refine Continuations.java and add Coroutines.java

test/extra/Continuations.java

@@ -6,23 +6,23 @@ import avian.CallbackReceiver;
 import avian.Callback;
 
 public class Continuations {
-  public static void main(String[] args) throws Exception {
-    System.out.println
-      ("result: " +
-       callWithCurrentContinuation(new CallbackReceiver<Integer>() {
-           public Integer receive(Callback<Integer> continuation) {
-             continuation.handleResult(42);
-             throw new RuntimeException("unreachable");
-           }
-         }));
+  private static void expect(boolean v) {
+    if (! v) throw new RuntimeException();
+  }
 
-    System.out.println
-      ("result: " +
-       callWithCurrentContinuation(new CallbackReceiver<Integer>() {
-           public Integer receive(Callback<Integer> continuation) {
-             return 43;
-           }
-         }));
+  public static void main(String[] args) throws Exception {
+    expect(callWithCurrentContinuation(new CallbackReceiver<Integer>() {
+          public Integer receive(Callback<Integer> continuation) {
+            continuation.handleResult(42);
+            throw new RuntimeException("unreachable");
+          }
+        }) == 42);
+
+    expect(callWithCurrentContinuation(new CallbackReceiver<Integer>() {
+          public Integer receive(Callback<Integer> continuation) {
+            return 43;
+          }
+        }) == 43);
 
     try {
       callWithCurrentContinuation(new CallbackReceiver<Integer>() {
@@ -31,6 +31,7 @@ public class Continuations {
             throw new RuntimeException("unreachable");
           }
         });
+      throw new RuntimeException("unreachable");      
     } catch (MyException e) {
       e.printStackTrace();
     }
@@ -43,6 +44,7 @@ public class Continuations {
             throw new MyException();
           }
         });
+      throw new RuntimeException("unreachable");
     } catch (MyException e) {
       e.printStackTrace();
     }

test/extra/Coroutines.java

@@ -0,0 +1,77 @@
+package extra;
+
+import static avian.Continuations.callWithCurrentContinuation;
+
+import avian.CallbackReceiver;
+import avian.Callback;
+
+public class Coroutines {
+  private static void expect(boolean v) {
+    if (! v) throw new RuntimeException();
+  }
+
+  private static void produce(Consumer<Character> consumer) throws Exception {
+    consumer.consume('a');
+    consumer.consume('b');
+    consumer.consume('c');
+  }
+
+  private static void consume(Producer<Character> producer) throws Exception {
+    expect(producer.produce() == 'a');
+    expect(producer.produce() == 'b');
+    expect(producer.produce() == 'c');
+  }
+
+  public static void main(String[] args) throws Exception {
+    final CoroutineState<Character> state = new CoroutineState<Character>();
+
+    final Consumer<Character> consumer = new Consumer<Character>() {
+      public void consume(final Character c) throws Exception {
+        callWithCurrentContinuation(new CallbackReceiver() {
+            public Object receive(Callback continuation) {
+              state.produceNext = continuation;
+
+              state.consumeNext.handleResult(c);
+
+              throw new RuntimeException("unreachable");
+            }
+          });
+      }
+    };
+
+    Producer<Character> producer = new Producer<Character>() {
+      public Character produce() throws Exception {
+        return callWithCurrentContinuation(new CallbackReceiver<Character>() {
+          public Character receive(Callback<Character> continuation)
+          throws Exception
+          {
+            state.consumeNext = continuation;
+
+            if (state.produceNext == null) {
+              Coroutines.produce(consumer);
+            } else {
+              state.produceNext.handleResult(null);
+            }
+
+            throw new RuntimeException("unreachable");
+          }
+        });
+      }
+    };
+
+    consume(producer);
+  }
+
+  private static class CoroutineState<T> {
+    public Callback<T> produceNext;
+    public Callback<T> consumeNext;
+  }
+
+  private interface Producer<T> {
+    public T produce() throws Exception;
+  }
+
+  private interface Consumer<T> {
+    public void consume(T value) throws Exception;
+  }
+}