conditionals

vm/vm.go

@@ -87,12 +87,35 @@ func (vm *VM) Run() error {
 				return err
 			}
 
+		case code.OpJump:
+			pos := int(code.ReadUint16(vm.instructions[ip+1:]))
+			ip = pos - 1
+
+		case code.OpJumpNotTruthy:
+			pos := int(code.ReadUint16(vm.instructions[ip+1:]))
+			ip += 2
+
+			condition := vm.pop()
+			if !isTruthy(condition) {
+				ip = pos - 1
+			}
 		}
 	}
 
 	return nil
 }
 
+func isTruthy(obj object.Object) bool {
+	switch obj := obj.(type) {
+
+	case *object.Boolean:
+		return obj.Value
+
+	default:
+		return true
+	}
+}
+
 func (vm *VM) push(o object.Object) error {
 	if vm.sp >= StackSize {
 		return fmt.Errorf("stack overflow")

vm/vm_test.go

@@ -142,3 +142,17 @@ func TestBooleanExpressions(t *testing.T) {
 
 	runVmTests(t, tests)
 }
+
+func TestConditionals(t *testing.T) {
+	tests := []vmTestCase{
+		{"if (true) { 10 }", 10},
+		{"if (true) { 10 } else { 20 }", 10},
+		{"if (false) { 10 } else { 20 } ", 20},
+		{"if (1) { 10 }", 10},
+		{"if (1 < 2) { 10 }", 10},
+		{"if (1 < 2) { 10 } else { 20 }", 10},
+		{"if (1 > 2) { 10 } else { 20 }", 20},
+	}
+
+	runVmTests(t, tests)
+}