comparisons and booleans

code/code.go

@@ -17,6 +17,11 @@ const (
 	OpSub
 	OpMul
 	OpDiv
+	OpTrue
+	OpFalse
+	OpEqual
+	OpNotEqual
+	OpGreaterThan
 )
 
 type Definition struct {
@@ -31,6 +36,11 @@ var definitions = map[Opcode]*Definition{
 	OpSub:         {"OpSub", []int{}},
 	OpMul:         {"OpMul", []int{}},
 	OpDiv:         {"OpDiv", []int{}},
+	OpTrue:        {"OpTrue", []int{}},
+	OpFalse:       {"OpFalse", []int{}},
+	OpEqual:       {"OpEqual", []int{}},
+	OpNotEqual:    {"OpNotEqual", []int{}},
+	OpGreaterThan: {"OpGreaterThan", []int{}},
 }
 
 func Lookup(op byte) (*Definition, error) {

compiler/compiler.go

@@ -37,6 +37,20 @@ func (c *Compiler) Compile(node ast.Node) error {
 		c.emit(code.OpPop)
 
 	case *ast.InfixExpression:
+		if node.Operator == "<" {
+			err := c.Compile(node.Right)
+			if err != nil {
+				return err
+			}
+
+			err = c.Compile(node.Left)
+			if err != nil {
+				return err
+			}
+			c.emit(code.OpGreaterThan)
+			return nil
+		}
+
 		err := c.Compile(node.Left)
 		if err != nil {
 			return err
@@ -56,6 +70,12 @@ func (c *Compiler) Compile(node ast.Node) error {
 			c.emit(code.OpMul)
 		case "/":
 			c.emit(code.OpDiv)
+		case ">":
+			c.emit(code.OpGreaterThan)
+		case "==":
+			c.emit(code.OpEqual)
+		case "!=":
+			c.emit(code.OpNotEqual)
 		default:
 			return fmt.Errorf("unknown operator %s", node.Operator)
 		}
@@ -64,6 +84,13 @@ func (c *Compiler) Compile(node ast.Node) error {
 		integer := &object.Integer{Value: node.Value}
 		c.emit(code.OpConstant, c.addConstant(integer))
 
+	case *ast.Boolean:
+		if node.Value {
+			c.emit(code.OpTrue)
+		} else {
+			c.emit(code.OpFalse)
+		}
+
 	}
 
 	return nil

compiler/compiler_test.go

@@ -73,6 +73,89 @@ func TestIntegerArithmetic(t *testing.T) {
 	runCompilerTests(t, tests)
 }
 
+func TestBooleanExpressions(t *testing.T) {
+	tests := []compilerTestCase{
+		{
+			input:             "true",
+			expectedConstants: []interface{}{},
+			expectedInstructions: []code.Instructions{
+				code.Make(code.OpTrue),
+				code.Make(code.OpPop),
+			},
+		},
+		{
+			input:             "false",
+			expectedConstants: []interface{}{},
+			expectedInstructions: []code.Instructions{
+				code.Make(code.OpFalse),
+				code.Make(code.OpPop),
+			},
+		},
+		{
+			input:             "1 > 2",
+			expectedConstants: []interface{}{1, 2},
+			expectedInstructions: []code.Instructions{
+				code.Make(code.OpConstant, 0),
+				code.Make(code.OpConstant, 1),
+				code.Make(code.OpGreaterThan),
+				code.Make(code.OpPop),
+			},
+		},
+		{
+			input:             "1 < 2",
+			expectedConstants: []interface{}{2, 1},
+			expectedInstructions: []code.Instructions{
+				code.Make(code.OpConstant, 0),
+				code.Make(code.OpConstant, 1),
+				code.Make(code.OpGreaterThan),
+				code.Make(code.OpPop),
+			},
+		},
+		{
+			input:             "1 == 2",
+			expectedConstants: []interface{}{1, 2},
+			expectedInstructions: []code.Instructions{
+				code.Make(code.OpConstant, 0),
+				code.Make(code.OpConstant, 1),
+				code.Make(code.OpEqual),
+				code.Make(code.OpPop),
+			},
+		},
+		{
+			input:             "1 != 2",
+			expectedConstants: []interface{}{1, 2},
+			expectedInstructions: []code.Instructions{
+				code.Make(code.OpConstant, 0),
+				code.Make(code.OpConstant, 1),
+				code.Make(code.OpNotEqual),
+				code.Make(code.OpPop),
+			},
+		},
+		{
+			input:             "true == false",
+			expectedConstants: []interface{}{},
+			expectedInstructions: []code.Instructions{
+				code.Make(code.OpTrue),
+				code.Make(code.OpFalse),
+				code.Make(code.OpEqual),
+				code.Make(code.OpPop),
+			},
+		},
+		{
+			input:             "true != false",
+			expectedConstants: []interface{}{},
+			expectedInstructions: []code.Instructions{
+				code.Make(code.OpTrue),
+				code.Make(code.OpFalse),
+				code.Make(code.OpNotEqual),
+				code.Make(code.OpPop),
+			},
+		},
+	}
+
+	runCompilerTests(t, tests)
+}
+
 func runCompilerTests(t *testing.T, tests []compilerTestCase) {
 	t.Helper()
 

