Merge pull request #48 from kemitix/generalised-tree

[tree] Add a generalised tree

LICENSE.txt

@@ -1,7 +1,7 @@
 /**
  * The MIT License (MIT)
  *
- * Copyright (c) 2017 Paul Campbell
+ * Copyright (c) 2018 Paul Campbell
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
  * and associated documentation files (the "Software"), to deal in the Software without restriction,

README.org

@@ -2,26 +2,32 @@
 
 ** TypeAlias, Maybe and Result for Java.
 
- [[https://oss.sonatype.org/content/repositories/releases/net/kemitix/mon][file:https://img.shields.io/nexus/r/https/oss.sonatype.org/net.kemitix/mon.svg?style=for-the-badge]]
+   [[https://oss.sonatype.org/content/repositories/releases/net/kemitix/mon][file:https://img.shields.io/nexus/r/https/oss.sonatype.org/net.kemitix/mon.svg?style=for-the-badge]]
- [[https://search.maven.org/#search%7Cga%7C1%7Cg%3A%22net.kemitix%22%20AND%20a%3A%22mon%22][file:https://img.shields.io/maven-central/v/net.kemitix/mon.svg?style=for-the-badge]]
+   [[https://search.maven.org/#search%7Cga%7C1%7Cg%3A%22net.kemitix%22%20AND%20a%3A%22mon%22][file:https://img.shields.io/maven-central/v/net.kemitix/mon.svg?style=for-the-badge]]
 
- [[https://sonarcloud.io/dashboard?id=net.kemitix%3Amon][file:https://img.shields.io/sonar/https/sonarcloud.io/net.kemitix%3Amon/coverage.svg?style=for-the-badge#.svg]]
+   [[https://sonarcloud.io/dashboard?id=net.kemitix%3Amon][file:https://img.shields.io/sonar/https/sonarcloud.io/net.kemitix%3Amon/coverage.svg?style=for-the-badge#.svg]]
- [[https://sonarcloud.io/dashboard?id=net.kemitix%3Amon][file:https://img.shields.io/sonar/https/sonarcloud.io/net.kemitix%3Amon/tech_debt.svg?style=for-the-badge#.svg]]
+   [[https://sonarcloud.io/dashboard?id=net.kemitix%3Amon][file:https://img.shields.io/sonar/https/sonarcloud.io/net.kemitix%3Amon/tech_debt.svg?style=for-the-badge#.svg]]
- [[https://sonarcloud.io/dashboard?id=net.kemitix%3Amon][file:https://sonarcloud.io/api/project_badges/measure?project=net.kemitix%3Amon&metric=sqale_rating#.svg]]
+   [[https://sonarcloud.io/dashboard?id=net.kemitix%3Amon][file:https://sonarcloud.io/api/project_badges/measure?project=net.kemitix%3Amon&metric=sqale_rating#.svg]]
- [[https://sonarcloud.io/dashboard?id=net.kemitix%3Amon][file:https://sonarcloud.io/api/project_badges/measure?project=net.kemitix%3Amon&metric=alert_status#.svg]]
+   [[https://sonarcloud.io/dashboard?id=net.kemitix%3Amon][file:https://sonarcloud.io/api/project_badges/measure?project=net.kemitix%3Amon&metric=alert_status#.svg]]
- [[https://sonarcloud.io/dashboard?id=net.kemitix%3Amon][file:https://sonarcloud.io/api/project_badges/measure?project=net.kemitix%3Amon&metric=reliability_rating#.svg]]
+   [[https://sonarcloud.io/dashboard?id=net.kemitix%3Amon][file:https://sonarcloud.io/api/project_badges/measure?project=net.kemitix%3Amon&metric=reliability_rating#.svg]]
- [[https://sonarcloud.io/dashboard?id=net.kemitix%3Amon][file:https://sonarcloud.io/api/project_badges/measure?project=net.kemitix%3Amon&metric=security_rating#.svg]]
+   [[https://sonarcloud.io/dashboard?id=net.kemitix%3Amon][file:https://sonarcloud.io/api/project_badges/measure?project=net.kemitix%3Amon&metric=security_rating#.svg]]
- [[https://sonarcloud.io/dashboard?id=net.kemitix%3Amon][file:https://sonarcloud.io/api/project_badges/measure?project=net.kemitix%3Amon&metric=sqale_index#.svg]]
+   [[https://sonarcloud.io/dashboard?id=net.kemitix%3Amon][file:https://sonarcloud.io/api/project_badges/measure?project=net.kemitix%3Amon&metric=sqale_index#.svg]]
- [[https://sonarcloud.io/dashboard?id=net.kemitix%3Amon][file:https://sonarcloud.io/api/project_badges/measure?project=net.kemitix%3Amon&metric=vulnerabilities#.svg]]
+   [[https://sonarcloud.io/dashboard?id=net.kemitix%3Amon][file:https://sonarcloud.io/api/project_badges/measure?project=net.kemitix%3Amon&metric=vulnerabilities#.svg]]
- [[https://sonarcloud.io/dashboard?id=net.kemitix%3Amon][file:https://sonarcloud.io/api/project_badges/measure?project=net.kemitix%3Amon&metric=bugs#.svg]]
+   [[https://sonarcloud.io/dashboard?id=net.kemitix%3Amon][file:https://sonarcloud.io/api/project_badges/measure?project=net.kemitix%3Amon&metric=bugs#.svg]]
- [[https://sonarcloud.io/dashboard?id=net.kemitix%3Amon][file:https://sonarcloud.io/api/project_badges/measure?project=net.kemitix%3Amon&metric=code_smells#.svg]]
+   [[https://sonarcloud.io/dashboard?id=net.kemitix%3Amon][file:https://sonarcloud.io/api/project_badges/measure?project=net.kemitix%3Amon&metric=code_smells#.svg]]
- [[https://sonarcloud.io/dashboard?id=net.kemitix%3Amon][file:https://sonarcloud.io/api/project_badges/measure?project=net.kemitix%3Amon&metric=ncloc#.svg]]
+   [[https://sonarcloud.io/dashboard?id=net.kemitix%3Amon][file:https://sonarcloud.io/api/project_badges/measure?project=net.kemitix%3Amon&metric=ncloc#.svg]]
 
