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;
+    }
+  }
+}
+
+main() {
+  A a = new A(1, 2);
+  a..check(1, 2)..swap()..check(2, 1)..x = 4
+   ..check(4, 1)..setX(10)..check(10, 1)..y = 5
+   ..check(10, 5)..swap()()()..check(5, 10)..[0] = 2
+   ..check(2, 10)..setX(10).setY(3)..check(10, 3)

[sra1, 2012/03/30 21:52:20]

Could you reformat it so that the assignment forms are not all on the right?
Otherwise you are not testing that .. adjacent to a number compiles.
E.g.

  a..check(1, 2)..swap()..check(2, 1)
   ..x = 4..check(4, 1)..setX(10)..check(10, 1)
   ..y = 5..check(10, 5)..swap()()()
   ..check(5, 10)..[0] = 2..check(2, 10)
   ..setX(10).setY(3)..check(10, 3)
   ..["swap"]()()()..check(3, 10);

[Lasse Reichstein Nielsen, 2012/04/10 08:12:43]

Good point. 
I wasn't expecting it to work, but that's just JS-related mental damage.
(In JS, "2." is a valid number literal, so you have to write "2..toString()" to
convert it to a string).

+   ..["swap"]()()()..check(3, 10);
+  a..(42);  /// 01: compile-time error
+}