Mercurial > hg > Members > tatsuki > functionaljava-master > core
view src/main/java/fj/data/Tree.java @ 0:fe80c1edf1be
add getLoop
author | tatsuki |
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date | Fri, 20 Mar 2015 21:04:03 +0900 |
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package fj.data; import fj.F; import fj.F2; import fj.F2Functions; import fj.P; import fj.P1; import fj.P2; import static fj.Function.*; import static fj.data.Stream.*; import fj.Monoid; import fj.Show; import java.util.Collection; import java.util.Iterator; /** * Provides a lazy, immutable, non-empty, multi-way tree (a rose tree). * * @version %build.number% */ public final class Tree<A> implements Iterable<A> { /** * Returns an iterator for this tree. This method exists to permit the use in a <code>for</code>-each loop. * * @return A iterator for this tree. */ public Iterator<A> iterator() { return flatten().iterator(); } private final A root; private final P1<Stream<Tree<A>>> subForest; private Tree(final A root, final P1<Stream<Tree<A>>> subForest) { this.root = root; this.subForest = subForest; } /** * 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.<Tree<A>>nil()); } /** * Creates a new tree given a root and a (potentially infinite) subforest. * * @param root The root element of the tree. * @param forest A stream of the tree's subtrees. * @return A newly sprouted tree. */ public static <A> Tree<A> node(final A root, final P1<Stream<Tree<A>>> forest) { return new Tree<A>(root, forest); } /** * Creates a new tree given a root and a (potentially infinite) subforest. * * @param root The root element of the tree. * @param forest A stream of the tree's subtrees. * @return A newly sprouted tree. */ public static <A> Tree<A> node(final A root, final Stream<Tree<A>> forest) { return new Tree<A>(root, P.p(forest)); } /** * Creates a new n-ary given a root and a subforest of length n. * * @param root The root element of the tree. * @param forest A list of the tree's subtrees. * @return A newly sprouted tree. */ public static <A> Tree<A> node(final A root, final List<Tree<A>> forest) { return node(root, forest.toStream()); } /** * First-class constructor of trees. * * @return A function that constructs an n-ary tree given a root and a subforest or length n. */ public static <A> F<A, F<P1<Stream<Tree<A>>>, Tree<A>>> node() { return curry(new F2<A, P1<Stream<Tree<A>>>, Tree<A>>() { public Tree<A> f(final A a, final P1<Stream<Tree<A>>> p1) { return node(a, p1); } }); } /** * Returns the root element of the tree. * * @return The root element of the tree. */ public A root() { return root; } /** * Returns a stream of the tree's subtrees. * * @return A stream of the tree's subtrees. */ public P1<Stream<Tree<A>>> subForest() { return subForest; } /** * Provides a transformation from a tree to its root. * * @return A transformation from a tree to its root. */ public static <A> F<Tree<A>, A> root_() { return new F<Tree<A>, A>() { public A f(final Tree<A> a) { return a.root(); } }; } /** * Provides a transformation from a tree to its subforest. * * @return A transformation from a tree to its subforest. */ public static <A> F<Tree<A>, P1<Stream<Tree<A>>>> subForest_() { return new F<Tree<A>, P1<Stream<Tree<A>>>>() { public P1<Stream<Tree<A>>> f(final Tree<A> a) { return a.subForest(); } }; } /** * 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(F2Functions.curry(this)).f(xs._1()))); } }; return squish.f(this, P.p(Stream.<A>nil())); } /** * flatten :: Tree a -> [a] * flatten t = squish t [] * where squish (Node x ts) xs = x:Prelude.foldr squish xs ts * Puts the elements of the tree into a Stream, in pre-order. * * @return The elements of the tree in pre-order. */ public static <A> F<Tree<A>, Stream<A>> flatten_() { return new F<Tree<A>, Stream<A>>() { public Stream<A> f(final Tree<A> t) { return t.flatten(); } }; } /** * Provides a stream of the elements of the tree at each level, in level order. * * @return The elements of the tree at each level. */ public Stream<Stream<A>> levels() { final F<Stream<Tree<A>>, Stream<Tree<A>>> flatSubForests = Stream.<Tree<A>, Tree<A>>bind_().f(compose(P1.<Stream<Tree<A>>>__1(), Tree.<A>subForest_())); final F<Stream<Tree<A>>, Stream<A>> roots = Stream.<Tree<A>, A>map_().f(Tree.<A>root_()); return iterateWhile(flatSubForests, Stream.<Tree<A>>isNotEmpty_(), single(this)).map(roots); } /** * Maps the given function over this tree. * * @param f The function to map over this tree. * @return The new Tree after the function has been applied to each element in this Tree. */ public <B> Tree<B> fmap(final F<A, B> f) { return node(f.f(root()), subForest().map(Stream.<Tree<A>, Tree<B>>map_().f(Tree.