simplify shift/reset API and add test (currently failing)

classpath/avian/Continuations.java

@@ -205,11 +205,11 @@ public class Continuations {
     }
   }
 
-  public static <Result, Argument> Result shift
+  public static <T> T shift
-    (final FunctionReceiver<Result, Argument> receiver)
+    (final FunctionReceiver<T> receiver)
     throws Exception
   {
-    return (Result) callWithCurrentContinuation(new CallbackReceiver() {
+    return (T) callWithCurrentContinuation(new CallbackReceiver() {
         public Object receive(final Callback continuation) {
           final Reset reset = latestReset.get();
           final Callback resetContinuation = reset.continuation;

classpath/avian/Function.java

@@ -10,6 +10,6 @@
 
 package avian;
 
-public interface Function<Argument, Result> {
+public interface Function<T> {
-  public Result call(Argument argument) throws Exception;
+  public T call(T argument) throws Exception;
 }

classpath/avian/FunctionReceiver.java

@@ -10,6 +10,6 @@
 
 package avian;
 
-public interface FunctionReceiver<Argument, Result> {
+public interface FunctionReceiver<T> {
-  public Result receive(Function<Argument, Result> function) throws Exception;
+  public T receive(Function<T> function) throws Exception;
 }

test/extra/ComposableContinuations.java

@@ -16,9 +16,8 @@ public class ComposableContinuations {
   public static void main(String[] args) throws Exception {
     expect(2 * reset(new Callable<Integer>() {
           public Integer call() throws Exception {
-            return 1 + shift(new FunctionReceiver<Integer, Integer>() {
+            return 1 + shift(new FunctionReceiver<Integer>() {
-                public Integer receive
+                public Integer receive(Function<Integer> continuation)
-                  (Function<Integer, Integer> continuation)
                   throws Exception
                 {
                   return continuation.call(5);
@@ -29,9 +28,8 @@ public class ComposableContinuations {
 
     expect(1 + reset(new Callable<Integer>() {
           public Integer call() throws Exception {
-            return 2 * shift(new FunctionReceiver<Integer, Integer>() {
+            return 2 * shift(new FunctionReceiver<Integer>() {
-                public Integer receive
+                public Integer receive(Function<Integer> continuation)
-                  (Function<Integer, Integer> continuation)
                   throws Exception
                 {
                   return continuation.call(continuation.call(4));
@@ -39,5 +37,74 @@ public class ComposableContinuations {
               });
           }
         }) == 17);
+
+    expect(equal(reset(new Callable<Cell<Integer>>() {
+            public Cell<Integer> call() throws Exception {
+              shift(new FunctionReceiver<Cell<Integer>>() {
+                  public Cell<Integer> receive
+                    (Function<Cell<Integer>> continuation)
+                    throws Exception
+                  {
+                    return cons(1, continuation.call(null));
+                  }
+                });
+
+              shift(new FunctionReceiver<Cell<Integer>>() {
+                  public Cell<Integer> receive
+                    (Function<Cell<Integer>> continuation)
+                    throws Exception
+                  {
+                    return cons(2, continuation.call(null));
+                  }
+                });
+
+              return null;
+            }
+          }), cons(1, cons(2, null))));
+  }
+
+  private static <T> boolean equal(T a, T b) {
+    return (a == null && b == null) || (a != null && a.equals(b));
+  }
+  
+  private static <Car> boolean equal(Cell<Car> a, Cell<Car> b) {
+    System.out.println(a + " vs " + b);
+
+    while (a != null) {
+      if (b == null || (! equal(a.car, b.car))) {
+        return false;
+      }
+      a = a.cdr;
+      b = b.cdr;
+    }
+
+    return b == null;
+  }
+
+  private static <Car> Cell<Car> cons(Car car, Cell<Car> cdr) {
+    return new Cell(car, cdr);
+  }
+
+  private static class Cell<Car> {
+    public final Car car;
+    public final Cell<Car> cdr;
+
+    public Cell(Car car, Cell<Car> cdr) {
+      this.car = car;
+      this.cdr = cdr;
+    }
+
+    public String toString() {
+      StringBuilder sb = new StringBuilder();
+      sb.append("(");
+      for (Cell<Car> c = this; c != null; c = c.cdr) {
+        sb.append(c.car);
+        if (c.cdr != null) {
+          sb.append(", ");
+        }
+      }
+      sb.append(")");
+      return sb.toString();
+    }
   }
 }