6 files changed, 269 insertions, 6 deletions
diff --git a/src/main/java/au/id/zancanaro/javacheck/Generator.java b/src/main/java/au/id/zancanaro/javacheck/Generator.java
index c28d967..557cf97 100644
--- a/src/main/java/au/id/zancanaro/javacheck/Generator.java
+++ b/src/main/java/au/id/zancanaro/javacheck/Generator.java
@@ -1,5 +1,6 @@
 package au.id.zancanaro.javacheck;
 
+import java.util.Iterator;
 import java.util.List;
 import java.util.Random;
 import java.util.function.Function;
@@ -128,4 +129,8 @@ public interface Generator<T> {
     default <R> Generator<R> flatMap(Function<T, Generator<R>> action) {
         return (random, size) -> RoseTree.join(this.generate(random, size).map(action).map(g -> g.generate(random, size)));
     }
+
+    default Iterator<T> sample(Random random, int maxSize) {
+        return new GeneratorSampleIterator<>(this, random, maxSize);
+    }
 }
diff --git a/src/main/java/au/id/zancanaro/javacheck/GeneratorSampleIterator.java b/src/main/java/au/id/zancanaro/javacheck/GeneratorSampleIterator.java
new file mode 100644
index 0000000..f7d8e17
--- /dev/null
+++ b/src/main/java/au/id/zancanaro/javacheck/GeneratorSampleIterator.java
@@ -0,0 +1,30 @@
+package au.id.zancanaro.javacheck;
+
+import java.util.Iterator;
+import java.util.Random;
+
+public class GeneratorSampleIterator<T> implements Iterator<T> {
+    private final Generator<T> generator;
+    private final Random random;
+    private final int maxSize;
+    private int size;
+
+    public GeneratorSampleIterator(Generator<T> generator, Random random, int maxSize) {
+        this.generator = generator;
+        this.random = random;
+        this.maxSize = maxSize;
+        this.size = 0;
+    }
+
+    @Override
+    public boolean hasNext() {
+        return true;
+    }
+
+    @Override
+    public T next() {
+        return generator
+                .generate(random, Math.min(size++, maxSize))
+                .getValue();
+    }
+}
diff --git a/src/main/java/au/id/zancanaro/javacheck/Generators.java b/src/main/java/au/id/zancanaro/javacheck/Generators.java
index 548bd29..4049149 100644
--- a/src/main/java/au/id/zancanaro/javacheck/Generators.java
+++ b/src/main/java/au/id/zancanaro/javacheck/Generators.java
@@ -91,10 +91,12 @@ public final class Generators {
         return (random, size) -> {
             Generator<Integer> countGen = sized(s -> integer(minElements, maxElements));
             int count = countGen.generate(random, size).getValue();
-            return Generator.list(count, gen).generate(random, size)
+            return Generator.list(count, gen)
+                    .generate(random, size)
                     .filter(list ->
                             minElements <= list.size()
-                                    && list.size() < maxElements);
+                                    && list.size() < maxElements)
+                    .map(Collections::unmodifiableList);
         };
     }
 
@@ -102,7 +104,9 @@ public final class Generators {
         return (random, size) -> {
             Generator<Integer> countGen = sized(s -> integer(0, s));
             int count = countGen.generate(random, size).getValue();
-            return Generator.list(count, gen).generate(random, size);
+            return Generator.list(count, gen)
+                    .generate(random, size)
+                    .map(Collections::unmodifiableList);
         };
     }
 
