Clean up (#64)

* [readme] use valid haskell example

* [tree] Immediately return this expression instead of assigning it to the temporary variable "treeList".

* [tree] Use normal defensive copying for array fields

README.org

@@ -34,9 +34,10 @@
   if you try and use them together. e.g.:
 
   #+BEGIN_SRC haskell
-  type PhoneNumber = String
-  type Name = String
-  type PhoneBook = [(Name,PhoneNumber)]
+    newtype PhoneNumber = PhoneNumber String
+    newtype Name = Name String
+    newtype PhoneBookEntry = PhoneBookEntry (Name, PhoneNumber)
+    newtype PhoneBook = PhoneBook [PhoneBookEntry]
   #+END_SRC
    
   In Java we don't have the ability to have that true alias, so TypeAlias is

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

@@ -50,7 +50,7 @@ class GeneralisedTree<T> implements Tree<T>, TreeMapper<T> {
      */
     GeneralisedTree(final T item, final Collection<Tree<T>> subTrees) {
         this.item = item;
-        this.subTrees = Collections.unmodifiableList(new ArrayList<>(subTrees));
+        this.subTrees = new ArrayList<>(subTrees);
     }
 
     /**
@@ -77,6 +77,6 @@ class GeneralisedTree<T> implements Tree<T>, TreeMapper<T> {
      */
     @Override
     public List<Tree<T>> subTrees() {
-        return subTrees;
+        return new ArrayList<>(subTrees);
     }
 }

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

@@ -29,7 +29,6 @@ import java.util.Collection;
 import java.util.List;
 import java.util.function.Function;
 import java.util.stream.Collectors;
-import java.util.stream.Stream;
 
 /**
  * A mutable {@link Tree}.
@@ -126,12 +125,8 @@ class MutableTree<T> implements Tree<T>, TreeMapper<T> {
     }
 
     @Override
-    @SuppressWarnings("unchecked")
     public List<Tree<T>> subTrees() {
-        final Stream<MutableTree<T>> mutableTreeStream = mySubTrees.stream();
-        final Stream<Tree<T>> treeStream = mutableTreeStream.map(Tree.class::cast);
-        final List<Tree<T>> treeList = treeStream.collect(Collectors.toList());
-        return treeList;
+        return new ArrayList<>(mySubTrees);
     }
 
     /**