1 files changed, 51 insertions, 0 deletions
diff --git a/src/main/java/au/id/zancanaro/Generator.java b/src/main/java/au/id/zancanaro/Generator.java
new file mode 100644
index 0000000..4b80e51
--- /dev/null
+++ b/src/main/java/au/id/zancanaro/Generator.java
@@ -0,0 +1,51 @@
+package au.id.zancanaro;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Random;
+import java.util.function.Function;
+
+public interface Generator<T> {
+    RoseTree<T> generate(Random random, int size);
+
+    static <T> Generator<T> pure(T value) {
+        return (random, size) -> RoseTree.pure(value);
+    }
+
+    default <R> Generator<R> genFlatmap(Function<RoseTree<T>, Generator<R>> f) {
+        return (random, size) -> {
+            RoseTree<T> inner = this.generate(random, size);
+            Generator<R> generator = f.apply(inner);
+            return generator.generate(random, size);
+        };
+    }
+
+    default <R> Generator<R> genFmap(Function<RoseTree<T>, RoseTree<R>> f) {
+        return (random, size) -> f.apply(this.generate(random, size));
+    }
+
+    @SafeVarargs
+    static <T> Generator<T[]> tuple(Generator<T>... generators) {
+        return (random, size) -> {
+            @SuppressWarnings("unchecked")
+            RoseTree<T>[] result = (RoseTree<T>[]) new RoseTree[generators.length];
+            int index = 0;
+            for (Generator<T> generator : generators) {
+                result[index++] = generator.generate(random, size);
+            }
+            return RoseTree.zip(Function.identity(), result);
+        };
+    }
+
+    default <R> Generator<R> fmap(Function<T, R> f) {
+        return (random, size) -> this.generate(random, size).fmap(f);
+    }
+
+    default <R> Generator<R> flatMap(Function<T, Generator<R>> action) {
+        return this.genFlatmap(rose -> {
+            Generator<RoseTree<R>> generator = (random, size) ->
+                    rose.fmap(action).fmap(g -> g.generate(random, size));
+            return generator.<R>genFmap(RoseTree::join);
+        });
+    }
+}