Stack management, stack frames, forever and repeat

src/engine/thread.js

@@ -21,6 +21,12 @@ function Thread (firstBlock) {
      */
     this.stack = [];
 
+    /**
+     * Stack frames for the thread. Store metadata for the executing blocks.
+     * @type {Array.<Object>}
+     */
+    this.stackFrames = [];
+
     /**
      * Status of the thread, one of three states (below)
      * @type {number}