- [[https://app.codacy.com/project/kemitix/mon/dashboard][file:https://img.shields.io/codacy/grade/d57096b0639d496aba9a7e43e7cf5b4c.svg?style=for-the-badge]]
+   [[https://app.codacy.com/project/kemitix/mon/dashboard][file:https://img.shields.io/codacy/grade/d57096b0639d496aba9a7e43e7cf5b4c.svg?style=for-the-badge]]
- [[http://i.jpeek.org/net.kemitix/mon/index.html][file:http://i.jpeek.org/net.kemitix/mon/badge.svg]]
+   [[http://i.jpeek.org/net.kemitix/mon/index.html][file:http://i.jpeek.org/net.kemitix/mon/badge.svg]]
 
+   - [Maven Usage]
+   - [TypeAlias]
+   - [Maybe]
+   - [Result]
+   - [Tree]
+   - [Either]
 
-** Maven
+** Maven Usage
 
 #+BEGIN_SRC xml
     <dependency>
@@ -798,7 +804,6 @@
                                            .thenWith(v -> () -> {throw new IOException();});
      #+END_SRC
 
-
 **** =Result<Maybe<T>> maybe(Predicate<T> predicate)=
 
      Wraps the value within the Result in a Maybe, either a Just if the
@@ -851,6 +856,75 @@
      #+END_SRC
 
 
+** Tree
+
+   A Generalised tree, where each node may or may not have an item, and may have
+   any number of sub-trees. Leaf nodes are Trees with zero sub-trees.
+
+*** Static Constructors
+
+**** =static <R> Tree<R> leaf(R item)=
+
+     Create a leaf containing the item. The leaf has no sub-trees.
+
+     #+BEGIN_SRC java
+       final Tree<String> tree = Tree.leaf("item");
+     #+END_SRC
+
+
+**** =static<R> Tree<R> of(R item, Collection<Tree<R>> subtrees)=
+
+     Create a tree containing the item and sub-trees.
+
+     #+BEGIN_SRC java
+       final Tree<String> tree = Tree.of("item", Collections.singletonList(Tree.leaf("leaf"));
+     #+END_SRC
+
+
+*** Instance Methods
+
+**** =<R> Tree<R> map(Function<T, R> f)=
+
+     Applies the function to the item within the Tree and to all sub-trees,
+     returning a new Tree.
+
+     #+BEGIN_SRC java
+       final Tree<UUID> tree = ...;
+       final Tree<String> result = tree.map(UUID::toString);
+     #+END_SRC
+
+
+**** =Optional<T> item()=
+
+     Returns the contents of the Tree node within an Optional.
+
+     #+BEGIN_SRC java
+       final Tree<Item> tree = ...;
+       final Optional<Item> result = tree.item();
+     #+END_SRC
+
+
+**** =int count()=
+
+     Returns the total number of items in the tree, including sub-trees. Null
+     items don't count.
+
+     #+BEGIN_SRC java
+       final Tree<Item> tree = ...;
+       final int result = tree.count();
+     #+END_SRC
+
+
+**** =List<Tree<T> subTrees()=
+
+     Returns a list of sub-trees within the tree.
+
+     #+BEGIN_SRC java
+       final Tree<Item> tree = ...;
+       final List<Tree<Item>> result = tree.subTrees();
+     #+END_SRC
+
+
 ** Either
 
