bind expression (:=) instead of let

vm/vm.go

@@ -181,6 +181,11 @@ func (vm *VM) Run() error {
 				vm.globals[globalIndex] = ref
 			}
 
+			err := vm.push(Null)
+			if err != nil {
+				return err
+			}
+
 		case code.OpAssignGlobal:
 			globalIndex := code.ReadUint16(ins[ip+1:])
 			vm.currentFrame().ip += 2
@@ -284,7 +289,17 @@ func (vm *VM) Run() error {
 
 			frame := vm.currentFrame()
 
-			vm.stack[frame.basePointer+int(localIndex)] = vm.pop()
+			ref := vm.pop()
+			if immutable, ok := ref.(object.Immutable); ok {
+				vm.stack[frame.basePointer+int(localIndex)] = immutable.Clone()
+			} else {
+				vm.stack[frame.basePointer+int(localIndex)] = ref
+			}
+
+			err := vm.push(Null)
+			if err != nil {
+				return err
+			}
 
 		case code.OpGetLocal:
 			localIndex := code.ReadUint8(ins[ip+1:])