Implement cascaded calls.

frog/tests/leg_only/src/CascadeTest.dart

+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// Test cascades.
+
+class A {
+  int x;
+  int y;
+
+  A(this.x, this.y);
+
+  A setX(int x) { this.x = x; return this; }
+
+  void setY(int y) { this.y = y; }
+
+  Function swap() {
+    int tmp = x;
+    x = y;
+    y = tmp;
+    return this.swap;
+  }
+
+  void check(int x, int y) {
+    Expect.equals(x, this.x);
+    Expect.equals(y, this.y);
+  }
+
+  int operator[](var i) {
+    if (i == 0) return x;
+    if (i == 1) return y;
+    if (i == "swap") return this.swap;
+    return null;
+  }
+
+  int operator[]=(int i, int value) {
+    if (i == 0) {
+      x = value;
+    } else if (i == 1) {
+      y = value;
+    }
+  }
+
+  /**
+   * A pseudo-keyword.
+   */
+  import() {
+    x++;
+  }
+}
+
+main() {
+  A a = new A(1, 2);
+  a..check(1, 2)
+   ..swap()..check(2, 1)
+   ..x = 4..y = 9..check(4, 9)
+   ..setX(10)..check(10, 9)
+   ..y = 5..check(10, 5)
+   ..swap()()()..check(5, 10)
+   ..[0] = 2..check(2, 10)
+   ..setX(10).setY(3)..check(10, 3)
+   ..setX(7)["swap"]()..check(3, 7)
+   ..import()..check(4, 7)
+   ..["swap"]()()()..check(7, 4);
+  a.check(7,4);
+  a..(42);  /// 01: compile-time error
+  a..37;  /// 02: compile-time error
+  a.."foo";  /// 03: compile-time error
+}