    Allows handling a value that can be one of two types, a left value/type or a

lombok.config

@@ -1 +1,2 @@
 lombok.addGeneratedAnnotation=false
+lombok.addLombokGeneratedAnnotation=true

src/main/java/net/kemitix/mon/Functor.java

@@ -1,7 +1,7 @@
 /**
  * The MIT License (MIT)
  *
- * Copyright (c) 2017 Paul Campbell
+ * Copyright (c) 2018 Paul Campbell
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
  * and associated documentation files (the "Software"), to deal in the Software without restriction,

src/main/java/net/kemitix/mon/Mon.java

@@ -1,7 +1,7 @@
 /**
  * The MIT License (MIT)
  *
- * Copyright (c) 2017 Paul Campbell
+ * Copyright (c) 2018 Paul Campbell
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
  * and associated documentation files (the "Software"), to deal in the Software without restriction,

src/main/java/net/kemitix/mon/TypeAlias.java

@@ -1,7 +1,7 @@
 /**
  * The MIT License (MIT)
  *
- * Copyright (c) 2017 Paul Campbell
+ * Copyright (c) 2018 Paul Campbell
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
  * and associated documentation files (the "Software"), to deal in the Software without restriction,

src/main/java/net/kemitix/mon/combinator/After.java

@@ -1,7 +1,7 @@
 /**
  * The MIT License (MIT)
  *
- * Copyright (c) 2017 Paul Campbell
+ * Copyright (c) 2018 Paul Campbell
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
  * and associated documentation files (the "Software"), to deal in the Software without restriction,

src/main/java/net/kemitix/mon/combinator/Around.java

@@ -1,7 +1,7 @@
 /**
  * The MIT License (MIT)
  *
- * Copyright (c) 2017 Paul Campbell
+ * Copyright (c) 2018 Paul Campbell
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
  * and associated documentation files (the "Software"), to deal in the Software without restriction,

src/main/java/net/kemitix/mon/combinator/Before.java

@@ -1,7 +1,7 @@
 /**
  * The MIT License (MIT)
  *
- * Copyright (c) 2017 Paul Campbell
+ * Copyright (c) 2018 Paul Campbell
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
  * and associated documentation files (the "Software"), to deal in the Software without restriction,

src/main/java/net/kemitix/mon/combinator/package-info.java

@@ -1,7 +1,7 @@
 /**
  * The MIT License (MIT)
  *
- * Copyright (c) 2017 Paul Campbell
+ * Copyright (c) 2018 Paul Campbell
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
  * and associated documentation files (the "Software"), to deal in the Software without restriction,

src/main/java/net/kemitix/mon/experimental/BeanBuilder.java

@@ -1,7 +1,7 @@
 /**
  * The MIT License (MIT)
  *
- * Copyright (c) 2017 Paul Campbell
+ * Copyright (c) 2018 Paul Campbell
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
  * and associated documentation files (the "Software"), to deal in the Software without restriction,

src/main/java/net/kemitix/mon/experimental/either/Either.java

@@ -1,7 +1,7 @@
 /**
  * The MIT License (MIT)
  *
- * Copyright (c) 2017 Paul Campbell
+ * Copyright (c) 2018 Paul Campbell
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
  * and associated documentation files (the "Software"), to deal in the Software without restriction,

