Implement LOOP blocks in interpreter

Author: GarboMuffin

src/engine/execute.js

@@ -55,6 +55,7 @@ const handleReport = function (resolvedValue, sequencer, thread, blockCached, la
     const opcode = blockCached.opcode;
     const isHat = blockCached._isHat;
     const isConditional = blockCached._isConditional;
+    const isLoop = blockCached._isLoop;
 
     thread.pushReportedValue(resolvedValue);
     if (isHat) {
@@ -87,6 +88,8 @@ const handleReport = function (resolvedValue, sequencer, thread, blockCached, la
     } else if (isConditional) {
         const branch = Math.round(resolvedValue);
         sequencer.stepToBranch(thread, branch, false);
+    } else if (isLoop && cast.toBoolean(resolvedValue)) {
+        sequencer.stepToBranch(thread, 1, true);
     } else {
         // In a non-hat, report the value visually if necessary if
         // at the top of the thread stack.
@@ -298,6 +301,7 @@ class BlockCached {
 
         const flowing = runtime._flowing[opcode];
         this._isConditional = !!(flowing && flowing.conditional);
+        this._isLoop = !!(flowing && flowing.loop);
 
         // Store the current shadow value if there is a shadow value.
         const fieldKeys = Object.keys(fields);

src/engine/runtime.js

@@ -1127,10 +1127,15 @@ class Runtime extends EventEmitter {
                             edgeActivated: blockInfo.isEdgeActivated,
                             restartExistingThreads: blockInfo.shouldRestartExistingThreads
                         };
-                    }
-                    if (blockInfo.blockType === BlockType.CONDITIONAL) {
+                    } else if (blockInfo.blockType === BlockType.CONDITIONAL) {
+                        this._flowing[opcode] = {
+                            conditional: true,
+                            loop: false
+                        };
+                    } else if (blockInfo.blockType === BlockType.LOOP) {
                         this._flowing[opcode] = {
-                            conditional: true
+                            conditional: false,
+                            loop: true
                         };
                     }
                 }

test/fixtures/tw-loop.sb3

@@ -89,20 +89,45 @@ compilerAndInterpreter('CONDITIONAL', (t, co) => {
     const vm = new VirtualMachine();
     vm.setCompilerOptions(co);
     vm.extensionManager.addBuiltinExtension('loopsAndThings', LoopsAndThings);
+    vm.runtime.on('COMPILE_ERROR', () => {
+        t.fail('Compile error');
+    });
 
     vm.loadProject(fs.readFileSync(path.join(__dirname, '../fixtures/tw-conditional.sb3'))).then(() => {
         let okayCount = 0;
         vm.runtime.on('SAY', (target, type, text) => {
             if (text === 'OK!') {
                 okayCount++;
             } else if (text === 'end') {
+                vm.stop();
                 t.equal(okayCount, 5);
-                vm.runtime.stop();
                 t.end();
             }
         });
 
         vm.greenFlag();
-        vm.runtime.start();
+        vm.start();
+    });
+});
+
+compilerAndInterpreter('LOOP', (t, co) => {
+    t.plan(1);
+
+    const vm = new VirtualMachine();
+    vm.setCompilerOptions(co);
+    vm.extensionManager.addBuiltinExtension('loopsAndThings', LoopsAndThings);    
+    vm.runtime.on('COMPILE_ERROR', () => {
+        t.fail('Compile error');
+    });
+
+    vm.loadProject(fs.readFileSync(path.join(__dirname, '../fixtures/tw-loop.sb3'))).then(() => {
+        vm.runtime.on('SAY', (target, type, text) => {
+            vm.stop();
+            t.equal(text, 'a 5 b 50 c 200');
+            t.end();
+        });
+
+        vm.greenFlag();
+        vm.start();
     });
 });