Bump kemitix-maven-tiles to 3.0.0 and kemitix-checkstye to 5.5.0 (#181)

* Bump kemitix-maven-tiles to 3.0.0

* Bump kemitix-maven-tiles to 3.0.1

* Bump kemitix-checkstyle to 5.5.0

* Docs updates - more to come

* Checkstyle and PMD compliance updates

* result: map on Success should become Error on exception

* README: reformat in markdown

README.md

@@ -0,0 +1,994 @@
+# Mon
+
+Wrapper, TypeAlias, Result, Lazy, Maybe and combinators for Java.
+
+![GitHub release (latest by date)](
+https://img.shields.io/github/v/release/kemitix/mon?style=for-the-badge)
+![GitHub Release Date](
+https://img.shields.io/github/release-date/kemitix/mon?style=for-the-badge)
+
+[![Nexus](
+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/)
+[![Maven-Central](
+https://img.shields.io/maven-central/v/net.kemitix/mon.svg?style=for-the-badge)](
+https://search.maven.org/artifact/net.kemitix/mon)
+
+- [Maven Usage](#Maven-Usage)
+- [Wrapper](#Wrapper)
+- [TypeAlias](#TypeAlias)
+- [Maybe](#Maybe)
+- [Result](#Result)
+- [Tree](#Tree)
+
+---
+## Maven Usage
+
+``` xml
+<dependency>
+    <groupId>net.kemitix</groupId>
+    <artifactId>mon</artifactId>
+    <version>${mon.version}</version>
+</dependency>
+```
+
+---
+## Wrapper
+
+A simple `@FunctionalInterface` that contains a value. Can be used to implement
+a form of type-alias in Java.
+
+In Haskell, it is possible to create an alias for a Type, and to then use
+that alias with the same behaviour as the original, except that the compiler
+doesn't treat the alias as the same Type and will generate compiler errors
+if you try to use them together. e.g.:
+
+``` haskell
+newtype PhoneNumber = PhoneNumber String
+newtype Name = Name String
+newtype PhoneBookEntry = PhoneBookEntry (Name, PhoneNumber)
+newtype PhoneBook = PhoneBook [PhoneBookEntry]
+```
+
+In Java, we don't have the ability to have that true alias, so `Wrapper` simply
+wraps the value within a new type. It's as close as I could get to a Haskell
+type alias in Java.
+
+The benefits of using `Wrapper` in this way are:
+
+- encapsulation of the wrapped type when passing references through code
+  that doesn't need to access the actual value, but only to pass it on
+- type-safe parameters where you would otherwise be passing generic `String`s,
+  `Integer`s, `List`s, or other general classes
+- less verbose than implementing your own
+
+### Example
+
+``` java
+interface PhoneNumber extends Wrapper<String> {}
+
+PhoneNumber pn = () -> "01234 567890";
+String v = pn.value();
+```
+
+### Instance Methods
+
+#### `T value()`
+
+Returns the value in the `Wrapper`.
+
+---
+## TypeAlias
+
+This was a precursor to `Wrapper` and should be considered deprecated. It is
+also a form of wrapper, but is also a Monadic wrapper, unlike `Wrapper`.
+
+### Example
+
+``` java
+class PhoneNumber extends TypeAlias<String> {
+    private PhoneNumber(final String value) {
+        super(value);
+    }
+    public static PhoneNumber of(final String phoneNumber) {
+        return new PhoneNumber(phoneNumber);
+    }
+}
+
+PhoneNumber pn = PhoneNumber.of("01234 567890");
+String v = pn.getValue();
+```
+
+### Instance Methods
+
+#### `final <R> R map(final Function<T, R> f)`
+
+Map the `TypeAlias` into another value.
+
+``` java
+StudentId studentId = StudentId.of(123);
+String idString = studentId.map(id -> String.valueOf(id));
+
+class StudentId extends TypeAlias<Integer> {
+    private StudentId(Integer value) {
+        super(value);
+    }
+    static StudentId of(Integer id) {
+        return new StudentId(id);
+    }
+}
+```
+---
+#### `final <R, U extends TypeAlias<R>> U flatMap(final Function<T, U> f)`
+
+Map the `TypeAlias` into another `TypeAlias`.
+
+``` java
+StudentId studentId = StudentId.of(123);
+StudentName studentName = studentId.flatMap(id -> getStudentName(id));
+
+class StudentName extends TypeAlias<String> {
+    private StudentName(String value) {
+        super(value);
+    }
+    static StudentName of(final String name) {
+        return new StudentName(name);
+    }
+}
+```
+---
+#### `T getValue()`
+
+Get the value of the `TypeAlias`.
+
+``` java
+String name = studentName.getValue();
+```
+---
+## Maybe
+
+Allows specifying that a value may or may not be present. Similar to
+`Optional`. `Maybe` provides additional methods that `Optional` doesn't (as of
+Java 8): `isNothing()`, `stream()`, `ifNothing()` and `match()`. `Maybe` does 
+not have a `get()` method.
+
+`Maybe` is a Monad.
+
+Unlike `Optional`, when a `map()` results in a `null`, the `Maybe` will
+continue to be a `Just` (i.e. have a value - that value is `null`). `Optional` 
+would switch to being empty.
+
+### Example
+
+``` java
+import net.kemitix.mon.maybe.Maybe;
+
+import java.util.function.Function;
+import java.util.function.Predicate;
+
+class MaybeExample {
+
+    public static void main(String[] args) {
+        Maybe.just(countArgs(args))
+             .filter(isEven())
+             .map(validMessage())
+             .match(
+                 just -> System.out.println(just),
+                 () -> System.out.println("Not an valid value")
+             );
+    }
+
+    private static Function<Integer, String> validMessage() {
+        return v -> String.format("Value %d is even", v);
+    }
+
+    private static Predicate<Integer> isEven() {
+        return v -> v % 2 == 0;
+    }
+
+    private static Integer countArgs(String[] args) {
+        return args.length;
+    }
+}
+```
+
+In the above example, the number of command line arguments are counted, if
+there are an even number of them then a message is created and printed by
+the `Consumer` parameter in the `match` call. If there is an odd number of
+arguments, then the filter will return `Maybe.nothing()`, meaning that the
+`nothing` drops straight through the `map` and triggers the `Runnable` parameter
+in the `match` call.
+
+### Static Constructors
+
+#### `static <T> Maybe<T> maybe(T value)`
+
+Create a Maybe for the value that may or may not be present.
+
+Where the value is `null`, that is taken as not being present.
+
+``` java
+Maybe<Integer> just = Maybe.maybe(1);
+Maybe<Integer> nothing = Maybe.maybe(null);
+```
+---
+#### `static <T> Maybe<T> just(T value)`
+
+Create a `Maybe` for the value that is present.
+
+The `value` must not be `null` or a `NullPointerException` will be thrown.
+
+``` java
+Maybe<Integer> just = Maybe.just(1);
+```
+---
+#### `static <T> Maybe<T> nothing()`
+
+Create a `Maybe` for a lack of a value.
+
+``` java
+Maybe<Integer> nothing = Maybe.nothing();
+```
+---
+#### `static <T> Maybe<T> findFirst(Stream<T> stream)`
+
+Creates a `Maybe` from the first item in the stream, or nothing if the stream 
+is empty.
+
+``` java
+Maybe<Integer> just3   = Maybe.findFirst(Stream.of(3, 4, 2, 4));
+Maybe<Integer> nothing = Maybe.findFirst(Stream.empty());
+```
+---
+### Instance Methods
+
+#### `Maybe<T> filter(Predicate<T> predicate)`
+
+Filter a Maybe by the predicate, replacing with Nothing when it fails.
+
+``` java
+Maybe<Integer> maybe = Maybe.maybe(getValue())
+                            .filter(v -> v % 2 == 0);
+```
+---
+#### `<R> Maybe<R> map(Function<T,R> f)`
+
+Applies the function to the value within the `Maybe`, returning the result 
+within another `Maybe`.
+
+``` java
+Maybe<Integer> maybe = Maybe.maybe(getValue())
+                            .map(v -> v * 100);
+```
+---
+#### `<R> Maybe<R> flatMap(Function<T,Maybe<R>> f)`
+
+Applies the function to the value within the `Maybe`, resulting in another 
+`Maybe`, then flattens the resulting `Maybe<Maybe<T>>` into `Maybe<T>`.
+
+``` java
+Maybe<Integer> maybe = Maybe.maybe(getValue())
+                            .flatMap(v -> Maybe.maybe(getValueFor(v)));
+```
+---
+#### `void match(Consumer<T> just, Runnable nothing)`
+
+Matches the `Maybe`, either to `just` or `nothing`, and performs either the
+`Consumer`, for a `Just` value, or the `Runnable` for a `Nothing` value.
+
+``` java
+Maybe.maybe(getValue())
+     .match(
+         just -> workWithValue(just),
+           () -> nothingToWorkWith()
+     );
+```
+---
+#### `<R> R matchValue(Function<T, R> justMatcher, Supplier<R> nothingMatcher)`
+
+Matches the `Maybe`, either `Just` or `Nothing`, and performs either the
+`Function`, for a `Just` value, or the `Supplier` for a `Nothing` value, 
+returning the result.
+
+``` java
+String value = Maybe.maybe(getValue())
+                    .matchValue(
+                                just -> Integer.toString(just),
+                                  () -> "nothing"
+                    );
+```
+---
+#### `T orElse(T otherValue)`
+
+A value to use when the `Maybe` is `Nothing`.
+
+``` java
+Integer value = Maybe.maybe(getValue())
+                     .orElse(1);
+```
+---
+#### `T orElseGet(Supplier<T> otherValueSupplier)`
+
+Provide a value to use when the `Maybe` is `Nothing`.