src/main/java/net/kemitix/mon/experimental/either/Left.java

@@ -1,7 +1,7 @@
 /**
  * The MIT License (MIT)
  *
- * Copyright (c) 2017 Paul Campbell
+ * Copyright (c) 2018 Paul Campbell
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
  * and associated documentation files (the "Software"), to deal in the Software without restriction,

src/main/java/net/kemitix/mon/experimental/either/Right.java

@@ -1,7 +1,7 @@
 /**
  * The MIT License (MIT)
  *
- * Copyright (c) 2017 Paul Campbell
+ * Copyright (c) 2018 Paul Campbell
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
  * and associated documentation files (the "Software"), to deal in the Software without restriction,

src/main/java/net/kemitix/mon/experimental/either/package-info.java

@@ -1,7 +1,7 @@
 /**
  * The MIT License (MIT)
  *
- * Copyright (c) 2017 Paul Campbell
+ * Copyright (c) 2018 Paul Campbell
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
  * and associated documentation files (the "Software"), to deal in the Software without restriction,

src/main/java/net/kemitix/mon/experimental/package-info.java

@@ -1,7 +1,7 @@
 /**
  * The MIT License (MIT)
  *
- * Copyright (c) 2017 Paul Campbell
+ * Copyright (c) 2018 Paul Campbell
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
  * and associated documentation files (the "Software"), to deal in the Software without restriction,

src/main/java/net/kemitix/mon/maybe/Just.java

@@ -1,7 +1,7 @@
 /**
  * The MIT License (MIT)
  *
- * Copyright (c) 2017 Paul Campbell
+ * Copyright (c) 2018 Paul Campbell
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
  * and associated documentation files (the "Software"), to deal in the Software without restriction,

src/main/java/net/kemitix/mon/maybe/Maybe.java

@@ -1,7 +1,7 @@
 /**
  * The MIT License (MIT)
  *
- * Copyright (c) 2017 Paul Campbell
+ * Copyright (c) 2018 Paul Campbell
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
  * and associated documentation files (the "Software"), to deal in the Software without restriction,

src/main/java/net/kemitix/mon/maybe/Nothing.java

@@ -1,7 +1,7 @@
 /**
  * The MIT License (MIT)
  *
- * Copyright (c) 2017 Paul Campbell
+ * Copyright (c) 2018 Paul Campbell
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
  * and associated documentation files (the "Software"), to deal in the Software without restriction,

src/main/java/net/kemitix/mon/maybe/package-info.java

@@ -1,7 +1,7 @@
 /**
  * The MIT License (MIT)
  *
- * Copyright (c) 2017 Paul Campbell
+ * Copyright (c) 2018 Paul Campbell
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
  * and associated documentation files (the "Software"), to deal in the Software without restriction,

src/main/java/net/kemitix/mon/package-info.java

@@ -1,7 +1,7 @@
 /**
  * The MIT License (MIT)
  *
- * Copyright (c) 2017 Paul Campbell
+ * Copyright (c) 2018 Paul Campbell
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
  * and associated documentation files (the "Software"), to deal in the Software without restriction,

src/main/java/net/kemitix/mon/result/Err.java

@@ -1,7 +1,7 @@
 /**
  * The MIT License (MIT)
  *
- * Copyright (c) 2017 Paul Campbell
+ * Copyright (c) 2018 Paul Campbell
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
  * and associated documentation files (the "Software"), to deal in the Software without restriction,

src/main/java/net/kemitix/mon/result/Result.java

@@ -1,7 +1,7 @@
 /**
  * The MIT License (MIT)
  *
- * Copyright (c) 2017 Paul Campbell
+ * Copyright (c) 2018 Paul Campbell
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
  * and associated documentation files (the "Software"), to deal in the Software without restriction,

src/main/java/net/kemitix/mon/result/Success.java

@@ -1,7 +1,7 @@
 /**
  * The MIT License (MIT)
  *
- * Copyright (c) 2017 Paul Campbell
+ * Copyright (c) 2018 Paul Campbell
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
  * and associated documentation files (the "Software"), to deal in the Software without restriction,

src/main/java/net/kemitix/mon/result/WithResultContinuation.java

@@ -1,7 +1,7 @@
 /**
  * The MIT License (MIT)
  *
- * Copyright (c) 2017 Paul Campbell
+ * Copyright (c) 2018 Paul Campbell
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
  * and associated documentation files (the "Software"), to deal in the Software without restriction,

