functionaljava · bakeemawaytoys · Jun 12, 2016 · Jun 12, 2016 · Jun 12, 2016 · Jun 12, 2016
diff --git a/core/src/main/java/fj/Equal.java b/core/src/main/java/fj/Equal.java
@@ -506,6 +506,11 @@ public static <A> Equal<V8<A>> v8Equal(final Equal<A> ea) {
     return streamEqual(ea).contramap(V8.toStream_());
   }
 
+  /**
+   * An equal instance for the <code>Natural</code> type.
+   */
+  public static Equal<Natural> naturalEqual = Equal.equal(l -> r -> bigintEqual.eq(l.bigIntegerValue(), r.bigIntegerValue()));
+
   /**
    * An equal instance for lazy strings.
    */

diff --git a/core/src/main/java/fj/Hash.java b/core/src/main/java/fj/Hash.java
@@ -535,4 +535,9 @@ public static <A> Hash<V7<A>> v7Hash(final Hash<A> ea) {
   public static <A> Hash<V8<A>> v8Hash(final Hash<A> ea) {
     return streamHash(ea).contramap(V8.toStream_());
   }
+
+  /**
+   * A hash instance for the {@link Natural} type.
+   */
+  public static Hash<Natural> naturalHash = Hash.hash(n -> bigintHash.hash(n.bigIntegerValue()));
 }
diff --git a/core/src/main/java/fj/Semigroup.java b/core/src/main/java/fj/Semigroup.java
@@ -219,7 +219,7 @@ public static <A> Semigroup<A> semigroup(final F2<A, A, A> sum) {
       semigroup(Natural::multiply);
 
   /**
-   * A semigroup that multiplies natural numbers.
+   * A semigroup that adds natural numbers.
    */
   public static final Semigroup<Natural> naturalAdditionSemigroup =
       semigroup(Natural::add);

diff --git a/core/src/main/java/fj/data/Natural.java b/core/src/main/java/fj/data/Natural.java
@@ -1,11 +1,16 @@
 package fj.data;
 
 import static fj.Bottom.error;
+
+import fj.Equal;
 import fj.F;
 
 import static fj.Monoid.naturalAdditionMonoid;
 import static fj.Monoid.naturalMultiplicationMonoid;
 import static fj.Function.curry;
+
+import fj.Hash;
+import fj.Show;
 import fj.data.vector.V2;
 import fj.data.vector.V;
 
@@ -121,7 +126,7 @@ public Natural add(final Natural n) {
    * @return The difference between the two numbers, if this number is larger than the given one. Otherwise none.
    */
   public Option<Natural> subtract(final Natural n) {
-    return natural(n.value.subtract(value));
+    return natural(value.subtract(n.value));
   }
 
   /**
@@ -286,4 +291,20 @@ public static Natural sum(final List<Natural> ns) {
   public static Natural product(final List<Natural> ns) {
     return naturalMultiplicationMonoid.sumLeft(ns);
   }
+
+
+  @Override
+  public int hashCode() {
+    return Hash.naturalHash.hash(this);
+  }
+
+  @Override
+  public boolean equals(final Object that) {
+    return Equal.equals0(Natural.class, this, that, Equal.naturalEqual);
+  }
+
+  @Override
+  public String toString() {
+    return Show.naturalShow.showS(this);
+  }
 }
diff --git a/quickcheck/src/main/java/fj/test/Arbitrary.java b/quickcheck/src/main/java/fj/test/Arbitrary.java
@@ -1,5 +1,6 @@
 package fj.test;
 
+import fj.Equal;
 import fj.F;
 import fj.F2;
 import fj.F3;
@@ -38,6 +39,7 @@
 import fj.data.Set;
 import fj.data.TreeMap;
 import fj.function.Effect1;
+import fj.function.Longs;
 
 import static fj.data.Stream.range;
 import static fj.test.Gen.choose;
@@ -760,7 +762,7 @@ public static <A> Gen<ArrayList<A>> arbArrayList(final Gen<A> aa) {
   /**
    * Returns an arbitrary implementation for a Java enumeration.
    *
-   * @param clazz The type of enum to return an arbtrary of.
+   * @param clazz The type of enum to return an arbitrary of.
    * @return An arbitrary for instances of the supplied enum type.
    */
   public static <A extends Enum<A>> Gen<A> arbEnumValue(final Class<A> clazz) {
@@ -1337,4 +1339,11 @@ public static <A, B, C, D, E> Gen<P5<A, B, C, D, E>> arbP5(final Gen<A> aa, fina
     return aa.bind(ab, ac, ad, ae, af, ag, ah,
         a -> b -> c -> d -> e -> f -> g -> h -> p(a, b, c, d, e, f, g, h));
   }
+
+  /**
+   * An arbitrary implementation for naturals.
+   */
+  public static Gen<Natural> arbNatural = arbLong.filter(l -> Equal.longEqual.notEq(l, Long.MIN_VALUE))
+          .map(Longs.abs).map(Natural::natural).map(o -> o.some());
+
 }
diff --git a/quickcheck/src/main/java/fj/test/Shrink.java b/quickcheck/src/main/java/fj/test/Shrink.java
@@ -30,6 +30,7 @@
 import fj.data.Either;
 import fj.data.Java;
 import fj.data.List;
+import fj.data.Natural;
 import fj.data.Option;
 import fj.data.Stream;
 
@@ -846,4 +847,10 @@ public static <A, B, C, D, E> Shrink<P5<A, B, C, D, E>> shrinkP5(final Shrink<A>
                           sg.shrink(p._7()), sh.shrink(p._8()), p8);
             });
   }
+
+  /**
+   * A shrink strategy for naturals.
+   */
+  public static Shrink<Natural> shrinkNatural = shrinkLong.map(bi -> Natural.natural(bi).orSome(Natural.ZERO), Natural::longValue);
+
 }