refactored list.crossproduct() to avoid JS stack overflows

HISTORY.md

@@ -9,7 +9,10 @@
 * **Documentation Updates:**
     * updated manual (e.g. p.20) with hyper-semantics of ITEM OF, thanks Brian 
 
-### 2021-02-06
+### 2021-02-09
+* lists: refactored matrix ops to avoid JS stack overflows
+
+### 2021-02-08
 * lists, objects, threads: new RESHAPE primitive
 * lists: added internal naive (recursive)  version of CROSSPRODUCT
 * lists: added TRANSPOSE for higher dimensions, thanks, Brian!

snap.html

@@ -9,7 +9,7 @@
         <script src="src/symbols.js?version=2020-10-07"></script>
         <script src="src/widgets.js?version=2021-01-05"></script>
         <script src="src/blocks.js?version=2021-02-08"></script>
-        <script src="src/threads.js?version=2021-02-08"></script>
+        <script src="src/threads.js?version=2021-02-09"></script>
         <script src="src/objects.js?version=2021-02-08"></script>
         <script src="src/gui.js?version=2021-02-04"></script>
         <script src="src/paint.js?version=2020-05-17"></script>

src/lists.js

@@ -63,7 +63,7 @@ MorphicPreferences, TableDialogMorph, SpriteBubbleMorph, SpeechBubbleMorph,
 TableFrameMorph, TableMorph, Variable, isSnapObject, Costume, contains, detect,
 ZERO, WHITE*/
 
-modules.lists = '2021-February-08';
+modules.lists = '2021-February-09';
 
 var List;
 var ListWatcherMorph;
@@ -544,7 +544,8 @@ List.prototype.getDimension = function (rank = 0) {
 };
 
 List.prototype.width = function () {
-    // private - answer the maximum length of my direct sub-lists (columns), if any
+    // private - answer the maximum length of my direct sub-lists (columns),
+    // if any
     var i, item,
         width = 0,
         len = this.length();
@@ -660,14 +661,27 @@ List.prototype.crossproduct = function () {
     // expects myself to be a list of lists.
     // answers a new list of all possible tuples
     // with one item from each of my sublists
-    if (this.isEmpty()) {
+    var result = new List(),
-        return new List([new List()]);
+        len = this.length(),
+        lengths = this.map(each => each.length()),
+        size = lengths.itemsArray().reduce((a, b) => a * b),
+        i, k, row, factor;
+
+    for (i = 1; i <= size; i += 1) {
+        row = new List();
+        factor = 1;
+        for (k = 1; k <= len; k += 1) {
+            row.add(
+                this.at(k).at(
+                    ((Math.ceil(i / ((size / lengths.at(k)) * factor)) - 1) %
+                        lengths.at(k)) + 1
+                )
+            );
+            factor /= lengths.at(k);
+        }
+        result.add(row);
     }
-    return this.at(1).map(
+    return result;
-        first => this.cdr().crossproduct().map(
-            each => this.cons(first, each)
-        )
-    ).flatten();
 };
 
 List.prototype.strideTranspose = function () {