+
+``` java
+Integer value = Maybe.maybe(getValue())
+                     .orElseGet(() -> getDefaultValue());
+```
+---
+#### `T or(Supplier<Maybe<T> alternative)`
+
+Provide an alternative `Maybe` to use when the `Maybe` is `Nothing`.
+
+``` java
+Maybe<Integer> value = Maybe.maybe(getValue())
+                            .or(() -> Maybe.just(defaultValue));
+```
+---
+#### `void orElseThrow(Supplier<Exception> error)`
+
+Throw the exception if the `Maybe` is `Nothing`.
+
+``` java
+Integer value = Maybe.maybe(getValue())
+                     .orElseThrow(() -> new RuntimeException("error"));
+```
+---
+#### `Maybe<T> peek(Consumer<T> consumer)`
+
+Provide the value within the `Maybe`, if it exists, to the `Consumer`, and
+returns the original `Maybe`.
+
+``` java
+Maybe<Integer> maybe = Maybe.maybe(getValue())
+                            .peek(v -> v.foo());
+```
+#### `void ifNothing(Runnable runnable)`
+
+Run the `Runnable` if the `Maybe` is `Nothing`, otherwise do nothing.
+
+``` java
+Maybe.maybe(getValue())
+     .ifNothing(() -> doSomething());
+```
+---
+#### `Stream<T> stream()`
+
+Converts the `Maybe` into either a single value stream or an empty stream.
+
+``` java
+Stream<Integer> stream = Maybe.maybe(getValue())
+                              .stream();
+```
+---
+#### `boolean isJust()`
+
+Checks if the `Maybe` is a `Just`.
+
+``` java
+boolean isJust = Maybe.maybe(getValue())
+                      .isJust();
+```
+---
+#### `boolean isNothing()`
+
+Checks if the `Maybe` is `Nothing`.
+
+``` java
+boolean isNothing = Maybe.maybe(getValue())
+                         .isNothing();
+```
+---
+#### `Optional<T> toOptional()`
+
+Convert the `Maybe` to an `Optional`.
+
+``` java
+Optional<Integer> optional = Maybe.maybe(getValue())
+                                  .toOptional();
+```
+---
+## Result
+
+Allows handling error conditions without the need to `catch` exceptions.
+
+When a `Result` is returned from a method, it will contain one of two values.
+Either the actual result, or an error in the form of an `Exception`. The
+exception is returned within the `Result` and is not thrown.
+
+`Result` is a Monad.
+
+### Example
+
+``` java
+import net.kemitix.mon.result.Result;
+
+import java.io.IOException;
+
+class ResultExample implements Runnable {
+
+    public static void main(final String[] args) {
+        new ResultExample().run();
+    }
+
+    @Override
+    public void run() {
+        Result.of(() -> callRiskyMethod())
+              .flatMap(state -> doSomething(state))
+              .match(
+                  success -> System.out.println(success),
+                  error -> error.printStackTrace()
+              );
+    }
+
+    private String callRiskyMethod() throws IOException {
+        return "I'm fine";
+    }
+
+    private Result<String> doSomething(final String state) {
+        return Result.of(() -> state + ", it's all good.");
+    }
+
+}
+```
+
+In the above example the string `"I'm fine"` is returned by
+`callRiskyMethod()` within a successful `Result`. The `.flatMap()` call,
+unwraps that `Result` and, as it is a success, passes the contents to
+`doSomething()`, which in turn returns a `Result` that the `.flatMap()` call
+returns. `match()` is called on the `Result` and, being a success, will call
+the success `Consumer`.
+
+Had `callRiskyMethod()` thrown an exception it would have been caught by the
+`Result.of()` method, which would then return an error `Result`. An error
+`Result` would skip the `flatMap` and continue at the `match()` where it
+would have called the error `Consumer`.
+
+### Static Constructors
+
+#### `static <T> Result<T> of(Callable<T> callable)`
+
+Create a `Result` for the output of the `Callable`.
+
+If the `Callable` throws an `Exception`, then the `Result` will be an error and
+will contain that exception.
+
+This will be the main starting point for most `Result`s where the callable
+could throw an `Exception`.
+
+``` java
+Result<Integer> okay = Result.of(() -> 1);
+Result<Integer> error = Result.of(() -> {throw new RuntimeException();});
+```
+---
+#### `static <T> Result<T> ok(T value)`
+
+Create a `Result` for a success.
+
+Use this where you have a value that you want to place into the `Result` context.
+
+``` java
+Result<Integer> okay = Result.ok(1);
+```
+---
+#### `static <T> Result<T> error(Throwable error)`
+
+Create a `Result` for an error.
+
+``` java
+Result<Integer> error = Result.error(new RuntimeException());
+```
+---
+### Static Methods
+
+These static methods provide integration with the `Maybe` class.
+
+#### `static <T> Maybe<T> toMaybe(Result<T> result)`
+
+Creates a `Maybe` from the `Result`, where the `Result` is a success, then
+the `Maybe` will be a `Just` contain the value of the `Result`. However, if the 
+`Result` is an error, then the `Maybe` will be `Nothing`.
+
+``` java
+Result<Integer> result = Result.of(() -> getValue());
+Maybe<Integer> maybe   = Result.toMaybe(result);
+```
+---
+#### `static <T> Result<T> fromMaybe(Maybe<T> maybe, Supplier<Throwable> error)`
+
+Creates a `Result` from the `Maybe`, where the `Result` will be an error
+if the `Maybe` is nothing. Where the `Maybe` is nothing, then the
+`Supplier<Throwable>` will provide the error for the `Result`.
+
+``` java
+Maybe<Integer> maybe = Maybe.maybe(getValue());
+Result<Integer> result = Result.fromMaybe(maybe, 
+        () -> new NoSuchFileException("filename"));
+```
+---
+#### `static <T> Result<Maybe<T>> invert(Maybe<Result<T>> maybeResult)`
+
+Swaps the `Result` within a `Maybe`, so that `Result` contains a `Maybe`.
+
+``` java
+Maybe<Result<Integer>> maybe = Maybe.maybe(Result.of(() -> getValue()));
+Result<Maybe<Integer>> result = Result.invert(maybe);
+```
+---
+#### `static <T,R> Result<Maybe<R>> flatMapMaybe(Result<Maybe<T>> maybeResult, Function<Maybe<T>,Result<Maybe<R>>> f)`
+
+Applies the function to the contents of a `Maybe` within the `Result`.
+
+``` java
+Result<Maybe<Integer>> result = Result.of(() -> Maybe.maybe(getValue()));
+Result<Maybe<Integer>> maybeResult = Result.flatMapMaybe(result,
+        maybe -> Result.of(() -> maybe.map(v -> v * 2)));
+```
+---
+### Instance Methods
+
+#### `<R> Result<R> map(Function<T,R> f)`
+
+If the `Result` is a success, then apply the function to the value within the 
+`Result`, returning the result within another `Result`. If the `Result` is an 
+error, then return the error.
+
+``` java
+Result<String> result = Result.of(() -> getValue())
+                              .map(v -> String.valueOf(v));
+```
+---
+#### `<R> Result<R> flatMap(Function<T,Result<R>> f)`
+
+If the `Result` is a success, then return a new `Result` containing the result
+of applying the function to the contents of the `Result`. If the `Result` is an 
+error, then return the error.
+
+``` java
+Result<String> result = 
+        Result.of(() -> getValue())
+              .flatMap(v -> Result.of(() -> String.valueOf(v)));
+```
+---
+#### `<R> Result<R> andThen(Function<T,Callable<R>> f)`
+
+Maps a successful `Result` to another `Result` using a `Callable` that is able
+to throw a checked exception.
+
+``` java
+Result<String> result =
+        Result.of(() -> getValue())
+              .andThen(v -> () -> {throw new IOException();});
+```
+---
+#### `void match(Consumer<T> onSuccess, Consumer<Throwable> onError)`
+
+Matches the `Result`, either success or error, and supplies the appropriate
+`Consumer` with the value or error.
+
+``` java
+Result.of(() -> getValue())
+      .match(
+          success -> System.out.println(success),
+          error -> System.err.println(error.getMessage())
+      );
+```
+---
+#### `Result<T> recover(Function<Throwable,Result<T>> f)`
+
+Provide a way to attempt to recover from an error state.
+
+``` java
+Result<Integer> result = Result.of(() -> getValue())
+                               .recover(e -> Result.of(() -> getSafeValue(e)));
+```
+---
+#### `Result<T> peek(Consumer<T> consumer)`
+
+Provide the value within the Result, if it is a success, to the `Consumer`,
+and returns this Result.
+
+``` java
+Result<Integer> result = Result.of(() -> getValue())
+                               .peek(v -> System.out.println(v));
+```
+---
+#### `Result<T> thenWith(Function<T,WithResultContinuation<T>> f)`
+
+Perform the continuation with the current `Result` value then return the
+current `Result`, assuming there was no error in the continuation.
+
+``` java
+Result<Integer> result =
+        Result.of(() -> getValue())
+              .thenWith(v -> () -> System.out.println(v))
+              .thenWith(v -> () -> {throw new IOException();});
+```
+---
+#### `Result<Maybe<T>> maybe(Predicate<T> predicate)
+
+Wraps the value within the `Result` in a `Maybe`, either a `Just` if the
+predicate is true, or `Nothing`.
+
+``` java