src/main/java/net/kemitix/mon/result/package-info.java

@@ -1,7 +1,7 @@
 /**
  * The MIT License (MIT)
  *
- * Copyright (c) 2017 Paul Campbell
+ * Copyright (c) 2018 Paul Campbell
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
  * and associated documentation files (the "Software"), to deal in the Software without restriction,

src/main/java/net/kemitix/mon/tree/GeneralisedTree.java

@@ -0,0 +1,100 @@
+/**
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2018 Paul Campbell
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
+ * and associated documentation files (the "Software"), to deal in the Software without restriction,
+ * including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all copies
+ * or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
+ * INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE
+ * AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+ * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+package net.kemitix.mon.tree;
+
+import lombok.EqualsAndHashCode;
+
+import java.util.*;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+
+/**
+ * A generic tree of trees and objects.
+ *
+ * <p>Each node may contain between 0 and n objects.</p>
+ *
+ * @param <T> the type of the objects help in the tree
+ *
+ * @author Paul Campbell (pcampbell@kemitix.net)
+ */
+@EqualsAndHashCode
+class GeneralisedTree<T> implements Tree<T> {
+
+    private final T item;
+    private final List<Tree<T>> subTrees;
+
+    /**
+     * Creates a new tree.
+     *
+     * @param item the item of this node
+     * @param subTrees the sub-trees under this node
+     */
+    GeneralisedTree(final T item, final Collection<Tree<T>> subTrees) {
+        this.item = item;
+        this.subTrees = Collections.unmodifiableList(new ArrayList<>(subTrees));
+    }
+
+    /**
+     * Maps the tree using the function onto a new tree.
+     *
+     * @param f   the function to apply
+     * @param <R> the type of object held in the resulting tree
+     * @return a tree
+     */
+    @Override
+    public <R> Tree<R> map(final Function<T, R> f) {
+        return Tree.of(f.apply(item), mapSubTrees(f));
+    }
+
+    @Override
+    public Optional<T> item() {
+        return Optional.ofNullable(item);
+    }
+
+    private <R> List<Tree<R>> mapSubTrees(final Function<T, R> f) {
+        return subTrees.stream()
+                .map(subTree -> subTree.map(f::apply))
+                .collect(Collectors.toList());
+    }
+
+    /**
+     * Counts the number of items in the subtree.
+     *
+     * @return the sum of the subtrees, plus 1 if there is an item in this node
+     */
+    @Override
+    @SuppressWarnings("avoidinlineconditionals")
+    public int count() {
+        return (item != null ? 1 : 0)
+                + subTrees.stream().mapToInt(Tree::count).sum();
+    }
+
+    /**
+     * Returns a list of subtrees.
+     *
+     * @return a List of trees
+     */
+    @Override
+    public List<Tree<T>> subTrees() {
+        return subTrees;
+    }
+}

src/main/java/net/kemitix/mon/tree/Tree.java

@@ -0,0 +1,88 @@
+/**
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2018 Paul Campbell
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
+ * and associated documentation files (the "Software"), to deal in the Software without restriction,
+ * including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all copies
+ * or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
+ * INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE
+ * AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+ * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+package net.kemitix.mon.tree;
+
+import net.kemitix.mon.Functor;
+
+import java.util.Collection;
+import java.util.Collections;
+import java.util.List;
+import java.util.Optional;
+import java.util.function.Function;
+
+/**
+ * A tree of objects.
+ *
+ * @param <T> the type of the objects help in the tree
+ *
+ * @author Paul Campbell (pcampbell@kemitix.net)
+ */
+public interface Tree<T> extends Functor<T, Tree<?>> {
+
+    /**
+     * Create a new generalised tree to hold object of a type.
+     *
+     * @param item the item for the leaf node
+     * @param <R> the type of the object to be held in the tree
+     *
+     * @return a empty generalised tree
+     */
+    public static <R> Tree<R> leaf(final R item) {
+        return new GeneralisedTree<>(item, Collections.emptyList());
+    }
+
+    /**
+     * Create a new generalised tree to hold the single item.
+     *
+     * @param item the item for the tree node
+     * @param subtrees the subtrees of the tree node
+     * @param <R> the type of the item
+     * @return a leaf node of a generalised tree
+     */
+    public static <R> Tree<R> of(final R item, final Collection<Tree<R>> subtrees) {
+        return new GeneralisedTree<>(item, subtrees);
+    }
+
+    @Override
+    public abstract <R> Tree<R> map(Function<T, R> f);
+
+    /**
+     * Return the item within the node of the tree, if present.
+     *
+     * @return an Optional containing the item
+     */
+    public abstract Optional<T> item();
+
+    /**
+     * Count the number of item in the tree, including subtrees.
+     *
+     * @return the number of items
+     */
+    public abstract int count();
+
+    /**
+     * The subtrees of the tree.
+     *
+     * @return a list of Trees
+     */
+    public abstract List<Tree<T>> subTrees();
+}

