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
-0003 OpConstant 2
-0006 OpConstant 65535
+	expected := `0000 OpAdd
+0001 OpConstant 2
+0004 OpConstant 65535
 `
 
 	concatted := Instructions{}