Threads: new Variable data structure

for refactoring upvar references, not yet used anywhere

history.txt

@@ -2130,3 +2130,4 @@ ______
 ------
 * Morphic: Prevent default action for ctrl-/cmd-key event
 * Snap.html: Focus the world canvas on startup, so Snap reacts to keyboard events right away
+* Threads: new Variable data structure, for refactoring upvar references, not yet used anywhere

threads.js

@@ -83,7 +83,7 @@ ArgLabelMorph, localize, XML_Element, hex_sha512*/
 
 // Global stuff ////////////////////////////////////////////////////////
 
-modules.threads = '2014-May-02';
+modules.threads = '2014-May-20';
 
 var ThreadManager;
 var Process;
@@ -3110,6 +3110,20 @@ VariableFrame.prototype.allNames = function () {
     return answer;
 };
 
+// Variable /////////////////////////////////////////////////////////////////
+
+function Variable(value) {
+    this.value = value;
+}
+
+Variable.prototype.toString = function () {
+    return 'a Variable [' + this.value + ']';
+};
+
+Variable.prototype.copy = function () {
+    return new Variable(this.value);
+};
+
 // UpvarReference ///////////////////////////////////////////////////////////
 
 // ... quasi-inherits some features from VariableFrame