diff --git a/_demo/async/async/async.go b/_demo/async/async/async.go
new file mode 100644
index 00000000..8883ee58
--- /dev/null
+++ b/_demo/async/async/async.go
@@ -0,0 +1,31 @@
+package async
+
+import (
+	_ "unsafe"
+)
+
+type Void = [0]byte
+
+type Future[T any] interface {
+	Then(cb func(T))
+}
+
+type future[T any] struct {
+	cb func(func(T))
+}
+
+func (f *future[T]) Then(cb func(T)) {
+	f.cb(cb)
+}
+
+func Async[T any](fn func(func(T))) Future[T] {
+	return &future[T]{fn}
+}
+
+func Run[T any](future Future[T]) T {
+	var ret T
+	future.Then(func(v T) {
+		ret = v
+	})
+	return ret
+}
diff --git a/_demo/async/main.go b/_demo/async/main.go
new file mode 100644
index 00000000..6bc63d82
--- /dev/null
+++ b/_demo/async/main.go
@@ -0,0 +1,23 @@
+package main
+
+import (
+	"time"
+
+	"github.com/goplus/llgo/_demo/async/async"
+	"github.com/goplus/llgo/_demo/async/timeout"
+)
+
+func Sleep(i int, d time.Duration) async.Future[int] {
+	return async.Async(func(resolve func(int)) {
+		timeout.Timeout(d).Then(func(async.Void) {
+			resolve(i)
+		})
+	})
+}
+
+func main() {
+	async.Run(async.Async(func(resolve func(async.Void)) {
+		println("read file")
+		defer resolve(async.Void{})
+	}))
+}
diff --git a/_demo/async/timeout/timeout.go b/_demo/async/timeout/timeout.go
new file mode 100644
index 00000000..20d632e7
--- /dev/null
+++ b/_demo/async/timeout/timeout.go
@@ -0,0 +1,16 @@
+package timeout
+
+import (
+	"time"
+
+	"github.com/goplus/llgo/_demo/async/async"
+)
+
+func Timeout(d time.Duration) async.Future[async.Void] {
+	return async.Async(func(resolve func(async.Void)) {
+		go func() {
+			time.Sleep(d)
+			resolve(async.Void{})
+		}()
+	})
+}