vm/vm.go

@@ -9,6 +9,9 @@ import (
 
 const StackSize = 2048
 
+var True = &object.Boolean{Value: true}
+var False = &object.Boolean{Value: false}
+
 type VM struct {
 	constants    []object.Object
 	instructions code.Instructions
@@ -53,6 +56,24 @@ func (vm *VM) Run() error {
 
 		case code.OpPop:
 			vm.pop()
+
+		case code.OpTrue:
+			err := vm.push(True)
+			if err != nil {
+				return err
+			}
+
+		case code.OpFalse:
+			err := vm.push(False)
+			if err != nil {
+				return err
+			}
+
+		case code.OpEqual, code.OpNotEqual, code.OpGreaterThan:
+			err := vm.executeComparison(op)
+			if err != nil {
+				return err
+			}
 		}
 	}
 
@@ -111,3 +132,44 @@ func (vm *VM) executeBinaryIntegerOperation(op code.Opcode, left, right object.O
 
 	return vm.push(&object.Integer{Value: result})
 }
+
+func (vm *VM) executeComparison(op code.Opcode) error {
+	right := vm.pop()
+	left := vm.pop()
+
+	if left.Type() == object.INTEGER_OBJ && right.Type() == object.INTEGER_OBJ {
+		return vm.executeIntegerComparison(op, left, right)
+	}
+
+	switch op {
+	case code.OpEqual:
+		return vm.push(nativeBoolToBooleanObject(right == left))
+	case code.OpNotEqual:
+		return vm.push(nativeBoolToBooleanObject(right != left))
+	default:
+		return fmt.Errorf("unknown operator: %d (%s %s)", op, left.Type(), right.Type())
+	}
+}
+
+func (vm *VM) executeIntegerComparison(op code.Opcode, left, right object.Object) error {
+	leftValue := left.(*object.Integer).Value
+	rightValue := right.(*object.Integer).Value
+
+	switch op {
+	case code.OpEqual:
+		return vm.push(nativeBoolToBooleanObject(rightValue == leftValue))
+	case code.OpNotEqual:
+		return vm.push(nativeBoolToBooleanObject(rightValue != leftValue))
+	case code.OpGreaterThan:
+		return vm.push(nativeBoolToBooleanObject(leftValue > rightValue))
+	default:
+		return fmt.Errorf("unknown operator: %d", op)
+	}
+}
+
+func nativeBoolToBooleanObject(input bool) *object.Boolean {
+	if input {
+		return True
+	}
+	return False
+}

vm/vm_test.go

@@ -48,6 +48,12 @@ func testExpectedObject(t *testing.T, expected interface{}, actual object.Object
 		if err != nil {
 			t.Errorf("testIntegerObject failed: %s", err)
 		}
+
+	case bool:
+		err := testBooleanObject(bool(expected), actual)
+		if err != nil {
+			t.Errorf("testBooleanObject failed: %s", err)
+		}
 	}
 }
 
@@ -70,6 +76,19 @@ func testIntegerObject(expected int64, actual object.Object) interface{} {
 	return nil
 }
 
+func testBooleanObject(expected bool, actual object.Object) interface{} {
+	result, ok := actual.(*object.Boolean)
+	if !ok {
+		return fmt.Errorf("object is not Boolean. got=%T (%+v", actual, actual)
+	}
+
+	if result.Value != expected {
+		return fmt.Errorf("object has wrong value. got=%t, want=%t", result.Value, expected)
+	}
+
+	return nil
+}
+
 func TestIntegerArithmetic(t *testing.T) {
 	tests := []vmTestCase{
 		{"1", 1},
@@ -83,6 +102,32 @@ func TestIntegerArithmetic(t *testing.T) {
 		{"5 * 2 + 10", 20},
 		{"5 + 2 * 10", 25},
 		{"5 * (2 + 10)", 60},
+		{"1 < 2", true},
+		{"1 > 2", false},
+		{"1 < 1", false},
+		{"1 > 1", false},
+		{"1 == 1", true},
+		{"1 != 1", false},
+		{"1 == 2", false},
+		{"1 != 2", true},
+		{"true == true", true},
+		{"false == false", true},
+		{"true == false", false},
+		{"true != false", true},
+		{"false != true", true},
+		{"(1 < 2) == true", true},
+		{"(1 < 2) == false", false},
+		{"(1 > 2) == true", false},
+		{"(1 > 2) == false", true},
+	}
+
+	runVmTests(t, tests)
+}
+
+func TestBooleanExpressions(t *testing.T) {
+	tests := []vmTestCase{
+		{"true", true},
+		{"false", false},
 	}
 
 	runVmTests(t, tests)