+Result<Maybe<Integer>> result = Result.of(() -> getValue())
+                                      .maybe(v -> v % 2 == 0);
+```
+---
+#### `T orElseThrow()`
+
+Extracts the successful value from the `Result`, or throws the error
+within a `CheckedErrorResultException`.
+
+``` java
+Integer result = Result.of(() -> getValue())
+                       .orElseThrow();
+```
+---
+#### `<E extends Exception> T orElseThrow(Class<E> type) throws E`
+
+Extracts the successful value from the `Result`, or throws the error when it
+is of the given type. Any other errors will be thrown inside an
+`UnexpectedErrorResultException`.
+
+``` java
+Integer result = Result.of(() -> getValue())
+                       .orElseThrow(IOException.class);
+```
+---
+#### `T orElseThrowUnchecked()`
+
+Extracts the successful value from the `Result`, or throws the error within
+an `ErrorResultException`.
+
+``` java
+Integer result = Result.of(() -> getValue())
+                       .orElseThrowUnchecked();
+```
+---
+#### `void onError(Consumer<Throwable> errorConsumer)`
+
+A handler for error states. If the `Result` is an error, then supply the error
+to the `Consumer`. Does nothing if the `Result` is a success.
+
+``` java
+Result.of(() -> getValue())
+      .onError(e -> handleError(e));
+```
+---
+#### `boolean isOkay()`
+
+Checks if the `Result` is a success.
+
+``` java
+boolean isOkay = Result.of(() -> getValue())
+                       .isOkay();
+```
+---
+#### `boolean isError()`
+
+Checks if the `Result` is an error.
+
+``` java
+boolean isError = Result.of(() -> getValue())
+                        .isError();
+```
+---
+## 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.
+
+``` java
+Tree<String> tree = Tree.leaf("item");
+```
+---
+#### `static<R> Tree<R> of(R item, Collection<Tree<R>> subtrees)`
+
+Create a tree containing the item and sub-trees.
+
+``` java
+Tree<String> tree = Tree.of("item", Collections.singletonList(Tree.leaf("leaf"));
+```
+---
+#### `static <B> TreeBuilder<B> builder(final Class<B> type)`
+
+Create a new `TreeBuilder` starting with an empty tree.
+
+``` java
+TreeBuilder<Integer> builder = Tree.builder(Integer.class);
+```
+---
+#### `static <B> TreeBuilder<B> builder(final Tree<B> tree)`
+
+Create a new `TreeBuilder` for the given tree.
+
+``` java
+Tree<Integer> tree = ...;
+TreeBuilder<Integer> builder = Tree.builder(tree);
+```
+---
+### 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`.
+
+``` java
+Tree<UUID> tree = ...;
+Tree<String> result = tree.map(UUID::toString);
+```
+---
+#### `Maybe<T> item()`
+
+Returns the contents of the `Tree` node within a `Maybe`.
+
+``` java
+Tree<Item> tree = ...;
+Maybe<Item> result = tree.item();
+```
+---
+#### `int count()`
+
+Returns the total number of items in the `Tree`, including sub-trees. `Null`
+items don't count.
+
+``` java
+Tree<Item> tree = ...;
+int result = tree.count();
+```
+---
+#### `List<Tree<T> subTrees()`
+
+Returns a list of sub-trees within the `Tree`.
+
+``` java
+Tree<Item> tree = ...;
+List<Tree<Item>> result = tree.subTrees();
+```
+---
+## TreeBuilder
+
+A mutable builder for a `Tree`. Each `TreeBuilder` allows modification of a
+single `Tree` node. You can use the `select(childItem)` method to get a
+`TreeBuilder` for the subtree that has the given child item.
+
+### Example
+
+``` java
+TreeBuilder<Integer> builder = Tree.builder();
+builder.set(12).addChildren(Arrays.asList(1, 3, 5, 7));
+TreeBuilder<Integer> builderFor3 = builder.select(3);
+builderFor3.addChildren(Arrays.asList(2, 4));
+Tree<Integer> tree = builder.build();
+```
+
+Will produce a `Tree` like:
+
+![](images/treebuilder-example.svg)
+---
+### Static Constructors
+
+None. The `TreeBuilder` is instantiated by `Tree.builder()`.
+
+### Instance Methods
+
+#### `Tree<T> build()`
+
+Create the immutable Tree.
+
+``` java
+TreeBuilder<Integer> builder = Tree.builder();
+Tree<Integer> tree = builder.build();
+```
+---
+#### `TreeBuilder<T> item(T item)`
+
+Set the current `Tree`'s item and return the `TreeBuilder`.
+
+#### `TreeBuilder<T> add(Tree<T> subtree)`
+
+Adds the subtree to the current tree.
+
+#### `TreeBuilder<T> addChild(T childItem)`
+
+Add the Child item as a sub-Tree.
+
+#### `TreeBuilder<T> addChildren(List<T> children)`
+
+Add all the child items as subTrees.
+
+#### `Maybe<TreeBuilder<T>> select(T childItem)`
+
+Create a `TreeBuilder` for the subTree of the current `Tree` that has the
+childItem.
+
+## Lazy
+
+A lazily evaluated expression. Using a `Supplier` to provide the value, only
+evaluates the value when required, and never more than once.
+
+### Static Constructors
+
+#### `static <R> Lazy<R> of(Supplier<R> supplier)`
+
+Create a new `Lazy` value from the `Supplier`.
+
+``` java
+Suppler<UUID> supplier = ...;
+Lazy<UUID> lazy = Lazy.of(supplier);
+```
+
+### Instance Methods
+
+#### `boolean isEvaluated()`
+
+Checks if the value has been evaluated.
+
+``` java
+Lazy<UUID> lazy = ...;
+boolean isEvaluated = lazy.isEvaluated();
+```
+---
+#### `T value()`
+
+The value, evaluating it if necessary.
+
+``` java
+Lazy<UUID> lazy = ...;
+UUID value = lazy.value();
+```
+---
+#### `<R> Lazy<R> map(Function<T, R> f)`
+
+Maps the `Lazy` instance into a new `Lazy` instance using the `Function`.
+
+``` java
+Lazy<UUID> uuidLazy = ...;
+Lazy<String> stringLazy = uuidLazy.map(v -> v.toString());
+```
+---
+## Either
+
+Allows handling a value that can be one of two types, a left value/type, or a
+right value/type.
+
+`Either` *is not* a Monad.
+
+When an `Either` is returned from a method it will contain either a left or a
+right.
+
+Where the `Either` is used to represent success/failure, the left case is, by
+convention, used to indicate the error, and right the success. An alternative
+is to use the `Result` which more clearly distinguishes success from failure.
+---
+### Static Constructors
+
+#### `static <L, R> Either<L, R> left(final L l)`
+
+Create a new `Either` holding a left value.
+
+``` java
+Either<Integer, String> left = Either.left(getIntegerValue());
+```
+---
+#### `static <L, R> Either<L, R> right(final R r)`
+
+Create a new `Either` holding a right value.
+
+``` java
+Either<Integer, String> right = Either.right(getStringValue());
+```
+---
+### Instance Methods
+
+#### `boolean isLeft()`
+
+Checks if the `Either` holds a left value.
+
+``` java
+Either<Integer, String> either = Either.left(getIntegerValue());
+boolean leftIsLeft = either.isLeft();
+boolean rightIsLeft = either.isLeft();
+```
+---
+#### `boolean isRight()`
+
+Checks if the `Either` holds a right value.
+
+``` java
+Either<Integer, String> either = Either.left(getIntegerValue());
+boolean leftIsRight = either.isRight();
+boolean rightIsRight = either.isRight();
+```
+---
+#### `void match(Consumer<L> onLeft, Consumer<R> onRight)`
+
+Matches the `Either`, invoking the correct `Consumer`.
+
+``` java
+Either<Integer, String> either = Either.left(getIntegerValue());
+either.match(
+    left -> handleIntegerValue(left),
+    right -> handleStringValue(right)
+);
+```
+---
+#### `<T> Either<T, R> mapLeft(Function<L, T> f)`
+
+Map the `Function` across the left value.
+
+``` java
+Either<Integer, String> either = Either.left(getIntegerValue());
+Either<Double, String> either = either.mapLeft(i -> i.doubleValue());
+```
+---
+#### `<T> Either<L, T> mapRight(Function<R, T> f)`
+
+Map the function across the right value.
+
+``` java
+Either<Integer, String> either = Either.left(getIntegerValue());
+Either<Integer, String> either = either.mapRight(s -> s + "x");
+```
+---
+#### `<T> Either<T, R> flatMapLeft(Function<L, Either<T, R>> f)`
+
+FlatMap the function across the left value.
+
+``` java
+Either<Integer, String> either = Either.left(2);
+Either<Integer, String> resultLeft = either.flatMapLeft(l -> Either.left(l * 2));
+Either<Integer, String> resultRight = either.flatMapLeft(l -> Either.right(l * 2));
+```
+---
+#### `<T> Either<T, R> flatMapRight(Function<L, Either<T, R>> f)`
+
+FlatMap the function across the right value.
+
+``` java
+Either<Integer, String> either = Either.right("2");
+Either<Integer, String> resultLeft = either.flatMapRight(l -> Either.left(l * 2));
+Either<Integer, String> resultRight = either.flatMapRight(l -> Either.right(l * 2));
+```
+---
+#### `Optional<L> getLeft()`
+
+Returns an `Optional` containing the left value, if is a left, otherwise returns
+an empty `Optional`.
+
+``` java
+Either<Integer, String> either = Either.right("2");
+Optional<Integer> left = either.getLeft();
+```
+---
+#### `Optional<R> getRight()`
+
+Returns an `Optional` containing the right value, if is a right, otherwise 
+returns an empty `Optional`.
+
+``` java
+Either<Integer, String> either = Either.right("2");
+Optional<String> right = either.getRight();
+```
+
+## Combinators
+
+### After
+
+TODO
+
+### Before
+
+TODO
+
+### Around
+
+TODO

