current node.
* @return A new tree zipper in which the focused node is replaced with the given tree.
*/
public TreeZipper setTree(final Tree t) {
return treeZipper(t, lefts, rights, parents);
}
/**
* Modifies the current node with the given function.
*
* @param f A function with which to modify the current tree.
* @return A new tree zipper in which the focused node has been transformed by the given function.
*/
public TreeZipper modifyTree(final F, Tree> f) {
return setTree(f.f(tree));
}
/**
* Modifies the label at the current node with the given function.
*
* @param f A function with which to transform the current node's label.
* @return A new tree zipper with the focused node's label transformed by the given function.
*/
public TreeZipper modifyLabel(final F f) {
return setLabel(f.f(getLabel()));
}
/**
* Replaces the label of the current node with the given value.
*
* @param v The new value for the node's label.
* @return A new tree zipper with the focused node's label replaced by the given value.
*/
public TreeZipper setLabel(final A v) {
return modifyTree(t -> Tree.node(v, t.subForest()));
}
/**
* Returns the label at the current node.
*
* @return the label at the current node.
*/
public A getLabel() {
return tree.root();
}
/**
* Inserts a tree to the left of the current position. The inserted tree becomes the current tree.
*
* @param t A tree to insert to the left of the current position.
* @return A new tree zipper with the given tree in focus and the current tree on the right.
*/
public TreeZipper insertLeft(final Tree t) {
return treeZipper(t, lefts, rights.cons(tree), parents);
}
/**
* Inserts a tree to the right of the current position. The inserted tree becomes the current tree.
*
* @param t A tree to insert to the right of the current position.
* @return A new tree zipper with the given tree in focus and the current tree on the left.
*/
public TreeZipper insertRight(final Tree t) {
return treeZipper(t, lefts.cons(tree), rights, parents);
}
/**
* Inserts a tree as the first child of the current node. The inserted tree becomes the current tree.
*
* @param t A tree to insert.
* @return A new tree zipper with the given tree in focus, as the first child of the current node.
*/
public TreeZipper insertDownFirst(final Tree t) {
return treeZipper(t, Stream.nil(), tree.subForest()._1(), downParents());
}
/**
* Inserts a tree as the last child of the current node. The inserted tree becomes the current tree.
*
* @param t A tree to insert.
* @return A new tree zipper with the given tree in focus, as the last child of the current node.
*/
public TreeZipper insertDownLast(final Tree t) {
return treeZipper(t, tree.subForest()._1().reverse(), Stream.nil(), downParents());
}
/**
* Inserts a tree at the specified location in the current node's stream of children. The inserted tree
* becomes the current node.
*
* @param n The index at which to insert the given tree, starting at 0.
* @param t A tree to insert.
* @return A new tree zipper with the given tree in focus, at the specified index in the current node's stream
* of children, or None if the current node has fewer than n children.
*/
public Option> insertDownAt(final int n, final Tree t) {
Option> r = none();
for (final P2>, Stream>> lr
: splitChildren(Stream.nil(), tree.subForest()._1(), n)) {
r = some(treeZipper(t, lr._1(), lr._2(), downParents()));
}
return r;
}
/**
* Removes the current node from the tree. The new position becomes the right sibling, or the left sibling
* if the current node has no right siblings, or the parent node if the current node has no siblings.
*
* @return A new tree zipper with the current node removed.
*/
public Option> delete() {
Option> r = none();
if (rights.isNotEmpty())
r = some(treeZipper(rights.head(), lefts, rights.tail()._1(), parents));
else if (lefts.isNotEmpty())
r = some(treeZipper(lefts.head(), lefts.tail()._1(), rights, parents));
else for (final TreeZipper loc : parent())
r = some(loc.modifyTree(t -> node(t.root(), Stream.nil())));
return r;
}
/**
* Zips the nodes in this zipper with a boolean that indicates whether that node has focus.
* All of the booleans will be false, except for the focused node.
*
* @return A new zipper of pairs, with each node of this zipper paired with a boolean that is true if that
* node has focus, and false otherwise.
*/
public TreeZipper> zipWithFocus() {
final F> f = flip(P.p2()).f(false);
return map(f).modifyLabel(P2.map2_(Booleans.not));
}
/**
* Maps the given function across this zipper (covariant functor pattern).
