prefix expressions

code/code.go

@@ -22,6 +22,8 @@ const (
 	OpEqual
 	OpNotEqual
 	OpGreaterThan
+	OpMinus
+	OpBang
 )
 
 type Definition struct {
@@ -41,6 +43,8 @@ var definitions = map[Opcode]*Definition{
 	OpEqual:       {"OpEqual", []int{}},
 	OpNotEqual:    {"OpNotEqual", []int{}},
 	OpGreaterThan: {"OpGreaterThan", []int{}},
+	OpMinus:       {"OpMinus", []int{}},
+	OpBang:        {"OpBang", []int{}},
 }
 
 func Lookup(op byte) (*Definition, error) {

compiler/compiler.go

@@ -91,6 +91,21 @@ func (c *Compiler) Compile(node ast.Node) error {
 			c.emit(code.OpFalse)
 		}
 
+	case *ast.PrefixExpression:
+		err := c.Compile(node.Right)
+		if err != nil {
+			return err
+		}
+
+		switch node.Operator {
+		case "!":
+			c.emit(code.OpBang)
+		case "-":
+			c.emit(code.OpMinus)
+		default:
+			return fmt.Errorf("unknown operator %s", node.Operator)
+		}
+
 	}
 
 	return nil

compiler/compiler_test.go

@@ -68,6 +68,15 @@ func TestIntegerArithmetic(t *testing.T) {
 				code.Make(code.OpPop),
 			},
 		},
+		{
+			input:             "-1",
+			expectedConstants: []interface{}{1},
+			expectedInstructions: []code.Instructions{
+				code.Make(code.OpConstant, 0),
+				code.Make(code.OpMinus),
+				code.Make(code.OpPop),
+			},
+		},
 	}
 
 	runCompilerTests(t, tests)
@@ -151,6 +160,15 @@ func TestBooleanExpressions(t *testing.T) {
 				code.Make(code.OpPop),
 			},
 		},
+		{
+			input:             "!true",
+			expectedConstants: []interface{}{},
+			expectedInstructions: []code.Instructions{
+				code.Make(code.OpTrue),
+				code.Make(code.OpBang),
+				code.Make(code.OpPop),
+			},
+		},
 	}
 
 	runCompilerTests(t, tests)

vm/vm.go

@@ -74,6 +74,19 @@ func (vm *VM) Run() error {
 			if err != nil {
 				return err
 			}
+
+		case code.OpBang:
+			err := vm.executeBangOperator()
+			if err != nil {
+				return err
+			}
+
+		case code.OpMinus:
+			err := vm.executeMinusOperator()
+			if err != nil {
+				return err
+			}
+
 		}
 	}
 
@@ -167,6 +180,30 @@ func (vm *VM) executeIntegerComparison(op code.Opcode, left, right object.Object
 	}
 }
 
+func (vm *VM) executeBangOperator() error {
+	operand := vm.pop()
+
+	switch operand {
+	case True:
+		return vm.push(False)
+	case False:
+		return vm.push(True)
+	default:
+		return vm.push(False)
+	}
+}
+
+func (vm *VM) executeMinusOperator() error {
+	operand := vm.pop()
+
+	if operand.Type() != object.INTEGER_OBJ {
+		return fmt.Errorf("unsupported type for negation: %s", operand.Type())
+	}
+
+	value := operand.(*object.Integer).Value
+	return vm.push(&object.Integer{Value: -value})
+}
+
 func nativeBoolToBooleanObject(input bool) *object.Boolean {
 	if input {
 		return True

vm/vm_test.go

@@ -119,6 +119,10 @@ func TestIntegerArithmetic(t *testing.T) {
 		{"(1 < 2) == false", false},
 		{"(1 > 2) == true", false},
 		{"(1 > 2) == false", true},
+		{"-5", -5},
+		{"-10", -10},
+		{"-50 + 100 + -50", 0},
+		{"(5 + 10 * 2 + 15 / 3) * 2 + -10", 50},
 	}
 
 	runVmTests(t, tests)
@@ -128,6 +132,12 @@ func TestBooleanExpressions(t *testing.T) {
 	tests := []vmTestCase{
 		{"true", true},
 		{"false", false},
+		{"!true", false},
+		{"!false", true},
+		{"!5", false},
+		{"!!true", true},
+		{"!!false", false},
+		{"!!5", true},
 	}
 
 	runVmTests(t, tests)