equality testing for scripts, experimental

HISTORY.md

@@ -70,6 +70,7 @@
 
 ### 2021-12-01
 * blocks, threads: block-assembly support refactorings, experimental
+* blocks, threads: equality testing for scripts, experimental
 
 ### 2021-11-30
 * blocks, threads: block-assembly support, experimental

src/blocks.js

@@ -3710,7 +3710,15 @@ BlockMorph.prototype.components = function () {
     throw new Error('subclass responsility');
 };
 
+BlockMorph.prototype.equalTo = function (other) {
+    // private - only to be called from a Context
+    return this.constructor.name === other.constructor.name &&
+        this.selector === other.selector &&
+        this.blockSpec === other.blockSpec;
+};
+
 BlockMorph.prototype.copyWithInputs = function (inputs) {
+    // private - only to be called from a Context
     var cpy = this.fullCopy(),
         slots = cpy.inputs(),
         dta = inputs.itemsArray().map(inp =>
@@ -5489,7 +5497,8 @@ CommandBlockMorph.prototype.components = function () {
         }
         expr.fixBlockColor(null, true);
         inputs = expr.inputs();
-        if (!inputs.length) {
+        if (!inputs.length ||
+                inputs.every(slot => slot.isEmptySlot && slot.isEmptySlot())) {
             return expr.reify();
         }
         parts = new List([expr.reify()]);

src/threads.js

@@ -87,8 +87,9 @@ const NONNUMBERS = [true, false, ''];
 })();
 
 function snapEquals(a, b) {
-    if (a instanceof List || (b instanceof List)) {
-        if (a instanceof List && (b instanceof List)) {
+    // lists, functions and blocks
+    if (a.equalTo || b.equalTo) {
+        if (a.constructor.name === b.constructor.name) {
             return a.equalTo(b);
         }
         return false;
@@ -7012,7 +7013,8 @@ Context.prototype.isInCustomBlock = function () {
 // Context components - EXPERIMENTAL
 
 Context.prototype.components = function () {
-    var expr = this.expression.components(),
+    var expr = this.expression.components ?
+            this.expression.components() : new Context(),
         parts;
     if (!this.inputs.length) {
         return expr;
@@ -7023,6 +7025,15 @@ Context.prototype.components = function () {
     return parts;
 };
 
+Context.prototype.equalTo = function (other) {
+    var c1 = this.components(),
+        c2 = other.components();
+    if (c1 instanceof Context && (c2 instanceof Context)) {
+        return snapEquals(c1.expression, c2.expression);
+    }
+    return snapEquals(c1, c2);
+};
+
 Context.prototype.copyWithInputs = function (inputs) {
     return this.expression.copyWithInputs(inputs);
 };