pom.xml

@@ -14,7 +14,7 @@
     <version>2.3.0</version>
 
     <name>Mon</name>
-    <description>TypeAlias, Result and Maybe for Java</description>
+    <description>Wrapper, TypeAlias, Result, Lazy, Maybe and combinators for Java</description>
 
     <issueManagement>
         <url>https://github.com/kemitix/mon/issues</url>
@@ -38,9 +38,9 @@
         <assertj.version>3.19.0</assertj.version>
         <lombok.version>1.18.18</lombok.version>
         <tiles-maven-plugin.version>2.19</tiles-maven-plugin.version>
-        <kemitix-maven-tiles.version>2.4.1</kemitix-maven-tiles.version>
+        <kemitix-maven-tiles.version>3.0.1</kemitix-maven-tiles.version>
         <digraph-dependency.basePackage>net.kemitix.mon</digraph-dependency.basePackage>
-        <kemitix-checkstyle.version>5.0.0</kemitix-checkstyle.version>
+        <kemitix-checkstyle.version>5.5.0</kemitix-checkstyle.version>
         <pitest-maven-plugin.version>1.6.4</pitest-maven-plugin.version>
         <pitest-junit5-plugin.version>0.12</pitest-junit5-plugin.version>
         <spotbugs.version>4.1.2</spotbugs.version>
@@ -105,7 +105,14 @@
                 <extensions>true</extensions>
                 <configuration>
                     <tiles>
-                        <tile>net.kemitix.tiles:all:${kemitix-maven-tiles.version}</tile>
+                        <tile>net.kemitix.tiles:maven-plugins:${kemitix-maven-tiles.version}</tile>
+                        <tile>net.kemitix.tiles:compiler-jdk-lts:${kemitix-maven-tiles.version}</tile>
+                        <tile>net.kemitix.tiles:pmd:${kemitix-maven-tiles.version}</tile>
+                        <tile>net.kemitix.tiles:testing:${kemitix-maven-tiles.version}</tile>
+                        <tile>net.kemitix.tiles:spotbugs:${kemitix-maven-tiles.version}</tile>
+                        <tile>net.kemitix.tiles:coverage:${kemitix-maven-tiles.version}</tile>
+                        <tile>net.kemitix.tiles:pitest:${kemitix-maven-tiles.version}</tile>
+                        <tile>net.kemitix.tiles:pmd-strict:${kemitix-maven-tiles.version}</tile>
                         <tile>net.kemitix.checkstyle:tile:${kemitix-checkstyle.version}</tile>
                     </tiles>
                 </configuration>

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

@@ -48,5 +48,5 @@ public interface Functor<T, F extends Functor<?, ?>> {
      *
      * @return a Functor containing the result of the function {@code f} applied to the value
      */
-    public abstract <R> F map(Function<T, R> f);
+    <R> F map(Function<T, R> f);
 }

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

@@ -32,7 +32,7 @@ import java.util.function.Function;
  * @param <T> the type of the alias
  * @author Paul Campbell (pcampbell@kemitix.net)
  */
-@SuppressWarnings("abstractclassname")
+@SuppressWarnings({"abstractclassname", "PMD.AbstractClassWithoutAbstractMethod"})
 public abstract class TypeAlias<T> {
 
     /**

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

@@ -37,6 +37,6 @@ public interface Wrapper<T> {
      *
      * @return the value
      */
-    public abstract T value();
+    T value();
 
 }

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

@@ -52,7 +52,7 @@ public interface After<T, R> extends
      * @return a partially applied Function that will take an argument and return the result of applying it to the
      * function parameter
      */
-    public static <T, R> Function<T, R> decorate(
+    static <T, R> Function<T, R> decorate(
             final Function<T, R> function,
             final BiConsumer<T, R> after
     ) {
@@ -68,7 +68,7 @@ public interface After<T, R> extends
      *
      * @return a curried function that will pass the argument and the result of the function to the supplied bi-consumer
      */
-    public static <T, R> After<T, R> create() {
+    static <T, R> After<T, R> create() {
         return function -> after -> argument -> {
             final R result = function.apply(argument);
             after.accept(argument, result);

