correctly identify list slots in primitives

HISTORY.md

@@ -54,6 +54,7 @@
 ### 2022-05-29
 * blocks, threads: new "slots" choice in the OF BLOCK block-attribute reporter's dropdown
 * blocks, threads: programmatically change slot shapes in custom blocks
+* blocks: correctly identify list slots in primitives
 
 ### 2022-05-28
 * new extension primitive for importing a costume from a url

src/blocks.js

@@ -8670,7 +8670,7 @@ ArgMorph.prototype.justDropped = function () {
 // ArgMorph spec extrapolation (for demo purposes)
 
 ArgMorph.prototype.getSpec = function () {
-    return '%s'; // default
+    return this.type === 'list' ? '%l' : '%s'; // default
 };
 
 // ArgMorph menu