2 files changed, 12 insertions, 11 deletions
diff --git a/src/main/java/au/id/zancanaro/javacheck/Generator.java b/src/main/java/au/id/zancanaro/javacheck/Generator.java
index 5a8fec3..24c23ca 100644
--- a/src/main/java/au/id/zancanaro/javacheck/Generator.java
+++ b/src/main/java/au/id/zancanaro/javacheck/Generator.java
@@ -111,7 +111,7 @@ public interface Generator<T> {
      * @param <R> The result of the transformation
      * @return A new generator resulting from mapping f over this
      */
-    default <R> Generator<R> map(Function<T, R> f) {
+    default <R> Generator<R> map(Function<? super T, ? extends R> f) {
         return (random, size) -> this.generate(random, size).map(f);
     }
 
@@ -127,7 +127,7 @@ public interface Generator<T> {
      * @return A new generator resulting from calling the provided action on the
      * result of this
      */
-    default <R> Generator<R> flatMap(Function<T, Generator<R>> action) {
+    default <R> Generator<R> flatMap(Function<? super T, ? extends Generator<R>> action) {
         return (random, size) -> ShrinkTree.join(
                 this.generate(random, size)
                         .map(action
@@ -148,7 +148,7 @@ public interface Generator<T> {
      * @return A new generator resulting from filtering this generator to only
      * terms which match the given predicate
      */
-    default Generator<T> suchThat(Predicate<T> predicate) {
+    default Generator<T> suchThat(Predicate<? super T> predicate) {
         return (random, size) -> {
             ShrinkTree<T> result = this.generate(random, size);
             if (predicate.test(result.getValue())) {
diff --git a/src/main/java/au/id/zancanaro/javacheck/ShrinkTree.java b/src/main/java/au/id/zancanaro/javacheck/ShrinkTree.java
index 4337c14..4f4eb62 100644
--- a/src/main/java/au/id/zancanaro/javacheck/ShrinkTree.java
+++ b/src/main/java/au/id/zancanaro/javacheck/ShrinkTree.java
@@ -53,7 +53,7 @@ public class ShrinkTree<T> {
     }
 
     @SuppressWarnings("unchecked")
-    public static <T> Stream<ShrinkTree<T>[]> promoteChildren(ShrinkTree<T>[] trees) {
+    public static <T> Stream<ShrinkTree<T>[]> promoteChildren(ShrinkTree<? super T>[] trees) {
         return IntStream.range(0, trees.length)
                 .mapToObj(index -> trees[index].getChildren().map(child ->
                         IntStream.range(0, trees.length)
@@ -63,7 +63,7 @@ public class ShrinkTree<T> {
                 .map(x -> (ShrinkTree<T>[]) x);
     }
 
-    public static <T> Stream<ShrinkTree<T>[]> removeChildren(ShrinkTree<T>[] trees) {
+    public static <T> Stream<ShrinkTree<T>[]> removeChildren(ShrinkTree<? super T>[] trees) {
         return IntStream.range(0, trees.length)
                 .mapToObj(index -> IntStream.range(0, trees.length)
                         .filter(i -> i != index)
@@ -71,7 +71,7 @@ public class ShrinkTree<T> {
                         .toArray(ShrinkTree[]::new));
     }
 
-    public static <T> Stream<ShrinkTree<T>[]> removeAndPromoteChildren(ShrinkTree<T>[] trees) {
+    public static <T> Stream<ShrinkTree<T>[]> removeAndPromoteChildren(ShrinkTree<? super T>[] trees) {
         return Stream.concat(removeChildren(trees), promoteChildren(trees));
     }
 
@@ -84,17 +84,17 @@ public class ShrinkTree<T> {
                         .map(shrinks -> combine(shrinks, processChildren)));
     }
 
-    public <R> ShrinkTree<R> map(Function<T, R> f) {
+    public <R> ShrinkTree<R> map(Function<? super T, ? extends R> f) {
         return new ShrinkTree<>(
                 f.apply(this.value),
                 () -> this.getChildren().map(tree -> tree.map(f)));
     }
 
-    public <R> ShrinkTree<R> flatMap(Function<T, ShrinkTree<R>> f) {
+    public <R> ShrinkTree<R> flatMap(Function<?super T, ? extends ShrinkTree<R>> f) {
         return ShrinkTree.join(this.map(f));
     }
 
-    public ShrinkTree<T> filter(Predicate<T> predicate) {
+    public ShrinkTree<T> filter(Predicate<? super T> predicate) {
         if (predicate.test(this.getValue())) {
             return new ShrinkTree<>(
                     this.getValue(),
@@ -111,14 +111,15 @@ public class ShrinkTree<T> {
     }
 
     private static <T> Stream<ShrinkTree<T>> strategyStream(final T value, final ShrinkStrategy<T> strategy) {
-        return strategy.shrink(value).map(v -> new ShrinkTree<>(v, () -> strategyStream(v, strategy)));
+        return strategy.shrink(value)
+                .map(v -> new ShrinkTree<T>(v, () -> strategyStream(v, strategy)));
     }
 
     public void print(Writer output) throws IOException {
         print(output, Object::toString);
     }
 
-    public void print(Writer output, Function<T, String> toString) throws IOException {
+    public void print(Writer output, Function<? super T, ? extends String> toString) throws IOException {
         output.write(toString.apply(this.getValue()));
         output.write('[');
         Iterator<ShrinkTree<T>> iterator = children.get().iterator();