Arithmetic

vm/vm.go

@@ -27,11 +27,8 @@ func New(bytecode *compiler.Bytecode) *VM {
 	}
 }
 
-func (vm *VM) StackTop() object.Object {
-	if vm.sp == 0 {
-		return nil
-	}
-	return vm.stack[vm.sp-1]
+func (vm *VM) LastPoppedStackElem() object.Object {
+	return vm.stack[vm.sp]
 }
 
 func (vm *VM) Run() error {
@@ -48,14 +45,14 @@ func (vm *VM) Run() error {
 				return err
 			}
 
-		case code.OpAdd:
-			right := vm.pop()
-			left := vm.pop()
-			leftValue := left.(*object.Integer).Value
-			rightValue := right.(*object.Integer).Value
+		case code.OpAdd, code.OpSub, code.OpMul, code.OpDiv:
+			err := vm.executeBinaryOperation(op)
+			if err != nil {
+				return err
+			}
 
-			result := leftValue + rightValue
-			vm.push(&object.Integer{Value: result})
+		case code.OpPop:
+			vm.pop()
 		}
 	}
 
@@ -78,3 +75,39 @@ func (vm *VM) pop() object.Object {
 	vm.sp--
 	return o
 }
+
+func (vm *VM) executeBinaryOperation(op code.Opcode) error {
+	right := vm.pop()
+	left := vm.pop()
+
+	leftType := left.Type()
+	rightRight := right.Type()
+
+	if leftType == object.INTEGER_OBJ && rightRight == object.INTEGER_OBJ {
+		return vm.executeBinaryIntegerOperation(op, left, right)
+	}
+
+	return fmt.Errorf("unsupported types for binary operation: %s %s", leftType, rightRight)
+}
+
+func (vm *VM) executeBinaryIntegerOperation(op code.Opcode, left, right object.Object) error {
+	leftValue := left.(*object.Integer).Value
+	rightValue := right.(*object.Integer).Value
+
+	var result int64
+
+	switch op {
+	case code.OpAdd:
+		result = leftValue + rightValue
+	case code.OpSub:
+		result = leftValue - rightValue
+	case code.OpMul:
+		result = leftValue * rightValue
+	case code.OpDiv:
+		result = leftValue / rightValue
+	default:
+		return fmt.Errorf("unknown integer operator: %d", op)
+	}
+
+	return vm.push(&object.Integer{Value: result})
+}

vm/vm_test.go

@@ -33,7 +33,7 @@ func runVmTests(t *testing.T, tests []vmTestCase) {
 			t.Fatalf("vm error: %s", err)
 		}
 
-		stackElem := vm.StackTop()
+		stackElem := vm.LastPoppedStackElem()
 
 		testExpectedObject(t, tt.expected, stackElem)
 	}
@@ -75,6 +75,14 @@ func TestIntegerArithmetic(t *testing.T) {
 		{"1", 1},
 		{"2", 2},
 		{"1 + 2", 3},
+		{"1 * 2", 2},
+		{"4 / 2", 2},
+		{"50 / 2 * 2 + 10 - 5", 55},
+		{"5 + 5 + 5 + 5 - 10", 10},
+		{"2 * 2 * 2 * 2 * 2", 32},
+		{"5 * 2 + 10", 20},
+		{"5 + 2 * 10", 25},
+		{"5 * (2 + 10)", 60},
 	}
 
 	runVmTests(t, tests)