<A, B>fmap_().f(f)))); } /** * Provides a transformation to lift any function so that it maps over Trees. * * @return A transformation to lift any function so that it maps over Trees. */ public static <A, B> F<F<A, B>, F<Tree<A>, Tree<B>>> fmap_() { return new F<F<A, B>, F<Tree<A>, Tree<B>>>() { public F<Tree<A>, Tree<B>> f(final F<A, B> f) { return new F<Tree<A>, Tree<B>>() { public Tree<B> f(final Tree<A> a) { return a.fmap(f); } }; } }; } /** * Folds this tree using the given monoid. * * @param f A transformation from this tree's elements, to the monoid. * @param m The monoid to fold this tree with. * @return The result of folding the tree with the given monoid. */ public <B> B foldMap(final F<A, B> f, final Monoid<B> m) { return m.sum(f.f(root()), m.sumRight(subForest()._1().map(foldMap_(f, m)).toList())); } /** * Projects an immutable collection of this tree. * * @return An immutable collection of this tree. */ public Collection<A> toCollection() { return flatten().toCollection(); } /** * Provides a function that folds a tree with the given monoid. * * @param f A transformation from a tree's elements to the monoid. * @param m A monoid to fold the tree with. * @return A function that, given a tree, folds it with the given monoid. */ public static <A, B> F<Tree<A>, B> foldMap_(final F<A, B> f, final Monoid<B> m) { return new F<Tree<A>, B>() { public B f(final Tree<A> t) { return t.foldMap(f, m); } }; } /** * Builds a tree from a seed value. * * @param f A function with which to build the tree. * @return A function which, given a seed value, yields a tree. */ public static <A, B> F<B, Tree<A>> unfoldTree(final F<B, P2<A, P1<Stream<B>>>> f) { return new F<B, Tree<A>>() { public Tree<A> f(final B b) { final P2<A, P1<Stream<B>>> p = f.f(b); return node(p._1(), p._2().map(Stream.<B, Tree<A>>map_().f(unfoldTree(f)))); } }; } /** * Applies the given function to all subtrees of this tree, returning a tree of the results (comonad pattern). * * @param f A function to bind across all the subtrees of this tree. * @return A new tree, with the results of applying the given function to each subtree of this tree. The result * of applying the function to the entire tree is the root label, and the results of applying to the * root's children are labels of the root's subforest, etc. */ public <B> Tree<B> cobind(final F<Tree<A>, B> f) { return unfoldTree(new F<Tree<A>, P2<B, P1<Stream<Tree<A>>>>>() { public P2<B, P1<Stream<Tree<A>>>> f(final Tree<A> t) { return P.p(f.f(t), t.subForest()); } }).f(this); } /** * Expands this tree into a tree of trees, with this tree as the root label, and subtrees as the labels of * child nodes (comonad pattern). * * @return A tree of trees, with this tree as its root label, and subtrees of this tree as the labels of * its child nodes. */ public Tree<Tree<A>> cojoin() { final F<Tree<A>, Tree<A>> id = identity(); return cobind(id); } private static <A> Stream<String> drawSubTrees(final Show<A> s, final Stream<Tree<A>> ts) { return ts.isEmpty() ? Stream.<String>nil() : ts.tail()._1().isEmpty() ? shift("`- ", " ", ts.head().drawTree(s)).cons("|") : shift("+- ", "| ", ts.head().drawTree(s)) .append(drawSubTrees(s, ts.tail()._1())); } private static Stream<String> shift(final String f, final String o, final Stream<String> s) { return Stream.repeat(o).cons(f).zipWith(s, Monoid.stringMonoid.sum()); } private Stream<String> drawTree(final Show<A> s) { return drawSubTrees(s, subForest._1()).cons(s.showS(root)); } /** * Draws a 2-dimensional representation of a tree. * * @param s A show instance for the elements of the tree. * @return a String showing this tree in two dimensions. */ public String draw(final Show<A> s) { return Monoid.stringMonoid.join(drawTree(s), "\n"); } /** * Provides a show instance that draws a 2-dimensional representation of a tree. * * @param s A show instance for the elements of the tree. * @return a show instance that draws a 2-dimensional representation of a tree. */ public static <A> Show<Tree<A>> show2D(final Show<A> s) { return Show.showS(new F<Tree<A>, String>() { public String f(final Tree<A> tree) { return tree.draw(s); } }); } /** * Zips this tree with another, using the given function. The resulting tree is the structural intersection * of the two trees. * * @param bs A tree to zip this tree with. * @param f A function with which to zip together the two trees. * @return A new tree of the results of applying the given function over this tree and the given tree, position-wise. */ public <B, C> Tree<C> zipWith(final Tree<B> bs, final F2<A, B, C> f) { return F2Functions.zipTreeM(f).f(this, bs); } /** * Zips this tree with another, using the given function. The resulting tree is the structural intersection * of the two trees. * * @param bs A tree to zip this tree with. * @param f A function with which to zip together the two trees. * @return A new tree of the results of applying the given function over this tree and the given tree, position-wise. */ public <B, C> Tree<C> zipWith(final Tree<B> bs, final F<A, F<B, C>> f) { return zipWith(bs, uncurryF2(f)); } /** * Folds a Tree<A> into a Tree<B> by applying the function f from the bottom of the Tree to the top * * @param t A tree to fold from the bottom to the top. * @param f A function transforming the current node and a stream of already transformed nodes (its children) into a new node * @return The folded tree */ public static <A, B> Tree<B> bottomUp(Tree<A> t, final F<P2<A, Stream<B>>, B> f) { final F<Tree<A>, Tree<B>> recursiveCall = new F<Tree<A>, Tree<B>>() { @Override public Tree<B> f(Tree<A> a) { return bottomUp(a, f); } }; final Stream<Tree<B>> tbs = t.subForest()._1().map(recursiveCall); return Tree.node(f.f(P.p(t.root(), tbs.map(Tree.<B> getRoot()))), tbs); } /** * @return a function getting the root of a Tree */ private static <A> F<Tree<A>, A> getRoot() { return new F<Tree<A>, A>() { @Override public A f(Tree<A> a) { return a.root(); } }; } }