diff --git a/src/test/java/au/id/zancanaro/javacheck/ListFunctorRulesTest.java b/src/test/java/au/id/zancanaro/javacheck/ListFunctorRulesTest.java
new file mode 100644
index 0000000..4e516a2
--- /dev/null
+++ b/src/test/java/au/id/zancanaro/javacheck/ListFunctorRulesTest.java
@@ -0,0 +1,110 @@
+package au.id.zancanaro.javacheck;
+
+import au.id.zancanaro.javacheck.annotations.DataSource;
+import au.id.zancanaro.javacheck.annotations.Property;
+import au.id.zancanaro.javacheck.junit.Properties;
+import org.junit.runner.RunWith;
+
+import java.util.List;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+
+import static au.id.zancanaro.javacheck.Generators.*;
+import static org.junit.Assert.assertEquals;
+
+@RunWith(Properties.class)
+public class ListFunctorRulesTest {
+
+    private final static int runs = 1000;
+    private final static int maxSize = 1000;
+
+    @DataSource
+    public static Generator<List<Integer>> listOfIntegers = listOf(integer());
+
+    @DataSource
+    public static Generator<Function<Integer, Integer>> integerFunction =
+            oneOf(
+                    integer().map(ListFunctorRulesTest::plusI),
+                    integer().map(ListFunctorRulesTest::timesI),
+                    integer().map(ListFunctorRulesTest::constantlyI));
+
+    @Property(maxSize = maxSize, runs = runs)
+    public void mappingCompositionsWithStreams(
+            List<Integer> list,
+            Function<Integer, Integer> f,
+            Function<Integer, Integer> g) {
+        List<Integer> left = list.stream()
+                .map(g)
+                .map(f)
+                .collect(Collectors.toList());
+
+        List<Integer> right = list.stream()
+                .map(x -> f.apply(g.apply(x)))
+                .collect(Collectors.toList());
+
+        assertEquals(left, right);
+    }
+
+    @Property(maxSize = maxSize, runs = runs)
+    public void mappingCompositionsWithIntermediateList(
+            List<Integer> list,
+            Function<Integer, Integer> f,
+            Function<Integer, Integer> g) {
+        List<Integer> intermediate = list.stream().map(g).collect(Collectors.toList());
+        List<Integer> left = intermediate.stream().map(f).collect(Collectors.toList());
+
+        List<Integer> right = list.stream()
+                .map(x -> f.apply(g.apply(x)))
+                .collect(Collectors.toList());
+
+        assertEquals(left, right);
+    }
+
+    @Property(maxSize = maxSize, runs = runs)
+    public void mapIdentityIsIdentity(List<Integer> list) {
+        List<Integer> mapped = list.stream().map(x -> x).collect(Collectors.toList());
+
+        assertEquals(list, mapped);
+    }
+
+    private static Function<Integer,Integer> plusI(final int i) {
+        return new Function<Integer, Integer>() {
+            @Override
+            public Integer apply(Integer integer) {
+                return i + integer;
+            }
+
+            @Override
+            public String toString() {
+                return "x -> x + " + i;
+            }
+        };
+    }
+
+    private static Function<Integer,Integer> timesI(final int i) {
+        return new Function<Integer, Integer>() {
+            @Override
+            public Integer apply(Integer integer) {
+                return i * integer;
+            }
+
+            @Override
+            public String toString() {
+                return "x -> x * " + i;
+            }
+        };
+    }
+    private static Function<Integer,Integer> constantlyI(final int i) {
+        return new Function<Integer, Integer>() {
+            @Override
+            public Integer apply(Integer integer) {
+                return i;
+            }
+
+            @Override
+            public String toString() {
+                return "x -> " + i;
+            }
+        };
+    }
+}
diff --git a/src/test/java/au/id/zancanaro/javacheck/OptionalFunctorRulesTest.java b/src/test/java/au/id/zancanaro/javacheck/OptionalFunctorRulesTest.java
new file mode 100644
index 0000000..b13fb8b
--- /dev/null
+++ b/src/test/java/au/id/zancanaro/javacheck/OptionalFunctorRulesTest.java
@@ -0,0 +1,110 @@
+package au.id.zancanaro.javacheck;
+
+import au.id.zancanaro.javacheck.annotations.DataSource;
+import au.id.zancanaro.javacheck.annotations.Property;
+import au.id.zancanaro.javacheck.junit.Properties;
+import org.junit.runner.RunWith;
+
+import java.util.Optional;
+import java.util.function.Function;
+
+import static au.id.zancanaro.javacheck.Generator.pure;
+import static au.id.zancanaro.javacheck.Generators.integer;
+import static au.id.zancanaro.javacheck.Generators.oneOf;
+import static org.junit.Assert.assertEquals;
+
+@RunWith(Properties.class)
+public class OptionalFunctorRulesTest {
+
+    private final static int runs = 1000;
+    private final static int maxSize = 1000;
+
+    @DataSource
+    public static Generator<Optional<Integer>> listOfIntegers = oneOf(
+            pure(Optional.empty()),
+            integer().map(Optional::of));
+
+    @DataSource
+    public static Generator<Function<Integer, Integer>> integerFunction =
+            oneOf(
+                    integer().map(OptionalFunctorRulesTest::plusI),
+                    integer().map(OptionalFunctorRulesTest::timesI),
+                    integer().map(OptionalFunctorRulesTest::constantlyI));
+
+    @Property(maxSize = maxSize, runs = runs)
+    public void mappingCompositionsWithStreams(
+            Optional<Integer> optional,
+            Function<Integer, Integer> f,
+            Function<Integer, Integer> g) {
+        Optional<Integer> left = optional
+                .map(g)
+                .map(f);
+
+        Optional<Integer> right = optional
+                .map(x -> f.apply(g.apply(x)));
+
+        assertEquals(left, right);
+    }
+
+    @Property(maxSize = maxSize, runs = runs)
+    public void mappingCompositionsWithIntermediateList(
+            Optional<Integer> optional,
+            Function<Integer, Integer> f,
+            Function<Integer, Integer> g) {
+        Optional<Integer> intermediate = optional.map(g);
+        Optional<Integer> left = intermediate.map(f);
+
+        Optional<Integer> right = optional
+                .map(x -> f.apply(g.apply(x)));
+
+        assertEquals(left, right);
+    }
+
+    @Property(maxSize = maxSize, runs = runs)
+    public void mapIdentityIsIdentity(Optional<Integer> optional) {
+        Optional<Integer> mapped = optional.map(x -> x);
+
+        assertEquals(optional, mapped);
+    }
+
+    private static Function<Integer,Integer> plusI(final int i) {
+        return new Function<Integer, Integer>() {
+            @Override
+            public Integer apply(Integer integer) {
+                return i + integer;
+            }
+
+            @Override
+            public String toString() {
+                return "x -> x + " + i;
+            }
+        };
+    }
+
+    private static Function<Integer,Integer> timesI(final int i) {
+        return new Function<Integer, Integer>() {
+            @Override
+            public Integer apply(Integer integer) {
+                return i * integer;
+            }
+
+            @Override
+            public String toString() {
+                return "x -> x * " + i;
+            }
+        };
+    }
+    private static Function<Integer,Integer> constantlyI(final int i) {
+        return new Function<Integer, Integer>() {
+            @Override
+            public Integer apply(Integer integer) {
+                return i;
+            }
+
+            @Override
+            public String toString() {
+                return "x -> " + i;
+            }
+        };
+    }
+}
diff --git a/src/test/java/au/id/zancanaro/javacheck/junit/SimpleListOperationsTest.java b/src/test/java/au/id/zancanaro/javacheck/SimpleListOperationsTest.java
index 089451e..972b5b6 100644
--- a/src/test/java/au/id/zancanaro/javacheck/junit/SimpleListOperationsTest.java
+++ b/src/test/java/au/id/zancanaro/javacheck/SimpleListOperationsTest.java
@@ -1,8 +1,9 @@
-package au.id.zancanaro.javacheck.junit;
+package au.id.zancanaro.javacheck;
 