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

@@ -54,7 +54,7 @@ public interface Around<T, R> extends
      *
      * @return a partially applied Function that will take an argument, and the result of applying it to function
      */
-    public static <T, R> Function<T, R> decorate(
+    static <T, R> Function<T, R> decorate(
             final Function<T, R> function,
             final BiConsumer<Executable<R>, T> around
     ) {
@@ -71,7 +71,7 @@ public interface Around<T, R> extends
      * @return a curried function that will execute the around function, passing an executable and the invocations
      * argument. The around function must {@code execute()} the executable and may capture the result.
      */
-    public static <T, R> Around<T, R> create() {
+    static <T, R> Around<T, R> create() {
         return function -> around -> argument -> {
             final AtomicReference<R> result = new AtomicReference<>();
             final Executable<R> callback = () -> {
@@ -89,13 +89,13 @@ public interface Around<T, R> extends
      * @param <R> the return type of the function
      */
     @FunctionalInterface
-    public static interface Executable<R> {
+    interface Executable<R> {
 
         /**
          * Executes the function.
          *
          * @return the result of applying the function
          */
-        public abstract R execute();
+        R execute();
     }
 }

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

@@ -53,7 +53,7 @@ public interface Before<T, R> extends
      * @return a partially applied Function that will take an argument and return the result of applying it to the
      * function parameter
      */
-    public static <T, R> Function<T, R> decorate(
+    static <T, R> Function<T, R> decorate(
             final Consumer<T> before,
             final Function<T, R> function
     ) {
@@ -69,7 +69,7 @@ public interface Before<T, R> extends
      *
      * @return a curried function that will pass the argument to before applying the supplied function
      */
-    public static <T, R> Before<T, R> create() {
+    static <T, R> Before<T, R> create() {
         return before -> function -> argument -> {
             before.accept(argument);
             return function.apply(argument);

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

@@ -43,7 +43,7 @@ public interface Either<L, R> {
      * @param <R> the type of the right value
      * @return a Either holding the left value
      */
-    public static <L, R> Either<L, R> left(final L l) {
+    static <L, R> Either<L, R> left(final L l) {
         return new Left<>(l);
     }
 
@@ -55,7 +55,7 @@ public interface Either<L, R> {
      * @param <R> the type of the right value
      * @return a Either holding the right value
      */
-    public static <L, R> Either<L, R> right(final R r) {
+    static <L, R> Either<L, R> right(final R r) {
         return new Right<>(r);
     }
 
@@ -64,14 +64,14 @@ public interface Either<L, R> {
      *
      * @return true if this Either is a left
      */
-    public abstract boolean isLeft();
+    boolean isLeft();
 
     /**
      * Checks if the Either holds a right value.
      *
      * @return true if this Either is a right
      */
-    public abstract boolean isRight();
+    boolean isRight();
 
     /**
      * Matches the Either, invoking the correct Consumer.
@@ -79,7 +79,7 @@ public interface Either<L, R> {
      * @param onLeft  the Consumer to invoke when the Either is a left
      * @param onRight the Consumer to invoke when the Either is a right
      */
-    public abstract void match(Consumer<L> onLeft, Consumer<R> onRight);
+    void match(Consumer<L> onLeft, Consumer<R> onRight);
 
     /**
      * Map the function across the left value.
@@ -88,7 +88,7 @@ public interface Either<L, R> {
      * @param <T> the type to change the left value to
      * @return a new Either
      */
-    public abstract <T> Either<T, R> mapLeft(Function<L, T> f);
+    <T> Either<T, R> mapLeft(Function<L, T> f);
 
     /**
      * Map the function across the right value.
@@ -97,7 +97,7 @@ public interface Either<L, R> {
      * @param <T> the type to change the right value to
      * @return a new Either
      */
-    public abstract <T> Either<L, T> mapRight(Function<R, T> f);
+    <T> Either<L, T> mapRight(Function<R, T> f);
 
     /**
      * FlatMap the function across the left value.
@@ -106,7 +106,7 @@ public interface Either<L, R> {
      * @param <T> the type to change the left value to
      * @return a new Either if is a Left, else this
      */
-    public abstract <T> Either<T, R> flatMapLeft(Function<L, Either<T, R>> f);
+    <T> Either<T, R> flatMapLeft(Function<L, Either<T, R>> f);
 
     /**
      * FlatMap the function across the right value.
@@ -115,7 +115,7 @@ public interface Either<L, R> {
      * @param <T> the type to change the right value to
      * @return a new Either if is a Right, else this
      */
-    public abstract <T> Either<L, T> flatMapRight(Function<R, Either<L, T>> f);
+    <T> Either<L, T> flatMapRight(Function<R, Either<L, T>> f);
 
     /**
      * Returns an Optional containing the left value, if is a left, otherwise
@@ -123,7 +123,7 @@ public interface Either<L, R> {
      *
      * @return An Optional containing any left value
      */
-    public abstract Optional<L> getLeft();
+    Optional<L> getLeft();
 
     /**
      * Returns an Optional containing the right value, if is a right, otherwise
@@ -131,5 +131,5 @@ public interface Either<L, R> {
      *
      * @return An Optional containing any right value
      */
-    public abstract Optional<R> getRight();
+    Optional<R> getRight();
 }

src/main/java/net/kemitix/mon/lazy/Lazy.java

@@ -42,7 +42,7 @@ public interface Lazy<T> extends Functor<T, Lazy<?>> {
      * @param <R> the type of the value
      * @return a Lazy wrapper of the Supplier
      */
-    public static <R> Lazy<R> of(final Supplier<R> supplier) {
+    static <R> Lazy<R> of(final Supplier<R> supplier) {
         return new LazySupplier<>(supplier);
     }
 
@@ -51,7 +51,7 @@ public interface Lazy<T> extends Functor<T, Lazy<?>> {
      *
      * @return true if the value has been evaluated.
      */
-    public abstract boolean isEvaluated();
+    boolean isEvaluated();
 
     /**
      * The value, evaluating it if necessary.
@@ -60,8 +60,8 @@ public interface Lazy<T> extends Functor<T, Lazy<?>> {
      *
      * @return the evaluated value
      */
-    public abstract T value();
+    T value();
 
     @Override
-    public abstract <R> Lazy<R> map(Function<T, R> f);
+    <R> Lazy<R> map(Function<T, R> f);
 }

src/main/java/net/kemitix/mon/lazy/LazySupplier.java

@@ -35,10 +35,10 @@ import java.util.function.Supplier;
  */
 class LazySupplier<T> implements Lazy<T> {
 
-    private final Supplier<T> supplier;
+    private transient final Supplier<T> supplier;
     private final AtomicBoolean evaluated = new AtomicBoolean(false);
-    private final AtomicReference<T> value = new AtomicReference<>();
+    private transient final AtomicReference<T> value = new AtomicReference<>();
-    private final Object lock = new Object();
+    private transient final Object lock = new Object();
 
     /**
      * Creates a new Lazy wrapper for the Supplier.

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

@@ -50,7 +50,7 @@ public interface Maybe<T> extends Functor<T, Maybe<?>> {
      * @param <T>   the type of the value
      * @return a Maybe of the value
      */
-    public static <T> Maybe<T> just(@NonNull final T value) {
+    static <T> Maybe<T> just(@NonNull final T value) {
         return new Just<>(value);
     }
 
@@ -61,7 +61,7 @@ public interface Maybe<T> extends Functor<T, Maybe<?>> {
      * @return an empty Maybe
      */
     @SuppressWarnings("unchecked")
-    public static <T> Maybe<T> nothing() {
+    static <T> Maybe<T> nothing() {
         return (Maybe<T>) Nothing.INSTANCE;
     }
 
@@ -74,7 +74,7 @@ public interface Maybe<T> extends Functor<T, Maybe<?>> {
      * @param <T>   the type of the value
      * @return a Maybe, either a Just, or Nothing if value is null
      */
-    public static <T> Maybe<T> maybe(final T value) {
+    static <T> Maybe<T> maybe(final T value) {
         if (value == null) {
             return nothing();
         }
@@ -88,7 +88,7 @@ public interface Maybe<T> extends Functor<T, Maybe<?>> {
      * @param <T> the type of the stream
      * @return a Maybe containing the first item in the stream
      */
-    public static <T> Maybe<T> findFirst(Stream<T> stream) {
+    static <T> Maybe<T> findFirst(Stream<T> stream) {
         return stream.findFirst()
                 .map(Maybe::just)
                 .orElseGet(Maybe::nothing);
@@ -99,14 +99,14 @@ public interface Maybe<T> extends Functor<T, Maybe<?>> {
      *
      * @return true if the Maybe is a Just
      */
-    public abstract boolean isJust();
+    boolean isJust();
 
