VM!

code/code.go

@@ -12,6 +12,7 @@ type Opcode byte
 
 const (
 	OpConstant Opcode = iota
+	OpAdd
 )
 
 type Definition struct {
@@ -21,6 +22,7 @@ type Definition struct {
 
 var definitions = map[Opcode]*Definition{
 	OpConstant: {"OpConstant", []int{2}},
+	OpAdd:      {"OpAdd", []int{}},
 }
 
 func Lookup(op byte) (*Definition, error) {
@@ -88,6 +90,8 @@ func (ins Instructions) fmtInstruction(def *Definition, operands []int) string {
 	}
 
 	switch operandCount {
+	case 0:
+		return def.Name
 	case 1:
 		return fmt.Sprintf("%s %d", def.Name, operands[0])
 	}

code/code_test.go

@@ -9,6 +9,7 @@ func TestMake(t *testing.T) {
 		expected []byte
 	}{
 		{OpConstant, []int{65534}, []byte{byte(OpConstant), 255, 254}},
+		{OpAdd, []int{}, []byte{byte(OpAdd)}},
 	}
 
 	for _, tt := range test {
@@ -28,14 +29,14 @@ func TestMake(t *testing.T) {
 
 func TestInstructions(t *testing.T) {
 	instructions := []Instructions{
-		Make(OpConstant, 1),
+		Make(OpAdd),
 		Make(OpConstant, 2),
 		Make(OpConstant, 65535),
 	}
 
-	expected := `0000 OpConstant 1
+	expected := `0000 OpAdd
-0003 OpConstant 2
+0001 OpConstant 2
-0006 OpConstant 65535
+0004 OpConstant 65535
 `
 
 	concatted := Instructions{}

compiler/compiler.go

@@ -1,6 +1,7 @@
 package compiler
 
 import (
+	"fmt"
 	"monkey/ast"
 	"monkey/code"
 	"monkey/object"
@@ -45,6 +46,13 @@ func (c *Compiler) Compile(node ast.Node) error {
 			return err
 		}
 
+		switch node.Operator {
+		case "+":
+			c.emit(code.OpAdd)
+		default:
+			return fmt.Errorf("unknown operator %s", node.Operator)
+		}
+
 	case *ast.IntegerLiteral:
 		integer := &object.Integer{Value: node.Value}
 		c.emit(code.OpConstant, c.addConstant(integer))

compiler/compiler_test.go

@@ -24,6 +24,7 @@ func TestIntegerArithmetic(t *testing.T) {
 			expectedInstructions: []code.Instructions{
 				code.Make(code.OpConstant, 0),
 				code.Make(code.OpConstant, 1),
+				code.Make(code.OpAdd),
 			},
 		},
 	}

vm/vm.go

@@ -0,0 +1,80 @@
+package vm
+
+import (
+	"fmt"
+	"monkey/code"
+	"monkey/compiler"
+	"monkey/object"
+)
+
+const StackSize = 2048
+
+type VM struct {
+	constants    []object.Object
+	instructions code.Instructions
+
+	stack []object.Object
+	sp    int // Always points to the next value. Top of stack is stack[sp-1]
+}
+
+func New(bytecode *compiler.Bytecode) *VM {
+	return &VM{
+		constants:    bytecode.Constants,
+		instructions: bytecode.Instructions,
+
+		stack: make([]object.Object, StackSize),
+		sp:    0,
+	}
+}
+
+func (vm *VM) StackTop() object.Object {
+	if vm.sp == 0 {
+		return nil
+	}
+	return vm.stack[vm.sp-1]
+}
+
+func (vm *VM) Run() error {
+	for ip := 0; ip < len(vm.instructions); ip++ {
+		op := code.Opcode(vm.instructions[ip])
+
+		switch op {
+		case code.OpConstant:
+			constIndex := code.ReadUint16(vm.instructions[ip+1:])
+			ip += 2
+
+			err := vm.push(vm.constants[constIndex])
+			if err != nil {
+				return err
+			}
+
+		case code.OpAdd:
+			right := vm.pop()
+			left := vm.pop()
+			leftValue := left.(*object.Integer).Value
+			rightValue := right.(*object.Integer).Value
+
+			result := leftValue + rightValue
+			vm.push(&object.Integer{Value: result})
+		}
+	}
+
+	return nil
+}
+
+func (vm *VM) push(o object.Object) error {
+	if vm.sp >= StackSize {
+		return fmt.Errorf("stack overflow")
+	}
+
+	vm.stack[vm.sp] = o
+	vm.sp++
+
+	return nil
+}
+
+func (vm *VM) pop() object.Object {
+	o := vm.stack[vm.sp-1]
+	vm.sp--
+	return o
+}

vm/vm_test.go

@@ -0,0 +1,81 @@
+package vm
+
+import (
+	"fmt"
+	"monkey/ast"
+	"monkey/compiler"
+	"monkey/lexer"
+	"monkey/object"
+	"monkey/parser"
+	"testing"
+)
+
+type vmTestCase struct {
+	input    string
+	expected interface{}
+}
+
+func runVmTests(t *testing.T, tests []vmTestCase) {
+	t.Helper()
+
+	for _, tt := range tests {
+		program := parse(tt.input)
+
+		comp := compiler.New()
+		err := comp.Compile(program)
+		if err != nil {
+			t.Fatalf("compiler error: %s", err)
+		}
+
+		vm := New(comp.Bytecode())
+		err = vm.Run()
+		if err != nil {
+			t.Fatalf("vm error: %s", err)
+		}
+
+		stackElem := vm.StackTop()
+
+		testExpectedObject(t, tt.expected, stackElem)
+	}
+}
+
+func testExpectedObject(t *testing.T, expected interface{}, actual object.Object) {
+	t.Helper()
+
+	switch expected := expected.(type) {
+	case int:
+		err := testIntegerObject(int64(expected), actual)
+		if err != nil {
+			t.Errorf("testIntegerObject failed: %s", err)
+		}
+	}
+}
+
+func parse(input string) *ast.Program {
+	l := lexer.New(input)
+	p := parser.New(l)
+	return p.ParseProgram()
+}
+
+func testIntegerObject(expected int64, actual object.Object) interface{} {
+	result, ok := actual.(*object.Integer)
+	if !ok {
+		return fmt.Errorf("object is not Integer. got=%T (%+v", actual, actual)
+	}
+
+	if result.Value != expected {
+		return fmt.Errorf("object has wrong value. got=%d, want=%d", result.Value, expected)
+	}
+
+	return nil
+}
+
+func TestIntegerArithmetic(t *testing.T) {
+	tests := []vmTestCase{
+		{"1", 1},
+		{"2", 2},
+		{"1 + 2", 3},
+	}
+
+	runVmTests(t, tests)
+}