 import au.id.zancanaro.javacheck.Generator;
 import au.id.zancanaro.javacheck.annotations.DataSource;
 import au.id.zancanaro.javacheck.annotations.Property;
+import au.id.zancanaro.javacheck.junit.Properties;
 import org.junit.runner.RunWith;
 
 import java.util.ArrayList;
@@ -15,13 +16,16 @@ import static org.junit.Assert.assertEquals;
 @RunWith(Properties.class)
 public class SimpleListOperationsTest {
 
+    private final static int runs = 1000;
+    private final static int maxSize = 1000;
+
     @DataSource
     public static Generator<List<Integer>> listOfIntegers = listOf(integer());
 
     @DataSource
     public static Generator<List<String>> listOfStrings = listOf(stringOf(alphaNumericCharacter()));
 
-    @Property(maxSize = 100, runs = 1000)
+    @Property(maxSize = maxSize, runs = runs)
     public void sortingIsIdempotent(List<Integer> list) {
         List<Integer> left = new ArrayList<>(list);
         Collections.sort(left);
@@ -33,7 +37,7 @@ public class SimpleListOperationsTest {
         assertEquals(left, right);
     }
 
-    @Property(maxSize = 100, runs = 1000)
+    @Property(maxSize = 100, runs = runs)
     public void reverseIsItsOwnInverse(List<String> list) {
         List<String> reversed = new ArrayList<>(list);
         Collections.reverse(reversed);