     /**
      * Checks if the Maybe is Nothing.
      *
      * @return true if the Maybe is Nothing
      */
-    public abstract boolean isNothing();
+    boolean isNothing();
 
     /**
      * Monad binder maps the Maybe into another Maybe using the binder method f.
@@ -115,10 +115,10 @@ public interface Maybe<T> extends Functor<T, Maybe<?>> {
      * @param <R> the type of the value in the final maybe
      * @return a Maybe with the mapped value
      */
-    public abstract <R> Maybe<R> flatMap(Function<T, Maybe<R>> f);
+    <R> Maybe<R> flatMap(Function<T, Maybe<R>> f);
 
     @Override
-    public abstract <R> Maybe<R> map(Function<T, R> f);
+    <R> Maybe<R> map(Function<T, R> f);
 
     /**
      * Provide a value to use when Maybe is Nothing.
@@ -126,7 +126,7 @@ public interface Maybe<T> extends Functor<T, Maybe<?>> {
      * @param supplier supplier for an alternate value
      * @return a Maybe
      */
-    public abstract T orElseGet(Supplier<T> supplier);
+    T orElseGet(Supplier<T> supplier);
 
     /**
      * A value to use when Maybe is Nothing.
@@ -134,14 +134,14 @@ public interface Maybe<T> extends Functor<T, Maybe<?>> {
      * @param otherValue an alternate value
      * @return the value of the Maybe if a Just, otherwise the otherValue
      */
-    public abstract T orElse(T otherValue);
+    T orElse(T otherValue);
 
     /**
      * Convert the Maybe to an {@link Optional}.
      *
      * @return an Optional containing a value for a Just, or empty for a Nothing
      */
-    public abstract Optional<T> toOptional();
+    Optional<T> toOptional();
 
     /**
      * Throw the exception if the Maybe is a Nothing.
@@ -151,14 +151,14 @@ public interface Maybe<T> extends Functor<T, Maybe<?>> {
      * @return the value of the Maybe if a Just
      * @throws X if the Maybe is nothing
      */
-    public abstract <X extends Throwable> T orElseThrow(Supplier<? extends X> e) throws X;
+    <X extends Throwable> T orElseThrow(Supplier<? extends X> e) throws X;
 
     /**
      * Converts the Maybe into either a single value stream or an empty stream.
      *
      * @return a Stream containing the value or nothing.
      */
-    public abstract Stream<T> stream();
+    Stream<T> stream();
 
     /**
      * Filter a Maybe by the predicate, replacing with Nothing when it fails.
@@ -166,7 +166,7 @@ public interface Maybe<T> extends Functor<T, Maybe<?>> {
      * @param predicate the test
      * @return the Maybe, or Nothing if the test returns false
      */
-    public abstract Maybe<T> filter(Predicate<T> predicate);
+    Maybe<T> filter(Predicate<T> predicate);
 
     /**
      * Provide the value within the Maybe, if it exists, to the Consumer, and returns this Maybe.
@@ -174,14 +174,14 @@ public interface Maybe<T> extends Functor<T, Maybe<?>> {
      * @param consumer the Consumer to the value if present
      * @return this Maybe
      */
-    public abstract Maybe<T> peek(Consumer<T> consumer);
+    Maybe<T> peek(Consumer<T> consumer);
 
     /**
      * Run the runnable if the Maybe is a Nothing, otherwise do nothing.
      *
      * @param runnable the runnable to call if this is a Nothing
      */
-    public abstract void ifNothing(Runnable runnable);
+    void ifNothing(Runnable runnable);
 
     /**
      * Matches the Maybe, either just or nothing, and performs either the Consumer, for Just, or Runnable for nothing.
@@ -191,7 +191,7 @@ public interface Maybe<T> extends Functor<T, Maybe<?>> {
      * @param justMatcher    the Consumer to pass the value of a Just to
      * @param nothingMatcher the Runnable to call if the Maybe is a Nothing
      */
-    public abstract void match(Consumer<T> justMatcher, Runnable nothingMatcher);
+    void match(Consumer<T> justMatcher, Runnable nothingMatcher);
 
     /**
      * Matches the Maybe, either just or nothing, and performs either the Function, for Just, or Supplier for nothing.
@@ -204,7 +204,7 @@ public interface Maybe<T> extends Functor<T, Maybe<?>> {
      *
      * @return the matched result, from either the justMatcher or the nothingMatcher
      */
-    public abstract <R> R matchValue(Function<T, R> justMatcher, Supplier<R> nothingMatcher);
+    <R> R matchValue(Function<T, R> justMatcher, Supplier<R> nothingMatcher);
 
     /**
      * Maps the Maybe into another Maybe only when it is nothing.
@@ -213,5 +213,5 @@ public interface Maybe<T> extends Functor<T, Maybe<?>> {
      *
      * @return the original Maybe if not nothing, or the alternative
      */
-    public abstract Maybe<T> or(Supplier<Maybe<T>> alternative);
+    Maybe<T> or(Supplier<Maybe<T>> alternative);
 }

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

@@ -50,7 +50,7 @@ final class Nothing<T> implements Maybe<T> {
     }
 
     @Override
-    @SuppressWarnings("unchecked")
+    @SuppressWarnings({"unchecked", "PMD.AvoidDuplicateLiterals"})
     public <R> Maybe<R> flatMap(final Function<T, Maybe<R>> f) {
         return (Maybe<R>) INSTANCE;
     }

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

@@ -30,6 +30,8 @@ package net.kemitix.mon.result;
  */
 public final class CheckedErrorResultException extends Exception {
 
+    private static final long serialVersionUID = 6388860431020999870L;
+
     private CheckedErrorResultException(final Throwable cause) {
         super(cause);
     }

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

@@ -37,7 +37,7 @@ import java.util.function.Predicate;
  * @param <T> the type of the value in the Result if it has been a success
  */
 @RequiredArgsConstructor
-@SuppressWarnings("methodcount")
+@SuppressWarnings({"methodcount", "PMD.CyclomaticComplexity"})
 class Err<T> implements Result<T> {
 
     private final Throwable error;

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

@@ -30,6 +30,8 @@ package net.kemitix.mon.result;
  */
 public final class ErrorResultException extends RuntimeException {
 
+    private static final long serialVersionUID = -949688489831104844L;
+
     private ErrorResultException(final Throwable cause) {
         super(cause);
     }

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

@@ -33,7 +33,7 @@ import java.util.function.*;
  * @param <T> the type of the result when a success
  * @author Paul Campbell (pcampbell@kemitix.net)
  */
-@SuppressWarnings("methodcount")
+@SuppressWarnings({"methodcount", "PMD.TooManyMethods"})
 public interface Result<T> extends Functor<T, Result<?>> {
 
     /**
@@ -44,7 +44,7 @@ public interface Result<T> extends Functor<T, Result<?>> {
      * @param <T>   the type of the Maybe and the Result
      * @return a Result containing the value of the Maybe when it is a Just, or the error when it is Nothing
      */
-    public static <T> Result<T> fromMaybe(final Maybe<T> maybe, final Supplier<Throwable> error) {
+    static <T> Result<T> fromMaybe(final Maybe<T> maybe, final Supplier<Throwable> error) {
         return maybe.map(Result::ok)
                 .orElseGet(() -> Result.error(error.get()));
     }
@@ -56,7 +56,7 @@ public interface Result<T> extends Functor<T, Result<?>> {
      * @param <T>   the type had the result been a success
      * @return an error Result
      */
-    public default <T> Result<T> err(final Throwable error) {
+    default <T> Result<T> err(final Throwable error) {
         return new Err<>(error);
     }
 
@@ -67,7 +67,7 @@ public interface Result<T> extends Functor<T, Result<?>> {
      * @param <T>   the type had the result been a success
      * @return an error Result
      */
-    public static <T> Result<T> error(final Throwable error) {
+    static <T> Result<T> error(final Throwable error) {
         return new Err<>(error);
     }
 
