added hook for "crossproduct" in threads

src/objects.js

@@ -1741,7 +1741,6 @@ SpriteMorph.prototype.blockAlternatives = {
     doShowVar: ['doHideVar'],
     doHideVar: ['doShowVar'],
 
-    // lists
     // HOFs
     reportMap: ['reportKeep', 'reportFindFirst'],
     reportKeep: ['reportFindFirst', 'reportMap'],
@@ -2786,7 +2785,6 @@ SpriteMorph.prototype.blockTemplates = function (category) {
         blocks.push('-');
         blocks.push(block('reportConcatenatedLists'));
         blocks.push(block('reportReshape'));
-        // blocks.push(block('reportTranspose'));
         blocks.push('-');
         blocks.push(block('doAddToList'));
         blocks.push(block('doDeleteFromList'));
@@ -8948,7 +8946,6 @@ StageMorph.prototype.blockTemplates = function (category) {
         blocks.push('-');
         blocks.push(block('reportConcatenatedLists'));
         blocks.push(block('reportReshape'));
-        // blocks.push(block('reportTranspose'));
         blocks.push('-');
         blocks.push(block('doAddToList'));
         blocks.push(block('doDeleteFromList'));

src/threads.js

@@ -1955,6 +1955,15 @@ Process.prototype.reportTranspose = function (list) {
     return list.transpose();
 };
 
+Process.prototype.reportCrossproduct = function (lists) {
+    this.assertType(lists, 'list');
+    if (lists.isEmpty()) {
+        return lists;
+    }
+    this.assertType(lists.at(1), 'list');
+    return lists.crossproduct();
+};
+
 Process.prototype.reportReshape = function (list, shape) {
     this.assertType(list, 'list');
     this.assertType(shape, 'list');