tweaked programmatic blocks-changing

HISTORY.md

@@ -50,6 +50,7 @@
 
 ### 2022-05-017
 * blocks: added experimental private isChangeableTo(type) method
+* blocks, threads: tweaked programmatic blocks-changing
 
 ### 2022-05-06
 * threads: include currently dragged sprites in the MY OTHER SPRITES/CLONES lists

snap.html

@@ -17,7 +17,7 @@
         <script src="src/symbols.js?version=2021-03-03"></script>
         <script src="src/widgets.js?version=2021-17-09"></script>
         <script src="src/blocks.js?version=2022-05-17"></script>
-        <script src="src/threads.js?version=2022-05-03"></script>
+        <script src="src/threads.js?version=2022-05-17"></script>
         <script src="src/objects.js?version=2022-05-02"></script>
         <script src="src/scenes.js?version=2022-03-03"></script>
         <script src="src/gui.js?version=2022-04-26"></script>

src/blocks.js

@@ -3577,28 +3577,19 @@ BlockMorph.prototype.isChangeableTo = function (type) {
     // a block is considered "changeable" if
     // -------------------------------------
     // * it's a command & the target type isn't also a command & doesn't have a
-    //   next block & its parent also isn't a syntax element (block or C-shaped
-    //   slot), except it can be a ring.
+    //   next block & is unattached (e.g. the only expression inside a context).
     //
-    // * it's a reporter or a predicate & the target type is a command & its
-    //   parent is not a block, except it can be a ring.
+    // * it's a reporter or a predicate & the target type is a command & is
+    //   unattached (e.g. the only expression inside a function context).
     //
     // * it's a reporter or a predicate & the target type is also a reporter or
     //   a predicate the type can always be changed
 
     var typ = this.type();
     if (typ === type) {return true; }
-    if (typ === 'command') {
-        if (this.nextBlock()) {return false; }
-        if (this.parent instanceof RingMorph) {return true; }
-        return !(this.parent instanceof SyntaxElementMorph);
+    if (typ === 'command' || type === 'command') {
+        return this.isUnattached();
     }
-    // typ is 'reporter' or 'predicate'
-    if (type === 'command') {
-        if (this.parent instanceof RingMorph) {return true; }
-        return !(this.parent instanceof BlockMorph);
-    }
-    // type is 'reporter' or 'predicate'
     return true;
 };
 
@@ -3608,6 +3599,13 @@ BlockMorph.prototype.type = function () {
         : (this.isPredicate ? 'predicate' : 'reporter');
 };
 
+BlockMorph.prototype.isUnattached = function () {
+    // private
+    return ((this.nextBlock && !this.nextBlock()) || !this.nextBlock) &&
+        !(this.parent instanceof SyntaxElementMorph) &&
+        !(this.parent instanceof ScriptsMorph)
+};
+
 BlockMorph.prototype.isInheritedVariable = function (shadowedOnly) {
     // private - only for variable getter template inside the palette
     if (this.isTemplate &&

src/threads.js

@@ -65,7 +65,7 @@ StagePickerMorph, CustomBlockDefinition*/
 
 /*jshint esversion: 11, bitwise: false, evil: true*/
 
-modules.threads = '2022-May-06';
+modules.threads = '2022-May-17';
 
 var ThreadManager;
 var Process;
@@ -5687,9 +5687,6 @@ Process.prototype.doSetBlockAttribute = function (attribute, block, val) {
             'other';
         break;
     case 'type':
-        if (isInUse()) {
-            throw new Error('cannot change this\nfor a block that is in use');
-        }
         this.assertType(val, ['number', 'text']);
         if (this.reportTypeOf(val) === 'text') {
             type = val;
@@ -5697,7 +5694,14 @@ Process.prototype.doSetBlockAttribute = function (attribute, block, val) {
             type = types[val - 1] || '';
         }
         if (!types.includes(type)) {return;}
-        def.type = type;
+
+        if (rcvr.allBlockInstances(def).every(block =>
+            block.isChangeableTo(type))
+        ) {
+            def.type = type;
+        } else {
+            throw new Error('cannot change this\nfor a block that is in use');
+        }
         break;
     case 'scope':
         if (isInUse()) {