src/main/java/net/kemitix/mon/tree/package-info.java

@@ -0,0 +1,28 @@
+/**
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2018 Paul Campbell
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
+ * and associated documentation files (the "Software"), to deal in the Software without restriction,
+ * including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all copies
+ * or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
+ * INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE
+ * AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+ * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+/**
+ * Tree data structures.
+ *
+ * @author Paul Campbell (pcampbell@kemitix.net)
+ */
+
+package net.kemitix.mon.tree;

src/test/java/net/kemitix/mon/Address.java

@@ -1,7 +1,7 @@
 /**
  * The MIT License (MIT)
  *
- * Copyright (c) 2017 Paul Campbell
+ * Copyright (c) 2018 Paul Campbell
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
  * and associated documentation files (the "Software"), to deal in the Software without restriction,

src/test/java/net/kemitix/mon/Customer.java

@@ -1,7 +1,7 @@
 /**
  * The MIT License (MIT)
  *
- * Copyright (c) 2017 Paul Campbell
+ * Copyright (c) 2018 Paul Campbell
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
  * and associated documentation files (the "Software"), to deal in the Software without restriction,

src/test/java/net/kemitix/mon/tree/GeneralisedTreeTest.java

@@ -0,0 +1,87 @@
+package net.kemitix.mon.tree;
+
+import org.assertj.core.api.WithAssertions;
+import org.junit.Test;
+
+import java.util.UUID;
+
+import static java.util.Arrays.asList;
+import static java.util.Collections.singletonList;
+
+public class GeneralisedTreeTest implements WithAssertions {
+
+    @Test
+    public void canCreateAnEmptyLeaf() {
+        //when
+        final Tree<String> leaf = Tree.leaf(null);
+        //then
+        assertThat(leaf.item()).isEmpty();
+    }
+
+    @Test
+    public void canCreateANonEmptyLeaf() {
+        //given
+        final String item = "item";
+        //when
+        final Tree<String> leaf = Tree.leaf(item);
+        //then
+        assertThat(leaf.item()).contains(item);
+    }
+
+    @Test
+    public void emptyLeafHasCountZero() {
+        //given
+        final Tree<Object> tree = Tree.leaf(null);
+        //when
+        final int count = tree.count();
+        //then
+        assertThat(count).isZero();
+    }
+
+    @Test
+    public void nonEmptyLeafHasCountOne() {
+        //given
+        final Tree<String> tree = Tree.leaf("value");
+        //when
+        final int count = tree.count();
+        //then
+        assertThat(count).isEqualTo(1);
+    }
+
+    @Test
+    public void canCreateTreeWithSubTrees() {
+        //given
+        final String treeItem = "tree";
+        final String leafItem = "leaf";
+        //when
+        final Tree<String> tree = Tree.of(treeItem, singletonList(Tree.leaf(leafItem)));
+        //then
+        assertThat(tree.subTrees()).containsExactly(Tree.leaf(leafItem));
+    }
+
+    @Test
+    public void canMapNestedTrees() {
+        //given
+        final UUID uid1 = UUID.randomUUID();
+        final UUID uid2 = UUID.randomUUID();
+        final UUID uid3 = UUID.randomUUID();
+        final String sid1 = uid1.toString();
+        final String sid2 = uid2.toString();
+        final String sid3 = uid3.toString();
+        final Tree<UUID> tree = Tree.of(
+                uid1,
+                asList(
+                        Tree.leaf(uid2),
+                        Tree.leaf(uid3)));
+        //when
+        final Tree<String> result = tree.map(UUID::toString);
+        //then
+        assertThat(result).isEqualTo(Tree.of(
+                sid1,
+                asList(
+                        Tree.leaf(sid2),
+                        Tree.leaf(sid3)))
+        );
+    }
+
+}