enable relabelling any loop prim to "forEach" and vice-versa

src/blocks.js

@@ -3275,7 +3275,11 @@ BlockMorph.prototype.restoreInputs = function (oldInputs, offset = 0) {
     this.inputs().forEach(inp => {
         old = oldInputs[offset];
         if (old instanceof ReporterBlockMorph) {
-            this.replaceInput(inp, old.fullCopy());
+            if (inp instanceof TemplateSlotMorph || inp.isStatic) {
+                leftOver.push(old);
+            } else {
+                this.replaceInput(inp, old.fullCopy());
+            }
         } else if (old && inp instanceof InputSlotMorph) {
             // original - turns empty numberslots to 0:
             // inp.setContents(old.evaluate());

src/objects.js

@@ -1525,6 +1525,10 @@ SpriteMorph.prototype.initBlockMigrations = function () {
 SpriteMorph.prototype.initBlockMigrations();
 
 SpriteMorph.prototype.blockAlternatives = {
+    // structure:
+    //      selector: [ersatz, ...]
+    //      ersatz can also be a 2-item array: [selector, input-offset]
+
     // motion:
     turn: ['turnLeft'],
     turnLeft: ['turn'],
@@ -1581,10 +1585,13 @@ SpriteMorph.prototype.blockAlternatives = {
     doBroadcastAndWait: ['doBroadcast'],
     doIf: ['doIfElse', 'doUntil'],
     doIfElse: ['doIf', 'doUntil'],
-    doRepeat: ['doUntil', ['doForever', -1], ['doFor', 2]],
-    doUntil: ['doRepeat', 'doIf', ['doForever', -1], ['doFor', 2]],
-    doForever: [['doUntil', 1], ['doRepeat', 1], ['doFor', 3]],
-    doFor: [['doForever', -3], ['doRepeat', -2], ['doUntil', -2]],
+    doRepeat: ['doUntil', ['doForever', -1], ['doFor', 2], ['doForEach', 1]],
+    doUntil: ['doRepeat', 'doIf', ['doForever', -1], ['doFor', 2],
+        ['doForEach', 1]],
+    doForever: [['doUntil', 1], ['doRepeat', 1], ['doFor', 3],
+        ['doForEach', 2]],
+    doFor: [['doForever', -3], ['doRepeat', -2], ['doUntil', -2],
+        ['doForEach', -1]],
 
     // sensing:
     doAsk: ['bubble', 'doThink', 'doSayFor', 'doThinkFor'],
@@ -1621,7 +1628,9 @@ SpriteMorph.prototype.blockAlternatives = {
     // lists - HOFs
     reportMap: ['reportKeep', 'reportFindFirst'],
     reportKeep: ['reportFindFirst', 'reportMap'],
-    reportFindFirst: ['reportKeep', 'reportMap']
+    reportFindFirst: ['reportKeep', 'reportMap'],
+    doForEach: [['doFor', 1], ['doForever', -2], ['doRepeat', -1],
+        ['doUntil', -1]]
 };
 
 // SpriteMorph instance creation