update example to match

test/plex.ul

@@ -8,10 +8,9 @@ plex Point {
     }
 
     toS() {
-        pln("[x:%d, y:%d]", 
-            this.x,
-            this.y);
-    } 
+        return "[x:" + (this.x as str) +
+        ", y:" + (this.y as str) + "]";
+    }
 }
 
 plex Rect {
@@ -28,13 +27,12 @@ plex Rect {
     }
 
     toS() {
-        pln("[top_left: [x:%d, y:%d], bottom_right: [x:%d, y:%d], width:%d, height:%d]]", 
-            this.top_left.x,
-            this.top_left.y, 
-            this.bottom_right.x, 
-            this.bottom_right.y,
-            this.width, 
-            this.height);
+        return "[top_left:" +
+        this.top_left.toS() +
+        ", bottom_right: " +
+        this.bottom_right.toS() +
+        ", width:" + (this.width as str)  +
+        ", height:" + (this.height as str) + "]";
     }   
 }