@@ -78,11 +78,11 @@ public interface Result<T> extends Functor<T, Result<?>> {
      * @param <T>      the type of the value
      * @return a Result
      */
-    @SuppressWarnings("illegalcatch")
+    @SuppressWarnings({"illegalcatch", "PMD.AvoidCatchingThrowable", "PMD.AvoidDuplicateLiterals"})
-    public default <T> Result<T> result(final Callable<T> callable) {
+    default <T> Result<T> result(final Callable<T> callable) {
         try {
             return Result.ok(callable.call());
-        } catch (final Exception e) {
+        } catch (final Throwable e) {
             return Result.error(e);
         }
     }
@@ -94,11 +94,11 @@ public interface Result<T> extends Functor<T, Result<?>> {
      * @param <T>      the type of the value
      * @return a Result
      */
-    @SuppressWarnings("illegalcatch")
+    @SuppressWarnings({"illegalcatch", "PMD.AvoidCatchingThrowable"})
-    public static <T> Result<T> of(final Callable<T> callable) {
+    static <T> Result<T> of(final Callable<T> callable) {
         try {
             return Result.ok(callable.call());
-        } catch (final Exception e) {
+        } catch (final Throwable e) {
             return Result.error(e);
         }
     }
@@ -110,7 +110,7 @@ public interface Result<T> extends Functor<T, Result<?>> {
      * @param <T>   the type of the value
      * @return a successful Result
      */
-    public default <T> Result<T> success(final T value) {
+    default <T> Result<T> success(final T value) {
         return new Success<>(value);
     }
 
@@ -121,7 +121,7 @@ public interface Result<T> extends Functor<T, Result<?>> {
      * @param <T>   the type of the value
      * @return a successful Result
      */
-    public static <T> Result<T> ok(final T value) {
+    static <T> Result<T> ok(final T value) {
         return new Success<>(value);
     }
 
@@ -134,7 +134,7 @@ public interface Result<T> extends Functor<T, Result<?>> {
      * @param <T>    the type of the Maybe and the Result
      * @return a Result containing the value of the Maybe when it is a Just, or the error when it is Nothing
      */
-    public static <T> Maybe<T> toMaybe(final Result<T> result) {
+    static <T> Maybe<T> toMaybe(final Result<T> result) {
         try {
             return Maybe.just(result.orElseThrow());
         } catch (final CheckedErrorResultException throwable) {
@@ -148,7 +148,7 @@ public interface Result<T> extends Functor<T, Result<?>> {
      * @return the value if a success
      * @throws CheckedErrorResultException if the result is an error
      */
-    public abstract T orElseThrow() throws CheckedErrorResultException;
+    T orElseThrow() throws CheckedErrorResultException;
 
     /**
      * Extracts the successful value from the result, or throws the error Throwable.
@@ -159,14 +159,14 @@ public interface Result<T> extends Functor<T, Result<?>> {
      * @return the value if a success
      * @throws E if the result is an error
      */
-    public abstract <E extends Exception> T orElseThrow(Class<E> type) throws E;
+    <E extends Exception> T orElseThrow(Class<E> type) throws E;
 
     /**
      * Extracts the successful value from the result, or throws the error in a {@link UnexpectedErrorResultException}.
      *
      * @return the value if a success
      */
-    public abstract T orElseThrowUnchecked();
+    T orElseThrowUnchecked();
 
     /**
      * Swaps the inner Result of a Maybe, so that a Result is on the outside.
@@ -177,7 +177,7 @@ public interface Result<T> extends Functor<T, Result<?>> {
      * original Maybe. If the original Maybe is Nothing, the Result will contain Nothing. If the original Result was an
      * error, then the Result will also be an error.
      */
-    public static <T> Result<Maybe<T>> swap(final Maybe<Result<T>> maybeResult) {
+    static <T> Result<Maybe<T>> swap(final Maybe<Result<T>> maybeResult) {
         return maybeResult.orElseGet(() -> Result.ok(null))
                 .flatMap(value -> Result.ok(Maybe.maybe(value)));
     }
@@ -189,7 +189,7 @@ public interface Result<T> extends Functor<T, Result<?>> {
      * @param <R> the type of the value withing the Result of the mapping function
      * @return a Result
      */
-    public abstract <R> Result<R> flatMap(Function<T, Result<R>> f);
+    <R> Result<R> flatMap(Function<T, Result<R>> f);
 
     /**
      * Applies the function to the contents of a Maybe within the Result.
@@ -200,7 +200,7 @@ public interface Result<T> extends Functor<T, Result<?>> {
      * @param <R>         the type of the updated Result
      * @return a new Maybe within a Result
      */
-    public static <T, R> Result<Maybe<R>> flatMapMaybe(
+    static <T, R> Result<Maybe<R>> flatMapMaybe(
             final Result<Maybe<T>> maybeResult,
             final Function<Maybe<T>, Result<Maybe<R>>> f
     ) {
@@ -212,17 +212,17 @@ public interface Result<T> extends Functor<T, Result<?>> {
      *
      * @return true if the Result is an error.
      */
-    public abstract boolean isError();
+    boolean isError();
 
     /**
      * Checks if the Result is a success.
      *
      * @return true if the Result is a success.
      */
-    public abstract boolean isOkay();
+    boolean isOkay();
 
     @Override
-    public abstract <R> Result<R> map(Function<T, R> f);
+    <R> Result<R> map(Function<T, R> f);
 
     /**
      * Matches the Result, either success or error, and supplies the appropriate Consumer with the value or error.
@@ -230,7 +230,7 @@ public interface Result<T> extends Functor<T, Result<?>> {
      * @param onSuccess the Consumer to pass the value of a successful Result to
      * @param onError   the Consumer to pass the error from an error Result to
      */
-    public abstract void match(Consumer<T> onSuccess, Consumer<Throwable> onError);
+    void match(Consumer<T> onSuccess, Consumer<Throwable> onError);
 
     /**
      * Wraps the value within the Result in a Maybe, either a Just if the predicate is true, or Nothing.
@@ -238,7 +238,7 @@ public interface Result<T> extends Functor<T, Result<?>> {
      * @param predicate the test to decide
      * @return a Result containing a Maybe that may or may not contain a value
      */
-    public abstract Result<Maybe<T>> maybe(Predicate<T> predicate);
+    Result<Maybe<T>> maybe(Predicate<T> predicate);
 
     /**
      * Provide the value within the Result, if it is a success, to the Consumer, and returns this Result.
@@ -246,7 +246,7 @@ public interface Result<T> extends Functor<T, Result<?>> {
      * @param consumer the Consumer to the value if a success
      * @return this Result
      */
-    public abstract Result<T> peek(Consumer<T> consumer);
+    Result<T> peek(Consumer<T> consumer);
 
     /**
      * Provide a way to attempt to recover from an error state.
@@ -254,7 +254,7 @@ public interface Result<T> extends Functor<T, Result<?>> {
      * @param f the function to recover from the error
      * @return a new Result, either a Success, or if recovery is not possible an other Err.
      */
-    public abstract Result<T> recover(Function<Throwable, Result<T>> f);
+    Result<T> recover(Function<Throwable, Result<T>> f);
 
     /**
      * A handler for error states.
@@ -264,7 +264,7 @@ public interface Result<T> extends Functor<T, Result<?>> {
      *
      * @param errorConsumer the consumer to handle the error
      */
-    public abstract void onError(Consumer<Throwable> errorConsumer);
+    void onError(Consumer<Throwable> errorConsumer);
 
     /**
      * Maps a Success Result to another Result using a Callable that is able to throw a checked exception.
@@ -284,7 +284,7 @@ public interface Result<T> extends Functor<T, Result<?>> {
      * @param <R> the type of the final Result
      * @return a new Result
      */
-    public abstract <R> Result<R> andThen(Function<T, Callable<R>> f);
+    <R> Result<R> andThen(Function<T, Callable<R>> f);
 
     /**
      * Perform the continuation with the current Result value then return the current Result, assuming there was no
@@ -304,7 +304,7 @@ public interface Result<T> extends Functor<T, Result<?>> {
      * @param f the function to map the Success value into the result continuation
      * @return the Result or a new error Result
      */
-    public abstract Result<T> thenWith(Function<T, WithResultContinuation<T>> f);
+    Result<T> thenWith(Function<T, WithResultContinuation<T>> f);
 
     /**
      * Reduce two Results of the same type into one using the reducing function provided.
@@ -316,5 +316,5 @@ public interface Result<T> extends Functor<T, Result<?>> {
      * @param operator the function to combine the values the Results
      * @return a Result containing the combination of the two Results
      */
-    public abstract Result<T> reduce(Result<T> identify, BinaryOperator<T> operator);
+    Result<T> reduce(Result<T> identify, BinaryOperator<T> operator);
 }