*
* @param f A function to map across this zipper.
* @return A new zipper with the given function applied to the label of every node.
*/
public TreeZipper map(final F f) {
final F, Tree> g = Tree.fmap_().f(f);
final F>, Stream>> h = Stream., Tree>map_().f(g);
return treeZipper(tree.fmap(f), lefts.map(g), rights.map(g), parents.map(
p -> p.map1(h).map2(f).map3(h)));
}
/**
* First-class conversion of a Tree to the corresponding tree zipper.
*
* @return A function that takes a tree to its tree zipper representation.
*/
public static F, TreeZipper> fromTree() {
return TreeZipper::fromTree;
}
/**
* A first-class version of the left() function.
*
* @return A function that focuses the given tree zipper on its left sibling.
*/
public static F, Option>> left_() {
return TreeZipper::left;
}
/**
* A first-class version of the right() function.
*
* @return A function that focuses the given tree zipper on its right sibling.
*/
public static F, Option>> right_() {
return TreeZipper::right;
}
/**
* Returns a zipper over the tree of all possible permutations of this tree zipper (comonad pattern).
* This tree zipper becomes the focused node of the new zipper.
*
* @return A tree zipper over the tree of all possible permutations of this tree zipper.
*/
public TreeZipper> positions() {
final Tree> t = unfoldTree(TreeZipper.dwn()).f(this);
final Stream>> l = uf(TreeZipper.left_());
final Stream>> r = uf(TreeZipper.right_());
final Stream>>, TreeZipper, Stream>>>> p = unfold(
o -> {
Option>>, TreeZipper, Stream>>>,
Option>>> r1 = none();
for (final TreeZipper z : o) {
r1 = some(P.p(P.p(z.uf(TreeZipper.left_()), z, z.uf(TreeZipper.right_())), z.parent()));
}
return r1;
}, parent());
return treeZipper(t, l, r, p);
}
private Stream>> uf(final F, Option>> f) {
return unfold(
o -> {
Option>, Option>>> r = none();
for (final TreeZipper c : o) {
r = some(P.p(unfoldTree(TreeZipper.dwn()).f(c), f.f(c)));
}
return r;
}, f.f(this));
}
private static F, P2, P1>>>> dwn() {
return tz -> P.p(tz, new P1>>() {
private F>, Option, Option>>>> fwd() {
return o -> {
Option, Option>>> r = none();
for (final TreeZipper c : o) {
r = some(P.p(c, c.right()));
}
return r;
};
}
public Stream> _1() {
return unfold(fwd(), tz.firstChild());
}
});
}
/**
* Maps the given function over the tree of all positions for this zipper (comonad pattern). Returns a zipper
* over the tree of results of the function application.
*
* @param f A function to map over the tree of all positions for this zipper.
* @return A zipper over the tree of results of the function application.
*/
public TreeZipper cobind(final F, B> f) {
return positions().map(f);
}
/**
* A first-class version of the findChild function.
*
* @return a function that finds the first child, of a given tree zipper, that matches a given predicate.
*/
public static F2, Boolean>, TreeZipper, Option>> findChild() {
return (f, az) -> az.findChild(f);
}
/**
* Zips this TreeZipper with another, applying the given function lock-step over both zippers in all directions.
* The structure of the resulting TreeZipper is the structural intersection of the two TreeZippers.
*
* @param bs A TreeZipper to zip this one with.
* @param f A function with which to zip together the two TreeZippers.
* @return The result of applying the given function over this TreeZipper and the given TreeZipper, location-wise.
*/
public TreeZipper zipWith(final TreeZipper bs, final F2 f) {
return F2Functions.zipTreeZipperM(f).f(this, bs);
}
/**
* Zips this TreeZipper with another, applying the given function lock-step over both zippers in all directions.
* The structure of the resulting TreeZipper is the structural intersection of the two TreeZippers.
*
* @param bs A TreeZipper to zip this one with.
* @param f A function with which to zip together the two TreeZippers.
* @return The result of applying the given function over this TreeZipper and the given TreeZipper, location-wise.
*/
public TreeZipper zipWith(final TreeZipper bs, final F> f) {
return zipWith(bs, uncurryF2(f));
}
}