new "if then else" reporter primitive in Control category

HISTORY.md

@@ -26,7 +26,7 @@
     * new "get pen attribute" reporter
     * new "write" command in pen category (used to be "label" in tools)
     * new "map","keep", "combine" and "for each" primitives in list category
-    * new "for" loop primitive in the Control category
+    * new "for" loop and "if then else" reporter primitives in the Control category
     * added "neg", "lg" (log2) and "2^" selectors to monadic function reporter in Operators
     * added "^" reporter (power of) in the Operators category
     * added "width" and "height" as attribute selectors of the OF primitive for the stage
@@ -73,6 +73,7 @@
 * Threads, Objects: new "combine" primitive in list category
 * Threads: added type-assertions for the new HOF prims
 * Threads, Objects: new "for" loop primitive in Control category
+* Threads, Objects: new "if then else" reporter primitive in Control category
 
 ### 2019-04-23
 * Threads: fixed JS stack overflow issue for MAP primitive

src/objects.js

@@ -752,6 +752,11 @@ SpriteMorph.prototype.initBlocks = function () {
             category: 'control',
             spec: 'if %b %c else %c'
         },
+        reportIfElse: {
+            type: 'reporter',
+            category: 'control',
+            spec: 'if %b then %s else %s'
+        },
         doStopThis: {
             type: 'command',
             category: 'control',
@@ -2182,6 +2187,7 @@ SpriteMorph.prototype.blockTemplates = function (category) {
         blocks.push('-');
         blocks.push(block('doIf'));
         blocks.push(block('doIfElse'));
+        blocks.push(block('reportIfElse'));
         blocks.push('-');
         blocks.push(block('doReport'));
         blocks.push(block('doStopThis'));
@@ -7758,6 +7764,7 @@ StageMorph.prototype.blockTemplates = function (category) {
         blocks.push('-');
         blocks.push(block('doIf'));
         blocks.push(block('doIfElse'));
+        blocks.push(block('reportIfElse'));
         blocks.push('-');
         blocks.push(block('doReport'));
         blocks.push(block('doStopThis'));

src/threads.js

@@ -716,6 +716,7 @@ Process.prototype.evaluateBlock = function (block, argCount) {
     // check for special forms
     if (selector === 'reportOr' ||
             selector ===  'reportAnd' ||
+            selector === 'reportIfElse' ||
             selector === 'doReport') {
         return this[selector](block);
     }
@@ -1837,6 +1838,23 @@ Process.prototype.doIfElse = function () {
     this.pushContext();
 };
 
+Process.prototype.reportIfElse = function (block) {
+    var inputs = this.context.inputs;
+
+    if (inputs.length < 1) {
+        this.evaluateNextInput(block);
+    } else if (inputs.length > 1) {
+        if (this.flashContext()) {return; }
+        this.returnValueToParentContext(inputs.pop());
+        this.popContext();
+    } else if (inputs[0]) {
+        this.evaluateNextInput(block);
+    } else {
+        inputs.push(null);
+        this.evaluateNextInput(block);
+    }
+};
+
 // Process process related primitives
 
 Process.prototype.doStop = function () {