Merge pull request #1032 from towerofnix/while-vm

Implement "while" block

src/blocks/scratch3_control.js

@@ -17,6 +17,7 @@ class Scratch3ControlBlocks {
         return {
             control_repeat: this.repeat,
             control_repeat_until: this.repeatUntil,
+            control_while: this.repeatWhile,
             control_for_each: this.forEach,
             control_forever: this.forever,
             control_wait: this.wait,
@@ -56,12 +57,20 @@ class Scratch3ControlBlocks {
 
     repeatUntil (args, util) {
         const condition = Cast.toBoolean(args.CONDITION);
-        // If the condition is true, start the branch.
+        // If the condition is false (repeat UNTIL), start the branch.
         if (!condition) {
             util.startBranch(1, true);
         }
     }
 
+    repeatWhile (args, util) {
+        const condition = Cast.toBoolean(args.CONDITION);
+        // If the condition is true (repeat WHILE), start the branch.
+        if (condition) {
+            util.startBranch(1, true);
+        }
+    }
+
     forEach (args, util) {
         const variable = util.target.lookupOrCreateVariable(
             args.VARIABLE.id, args.VARIABLE.name);

src/serialization/sb2_specmap.js

@@ -799,6 +799,19 @@ const specMap = {
             }
         ]
     },
+    'doWhile': {
+        opcode: 'control_while',
+        argMap: [
+            {
+                type: 'input',
+                inputName: 'CONDITION'
+            },
+            {
+                type: 'input',
+                inputName: 'SUBSTACK'
+            }
+        ]
+    },
     'doForLoop': {
         opcode: 'control_for_each',
         argMap: [

test/unit/blocks_control.js

@@ -52,6 +52,28 @@ test('repeatUntil', t => {
     t.end();
 });
 
+test('repeatWhile', t => {
+    const rt = new Runtime();
+    const c = new Control(rt);
+
+    // Test harness (mocks `util`)
+    let i = 0;
+    const repeat = 10;
+    const util = {
+        stackFrame: Object.create(null),
+        startBranch: function () {
+            i++;
+            // Note !== instead of ===
+            c.repeatWhile({CONDITION: (i !== repeat)}, util);
+        }
+    };
+
+    // Execute test
+    c.repeatWhile({CONDITION: (i !== repeat)}, util);
+    t.strictEqual(i, repeat);
+    t.end();
+});
+
 test('forEach', t => {
     const rt = new Runtime();
     const c = new Control(rt);