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

@@ -37,7 +37,7 @@ import java.util.function.Predicate;
  * @param <T> the type of the value in the Result
  */
 @RequiredArgsConstructor
-@SuppressWarnings("methodcount")
+@SuppressWarnings({"methodcount", "PMD.CyclomaticComplexity"})
 class Success<T> implements Result<T> {
 
     private final T value;
@@ -53,8 +53,13 @@ class Success<T> implements Result<T> {
     }
 
     @Override
+    @SuppressWarnings({"illegalcatch", "PMD.AvoidCatchingThrowable"})
     public <R> Result<R> map(final Function<T, R> f) {
-        return success(f.apply(value));
+        try {
+            return success(f.apply(this.value));
+        } catch (Throwable e) {
+            return err(e);
+        }
     }
 
     @Override

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

@@ -31,6 +31,8 @@ package net.kemitix.mon.result;
  */
 public final class UnexpectedErrorResultException extends RuntimeException {
 
+    private static final long serialVersionUID = 959355287011172256L;
+
     private UnexpectedErrorResultException(final Throwable cause) {
         super(cause);
     }

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

@@ -35,10 +35,18 @@ public interface WithResultContinuation<T> {
      *
      * @throws Exception to replace the current Result with an error
      */
-    public abstract void run() throws Exception;
+    @SuppressWarnings("PMD.SignatureDeclareThrowsException")
+    void run() throws Exception;
 
-    @SuppressWarnings({"illegalcatch", "javadocmethod"})
+    /**
-    public default Result<T> call(final Result<T> currentResult) {
+     * Internal. Called when the result of the previous {@link Result} is a
+     * {@link Success}.
+     *
+     * @param currentResult the previous result.
+     * @return the previous result if no exceptions thrown, or an {@link Err}
+     */
+    @SuppressWarnings({"illegalcatch", "javadocmethod", "PMD.AvoidCatchingThrowable"})
+    default Result<T> call(final Result<T> currentResult) {
         try {
             run();
         } catch (Throwable e) {

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

@@ -41,8 +41,8 @@ import java.util.function.Function;
 @EqualsAndHashCode
 class GeneralisedTree<T> implements Tree<T>, TreeMapper<T> {
 
-    private final T item;
+    private transient final T item;
-    private final List<Tree<T>> subTrees;
+    private transient final List<Tree<T>> subTrees;
 
     /**
      * Creates a new tree.

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

@@ -43,9 +43,9 @@ import java.util.stream.Collectors;
 @SuppressWarnings("methodcount")
 class MutableTree<T> implements Tree<T>, TreeMapper<T> {
 
-    private final List<MutableTree<T>> mySubTrees = new ArrayList<>();
+    private transient final List<MutableTree<T>> mySubTrees = new ArrayList<>();
 
-    private T item;
+    private transient T item;
 
     /**
      * Create a new {@link MutableTree}.

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

@@ -35,7 +35,7 @@ import java.util.function.Function;
  */
 class MutableTreeBuilder<T> implements TreeBuilder<T> {
 
-    private final MutableTree<T> root;
+    private transient final MutableTree<T> root;
 
     /**
      * Create empty tree builder.

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

@@ -47,7 +47,7 @@ public interface Tree<T> extends Functor<T, Tree<?>> {
      *
      * @return a empty generalised tree
      */
-    public static <R> Tree<R> leaf(final R item) {
+    static <R> Tree<R> leaf(final R item) {
         return new GeneralisedTree<>(item, Collections.emptyList());
     }
 
@@ -59,7 +59,7 @@ public interface Tree<T> extends Functor<T, Tree<?>> {
      * @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) {
+    static <R> Tree<R> of(final R item, final Collection<Tree<R>> subtrees) {
         return new GeneralisedTree<>(item, subtrees);
     }
 
@@ -73,7 +73,7 @@ public interface Tree<T> extends Functor<T, Tree<?>> {
      */
     @SuppressFBWarnings(value = "UP_UNUSED_PARAMETER",
             justification = "Use the type parameter to fingerprint the return type")
-    public static <B> TreeBuilder<B> builder(final Class<B> type) {
+    static <B> TreeBuilder<B> builder(final Class<B> type) {
         return new MutableTreeBuilder<>();
     }
 
@@ -85,26 +85,26 @@ public interface Tree<T> extends Functor<T, Tree<?>> {
      *
      * @return a TreeBuilder
      */
-    public static <B> TreeBuilder<B> builder(final Tree<B> tree) {
+    static <B> TreeBuilder<B> builder(final Tree<B> tree) {
         return new MutableTreeBuilder<>(MutableTree.of(tree));
     }
 
     @Override
-    public abstract <R> Tree<R> map(Function<T, R> f);
+    <R> Tree<R> map(Function<T, R> f);
 
     /**
      * Return the item within the node of the tree, if present.
      *
      * @return a Maybe containing the item
      */
-    public abstract Maybe<T> item();
+    Maybe<T> item();
 
     /**
      * Count the number of item in the tree, including subtrees.
      *
      * @return the sum of the subtrees, plus 1 if there is an item in this node
      */
-    public default int count() {
+    default int count() {
         return item().matchValue(x -> 1, () -> 0)
                 + subTrees().stream().mapToInt(Tree::count).sum();
     }
@@ -114,5 +114,5 @@ public interface Tree<T> extends Functor<T, Tree<?>> {
      *
      * @return a list of Trees
      */
-    public abstract List<Tree<T>> subTrees();
+    List<Tree<T>> subTrees();
 }

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

@@ -39,7 +39,7 @@ public interface TreeBuilder<T> {
      *
      * @return a {@link Tree}
      */
-    public abstract Tree<T> build();
+    Tree<T> build();
 
     /**
      * Set the current {@link Tree}'s item.
@@ -48,7 +48,7 @@ public interface TreeBuilder<T> {
      *
      * @return the TreeBuilder
      */
-    public abstract TreeBuilder<T> item(T item);
+    TreeBuilder<T> item(T item);
 
     /**
      * Adds the subtree to the current tree.
@@ -57,7 +57,7 @@ public interface TreeBuilder<T> {
      *
      * @return the TreeBuilder
      */
-    public abstract TreeBuilder<T> add(Tree<T> subtree);
+    TreeBuilder<T> add(Tree<T> subtree);
 
     /**
      * Add the Child item as a subTree.
@@ -65,7 +65,7 @@ public interface TreeBuilder<T> {
      * @param childItem the item to add as a subtree
      * @return the TreeBuilder
      */
-    public abstract TreeBuilder<T> addChild(T childItem);
+    TreeBuilder<T> addChild(T childItem);
 
     /**
      * Add all the child items as subTrees.
@@ -73,7 +73,7 @@ public interface TreeBuilder<T> {
      * @param children the items to add as a subtree
      * @return the TreeBuilder
      */
-    public default TreeBuilder<T> addChildren(List<T> children) {
+    default TreeBuilder<T> addChildren(List<T> children) {
         children.forEach(this::addChild);
         return this;
     }
@@ -84,5 +84,5 @@ public interface TreeBuilder<T> {
      * @param childItem the item of search the subtrees for
      * @return a Maybe containing the TreeBuilder for the subtree, or Nothing if there child item is not found
      */
-    public abstract Maybe<TreeBuilder<T>> select(T childItem);
+    Maybe<TreeBuilder<T>> select(T childItem);
 }

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

@@ -43,7 +43,7 @@ interface TreeMapper<T> {
      *
      * @return a List of mapped sub-trees
      */
-    public default <R> List<Tree<R>> mapTrees(
+    default <R> List<Tree<R>> mapTrees(
             final Function<T, R> f,
             final List<Tree<T>> trees
     ) {

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

@@ -144,7 +144,7 @@ class ResultTest implements WithAssertions {
     }
 
     @Test
-    void okay_whenMap_isOkay() {
+    void okay_whenMapToOkay_isOkay() {
         //given
         final Result<Integer> okResult = Result.ok(1);
         //when
@@ -157,6 +157,22 @@ class ResultTest implements WithAssertions {
         );
     }
 
+    @Test
+    void okay_whenMapToError_isError() {
+        //given
+        final Result<Integer> okResult = Result.ok(1);
+        //when
+        final Result<String> result = okResult.map(value -> {
+            throw new RuntimeException("map error");
+        });
+        //then
+        assertThat(result.isError()).isTrue();
+        result.match(
+                success -> fail("not an success"),
+                error -> assertThat(error).hasMessage("map error")
+        );
+    }
+
     @Test
     void error_whenMap_isError() {
         //given